JPH05263443A - Hydraulic circuit structure for working vehicle - Google Patents

Abstract

PURPOSE:To prevent a large pressure loss and an oil temperature rise when pumps are operated to the discharge quantity increase side by connecting relief valves opened at the first preset value or above for unloading to the upstream side sections of throttle sections of the pumps. CONSTITUTION:Multiple center bypass type control valves 12, 14, 18, 20, 22 are connected in parallel to multiple variable-displacement pumps 10, 15, and the operating oil is fed to or discharged from multiple hydraulic actuators 7-9, 17, 24. Throttle sections 31, 36 are provided at the most downstream side sections of center drain oil paths 28, 29 of the pumps 10, 15, and relief valves 37, 38 opened when the minimum pressure difference is the first preset value or above for unloading are connected to the upstream side sections. When the minimum pressure difference generated between the front and rear of the throttle sections 31, 36 becomes the first preset value or above, the pumps 10, 15 are operated to the discharge quantity decrease side. When the minimum pressure difference becomes the second preset value or below, the pumps 10, 15 are operated to the discharge quantity increase side. When the pumps 10, 15 are operated to the discharge quantity increase side, a large pressure difference rise of the throttle sections 31, 36 on the large pressure difference side can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit structure for a work vehicle.

[0002]

2. Description of the Related Art Some backhoes, which are one type of work vehicle, have a structure as shown in FIG. That is, a control valve 42 of a center bypass type is prepared for a plurality of sets of hydraulic actuators 41, and each control valve 42 is connected in parallel to each of the two pumps 43 and 44 by an oil passage 45. is there. In this case, even if the control valve 42 is set to the neutral position and the hydraulic actuator 41 is not used, if hydraulic oil is supplied from both pumps 43 and 44, problems such as pressure loss and oil temperature rise will occur.

Therefore, in the structure shown in FIG.
The actuators 3 and 44 are variable displacement type, and the discharge amounts of the pumps 43 and 44 can be increased / decreased in the same direction.
(Corresponding to the changing means), and the throttle portion 49,
Of the differential pressures generated before and after both throttle portions 49, 50, the smaller differential pressure is taken out to the comparison circuit 51, and the actuator 46 is operated by the operating means 52 based on this smaller differential pressure. There is. In this case, when the number of operating hydraulic actuators 41 decreases, the flow rate of the hydraulic oil passing through the center oil discharge passages 47, 48 increases, so that the differential pressure across the throttle portions 49, 50 increases. On the contrary, when the number of hydraulic actuators 41 that are operating increases, the flow rate of the hydraulic oil that passes through the center oil discharge passages 47 and 48 decreases, so that the differential pressure across the throttle portions 49 and 50 decreases. As a result, the throttle unit 4 of both pumps 43, 44 system
The smaller differential pressure among the differential pressures of 9 and 50, that is, the pump 4 with the larger number of operating hydraulic actuators 41.
Based on the differential pressure of the 3,44 system, when this differential pressure becomes large, the actuator 46 operates so that the discharge amounts of both pumps 43,44 are on the decreasing side. On the contrary, when the above-mentioned differential pressure becomes small, the actuator 46 operates so that the discharge amounts of the two pumps 43 and 44 are increased.

As described above, the number of hydraulic actuators to be used is detected and the discharge amount of the pump is changed according to the magnitude of the differential pressure generated in the throttle provided in the center oil discharge passage. The hydraulic fluid having a flow rate corresponding to the number of is discharged from the pump, so that each hydraulic actuator can be operated without hindrance while suppressing pressure loss and oil temperature rise. In this case, two pumps are operated in the same direction by increasing and decreasing by one actuator, because the manufacturing cost increases if two pumps are operated independently by two actuators. Is. And, it is the difference of the smaller one that operates both pumps based on the smaller of the difference pressure,
That is, the work can be performed without any trouble by supplying the hydraulic fluid having a flow rate corresponding to this to the pump system having the larger number of operating hydraulic actuators.

[0005]

In the conventional structure shown in FIG. 3, the number of hydraulic actuators operating in the pump 43 system is small and the number of hydraulic actuators operating in the pump 44 system is large. To do. In this state, the flow rate of the center oil drain passage 47 of the pump 43 system is large, and the flow rate of the center oil drain passage 48 of the pump 44 system is small.
The discharge amounts of the two pumps 43 and 44 are changed based on the differential pressure generated at. In this case, since the pump 44 system is supplied with hydraulic oil at a flow rate corresponding to the number of hydraulic actuators that are operating, there is no particular problem for the pump 44 system. On the other hand, since the number of hydraulic actuators operating in the pump 43 system is small, the flow rate of the center oil discharge passage 47 is originally large. In this state, if the discharge amounts of the two pumps 43, 44 are operated to increase on the basis of the differential pressure of the pump 44 system, the number of hydraulic actuators in operation is small, so the flow rate of the center oil discharge passage 47 is reduced. It will be even more. As a result, a very large differential pressure is generated in the throttle portion 49 of the pump 43 system, which causes a large pressure loss and a rise in oil temperature in the throttle portion 49. An object of the present invention is to suppress a large pressure loss and a rise in oil temperature that occur in the throttle portion when the discharge amounts of a plurality of pumps are increased / decreased in the same direction according to the usage state of the hydraulic actuator as described above. There is.

