(19)
(11)EP 2 354 601 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
04.09.2013 Bulletin 2013/36

(21)Application number: 10013215.8

(22)Date of filing:  15.04.2003
(51)International Patent Classification (IPC): 
F16H 61/46(2010.01)
F16H 61/4035(2010.01)
F16H 61/452(2010.01)
B60K 17/10(2006.01)
F16H 61/433(2010.01)

(54)

Smooth pilot-operated series-parallel hydrostatic transmission

Ruckfreie reihe- oder parallelgeschaltete, Steuerdruck gesteuerte Transmission

Transmission hydraulique à passages manuels progressifs entre les modes série et paralléle


(84)Designated Contracting States:
DE ES FR GB IT

(43)Date of publication of application:
10.08.2011 Bulletin 2011/32

(62)Application number of the earlier application in accordance with Art. 76 EPC:
03008650.8 / 1469237

(73)Proprietor: Caterpillar Paving Products Inc.
Brooklyn MN 55445 (US)

(72)Inventor:
  • Mares, Riccardo
    44100 Ferrara (IT)

(74)Representative: Carstens, Dirk Wilhelm 
Wagner & Geyer Gewürzmühlstrasse 5
80538 München
80538 München (DE)


(56)References cited: : 
WO-A-02/093043
US-A- 5 897 176
US-A- 4 480 438
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The present invention relates to a hydraulic transmission system and a method of operating the same. In particular it relates to a hydraulic transmission system with a closed circuit connection configuration and preferably having at least two motors connected to one hydraulic working fluid supply means.

    Background of the Invention



    [0002] Hydraulic transmission systems are widely used in particular in environments where large forces and torques have to be handled. For example, one particular field of application of hydraulic transmission systems is self propelled or mobile working machines, such as construction machines or load lifting machines. Typically, in one such hydraulic transmission system, two or more motors may be connected in parallel to one hydraulic working fluid supply. Further, in case a variable displacement pump is employed as the hydraulic working fluid supply, a high motor torque can be achieved from a relatively small displacement pump, which is important in mobile working machines where space is limited.

    [0003] In hydraulically operated working systems the flow of hydraulic working fluid supplied to the motors may be controlled either by a hydraulic or by an electronic control or by combinations thereof. This offers flexibility in designing the system according to the specific needs. For example, in a hydraulic system with parallel connected motors in which the flow of hydraulic working fluid in the individual branches is governed by the load on the motors, problems may arise in case one of the motors is not sufficiently loaded and the flow resistance of this transmission branch gets so low that nearly all the hydraulic working fluid supplied by the displacement pump flows through this branch. This may cause "slippage" of the respective motor and the other motor(s) will not receive enough hydraulic working fluid. Attempts to avoid such a situation include the regulation of flow in the individual branches that is controlled hydraulically and/or electronically. One prior art approach is to use flow dividers that split the flow supplied from a pump in predetermined portions at any time. This, however, causes extra pressure drop or resistance in the hydraulic transmission system and increases the overall costs. Further, in most systems, variable displacement pumps are used and also the available flow of the working fluid supply may be controlled according to the specific need and instant load of the system hydraulically and/or electronically so as to achieve optimum performance of the whole system. Yet, often the results leave room for improvements in particular concerning the reduction of complexity while achieving, at the same time, accurate smooth control of the hydraulic system and its components.

    [0004] US 4 480 438 A discloses a hydraulic transmission system according to the preamble of claim 1, and a method for controlling such a system according to the preamble of claim 27, the hydraulic system comprising a reversible variable displacement pump, a hydraulic servo motor for controlling the direction and amount of displacement of the pump, a fluid motor connected in parallel to the pump and adapted to be driven by the pump, a pilot operated directional valve for controlling the position and direction of the servo motor system, and a valve for sensing the displacement of said pump and applying a force to the directional valve opposite to the force of the pilot pressure for moving the valve.

    [0005] It is an object of the invention to find an alternative simplified construction of the system, with an accurate, smooth control of the system.

    Summary of the Invention



    [0006] According to the present invention, a hydraulic transmission system is provided as set forth in claim 1. The invention also provides for a method for controlling a hydraulic transmission system as set forth in claim 27.

    [0007] Preferred embodiments of the present invention may be gathered from the dependent claims.

    Brief description of the Drawings



    [0008] Further objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the following description of embodiments of the invention in conjunction with the appended drawings, in which:

    Fig. 1 shows a schematic representation of an embodiment of a hydraulic system;

    Fig. 2 shows a detail of the hydraulic system of Fig. 1;

    Fig. 3 shows a schematic representation of the hydraulic system of Fig. 1 in another condition;

    Fig. 4 shows the detail of Fig. 2 in the condition of the hydraulic system as shown in Fig. 3;

    Fig. 5 shows a diagram representing a motor and pump flow rate in the system of Fig. 1.


    Detailed Description



    [0009] Fig. 1 shows a schematic representation of a hydraulic system 1 used in a machine which may be a working machine with hydraulically driven implements such as, for example, but not restricted thereto, a compactor or asphalt roller, a skids steer loader, a hydraulic winch, a construction machine as a paver or a road scarifier with hydraulic implements and traction system, such as hydraulically driven wheels or tracks, or any other utility machine.

    [0010] The hydraulic system 1 of the preferred embodiment constitutes a closed circuit connection and comprises a supply means 3 supplying a variable flow of hydraulic working fluid at first and second supply ports 5, 7 to first and second working lines 9, 11. The hydraulic system 1 also comprises a first motor or user 13 and a second motor or user 15 both being connected to the supply means 3 via the first and second working lines 9, 11, respectively. Just for reasons of explanation, the first and second motors 13, 15 may be used to drive front and rear rollers of an asphalt roller. They may be also used for driving left and right wheels of, for example, a front and/or rear axel of any self-propelled utility machine or for controlling the operation of any other working implement such as a bucket of an excavator or a conveyor means in a construction machine etc. It is also clear, that more than two motors may be provided depending on the particular use of the hydraulic system 1. The circuit of the hydraulic system 1 comprising the supply means 3 and the first and second motors 13, 15 is closed via first, second, third, and fourth working line portions 21, 23, 25, 27 which are connectable via ports provided on a connection control device 29.

    [0011] The hydraulic system 1 further comprises a remote control means 31 for facilitating manual remote control of the operation of the supply means 3 and hence the operation of the first and second motors 13, 15. The remote control means 31 is actuatable by the operator of the machine comprising the hydraulic transmission system and has a control lever or joy stick 33 which is manipulated by the operator, for example, to drive the machine at a desired speed in the forward or in the rearward direction. In the preferred embodiment, the actuatable remote control means 31 is of the hydraulic type that includes a pressure variation means 35. Upon manipulating the joystick 33, the pressure variation means 35 of the hydraulic remote control means 31 vary the pressure of a hydraulic control fluid which is introduced at a constant pressure into the hydraulic remote control means 31 via a constant pressure inlet port 37. The hydraulic control fluid with varied pressure is output from the hydraulic remote control means 31 via either a first control output port 39, e.g. for forward drive, or a second control output port 41, e.g. for rearward drive in the above example of an asphalt roller. In the preferred embodiment, the modulated or varied pressure may range from 5 to 20 bar, for example, but any pressure range suited to the particular application of the hydraulic system 1 can be readily substituted.

    [0012] The first and second control output ports 39, 41 are connected to first and second remote control input ports 43, 45 of the supply means 3 via first and second remote control lines 47, 49, respectively, to control operation of the supply means 3.

    [0013] The supply means 3 comprises a variable displacement pump 51 which is illustrated in the preferred embodiment as a pump of the axial piston type with swash plate design driven via an input shaft 53 by means of a prime mover or engine not shown. The variable displacement pump 51 may be also of another design suitable to supply the hydraulic working fluid at variable flow rate. The pump 51 is connected to the first and second supply ports 5, 7 of the supply means 3 via first and second internal connection lines 55, 57. The supply means 3 also comprises first and second relief valves 59, 61 provided in an internal connection branch parallel to the first and second supply ports 5, 7 between the first and second internal connection lines 55, 57. Said first and second relief valves 59, 61 protect the hydraulic system 1 against overpressure and prevent overloading of the motors 13, 15, as is known in the art.

    [0014] Further, as is well known in the art, there is provided an auxiliary or boost pump 63 which serves to supply boost hydraulic fluid to the variable displacement pump 51 and hydraulic fluid at constant pressure, for example at 20 bar, for control purposes in the hydraulic system 1. The auxiliary pump 63 is connected to a hydraulic fluid tank 65 via a hydraulic fluid supply line 67 and a hydraulic fluid suction port 69 being provided with a filter. The pressure of the hydraulic fluid supplied by the auxiliary pump 63 is limited by a third relief valve 71 connected to an outlet of the auxiliary pump 63 and the hydraulic fluid tank 65, as is known in the art. The outlet of the auxiliary pump 63 is also connected via an internal constant pressure line 73 to a constant pressure output port 75 of the supply means 3.

    [0015] The variable displacement pump 51 comprises an adjustment means 77 for controlling the output flow of the pump 51, for example by adjusting the angle of the swash plate of the axial piston pump with swash plate design. In a preferred embodiment, the adjustment means 77 is an hydraulic adjustment means and comprises, for example, a double acting servo piston 79 having its two piston chambers connected to first and second servo piston control lines 81, 83. The first and second servo piston control lines 81, 83 are internally connected to a distributor means 89. The adjustment means 77 are operated by the pressure or flow of hydraulic fluid supplied to the piston chambers of the servo piston 79 via the first and second servo piston control lines 81, 83 from the distributor means 89 as will be described in more detail below.

