Hydraulic system

Abstract

The present invention relates to a hydraulic system having a load sensing function, and tries to prevent a hunting state, improve machining, and save driving power of a hydraulic pump. The hydraulic system comprises a pump operating unit that controls a discharge amount of the hydraulic pump by receiving pilot hydraulic oil from a sensing oil passage 37. An operation valve 30 provided in the sensing oil passage 37 is switchable between an open state to allow communication with the sensing oil passage 37 and a closed state to block a flow of the pilot hydraulic oil toward control valves 25, 26 in the sensing oil passage 37, and is kept in the open state when an operation pressure which is the pressure of the pilot hydraulic oil in a portion 37b between the operation valve 30 and the control valves 25, 26 in the sensing oil passage 37 is less than a set pressure, and switched to the closed state when the operation pressure is greater than or equal to the set pressure.

Description

[Technical Field]

[0001] The present invention relates to a configuration for controlling the discharge volume of a hydraulic pump in a hydraulic system configured to supply hydraulic oil from a variable displacement hydraulic pump to a hydraulic actuator. [Background technology]

[0002] Conventional hydraulic systems include a variable displacement hydraulic pump, a control valve that supplies hydraulic oil from the hydraulic pump to a hydraulic actuator, a sensing oil passage that branches off and extracts pilot hydraulic oil from the hydraulic oil supplied from the control valve to the hydraulic actuator, and a pump operating unit that receives the pilot hydraulic oil from the sensing oil passage and operates the discharge volume of the hydraulic pump.

[0003] When the pressure of the pilot hydraulic oil in the sensing oil passage increases, it is assumed that the load on the hydraulic actuator has increased, and the pump operating unit operates to increase the discharge volume of the hydraulic pump. When the pressure of the pilot hydraulic oil in the sensing oil passage decreases, it is assumed that the load on the hydraulic actuator has decreased, and the pump operating unit operates to decrease the discharge volume of the hydraulic pump. The above function is called the load sensing function.

[0004] The load sensing function described above is a feedback control that transmits changes in the load on the hydraulic actuator to the pump operating unit to control the discharge volume of the hydraulic pump. As a result, if the load on the hydraulic actuator frequently changes from high to low, for example, the discharge volume of the hydraulic pump may be frequently increased or decreased with a slight delay. This state is called a hunting state.

[0005] In order to prevent hunting in the load sensing function, as disclosed in Patent Document 1, a check valve is provided in the sensing oil passage, and a throttle portion communicating with the tank is connected to the sensing oil passage.

[0006] In Patent Document 1, when the load on the hydraulic actuator increases, pilot hydraulic oil is supplied to the pump operating unit through a check valve, and the pump operating unit operates to increase the discharge rate of the hydraulic pump. Next, when the load on the hydraulic actuator decreases, even if the pilot hydraulic oil tries to return from the pump operating unit through the sensing oil passage, it is stopped by the check valve, and the pilot hydraulic oil returns slowly from the pump operating unit through the throttle unit to the tank. This makes it easier for the pilot hydraulic oil to be held in the pump operating section, and the pump operating section operates the hydraulic pump to gradually decrease its discharge rate, thereby preventing hunting. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 9-317702 (see Figures 1, 7, 11, and 12) Summary of the Invention [Problem to be solved by the invention]

[0008] In the configuration of Patent Document 1, when the load on the hydraulic actuator increases and then decreases, the pilot hydraulic oil cannot pass through the check valve but returns to the tank through the throttle section, so the pilot hydraulic oil is not retained in the pump operating section for very long, and there is room for improvement in terms of preventing hunting.

[0009] In the above-described state, the restriction portion can be set to an extremely small diameter in order to extend the time that the pilot hydraulic oil is retained in the pump operating portion. However, obtaining an extremely small diameter restriction portion requires high-precision machining, and it is difficult to obtain extremely small diameter restriction portions without variation when mass-producing hydraulic systems.

[0010] In addition, for example, if the control valve is operated to the neutral position to stop the hydraulic actuator after a load is applied to the hydraulic actuator, when the control valve is operated to the neutral position, the pilot hydraulic oil needs to be quickly discharged from the pump operating unit.

[0011] In the configuration of Patent Document 1, the pilot hydraulic oil is discharged from the pump operating unit through a throttle, so it takes time for the pilot hydraulic oil to be discharged from the pump operating unit. As a result, even though the control valve is operated to the neutral position, the state in which the hydraulic pump's discharge rate is increased is maintained for a predetermined time, leaving room for improvement in terms of saving drive power for the hydraulic pump.

[0012] The present invention aims to prevent hunting, improve machining, and save hydraulic pump drive power in a hydraulic system equipped with a load sensing function. [Means for solving the problem]

[0013] The hydraulic system of the present invention comprises a variable displacement hydraulic pump, a control valve that controls the supply state of hydraulic oil from the hydraulic pump to the hydraulic actuator, a sensing oil line that branches off and extracts pilot hydraulic oil from the hydraulic oil supplied from the control valve to the hydraulic actuator, a pump operating unit that increases the discharge rate of the hydraulic pump when the pressure of the pilot hydraulic oil in the sensing oil line increases, and decreases the discharge rate of the hydraulic pump when the pressure of the pilot hydraulic oil in the sensing oil line decreases, and an operating valve provided in the sensing oil line, the operating valve being switchable between an open state that connects the sensing oil line and a closed state that blocks the flow of pilot hydraulic oil in the sensing oil line toward the control valve, and is maintained in the open state when the operating pressure, which is the pressure of the pilot hydraulic oil in the portion of the sensing oil line between the operating valve and the control valve, becomes less than a set pressure, and is switched to the closed state when the operating pressure becomes equal to or greater than the set pressure.

