DRIVE SYSTEM FOR A WORK VEHICLE

Abstract

 Drive system for a work vehicle with at least two driven wheels (4) and at least one hydraulic actuator (7, 21, 26), wherein the drive system comprises a first electric motor (1A) which is mechanically coupled to a first hydraulic pump (2) for the purpose of driving the at least two wheels, and wherein the drive system comprises a second electric motor (1B) which is mechanically coupled to a second hydraulic pump (5) for the purpose of driving the at least one hydraulic actuator, wherein the first hydraulic pump is a two-way pump which is connected directly to two-way rotors at the wheels so that a rotation of the two-way pump is proportionally transferred to the wheels, and wherein the first electric motor is provided with a controller for controlling the electric motor on the basis of a first input which relates to a desired displacement of the work vehicle.

Description

[0001] The present invention relates to a drive system for a work vehicle with at least two driven wheels and at least one hydraulic cylinder.

[0002] The invention relates particularly to hydraulic work vehicles, preferably compact hydraulic work vehicles, wherein the wheels are driven by means of hydraulic motors and at least one operating component is driven by a hydraulic actuator. An example of such a hydraulic work vehicle is an excavator with a bucket, a small crane, a forklift truck or other work vehicle. The hydraulic work vehicle is particularly an articulated loader. An articulated loader is a work vehicle with a rear segment and a front segment which are pivotable relative to each other round an upright shaft. The wheels in the rear segment are here connected substantially fixedly to this rear segment, and the wheels in the front segment are connected substantially fixedly to this front segment. Steering the work vehicle to the left and to the right is primarily realized by pivoting the front part relative to the rear part of the vehicle.

[0003] Such work vehicles typically have a drive system with a combustion engine. The combustion engine has an output shaft which is mechanically coupled to one or more hydraulic pumps. These hydraulic pumps produce oil pressure whereby hydraulic actuators, both rotors and cylinders, can be operated. For the purpose of operating the rotors and cylinders a hydraulic control system with controlled valves, pressure controllers and so on is provided. Such a hydraulic control system is also referred to as the hydraulic control mechanism and can be very complex and expensive. In a known control the input from the user, with which the user indicates desired movements of the various components and elements of the work vehicle, is converted by the hydraulic control means into movements of respective hydraulic actuators. The hydraulic pump is here provided to control the hydraulic power, while the hydraulic pump receives power from the combustion engine.

[0004] As is the case with commercial vehicles, in respect of work vehicles there is also commercial demand for electrically driven units. EP 2 444 555 describes a hydraulic system which is driven by two electric motors. The first electric motor supplies here energy for a primary group of actuators, and a second electric motor supplies energy for a secondary group of actuators. A drawback of this construction is that it is sub-optimal for smaller hydraulic work vehicles, more specifically for articulated loaders.

[0005] It is an object of the invention to provide a drive system for a work vehicle which can be given a compact construction and can be controlled in simple manner.

[0006] The invention provides for this purpose a drive system for a work vehicle with at least one driven wheel, wherein the drive system comprises a first electric motor which is mechanically coupled to a first hydraulic pump which forms part of a first hydraulic circuit for driving the at least one wheel, wherein the first hydraulic pump is a two-way pump which is directly connected via the first hydraulic circuit to a hydraulic two-way rotor at the at least one wheel so that a rotation of the two-way pump induces an almost proportional rotation of the two-way rotor in order to drive the at least one wheel, wherein the drive system comprises a second electric motor which is mechanically coupled to a second hydraulic pump which forms part of a second hydraulic circuit, wherein the second hydraulic circuit is coupled to the first circuit in order to control a hydraulic filling pressure in the first circuit via the second hydraulic circuit.

[0007] The drive system preferably further comprises at least one hydraulic actuator which is driveable via a hydraulic circuit which is coupled to the second electric motor.

[0008] The invention is based on the insight that the torque map of an electric motor is fundamentally different from the torque map of a combustion engine, which allows an electric motor to be used fundamentally differently in a hydraulic system than a combustion engine. In the drive system according to the invention a distinction is made between advancing the vehicle on the one hand and operating hydraulic actuators on the other. It will be apparent to the skilled person here that at least one hydraulic actuator, which is described as such in the dependent claims and description, is a different actuator than the actuators that drive the wheels. This will be apparent from the context and structure of the claims. In other words, the drive system for the work vehicle according to the invention is divided into two drive lines.

[0009] A first drive line preferably serves to drive the wheels for the purpose of advancing the work vehicle. A second drive line preferably serves to operate the at least one hydraulic actuator. Because the drive lines are disconnected from each other, the first electric motor, which is provided in the first drive line, in particular can be used fundamentally differently than the second electric motor, which is provided in the second drive line. More specifically, the first electric motor will be coupled to a two-way pump. This two-way pump is directly connected to hydraulic two-way rotors at the wheels. The skilled person will appreciate that a rotation of the pump can hereby be transferred directly to a proportional rotation of the rotors at the wheels. Owing to this construction, the complex hydraulic control mechanism, which is typically provided between the pump and the rotors at the wheels, can be substantially wholly dispensed with. This is because this specific construction allows a rotation of the electric motor to be transferred directly to the wheels. This is possible because the electric motor which is coupled to the first hydraulic pump can supply a maximum torque from standstill. This is a feature which is known in electric motors and which can be optimally utilized in this context.

[0010] A direct mechanical coupling between the electric motor and the first hydraulic two-way pump allows the pump to be driven in two directions via the first electric motor. The skilled person will appreciate that the combination of direct coupling between the first electric motor and the two-way pump, and the direct connection between the two-way rotors and the pump, allows a rotation of the electric motor to be directly transferred to the wheels. This construction allows the controlling of the drive of the wheels to be done by directly controlling the drive of the electric motor. Electric motors can be controlled well and cheaply and reliably, whereby this has been found to be an optimal solution. The controller necessary for controlling the electric motor has been found to be more compact and notably cheaper than a similar hydraulic control mechanism for controlling the drive of the wheels.

