Work machine

Abstract

Provided is a work machine in which responsiveness at low temperatures can be improved. A work machine (1) comprises: a first discharge port (P1) and a second discharge port (P2) that discharge hydraulic oil; a plurality of first hydraulic actuators (A1) to which hydraulic oil discharged from the first discharge port can be supplied; a plurality of second hydraulic actuators (A2) to which the hydraulic oil discharged from the second discharge port can be supplied; a load pressure selection valve (V15) to which the load pressures of the first hydraulic actuator and the second hydraulic actuator are inputted and which outputs the highest load pressure, which is the higher one of the load pressure of the first hydraulic actuator and the load pressure of the second hydraulic actuator; a regulator (20) to which the highest load pressure outputted from the load pressure selection valve is inputted and which controls the discharge amounts of the first discharge port and the second discharge port in accordance with the inputted highest load pressure; a pipeline throttle (43) provided in a load pressure transmission pipeline (x3) between the regulator and the load pressure selection valve; and a bleed circuit (45) for releasing some of the hydraulic oil in the section pipeline (44) between the load pressure selection valve and the pipeline throttle in the load pressure transmission pipeline to a discharge destination different from the regulator.

Description

Work equipment

[0001] The present invention relates to a work machine such as a backhoe.

[0002] BACKGROUND ART A working machine disclosed in Patent Document 1 is known in the prior art.

[0003] The work machine disclosed in Patent Document 1 has a first discharge port and a second discharge port for discharging hydraulic oil, and is equipped with a load pressure selection valve that receives the load pressures of a plurality of first hydraulic actuators to which the hydraulic oil discharged from the first discharge port can be supplied and the load pressures of a plurality of second hydraulic actuators to which the hydraulic oil discharged from the second discharge port can be supplied, and outputs a maximum load pressure which is the higher of the load pressures of the first hydraulic actuators and the second hydraulic actuators.

[0004] The maximum load pressure output from the load pressure selection valve is input to a regulator, which controls the discharge rates of the first and second discharge ports according to the input maximum load pressure. A throttle is provided in the line between the load pressure selection valve and the regulator, and the load pressure output from the load pressure selection valve is transmitted to the regulator via the throttle.

[0005] Japanese Patent Publication "Patent No. 5480847"

[0006] In the above-described work machine, the load pressures of the first hydraulic actuator and the second hydraulic actuator are input to the load pressure selection valve, and the higher load pressure, which is the maximum load pressure, is output from the load pressure selection valve and enters the regulator via the throttle. Therefore, when the viscosity of the hydraulic oil increases at low temperatures, there is a problem in that the response is delayed due to the resistance in the load pressure selection valve and the throttle.

[0007] In view of the above problems, the present invention has an object to improve responsiveness at low temperatures in a work machine which is provided with a first discharge port and a second discharge port for discharging hydraulic oil, a load pressure selection valve which outputs a maximum load pressure which is the higher of the load pressures of a plurality of first hydraulic actuators to which the hydraulic oil discharged from the first discharge port can be supplied and a plurality of second hydraulic actuators to which the hydraulic oil discharged from the second discharge port can be supplied, a regulator which controls the discharge amount of the first discharge port and the second discharge port in accordance with the maximum load pressure, and a pipe restriction provided in the load pressure transmission pipe between the regulator and the load pressure selection valve.

[0008] a load pressure selection valve that receives the load pressures of the first hydraulic actuators and the second hydraulic actuators and outputs a maximum load pressure that is the higher of the load pressures of the first hydraulic actuators and the second hydraulic actuators; a regulator that receives the maximum load pressure output from the load pressure selection valve and controls the discharge amount of the first discharge port and the second discharge port in accordance with the input maximum load pressure; a line restriction provided in a load pressure transmission line between the regulator and the load pressure selection valve; and a bleed circuit that releases a portion of the hydraulic oil in a section of the load pressure transmission line between the load pressure selection valve and the line restriction to a discharge destination other than the regulator.

[0009] The work machine may be provided with a hydraulic oil tank that stores the hydraulic oil, and the bleed circuit may have a bleed pipe line having one end connected to the section pipe line and the other end communicating with the hydraulic oil tank, and a bleed restrictor provided in the bleed pipe line.

[0010] One end of the bleed pipe may be connected to the section pipe near the pipe restriction.

[0011] The work machine may include a hydraulic oil tank that stores the hydraulic oil, a first line connected to one input port of the load pressure selection valve, a second line connected to the other input port of the load pressure selection valve, a plurality of first load transmission oil lines that are provided for each of the plurality of first hydraulic actuators and transmit loads of the corresponding first hydraulic actuators, the plurality of first load transmission oil lines connected to the first lines, a plurality of second load transmission oil lines that are provided for each of the plurality of second hydraulic actuators and transmit loads of the corresponding second hydraulic actuators, the plurality of second load transmission oil lines connected to the second lines, a first relief circuit that is located upstream of the load pressure selection valve and releases a portion of the hydraulic oil in the first line to the hydraulic oil tank, and a second relief circuit that is located upstream of the load pressure selection valve and releases a portion of the hydraulic oil in the second line to the hydraulic oil tank.

[0012] The work machine includes a plurality of first control valves provided corresponding to the plurality of first hydraulic actuators and controlling the flow of hydraulic oil to the first hydraulic actuators, a plurality of second control valves provided corresponding to the plurality of second hydraulic actuators and controlling the flow of hydraulic oil to the second hydraulic actuators, and a control valve incorporating the plurality of first control valves, the plurality of second control valves, the load pressure selection valve, and the pipeline restriction, and the pipeline between the control valve and the regulator in the load pressure transmission pipeline may be constituted by a hydraulic hose.

[0013] The bleed restriction may be attached directly or indirectly to the control valve.

[0014] The bleed pipe may be incorporated in the control valve, one end of which is connected to the section pipe, and the other end of which is connected to the hydraulic oil tank via a drain pipe provided within the control valve.

[0015] According to the above-described work machine, a flow of hydraulic oil is generated in the section of the pipe between the load pressure selection valve and the pipe restriction by using a bleed circuit to release a portion of the hydraulic oil to a discharge destination other than the regulator, thereby improving the warm-up performance of the pipe restriction. Furthermore, a flow of hydraulic oil is also generated in the load pressure selection valve by using a bleed circuit to release a portion of the hydraulic oil to a discharge destination other than the regulator, thereby improving the warm-up performance of the load pressure selection valve. These features improve responsiveness at low temperatures.

[0016] It is an overall side view of a backhoe. It is a schematic configuration diagram of a hydraulic system. It is a schematic hydraulic circuit diagram of the hydraulic system. It is a hydraulic circuit diagram of an inlet block portion. It is a hydraulic circuit diagram related to a right travel control valve, a first dozer control valve, a swing control valve, an arm control valve, a swing control valve, and a first SP control valve. It is a hydraulic circuit diagram related to a left travel control valve, a second dozer control valve, a boom control valve, a bucket control valve, and a second SP control valve. It is a hydraulic circuit diagram of a travel unit.