[0014] According to the present invention, when no load is applied to the hydraulic actuator, the operating valve is operated to an open state and the sensing oil passage is in communication. When a load is applied to the hydraulic actuator, pilot hydraulic oil is supplied to the pump operating unit through the operating valve (open), and the pump operating unit operates to increase the discharge volume of the hydraulic pump. When the load on the hydraulic actuator increases and the operating pressure, which is the pressure of the pilot hydraulic oil in the part of the sensing oil line between the operating valve and the control valve, increases, the operating valve is operated to the closed state.

[0015] Next, when the load on the hydraulic actuator decreases, even if the pilot hydraulic oil tries to return from the pump operating unit to the control valve, it is stopped by the operating valve (closed), so the pilot hydraulic oil is retained in the pump operating unit and the discharge volume of the hydraulic pump is likely to be maintained on the increasing side. As a result, even if the load on the hydraulic actuator frequently changes between high and low, the pump operating unit is less likely to frequently increase or decrease the hydraulic pump's discharge volume, preventing a hunting condition and stabilizing the operation of the load sensing function.

[0016] For example, suppose that a load is applied to the hydraulic actuator, and then the control valve is operated to the neutral position, causing the hydraulic actuator to stop. According to the present invention, when the control valve is operated to the neutral position and the hydraulic actuator is stopped, the operating pressure is quickly reduced, the operating valve is operated to the open state, and the sensing oil passage is opened.

[0017] As a result, the pilot hydraulic oil of the pump operating unit flows out quickly through the operating valve (open state), and the pump operating unit operates the hydraulic pump to decrease its discharge volume without delay. Therefore, when the control valve is operated to the neutral position, the time during which the discharge volume of the hydraulic pump is maintained at an increased volume can be shortened, thereby saving the driving power of the hydraulic pump.

[0018] According to the present invention, there is no need for an extremely small diameter restriction portion that requires high-precision machining, and the function of preventing the hunting state described above and the function of shortening the time during which the discharge volume of the hydraulic pump is maintained on the increased side when the control valve is operated to the neutral position can be obtained with an operating valve that has a relatively simple structure, thereby simplifying the structure and reducing costs.

[0019] In the present invention, it is preferable that in the closed state, the flow of pilot hydraulic oil toward the control valve is blocked and the flow of pilot hydraulic oil toward the pump operating unit is permitted.

[0020] According to the present invention, for example, when a load is applied to the hydraulic actuator, if the operating valve is operated to the closed state before sufficient pilot hydraulic oil is supplied to the pump operating unit, or if an even greater load is applied to the hydraulic actuator after the operating valve is operated to the closed state, the pilot hydraulic oil in the portion of the sensing oil passage between the operating valve and the control valve is supplied to the pump operating unit through the operating valve (closed state), and the pump operating unit operates to increase the discharge volume of the hydraulic pump. As a result, the discharge rate of the hydraulic pump is unlikely to be insufficient in response to an increase in the load on the hydraulic actuator, and workability is not reduced due to an insufficient discharge rate of the hydraulic pump.

[0021] In the present invention, the operating valve preferably has a spool that is movable between an open position where the operating valve is in the open state and a closed position where the operating valve is in the closed state, a biasing portion that biases the spool to the open position, and a pressure-receiving portion that receives the operating pressure, and when the operating pressure acting on the pressure-receiving portion becomes less than the set pressure, the spool is held in the open position by the biasing force of the biasing portion, and when the operating pressure acting on the pressure-receiving portion becomes equal to or greater than the set pressure, the spool is operated to the closed position against the biasing force of the biasing portion.

[0022] According to the present invention, the hydraulic system of the present invention can be obtained with a simple configuration having a spool that can be moved to an open position corresponding to the open state and a closed position corresponding to the closed state, and a biasing portion that biases the spool to the open position.

[0023] In the present invention, the operation valve is provided with: a first internal space; a second internal space connected to the first internal space; a first port that communicates a portion of the sensing oil passage on the pump operation unit side with the first internal space; a second port that communicates a portion of the sensing oil passage on the control valve side with the second internal space; a first land portion that is disposed on the opposite side of the second port with respect to the first port; a second land portion that is disposed on the second port side with respect to the first port; and a notch portion that is formed on an end of an outer periphery of the second land portion on the first land portion side; the spool that is movably supported in the first internal space; a communication passage that is provided in the spool separately from the second land portion and the notch portion so as to communicate between the first port and the second port; and a check valve that blocks the flow of oil and allows the flow of pilot hydraulic oil from the second port toward the first port in the communication passage, wherein a portion of the second land portion facing the second internal space is the pressure-receiving portion, and when the operating pressure acting on the pressure-receiving portion becomes less than the set pressure, the spool is moved by the biasing force of the biasing portion to the open position in which the first port and the second port communicate with each other via the notch portion while the first land portion and the second land portion are supported in the first internal space, and when the operating pressure acting on the pressure-receiving portion becomes equal to or greater than the set pressure, the spool is moved against the biasing force of the biasing portion to the closed position in which the communication between the first port and the second port via the notch portion is blocked by the second land portion while the first land portion and the second land portion are supported in the first internal space.

[0024] According to the present invention, when the operating pressure acting on the pressure-receiving portion of the spool decreases and the spool moves to the open position due to the biasing force of the biasing portion, the notch portion of the spool opens to the second internal space, the first port and the second port communicate with each other via the notch portion of the spool, and the sensing oil passage communicates. In this case, since the first land portion and the second land portion, which are spaced apart from each other, on the spool are supported in the first internal space, the movement of the spool to the open position is smooth, and the spool is stably supported in the first internal space in the open position.