[0006]

The features of the present invention are as described above.
In the hydraulic circuit structure of such a work vehicle, the following configuration is used.
There is something to do. In other words, for multiple sets of variable displacement pumps
Apply hydraulic fluid to multiple hydraulic actuators for each
Control of multiple center bypass types that supply and discharge each
Connect valves in parallel to increase or decrease the discharge rate of multiple pump sets
Changing means that can be changed in the same direction and the center of each pump
-Because it occurs before and after the throttle part provided on the lowest side of the oil drainage passage.
Differential pressure detecting means for detecting the differential pressure, and each throttle of each pump system
Based on the minimum differential pressure of the parts, this minimum differential pressure is
When it becomes larger than the first set value, the changing means is set to the discharge amount decreasing side.
And the minimum differential pressure is smaller than the first set value.
2 When the value becomes smaller than the set value, the changing means is changed to the discharge amount increasing side.
And a control means for operating the pump system.
Unlock by opening above the first set value on the upper side of the aperture.
Connected to the relief valve.

[0007]

With the above-described structure, the flow rate of the center oil drain passage 28 of the pump 10 system is larger than that of the center oil drain passage 29 of the pump 15 system in the configuration shown in FIG. 1, for example. It is assumed that the hydraulic actuator of the pump 15 system is operating more. In this case, the differential pressure of the throttle portion 36 of the pump 15 system is equal to that of the throttle portion 3 of the pump 10 system.
Since it is smaller than the differential pressure of 1, the discharge amount of the pumps 10, 15 is changed by the smaller differential pressure (throttle portion 36). Therefore, the smaller differential pressure (throttle portion 36) is the second set value (smaller than the first set value described later).
When it becomes smaller than the following, it is determined that many hydraulic actuators are operating in the pump 15 system, and the pump 1
0 and 15 are operated to increase the discharge amount.

As described above, when the pumps 10 and 15 are operated to increase the discharge amount, the flow rate of the center oil discharge passage 29 of the pump 15 system also increases, and the differential pressure of the throttle portion 36 increases. .. In this case, the flow rate of the center oil discharge passage 28 of the pump 10 system also increases, and the differential pressure of the throttle portion 31 of the pump 10 system is greater than or equal to the first set value or a predetermined pressure higher than the first set value. It is assumed that the value exceeds a large value. In this case, the relief valve 37 opens and the differential pressure of the throttle portion 31 becomes
The first set value or a value larger than the first set value by a predetermined pressure is maintained. Before this operation, if the differential pressure of the throttle portion 31 has already reached the first set value or a value larger than the first set value by a predetermined pressure, the relief valve 37 is already open and the differential pressure of the throttle portion 31 is already open. Is maintained at the first set value or at a value larger than the first set value by a predetermined pressure.

[0009]

As described above, when the discharge amounts of a plurality of sets of pumps are operated to increase, in a pump system in which the number of operating hydraulic actuators is small, the differential pressure generated before and after the throttle portion is reduced. I was able to suppress a big rise. As a result, it is possible to suppress pressure loss and hydraulic pressure increase that occur in the throttle portion of the pump system where the number of hydraulic actuators that are operating is small, and suppress deterioration of hydraulic oil due to pressure loss and hydraulic pressure increase. I was able to.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows the entire side surface of a backhoe which is an example of a work vehicle. A swivel base 2 is supported on the upper part of a crawler type traveling device 1, and a backhoe device 3 is provided in front of the swivel base 2. The backhoe device 3 includes a boom 4 vertically rocked by a first hydraulic cylinder 7 (corresponding to a hydraulic actuator), an arm 5 rockable back and forth by a second hydraulic cylinder 8 (corresponding to a hydraulic actuator), And a bucket 6 which is driven by the third hydraulic cylinder 9 (corresponding to a hydraulic actuator) to be swung in and rocked.