    [0016] In particular, the distributor means 89 comprises a directional distributor valve 91 which has a neutral position 93 as represented in Fig. 1, and a first and second control position 95, 97 in which either the first or the second servo piston control lines 81, 83 are connected selectively to an internal servo pressure supply line 99 so as to supply pressurized hydraulic fluid to the piston chambers of the servo piston 79 to control the position thereof. In the neutral position 93 the directional distributor valve 91 connects the first and second servo piston control lines 81, 83 to the hydraulic fluid reservoir or tank 65 in order to balance the neutral position of the servo piston 79.

    [0017] Contrary to conventional design in which the distributor valve 91 connects in its first or second control position 93, 95 the first and second servo piston control lines 81, 83, respectively, to the constant pressure hydraulic fluid present at the outlet of the auxiliary pump 63 to receive the full boost or charge pressure thereof, a conventional connection between the auxiliary pump 63 and the distributor valve 91 is indicated as being blocked by a plug 101. Instead, the internal servo pressure supply line 99 is connected to a servo pressure inlet port 103 of the supply means 3 receiving a pressure or flow of hydraulic fluid which is controlled in a manner to be described later.

    [0018] The distributor valve 91 may be a proportional valve and it is pilot operated. Thus, its position is controlled by a pilot or control signal for example in the form of pressurized fluid received via first and second distributor pilot lines 105, 107 which are connected to the first and second remote control input ports 43, 45, respectively. As indicated in Fig. 1, the distributor valve 91 also has a swash plate feedback 109, as is known in the art.

    [0019] The first and second remote control input ports 43, 45, the constant pressure output port 75, and the servo pressure inlet port 103 of the supply means 3 are connected to a first control portion 121 of the connection control device 29 adapted to selectively connect or disconnect hydraulic fluid having a constant pressure as supplied from the auxiliary pump 63 and the hydraulic control fluid having a varied pressure as supplied from either the first or the second control output ports 39, 41 of the hydraulic remote control means 31. In other words, the hydraulic transmission system 1 comprises a first connection control means 122 adapted to direct hydraulic control fluid from the hydraulic remote control means 31 to the hydraulic adjustment means 77 of the variable displacement pump 51, said first connection control means 122 comprising the distributor means 89 and the first control portion 121 of the connection control device 29.

    [0020] Specifically, the constant pressure output port 75 of the supply means 3 is connected via a first external constant pressure supply line 123 to a first input port 125 of the first control portion 121. The servo pressure inlet port 103 of the supply means 3 is connected via an external servo pressure supply line 135 to a third output port 137 of the first control portion 121.

    [0021] As mentioned previously, the first and second remote control input ports 43, 45 are connected via the first and second remote control lines 47, 49 to the first and second remote control output ports 39, 41, respectively, of the hydraulic remote control means 31. In particular, both the first and second remote control lines 47, 49 are connected to the first and second remote control input ports 43, 45 via the connection control device 29 and comprise respective first external line portions 139, 141 connecting the first and second remote control output ports 39, 41 with second and third input ports 143, 145 of the connection control device 29. Further, they comprise second line portions 147, 149 internal to the connection control device 29 and connecting the second and third input ports 143, 145 with fourth and fifth output ports 151, 153 of the connection control device 29. Finally there are provided third external line portions 155, 157 of the first and second remote control lines 47, 49 connecting the fourth and fifth output ports 151, 153 with the first and second remote control input ports 43, 45 of the supply means 3.

    [0022] The first control portion 121 of the connection control device 29 also comprises a sixth output port 159 internally connected to the first input port 125 of the connection control device 29 and providing hydraulic fluid with the constant pressure of the auxiliary pump 63. The sixth output port 159 is connected via a fourth external constant pressure supply line 161 to the constant pressure inlet port 37 of the hydraulic remote control means 31.

    [0023] The first control portion 121 of the connection control device 29 has a first switching means 171 adapted to selectively supply the hydraulic fluid with constant pressure from the auxiliary pump 63.

    [0024] Referring to an enlarged schematic representation of the connection control device 29 in Fig. 2, the first control portion 121 comprises a first internal connection line 175 connecting the first input port 125 to the first switching means 171 and, as mentioned above, to the sixth output port 159. The first switching means 171 is also connected to a second internal connection line 177 which is selectively connectable to one of the second or third inputs 143, 145 of the connection control device 29 to receive hydraulic control fluid varied in pressure and as output from one of the first and second control output ports 39, 41 of the hydraulic remote control means 31, as will be described later. Finally there is provided a fourth internal connection line 181 connecting the first switching means 171 with the third output port 137.

    [0025] The switching means 171 of the preferred embodiment comprises an on-off directional valve 183 which has a neutral position 185 (see Figs. 1 and 2).

    [0026] The on-off directional valve 183 has also an activated position 187 in which it connects the second internal connection line 177 to the fourth internal connection line 181 to supply the hydraulic fluid varied in pressure from one of the first and second control output ports 39, 41 of the hydraulic remote control means 31 to the servo pressure inlet port 103 of the supply means 3. In the neutral position 185, the third output port 137 is disconnected from the hydraulic fluid as supplied from either one of the first and second control output ports 39, 41 of the hydraulic remote control means 31.

    [0027] Preferably the on-off directional valve 183 is pilot operated and connected to a first internal pilot line 189 which is selectively connectable via a second switching means 191 of the connection control device 29 to one of the first and second control output ports 39, 41 of the remote control means 31. Specifically, the first internal pilot line 189 is connected at a first connection point 193 to the second internal connection line 177, which in turn is connected to the second switching means 191 of the connection control device 29. Opening and closing of the second switching means 191, therefore, selectively supplies the hydraulic control fluid from one of the control output ports 39, 41 to the first internal pilot line 189 and the second internal connection line 177. By supplying sufficient pilot pressure via the first internal pilot line 189, the first switching means 171, i.e. the on-off directional valve 183 is switched to its activated position 187 in which the second internal connection line 177 is connected to the third output port 137. The second switching means 191, in this context, also forms part of the first connection control means 122 controlling the supply of hydraulic control fluid from the hydraulic remote control means 3 to the hydraulic adjustment means 77 of the variable displacement pump 51.

    [0028] Specifically, the second switching means 191 comprises first and a second check valves 195, 197. The inlet side of the first and second check valves 195, 197, respectively, is connected in parallel to the first and second remote control lines 45, 47, in particular to their respective second line portions 147, 149 at second and third connection points 201, 203. The outlet side of the first and second check valves 195, 197 is connected via a fourth connection point 205 to the second internal connection line 177 and thus also to the first internal pilot line 189.

    [0029] The hydraulic remote control means 31 receives at the constant pressure inlet port 37 the constant pressure supplied from the sixth output port 159 of the connection control means 29 and modulates the same by means of the pressure variation means 35 between an initial control pressure and a maximum control pressure. The hydraulic fluid with the modulated pressure is directed to one of the first or second control output ports 39, 41 depending on the inclination of the control lever 33, the inclination direction of which indicating a desired mode of operation of the hydraulic transmission system, e.g. a "forward" or a "rearward" drive or rotation direction of a working implement such as the forward and rear rollers of a compactor. The modulating curve or characteristics of the pressure variation means 35 can be chosen as linear or non-linear, depending on the particular situation of application.

    [0030] Once the control lever 33 is manipulated by the operator in either one of the directions indicating, for example, forward or rearward drive, a smooth modulated pressure signal is output from one of the first and second control output ports 39, 41 associated with the desired mode of operation. This modulated pressure signal is input into the connection control device 29 via one of the second and third input ports 143, 145 and operates selectively one of the first or second check valves 195, 197. As, under normal conditions, the hydraulic control fluid with sufficient pressure is only present in one of the second line portions 147, 149, and the other of the second line portions 147, 149 is depressurized, the respective one of the first or second check valves 195, 197 opens so as to communicate the hydraulic control fluid to the fourth connection point 205. The modulated pressure signal is then directed via the first connection point 193, 205 to the first internal pilot line 189 to position the on-off directional valve 183 in its activated position 187. The modulated pressure signal is also communicated via the fourth connection point 205 to the second internal connection line 177, and, in the activated position 187 of the on-off directional valve 183, it is directed via the fourth internal connection line 181 to the third output port 137 of the first control portion 121 of the connection control device 29.

    [0031] The first switching means 171, when operated by manipulating the control lever 33 of the hydraulic remote control means 31 as described above, thus supplies the modulated pressure signal of the hydraulic remote control means 31 to the servo pressure inlet port 103 and the internal servo pressure supply line 99 of the supply means 3.

    [0032] With further reference to Figs. 3 and 4 showing the first switching means 171 in the activated position 187, at the same time the modulated pressure is sent via one of the fourth and fifth output ports 151, 153 to the respective remote control input ports 43, 45 of the supply means 3 and pilots the directional distributor valve 91 into one of its first or second control positions 95, 97 so as to communicate the modulated pressure signal present on the internal servo pressure supply line 99 to one of the piston chambers of the servo piston 79.

    [0033] Thus, the first connection control means 122 comprising the distributor means 89 and the first control portion 121 is operated by the hydraulic control fluid supplied from the hydraulic remote control means 31 and directs, upon actuation of the hydraulic remote control means 31, the hydraulic control fluid to the hydraulic adjustment means 77. In particular, when operating the hydraulic remote control means 31, initially only a slight movement of the directional distributor valve 91 is permitted. Also, because of the plug 101, the full charge pressure of the auxiliary pump 63 is not applied to the servo piston 79 at once, but instead it is supplied with hydraulic control fluid having the smoothly modulated pressure from the hydraulic remote control means 31 via the internal servo pressure supply line 99 and the servo pressure input port 103.

    [0034] As mentioned above and with further reference to Fig. 1, besides the function provided by the first control portion 121 relating to the control of the adjustment means 77 of the variable displacement pump 51, the connection control device 29 also provides control of the connection of the first through fourth working line portions 21, 23, 25, 27 of the closed circuit hydraulic system 1. In particular, the connection control device 29 comprises a second control portion 221 adapted to control the connection of the first through fourth working line portions 21, 23, 25, 27 so that the motors 13, 15 of the hydraulic system 1 can be selectively connected in series and/or in parallel.