[0025] According to the present invention, when the operating pressure acting on the pressure-receiving portion of the spool increases and the spool moves to the closed position due to the operating pressure, the notch portion of the spool closes to the second internal space, and communication between the first port and the second port via the notch portion is blocked by the second land portion of the spool. In this case, since the first land portion and the second land portion, which are spaced apart from each other, on the spool are supported in the first internal space, the movement of the spool to the closed position is smooth, and the spool is stably supported in the first internal space in the closed position. Even when the spool moves to the closed position, the communication passage and the check valve block the flow of pilot hydraulic oil from the first port in the communication passage toward the second port (control valve), and allow the flow of pilot hydraulic oil from the second port in the communication passage toward the first port (pump operating unit).

[0026] In the present invention, it is preferable that when the spool is moved to the open position by the biasing force of the biasing portion, the first port and the second port are communicated via the notch portion, and a stopper portion is provided to stop the spool at a position where the second land portion does not come out of the first internal space.

[0027] According to the present invention, when the spool moves to the open position due to the biasing force of the biasing portion and the first port and the second port communicate through the notch portion of the spool, the spool is stopped by the stopper portion at a position where the second land portion of the spool does not come out of the first internal space, and the position where the spool is stopped by the stopper portion is the open position.

[0028] When the spool is moved to the open position by the biasing portion, if the spool moves beyond the open position and the second land portion of the spool moves out of the first internal space and into the second internal space, the second land portion of the spool may not be able to move from the second internal space into the first internal space when the spool moves from the open position to the closed position.

[0029] In the present invention, it is preferable that the second internal space is formed to have a larger diameter than the first internal space.

[0030] According to the present invention, when operating pressure acts on the pressure-receiving portion of the spool, the second internal space is formed with a larger diameter than the first internal space, which makes it easier for the operating pressure to act uniformly on the pressure-receiving portion of the spool without bias, thereby allowing the spool to move smoothly to the closed position. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 2 is a left side view of the tractor. [Figure 2] FIG. 2 is a hydraulic circuit diagram of the vicinity of the hydraulic pump and the pump operating unit. [Figure 3] FIG. 2 is a hydraulic circuit diagram in the vicinity of the control valve unit. [Figure 4] FIG. 2 is a cross-sectional view of the operating valve in the open position. [Figure 5] FIG. 2 is a cross-sectional view of the operating valve in a state where it is operated to a closed position. DETAILED DESCRIPTION OF THE INVENTION

[0032] A tractor, which is an example of a work vehicle equipped with a hydraulic system according to one embodiment of the present invention, is shown in Figures 1 to 5. In Figure 1, F indicates the forward direction, B indicates the rearward direction, U indicates the upward direction, and D indicates the downward direction.

[0033] (Overall configuration of the tractor) As shown in Figure 1, a vehicle body 3 is supported by right and left front wheels 1 and right and left rear wheels 2. The vehicle body 3 has an engine 4, a clutch housing 5 connected to the rear of the engine 4, a transmission case 6 connected to the rear of the clutch housing 5, a front frame 7 connected to the front of the engine 4, etc. The front wheels 1 are supported by the front frame 7, and the rear wheels 2 are supported at the rear of the transmission case 6.

[0034] A bonnet 8 is provided at the front of the aircraft body 3, and the bonnet 8 covers the engine 4. A driver's section 9 is provided at the rear of the aircraft body 3, and the driver's section 9 is covered by a cabin 10. The driver's section 9 is provided with a driver's seat 11 and a steering wheel 12 for steering the front wheels 1.

[0035] (Configuration related to support of working equipment) As shown in FIG. 1, a top link 13 and right and left lower links 14 are supported at the rear of the transmission case 6 so as to be able to swing up and down, and a work implement such as a rotary tiller (not shown) or a plow (not shown) is connected to the top link 13 and the lower links 14.

[0036] Right and left lift arms 15 are supported on the upper rear part of the transmission case 6 so that they can swing up and down, and right and left lift cylinders 16 (equivalent to hydraulic actuators) are connected between the right and left lift arms 15 and the lower rear part of the transmission case 6.

[0037] A rolling cylinder 17 is connected between the right lift arm 15 and the right lower link 14, and a linking rod 18 is connected between the left lift arm 15 and the left lower link 14.

[0038] When the lift arm 15 is raised and lowered by the lift cylinder 16, the lower link 14 is raised and lowered, and the working device is raised and lowered. When the rolling cylinder 17 is extended and contracted, the right lower link 14 is raised and lowered, and the working device is rolled with the left lower link 14 as a fulcrum.

[0039] (Hydraulic circuit overview) As shown in FIGS. 2 and 3, a hydraulic pump 19 driven by the engine 4 is provided, and lubricating oil stored in the transmission case 6 is sucked into the hydraulic pump 19 as hydraulic oil.

[0040] A control valve unit 20 that supplies and discharges hydraulic oil to and from the lift cylinder 16, and hydraulic units 21, 22 that supply and discharge hydraulic oil to a work device (not shown) such as a front loader that is equipped on the machine body 3 are provided.

[0041] An oil passage 23 of the hydraulic pump 19 is connected to the control valve unit 20, and an oil passage 24 branching from the oil passage 23 is connected to the hydraulic units 21 and 22, and the operating oil of the hydraulic pump 19 is supplied to the control valve unit 20 and the hydraulic units 21 and 22.

[0042] The lift cylinder 16 is configured as a single-acting type. When hydraulic oil is supplied to the lift cylinder 16 in the control valve unit 20, the lift cylinder 16 extends, raising the lift arm 15. When hydraulic oil is discharged from the lift cylinder 16, the lift cylinder 16 contracts, lowering the lift arm 15.