[0011] An initial drawback of this construction is that, in a closed hydraulic system, it is difficult to realize hydraulic flushing and/or filtering and/or that it is difficult to apply a base pressure in order to allow such a closed hydraulic system to function. This is solved in the invention by using the second drive line or the second hydraulic circuit to produce a filling pressure in the first hydraulic circuit or in the first drive line.

[0012] The second drive line comprises a second electric motor with a second hydraulic pump, which supplies oil pressure for preferably at least one hydraulic actuator. The control of the second drive line can here be constructed in a more traditional manner. This means that an input by the user will primarily be processed by hydraulic control means in order to realize a movement in the relevant hydraulic actuator. This will influence the oil pressure, which is compensated by the second hydraulic pump. The second hydraulic pump can here control the second electric motor.

[0013] Tests have shown that providing one electric motor for driving the wheels, which one electric motor is coupled via a two-way pump to hydraulic rotors at the wheels, is cheaper and more reliable than providing each wheel with one electric motor. Hydraulic rotors have been found better able to withstand the rough operating conditions in which a work vehicle operates. Hydraulic rotors are further more compact than electric motors of comparable power. Hydraulic rotors can be provided with known techniques in a robust and reliable manner for the purpose of driving the wheels. The first drive line can be provided with pressure and flushing in simple and efficient manner by coupling to the second drive line.

[0014] Features of preferred embodiments of the invention are included in the dependent claims and further described hereinbelow.

[0015] The first electric motor and the first hydraulic pump preferably form a first drive line which is primarily controlled by the electric motor on the basis of a first input. The input comes from a user and relates to a desired displacement of the vehicle. This first input is supplied to the first electric motor. Owing to the construction of the first drive line, rotation of the first electric motor will directly result in a corresponding displacement of the work vehicle. This allows a simple control and provides for a reliable system.

[0016] The first input preferably comprises a displacement speed and a displacement direction, and the controller preferably comprises a function for determining a rotation speed and a rotation direction of the electric motors on the basis of the displacement speed and the displacement direction. The work vehicle can be moved forward or rearward, and a user can determine the desired speed of the vehicle. The speed can be determined in absolute terms or can be determined in relative terms in that a predetermined acceleration is requested over a predetermined time. This input of the displacement speed and the displacement direction can be directly converted by a controller into a rotation speed and rotation direction of the electric motor. Because the electric motor is coupled directly, via the hydraulic two-way pump, to the hydraulic two-way rotors at the wheels, the rotation speed and rotation direction of the electric motor will directly cause a corresponding displacement speed and displacement direction of the work vehicle. This can be implemented in a function, preferably a mathematical function, typically a linear function, by the controller.

[0017] Hydraulic control means are preferably provided between the second hydraulic pump and the at least one hydraulic actuator for the purpose of controlling the at least one hydraulic actuator on the basis of a second input which relates to a desired movement of the at least one hydraulic actuator. The second drive line comprises hydraulic control means between the second hydraulic pump and the at least one hydraulic actuator. Hydraulic control means provided for the control of the hydraulic actuator on the basis of an input from the user, referred to here as the second input.

[0018] The second hydraulic pump is preferably operatively coupled to the second electric motor for the purpose of controlling it. The second hydraulic pump requests an operation from the second electric motor to request the required energy. Other than in the first drive line, where the electric motor is driven by a controller on the basis of the first input, in the second drive line the electric motor will be controlled by the hydraulic pump. In other words, in the first drive line the electric motor determines the movements and pressures in the first drive line, while in the second drive line the hydraulic control means together with the pump determine the pressures and movement in the second drive line. In the second drive line the electric motor receives control signals from its load and is thereby a slave (master-slave) to its load. In the first drive line the first electric motor is controlled by the controller on the basis of the first input, and no noticeable feedback is provided from the load, being the first hydraulic pump and the hydraulic two-way rotors at the wheels, to the first electric motor. This means that the first electric motor is a master to its load.

[0019] The first hydraulic pump is preferably of the displacement type, such that an input rotation supplied by the motor is converted into a proportional amount of displaced oil. When the first hydraulic pump is of the displacement type, a substantially linear ratio can be determined between the rotation of the electric motor on the one hand and the oil which is displaced by the first hydraulic pump on the other. This allows a simple control of displacement of the work vehicle by controlling the first electric motor. The first hydraulic pump is and/or the rotors are preferably provided here in order to set a variable flow rate. By variably setting a flow rate the above stated linear ratio can be set and/or changed during use.

[0020] Each driven wheel preferably comprises a wheel slip sensor which is operatively coupled to a valve between the first hydraulic pump and the two-way rotor of the respective wheel, so that slip can be minimized by operating the valve. The skilled person will appreciate that under normal operating conditions the valves have no noticeable influence on the speed and direction and movement of the vehicle, and are intended only to intervene when wheel slip occurs. The valve forms a mechanism for reducing the power that is supplied to the wheel when this power cannot be transmitted to a ground surface. In vehicles this is known as traction control in acceleration and anti-lock braking system (ABS) in deceleration. The skilled person will appreciate that the valve between the hydraulic pump and the two-way rotor is typically fully open such that the valve does not influence the operation of the drive, until wheel slip is detected, after which valves can be operated on the basis of rules and/or algorithms in order to compensate for and minimize the wheel slip.

[0021] The at least one hydraulic cylinder preferably comprises a steering cylinder which controls an angle of at least a front wheel relative to at least a rear wheel. The work vehicle can be steered left-right via the steering cylinder. By providing a left-right steering via the steering cylinder all wheels can be connected in parallel to a hydraulic two-way pump. This is because steering is realized primarily by the position of the steering cylinder and not by rotation differences between left-hand and right-hand wheels.