    [0035] As shown in more detail in Fig. 2, the second control portion 221 comprises first and second ports 231, 233 connected to the first and second working line portions 21, 23, respectively, and third and fourth ports 235, 237 connected to the third and fourth working line portions 25, 27, respectively. It further comprises first and second internal working lines 241, 243 which are respectively connected to the first and second ports 231, 233, and third and fourth internal working lines 245, 247 connected respectively to the third and fourth ports 235, 237. There are also provided first and second branch lines 249, 251 of the first and second internal working lines 241, 243, respectively.

    [0036] The first through fourth internal working lines 241, 243, 245, 247 and the first and second branch lines 249, 251 are connected to a third switching means 261 of the second control portion 221 adapted to controllably connect the internal working lines 241, 243, 245, 247 and the first and second branch lines 249, 251 in a selected manner.

    [0037] Preferably, the third switching means 261 comprises a proportional 6-way directional valve 263 which is pilot operated by a pilot pressure provided on a second internal pilot line 265 into a position between a first extreme position 267 as shown in Figs. 1 and 2 and a second extreme position 269.

    [0038] In the first extreme position 267 which may be also referred to as the neutral position of the proportional directional valve 263, the first and second internal working lines 241, 243 are connected and the third and fourth internal working lines 245, 247 and the first and second branch lines 249, 251 are disconnected from each other so that effectively the first and second ports 231, 233 are connected with each other. Thus, with reference to Fig. 1, the first and second working line portions 21, 23 of the closed circuit are connected with each other and provide for a serial connection of the first and second motors 13, 15, i.e. starting from the first supply port 5 via the first working line 9 to the first motor 13, the circuit of the hydraulic system 1 is closed via the second working line portion 23, second internal working line 243, first internal working line 241, first working line portion 21 to the second motor 15 and back to the second supply port 7 via the second working line 11.

    [0039] In the second extreme position 269 of the third switching means 261, the first branch line 249 is connected to the third internal working line 245 and the second branch line 251 is connected to the fourth internal working line 247 so that effectively the first and the third ports 231, 235 are connected with one another and the second and the fourth ports 233, 237 are connected with one another. Thus, the first through fourth working line portions 21, 23, 25, 27 are connected with one another so as to provide a parallel connection of the first and second motors 13, 15 in the hydraulic system 1. In particular the first motor 13 is connected to the first and second supply ports 5, 7 of the supply means via the first working line 9 leading to the first motor 13, the second working line portion 23, the second internal working line portion 243 and its second branch line 251, the fourth internal working line portion 247 and the fourth working line portion 27 back to the second supply port 7. The second motor 15 is connected to the first supply port 5 via the first working line 9, the third working line portion 25, the third internal working line portion 245, the first internal working line portion 241 and its first branch line 249, the first working line portion 21 to the second motor 15 and back to the second supply port 7 via the second working line 11.

    [0040] The pilot pressure to operate the third switching means 261 is provided via the second internal pilot line 265 which is also connected to the fourth connection point 205 receiving the modulated pressure of one of the first and second remote control lines 47, 49 through one of the first and second check valves 195, 197 of the second switching means 191 of the connection control device 29. In other words, the hydraulic transmission system 1 has a second connection control means 271 comprising the second switching means 191 and the second control portion 221 and responsive to a control signal, e.g. the hydraulic control fluid supplied from the hydraulic remote control means 31, so as to control the connection of the working line portions 21 to 25 selectively between a serial and a parallel connection.

    [0041] The third switching means 261 is preferably proportional, e.g. it shifts from the first extreme position 267 to the second extreme position 269 proportional to the control signal, which is in the preferred case the pilot pressure applied through the second internal pilot line 265 to the proportional 6-way directional valve 263. This pilot pressure corresponds to the smoothly modulated pressure of the hydraulic control fluid from the hydraulic remote control means 31. Thus, the third switching means 261 provides a smooth change from series to parallel connection of the first and second motors 13, 15 in the hydraulic system 1. The lower the pilot pressure, the more the third switching means 261 is positioned towards the first extreme position 267.

    [0042] A 6-way valve is preferred inasmuch in changing from the series configuration of the system 1 to the parallel configuration, the first and second working line portions 21, 23 having been connected in series are initially depressurized. This type of connection is less affected by forces when operating the proportional directional valve 263.

    [0043] Figs. 3 and 4 show an intermediate state of the proportional 6-way directional valve 263 in which the connection configuration of the system 1 is transferred from series to parallel connection of the first and second motors 13, 15. It is illustrated that the higher the pilot pressure in the second pilot line 265, the more the connection between the first branch line 249 and the third internal working line 245 and the connection between the second branch line 251 and the fourth internal working line 247 are opened and the more the connection between the first and second internal working lines 241, 243 is closed.

    [0044] The switching operation corresponds to opening and closing variable orifices of the proportional directional valve 263 and thus to proportional throttling which allows a smooth change of the flow rate and the pressure during the transition from serial to parallel connection of the first and second motors 13, 15. If, for example, the pilot pressure signal on the second internal pilot line 265 ranges from 5 to 20 bar, the proportional directional valve 263 allows a first switching stage (e.g. in a range of 5 to 8 bar) during which the connection is almost series, and a second switching stage during which the first and second motors 13, 15 are connected in parallel.

    [0045] Fig. 3 schematically represents the hydraulic system 1 in the intermediate condition. It shows that the modulated pressure of the hydraulic remote control means 31, e.g. from the second control output port 41 acting as pilot pressure on both the first and second internal pilot lines 189, 265 has effected also switching of the first switching means 171 to the activated position 187 so as to provide the same modulated pressure to the servo piston 79. The same modulated pressure from the second control output port 41 of the hydraulic remote control means 31 acts also as pilot pressure on the second distributor pilot line 107 of the distributor directional valve 91 and has moved the same into the first control position 95 so that the servo pressure corresponding to the modulated pressure on the servo pressure supply line 99 is supplied to a selected piston chamber of the servo piston 79 via the first servo piston control line 81.

    [0046] The transition from serial to parallel connection is shown in a diagram as represented in Fig. 5 from which it can be seen that the behavior or change of the flow rate of the first and second motors 13, 15 during the transition from serial to parallel remains smooth. In the diagram of Fig. 5, the flow rate Qmotor of one of the motors 13, 15 is shown versus the pressure of the hydraulic control fluid as supplied from the hydraulic control means 31. Further, the variable flow rate of the displacement pump 51 is indicated by Qpump. The maximum flow rate of the pump 51 is Qmax. With Q1max and Q2max indicating the maximum flow rates of the two motors 13 and 15, in the specifically shown embodiment of Fig. 5, the motors 13, 15 are of identical construction and their respective maximum flow rates are the same, i.e. Q1 max = Q2max.

    [0047] During a first stage of operation of the hydraulic system 1, the flow rate Qmotor is equal or close to the flow rate Qpump because of the predominantly serial connection configuration in which the flow rate of the whole hydraulic system 1 is constant. In a later stage with higher pressure of the hydraulic control fluid, in the parallel connection configuration the flow rate Qpump is divided to the motors 13, 15 according to the loading. With equal loading on both motors, the flow rate Qpump is equally partitioned to the motors 13, 15 so that Qmotor substantially corresponds to one half of Qpump.

    [0048] Although in the preferred embodiment the connection control device 29, i.e. the first and third switching means 171, 261, and also the directional distributor valve 91 are embodied as valves pilot operated by the hydraulic control fluid supplied by the hydraulic remote control means 31, it may be contemplated to provide a different control signal for the appropriate operation of the components of the connection control device 29 and the directional distributor valve 91. In particular, it may be envisaged to generate an electric signal indicative of the desired flow rate of the hydraulic working fluid, i.e. the operational speed of the system, which may be generated by sensing the inclination of the control lever 33, for example. Such a control signal can then be used to operate, for example by means of a solenoid, the respective switching valves. In particular, this offers an option in the case of the second connection control means 271 comprising the third switching means 261 which is provided to control the serial/parallel connection of the at least two motors 13, 15.

    [0049] Although a major part of the first connection control means 122 and the second connection control means 271 are shown to be realized in one connection control device 29, it is to be noted that the second connection control means 271 controlling the connection configuration of the at least two motors 13, 15 can be realized independent from the first connection control means 122 controlling the supply of hydraulic control fluid to the hydraulic adjustment means 77 of the variable displacement pump 51. By providing the second connection control means 271 independently from the first connection control means 122 the same advantages may be achieved as the connection of the at least two motors 13, 15 in the closed circuit hydraulic system 1 can be changed from serial to parallel configuration in response to a control signal, e.g. the pressure or flow rate of hydraulic working fluid supplied by the supply means 3.

    Industrial applicability



    [0050] According to one aspect, the hydraulic transmission system 1 is used in any closed circuit hydraulic system in which the supply means for hydraulic working fluid is connected to one or more users, as for example the motors 13, 15, in a closed circuit and in which the supply means is controlled by a hydraulic adjustment means. In hydraulic transmission systems of the prior art, no matter how fine the pressure modulation given by a pilot lever of a hydraulic remote control for operating the system, during the first instant of operation or movement of the system, one of the chambers of, for example, a servo piston of an axial piston pump receives the full charge pressure of the auxiliary pump causing a sudden flow peak of the hydraulic working fluid in the hydraulic transmission. This can result in undesirable consequences, for example if the hydraulic transmission system is used for driving an asphalt roller or compactor this may lead to a marking which is left in the asphalt surface by the compactor upon start. Such a drawback is avoided by the improved hydraulic transmission system 1 described herein, inasmuch upon actuation of the hydraulic remote control means 31 only a slight movement of the directional distributor valve 91 is permitted at the first instant of movement of the control lever 33.