[0043] (Configuration of control valve unit) As shown in FIG. 3, the control valve unit 20 includes an ascending control valve 25 (corresponding to a control valve), a descending control valve 26 (corresponding to a control valve), a check valve 27, a relief valve 28, an on-off valve 29, an operating valve 30, and the like.

[0044] 2 and 3, an oil passage 23 from the hydraulic pump 19 is connected to an oil passage 31 of the control valve unit 20, and the lift control valve 25 is connected to the oil passage 31. The lift control valve 25 has an elevated position 25a and a neutral position 25b, is electromagnetically operated, and is biased to the neutral position 25b by a spring. An oil passage 32 is connected between the lift control valve 25 and the lift cylinder 16, and a check valve 27 is provided in the oil passage 32, and a relief valve 28 is connected to the oil passage 32.

[0045] An oil passage 33 is connected to the oil passage 32, and an on-off valve 29 is provided in the oil passage 33, which is connected to the descent control valve 26. The on-off valve 29 has an open position and a closed position, and is provided with a variable throttling function.

[0046] The descent control valve 26 has a descent position 26a with a variable throttle function and a neutral position 26b, and is configured to be electromagnetically operated and is biased toward the neutral position 26b by a spring. An oil passage 34 from the descent control valve 26 is connected to the transmission case 6.

[0047] The state shown in Figure 3 is a state in which the ascent control valve 25 and the descent control valve 26 are operated to the neutral positions 25b and 26b, respectively, and the hydraulic oil in the lift cylinder 16 is stopped by the descent control valve 26 (neutral position 26b) and the check valve 27, causing the lift cylinder 16 to stop.

[0048] When the lift control valve 25 is operated to the lift position 25a from the state shown in Figure 3, the hydraulic oil from the hydraulic pump 19 is supplied to the lift cylinder 16 via the oil passages 23, 31, the lift control valve 25 (lift position 25a), the check valve 27, and the oil passage 32, causing the lift cylinder 16 to extend.

[0049] When the descent control valve 26 is operated to the descent position 26a from the state shown in Figure 3, the hydraulic oil in the lift cylinder 16 is discharged to the transmission case 6 via the oil passage 32, the on-off valve 29 (open position), the oil passage 33, the descent control valve 26 (descent position 26a), and the oil passage 34, and the lift cylinder 16 contracts. As described above, the supply state of hydraulic oil from the hydraulic pump 19 to the lift cylinder 16 is controlled by the ascent control valve 25 and the descent control valve 26.

[0050] (Load sensing function overview) 3, in the lift cylinder 16, in which hydraulic oil is supplied and discharged by the control valve unit 20, and the work device, in which hydraulic oil is supplied and discharged by the hydraulic units 21 and 22, the load acting on the lift cylinder 16 and the work device is extracted as pilot hydraulic oil pressure. If the pilot hydraulic oil pressure is high, the load can be considered large, and if the pilot hydraulic oil pressure is low, the load can be considered small.

[0051] Pilot hydraulic oil extracted by the control valve unit 20 is supplied to an oil passage 49, and pilot hydraulic oil extracted by the hydraulic units 21 and 22 is supplied to an oil passage 50. Of the pilot hydraulic oils from the control valve unit 20 and the hydraulic units 21 and 22, the pilot hydraulic oil with the highest pressure is selected by a high-pressure selection valve 53 and supplied to an oil passage 54.

[0052] As shown in FIG. 2, the hydraulic pump 19 is configured as a variable displacement type, and is provided with an operating cylinder 35 that operates to increase or decrease the discharge rate of the hydraulic pump 19, and a pump operating unit 36 ​​that operates the operating cylinder 35.

[0053] Based on the above-mentioned maximum pressure pilot hydraulic oil, the discharge rate of the hydraulic pump 19 is controlled by the pump control unit 36 ​​and the control cylinder 35. When the pressure of the maximum pressure pilot hydraulic oil increases, the control cylinder 35 controls the discharge rate of the hydraulic pump 19 to increase, and when the pressure of the maximum pressure pilot hydraulic oil decreases, the control cylinder 35 controls the discharge rate of the hydraulic pump 19 to decrease.

[0054] (Overview of the control valve) 3, in the control valve unit 20, the sensing oil passage 37 branches off from a portion of the oil passage 32 between the lift control valve 25 and the check valve 27, and is connected to an oil passage 49. Pilot hydraulic oil branches off from the hydraulic oil supplied from the lift control valve 25 to the lift cylinder 16, and is taken out to the sensing oil passage 37.

[0055] 3, 4, and 5, the operating valve 30 is provided in the sensing oil passage 37. The operating valve 30 has a first internal space 41, a second internal space 42, a spool 38, a spring 43 (corresponding to a biasing portion), a check valve 44, a notch portion 45, a groove portion 46 (corresponding to a communicating passage), communicating passages 47 and 48, a first port 51, and a second port 52, etc.

[0056] As shown in Figures 4 and 5, the first port 51 is connected to the first internal space 41, and the portion 37a of the sensing oil passage 37 on the pump operating unit 36 ​​side and the first internal space 41 are connected via the first port 51.

[0057] The second internal space 42 is connected to the first internal space 41 and has a larger diameter than the first internal space 41. A second port 52 is connected to the second internal space 42, and a portion 37b of the sensing oil passage 37 on the rise control valve 25 side and the second internal space 42 communicate with each other via the second port 52. A similar operation valve 30 is also provided in each of the hydraulic units 21 and 22.

[0058] As described above, a hydraulic system is configured that includes the hydraulic pump 19, the up control valve 25 and down control valve 26 of the control valve unit 20, the operation valve 30, the sensing oil passage 37, and the pump operation unit 36.