Next, the first, second and third hydraulic cylinders 7, 8,
The hydraulic circuit structure for No. 9 will be described. As shown in FIG. 1, an oil passage 11 from the first pump 10 is connected to a control valve 12 for a hydraulic motor 24 (corresponding to a hydraulic actuator) of the right traveling device 1 and a supply branched from the oil passage 11 is provided. The passage 13 is connected to a control valve 14 for the second hydraulic cylinder 8 of the arm 5.

An oil passage 16 from the second pump 15 is connected to a control valve 18 for a hydraulic motor 17 (corresponding to a hydraulic actuator) of the left traveling device 1. The supply passage 19 branched from the oil passage 16 is a supply passage 21 for the control valve 20 of the first hydraulic cylinder 7 for the boom 4 and a supply passage 23 for the control valve 22 of the third hydraulic cylinder 9 for the bucket 6. , Branching in parallel. The first and second pumps 10, 15 are of variable displacement type, and one hydraulic cylinder 25 (corresponding to the changing means) can change the discharge amount by the same amount in the same direction as the control valve 12, 1
4, 18, 20, 22 are constructed in a center bypass type.

As shown in FIG. 1, an operating valve 26 (corresponding to control means) for the hydraulic cylinder 25 and an operating cylinder 27 (corresponding to control means) for switching the operating valve 26 are provided. On the other hand, the center oil drain passages 28 and 29 of the first and second pumps 10 and 15 are returned to the tank 30, and the throttle portions 31 and 3 are respectively provided in the center oil drain passages 28 and 29.
6 is provided. A pilot operated switching valve 32 for the operation cylinder 27 is provided, and the center oil discharge passage 2
Control valves 14, 20 and throttles 31, 36 in 8, 29
From each of the parts between and
(Corresponding to the differential pressure detecting means) is connected to connect the pilot oil passages 34 and 35 to the switching valve 32. This allows
Due to the flow of the hydraulic oil in the center oil discharge passages 28 and 29, a differential pressure is generated before and after the throttle portions 31 and 36, and this differential pressure is taken out from the pilot oil passages 34 and 35 as pilot pressure.

Further, relief valves 37 and 38 are connected to the respective portions of the center oil drain passages 28 and 29 between the control valves 14 and 20 and the throttle portions 31 and 36. When the flow rate of the center oil discharge passages 28 and 29 increases and the differential pressure generated before and after the throttle portions 31 and 36, that is, the pilot pressure increases, the relief valves 37 and 38 are used as first relief valves to be described later.
By opening at the set pressure, the pilot pressure (differential pressure) in the pilot oil passages 34, 35 is maintained at the first set pressure.

With the above structure, for example, the first pump 10
The flow rate of the center oil drain passage 28 of the system is the second pump 15
It is assumed that the flow rate is larger than the center oil discharge passage 29 of the system (that is, the hydraulic cylinders of the second pump 15 system are operating more). In this case, the pilot pressure (differential pressure) is higher in the pilot oil passage 34 of the first pump 10 system, so that the switching valve 32 is operated by the pilot pressure (differential pressure) from the pilot oil passage 34 of the first pump 10 system. First position 32
The pilot pressure (differential pressure) from the pilot oil passage 35 of the second pump 15 system is changed to the operation cylinder 27 by switching to a.
Is ready to be supplied to. That is, the center oil drain passage 2
In Nos. 8 and 29, the switching valve 32 supplies the pilot pressure (differential pressure) on the side with the smaller flow rate to the operation cylinder 27.

As described above, when the pilot pressure (differential pressure) from the center oil discharge passage 29 is supplied to the operation cylinder 27, the pilot pressure (differential pressure) on the center oil discharge passage 29 side becomes the second pressure. When it becomes smaller than a set value (smaller than a first set value described later), in the second pump 15 system,
Many hydraulic cylinders and hydraulic motors are in operation. In this case, the operation valve 26 is moved to the first position by the spring 26c.
When operated to the position 26a, the pilot pressure of the pilot oil passage 33 from the oil passages 11 and 16 is supplied to the first oil chamber 25a of the hydraulic cylinder 25. As a result, the hydraulic cylinder 25 contracts and the first and second pumps 10 and 15 are operated to the discharge amount increasing side.

Thus, the first and second pumps 10, 1
When 5 is operated to the discharge amount increasing side, the second pump 15
The flow rate of the system center oil discharge passage 29 also increases, and the pilot pressure (differential pressure) increases above the second set pressure. In this case, the flow rate of the center oil discharge passage 28 of the first pump 10 system also increases, and the pilot pressure (differential pressure) of the pilot oil passage 34 of the first pump 10 system cannot be larger than the first set value. For example, the relief valve 37 opens and the pilot pressure, that is, the differential pressure generated before and after the throttle portion 31 is maintained at the first set value. Further, before the first and second pumps 10 and 15 start to be operated to the discharge amount increasing side, the flow rate of the center oil discharge passage 28 has already increased and the differential pressure generated before and after the throttle portion 31 is the first set value. If it has reached, the relief valve 37 is already open and the differential pressure generated before and after the throttle portion 31 is maintained at the first set value.