    [0051] As mentioned before, in hydraulic closed circuit transmission systems of the prior art the directional distributor valve is pilot operated in a standard manner to apply the full constant pressure of the auxiliary pump to the supply lines for the hydraulic adjustment means 77. Fixed orifices are used downstream of the distributor valve to control the acceleration and deceleration ramp of the system. In such a situation it is very difficult to achieve a smooth regular ramp for the movement of a machine without using heavy duty or expensive electronics. Advantageously, the operation of the hydraulic adjustment means 77, e.g. the servo piston 79 of the variable displacement pump 51 of the hydraulic transmission system 1 of the present invention is ramped up in a controlled and smooth manner as the hydraulic control fluid having the control pressure which is supplied from the hydraulic remote control means 31 is applied to the chambers of the servo piston 79 directly.

    [0052] In a typical hydraulic traction system for a utility machine, such as an asphalt roller having front and rear rollers driven by two hydraulic motors, the motors are connected in parallel to one supply means for hydraulic working fluid, e.g. a pump such as the variable displacement pump 51. The torque developed by parallel-connected motors is flow dependent and is affected by the shaft loading on each motor. If one of the motors is not shaft loaded it may receive all the flow and the torque value is very low. In an asphalt roller, for example, this may result in slippage on the front drum or roller when the compactor is ascending an inclined road surface with a low frictional coefficient. On the other hand, a series connection may result in over pressurization of the hydraulic circuit and cavitation of the motors.

    [0053] According to another aspect of the invention, the at least two motors of, for example, a front and a rear roller of an asphalt compactor are initially connected in series. Upon start of the hydraulic transmission system 1, all of the motors are provided with sufficient hydraulic working fluid so as to initiate movement of the associated working implements, e.g. the asphalt front and rear rollers. Only after the working implements have reached a desired working condition, the connection configuration of the motors is transferred to a parallel configuration depending on the pressure of the hydraulic working fluid as indicated by the variable pressure of the hydraulic control fluid.

    [0054] In the preferred embodiment as described above, both the control of the hydraulic adjustment means 77 of the supply means 3 and the control of the connection configuration of the at least two motors or users 13, 15 are achieved via one common control signal, e.g. the hydraulic control fluid supplied by the hydraulic remote control means 31, which acts as the pilot signal for operating the first and second connection control means 122, 271 which comprise the first and second control portions 121, 221 of the connection control device 29 and the directional distributor valve 91. In addition, the same hydraulic control fluid is supplied to the hydraulic adjustment means 77 of the variable displacement pump 51 to smoothly control the flow of the hydraulic working fluid in the hydraulic transmission system 1. Thus, in an effective and compact manner, both the change of the connection configuration from serial to parallel and the ramp of the pressure of the hydraulic working fluid are controlled by means of one control signal, e.g. the hydraulic control fluid supplied by the hydraulic remote control means 31.


    Claims

    1. Hydraulic transmission system (1) comprising:

    - supply means (3) adapted to supply a variable flow rate of hydraulic working fluid;

    - said supply means (3) comprising hydraulic adjustment means (77) for adjusting the variable flow rate of the hydraulic working fluid;

    - actuatable hydraulic control means (31) having an actuated condition in which the actuatable hydraulic control means (31) generates a hydraulic control fluid having a control pressure which is adjustable between an initial control pressure and a maximum control pressure;

    - first connection control means (122) operable by said hydraulic control fluid supplied from said hydraulic control means (31) and adapted to direct, upon actuation of said hydraulic control means (31), said hydraulic control fluid to said hydraulic adjustment means (77),
    wherein said first connection control means (122) comprises distributor means (89) connected to said hydraulic adjustment means (77), said distributor means (89) has a control position (95, 97) in which it directs said hydraulic control fluid to said hydraulic adjustment means (77) upon actuation of said hydraulic control means (31),
    characterized in that
    said distributor means has further a neutral position (93) in which it connects the hydraulic adjustment means (77) to a hydraulic fluid tank (65).


     
    2. The hydraulic system (1) of claim 1, further comprising:

    - at least two working lines (9, 11) receiving said hydraulic working fluid at variable flow rate from said supply means (3);

    - at least two hydraulic users (13, 15) connected to said supply means (3) via said at least two working lines (9, 11, 21, 23, 25, 27) in a closed circuit configuration;
    second connection control means (271) adapted to control the connection of working line portions (21, 23, 25, 27) connected to the at least two users (13, 15);
    said hydraulic control means (31) are adapted to generate a control signal indicative of a desired flow rate of the hydraulic working fluid supplied by said supply means (3), and

    - said second connection control means (271) are responsive to said control signal so as to selectively provide serial and/or parallel connection of the at least two hydraulic users (13, 15) by selectively connecting the working line portions (21, 23, 25, 27).


     
    3. The hydraulic system (1) of claim 2, wherein said control signal is the hydraulic control fluid with variable pressure supplied by said hydraulic control means (31).
     
    4. The hydraulic system (1) of any of the preceding claims, wherein said hydraulic control means (31) has at least first and second control outputs (39, 41) supplying hydraulic control fluid and associated with respective first and second modes of operation of the hydraulic transmission system.
     
    5. The hydraulic system (1) of any of the preceding claims, wherein said distributor means (89) comprise a pilot operated directional distributor valve (91) having a distributor pilot line (105, 107) connected to said hydraulic control fluid from the hydraulic control means (31) and being movable into said control position (95, 97) upon supply of said hydraulic control fluid on said distributor pilot line (105, 107) so as to selectively direct said hydraulic control fluid from the hydraulic control means (31) to said hydraulic adjustment means (77).
     
    6. The hydraulic system (1) of claim 5, wherein said first and second control outputs (39, 41) being connected to first and second distributor pilot lines (105, 107) of the directional distributor valve (91) to move the distributor valve (91) in an associated first or second control position (95, 97), said hydraulic adjustment means (77) being responsive to the first or second control position (95, 97) so as to cause said supply means (3) to supply said hydraulic working fluid in a selected one of first and second flow directions in the hydraulic system (1), said first and second flow directions being associated to said first and second control positions (95, 97).
     
    7. The hydraulic system (1) of any of the preceding claims, wherein said first connection control means (122) comprise a first switching means (171) adapted to connect a supply line (99) of said distributor means (89) to the hydraulic control fluid from the hydraulic control means (31) in response to actuation of the hydraulic control means (31).
     
    8. The hydraulic system (1) of claim 7, wherein said first switching means (171) is adapted to connect said hydraulic adjustment means (77) to a supply of hydraulic fluid having constant pressure in the non activated condition of the hydraulic control means (31) and to disconnect said supply of hydraulic fluid having constant pressure from the hydraulic adjustment means (77) in the activated condition of the hydraulic control means (31).
     
    9. The hydraulic system (1) of claim 7 or 8, wherein said first switching means (171) is a pilot operated directional on-off valve (183) having an activated position (187) in which the directional on-off valve (183) directs said hydraulic control fluid from said hydraulic control means (31) to the distributor means (89).
     
    10. The hydraulic system (1) of claim 9, wherein said directional on-off valve (183) further has a neutral position (185) in which it connects said hydraulic adjustment means (77) to said supply of hydraulic fluid having constant pressure.
     
    11. The hydraulic system (1) of claim 9 or 10, wherein said directional on-off valve (183) has a first pilot line (189) selectively connectable to the hydraulic control fluid of the hydraulic control means (31), said directional on-off valve (183) being movable to its activated position (187) upon receiving hydraulic control fluid on said first pilot line (189).
     
    12. The hydraulic system (1) of claim 11, wherein said hydraulic system (1) further comprises second switching means (191) selectively connecting the first pilot line (189) of the directional on-off valve (183) to the first or second control outputs (39, 41) of the hydraulic control means (31).
     
    13. The hydraulic system (1) of claim 12, wherein said second switching means (191) comprises first and second check valves (195, 197) having their respective inputs connected to the first and second control outputs (39, 41) of the hydraulic control means (31) and having their respective outputs connected to the first pilot line (189) of the directional on-off valve (183).
     
    14. The hydraulic system (1) of any of claims 12 or 13, wherein said second switching means (191) selectively directs hydraulic control fluid of one of the first and second outputs (39, 41) of the hydraulic control means (31) to a control fluid input of the directional on-off valve (183), said control fluid input being connected to a control fluid output of the directional on-off valve (183) in its activated position (187).
     
    15. The hydraulic system (1) of any of the preceding claims, wherein said supply means (3) comprise a variable displacement pump (51) of the axial piston type with swash plate design and said hydraulic adjustment means (77) comprises a double acting servo piston (79) connected to said variable displacement pump (51).
     
    16. The hydraulic system (1) of claim 15, wherein, in said control position (95, 97), said directional distributor valve (91) directs said hydraulic control fluid from the hydraulic control means (31) to an associated one of the piston chambers of the servo piston (79).
     
    17. The hydraulic system (1) of claim 16, wherein said directional distributor valve (91) has a neutral position when no hydraulic control fluid is supplied to the distributor pilot line (105, 107), and wherein said neutral position of said directional distributor valve (91) connects both chambers of the servo piston to a tank (65) in order to balance the position of said servo piston (79).
     
    18. The hydraulic system (1) of any of the preceding claims, wherein said hydraulic control means (31) generates said hydraulic control fluid at continuously variable pressure between an initial control pressure and a maximum control pressure; wherein said second control means (271) is adapted to control the connection of the working line portions (21, 23, 25, 27) so as to change substantially smoothly from a serial connection configuration at the initial control pressure to a parallel connection configuration at the maximum control pressure.
     