[0059] (Configuration of spool in control valve) As shown in FIGS. 4 and 5, the spool 38 has a first portion 39 and a second portion 40, and the first portion 39 is provided with a first land portion 39a and a second land portion 39b.

[0060] The first land portion 39a of the spool 38 (first portion 39) is disposed on the opposite side of the second port 52 with respect to the first port 51. The second land portion 39b of the spool 38 (first portion 39) is disposed on the second port 52 side with respect to the first port 51, and the first land portion 39a and the second land portion 39b of the spool 38 (first portion 39) are disposed apart from each other.

[0061] The first land portion 39a and the second land portion 39b of the spool 38 (first portion 39) are supported on the inner surface of the first internal space 41, thereby movably supporting the spool 38 in the first internal space 41. A spring 43 is attached to the second portion 40 of the spool 38, and the spool 38 is urged toward the second internal space 42 by the spring 43.

[0062] In the second land portion 39b of the spool 38 (first portion 39), a wall portion 39c (corresponding to a pressure-receiving portion) on the opposite side to the first land portion 39a faces the second internal space 42. The pressure (operating pressure) of the pilot hydraulic oil in the portion 37b (second port 52) ​​between the operation valve 30 and the rise control valve 25 in the sensing oil passage 37 is applied to the wall portion 39c of the spool 38 (first portion 39).

[0063] Notches 45 are formed on the outer periphery of the second land portion 39b of the spool 38 (first portion 39) at the end on the first land portion 39a side. The notches 45 are formed in two locations, and the two notches 45 are located 180 degrees apart from each other.

[0064] A groove 46 is formed in a wall 39c of a second land 39b of the spool 38 (first portion 39). In the first portion 39 of the spool 38, a single communication passage 48 is formed penetrating the portion between the first land 39a and the second land 39b, and a communication passage 47 is formed penetrating from the groove 46 to the communication passage 48. A ball-shaped check valve 44 is disposed at the intersection of the communication passages 47, 48.

[0065] Thus, a groove 46 and communication passages 47, 48 are provided in the spool 38 (first portion 39) separately from the second land portion 39b and notch portion 45 of the spool 38 (first portion 39) to communicate between the first port 51 and the second port 52. A check valve 44 is provided in the spool 38 (first portion 39) separately from the second land portion 39b and notch portion 45 of the spool 38 (first portion 39).

[0066] (Operating valve is in the open position) The state shown in Figures 3 and 4 is a state in which no load is applied to the lift cylinder 16, the pressure (operating pressure) of the pilot hydraulic oil in the portion 37b (second port 52) ​​of the sensing oil passage 37 is low, and the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) is low.

[0067] The operating valve 30 (spool 38) is biased to the open position 30a shown in Figure 4 by a spring 43. The biasing force of the spring 43 (corresponding to the set pressure determined by the biasing force of the biasing portion (spring 43)) is set small enough to overcome the low pressure (operating pressure) of the pilot hydraulic oil in the portion 37b (second port 52) ​​of the sensing oil passage 37 when no load is applied to the lift cylinder 16.

[0068] As a result, with no load applied to the lift cylinder 16, the spool 38 is moved to the open position 30a by the spring 43, and the operating valve 30 is operated to the open position 30a. When the operating valve 30 (spool 38) is operated to the open position 30a, the notch portion 45 of the spool 38 opens to the second internal space 42, the first port 51 and the second port 52 communicate with each other through the notch portion 45 of the spool 38, and the sensing oil passage 37 (portions 37a, 37b) communicates with each other.

[0069] The above state is the state in which the operating pressure, which is the pressure of the pilot hydraulic oil in the portion 37b between the operating valve 30 and the rise control valve 25 in the sensing oil passage 37, becomes less than the set pressure, causing the operating valve 30 to be switched to and maintained in the open state.

[0070] The wall portion 39c of the second land portion 39b of the spool 38 (first portion 39) hits the wall portion 42a (corresponding to the stopper portion) of the second internal space 42, so that the spool 38 cannot move beyond the open position 30a of the operating valve 30 shown in Figure 4 to the right in Figure 4.

[0071] Since the width of the second internal space 42 is set to be sufficiently smaller than the width of the first internal space 41, the end portion (the portion near the notch portion 45) of the second land portion 39b of the spool 38 (first portion 39) on the first land portion 39a side is supported on the inner surface of the first internal space 41 without coming off the first internal space 41.

[0072] In the groove portion 46 and the communication passages 47, 48, the flow of pilot hydraulic oil from the second port 52 toward the first port 51 is permitted by the check valve 44. The flow of pilot hydraulic oil from the first port 51 toward the second port 52 is blocked by the check valve 44.

[0073] With the above configuration, when the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) decreases, the spool 38 moves to the open position 30a of the operating valve 30, where the first port 51 and the second port 52 are connected via the notch portion 45 of the spool 38, by the biasing force of the spring 43, while the first land portion 39a and the second land portion 39b of the spool 38 (first portion 39) are supported on the inner peripheral portion of the first internal space 41.

[0074] (Operation valve is in the closed position) The state shown in Figure 5 is a state in which a load is applied to the lift cylinder 16, the pressure (operating pressure) of the pilot hydraulic oil in the portion 37b (second port 52) ​​of the sensing oil passage 37 is high, and the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) is high.

[0075] When the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) increases, the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) moves the spool 38 to the left in Figure 4 against the biasing force of the spring 43 (corresponding to the set pressure determined by the biasing force of the biasing portion (spring 43)), and the operating valve 30 (spool 38) is operated to the closed position 30b shown in Figure 5.