On the contrary, when the pilot pressure (differential pressure) on the center oil discharge passage 29 side becomes larger than the first set value, it means that the hydraulic cylinder and the hydraulic motor in the second pump 15 system are not operating so much. Become. In this case, the switching valve 32
The pilot pressure (differential pressure) from the operating cylinder 27
Operates the operation valve 26 to the second position 26b. In this case, the pilot pressure from the pilot oil passage 33 is supplied in parallel to the first oil chamber 25a and the second oil chamber 25b of the hydraulic cylinder 25.
The hydraulic cylinder 25 expands due to the difference in the pressure receiving areas of the pistons a and 25b. As a result, the first and second pumps 10 and 15 are operated toward the discharge amount decreasing side.

Thus, the first and second pumps 10, 1
When 5 is operated to the discharge amount decreasing side, the second pump 15
The flow rate of the system center oil discharge passage 29 also decreases, and the pilot pressure (differential pressure) also decreases below the first set pressure.
In this case, the flow rate of the center oil discharge passage 28 of the first pump 10 system also decreases, and the pilot pressure (differential pressure) of the pilot oil passage 34 of the first pump 10 system does not decrease below the first set value. That is, the relief valve 37 is closed.

In the above operation, the flow rate of the center oil drain passage 29 of the second pump 15 system is larger than that of the center oil drain passage 28 of the first pump 10 system (that is, the first pump 10 system). The same operation is performed in a state opposite to the above, such as a state in which more hydraulic cylinders of the system are operating). That is, when the pilot pressure (differential pressure) of the center oil discharge passage 28 of the first pump 10 system becomes smaller than the second set value, the first and second pumps 10 and 15 are operated to the discharge amount increasing side. Then, due to the action of the relief valve 38, the differential pressure generated before and after the throttle portion 36 of the second pump system 15 is maintained at the first set value. On the contrary, the center oil drain passage 28
When the side pilot pressure (differential pressure) becomes larger than the first set value, the first and second pumps 10 and 15 are operated to the discharge amount decreasing side. Then, when the pilot pressure (differential pressure) of the pilot oil passage 35 of the second pump 15 system becomes smaller than the first set value, the relief valve 38 is closed.

[Other Embodiments] In the above embodiment, the present invention is applied to two pump systems, but in contrast to the configuration in which three pumps are operated by one hydraulic cylinder 25, The present invention may be applied. When the discharge amounts of the plurality of pumps are increased / decreased and operated in the same direction, the respective pumps may be operated in the increased / decreased and same direction at different ratios. Further, the relief valves 37 and 38 may be configured to open at a pressure higher than the first set pressure by a predetermined pressure.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of first and second pump systems.

[Fig. 2] Overall side view of the backhoe

FIG. 3 is a hydraulic circuit diagram showing a conventional structure.

[Explanation of symbols]

 7,8,9,17,24 Hydraulic actuator 10,15 Pump 12,14,18,20,22 Control valve 25 Change means 26,27 Control means 28,29 Center drain passage 31,36 Throttle portion 34,35 Difference Pressure detecting means 37,38 Relief valve

Claims (1)

[Claims] 1. A plurality of sets of variable displacement pumps (10),
Control of a plurality of center bypass types for supplying / discharging hydraulic oil to / from a plurality of hydraulic actuators (7), (8), (9), (17), (24) for each of (15). Valves (12), (14), (18), (20), (2
2) are connected in parallel, and the plurality of sets of pumps (1
Change means (25) capable of changing the discharge amount of 0) and (15) in the same direction as increasing and decreasing, and the pumps (10) and (15)
Differential pressure detection means (34), (35) for detecting the differential pressure generated before and after the throttle parts (31), (36) provided on the lowermost side parts of the center oil discharge passages (28), (29). And the throttle parts (31), (3) of the pumps (10), (15) system.
Based on the minimum differential pressure among the differential pressures of 6), when the minimum differential pressure becomes greater than the first set value, the changing means (25).
Control means (2) for operating the discharge amount decreasing side, and for operating the changing means (25) for the discharge amount increasing side when the minimum differential pressure becomes smaller than the second setting value which is smaller than the first setting value.
6) and (27), and each pump (1
Relief valves (37) and (38) that open and unload above the first set value are connected to the upper side portions of the throttle portions (31) and (36) of the 0) and (15) systems. Hydraulic circuit structure of work vehicle.