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(11) | EP 0 433 454 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | HYDRAULIC CIRCUIT APPARATUS |
| (57) This invention relates to a hydraulic circuit apparatus which introduces a load pressure
of one of a plurality of hydraulic actuators and thus improves temporarily the function
of one pressure compensation valve in order to prevent the load pressure of one hydraulic
actuator at the start from becoming abnormally high and to prevent relief of the pressure
oil from a safety valve when a plurality of hydraulic actuators are operated simultaneously,
supplies large quantities of pressure oil to the actuator connected to this pressure
compensation valve and improves its operation speed. This hydraulic circuit apparatus
is equipped with a compensation pressure change-over valve (26) for supplying normally
the highest load pressure to a spring chamber (9a, 10a) side of each pressure compensation
valve (9, 10) and for supplying the load pressure of each hydraulic actuator (5 ∼
6) connected to each pressure compensation valve to the spring chamber side of each
pressure compensation valve when either one of the operation valves (3 or 4) is changed
over at a full stroke. |
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to a hydraulic circuit means for supplying fluid under pressure discharged by a hydraulic pump to a plurality of hydraulic driving means such as hydraulic motors or hydraulic cylinders or the like (which are referred to simply as "hydraulic actuators" hereinbelow).
BACKGROUND TECHNIQUES OF THE INVENTION
[0002] In order to supply fluid under pressure discharged by a hydraulic pump to a plurality of hydraulic actuators, it is only necessary to provide a plurality of operating valves in the delivery passage of the hydraulic pump and supply fluid under pressure to each of the hydraulic actuators by changing over each of the operating valves. However, if such a procedure is taken, when fluid under pressure is supplied to the plurality of hydraulic actuators at the same time, fluid under pressure is supplied only to hydraulic actuators whose load is low, but is not supplied to hydraulic actuators whose loads are high.
[0003] As the hydraulic circuit means which can solve the above-mentioned difficulties, for example, that as shown in Japanese Laid-open Patent Application No. SHO 59-197603 is proposed.
[0004] This hydraulic circuit means is shown schematically in Fig. 1. In this hydraulic circuit means, a hydraulic passage 1 has a fluid discharge passage 2 which is provided with a first operating valve 3 and a second operating valve 4, and a first circuit 7 connecting the first operating valve 3 and a first hydraulic actuator 5, and a second circuit 8 connecting the second operating valve 4 and a second hydraulic actuator 6 are provided with a first pressure compensating valve 9 and a second pressure compensating valve 10, respectively. The arrangement is made such that the load pressures P₁ and P₂ in the first and second hydraulic actuators 5 and 6, respectively, are introduced into a shuttle valve 11 where P₁ is compared with P₂, and as a result a higher load pressure is supplied to the first and second pressure compensating valves 9 and 10, respectively, so as to set the latter at the higher load pressure and keep the pressures at the outlets of the first and second operating valves 3 and 4 equal to each other so that when the first and second operating valves 3 and 4 are operated at the same time the fluid under pressure can be supplied to the first and second hyraulic actuators, respectively, at a flow division ratio which is proportional to the area of openings of the spools of the operating valves.
[0005] In such a hydraulic circuit means, in order to prevent the load in the first hydraulic actuator 5 at the time of starting from becoming excessive so as to prevent the load pressure at the time of starting from becoming abnormally high, the first circuit 7 is provided with a safety valve 12 so as to relieve the abnormally high load pressure at the tiem of starting the first hydraulic actuator 5 to thereby set the safety valve 12 at a pressure P₀.
[0006] Therefore, when the first and second operating valves 3 and 4 are operated at the same time, the pressure P₀ for setting the safety valve 12 becomes higher than the load pressure P₂ in the second hydraulic actuator 6, and the setting pressure P₀ is applied through the shuttle valve 11 to spring chambers 9a and 10a of the first and second pressure compensating valves 9 and 10, respectively, thereby restricting the area of opening of each of the first and second pressure compensating valves 9 and 10 to set the latter at a pressure corresponding to the setting pressure P₀. As a result, the fluid under pressure discharged by the hydraulic pump 1 is restricted when passing through the second pressure compensating valve 10, and at the same time relieved from the safety valve 12 to the fluid tank, thereby reducing the amount of fluid to be supplied to the second hydraulic actuator 6, thus reducing the operating speed of the second hydraulic actuator 6.