[0076] As shown in Figures 3 and 5, when the operating valve 30 (spool 38) is operated to the closed position 30b, the notch portion 45 of the spool 38 is closed to the second internal space 42, and communication between the first port 51 and the second port 52 via the notch portion 45 is blocked by the second land portion 39b of the spool 38 (first portion 39).

[0077] The spool 38 (first portion 39) is provided with the groove 46, the communication passages 47, 48, and the check valve 44, so even if the operating valve 30 (spool 38) is operated to the closed position 30b, the flow of pilot hydraulic oil from the second port 52 to the first port 51 is permitted by the groove 46 and the communication passages 47, 48. The flow of pilot hydraulic oil from the first port 51 to the second port 52 is blocked by the check valve 44.

[0078] The above state is the state in which the operating valve 30 is switched to the closed state when the operating pressure, which is the pressure of the pilot hydraulic oil in the portion 37b between the operating valve 30 and the rise control valve 25 in the sensing oil passage 37, becomes equal to or higher than the set pressure.

[0079] With the above configuration, when the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) increases, the spool 38 moves against the biasing force of the spring 43 to the closed position 30b of the operating valve 30, in which the first port 51 and the second port 52 are blocked by the second land portion 39b of the spool 38 (first portion 39), while the first land portion 39a and the second land portion 39b of the spool 38 (first portion 39) are supported by the inner peripheral portion of the first internal space 41.

[0080] As shown in Figures 2 and 3, when the operating valve 30 is in the closed position 30b, the flow of pilot hydraulic oil toward the rise control valve 25 is blocked, and the flow of pilot hydraulic oil toward the pump operating unit 36 ​​is allowed.

[0081] (Configuration of pump operation section) As shown in FIG. 2, the operating cylinder 35 is biased in the increase direction by a spring 55, and operates in the decrease direction when hydraulic oil is supplied from the pump operating unit 36.

[0082] The pump operating unit 36 ​​has a first pump operating valve 61 and a second pump operating valve 62 . The first pump operating valve 61 and the second pump operating valve 62 are configured to be pilot operated, have first positions 61a, 62a and second positions 61b, 62b, and are biased to the first positions 61a, 62a by springs.

[0083] An oil passage 56 branching from the oil passage 23 is connected to an oil passage 57 of the pump operation unit 36. The oil passage 57 branches in the pump operation unit 36, and the branched oil passage 57 is connected to a first pump operation valve 61, a pressure-receiving portion of the first pump operation valve 61 at its second position 61b, a second pump operation valve 62, and a pressure-receiving portion of the second pump operation valve 62 at its second position 62b.

[0084] The oil passage 54 (see FIG. 3) is connected to an oil passage 58 of the pump operating unit 36, and the oil passage 58 is connected to a pressure-receiving portion of the first position 61a of the first pump operating valve 61. Of the pilot hydraulic oils of the control valve unit 20 and the hydraulic units 21, 22, the pilot hydraulic oil with the highest pressure is supplied to the pressure-receiving portion of the first position 61a of the first pump operating valve 61 via the oil passages 54, 58.

[0085] An oil passage 59 is connected between the first pump operation valve 61 and the second pump operation valve 62, and an oil passage 60 is connected between the second pump operation valve 62 and the operation cylinder 35. An oil passage 63 from the first pump operation valve 61 and the second pump operation valve 62 is connected to an oil passage 64, and the oil passage 64 is connected to the transmission case 6.

[0086] (Operation status of hydraulic pump discharge volume by operation valve and pump operation unit) (Part 1) Assuming that the pilot hydraulic oil of the control valve unit 20 is at the highest pressure among the pilot hydraulic oils of the control valve unit 20 and the hydraulic units 21 and 22, the following describes the state in which the pilot hydraulic oil of the control valve unit 20 operates the operating cylinder 35 and the pump operating unit 36 ​​and controls the discharge volume of the hydraulic pump 19.

[0087] As shown in Figures 3 and 4, assume that the up-control valve 25 and the down-control valve 26 are operated to the neutral positions 25b and 26b, the lift cylinder 16 is stopped, the pressure (operating pressure) of the pilot hydraulic oil (portion 37b of the sensing oil passage 37) of the control valve unit 20 is low, and the operating valve 30 (spool 38) is operated to the open position 30a.

[0088] When the operating valve 30 (spool 38) is operated to the open position 30a, the notch portion 45 of the spool 38 opens to the second internal space 42, the first port 51 and the second port 52 communicate with each other through the notch portion 45 of the spool 38, and the sensing oil passage 37 (portions 37a, 37b) communicates with each other.

[0089] As shown in Figure 2, since the pressure (operating pressure) of the pilot hydraulic oil (portion 37b of the sensing oil passage 37) of the control valve unit 20 is low, the hydraulic oil in the oil passage 57 operates the first pump operating valve 61 to the second position 61b, and the second pump operating valve 62 to the second position 62b.

[0090] The hydraulic oil in the oil passage 57 is supplied to the operating cylinder 35 via the second position 61b of the first pump operating valve 61, the oil passage 59, the second position 62b of the second pump operating valve 62, and the oil passage 60, and the operating cylinder 35 operates to the decreasing side, thereby decreasing the discharge volume of the hydraulic pump 19.

[0091] (Operation status of hydraulic pump discharge volume by operation valve and pump operation unit) (Part 2) As shown in Figures 3 and 4, when the lift control valve 25 is operated to the raised position 25a and the lift cylinder 16 is extended, and the pressure (operating pressure) of the pilot hydraulic oil of the control valve unit 20 increases, the pilot hydraulic oil of the control valve unit 20 is supplied from portion 37b of the sensing oil passage 37 to portion 37a through the notch portion 45 of the operating valve 30 (spool 38).