[0022] A desired forward displacement preferably corresponds with a rotation of the first electric motor in a first rotation direction, while a desired rearward displacement corresponds with a rotation of the first electric motor in a second rotation direction, which is opposite to the first rotation direction. A desired speed further preferably corresponds with a rotation speed of the first electric motor. As described above, the direct coupling of the electric motor via the hydraulic pump and hydraulic rotors to the wheels of the vehicle allows the speed and direction of movement of the vehicle to be controlled by a corresponding speed and rotation direction of the first electric motor.

[0023] At least one battery is preferably provided for the purpose of supplying power to the first electric motor and to the second electric motor. The at least one battery can be a high-tension battery or can be a different battery or combination of batteries as known in the prior art.

[0024] The second hydraulic pump is preferably operatively connected to a hydraulic circuit which forms the direct connection between the two-way pump and the hydraulic two-way rotors and is provided to supply a predetermined operating pressure to the hydraulic circuit. When the first hydraulic pump is directly connected to the rotors and can drive them in two directions, an external element is provided in order to supply an operating pressure in the hydraulic circuit extending between the first hydraulic pump and the rotors. This operating pressure is preferably supplied by the second hydraulic pump. The hydraulic control means in the second drive line more preferably comprises a mechanism and coupling to the hydraulic circuit for the purpose of supplying a predetermined operating pressure. Alternatively, an accumulator is provided in the hydraulic circuit in order to supply an operating pressure.

[0025] The invention further relates to a hydraulic work vehicle with a drive system according to the invention. The first and second electric motor and the first and second hydraulic pump are preferably provided in a motor compartment, and the hydraulic pumps are preferably operatively connected via hydraulic conduits to the at least one hydraulic actuator and the two-way rotors. This construction allows a hydraulic work vehicle to be given a modular construction in the sense that the end customer is able to choose between driving by a combustion engine or by the drive system according to the invention. In both drive systems the hydraulic actuators are connected via hydraulic conduits to two-way rotors at the wheels from the motor compartment. This construction is therefore significantly advantageous in the production and marketing of the hydraulic work vehicles.

[0026] The invention will now be further described with reference to an exemplary embodiment shown in the drawing.

[0027] In the drawing:

figure 1 shows a hydraulic work vehicle according to the prior art;

figure 2 shows a hydraulic work vehicle according to an embodiment of the invention;

figure 3 shows a top view of a hydraulic vehicle according to a further embodiment of the invention;

figure 4 shows a working diagram of a drive according to an embodiment of the invention;

figure 5 shows an embodiment of a first hydraulic circuit, coupled to the second hydraulic circuit; and

figure 6 shows an embodiment of how a plurality of rotors can be connected in the first hydraulic circuit.

[0028] The same or similar elements are designated in the drawing with the same reference numerals.

[0029] Figure 1 shows a vehicle in which a combustion engine 11 is coupled via a shaft to a hydraulic pump 12. Hydraulic pump 12 provides hydraulics for driving of wheels 4, for advancement of the vehicle, and for driving of systems 17, for operation of the vehicle.

[0030] Hydraulic pump 12 is connected via hydraulic control means 13 to wheels 14. Pump 12 supplies a pressure while control means 13 determine the flow rate and the flow direction to wheels 14. Hydraulic actuators, particularly rotors (not shown in figure 1), are provided at the position of wheels 14.

[0031] Hydraulic pump 12 is further connected via hydraulic control means 16 to the actuators 17, only one cylinder of which is shown by way of example. Pump 12 supplies a pressure while control means 16 determine the flow rate and the flow direction to actuators 17. This construction allows a prior art vehicle to move and operate. More specifically, wheels 14 can be rotated in a rotation direction and at a speed requested by a user. This rotation direction and speed are provided by control means 13. Hydraulic operating elements 17 can also be operateded by a user, wherein control means 16 control operating elements 17 on the basis of a user input.

[0032] Figure 2 shows an embodiment of the invention for driving a similar vehicle using an electric motor. The final stage of the drive is similar to the traditional construction. In particular, the wheels are still driven hydraulically and the actuators are still driven hydraulically. Tests have shown that this is optimal.

[0033] Two electric motors 1A and 2A are provided in the drive according to the invention. First electric motor 1A is here connected mechanically to the first hydraulic pump 2. First hydraulic pump 2 can take the form of a single pump or a double pump. When the first hydraulic pump takes a single form, all driven wheels will be connected to the one pump. When the first hydraulic pump takes a double form, half of the driven wheels will be connected to the one and the other half of the driven wheels to the other of the double pump. The first hydraulic pump 2 is a two-way pump, preferably of the displacement type. This means that the pump is mechanically driveable in a first direction in order to move the oil in a first direction and that the pump is mechanically driveable in a second direction in order to move the oil in a second direction. Because an electric motor can be driven in two rotation directions in simple manner and can develop a maximum torque from standstill, first hydraulic pump 2 is coupled directly to the rotors at wheels 4. In principle, a control mechanism similar to prior art control mechanism 13 is no longer necessary here. This is a great advantage in practice.

[0034] A valve (not shown) can optionally be provided between first hydraulic pump 2 and each of the rotors at the wheels 4. In normal operation this valve will be fully open and thus have no influence on the driving of wheels 4. When wheel slip is detected, the valve can be activated in order to reduce the power to the slipping wheel and thus minimize or compensate for the slip. Even when such a valve is placed between the rotors at wheels 4 and the first hydraulic pump 2, the rotors will still be deemed directly connected to the pump, because the valve has no direct influence on the operation under normal conditions. In order to reduce the chance of wheel slip a plurality of rotors can be placed hydraulically in series.

[0035] In order to provide independent operation of the hydraulic actuators, one cylinder 7 of which is shown, a second electric motor 1B is provided, which is coupled to the second hydraulic pump 5. Second hydraulic pump 5 can take the form of a single or double pump. This pump 5 is connected via control means 6 to cylinders 7 in conventional manner. Control means 6 are similar to known control means 16 for controlling cylinder 7, which is similar to operating elements 17.