[0007] In case, for example, the first hydraulic actuator 5 serves as a turning motor for a power shovel and a second hydraulic actuator 6 serves as a boom actuating cylinder, and a boom is moved upwards by the boom actuating cylinder while the upper turning body is being gyrated, the load pressure at the time of starting the turning motor becomes higher than the pressure P₀ at which the safety valve 12 is set, whilst the load pressure at the time of starting the boom actuating cylinder becomes lower than the pressure P₀ at which the safety valve 12 is set.
[0008] As a result, the area of opening of the second pressure compensating valve 10 is restricted by the pressure P₀ at which the safety valve 12 is set, and fluid pressure is relieved from the safety valve 12 to the fluid tank, and in consequence the fluid under pressure to be supplied to the boom actuating cylinder is reduced, thereby reducing the operating speed of the boom actuating cylinder, which results in reduction in the upwardly moving speed of the boom, thus causing insufficiency in the amount of upward movement thereof.
SUMMARY OF THE INVENTION
[0009] The present invention has been made in view of the above-mentioned circumstances, and has for its object to provide a hydraulic circuit means arranged such that by changing over one operating valve for the full stroke and at the same time another operating valve one pressure compensating valve is supplied with the load pressure in the hydraulic actuator connecting with the pressure compensating valve.
[0010] To achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a hydraulic circuit means comprising: a plurality of operating valves connected to a discharge passage of a hydraulic pump, the operating valves each supplying fluid under pressure to a plurality of hydraulic actuators, each of the operating valves having a pressure compensating valve provided on the side of the outlet thereof, each of the pressure compensating valves being arranged to be set by the load pressure in the hydraulic actuator kept at the highest pressure, characterized in that it comprises a compensation pressure change-over valve adapted to supply normally the highest load pressure to the spring chamber of each of the pressure compensating valves, and supply the load pressure in the hydraulic actuator connected to each of the pressure compensating valves to the spring chamber of each of the pressure compensating valves when either one of the operating valves is changed over for the full stroke.
[0011] Further, to achieve the above-mentioned object, according to a second aspect of the present invention, there is provided a hydraulic circuit means comprising: a plurality of operating valves connected to a discharge passage of a hydraulic pump, the operating valves each supplying fluid under pressure to a plurality of hydraulic actuators, each of the operating valves having a pressure compensating valve provided on the side of the outlet thereof, each of the pressure compensating valves being arranged to be set by the load pressure in the hydraulic actuator kept at the highest pressure characterized in that it comprises a compensation pressure change-over valve provided in a circuit which supplies load pressure to either one of the pressure compensating valves the compensation pressure change-over valve having a first position supplying the highest load pressure, and a second position supplying the load pressure in the hydraulic actuator connected to the pressure compensating valve; and it further comprises a means for holding the compensation pressure change-over valve normally at the first position and changing over the compensation pressure change-over valve to the second position when the operating valve connected to the pressure compensating valve is changed over for the full stroke, and at the same time the other operating valve is changed over.
[0012] As is apparent from the above-mentioned aspects, the present invention provides a hydraulic control unit comprising a compensation pressure change-over valve in a fluid conduit which supplies load pressure to one pressure compensating valve, the arrangement being made such that, when one of the operating valves is changed over for the full stroke and at the same time the operating valve is changed over, the compensation pressure change-over valve is changed over so as to supply the load pressure in the hydraulic actuator connected to the compensation pressure change-over valve to the spring chamber of the above-mentioned pressure compensating valve. Thus, to prevent the load pressure in one of the hydraulic actuators at the time of starting it from becoming abnormally high thereby preventing fluid under pressure from relieving from the safety valve when the plurality of hydraulic actuators are operated at the same time, the pressure compensating function of one of the pressure compensating valves is enhanced temporarily by introducing the load pressure in the hydraulic actuator so as to supply a large quantity of fluid under pressure to the hydraulic actuator counnected to the pressure compensating valve so that the operating speed of the hydraulic actuator can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] The present invention will now be described in detail below by way of preferred embodiments thereof with reference to the accompanying drawings.