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate.

[0018] 1 is a schematic side view showing the overall configuration of a work machine 1 according to this embodiment. In this embodiment, the work machine 1 is exemplified by a backhoe, which is a rotating work machine.

[0019] The backhoe 1 is mainly composed of a lower running body 2 and an upper rotating body 3 mounted on the running body 2 so as to be rotatable (fully rotatable) around a rotation axis extending in the vertical direction.

[0020] The running body 2 is equipped with a crawler-type running device 5 on both the left and right sides of a track frame 6, which is configured to circulate an endless belt-shaped crawler belt 4 in a circumferential direction using running motors ML and MR consisting of hydraulic motors (hydraulic actuators).

[0021] A dozer device 7 is provided at the front of the truck frame 6. The dozer device 7 has a blade 9 at the front end of a support arm 8 whose rear end is pivotally connected to the truck frame 6 and which is swingable up and down. The support arm 8 is driven to move up and down by the extension and contraction of a dozer cylinder C1 which is a hydraulic cylinder (hydraulic actuator).

[0022] The rotating body 3 comprises a rotating base 10 mounted on the track frame 6 so as to be rotatable about the rotation axis, a front working device 11 provided at the front of the rotating base 10, and a cabin 12 mounted on the rotating base 10.

[0023] The swivel base 10 is provided with an engine E, a radiator, a fuel tank, a hydraulic oil tank T (see FIG. 2, etc.), a battery, etc. The hydraulic oil tank T is a tank for storing hydraulic oil. The swivel base 10 is driven to rotate by a rotation motor MT consisting of a hydraulic motor (hydraulic actuator).

[0024] A support bracket 13 is provided at the front of the swivel base 10 so as to protrude forward from the swivel base 10. A swing bracket 14 is supported on the support bracket 13 so as to be swingable left and right about an axis extending in the vertical direction. The swing bracket 14 is driven to swing left and right by a swing cylinder C2, which is a hydraulic cylinder (hydraulic actuator).

[0025] The front working mechanism 11 is mainly composed of a boom 15 whose base side is pivotally connected to the upper part of the swing bracket 14 so as to be rotatable around an axis extending in the width direction of the machine body and so as to be swingable up and down, an arm 16 which is pivotally connected to the tip end of the boom 15 so as to be rotatable around an axis extending in the width direction of the machine body and so as to be swingable, and a bucket 17 (work implement) which is pivotally connected to the tip end of the arm 16 so as to be rotatable around an axis extending in the width direction of the machine body and so as to be swingable.

[0026] The boom 15 is driven to swing by a boom cylinder C3 interposed between the boom 15 and the swing bracket 14, the arm 16 is driven to swing by an arm cylinder C4 interposed between the arm 16 and the boom 15, and the bucket 17 is driven to swing by a bucket cylinder C5 (work tool cylinder) interposed between the bucket 17 and the arm 16.

[0027] The boom cylinder C3, arm cylinder C4, and bucket cylinder C5 are configured by hydraulic cylinders (hydraulic actuators).

[0028] Furthermore, in the backhoe 1 of this embodiment, one or more other working tools (hydraulic attachments) that can be driven by a hydraulic actuator can be attached instead of or in addition to the bucket 17. Examples of other working tools include a hydraulic breaker, a hydraulic crusher, an angle broom, an earth auger, a pallet fork, a sweeper, a mower, and a snow blower.

[0029] In this embodiment, as shown in FIGS. 2, 5 and 6, up to two hydraulic actuators (hydraulic actuator C6 and hydraulic actuator C7) equipped on the hydraulic attachment can be controlled (operated).

[0030] Next, a hydraulic system for operating the various hydraulic actuators ML, MR, MT, and C1 to C7 equipped on the backhoe 1 will be described with reference to FIGS.

[0031] 2, the hydraulic system of the backhoe 1 includes a control valve CV that controls the various hydraulic actuators ML, MR, MT, and C1 to C7, a main pump 18 that supplies hydraulic oil to operate the various hydraulic actuators ML, MR, MT, and C1 to C7, and a sub-pump 19 that supplies signal pressure oil such as pilot pressure and detection signals. The main pump 18 and the sub-pump 19 are driven by an engine (prime mover) E mounted on the swivel base 10. Note that an electric motor may be provided instead of the engine E.

[0032] The main pump 18 is a swash plate type variable displacement axial pump that functions as an equal flow rate double pump, sucking hydraulic oil from a hydraulic oil tank T and discharging equal amounts of hydraulic oil (pressurized oil) from two independent discharge ports P1, P2. More specifically, the main pump 18 is a split flow hydraulic pump that has a mechanism for alternately discharging hydraulic oil (pressurized oil) from one piston-cylinder barrel kit to discharge grooves formed inside and outside the valve plate.

[0033] One discharge port P1 from which hydraulic oil is discharged from the main pump 18 is referred to as a first discharge port P1, and the other discharge port P2 is referred to as a second discharge port P2.

[0034] The hydraulic system also includes a regulator 20 that controls the tilt angle of the swash plate of the main pump 18 .

[0035] The main pump 18 may be configured with two swash plate type variable displacement hydraulic pumps. More specifically, the main pump 18 may be configured with one swash plate type variable displacement hydraulic pump having one discharge port (first discharge port P1) and one swash plate type variable displacement hydraulic pump having one discharge port (second discharge port P2).

[0036] The sub-pump 19 is configured by a fixed displacement gear pump that discharges hydraulic oil drawn from a hydraulic oil tank T. The port that discharges hydraulic oil (pressurized oil) from the sub-pump 19 is called a third discharge port P3.

[0037] As shown in FIG. 2, the control valve CV is composed of control valves V1 to V11 that control various hydraulic actuators ML, MR, MT, and C1 to C7, and an inlet block B for taking in pressure oil, which are arranged in one direction.

[0038] In this embodiment, the control valve CV comprises a first SP control valve V1 that controls the hydraulic actuator C6, a swing control valve V2 that controls the swing cylinder C2, an arm control valve V3 that controls the arm cylinder C4, a swing control valve V4 that controls the swing motor MT, a first dozer control valve V5 that controls the dozer cylinder C1, a right-side travel control valve V6 that controls the travel motor MR of the right-side traveling unit 5, an inlet block B for taking in pressure oil, a left-side travel control valve V7 that controls the travel motor ML of the left-side traveling unit 5, a second dozer control valve V8 that controls the dozer cylinder C1, a boom control valve V9 that controls the boom cylinder C3, a bucket control valve V10 that controls the bucket cylinder C5, and a second SP control valve V11 that controls the hydraulic actuator C7, which are arranged in this order (arranged in this order from right to left in FIG. 2 ) and connected to each other.

[0039] In this embodiment, the hydraulic actuator C6, swing cylinder C2, arm cylinder C4, swing motor MT, dozer cylinder C1, and travel motor MR are a plurality of first hydraulic actuators A1 to which hydraulic oil discharged from the first discharge port P1 can be supplied. Also, the travel motor ML, dozer cylinder C1, boom cylinder C3, bucket cylinder C5, and hydraulic actuator C7 are a plurality of second hydraulic actuators A2 to which hydraulic oil discharged from the second discharge port P2 can be supplied.