[0036] This construction of the invention as shown in figure 2 is a simplification relative to the existing construction as shown in figure 1 because the control means 13, which are complex and expensive, are unnecessary. The robustness and flexibility during operation however remain high. It has also been found that controlling of the wheels can be realized in simple manner by controlling first electric motor 1A.

[0037] In the invention two electric motors 1A and 1B are provided in a work vehicle 10, wherein the first electric motor 1A serves to drive the wheels 4 via a hydraulic two-way pump 2. Hydraulic control systems are here unnecessary in the drive because rotation of the first electric motor 1A is transferred directly via hydraulic pump 2 to the rotors at wheels 4.

[0038] Shown in both figure 1 and figure 2 is a motor compartment 9. Constructing vehicle 10 with a motor compartment 9 has the advantage that a drive according to the invention can be replaced with a traditional drive, and vice versa. This is because hydraulic conduits depart from motor compartment 9 both to the rotors at wheels 4, 14 and to the hydraulic operating elements 7, 17.

[0039] Figure 2 further shows an operative connection 19 between the second drive line and the first drive line. More specifically, the hydraulic control means 6 are connected to the hydraulic circuit extending between the first hydraulic pump 2 and the rotors at wheels 4. With this connection an operating pressure can be supplied by second hydraulic pump 5 to the hydraulic circuit. This connection further allows oil in the hydraulic circuit to be changed and/or flushed and/or cleaned. Cooling of oil can further be provided for via the operational connection 19. This will be further elucidated below with reference to figures 5 and 6.

[0040] Figure 3 shows a top view of a preferred embodiment of the invention. Figure 3 shows particularly a top view of the work vehicle which is highly suitable for application of the drive according to the invention. The work vehicle of figure 3 has a front segment 22 and a rear segment 23 which can pivot relative to each other round and upright pivot point 25. A work vehicle with such a construction is also referred to as an articulated vehicle or, when a loading shovel or a bucket 8 is provided, an articulated loader. In an articulated vehicle or articulated loader the wheels 4 of front segment 22 are connected fixedly to the chassis of that segment. The wheels 4 in rear segment 23 are connected fixedly to the chassis of that segment. Rotation of the vehicle takes place primarily by pivoting the segments 22 and 23 relative to each other round shaft 25. A steering cylinder 21 is typically provided for this purpose. The advantage of such a construction is that the wheel speed of the different wheels remains substantially the same. This is different when all wheels are provided fixedly on the same rigid chassis, wherein the right-hand wheels are forcibly driven faster than the left-hand wheels or vice versa in order to force turning of the vehicle. The invention can preferably be applied in all types of vehicle wherein turning of the vehicle is done by a steering mechanism or steering cylinder and not by forcibly driving determined wheels faster/more slowly. Such constructions are known to the skilled person and are therefore not elucidated further in this description.

[0041] The top view of figure 3 shows how each of the wheels 4 has a rotor 20. This rotor 20 is a two-way rotor and drives wheels 4. Each two-way rotor 20 is in fluid connection with motor compartment 9 via hydraulic conduits. Figure 3 further also shows the bucket cylinder 24 used to tilt bucket 8.

[0042] Figure 4 shows in principle how the drive according to the invention is constructed and can be controlled. Figure 4 illustrates here that the drive has a first drive line comprising a first hydraulic circuit 27, and a second drive line comprising a second hydraulic circuit 28. First drive line 27 comprises first electric motor 1A, first hydraulic two-way pump 2 and the two-way rotors 20 that drive wheels 4. Only three wheels 4 are shown in figure 4. It will be apparent to the skilled person that embodiments can be envisaged wherein front segment 22 or rear segment 23, as shown in figure 3, is provided with only one centrally positioned wheel 4. In first drive line 27 the hydraulic operating pressure is primarily supplied by an element other than the first hydraulic pump 2. First hydraulic pump 2 primarily controls the flow speed and flow direction of the oil in first drive line 27. The hydraulic operating pressure or filling pressure in first drive line 27 is primarily controlled by a coupling to second drive line 28, further elucidated below with reference to figure 5. It will be apparent to the skilled person that first hydraulic pump 2 does provide pressure in first drive line 27, particularly when rotors 20 produce counterpressure.

[0043] Second drive line 28 comprises the second electric motor 1B which is mechanically coupled to the second hydraulic pump 5. Second hydraulic pump 5 is coupled to the hydraulic control means 6 which drive the hydraulic operating elements 21, 7, 26. Figure 4 shows steering cylinder 21, shows hydraulic cylinder 7 for moving the arm with the bucket 8 up and downward, and further shows a hydraulic cylinder 26. The further hydraulic cylinder 26 can for instance be used for providing a clamp at the front end of the vehicle for the purpose of clamping goods. Alternatively or additionally, the further hydraulic cylinder 26 can be used to tilt bucket 8. It will be apparent to the skilled person that further hydraulic actuators can be provided. In second drive line 28 the second hydraulic pump 5 will primarily supply the operating pressure. The flow speed and flow direction of the oil in second drive line 28 is primarily controlled by control means 6.

[0044] Figure 4 illustrates how a user can operate the vehicle. Provided for this purpose is user input 29 which sends control signals 29A, 29B to the different components of the vehicle. When the user requests a displacement of the vehicle, control signals 29A will be sent to first electric motor 1A. First electric motor 1A is driven in a direction which corresponds directly to the requested displacement. Owing to the direct mechanical coupling between first electric motor 1A, hydraulic pump 2 and rotors 20, a rotation of electric motor 1A is transferred directly to wheels 4. The control signals of user interface 29, which relate to the forward movement of the vehicle, will therefore be sent to first electric motor 1A in the first drive line 27.

[0045] When a user requests an operation from a hydraulic operating element 7, 21, 26 via user input 29, control signals 29 are primarily sent to the hydraulic control means 6. Hydraulic control means 6 operate the hydraulic operating elements and can initiate and control the movement requested by the user. Because hydraulic control means 6 require power for this purpose, typically in the form of oil pressure, control means 6 will control the second electric motor 1B directly or indirectly. Control means 6 can control the second electric motor 1B directly when intelligence is provided in the control means 6 for determining the necessary power, and by controlling the rotation speed of the second electric motor on the basis of the necessary power. Alternatively, control means 6 will use oil, whereby the oil pressure changes, which is sensed by the second hydraulic pump 5. Second hydraulic pump 5 can request an operation from second electric motor 1B when more or less power is necessary. Both options are shown schematically in the figure with arrow 29C.