[0018] First of all, the first embodiment will be described with reference to Fig. 2. In Fig. 2, a spring chamber 9a of a first pressure compensating valve 9 is connected with an outlet 20a of a first shuttle valve 20, and a first inlet 20b and a second inlet 20c of the latter are connected with a first pilot path 21 and a second pilot path 22, respectively. Further, the second pilot path 22 is connected with a spring chamber 10a of a second pressure compensating valve 10, an outlet 23a of a second shuttle valve 23, and a displacement controlling member 1a of a hydraulic pump 1, respectively.
[0019] A first inlet 23b and a second inlet 23c of the above-mentioned second shuttle valve 23 are connected with a third pilot path 24 and a fourth pilot path 25, respectively. And, the third pilot path 24 and the first pilot path 21 are controlled to be connected by a compensation pressure change-over valve 26 with a first circuit 7, and the fourth pilot path 25 is connected with a second circuit 8.
[0020] The above-mentioned compensation pressure change-over valve 26 has a first position 1 where the first circuit 7 is connected with the third pilot path 24, and the first pilot path 21 is conencted with a fluid tank or reservoir thereby transmitting a load pressure P₁ generated by a first hydraulic actuator 5 to the second shuttle valve 23, and a second position II where the first circuit 7 is connected with the first pilot path 21, and the third pilot path 24 is disconnected, thereby transmitting the load pressure P₁ from the first hydraulic actuator 5 to the first shuttle valve 20. The compensation pressure change-over valve 26 is normally held by a spring 26a at its first position I, and changed over to its second position II when its pilot pressure receiving portion 26b is supplied with a pilot pressure. The pilot pressure receiving portion 26b is supplied with a pilot pressure for changing over a second operating valve 4. The pilot pressure for changing over the second operating valve 4 is proportional to the operating stroke of a change-over lever. The arrangement is made such that when the change-over lever is operated for the full stroke to change-over the second operating valve 4 for the full stroke, the pilot pressure will reach its maximum value so that the compensation pressure change-over valve 26 may assume its second position II against the biasing force of the spring 26a. Thus, when the operating lever of the second operating valve 4 is operated for the full stroke to change-over the second operating valve 4 for the full stroke, the pilot pressure for changing over the second operating valve 4 will reach a maximum value to allow the compensation pressure change-over valve 26 assume its second position II so that the load pressure P₁ from the first hydraulic actuator 5 flows into through the first pilot path 21 into the first shuttle valve 20 and is compared by the latter with the load pressure P₂ from the second hydraulic actuator 6, and as a result of the comparison, higher load pressure is transmitted to the spring chamber 9a of the first pressure compensating valve 9.
[0021] Such being the arrangement, if the load pressure P₁ at the time of starting the first hydraulic actuator 5 is abnormally high and the load pressure P₂ at the time of starting the second hydraulic actuator 6 is low when the first and second operating valves 3 and 4 are operated at the same time, the load pressures P₁ and P₂ at the time of starting the first and second hydraulic actuators 5 and 6 are supplied to the spring chambers 9a and 10a of the first and second pressure compensating valves 9 and 10, respectively.
[0022] Thus, since the first and second pressure compensating valves 9 and 10 are pressure-compensated by their respective load pressures P₁ and P₂ and the load pressure P₂ is supplied to the pump displacement controlling unit 1a as a load sensing pressure, the pump delivery pressure will become the load pressure P₂ plus the load sensing pressure differential, with the result that there is no relief loss from a safety valve 12 and the amount of fluid passing through the second pressure compensating valve 10 will increase, thereby increasing the amount of fluid to be supplied to the second hydraulic actuator 6, and hence, increasing the operating speed.
[0023] And, when the first hydraulic actuator 5 is started and its load pressure P₁ becomes lower than the load pressure P₂ at the second hydraulic actuator 6, the higher load pressure P₂ is supplied through the first shuttle valve 20 to the spring chamber 9a of the first pressure compensating valve 9 so that the first and second pressure compensating valves 9 and 10 are pressure-compensated by the load pressure P₂ from the second hydraulic actuator 6, thereby distributing fluid under pressure to the first and second hyraulic actuators 5 and 6 in proportion to the degree of opening of the first and second operating valves 3 and 4, respectively.