    19. The hydraulic system (1) of any of the preceding claims, wherein said second connection control means (271) comprises a directional valve (263) having a first extreme position (267) in which it connects the working line portions (21, 23, 25, 27) in a serial connection configuration of the at least two users (13, 15) and having a second extreme position (269) in which it connects the working line portion (21, 23, 25, 27) in a parallel connection configuration of the at least two users (13, 15), said directional valve (263) being adapted to change its position responsive to the control signal.
     
    20. The hydraulic system (1) of claim 19, wherein said directional valve (263) is proportional and changes its position from the first extreme position (267) to the second extreme position (269) responsive and proportional to said control signal.
     
    21. The hydraulic system (1) of claim 20, wherein said directional valve (263) is a 6-way proportional valve adapted to depressurize the working line portions (21, 23) connected in a serial connection configuration when changing its position from the first extreme position (267) to the second extreme position (269).
     
    22. The hydraulic system (1) of any of claims 19 to 21, wherein said directional valve (263) is pilot operated by said hydraulic control fluid supplied by said hydraulic control means (31).
     
    23. The hydraulic system (1) of claim 22, wherein said directional valve (263) has a second pilot line (265) selectively connectable to the hydraulic control fluid of the hydraulic control means (31), said directional valve being movable from the first extreme position (267) towards the second extreme position (269) dependent on said varied pressure of said hydraulic control fluid.
     
    24. The hydraulic system (1) of claim 23, wherein said first and second control outputs (39, 41) of said hydraulic control means (31) are selectively connectable to said second pilot line (265) of said directional valve (263).
     
    25. The hydraulic system (1) of claim 24, wherein said second switching means (191) of said hydraulic system also are adapted to selectively connect the second pilot line (265) of the directional valve (263) to the first or second control outputs (39, 41) of the hydraulic control means (31).
     
    26. The hydraulic system (1) of claim 25, wherein said second switching means (191) comprises first and second check valves (195, 197) having their respective inputs connected to the first and second control outputs (39, 41) of the hydraulic control means (31) and having their respective outputs connected to the second pilot line (265) of the directional valve (263).
     
    27. A method for controlling a hydraulic transmission system (1), said hydraulic transmission system (1) comprising supply means (3) for supplying hydraulic working fluid at variable flow rate; wherein said supply means (3) comprising hydraulic adjustment means (77) for adjusting the variable flow rate of the hydraulic working fluid;
    said method comprises the steps of:

    - providing a hydraulic control fluid having a control pressure which is adjustable between an initial control pressure and a maximum control pressure, said control pressure being indicative of a desired flow rate of the hydraulic working fluid;

    - selectively directing said hydraulic control fluid during an actuated condition to said hydraulic adjustment means (77), and

    - operating said hydraulic adjustment means (77) by means of said hydraulic control fluid,

    characterized in that
    said actuated condition during which said hydraulic control fluid is selectively directed to said hydraulic adjustment means starts with providing said hydraulic control fluid with said initial pressure at minimum.
     
    28. The method of claim 27, further comprising, in a non-actuated condition, providing hydraulic fluid at constant pressure to said hydraulic adjustment means (77) and connecting the same to a tank (65) of hydraulic fluid.
     
    29. The method of claim 27 or 28, wherein said hydraulic transmission system (1) further comprises first connection control means (122) adapted to selectively direct said hydraulic control fluid to said hydraulic adjustment means, said method comprises the step of operating said first connection control means (122) by said hydraulic control fluid.
     
    30. The method of any of claims 27 to 29, wherein said supply means (3) are adapted to supply hydraulic working fluid at variable flow rate to at least two working lines (9, 11), and said hydraulic system (1) further comprises at least two hydraulic users (13, 15) connected to said supply means (3) via said at least two working lines (9, 11) in a closed circuit configuration; said method further comprises the steps of:

    - providing a control signal indicative of a desired flow rate of the hydraulic working fluid supplied by said supply means (3);

    - controlling the connection of working line portions (21, 23, 25, 27) connected to the at least two users (13, 15) so as to selectively provide serial and/or parallel connection of the at least two hydraulic users (13, 15) in response to said control signal.


     
    31. The method of claim 30, wherein said control signal is provided continuously variable between an initial control signal value and a maximum control signal value; wherein said connection of the working line portions (21, 23, 25, 27) is controlled so as to change substantially smoothly from a serial connection configuration at the initial control signal value to a parallel connection configuration at the maximum control signal value.
     
    32. The method of claim 30 or 31, wherein said connection of the working line portions (21, 23, 25, 27) is controlled by second connection control means (271) which are operated by said control signal.
     
    33. The method of claim 32, wherein said second connection control means (271) are operable by a hydraulic pilot pressure, wherein said control signal is provided in the form of said hydraulic control fluid having variable pressure corresponding to the desired pressure of the working fluid, said method further comprises the step of pilot operating said second connection control means (271) by said hydraulic control fluid.
     


    Ansprüche

    1. Hydraulikübertragungssystem (1), welches Folgendes aufweist:

    Liefermittel (3), die geeignet sind, um ein Hydraulikarbeitsströmungsmittel mit variabler Flussrate zu liefern;

    wobei die Liefermittel (3) Hydraulikeinstellmittel (77) aufweisen, um die variable Flussrate des hydraulischen Arbeitsströmungsmittels einzustellen;

    betätigbare Hydrauliksteuermittel (31), welche einen betätigten Zustand haben, in dem die betätigbaren Hydrauliksteuermittel (31) ein hydraulisches Steuerströmungsmittel mit einem Steuerdruck erzeugen, der zwischen einem anfänglichen Steuerdruck und einem maximalen Steuerdruck einstellbar ist;

    erste Verbindungssteuermittel (122), die durch das hydraulische Steuerströmungsmittel, welches von den Hydrauliksteuermitteln (31) geliefert wird, betätigbar sind und geeignet sind, um auf eine Betätigung der Hydrauliksteuermittel (31) hin das hydraulische Steuerströmungsmittel zu den Hydraulikeinstellmitteln (77) zu leiten,

    wobei die ersten Verbindungssteuermittel (122) Verteilermittel (89) aufweisen, die mit den Hydraulikeinstellmitteln (77) verbunden sind, wobei die Verteilermittel (89) eine Steuerposition (95, 97) haben, in der sie das hydraulische Steuerströmungsmittel auf eine Betätigung der Hydrauliksteuermittel (31) hin zu den Hydraulikeinstellmitteln (77) leiten,

    dadurch gekennzeichnet, dass

    die Verteilermittel weiter eine Neutralposition (93) haben, in der sie die Hydraulikeinstellmittel (77) mit einem Hydraulikströmungsmitteltank (65) verbinden.


     
    2. Hydrauliksystem (1) nach Anspruch 1, welches weiter Folgendes aufweist:

    zumindest zwei Arbeitsleitungen (9, 11), welche das hydraulische Arbeitsströmungsmittel mit variabler Flussrate von den Liefermitteln (3) aufnehmen;

    zumindest zwei hydraulische Verbraucher (13, 15), die mit den Liefermitteln (3) über die mindestens zwei Arbeitsleitungen (9, 11, 21, 23, 25, 27) in einer Konfiguration mit geschlossenem Kreislauf verbunden sind;

    zweite Verbindungssteuermittel (271), die geeignet sind, um die Verbindung der Arbeitsleitungsteile (21, 23, 25, 27) zu steuern, welche mit den mindestens zwei Verbrauchern (13, 15) verbunden sind;

    wobei die Hydrauliksteuermittel (31) geeignet sind, um ein Steuersignal zu erzeugen, welches eine erwünschte Flussrate des hydraulischen Arbeitsströmungsmittels anzeigt, welches von den Liefermitteln (3) geliefert wird,

    und

    wobei die zweite Verbindungssteuermittel (271) auf das Steuersignal ansprechen, um selektiv eine serielle und/oder parallele Verbindung der mindestens zwei hydraulischen Verbraucher (13, 15) durch selektives Verbinden der Arbeitsleitungsteile (21, 23, 25, 27) vorzusehen.


     
    3. Hydrauliksystem (1) nach Anspruch 2, wobei das Steuersignal das hydraulische Steuerströmungsmittel mit variablem Druck ist, welches von den Hydrauliksteuermitteln (31) geliefert wird.
     
    4. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die Hydrauliksteuermittel (31) zumindest erste und zweite Steuerausgänge (39, 41) haben, welche hydraulisches Steuerströmungsmittel liefern und mit jeweiligen ersten und zweiten Betriebsmodi des Hydraulikübertragungssystems assoziiert sind.
     
    5. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die Verteilermittel (89) ein pilot- bzw. vorsteuerbetätigtes Richtungsverteilerventil (91) mit einer Verteilervorsteuerleitung (105, 107) aufweisen, die mit dem hydraulischen Steuerströmungsmittel von den Hydrauliksteuermitteln (31) verbunden sind und in die Steuerposition (95, 97) daraufhin bewegbar sind, dass hydraulisches Steuerströmungsmittel auf der Verteilervorsteuerleitung (105, 107) geliefert wird, um selektiv das hydraulische Steuerströmungsmittel von den Hydrauliksteuermitteln (31) zu den Hydraulikeinstellmitteln (77) zu leiten.
     
    6. Hydrauliksystem (1) nach Anspruch 5, wobei die ersten und zweiten Steuerausgänge (39, 41) mit den ersten und zweiten Verteilervorsteuerleitungen (105, 107) des Richtungsverteilerventils (91) verbunden sind, um das Richtungsverteilerventil (91) in eine assoziierte erste oder zweite Steuerposition (95, 97) zu bewegen, wobei die Hydraulikeinstellmittel (77) auf die erste oder zweite Steuerposition (95, 97) ansprechen, um zu bewirken, dass die Liefermittel (3) das hydraulische Arbeitsströmungsmittel in eine ausgewählte eine Richtung der ersten und zweiten Flussrichtungen in dem Hydrauliksystem (1) liefern, wobei die ersten und zweiten Flussrichtungen mit den ersten und zweiten Steuerpositionen (95, 97) assoziiert sind.
     