[0046] In master-slave terms, the first electric motor will be the master in first drive line 27, while the hydraulic pump and rotors 20 are slaves. In second drive line 28 the hydraulic control means 6 will be the master and the second hydraulic pump 5 and second electric motor 1B will be slaves. The two drive lines are thereby controlled in different ways. This has been found to significantly simplify the drive according to the invention. This further allows considerably less energy to be consumed while working with the hydraulic work vehicle.

[0047] Figure 5 shows a hydraulic diagram and in detail how a second hydraulic circuit 28 can be coupled to a first hydraulic circuit 27 in order to supply a filling pressure in the first hydraulic circuit 27. First hydraulic circuit 27 comprises a first hydraulic two-way pump 2 which has connections for displacing hydraulic fluid in two directions, from the one connection to the other when the pump runs in a first direction or from the other connection to the one when the pump runs in the other direction. This two-way pump, placed in a closed circuit, thereby differs to some extent from the pumps which are conventionally used in an open hydraulic circuit. A classic pump runs in only one direction and can control a rotor in two directions by means of an internal valve which sends fluid in direction A or direction B. The other connection to the pump is just the supply connection, typically connected to the hydraulic tank. The feedback of the hydraulic fluid always runs via the tank. In the drive system with closed circuit the hydraulic fluid returning from the rotor or hydraulic motor is carried to the feed of the pump. This allows the pump to run in two directions, while the only hydraulic fluid coming from the tank runs via the filling pressure system via valves 34 and 35.

[0048] The first hydraulic circuit 27 has a first hydraulic conduit 31 and a second hydraulic conduit 32. Via the hydraulic conduits 31 and 32 the pump 2 is connected directly to a two-way rotor 20. Figure 5 shows only one rotor 20, and connections A and B are shown. Figure 6 shows that a plurality of rotors 20 can be connected between these connections A and B. Only one rotor 20 suffices to explain how filling pressure is supplied and safety is ensured in first circuit 27.

[0049] Because pump 2 is a two-way pump, and because rotor 20 is connected directly to pump 2 via hydraulic conduits 31 and 32, hydraulic fluid can be circulated in two directions, indicated with arrow 33. When pump 2 is driven in a first direction, the circulation direction will be clockwise, the first hydraulic conduit 31 will be a high-pressure conduit and the second hydraulic conduit 32 will be a return conduit for hydraulic fluid or low-pressure conduit. A rotation of pump 2 will be transferred proportionally in magnitude and in rotation direction to a rotation of rotor 20. When pump 2 is driven in a second direction, the circulation direction will be counter-clockwise, the second hydraulic conduit 32 will be a high-pressure conduit and the first hydraulic conduit 31 will be a return conduit for hydraulic fluid or low-pressure conduit. A rotation of pump 2 will in this situation also be transferred proportionally to a rotation of rotor 20. Because pump 2 is directly mechanically coupled to the first electric motor 1A, and because rotor 20 is directly mechanically coupled to wheel 4, a rotation of electric motor 1A will be transferred proportionally in magnitude and in rotation direction to a rotation of wheel 4 via first hydraulic circuit 27 .

[0050] The second hydraulic circuit 28 of the embodiment of figure 5 has two separate second hydraulic pumps 5A and 5B. This is an embodiment wherein use of energy can be optimized. Hydraulic pump 5A is primarily intended to control the actuators via the control means, as discussed at length above. Hydraulic pump 5B is primarily provided to supply filling pressure in first hydraulic circuit 27, as will be described further hereinbelow.

[0051] The second hydraulic pump 5B is coupled to first hydraulic circuit 27 in order to supply filling pressure. More specifically, the second hydraulic pump 5B is connected via a filling pressure conduit 36 and a first one-way valve 34 to first hydraulic conduit 31. The one-way valve 34 will open when the pressure in hydraulic conduit 31 is lower than the pressure in filling pressure conduit 36 in order to allow hydraulic fluid to flow to the first hydraulic conduit 31. In this way the filling pressure conduit 36, via one-way valve 34, keeps the pressure in first hydraulic conduit 31 at least substantially equal to the pressure in filling pressure conduit 36. When the first hydraulic conduit 31 forms the high-pressure side of first circuit 27, one-way valve 34 will remain closed. Second hydraulic pump 5B is further connected via filling pressure conduit 36 and a second one-way valve 35 to the second hydraulic conduit 32. One-way valve 35 will open when the pressure in second hydraulic conduit 32 is lower than the pressure in filling pressure conduit 36 in order to allow hydraulic fluid to flow to the second hydraulic conduit 32. In this way the filling pressure conduit 36, via one-way valve 35, keeps the pressure in second hydraulic conduit 32 at least substantially equal to the pressure in filling pressure conduit 36. When the second hydraulic conduit 32 forms the high-pressure side of first circuit 27, one-way valve 35 will remain closed. Via this mechanism a minimal pressure is always supplied via filling pressure conduit 36 on the low-pressure side. This also allows hydraulic fluid to be flushed away on the low-pressure side in order to supply fresh hydraulic fluid via filling pressure conduit 36 and one-way valves 34 and 35. For this purpose first hydraulic circuit 27 preferably has a flush valve 43. The flush valve opens, with a hydraulic resistance, on the low-pressure side in order to flush away part of the hydraulic fluid.