[0040] In this embodiment, the dozer cylinder C1 belongs to the first hydraulic actuator A1 and the second hydraulic actuator A2, but when it is controlled only by the first dozer control valve V5, it is the first hydraulic actuator A1, and when it is controlled only by the second dozer control valve V8, it is the second hydraulic actuator A2.

[0041] The first SP control valve V1, swing control valve V2, arm control valve V3, swing control valve V4, first dozer control valve V5, and right-side travel control valve V6 constitute the first control valve VA1 that controls the flow of hydraulic oil to the first hydraulic actuator A1. The left-side travel control valve V7, second dozer control valve V8, boom control valve V9, bucket control valve V10, and second SP control valve V11 constitute the second control valve VA2 that controls the flow of hydraulic oil to the second hydraulic actuator A2.

[0042] Therefore, each first control valve VA1 is provided corresponding to each first hydraulic actuator A1, and each second control valve VA2 is provided corresponding to each second hydraulic actuator A2.

[0043] As shown in FIGS. 3 to 7, each of the control valves V1 to V11 is configured by incorporating a directional control valve DV1 to DV11 and a pressure compensation valve V12 in a valve body.

[0044] The directional control valves DV1 to DV11 switch the direction of pressure oil to the hydraulic actuators ML, MR, MT, and C1 to C7 that are to be controlled, and the pressure compensation valve V12 is arranged on the downstream side of the pressure oil supply to the directional control valves DV1 to DV11 and on the upstream side of the pressure oil supply to the hydraulic actuators ML, MR, MT, and C1 to C7 that are to be controlled.

[0045] The directional control valves DV1 to DV11 of the control valves V1 to V11 are configured as direct acting spool type changeover valves and are configured as pilot operated changeover valves that are changed over by pilot pressure.

[0046] Furthermore, the directional control valves DV1 to DV11 of each control valve V1 to V11 are configured so that a spool is moved in proportion to the amount of operation of each operating means that operates each directional control valve DV1 to DV11, and an amount of pressurized oil proportional to the amount the spool is moved is supplied to the hydraulic actuators ML, MR, MT, C1 to C7 that are the control targets (the operating speed of the hydraulic actuators ML, MR, MT, C1 to C7 that are the control targets can be changed in proportion to the amount of operation of each operating means).

[0047] The directional control valve DV5 of the first dozer control valve V5 and the directional control valve DV8 of the second dozer control valve V8 are simultaneously operated by a single operating means such as a dozer lever for operating the dozer device 7.

[0048] The inlet block B incorporates a travel independent valve V13, a PPS signal shuttle valve V14, a PLS signal shuttle valve (also called a load pressure selection valve) V15, a travel bypass valve V16, a relief valve V17, a first unloading valve V18, a second unloading valve V19, a first relief circuit 41, a second relief circuit 42, and a pipe restriction 43.

[0049] A first discharge passage a is connected to a first discharge port P1 of the main pump 18. A second discharge passage b is connected to a second discharge port P2 of the main pump 18. Both the first discharge passage a and the second discharge passage b are drawn into the inlet block B.

[0050] As shown in FIG. 5, the first discharge passage a runs from the inlet block B through the valve body of the right-side travel control valve V6 → the valve body of the first dozer control valve V5 → the valve body of the swing control valve V4 → the valve body of the arm control valve V3 → the valve body of the swing control valve V2 to the valve body of the first SP control valve V1, and is closed at the end of the passage.

[0051] Hydraulic oil (pressurized oil) can be supplied from this first discharge passage a to each of the directional control valves DV6, DV5, DV4, DV3, DV2, and DV1 of the right-hand travel control valve V6, the first dozer control valve V5, the swing control valve V4, the arm control valve V3, the swing control valve V2, and the first SP control valve V1 via pressure oil branch passages f.

[0052] As shown in FIG. 6, the second discharge passage b runs from the inlet block B through the valve body of the left travel control valve V7 → the valve body of the second dozer control valve V8 → the valve body of the boom control valve V9 → the valve body of the bucket control valve V10 to the valve body of the second SP control valve V11, and is closed at the end of the passage.

[0053] Hydraulic oil (pressurized oil) can be supplied from this second discharge passage b to each of the directional control valves DV7, DV8, DV9, DV10, and DV11 of the left-side travel control valve V7, the second dozer control valve V8, the boom control valve V9, the bucket control valve V10, and the second SP control valve V11 via pressure oil branch passages h.

[0054] A drain oil passage g for returning hydraulic oil (pressurized oil) to the hydraulic oil tank T is provided from the valve body of the first SP control valve V1 through the inlet block B to the valve body of the second control valve V11.

[0055] As shown in FIG. 3, the first discharge passage a and the second discharge passage b are connected to each other within the inlet block B via a communication passage j that crosses the travel independent valve V13.

[0056] The travel independent valve V13 is a direct acting spool type switching valve that is switched by pilot pressure. The travel independent valve V13 is switchable between a confluence position 22 that allows the flow of pressure oil through the communication passage j and an independent supply position 23 that blocks the flow of pressure oil through the communication passage j, and is biased by a spring in the direction of switching to the confluence position 22.

[0057] Therefore, when the traveling independent valve V13 is switched to the confluence position 22, the oil discharged from the first discharge port P1 and the oil discharged from the second discharge port P2 are merged, and the merged oil discharged can be supplied to the directional control valves DV1 to DV11 of each control valve V1 to V11.

[0058] Furthermore, when the independent travel valve V13 is switched to the independent supply position 23, the oil discharged from the first discharge port P1 can be supplied to the directional control valves DV6, DV5 of the right-side travel control valve V6 and the first dozer control valve V5, and the pressurized oil from the second discharge port P2 can be supplied to the directional control valves DV7, DV8 of the left-side travel control valve V7 and the second dozer control valve V8.

[0059] 3, a third discharge passage m is connected to the third discharge port P3, and the flow path start ends of the first detection oil passage r1 and the second detection oil passage r2 are connected to this third discharge passage m.

[0060] The first detection oil passage r1 is connected to the drain oil passage g from the third discharge passage m via the directional control valve DV8 of the second dozer control valve V8 → the directional control valve DV7 of the left-hand travel control valve V7 → the directional control valve DV6 of the right-hand travel control valve V6 → the directional control valve DV5 of the first dozer control valve V5.

[0061] The first detection oil passage r1 is connected to a first signal oil passage n1 upstream of the directional control valve DV8 of the second dozer control valve V8, and the first signal oil passage n1 has a terminal connected to one pressure receiving portion 24 of the travel independent valve V13.