[0092] As shown in Figures 2, 3, and 4, pilot hydraulic oil from the control valve unit 20 is supplied to the pressure-receiving portion of the first position 61a of the first pump operating valve 61 via oil passages 54 and 58, causing the first pump operating valve 61 to be operated to the first position 61a and the second pump operating valve 62 to be operated to the first position 62a.

[0093] The hydraulic oil in the operating cylinder 35 is discharged to the transmission case 6 through the oil passage 60, the second pump operating valve 62 (first position 62a), the oil passage 59, the first pump operating valve 61 (first position 61a), and the oil passages 63 and 64, and the operating cylinder 35 is actuated to the increasing side by the spring 55, thereby increasing the discharge volume of the hydraulic pump 19.

[0094] As described above, as the pressure (operating pressure) of the pilot hydraulic oil (portion 37b of the sensing oil passage 37) of the control valve unit 20 increases, as shown in FIG. 5, the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) moves the spool 38 to the left in FIG. 5 against the biasing force of the spring 43, and the operating valve 30 (spool 38) is operated to the closed position 30b.

[0095] Even when the operating valve 30 (spool 38) is operated to the closed position 30b, the groove portion 46 of the operating valve 30 (spool 38), the connecting passages 47, 48, and the check valve 44 allow the pilot operating oil of the control valve unit 20 to be supplied to the pressure-receiving portion of the first position 61a of the first pump operating valve 61.

[0096] (Operation status of hydraulic pump discharge volume by operation valve and pump operation unit) (Part 3) As shown in FIGS. 2, 3, and 5, it is assumed that the pressure (operating pressure) of the pilot hydraulic oil in the control valve unit 20 drops slightly when the rise control valve 25 is operated to the rise position 25a.

[0097] Even if the pilot hydraulic oil in the pressure-receiving section of the first pump operating valve 61 at the first position 61a attempts to return toward the rise control valve 25 through the sensing oil passage 37 due to a slight drop in the pressure (operating pressure) of the pilot hydraulic oil in the control valve unit 20, the pilot hydraulic oil is stopped by the closed position 30b of the operating valve 30 (spool 38). As a result, the first pump operating valve 61 is maintained at the first position 61a, the second pump operating valve 62 is maintained at the first position 62a, and the discharge rate of the hydraulic pump 19 is maintained on the increasing side.

[0098] With the above configuration, when the load on the lift cylinder 16 frequently changes between high and low, even if the pilot hydraulic oil in the pressure-receiving section at the first position 61a of the first pump operating valve 61 attempts to return toward the rise control valve 25 through the sensing oil passage 37, it is stopped by the closed position 30b of the operating valve 30 (spool 38). This reduces the frequency with which the pump operating section 36 increases or decreases the discharge volume of the hydraulic pump 19, preventing a hunting condition.

[0099] When the pressure (operating pressure) of the pilot hydraulic oil of the control valve unit 20 further increases, the pilot hydraulic oil of the control valve unit 20 is supplied to the pressure-receiving portion of the first position 61a of the first pump operating valve 61 via the groove portion 46 of the operating valve 30 (spool 38), the connecting passages 47, 48, and the check valve 44, and the discharge volume of the hydraulic pump 19 is further increased.

[0100] (Operation status of hydraulic pump discharge volume by operation valve and pump operation unit) (Part 4) Assume that the lift control valve 25 is operated to the lift position 25a, and then the lift control valve 25 is operated to the neutral position 25b to stop the lift cylinder 16.

[0101] As shown in Figures 2, 3, and 5, when the lift control valve 25 is operated to the neutral position 25b and the lift cylinder 16 stops, the pressure (operating pressure) of the pilot hydraulic oil (portion 37b of the sensing oil passage 37) of the control valve unit 20 quickly decreases.

[0102] As the pressure (operating pressure) of the pilot hydraulic oil (portion 37b of the sensing oil passage 37) of the control valve unit 20 decreases, the pressure (operating pressure) of the pilot hydraulic oil received by the wall portion 39c of the spool 38 (first portion 39) decreases, and the spool 38 moves to the right in Figure 5 due to the biasing force of the spring 43, and the operating valve 30 (spool 38) is operated to the open position 30a as shown in Figure 4, thereby connecting the portions 37a and 37b of the sensing oil passage 37.

[0103] As a result, as shown in Figures 2, 3, and 4, the pilot hydraulic oil in the pressure-receiving section of the first position 61a of the first pump operating valve 61 passes through the sensing oil passage 37 and the operating valve 30 (open position 30a) and quickly returns toward the rise control valve 25.

[0104] The hydraulic oil in the oil passage 57 quickly operates the first pump operating valve 61 to the second position 61b, and the second pump operating valve 62 to the second position 62b. The hydraulic oil in the oil passage 57 is supplied to the operating cylinder 35 via the second position 61b of the first pump operating valve 61, the oil passage 59, the second position 62b of the second pump operating valve 62, and the oil passage 60, and the operating cylinder 35 operates to the decreasing side, and the discharge volume of the hydraulic pump 19 is quickly operated to the decreasing side.

[0105] With the above configuration, when the rise control valve 25 is operated to the neutral position 25b, the time during which the discharge volume of the hydraulic pump 19 is maintained on the increasing side can be shortened, thereby saving the driving power of the hydraulic pump 19.

[0106] (First Alternative Embodiment of the Invention) 2 to 5, one operating valve 30 is provided for one control valve unit 20 (rise control valve 25), and the hydraulic units 21 and 22 are also provided with operating valves 30. In contrast to this, the operating valve 30 may be eliminated from multiple sets of hydraulic actuators and control valves, and the pilot operating oil with the highest pressure may be extracted from the pilot operating oil of each set of hydraulic actuators and control valves by a high-pressure selection valve 53 or the like, and the extracted pilot operating oil with the highest pressure may be supplied to one operating valve 30, and then supplied from the operating valve 30 to the pump operating unit 36.