[0052] A control module (not shown) is preferably used to control the pressure in filling pressure conduit 36. The control module is operatively connected to a sensor 39 which measures a hydraulic pressure in filling pressure conduit 36. The control module is further preferably operatively connected, directly or indirectly, to the first electric motor 1A. This is because filling pressure is only useful in first hydraulic circuit 27 when this circuit is operational, i.e. when the first electric motor 1A is running. During standstill, supplying filling pressure would only cost energy, which has no direct advantage. Filling pressure is therefore preferably maintained only when electric motor 1A is active or is being controlled. It will be apparent here that the filling pressure is preferably maintained when it is expected that electric motor 1A will be controlled. This is because it is preferable for the pressure to be at the right level when driving of the vehicle starts.

[0053] When electric motor 1A is controlled, the filling pressure may be too low or too high. When no hydraulic actuators for which second electric motor 1B must run are operative, the hydraulic pump 5B thus does not run either, and the filling pressure may be insufficient. In such a situation the control module will request an operation from second electric motor 1B to run faster so that the pressure supplied by second pump 5B rises until the filling pressure has reached a minimum value. In this situation pressure shut-off valve 38 and control module 37 will not intervene, or not to any noticeable extent, and therefore will not make any noticeable contribution to the pressure in filling pressure conduit 36 being reached or reduced.

[0054] When hydraulic actuators are operative in second hydraulic circuit 28, whereby second electric motor 1B does run at a determined rotation speed, the filling pressure may be too high. In such a situation the control module will control the pressure controller 37 to release part of the hydraulic pressure to the tank. In this way the control module can keep the pressure in filling pressure conduit 36 below a predetermined maximum value. Pressure controller 37 is preferably formed by a pressure relief valve which operates wholly mechanically. The operating pressure is for instance set to a desired pressure, for instance 25 bar, in the factory. If the pressure exceeds 25 bar, the valve will open automatically. The control module thus need not intervene, and has no direct control over the filling pressure. In this way the pressure in filling pressure conduit 36 is automatically kept below a predetermined maximum value. When the first electric motor 1A stops, the control module can operate the pressure shut-off valve 38, whereby the pressure in filling pressure conduit 36 is drained substantially wholly to the tank. In such a situation the second hydraulic pump 5B will not provide any noticeable resistance either when it is driven along with the second hydraulic pump 5A by second electric motor 1B.

[0055] A pressure relief valve is preferably provided in each of first hydraulic conduit 31 and second hydraulic conduit 32. The pressure relief valve ensures that when the pressure exceeds a predetermined maximum, hydraulic fluid is released in order to prevent a further increase of the pressure. If for example the rotor 20 were to become blocked, and pump 2 does continue to run, the hydraulic pressure may exceed a predetermined maximum. In figure 5 the pressure relief valve is formed by a combination of a high-pressure control valve 40 with a one-way valve 41 from each of the first and second hydraulic conduits 31, 32 to the high-pressure control valve 40. The high-pressure control valve 40 keeps the pressure behind the valve at the predetermined maximum pressure so that, when the pressure in one of the first and second hydraulic conduits 31, 32 exceeds this predetermined maximum pressure, the one-way valve 41 opens and hydraulic fluid flows through one-way valve 41 to high-pressure control valve 40.

[0056] Figure 5 further shows that each of the hydraulic conduits 31 and 32 comprise a on-off valve 42 whereby the hydraulic conduits 31 and 32 can be opened and thereby be fully operational. In order to increase safety, this on-off valve 42 is configured such that it opens when a voltage is applied to the valve. In a voltage-free state the valve is thus at least partially closed, and rotation of rotor 20 is thereby prevented. In other words, the wheels 4 of the work vehicle can only turn when voltage is provided to on-off valves 42. In order to increase safety and prevent overload due to an undesirably or ill-chosen shut-off of the voltage, flow of hydraulic fluid toward rotor 20 is allowed in the shut-off state, while an opposite flow is prevented. By connecting the filling pressure conduit 36 on the side of pump 2 and connecting the pressure relief valve on the side of the rotor 20, relative to on-off valves 42, a safe system is obtained wherein overload can be prevented and wherein hydraulic fluid cannot come under underpressure.

[0057] Figure 6 shows an exemplary embodiment of how a plurality of rotors 20 can be connected in first hydraulic circuit 27. Figure 6 shows here four rotors, designated with 201, 202, 203 and 204. Each of these rotors is preferably directly mechanically coupled to a corresponding wheel 4 in order to drive the wheels. Figure 6 shows the connecting points A and B, which are also shown in figure 5. On the basis hereof the skilled person can understand how the hydraulic fluid can flow through the circuit shown in figure 6 in two directions, depending on the rotation direction of pump 2. Depending on the rotation direction which has also been elucidated above, connection A will here form the high-pressure side and connection B will form the low-pressure side, or vice versa. Figure 6 also shows connection C, which is likewise shown in figure 5 and which will make apparent to the skilled person how filling pressure conduit 36 is integrated in the circuit of figure 6.

[0058] In the embodiment of figure 6 the first rotor 201 is placed in series with the second rotor 202 via a first hydraulic connection 50. This means that the first rotor 201 and the second rotor 202 run at the same speed and in the same rotation direction, provided that the first hydraulic connection 50 allows fluid to pass directly and without active locking connections described below. In the embodiment of figure 6 the third rotor 203 is further placed in series with the fourth rotor 204 via a second hydraulic connection 51. As above, this means that the third rotor 203 and the fourth rotor 204 run at the same speed and in the same rotation direction, provided that the second hydraulic connection 51 allows fluid to pass directly and without active locking connections described below. First rotor 201 and second rotor 202 form a first pair of rotors 201 and 202. Third rotor 203 and fourth rotor 204 form a second pair of rotors 203 and 204. The first pair of rotors 201 and 202 and the second pair of rotors 203 and 204 are placed in parallel in the embodiment of figure 6. This means that the force supplied to first rotor 201 and to third rotor 203 is the same. The rotation speed could however be different if a resistance were greater in one of the rotors.