[0062] The second detection oil passage r2 is connected from the third discharge passage m to the drain oil passage g via the directional control valve DV11 of the second SP control valve V11 → the directional control valve DV10 of the bucket control valve V10 → the directional control valve DV9 of the boom control valve V9 → the directional control valve DV4 of the swing control valve V4 → the directional control valve DV3 of the arm control valve V3 → the directional control valve DV2 of the swing control valve V2 → the directional control valve DV1 of the second SP control valve V1.

[0063] The second detection oil passage r2 is connected to a flow path starting end of a second signal oil passage n2 upstream of the directional control valve DV11 of the second SP control valve V11, and the flow path terminal end of the second signal oil passage n2 is connected to the other pressure receiving portion 25 of the travel independent valve V13.

[0064] The travel independent valve V13 is held at the joining position 22 by the force of a spring when the directional control valves DV1 to DV11 of the control valves V1 to V11 are in the neutral position.

[0065] When any of the directional control valves DV6, DV7, DV5, DV8 of the right-side travel control valve V6, the left-side travel control valve V7, the first dozer control valve V5, and the second dozer control valve V8 is operated from the neutral position, pressure is generated in the first detection oil passage r1, and the independent travel valve V13 is switched from the confluence position 22 to the independent supply position 23.

[0066] Therefore, when only traveling, when only the dozer device 7 is driven, or when the dozer device 7 is used while traveling without driving the front working device 11, the swivel base 10, the swing bracket 14, the first SP control valve V1, and the second SP control valve V11, the traveling independent valve V13 is set to the independent supply position 23.

[0067] At this time, when any of the second SP control valve V11, bucket control valve V10, boom control valve V9, slewing control valve V4, arm control valve V3, swing control valve V2, and directional control valves DV11, DV10, DV9, DV4, DV3, DV2, and DV1 of the first SP control valve V1 is operated from the neutral position, pressure is generated in the second detection oil line r2, and the traveling independent valve V13 is switched from the independent supply position 23 to the confluence position 22.

[0068] Therefore, when at least one of the left and right traveling devices 5 and the dozer device 7 is operated in combination with at least one of the boom 15, the arm 16, the bucket 17, the swivel base 10, the swing bracket 14, and the hydraulic attachment, the traveling independent valve V13 is set to the confluence position 22.

[0069] Furthermore, when the directional control valves DV1 to DV11 of each control valve V1 to V11 are in neutral, and any of the second SP control valve V11, bucket control valve V10, boom control valve V9, slewing control valve V4, arm control valve V3, swing control valve V2, and directional control valves DV11, DV10, DV9, DV4, DV3, DV2, and DV1 of the first SP control valve V1 is operated from the neutral position, the traveling independent valve V13 remains in the confluence position 22.

[0070] This hydraulic system is also equipped with an auto-idling control system (AI system) that automatically operates the accelerator device of the engine E.

[0071] This AI system includes a pressure switch 129 connected to the first signal oil line n1 (first detection oil line r1) and the second signal oil line n2 (second detection oil line r2) via sensing oil lines s1, s2 and a shuttle valve V22, an electric actuator that controls the governor of engine E, and a control device that controls this electric actuator, and the pressure switch 129 is connected to the control device.

[0072] In this AI system, when the directional control valves DV1 to DV11 of the control valves V1 to V11 are in neutral, no pressure is generated in the first signal oil line n1 and the second signal oil line n2, so the pressure switch 129 does not operate in response to pressure. In this state, the governor is automatically controlled by an electric actuator or the like to throttle down to a preset idling position.

[0073] Furthermore, when any one of the directional control valves DV1 to DV11 of the control valves V1 to V11 is operated, pressure is generated in the first signal oil line n1 or the second signal oil line n2, and this pressure is detected by the pressure switch 129, which then operates in a pressure-sensitive manner. Then, a command signal is sent from the control device to an electric actuator or the like, which automatically controls the governor to increase the accelerator to the set accelerator position.

[0074] In this embodiment, the relief valve V17 of the system is common to the first discharge passage a and the second discharge passage b.

[0075] That is, the starting end of the first relief oil passage d1 is connected to the first discharge passage a, and the starting end of the second relief oil passage d2 is connected to the second discharge passage b, and the ends of these first and second relief oil passages d1, d2 are connected to each other, and a drain oil passage e communicating with the tank T is connected to the ends of the first and second relief oil passages d1, d2, and a relief valve V17 is interposed in the drain oil passage e.

[0076] Further, a check valve V23 is provided in each of the relief oil passages d1 and d2.

[0077] It is also possible to provide separate relief valves for the first discharge passage a and the second discharge passage b.

[0078] This hydraulic system employs a load sensing system.

[0079] The load sensing system of this embodiment includes a pressure compensation valve V12 provided in each control valve V1 to V11, a regulator 20 that controls the swash plate of the main pump 18, the first and second unloading valves V18 and V19, a shuttle valve V14 for PPS signals, and a shuttle valve V15 for PLS signals.

[0080] The load sensing system of this embodiment employs an after-orifice type load sensing system in which the pressure compensation valve V12 is disposed downstream of the pressure oil supply to the directional control valves DV1 to DV11.

[0081] In this load sensing system, when multiple hydraulic actuators ML, MR, MT, C1 to C7 equipped on the backhoe 1 are operated simultaneously, the pressure compensation valve V12 functions to adjust the load between the hydraulic actuators ML, MR, MT, C1 to C7, and generates a pressure loss in the control valves V1 to V11 on the low load pressure side equal to the differential pressure with respect to the maximum load pressure, making it possible to flow (distribute) a flow rate according to the amount of operation of the spools of the directional control valves DV1 to DV11, regardless of the magnitude of the load.

[0082] In addition, the load sensing system controls the discharge volume of the main pump 18 (first discharge port P1 and second discharge port P2) according to the load pressure of each hydraulic actuator ML, MR, MT, C1 to C7 equipped on the backhoe 1, and discharges the hydraulic power required for the load from the main pump 18, thereby saving power and improving operability.

[0083] In other words, the load pressures of the first hydraulic actuator A1 and the second hydraulic actuator A2 are input to the load pressure selection valve (PLS signal shuttle valve) V15, and the load pressure selection valve V15 outputs a maximum load pressure, which is the higher of the load pressure of the first hydraulic actuator A1 and the load pressure of the second hydraulic actuator A2. The maximum load pressure output from the load pressure selection valve V15 is input to the regulator 20, and the regulator 20 controls the discharge amount of the first discharge port P1 and the second discharge port P2 in accordance with the input load pressure.

[0084] The load sensing system of this embodiment will now be described in more detail.

[0085] The load sensing system has a PPS signal transmission circuit that transmits the discharge pressure of the main pump 18 to the regulator 20 as a PPS signal pressure, and a PLS signal transmission circuit (load signal transmission circuit) that transmits the highest load pressure among the load pressures of each of the operated control valves V1 to V11 to the regulator 20 as a PLS signal pressure (load signal pressure).

[0086] The PPS signal transmission circuit has a PPS signal shuttle valve V14, one input port 26 of which is connected to the first discharge passage a via a first PPS input oil passage k1, the other input port 27 of which is connected to the second discharge passage b via a second PPS input oil passage k2, and the output port 28 of which is connected to the regulator 20 via a PPS output oil passage k3.