[0024] Further, when the second operating valve 4 is not changed over for its full stroke, but changed over in a fine control zone, the pilot pressure for changing over the second operating valve 4 will not reach its maximum value, and the compensation pressure change-over valve 26 is held by its spring 26a at its first position I. As a result, even if the first and second operating valves 9 and 10 are operated at the same time, the compensation pressure change-over valve 26 is held at its first position I so that the load pressure P₁ from the first hydraulic actuator 5 acts on the spring chamber 10a of the second pressure compensating valve 10 the through the second shuttle valve 23, thereby compensating the second pressure compensating valve 10.
[0025] Thus, when the first hydraulic actuator 5 serves as a turning motor for a power shovel and the second hydraulic actuator 6 serves as a boom actuating cylinder, and a boom operating valve is operated by means of a boom operating lever for its full stroke, and at the same time a turning operation valve is operated by means of a turning operation lever for its full stroke, the second pressure compensating valve 10 is pressure-compensated by its own load pressure P₂, thereby increasing the area of the opening thereof and starting the turning motor by the load pressure of the boom. As a result, a great deal of fluid under pressure can be supplied to the boom actuating cylinder without having to relieve fluid pressure by the safety valve 12, thereby increasing the upwardly moving speed of the boom and preventing the amount of upward movement from becoming insufficient.
[0026] Further, when the boom operating valve changed over in a fine control zone, the second pressure compensating valve 10 is pressure-compensated by a higher load pressure, and therefore when the hydraulic actuator is subjected to heavy load while excavating the earth by turning the upper turning body and contacting one side surface of the bucket with one side surface of the hole to the digged, guick operation of the boom in the fine control zone can be prevented.
[0027] In the above-mentioned embodiment, the compensation pressure change-over valve 26 of a pilot pressure actuated type is used, however, it may be of a solenoid operated type wherein it is actuated by supplying to its solenoid electric current whose value is in proportion to the operating stroke of the operating valve.
[0028] In the next place, the second embodiment of the present invention will be described below with reference to Fig. 3. As shown in Fig. 3, a circuit 31, which connects the spring chamber 10a of the second compressure compensating valve 10 and a shuttle valve 30, is provided with a compensation pressure change-over valve 36. The compensation pressure change-over valve 36 is normally held by the resiliency of its spring at its first position I where the output pressure from the shuttle valve 30 is supplied to the spring chamber 10a of the second pressure compensating valve 10. When the second pressure compensating valve 10 is supplied with a pilot pressure through the second circuit 8, it is changed over to its second position II where the pressure in the second circuit 8, i.e., the load pressure P₂ from the second hydraulic actuator 6 is supplied to the spring chamber 10a of the second pressure compensating valve 10.
[0029] The above-mentioned compensation pressure change-over valve 36 has a pilot circuit 32 which is connected through a shuttle valve 33 with a pilot circuit 34 for changing over the first operating valve 3. The pilot circuit 32 is provided with a change-over valve 35.
[0030] The above-mentioned change-over valve 35 is normally held by the resiliency of its spring at its closed position III where the pilot circuit 32 is connected with the fluid tank or reservoir. When the change-over valve 35 receives a pilot pressure, it is changed over to its open position IV where the pilot circuit 32 is connected with the shuttle valve 33. The pilot pressure receiving portion 35a of the change-over valve 35 is supplied with a pilot pressure for changing over the second operating valve 4, whose valve is proportional to the operating stroke of the change-over lever. The pilot pressure will reach the maximum value when the change-over lever is operated for the full stroke to change over the second operating valve 4 for the full stroke. The arrangement is made such that when the change-over valve 35 receives the maximum value it is changed over to the open position IV against the resilient force of the spring 35b.
[0031] Such being the arrangement, when the first and second operating valves 3 and 4 are operated at the same time, the pilot pressure for changing over the second operating valve 4 is supplied to the pilot pressure receiving portion 35a of the change-over valve 35 so as to change over the second operating valve 4, and when the pilot pressure reaches the maximum value the change-over valve 35 is changed over to its open position IV. Simultaneously therewith, the pilot pressure for changing over the first operating valve 3 in the pilot circuit 34 will flow through the shuttle valve 33 into the pilot circuit 32. The pilot pressure is supplied through the change-over valve 35 into the compensation pressure change-over valve 36 so as to cause the change-over valve 36 to assume its second position II.