    7. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die ersten Verbindungssteuermittel (122) erste Schaltmittel (171) aufweisen, die geeignet sind, um eine Lieferleitung (99) der Verteilermittel (89) mit dem hydraulischen Steuerströmungsmittel von den Hydrauliksteuermitteln (31) ansprechend auf eine Betätigung der Hydrauliksteuermittel (31) zu verbinden.
     
    8. Hydrauliksystem (1) nach Anspruch 7, wobei die ersten Schaltmittel (171) geeignet sind, um die Hydraulikeinstellmittel (77) mit einer Versorgung für Hydraulikströmungsmittel mit konstantem Druck in dem nicht aktivierten Zustand der Hydrauliksteuermittel (31) zu verbinden, und die Versorgung für Hydraulikströmungsmittel mit konstantem Druck von den Hydraulikeinstellmitteln (77) im aktivierten Zustand der Hydrauliksteuermittel (31) zu trennen.
     
    9. Hydrauliksystem (1) nach Anspruch 7 oder 8, wobei die ersten Schaltmittel (171) ein pilot- bzw. vorsteuerbetätigtes An-Aus-Richtungsventil (183) sind, welches eine aktivierte Position (187) hat, in der das An-Aus-Richtungsventil (183) das hydraulische Steuerströmungsmittel von den Hydrauliksteuermitteln (31) zu den Verteilermitteln (89) leitet.
     
    10. Hydrauliksystem (1) nach Anspruch 9, wobei das An-Aus-Richtungsventil (183) weiter eine Neutralposition (185) hat, in der es die Hydraulikeinstellmittel (77) mit der Versorgung für Hydraulikströmungsmittel mit konstantem Druck verbindet.
     
    11. Hydrauliksystem (1) nach Anspruch 9 oder 10, wobei das An-Aus-Richtungsventil (183) eine erste Pilot- bzw. Vorsteuerleitung (189) hat, die selektiv mit dem hydraulischen Steuerströmungsmittel der Hydrauliksteuermittel (31) verbindbar ist, wobei das An-Aus-Richtungsventil (183) in seine aktivierte Position (187) daraufhin bewegbar ist, dass es hydraulisches Steuerströmungsmittel von der ersten Vorsteuerleitung (189) empfängt.
     
    12. Hydrauliksystem (1) nach Anspruch 11, wobei das Hydrauliksystem (1) weiter zweite Schaltmittel (191) aufweist, welche selektiv die erste Vorsteuerleitung (189) des An-Aus-Richtungsventils (183) mit den ersten oder zweiten Steuerausgängen (39, 41) der Hydrauliksteuermittel (31) verbinden.
     
    13. Hydrauliksystem (1) nach Anspruch 12, wobei die zweiten Schaltmittel (191) erste und zweite Rückschlagventile (195, 197) aufweisen, wobei deren jeweilige Eingänge mit den ersten und zweiten Steuerausgängen (39, 41) der Hydrauliksteuermittel (31) verbunden sind, und wobei deren jeweilige Ausgänge mit der ersten Vorsteuerleitung (189) des An-Aus-Richtungsventils (183) verbunden ist.
     
    14. Hydrauliksystem (1) nach einem der Ansprüche 12 oder 13, wobei die zweiten Schaltmittel (191) selektiv hydraulisches Steuerströmungsmittel von einem der ersten und zweiten Ausgänge (39, 41) der Hydrauliksteuermittel (31) zu einem Steuerströmungsmitteleingang des An-Aus-Richtungsventils (183) leiten, wobei der Steuerströmungsmitteleingang mit einem Steuerströmungsmittelausgang des An-Aus-Richtungsventils (183) in dessen aktivierter Position (187) verbunden ist.
     
    15. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die Liefermittel (3) eine Pumpe (51) mit variabler Verdrängung der Axialkolbenbauart mit Taumelscheibenkonstruktion aufweisen, und wobei die Hydraulikeinstellmittel (77) einen doppelt wirkenden Servokolben (79) aufweisen, der mit der Pumpe (51) mit variabler Verdrängung verbunden ist.
     
    16. Hydrauliksystem (1) nach Anspruch 15, wobei das Richtungsverteilerventil (91) in der Steuerposition (95, 97) das hydraulische Steuerströmungsmittel von den Hydrauliksteuermitteln (31) zu einer assoziierten Kammer der Kolbenkammern des Servokolbens (79) leitet.
     
    17. Hydrauliksystem (1) nach Anspruch 16, wobei das Richtungsverteilerventil (91) eine Neutralposition hat, wenn kein hydraulisches Steuerströmungsmittel zu der Verteilervorsteuerleitung (105, 107) geliefert wird, und wobei die Neutralposition des Richtungsverteilerventils (91) beide Kammern des Servokolbens mit einem Tank (65) verbindet, um die Position des Servokolbens (79) auszubalancieren.
     
    18. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die Hydrauliksteuermittel (31) hydraulisches Steuerströmungsmittel mit einem kontinuierlich variablen Druck zwischen einem anfänglichen Steuerdruck und einem maximalen Steuerdruck erzeugen; wobei die zweiten Steuermittel (271) geeignet sind, um die Verbindung der Arbeitsleitungsteile (21, 23, 25, 27) so zu steuern, dass sie sich im Wesentlichen sanft von einer seriellen Verbindungskonfiguration bei dem anfänglichen Steuerdruck zu einer parallelen Verbindungskonfiguration bei dem maximalen Steuerdruck verändern bzw. umschalten.
     
    19. Hydrauliksystem (1) nach einem der vorhergehenden Ansprüche, wobei die zweiten Verbindungssteuermittel (271) ein Richtungsventil (263) aufweisen, welches eine erste extreme Position (267) hat, in der es die Arbeitsleitungsteile (21, 23, 25, 27) in einer seriellen Verbindungskonfiguration der mindestens zwei Verbraucher (13, 15) verbindet, und welches eine zweite extreme Position (269) hat, in der es die Arbeitsleitungsteile (21, 23, 25, 27) in einer parallelen Verbindungskonfiguration der mindestens zwei Verbraucher (13, 15) verbindet, wobei das Richtungsventil (263) geeignet ist, um seine Position ansprechend auf das Steuersignal zu verändern.
     
    20. Hydrauliksystem (1) nach Anspruch 19, wobei das Richtungsventil (263) proportional ist und seine Position von der ersten extremen Position (267) zur zweiten extremen Position (269) ansprechend auf und proportional zu dem Steuersignal verändert.
     
    21. Hydrauliksystem (1) nach Anspruch 20, wobei das Richtungsventil (263) ein Sechs-Wege-Proportionalventil ist, welches geeignet ist, um die Arbeitsleitungsteile (21, 23), die in serieller Verbindungskonfiguration verbunden sind, vom Druck zu entlasten, wenn es seine Position von der ersten extremen Position (267) zur zweiten extremen Position (269) verändert.
     
    22. Hydrauliksystem (1) nach einem der Ansprüche 19 bis 21, wobei das Richtungsventil (263) durch das hydraulische Steuerströmungsmittel, welches von den Hydrauliksteuermitteln (31) geliefert wird, pilot- bzw. vorsteuerbetätigt wird.
     
    23. Hydrauliksystem (1) nach Anspruch 22, wobei das Richtungsventil (263) eine zweite Pilot- bzw. Vorsteuerleitung (265) hat, die selektiv mit dem hydraulischen Steuerströmungsmittel der Hydrauliksteuermittel (31) verbindbar ist, wobei das Richtungsventil von der ersten extremen Position (267) zur zweiten extremen Position (269) abhängig von dem variierten Druck des hydraulischen Steuerströmungsmittels bewegbar ist.
     
    24. Hydrauliksystem (1) nach Anspruch 23, wobei die ersten und zweiten Steuerausgänge (39, 41) der Hydrauliksteuermittel (31) selektiv mit der zweiten Vorsteuerleitung (265) des Richtungsventils (263) verbindbar sind.
     
    25. Hydrauliksystem (1) nach Anspruch 24, wobei die zweiten Schaltmittel (191) des Hydrauliksystems auch geeignet sind, um selektiv die zweite Vorsteuerleitung (265) des Richtungsventils (263) mit den ersten oder zweiten Steuerausgängen (39, 41) der Hydrauliksteuermittel (31) zu verbinden.
     
    26. Hydrauliksystem (1) nach Anspruch 25, wobei die zweiten Schaltmittel (191) erste und zweite Rückschlagventile (195, 197) aufweisen, deren Eingänge jeweils mit den ersten und zweiten Steuerausgängen (39, 41) der Hydrauliksteuermittel (31) verbunden sind, und deren jeweilige Ausgänge mit der zweiten Vorsteuerleitung (265) des Richtungsventils (263) verbunden sind.
     
    27. Verfahren zur Steuerung eines Hydraulikübertragungssystems (1), wobei das Hydraulikübertragungssystems (1) Liefermittel (3) aufweist, um hydraulisches Arbeitsströmungsmittel mit einer variablen Flussrate zu liefern; wobei die Liefermittel (3) Hydraulikeinstellmittel (77) zum Einstellen der variablen Flussrate des hydraulischen Arbeitsströmungsmittels aufweisen; wobei das Verfahren folgende Schritte aufweist:

    Liefern eines hydraulischen Steuerströmungsmittels mit einem Steuerdruck, der zwischen einem anfänglichen Steuerdruck und einem maximalen Steuerdruck einstellbar ist, wobei der Steuerdruck eine erwünschte Flussrate des hydraulischen Arbeitsströmungsmittels anzeigt;

    Selektives Leiten des hydraulischen Steuerströmungsmittels während eines aktivierten Zustandes zu den Hydraulikeinstellmitteln (77); und Betätigen der Hydraulikeinstellmittel (77) mittels des hydraulischen Steuerströmungsmittels,

    dadurch gekennzeichnet, dass

    der betätigte Zustand, während dem das hydraulische Steuerströmungsmittel selektiv zu den Hydraulikeinstellmitteln geleitet wird, beginnt, wenn das hydraulische Steuerströmungsmittel mit dem anfänglichen Druck beim Minimum geliefert wird.