[0087] Therefore, when the traveling independent valve V13 is at the confluence position 22, the first discharge path a and the second discharge path b of the main pump 18 are at the same pressure, and the discharge pressure of the main pump 18 is sent to the regulator 20 from the input ports 26, 27 on the open side of the PPS signal shuttle valve V14.

[0088] Furthermore, when the travel independent valve V13 is in the independent supply position 23, the higher of the pressures in the first discharge line a and the second discharge line b is sent to the regulator 20 via the PPS signal shuttle valve V14, or when the pressures in the first discharge line a and the second discharge line b are the same, the discharge pressure of the main pump 18 is sent to the regulator 20 from the input ports 26, 27 on the open side of the PPS signal shuttle valve V14.

[0089] The PLS signal transmission circuit has a PLS signal transmission oil passage w that transmits the load pressure of each of the control valves V1 to V11, and a PLS signal shuttle valve V15.

[0090] 5 and 6, the PLS signal transmission oil passage w extends from the valve body of the first SP control valve V1 to the valve body of the swing control valve V2, the valve body of the arm control valve V3, the valve body of the swing control valve V4, the valve body of the first dozer control valve V5, the valve body of the right-side travel control valve V6, the inlet block B, the valve body of the left-side travel control valve V7, the valve body of the second dozer control valve V8, the valve body of the boom control valve V9, the valve body of the bucket control valve V10, and the valve body of the second SP control valve V11. The PLS signal transmission oil passage w is connected to the pressure compensating valve V12 in each of the control valves V1 to V11 via the load transmission oil passage y.

[0091] In addition, the PLS signal transmission oil line w crosses the traveling independent valve V13 within the inlet block B, and when the traveling independent valve V13 is in the independent supply position 23, the PLS signal transmission oil line w is divided into a first line w1 leading from the traveling independent valve V13 to the first SP control valve V1, and a second line w2 leading from the traveling independent valve V13 to the second SP control valve V11, and when the traveling independent valve V13 is in the merging position 22, the first line w1 and the second line w2 are connected.

[0092] The first line w1 transmits the load pressure of the first hydraulic actuator A1, and the second line w2 transmits the load pressure of the second hydraulic actuator A2.

[0093] More specifically, the first line w1 is connected to a plurality of first load transmission oil passages y1 that are provided for each of the plurality of first hydraulic actuators A1 (hydraulic actuator C6, swing cylinder C2, arm cylinder C4, swing motor MT, dozer cylinder C1, and travel motor MR) and transmit the loads of the corresponding first hydraulic actuators A1. The second line w2 is connected to a plurality of second load transmission oil passages y2 that are provided for each of the plurality of second hydraulic actuators A2 (travel motor ML, dozer cylinder C1, boom cylinder C3, bucket cylinder C5, and hydraulic actuator C7) and transmit the loads of the corresponding second hydraulic actuators A2.

[0094] 4, one input port 29 of the PLS signal shuttle valve (load pressure selection valve) V15 is connected to the first line w1 via a first PLS input oil passage x1. The other input port 30 of the PLS signal shuttle valve (load pressure selection valve) V15 is connected to the second line w2 via a second PLS input oil passage x2. The output port 31 of the PLS signal shuttle valve V15 is connected to the regulator 20 via a PLS output oil passage x3.

[0095] Therefore, when the traveling independent valve V13 is at the confluence position 22, the highest load pressure of the hydraulic actuators controlled by each of the control valves V1 to V11 of the control valve CV is sent to the regulator 20 from the input ports 29, 30 on the open side of the PLS signal shuttle valve V15.

[0096] Furthermore, when the travel independent valve V13 is in the independent supply position 23, the higher pressure of the first line w1 or the second line w2 (the maximum load pressure, which is the higher of the load pressure of the first hydraulic actuator A1 and the load pressure of the second hydraulic actuator A2) is sent to the regulator 20, or if the pressure of the first line w1 and the pressure of the second line w2 are the same, the pressure is sent to the regulator 20 from the input ports 29, 30 on the open side of the PLS signal shuttle valve V15.

[0097] The PLS output oil line x3 is a load pressure transmission line between the regulator 20 and the load pressure selection valve (PLS signal shuttle valve) V15. The PLS output oil line x3 is also referred to as a load pressure transmission line.

[0098] The PPS signal shuttle valve V14 and the PLS signal shuttle valve V15 constitute a signal selection valve device VE. When the travel independent valve V13 is in the merging position 22, the signal selection valve device VE can transmit the highest load pressure of the hydraulic actuators MR, ML, MR, and C1 to C7 and the discharge pressure of the main pump 18 to the regulator 20. When the travel independent valve V13 is in the independent supply position 23, the signal selection valve device VE can transmit the higher-pressure load pressure of the travel motor MR of the right-side travel unit 5 and the load pressure of the hydraulic motor ML of the left-side travel unit 5, and the higher-pressure discharge pressure of the first discharge port P1 and the second discharge port P2 to the regulator 20.

[0099] The first unloading valve V18 is connected to the first discharge passage a via a first unloading oil passage z1, and the second unloading valve V19 is connected to the second discharge passage b via a second unloading oil passage z2.

[0100] These first and second unloading valves V18, V19 are biased in the closing direction by the biasing force of a spring, and the pressure in the first line w1 acts on the first unloading valve V18 in the closing direction, and the pressure in the second line w2 acts on the second unloading valve V19 in the closing direction.

[0101] 3, 4, and 7, the travel bypass valve V16 is a direct-acting spool-type switching valve that is switched by pilot pressure. The travel bypass valve V16 is disposed in the first bypass oil passage t1 and the second bypass oil passage t2 that connect the first discharge passage a and the second discharge passage b in parallel. In other words, the travel bypass valve V16 is disposed in parallel with the travel independent valve V13 between the first discharge passage a and the second discharge passage b.

[0102] This traveling bypass valve V16 can be freely switched between a blocking position (neutral position) 32 that blocks the flow of pressure oil through the first bypass oil passage t1 and the second bypass oil passage t2, a first switching position 33 that allows the flow of pressure oil through the first bypass oil passage t1 and blocks the flow of pressure oil through the second bypass oil passage t2, and a second switching position 34 that blocks the flow of pressure oil through the first bypass oil passage t1 and allows the flow of pressure oil through the second bypass oil passage t2.

[0103] The first bypass oil passage t1 is provided with a check valve V24 that prevents the flow of pressurized oil from the first discharge passage a to the second discharge passage b, and the second bypass oil passage t2 is provided with a check valve V25 that prevents the flow of pressurized oil from the second discharge passage b to the first discharge passage a.

[0104] In addition, the traveling bypass valve V16 is held in the shut-off position 32 by a spring, and the pilot pressure output from the right-side traveling operation valve V26 that operates the right-side traveling control valve V6 acts in a direction to switch the traveling bypass valve V16 from the shut-off position 32 to the first switching position 33, and the pilot pressure output from the left-side traveling operation valve V27 that operates the left-side traveling control valve V7 acts in a direction to switch the traveling bypass valve V16 from the shut-off position 32 to the second switching position 34.