[0032] As a result, the load pressure P₂ from the second hydraulic actuator 6 is transmitted to the spring chamber 10a of the second pressure compensating valve 10 so that no pressure compensating effect is provided, and the area of the opening thereof is increased, thereby increasing the mount of fluid supplied to the second hydraulic actuator 6 so as to increase the operating speed of the same.
[0033] Further, when the second operating valve 10 is not changed over for the full stroke, but changed over in a fine control zone, the pilot pressure for changing over the second operating valve 10 will not reach its maximum value, so that the change-over valve 35 is held by its spring 35b at its closed position III, and as a result, even if the first and second operating valves 3 and 4 are operated at the same time, the compensation pressure change-over valve 36 is held at its first position I so as to transmit the load pressure P₁ from the first hydraulic actuator 5 to the spring chamber 10a of the second pressure compensating valve 10 to thereby compensate the latter.
[0034] Accordingly, when the first hydraulic actuator 5 serves as a power shovel turning motor and the second hydraulic actuator 6 serves as a boom actuating cylinder, and the boom operating valve is operated by a boom operating valve for the full stroke, and at the same time the turning operation valve is operated by a turning operation lever for the full stroke, the second pressure compensating valve 10 is not pressure-compensated and the area of the opening thereof is increased so that no fluid under pressure is relieved from the safety valve 12 and excessive load pressure is not applied to the turning motor at the time of starting it, thereby supplying a large quantity of fluid under pressure to the boom actuating cylinder, thus increasing the upwardly moving speed of the boom and preventing the amount of upward movement of the boom from becoming insufficient.
[0035] Further, when the boom operating valve is changed over in a fine control zone, the second pressure compensating valve is pressure-compensated by a higher load pressure, and therefore when the hydraulic actuator is subjected to heavy load while excavating the earth by turning the upper turning body and cotacting one side surface of the bucket with one side surface of the hole to be digged out, quick operation of the boom in the fine control zone can be prevented.
[0036] In this second embodiment, too, the compensation pressure change-over valve 36 and the change-over valve 35, which are of a pilot pressure actuated type, are used, however, it is needless to say that they may be of a solenoid actuated type, wherein they are actuated by supplying their solenoids with electric current whose value is proportional to the operational stroke of their respective operating valves.
1. A hydraulic circuit means comprising: a plurality of operating valves connected to
a discharge passage of a hydraulic pump, the operating valves each supplying fluid
under pressure to a plurality of hydraulic actuators, each of the operating valves
having a pressure compensating valve provided on the side of the outlet thereof, each
of the pressure compensating valves being arranged to be set by the load pressure
in the hydraulic actuator kept at the highest pressure, characterized in that it comprises
a compensation pressure change-over valve 26 adapted to supply normally the highest
load pressure to the spring chamber of each of the pressure compensating valves, and
supply the load pressure in the hydraulic actuator connected to each of the pressure
compensating valves to the spring chamber of each of the pressure compensating valves
when either one of the operating valves is changed over for the full stroke.
2. A hydraulic circuit means comprising: a plurality of operating valves connected to
a discharge passage of a hydraulic pump, the operating valves each supplying fluid
under pressure to a plurality of hydraulic actuators, each of the operating valves
having a pressure compensating valve provided on the side of the outlet thereof, each
of the pressure compensating valves being arranged to be set by the load pressure
in the hydraulic actuator kept at the highest pressure, characterized in that it comprises
a compensation pressure change-over valve provided in a circuit which supplies load
pressure to either one of the pressure compensating valves, the compensation pressure
change-over valve 26 having a first position I supplying the highest load pressure,
and a second position II supplying the load pressure in the hydraulic actuator connected
to the pressure compensating valve; and it further comprises a means for holding said
compensation pressure change-over valve 26 normally at the first position I and changing
over the compensation pressure change-over valve to the second position II when the
operating valve connected to the pressure compensating valve is changed over for the
full stroke, and at the same time the other operating valve is changed over.