     
    28. Verfahren nach Anspruch 27, welches weiter einen nicht betätigten Zustand aufweist, wobei hydraulisches Strömungsmittel mit konstantem Druck zu den Hydraulikeinstellmitteln (77) geliefert wird und dieses mit einem Tank (65) für hydraulisches Strömungsmittel verbunden wird.
     
    29. Verfahren nach Anspruch 27 oder 28, wobei das Hydraulikübertragungssystem (1) weiter erste Verbindungssteuermittel (122) aufweist, die geeignet sind, um selektiv das hydraulische Steuerströmungsmittel zu den Hydraulikeinstellmitteln (77) zu leiten, wobei das Verfahren den Schritt aufweist, die ersten Verbindungssteuermittel (122) durch das hydraulische Steuerströmungsmittel zu betätigen.
     
    30. Verfahren nach einem der Ansprüche 27 bis 29, wobei die Liefermittel (3) geeignet sind, um hydraulisches Arbeitsströmungsmittel mit einer variablen Flussrate mit mindestens zwei Arbeitsleitungen (9, 11) zu liefern, und wobei das Hydrauliksystem (1) weiter zumindest zwei hydraulische Verbraucher (13, 15) aufweist, die mit den Liefermitteln (3) über die mindestens zwei Arbeitsleitungen (9, 11) in einer Konfiguration mit geschlossenem Kreislauf verbunden sind, wobei das Verfahren weiter folgende Schritte aufweist:

    Liefern eines Steuersignals, welches eine erwünschte Flussrate des hydraulischen Arbeitsströmungsmittels anzeigt, welches von den Liefermitteln (3) geliefert wird;

    Steuern der Verbindung der Arbeitsleitungsteile (21, 23, 25, 27), die mit den mindestens zwei Verbrauchern (13, 15) verbunden sind, ansprechend auf das Steuersignal, um selektiv eine serielle und/oder parallele Verbindung der mindestens zwei hydraulischen Verbraucher (13, 15) vorzusehen.


     
    31. Verfahren nach Anspruch 30, wobei das Steuersignal kontinuierlich variabel zwischen einem anfänglichen Steuersignalwert und einem maximalen Steuersignalwert geliefert wird; wobei die Verbindung der Arbeitsleitungsteile (21, 23, 25, 27) so gesteuert wird, dass sie sich im Wesentlichen sanft von einer seriellen Verbindungskonfiguration beim anfänglichen Steuersignalwert zu einer parallelen Verbindungskonfiguration bei dem maximalen Steuersignalwert verändert bzw. umschaltet.
     
    32. Verfahren nach Anspruch 30 oder 31, wobei die Verbindung der Arbeitsleitungsteile (21, 23, 25, 27) durch zweite Verbindungssteuermittel (271) gesteuert wird, die von dem Steuersignal betätigt werden.
     
    33. Verfahren nach Anspruch 32, wobei die zweiten Verbindungssteuermittel (271) durch einen hydraulischen Vorsteuerdruck betätigbar sind, wobei das Steuersignal in Form des hydraulischen Steuerströmungsmittels mit einem variablen Druck geliefert wird, der dem erwünschten Druck des Arbeitsströmungsmittels entspricht, wobei das Verfahren weiter den Schritt aufweist, die zweiten Verbindungssteuermittel (271) durch das hydraulische Steuerströmungsmittel pilot- bzw. vorsteuerzubetätigen.
     


    Revendications

    1. Système de transmission hydraulique (1) comprenant :

    des moyens d'alimentation (3) adaptés à fournir un flux à débit variable d'un fluide d'actionnement hydraulique ;

    les moyens d'alimentation (3) comprenant des moyens d'ajustement hydraulique (77) pour ajuster le flux à débit variable du fluide d'actionnement hydraulique ;

    des moyens de commande hydraulique actionnables (31) ayant un état actionné dans lequel les moyens de commande hydraulique actionnables (31) génèrent un fluide de commande hydraulique ayant une pression de commande qui est ajustable entre une pression de commande initiale et une pression de commande maximum ;

    des premiers moyens de commande de connexion (122) actionnables par le fluide de commande hydraulique fourni par les moyens de commande hydraulique (31) et adaptés à diriger, lors d'un actionnement des moyens de commande hydraulique (31), le fluide de commande hydraulique vers les moyens d'ajustement hydraulique (77),

    dans lequel les premiers moyens de commande de connexion (122) comprennent des moyens de distribution (89) connectés aux moyens d'ajustement hydraulique (77), les moyens de distribution (89) ayant une position de commande (95, 97) dans laquelle ils dirigent le fluide de commande hydraulique vers les moyens d'ajustement hydraulique (77) lors de l'actionnement des moyens de commande hydraulique (31),

    caractérisé en ce que

    les moyens de distribution ont une autre position neutre (93) dans laquelle ils connectent les moyens d'ajustement hydraulique (77) à un réservoir de fluide hydraulique (65).


     
    2. Système hydraulique (1) selon la revendication 1, comprenant en outre :

    au moins deux conduites de travail (9, 11) recevant le fluide d'actionnement hydraulique à débit variable provenant des moyens d'alimentation (3) ;

    au moins deux utilisateurs hydrauliques (13, 15) connectés aux moyens d'alimentation (3) par l'intermédiaire desdites au moins deux conduites de travail (9, 11, 21, 23, 25, 27) dans une configuration en circuit fermé ;

    des deuxièmes moyens de commande de connexion (271) adaptés à commander la connexion de portions de conduites de travail (21, 23, 25, 27) connectées auxdits au moins deux utilisateurs (13, 15) ;

    les moyens de commande hydraulique (31) sont adaptés à générer un signal de commande indicatif d'un débit souhaité du fluide d'actionnement hydraulique fourni par les moyens d'alimentation (3), et

    les deuxièmes moyens de commande de connexion (271) agissent en réponse au signal de commande de façon à assurer sélectivement une connexion en série et/ou en parallèle desdits au moins deux utilisateurs hydrauliques (13, 15) en connectant sélectivement les portions de conduites de travail (21, 23, 25, 27).


     
    3. Système hydraulique (1) selon la revendication 2, dans lequel le signal de commande est le fluide de commande hydraulique ayant une pression variable fourni par les moyens de commande hydraulique (31).
     
    4. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les moyens de commande hydraulique (31) comportent au moins une première et une deuxième sortie de commande (39, 41) fournissant du fluide de commande hydraulique et associées à des premiers et deuxième modes de fonctionnement respectifs du système de transmission hydraulique.
     
    5. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les moyens de distribution (89) comprennent une vanne distributrice directionnelle actionnée par pilote (91) comportant une conduite de pilotage de distributeur (105, 107) connectée au fluide de commande hydraulique provenant des moyens de commande hydraulique (31) et mobile vers la position de commande (95, 97) lors d'une fourniture du fluide de commande hydraulique sur la conduite de pilotage de distributeur (105, 107) de façon à diriger sélectivement le fluide de commande hydraulique provenant des moyens de commande hydraulique (31) vers les moyens d'ajustement hydraulique (77).
     
    6. Système hydraulique (1) selon la revendication 5, dans lequel les première et deuxième sorties de commande (39, 41) sont connectées aux première et deuxième conduites de pilotage de distributeur (105, 107) de la vanne distributrice directionnelle (91) pour déplacer la vanne distributrice (91) dans une première ou une deuxième position de commande associée (95, 97), les moyens d'ajustement hydraulique (77) agissant en réponse à la première ou la deuxième position de commande (95, 97) de façon à amener les moyens d'alimentation (3) à fournir le fluide d'actionnement hydraulique dans l'une sélectionnée des première et deuxième directions de flux dans le système hydraulique (1), les première et deuxième directions de flux étant associées aux première et deuxième position de commande (95, 97).
     
    7. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les premiers moyens de commande de connexion (122) comprennent des premiers moyens de commutation (171) adaptés à connecter une conduite d'alimentation (99) des moyens de distribution (89) au fluide de commande hydraulique provenant des moyens de commande hydraulique (31) en réponse à l'actionnement des moyens de commande hydraulique (31).
     
    8. Système hydraulique (1) selon la revendication 7, dans lequel les premiers moyens de commutation (171) sont adaptés à connecter les moyens d'ajustement hydraulique (77) à une alimentation de fluide hydraulique ayant une pression constante dans l'état non actionné des moyens de commande hydraulique (31) et à déconnecter l'alimentation de fluide hydraulique ayant une pression constante des moyens d'ajustement hydraulique (77) dans l'état actionné des moyens de commande hydraulique (31).
     
    9. Système hydraulique (1) selon la revendication 7 ou 8, dans lequel les premiers moyens de commutation (171) sont une vanne marche-arrêt directionnelle actionnée par pilote (183) ayant une position actionnée (187) dans laquelle la vanne marche-arrêt directionnelle (183) dirige le fluide de commande hydraulique provenant des moyens de commande hydraulique (31) vers les moyens de distribution (89).
     
    10. Système hydraulique (1) selon la revendication 9, dans lequel la vanne marche-arrêt directionnelle (183) comporte en outre une position neutre (185) dans laquelle elle connecte les moyens d'ajustement hydraulique (77) à l'alimentation de fluide hydraulique ayant une pression constante.
     
    11. Système hydraulique (1) selon la revendication 9 ou 10, dans lequel la vanne marche-arrêt directionnelle (183) comporte une première conduite de pilotage (189) pouvant être connectée sélectivement au fluide de commande hydraulique des moyens de commande hydraulique (31), la vanne marche-arrêt directionnelle (183) étant mobile vers sa position actionnée (187) lorsqu'elle reçoit du fluide de commande hydraulique sur la première conduite de pilotage (189).
     