[0059] Figure 6 further shows a brake 45 on rotors 202 and 204. It will be apparent that the brake 45 can also be provided on all rotors. As further alternative, the brake can be provided on the wheels or wheel shafts which are coupled to the rotors. With a view to safety, brake 45 is active in rest. This means that when no external force is applied, the brake exerts a braking force. In the shown embodiment the external force can be applied by energizing brake valve 46. The brake valve connects the brake to the filling pressure conduit so that a hydraulic pressure is exerted on the brake in order to release the brake. Releasing the brake via filling pressure conduit 36 has the additional advantage that the brake is only released when filling pressure is also supplied in the first hydraulic circuit 27. As described above, the filling pressure will not be supplied when the work vehicle is stationary and the electric motor 1A is not being driven, so that the brake also becomes active at that moment. This once again increases safety in that the braking function is indirectly coupled to the operation of electric motor 1A.

[0060] Figure 6 shows a pressure relief valve on each of the first and second hydraulic connections 50 and 51. A maximum pressure can hereby be set between the rotors placed in series in order to protect the hydraulic connections 50 and 51 against overload. The pressure relief valves are designated in figure 7 with reference numeral 48. In the embodiment of figure 6 use is not made of one high-pressure valve and a plurality of one-way valves, but a high-pressure valve is placed at each connection 50, 51. This is an alternative embodiment for implementing a pressure relief valve. The skilled person will appreciate that a pressure relief valve can be implemented in different ways.

[0061] Figure 6 further shows a locking connection 52 with a valve extending between the first hydraulic connection 50 and the second hydraulic connection 51. In the shown state the lock is not operational, and a connection is created between first hydraulic connection 50 and second hydraulic connection 51. This is the state in which the lock is not operational. The serial connection between the rotors is hereby broken, and first and second rotors 201 and 202, as well as third and fourth rotors 203 and 204, can rotate at different speeds. By closing the locking connection via the valve the lock will be set into operation and, provided that the pressure relief valve is not operational, the serial connection becomes the only connection between first rotor 201 and second rotor 202 and between third rotor 203 and fourth rotor 204, so that first rotor 201 and second rotor 202 rotate at the same speed and so that third rotor 203 and fourth rotor 204 rotate at the same speed. The effect on the wheels is similar to locking a differential of a drive. When the locking connection is open, there is a differential action. When the locking connection is closed, there is an action analogous to a locked differential.

[0062] According to a first implementation, rotor 201 is coupled to the rear right wheel, rotor 202 is coupled to the front right wheel, rotor 203 is coupled to the rear left wheel and rotor 204 is coupled to the front left wheel. In such an arrangement a lock can be realized between the front wheels and the rear wheels, wherein the wheels on the left-hand side in each case rotate at the same speed and the wheels on the right-hand side rotate at the same speed. In an alternative implementation rotor 201 is coupled to the rear right wheel, rotor 202 is coupled to the rear left wheel, rotor 203 is coupled to the front right wheel and rotor 204 is coupled to the front left wheel. In such a setup a lock can be realized between the left-hand wheels and the right-hand wheels, wherein the front wheels in each case rotate at the same speed, and the rear wheels rotate at the same speed.

[0063] The skilled person will appreciate that rotors 201-204 can be connected in alternative manner, for instance via proportional valves, so that the quantity of hydraulic fluid to each of the rotors can be controlled. As further alternative, in the configuration of figure 6 a proportioning valve can be added on the side of connection A and/or on the side of connection B in order to increase control of the drive.

[0064] The skilled person will appreciate on the basis of the above description that the invention can be embodied in different ways and on the basis of different principles. The invention is not limited here to the above described embodiments. The above described embodiments and the figures are purely illustrative and serve only to increase understanding of the invention. The invention is not therefore limited to the embodiments described herein, but is defined in the claims. A number of clauses is added below solely as a basis.

Clause 1: Drive system for a work vehicle with at least two driven wheels and at least one hydraulic actuator, wherein the drive system comprises a first electric motor which is mechanically coupled to a first hydraulic pump for the purpose of driving the at least two wheels, and wherein the drive system comprises a second electric motor which is mechanically coupled to a second hydraulic pump for the purpose of driving the at least one hydraulic actuator, wherein the first hydraulic pump is a two-way pump which is connected directly to hydraulic two-way rotors at the wheels so that a rotation of the two-way pump is proportionally transferred to the wheels, and wherein the first electric motor is provided with a controller for controlling the electric motor on the basis of a first input which relates to a desired displacement of the work vehicle.

Clause 2: Drive system according to the foregoing clause, wherein the first electric motor and the first hydraulic pump form a first drive line which is primarily controlled by the electric motor on the basis of the first input.

Clause 3: Drive system according to any one of the foregoing clauses, wherein the first input comprises a displacement speed and a displacement direction, and wherein the controller comprises a mathematical function for determining a rotation speed and a rotation direction of the electric motor on the basis of the displacement speed and the displacement direction.

Clause 4: Drive system according to any one of the foregoing clauses, wherein hydraulic control means are provided between the second hydraulic pump and the at least one hydraulic actuator for the purpose of controlling the at least one hydraulic actuator on the basis of a second input which relates to a desired movement of the at least one hydraulic actuator.

Clause 5: Drive system according to the foregoing clause, wherein the second electric motor, the second hydraulic pump and the hydraulic control means form a second drive line which is primarily controlled by the hydraulic control means on the basis of the second input.

Clause 6: Drive system according to any one of the foregoing clauses, wherein the second hydraulic pump is operatively coupled to the second electric motor for the purpose of controlling it.

Clause 7: Drive system according to any one of the foregoing clauses, wherein the first hydraulic pump is of the displacement type, such that an input rotation supplied by the motor is converted into a proportional amount of displaced oil.

Clause 8: Drive system according to any one of the foregoing clauses, wherein each driven wheel comprises a wheel slip sensor which is operatively coupled to a valve between the first hydraulic pump and the two-way rotor of the respective wheel, so that slip can be minimized by operating the valve.

Clause 9: Drive system according to any one of the foregoing clauses, wherein the at least one hydraulic actuator comprises a steering cylinder which controls an angle of at least one front wheel relative to at least one rear wheel.