[0107] (Second Alternative Embodiment of the Invention) In the operating valve 30 (spool 38), the check valve 44 and the communication passages 47, 48 may be eliminated.

[0108] In this configuration, by setting the biasing force of the spring 43 slightly stronger, when the rise control valve 25 is operated to the rise position 25a, as shown in Figures 2, 3, and 4, the pilot hydraulic oil of the control valve unit 20 is sufficiently supplied to the pressure-receiving portion of the first position 61a of the first pump operating valve 61 via the sensing oil passage 37 and the operating valve 30 (open position 30a), so that the operating valve 30 is maintained in the open position 30a for a short time.

[0109] (Third Alternative Embodiment of the Invention) Instead of the lift cylinder 16, a hydraulic motor (not shown) that drives the working device may be provided as a hydraulic actuator. [Industrial Applicability]

[0110] The present invention can be applied not only to hydraulic systems for tractors, but also to hydraulic systems for other agricultural work vehicles such as combine harvesters, hydraulic systems for construction work vehicles and transport work vehicles such as backhoes and wheel loaders, and hydraulic systems installed in devices other than work vehicles (for example, lifting devices installed in factories or work sites). [Explanation of symbols]

[0111] 16 Lift cylinder (hydraulic actuator) 19 Hydraulic pump 25 Rise control valve (control valve) 26 Downward control valve (control valve) 30 Control valve 30a open position 30b Closed position 36 Pump operation unit 37 Sensing oil passage 37a part 37b part 38 spools 39a 1st Land Section 39b 2nd Land Section 39c Wall part (pressure receiving part) 41 1st interior space 42 Second interior space 42a Wall (stopper) 43 Spring (biasing part) 44 Check valve 45 Notch 46 Groove (communication path) 47 Communication path 48 Communication path 51 Port 1 52 Second Port

Claims

1. A variable displacement hydraulic pump; a control valve for controlling the supply state of hydraulic oil from the hydraulic pump to the hydraulic actuator; a sensing oil passage that branches off pilot hydraulic oil from the hydraulic oil supplied from the control valve to the hydraulic actuator; a pump operation unit that increases the discharge rate of the hydraulic pump when the pressure of the pilot hydraulic oil in the sensing oil passage increases, and decreases the discharge rate of the hydraulic pump when the pressure of the pilot hydraulic oil in the sensing oil passage decreases; an operating valve provided in the sensing oil passage, The operating valve is The sensing oil passage is switchable between an open state in which the sensing oil passage is connected and a closed state in which the flow of pilot hydraulic oil in the sensing oil passage toward the control valve is blocked, A hydraulic system in which the open state is maintained when the operating pressure, which is the pressure of the pilot hydraulic oil in the portion of the sensing oil passage between the operating valve and the control valve, becomes less than a set pressure, and the system is switched to the closed state when the operating pressure becomes equal to or greater than the set pressure.

2. 2. The hydraulic system according to claim 1, wherein in the closed state, the flow of pilot hydraulic oil toward the control valve is blocked and the flow of pilot hydraulic oil toward the pump operating unit is permitted.

3. The operating valve is a spool movable between an open position in which the open state is achieved and a closed position in which the closed state is achieved; a biasing portion that biases the spool to the open position; a pressure receiving portion that receives the operating pressure, 3. The hydraulic system according to claim 1, wherein when the operating pressure acting on the pressure-receiving portion becomes less than the set pressure, the spool is held in the open position by the biasing force of the biasing portion, and when the operating pressure acting on the pressure-receiving portion becomes equal to or greater than the set pressure, the spool is operated to the closed position against the biasing force of the biasing portion.

4. The operating valve is a first interior space; a second internal space connected to the first internal space; a first port that communicates a portion of the sensing oil passage on the pump operation unit side with the first internal space; a second port that communicates a portion of the sensing oil passage on the control valve side with the second internal space; the spool is provided with a first land portion disposed on the opposite side of the second port with respect to the first port, a second land portion disposed on the second port side with respect to the first port, and a notch portion formed at an end of an outer periphery of the second land portion on the first land portion side, and is movably supported in the first internal space; a communication passage provided in the spool separately from the second land portion and the notch portion so as to communicate between the first port and the second port; a check valve that blocks the flow of pilot hydraulic oil from the first port toward the second port in the communication passage and allows the flow of pilot hydraulic oil from the second port toward the first port in the communication passage, a portion of the second land portion facing the second internal space is the pressure-receiving portion, when the operating pressure acting on the pressure-receiving portion becomes less than the set pressure, the spool is moved by the biasing force of the biasing portion to the open position in which the first port and the second port communicate with each other via the notch portion while the first land portion and the second land portion are supported in the first internal space, 4. The hydraulic system according to claim 3, wherein, when the operating pressure acting on the pressure-receiving portion becomes equal to or greater than the set pressure, the spool moves against the biasing force of the biasing portion to the closed position in which communication between the first port and the second port via the notch portion is blocked by the second land portion, while the first land portion and the second land portion are supported in the first internal space.

5. 5. The hydraulic system according to claim 4, further comprising a stopper portion that stops the spool at a position where, when the spool is moved to the open position by the biasing force of the biasing portion, the first port and the second port communicate with each other via the notch portion and the second land portion does not come out of the first internal space.

6. The hydraulic system according to claim 4 , wherein the second internal space has a larger diameter than the first internal space.

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