    12. Système hydraulique (1) selon la revendication 11, dans lequel le système hydraulique (1) comprend en outre des deuxièmes moyens de commutation (191) connectant sélectivement la première conduite de pilotage (189) de la vanne marche-arrêt directionnelle (183) à la première ou la deuxième sortie de commande (39, 41) des moyens de commande hydraulique (31).
     
    13. Système hydraulique (1) selon la revendication 12, dans lequel les deuxièmes moyens de commutation (191) comprennent une première et une deuxième vanne d'arrêt (195, 197) ayant leurs entrées respectives connectées aux première et deuxième sorties de commande (39, 41) des moyens de commande hydraulique (31) et ayant leurs sorties respectives connectées à la première conduite de pilotage (189) de la vanne marche-arrêt directionnelle (183).
     
    14. Système hydraulique (1) selon l'une quelconque des revendications 12 ou 13, dans lequel les deuxièmes moyens de commutation (191) dirigent sélectivement le fluide de commande hydraulique de l'une des première et deuxième sorties (39, 41) des moyens de commande hydraulique (31) vers une entrée de fluide de commande de la vanne marche-arrêt directionnelle (183), l'entrée de fluide de commande étant connectée à une sortie de fluide de commande de la vanne marche-arrêt directionnelle (183) dans sa position actionnée (187).
     
    15. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les moyens d'alimentation (3) comprennent une pompe à cylindrée variable (51) du type à piston axial ayant une conception à plateau oscillant et les moyens d'ajustement hydraulique (77) comprennent un servo-piston à double action (79) connecté à la pompe à cylindrée variable (51).
     
    16. Système hydraulique (1) selon la revendication 15, dans lequel, dans la position de commande (95, 97), la vanne distributrice directionnelle (91) dirige le fluide de commande hydraulique provenant des moyens de commande hydraulique (31) vers l'une associée des chambres de piston du servo-piston (79).
     
    17. Système hydraulique (1) selon la revendication 16, dans lequel la vanne distributrice directionnelle (91) comporte une position neutre lorsque aucun fluide de commande hydraulique n'est fourni à la conduite de pilotage de distributeur (105, 107), et dans lequel la position neutre de la vanne distributrice directionnelle (91) connecte les deux chambres du servo-piston à un réservoir (65) afin d'équilibrer la position du servo-piston (79).
     
    18. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les moyens de commande hydraulique (31) génèrent le fluide de commande hydraulique avec une pression continuellement variable entre une pression de commande initiale et une pression de commande maximum ; dans lequel les deuxièmes moyens de commande (271) sont adaptés à commander la connexion des portions de conduites de travail (21, 23, 25, 27) de façon à passer sensiblement progressivement d'une configuration de connexion en série, pour la pression de commande initiale, à une configuration de connexion en parallèle, pour la pression de commande maximum.
     
    19. Système hydraulique (1) selon l'une quelconque des revendications précédentes, dans lequel les deuxièmes moyens de commande de connexion (271) comprennent une vanne directionnelle (263) ayant une première position extrême (267) dans laquelle elle connecte les portions de conduites de travail (21, 23, 25, 27) dans une configuration de connexion en série d'au moins deux utilisateurs (13, 15), et ayant une deuxième position extrême (269) dans laquelle elle connecte la portion de conduite de travail (21, 23, 25, 27) dans une configuration de connexion en parallèle desdits au moins deux utilisateurs (13, 15), la vanne directionnelle (263) étant adaptée à changer de position en fonction du signal de commande.
     
    20. Système hydraulique (1) selon la revendication 19, dans lequel la vanne directionnelle (263) est proportionnelle et modifie sa position entre la première position extrême (267) et la deuxième position extrême (269) en fonction et en proportion du signal de commande.
     
    21. Système hydraulique (1) selon la revendication 20, dans lequel la vanne directionnelle (263) est une vanne proportionnelle à 6 voies adaptée à dépressuriser les portions de conduites de travail (21, 23) connectées dans une configuration de connexion en série lorsqu'elle change sa position de la première position extrême (267) à la deuxième position extrême (269).
     
    22. Système hydraulique (1) selon l'une quelconque des revendications 19 à 21, dans lequel la vanne directionnelle (263) est actionnée par pilote par l'intermédiaire du fluide de commande hydraulique fourni par les moyens de commande hydraulique (31).
     
    23. Système hydraulique (1) selon la revendication 22, dans lequel la vanne directionnelle (263) comporte une deuxième conduite de pilotage (265) pouvant être connectée sélectivement au fluide de commande hydraulique des moyens de commande hydraulique (31), la vanne directionnelle étant mobile à partir de la première position extrême (267) vers la deuxième position extrême (269) en fonction de la pression variable du fluide de commande hydraulique.
     
    24. Système hydraulique (1) selon la revendication 23, dans lequel les première et deuxième sorties de commande (39, 41) des moyens de commande hydraulique (31) peuvent être connectées sélectivement à la deuxième conduite de pilotage (265) de la vanne directionnelle (263).
     
    25. Système hydraulique (1) selon la revendication 24, dans lequel les deuxièmes moyens de commutation (191) du système hydraulique sont aussi adaptés à connecter sélectivement la deuxième conduite de pilotage (265) de la vanne directionnelle (263) aux première et deuxième sorties de commande (39, 41) des moyens de commande hydraulique (31).
     
    26. Système hydraulique (1) selon la revendication 25, dans lequel les deuxièmes moyens de commutation (191) comprennent une première et une deuxième vanne d'arrêt (195, 197), ayant leurs entrées respectives connectées aux première et deuxième sorties de commande (39, 41) des moyens de commande hydraulique (31) et ayant leurs sorties respectives connectées à la deuxième conduite de pilotage (265) de la vanne directionnelle (263).
     
    27. Procédé pour commander un système de transmission hydraulique (1), le système de transmission hydraulique comprenant des moyens d'alimentation (3) pour fournir un fluide d'actionnement hydraulique à débit variable ; dans lequel les moyens d'alimentation (3) comprennent des moyens d'ajustement hydraulique (77) pour ajuster le débit variable du fluide d'actionnement hydraulique ;
    le procédé comprenant les étapes suivantes :

    fournir un fluide de commande hydraulique ayant une pression de commande qui est ajustable entre une pression de commande initiale et une pression de commande maximum, la pression de commande étant indicative d'un débit souhaité du fluide d'actionnement hydraulique ;

    diriger sélectivement le fluide de commande hydraulique pendant un état actionné des moyens d'ajustement hydraulique (77), et

    actionner les moyens d'ajustement hydraulique (77) au moyen du fluide de commande hydraulique,

    caractérisé en ce que

    l'état actionné pendant lequel le fluide de commande hydraulique est dirigé sélectivement vers les moyens d'ajustement hydraulique commence par la fourniture du fluide de commande hydraulique avec une pression initiale au minimum.


     
    28. Procédé selon la revendication 27, comprenant en outre, dans un état non actionné, la fourniture de fluide hydraulique à pression constante aux moyens d'ajustement hydraulique (77) et la connexion de ceux-ci à un réservoir (65) de fluide hydraulique.
     
    29. Procédé selon la revendication 27 ou 28, dans lequel le système de transmission hydraulique (1) comprend en outre des premiers moyens de commande de connexion (122) adaptés à diriger sélectivement le fluide de commande hydraulique vers les moyens d'ajustement hydraulique, le procédé comprenant une étape consistant à actionner les premiers moyens de commande de connexion (122) par le fluide de commande hydraulique.
     
    30. Procédé selon l'une quelconque des revendications 27 à 29, dans lequel les moyens d'alimentation (3) sont adaptés à fournir du fluide d'actionnement hydraulique avec un débit variable à au moins deux conduites de travail (9, 11), et le système hydraulique (1) comprend en outre au moins deux utilisateurs hydrauliques (13, 15) connectés aux moyens d'alimentation (3) par l'intermédiaire desdites au moins deux conduites de travail (9, 11) dans une configuration en circuit fermé ; le procédé comprenant en outre les étapes suivantes :

    fournir un signal de commande indicatif d'un débit souhaité du fluide d'actionnement hydraulique fourni par les moyens d'alimentation (3) ;

    contrôler la connexion de portions de conduites de travail (21, 23, 25, 27) connectées auxdits au moins deux utilisateurs (13, 15) de façon à fournir sélectivement une connexion en série et/ou en parallèle desdits au moins deux utilisateurs hydrauliques (13, 15) en réponse au signal de commande.


     
    31. Procédé selon la revendication 30, dans lequel le signal de commande est fourni de façon continument variable entre une valeur de signal de commande initiale et une valeur de signal de commande maximum ; dans lequel la connexion des portions de conduites de travail (21, 23, 25, 27) est commandée de façon à passer sensiblement progressivement d'une configuration de connexion en série, pour la valeur initiale du signal de commande, à une configuration de connexion en parallèle, pour la valeur maximum du signal de commande.
     
    32. Procédé selon la revendication 30 ou 31, dans lequel la connexion des portions de conduites de travail (21, 23, 25, 27) est commandée par des deuxièmes moyens de commande de connexion (271) qui sont actionnés par le signal de commande.
     
    33. Procédé selon la revendication 32, dans lequel les deuxièmes moyens de commande de connexion (271) sont actionnables par une pression hydraulique pilote, dans lequel le signal de commande est fourni sous la forme du fluide de commande hydraulique ayant une pression variable correspondant à la pression souhaitée du fluide d'actionnement, le procédé comprenant en outre une étape d'actionnement de pilote des deuxièmes moyens de commande de connexion (271) par le fluide de commande hydraulique.
     




    Drawing




















    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description