Clause 10: Drive system according to any one of the foregoing clauses, wherein a desired forward displacement preferably corresponds with a rotation of the first electric motor in a first rotation direction, while a desired rearward displacement corresponds with a rotation of the first electric motor in a second rotation direction, which is opposite to the first rotation direction.

Clause 11: Drive system according to any one of the foregoing clauses, wherein at least one battery is further provided for the purpose of supplying power to the first electric motor and to the second electric motor.

Clause 12: Drive system according to any one of the foregoing clauses, wherein the second hydraulic pump is operatively connected to a hydraulic circuit which forms the direct connection between the two-way pump and the hydraulic two-way rotors and is provided to supply a predetermined operating pressure to the hydraulic circuit.

Clause 13: Hydraulic work vehicle with a drive system according to any one of the foregoing clauses.

Clause 14: Hydraulic work vehicle according to the foregoing clause, wherein the first and second electric motor and the first and second hydraulic pump are provided in a motor compartment, and wherein the hydraulic pumps are operatively connected via hydraulic conduits to the at least one hydraulic actuator and to the two-way rotors.

Claims

1. Drive system for a work vehicle with at least one driven wheel, wherein the drive system comprises a first electric motor which is mechanically coupled to a first hydraulic pump which forms part of a first hydraulic circuit for driving the at least one wheel, wherein the first hydraulic pump is a two-way pump which is directly connected via the first hydraulic circuit to a hydraulic two-way rotor at the at least one wheel so that a rotation of the two-way pump induces an almost proportional rotation of the two-way rotor in order to drive the at least one wheel, wherein the drive system comprises a second electric motor which is mechanically coupled to a second hydraulic pump which forms part of a second hydraulic circuit, wherein the second hydraulic circuit is coupled to the first circuit in order to control a hydraulic filling pressure in the first circuit via the second hydraulic circuit.

2. Drive system according to the foregoing claim, wherein the first hydraulic circuit comprises a first hydraulic conduit and a second hydraulic conduit which are connected to two connections of the two-way pump such that, when the two-way pump runs in a first direction, the first hydraulic conduit forms a high-pressure side while the second hydraulic conduit forms a low-pressure side and wherein, when the two-way pump runs in a second direction opposite to the first direction, the second hydraulic conduit forms a high-pressure side while the first hydraulic conduit forms a low-pressure side.

3. Drive system according to the foregoing claim, wherein the second hydraulic circuit comprises a hydraulic filling pressure conduit which is coupled to each of the first and second hydraulic conduits.

4. Drive system according to the foregoing claim, wherein the hydraulic filling pressure conduit is coupled to the first hydraulic conduit via a first one-way valve which allows hydraulic flow toward the first hydraulic conduit and which is coupled to the second hydraulic conduit via a second one-way valve which allows hydraulic flow toward the second hydraulic conduit.

5. Drive system according to the foregoing claim, wherein the second hydraulic circuit comprises a pressure controller for controlling a hydraulic pressure in the filling pressure conduit.

6. Drive system according to any one of the claims 2-5, wherein the first hydraulic conduit and the second hydraulic conduit are provided, preferably on the side of the two-way rotor, with a flush valve which closes toward the high-pressure side and opens towards a low-pressure side so as to discharge part of the hydraulic fluid from the low-pressure side.

7. Drive system according to any one of the foregoing claims 2-6, wherein the first hydraulic conduit and the second hydraulic conduit each have a pressure relief valve, wherein the pressure relief valve is preferably formed as a combination of a first further one-way valve which allows hydraulic flow of the first hydraulic conduit toward a high-pressure control valve and a second further one-way valve which allows hydraulic flow toward the high pressure control valve, wherein the high pressure control valve determines the overpressure.

8. Drive system according to any one of the foregoing claims, wherein the second hydraulic circuit comprises a control module which supplies filling pressure only when the first electric motor is being controlled.

9. Drive system according to the foregoing claims, wherein the control module is provided to control the second electric motor on the basis of a pressure sensor which measures the hydraulic filling pressure in order to keep the hydraulic filling pressure above a predetermined minimum.

10. Drive system according to the foregoing claim and claim 5, wherein the control module is provided to control the pressure controller on the basis of the pressure sensor in order to keep the hydraulic filling pressure below a predetermined maximum.

11. Drive system according to any one of the foregoing claims, wherein provided on the at least one wheel is a brake which exerts braking force when no external pressure is being supplied and which is de-energized by supplying the external pressure via the second hydraulic circuit.

12. Drive system according to any one of the foregoing claims, wherein the at least one wheel comprises at least a first, second, third and fourth wheel which each have a corresponding hydraulic two-way rotor, and wherein the first and second rotor are placed in the first hydraulic circuit in series and form a first pair of rotors, the third and fourth rotor are placed in the first hydraulic circuit in series and form a second pair of rotors, and wherein the first pair of rotors and the second pair of rotors are placed in the first hydraulic circuit in parallel, wherein a pressure relief valve is preferably provided between the first and second rotor and wherein a further overpressure valve is provided between the third and fourth rotor, wherein the first rotor is preferably connected via a first hydraulic connection to the second rotor and wherein the third rotor is connected via a second hydraulic connection to the fourth rotor, and wherein a locking connection is provided between the first hydraulic connection and the second hydraulic connection, wherein the locking connection comprises a controllable valve which is settable to closed position or to open position.

13. Drive system according to any one of the foregoing claims, wherein the first electric motor is provided with a controller for controlling the first electric motor on the basis of a first input which is related to a desired displacement of the work vehicle.

14. Drive system according to any one of the foregoing claims, further comprising at least one hydraulic actuator which is driveable via a hydraulic circuit which is coupled to the second electric motor, wherein the second electric motor is preferably further coupled to a hydraulic actuator pump which forms part of a third hydraulic circuit for driving the at least one hydraulic actuator.

15. Hydraulic work vehicle with a drive system according to any one of the foregoing claims.

Drawing