[0105] When a differential pressure greater than a predetermined pressure occurs between the pilot pressures of the right-side travel control valve V26 and the left-side travel control valve V27, the higher-pressure pilot pressure switches the valve from the shut-off position 32 to the first switching position 33 or the second switching position 34.

[0106] The right-side travel operation valve V26 and the left-side travel operation valve V27 are operated by travel levers 36R and 36L, respectively, and pressure oil is supplied from the sub-pump 19 to each of the travel operation valves V26 and V27.

[0107] By tilting the travel levers 36R, 36L forward or backward, the pilot pressure of the command oil line q from the travel operation valves V26, V27 acts on one pressure receiving portion 37a of the directional control valves DV6, DV7 of the travel control valves V6, V7, switching the directional control valves DV6, DV7 from the neutral position to one of the switching positions, and pressure oil is supplied to the travel motors ML, MR from one of a pair of pressure oil supply lines u and discharged via the other pressure oil supply line u. Furthermore, by tilting the travel levers 36R, 36L forward or backward, the pilot pressure from the travel operation valves V26, V27 through the command oil line q acts on the other pressure receiving portion 37b of the directional control valves DV6, DV7 of the travel control valves V6, V7, switching the directional control valves DV6, DV7 from the neutral position to the other switching position, supplying pressure oil to the travel motors ML, MR from the other of the pair of pressure oil supply lines u and draining the oil through one of the pressure oil supply lines u, thereby driving the travel motors ML, MR in forward and reverse directions.

[0108] The pilot pressure of the command oil line q of the right-side travel control valve V26 acts on one pressure receiving portion 38a of the travel bypass valve V16 via the shuttle valve V28 and the first transmission oil line o1, and the pilot pressure of the command oil line q of the left-side travel control valve V27 acts on one pressure receiving portion 38b of the travel bypass valve V16 via the shuttle valve V29 and the second transmission oil line o2.

[0109] In the hydraulic system configured as described above, when the directional control valves DV1 to DV11 of the control valves V1 to V11 are in the neutral position, the travel independent valve V13 is in the confluence position 22. At this time, the first unloaded oil passage z1 connected to the first discharge passage a is blocked by the first unloaded valve V18, and the second unloaded oil passage z2 connected to the second discharge passage b is blocked by the second unloaded valve V19. Therefore, when the discharge pressure (PPS signal pressure) of the main pump 18 rises and the difference between this PPS signal pressure and the PLS signal pressure (zero at this time) becomes greater than the control differential pressure, the main pump 18 is flow controlled in a direction to reduce the discharge rate, and the first and second unloaded valves V18 and V19 open, causing the oil discharged from the main pump 18 to drop into the tank T.

[0110] In this state, the discharge pressure of the first discharge path a and the second discharge path b of the main pump 18 becomes the pressure set by the first and second unloading valves V18 and V19, and the discharge flow rate of the main pump 18 becomes the minimum discharge rate.

[0111] Next, a description will be given of a case where one or more of the first SP control valve V1, swing control valve V2, arm control valve V3, slewing control valve V4, boom control valve V9, bucket control valve V10, and second SP control valve V11 are operated without driving the traveling unit 5 and the dozer unit 7, or a case where one or more of the first SP control valve V1, swing control valve V2, arm control valve V3, slewing control valve V4, boom control valve V9, bucket control valve V10, and second SP control valve V11 are simultaneously operated with one or more of the right side traveling control valve V6, left side traveling control valve V7, and first and second dozer control valves V5 and V8.

[0112] In this case, the travel independent valve V13 is at the confluence position 22, the pressure of the first discharge path a and the second discharge path b is sent as a PPS signal pressure to the regulator 20 via the PPS signal shuttle valve V14, and the maximum load pressure acting on the operated hydraulic actuators ML, MR, MT, C1 to C7 is sent as a PLS signal pressure to the regulator 20 via the PLS signal shuttle valve V15.

[0113] The discharge pressure (discharge flow rate) of the main pump 18 is automatically controlled so that the PPS signal pressure minus the PLS signal pressure becomes the control differential pressure (so that the difference between the PPS signal pressure and the PLS signal pressure is maintained at a set value).

[0114] In other words, when the unloading flow rate through the first and second unloading valves V18 and V19 becomes zero, the discharge flow rate of the main pump 18 begins to increase, and the entire amount of oil discharged from the main pump 18 flows to the operated hydraulic actuators ML, MR, MT, C1 to C7 in accordance with the operation amounts of the operated control valves V1 to V11.

[0115] Furthermore, the pressure compensation valve V12 keeps constant the differential pressure across the spool of the directional control valve DV1 to DV11 of the operated control valve V1 to V11, and the discharge flow rate of the main pump 18 is diverted to each of the operated hydraulic actuators ML, MR, MT, C1 to C7 by an amount corresponding to the amount of operation, regardless of differences in the magnitude of the load acting on the operated hydraulic actuators ML, MR, MT, C1 to C7.

[0116] In addition, if the required flow rate of the hydraulic actuators ML, MR, MT, C1 to C7 exceeds the maximum discharge flow rate of the main pump 18, the oil discharged from the main pump 18 is proportionally distributed to each of the operated hydraulic actuators ML, MR, MT, C1 to C7.

[0117] In this case, even if the traveling bypass valve V16 is switched to the first switching position 33 or the second switching position 34, there is no problem because the oil discharged from the first discharge path a and the second discharge path b of the main pump 18 is merged.

[0118] In the hydraulic system of this embodiment, when the traveling device 5 and the front working device 11 are operated in combination, the traveling device 5 and the front working device 11 are driven by the combined oil from the first discharge port P1 and the second discharge port P2 of the main pump 18, and the flow rate of the oil discharged from the main pump 18 is controlled during combined operation of the traveling device 5 and the front working device 11. This makes it possible to operate the traveling device 5 and the front working device 11 simultaneously (combined operation) with an efficient system, and achieves both high levels of work equipment performance and energy savings (fuel consumption and heat balance).

[0119] Furthermore, even when the front working implement 11 and the traveling implement 5 are operated in combination, the front working implement 11 does not experience a speed deficiency (flow rate deficiency).

[0120] Next, we will explain the case where one or more of the right side travel control valve V6, left side travel control valve V7, and first and second dozer control valves V5 and V8 are operated without operating the first SP control valve V1, swing control valve V2, arm control valve V3, slewing control valve V4, boom control valve V9, bucket control valve V10, and second SP control valve V11.

[0121] In this case, the travel independent valve V13 is switched to the independent supply position 23, the communication passage j and the PLS signal transmission oil line w are blocked by the travel independent valve V13, the pressurized oil output from the first discharge port P1 flows to the right-side travel control valve V6 and the first dozer control valve V5, the pressurized oil output from the second discharge port P2 flows to the left-side travel control valve V7 and the second dozer control valve V8, and the PLS signal transmission oil line w is divided into the first line w1 and the second line w2.

[0122] In addition, the higher of the pressures in the first discharge path a and the second discharge path b is sent as a PPS signal pressure to the regulator 20 via the PPS signal shuttle valve V14 (if the pressures in the first discharge path a and the second discharge path b are the same, it is sent from the open input ports 26, 27 of the PPS signal shuttle valve V14 to the regulator 20), and the higher of the pressures in the first line w1 and the second line w2 is sent as a PLS signal pressure to the regulator 20 via the PLS signal shuttle V15 (if the pressures in the first line w1 and the second line w2 are the same, it is sent from the open input ports 29, 30 of the PLS signal shuttle valve V15 to the regulator 20).

[0123] In this case, too, the discharge pressure (discharge flow rate) of the main pump 18 is automatically controlled so that the PPS signal pressure - PLS signal pressure becomes the control differential pressure (so that the difference between the PPS signal pressure and the PLS signal pressure is maintained at a set value).

[0124] In the hydraulic system of this embodiment, the first dozer control valve V5 and the second dozer control valve V8 allow pressurized oil to be evenly extracted from the first discharge line a and the second discharge line b and sent to the dozer cylinder C1, thereby ensuring the straight-line traveling ability of the backhoe 1, and also enabling energy savings since the flow rate of the main pump 18 is controlled in accordance with the amount of operation of the control valves V5, V6, V7, and V8.

[0125] Furthermore, when turning the backhoe 1 to the left or right, the pressure compensating valve V12 performs flow division control, so even if the load on the travel motors ML, MR is high and the load on the dozer cylinder C1 is low, pressurized oil will not flow into the dozer cylinder C1 at a rate greater than the set flow rate. This makes it possible to maintain an independent circuit configuration in which pressurized oil from the first discharge port P1 is supplied independently to the right travel control valve V6, and pressurized oil from the second discharge port P2 is supplied independently to the left travel control valve V7, and since the pressurized oil is extracted equally from the first and second discharge ports P1, P2, the flow rate of pressurized oil supplied to the left and right travel motors ML, MR is secured, and turning performance is ensured.

[0126] In the above case, when traveling on flat ground, for example, when making a left turn, if the right-side travel control valve V6 is operated to increase the rotation speed of the hydraulic motor MR of the right-side traveling unit 5, the load pressure of the hydraulic motor MR of the right-side traveling unit 5 becomes higher than that of the left-side traveling unit 5, and the hydraulic oil sent to the hydraulic motor MR of the right-side traveling unit 5 becomes higher than that of the left-side traveling unit 5. Therefore, the load pressure (PLS signal pressure) of the hydraulic motor MR of the right-side traveling unit 5 is sent to the regulator 20 via the PLS signal shuttle valve V15, and the hydraulic oil of the hydraulic motor MR of the right-side traveling unit 5 becomes higher than that of the left-side traveling unit 5. The pressure (PPS signal pressure) of the first discharge line a sent to the MR is sent to the regulator 20, and the discharge flow rate of the main pump 18 is controlled based on these PLS signal pressure and PPS signal pressure, allowing for a smooth left turn (conversely, when turning right, the load pressure of the left hydraulic motor ML is sent to the regulator 20 via the PLS signal shuttle valve V15, and the pressure of the second discharge line b sent to the left hydraulic motor ML is sent to the regulator 20, and the discharge flow rate of the main pump 18 is controlled based on these PLS signal pressure and PPS signal pressure).

[0127] However, when traveling forward down a slope, for example, when making a left turn, the right-side travel control valve V6 is operated to increase the rotation speed of the hydraulic motor MR of the right-side traveling device 5. However, when traveling down a slope, the weight of the backhoe 1 acts positively in the direction of travel, so no load pressure is generated in the hydraulic motor MR of the right-side traveling device 5.

[0128] On the other hand, the pressure in the second discharge line b sent to the left-hand drive control valve V7 rises to the unload pressure, and this pressure in the second discharge line b sent to the left-hand drive control valve V7 is sent to the regulator 20 as the PPS signal pressure.

[0129] Therefore, if no load pressure is generated in the hydraulic motor MR of the right-side traveling device 5, the differential pressure between the PLS signal pressure and the PPS signal pressure will be in a surplus state, the discharge flow rate of the main pump 18 will not increase, and turning will not be possible.

[0130] However, in this embodiment, in this case, the pilot pressure output from the right-side traveling operation valve V26 is higher than the pilot pressure output from the left-side traveling operation valve V27, so the traveling bypass valve V16 is switched to the first switching position 33, and the oil discharged from the second discharge port P2 flows from the second discharge path b to the first discharge path a via the first bypass oil path t1 (in the case of a right turn, the traveling bypass valve V16 is switched to the second switching position 34, and the oil discharged from the first discharge port P1 flows from the first discharge path a to the second discharge path b via the second bypass oil path t2).

[0131] As a result, the pressure oil supply system to the hydraulic motor MR of the right-side traveling device 5 is maintained at high pressure, making it possible to control the flow rate of the main pump 18 based on the PLS signal pressure and PPS signal pressure from the right side, and enabling smooth turns even on downhill slopes.

[0132] Furthermore, when turning left on flat ground, even if the traveling bypass valve V16 is switched to the first switching position 33, pressurized oil does not flow from the first discharge line a to the second discharge line b via the first bypass oil line t1 due to the presence of the check valve V24 (when turning right, even if the traveling bypass valve V16 is switched to the second switching position 34, pressurized oil does not flow from the second discharge line b to the first discharge line a via the second bypass oil line t2), so there is no problem when turning on flat ground.

[0133] Furthermore, when the pilot pressures of the left and right travel control valves V26, V27 are the same, the travel bypass valve V16 is set to the shutoff position 32, and no pressure oil flows between the first discharge path a and the second discharge path b of the main pump 18, ensuring straight-line travel.

[0134] As shown in FIG. 4 , the first relief circuit 41 has one end connected to the first line w1 and the other end connected to a drain oil passage (tank circuit) g. The first relief circuit 41 releases a portion of the hydraulic oil in the first line w1 to the hydraulic oil tank T via the drain oil passage g. Specifically, the first relief circuit 41 includes a first relief flow path 41a, a first relief throttle V20, and an oil filter. One end of the first relief flow path 41a is connected to the first line w1 downstream of a connection point with a first load transmission oil passage y1, which transmits the load pressure of the travel motor MR, and the other end is connected to the drain oil passage g. The first relief throttle V20 is provided in the first relief flow path 41a to restrict the flow of hydraulic oil. The oil filter 41b is provided in the first relief flow path 41a upstream of the first relief throttle V20.

[0135] The first relief circuit 41 makes it possible to release pressure from the first line w1 when the operation of all of the first hydraulic actuators A1 (hydraulic actuator C6, swing cylinder C2, arm cylinder C4, swing motor MT, dozer cylinder C1, and travel motor MR) is stopped (when the first SP control valve V1, swing control valve V2, arm control valve V3, swing control valve V4, first dozer control valve V5, and right-side travel control valve V6 are all set to the neutral position).

[0136] The second relief circuit 42 has one end connected to the second line w2 and the other end connected to the drain oil passage g, and releases a portion of the hydraulic oil in the second line w2 to the hydraulic oil tank T via the drain oil passage g. Specifically, the second relief circuit 42 has a second relief flow path 42a, a second relief throttle V21, and an oil filter 42b. One end of the second relief flow path 42a is connected to the second line w2 downstream of a connection with the second load transmission oil passage y2, which transmits the load pressure of the travel motor ML, and the other end is connected to the drain oil passage g. The second relief throttle V21 is provided in the second relief flow path 42a and restricts the flow of hydraulic oil. The oil filter 42b is provided in the second relief flow path 42a upstream of the second relief throttle V21.

[0137] The second relief circuit 42 makes it possible to release pressure from the second line w2 when the operation of all second hydraulic actuators A2 (travel motor ML, dozer cylinder C1, boom cylinder C3, bucket cylinder C5, and hydraulic actuator C7) is stopped (when the left-side travel control valve V7, second dozer control valve V8, boom control valve V9, bucket control valve V10, and second SP control valve V11 are all set to the neutral position).

[0138] 2, 3, and 4, the hydraulic system of this embodiment has a line restriction 43 that is provided in the load pressure transmission line x3 between the regulator 20 and the load pressure selection valve V15 and controls the responsiveness of the regulator 20. In this embodiment, the line restriction 43 is provided in the inlet block B of the control valve CV, but is not limited to this.

[0139] The hydraulic system also includes a bleed circuit 45 that leaks a portion of the hydraulic oil in a section line 44 between the load pressure selection valve V15 and the line restriction 43 in the load pressure transmission line x3 (bleeding the hydraulic oil to a discharge destination (hydraulic oil tank T) different from the regulator 20). More specifically, the bleed circuit 45 includes a bleed line 45a, a bleed restriction 45b, and an oil filter 45c. The bleed line 45a includes a first bleed line 45a1 formed within the control valve CV and having one end connected to the section line 44, and a second bleed line 45a2 having one end connected to the other end of the first bleed line 45a1 and the other end communicating with the hydraulic oil tank T. In this embodiment, as shown in FIG. 4 , the one end of the first bleed line 45a1 is connected to the section line 44 upstream of the line restriction 43 and in the vicinity of the line restriction 43. The other end of the first bleed line 45a1 is connected to a discharge port 47 provided in the control valve CV. One end of the second bleed line 45a2 is connected to the discharge port 47. A bleed throttle 45b is provided in the second bleed line 45a2 to restrict the flow of hydraulic oil. An oil filter 45c is provided in the second bleed line 45a2 upstream of the bleed throttle 45b.

[0140] The bleed orifice 45b and the oil filter 45c may be configured by attaching a bushing or the like provided with either or both of the bleed orifice 45b and the oil filter 45c to the control valve CV. Alternatively, either or both of the bleed orifice 45b and the oil filter 45c may be directly attached to the control valve CV. Alternatively, either or both of the bleed orifice 45b and the oil filter 45c may be provided in the first bleed line 45a1. Alternatively, the bleed orifice 45b may be formed in the control valve CV, and the hydraulic oil passing through the bleed orifice 45b may be discharged to the hydraulic oil tank T via a drain oil line (tank circuit) g within the control valve CV. Specifically, the section line 44 and the drain oil line g within the control valve CV may be connected by a bleed line 45a, and the bleed orifice 45b may be provided in the bleed line 45a. As a result, the flow rate of the hydraulic oil passing through the bleed restrictor 45b can be further stabilized by the action of the exhaust pressure of the drain oil passage g.

[0141] The work machine 1 has a pump unit including a main pump 18 and a sub-pump 19, and the pump unit is attached to the prime mover E. A regulator 20 is provided in the pump unit. The control valve CV is mounted on the swivel base 10 and is located, for example, in the front part of the swivel base 10. The control valve CV (downstream of the conduit restriction 43) in the load pressure transmission conduit x3 and the regulator 20 are connected by a hydraulic hose 46 (see FIG. 4 ).

[0142] If the conduit restriction 43 is not provided, the hydraulic hose 46 will expand when the load pressure output from the load pressure selection valve V15 enters the hydraulic hose 46, but in this embodiment, the conduit restriction 43 is provided in the load pressure transmission conduit x3 to accommodate the expansion of the hydraulic hose 46. In other words, the hydraulic hose 46 is elastic and will expand when pressure is applied, but the conduit restriction 43 works to slow down and stabilize the response to the increase in the amount of hydraulic oil passing through due to this expansion.

[0143] However, in the conventional system, when the viscosity of the hydraulic oil increases due to a drop in outside air temperature, a delay in response occurs because the transmission of load pressure is hindered by the conduit restriction 43. Furthermore, although the load pressure selection valve V15 acts as a resistance, in the conventional system, almost no hydraulic oil flow occurs beyond the connection 41 c (see FIG. 3) of the first relief circuit 41 in the first line w1 and the connection 42 c (see FIG. 3) of the second relief circuit 42 in the second line w2 (downstream of the connection 41 c of the first relief circuit 41 and the connection 42 c of the second relief circuit 42), so when the viscosity of the hydraulic oil increases at low temperatures, a delay in response also occurs in the load pressure selection valve V15.

[0144] If the response is delayed by a certain amount, the phase may be reversed, causing periodic so-called hunting.

[0145] In the work machine 1 of this embodiment, when load pressure is output from the load pressure selection valve V15, a portion of the hydraulic oil in the section line 44 between the load pressure selection valve V15 and the conduit throttle 43 flows to the hydraulic oil tank T via the bleed circuit 45 (leaks to the hydraulic oil tank T). This allows the conduit throttle 43 and the load pressure selection valve V15 to warm up. Specifically, by leaking a portion of the hydraulic oil in the section line 44 between the load pressure selection valve V15 and the conduit throttle 43 via the bleed circuit 45 (bleeding to a discharge destination (hydraulic oil tank T) different from the regulator 20), a flow of hydraulic oil occurs in the section line 44, improving the warm-up performance of the conduit throttle 43. Furthermore, a flow of hydraulic oil caused by the leakage of hydraulic oil via the bleed circuit 45 also occurs in the load pressure selection valve V15, improving the warm-up performance of the load pressure selection valve V15. These features improve responsiveness at low temperatures.

[0146] It is also possible, for example, to allow a portion of the hydraulic oil to flow into the hydraulic oil tank T downstream of the conduit restriction 43 (for example, by providing a conduit inside the regulator 20 and allowing a portion of the hydraulic oil to flow into the hydraulic oil tank T through the conduit restriction), but in this case, a flow of hydraulic oil will occur in the conduit restriction 43 due to the portion of the hydraulic oil flowing into the hydraulic oil tank T through the conduit restriction, which will cause a pressure loss and a decrease in the speed of the hydraulic actuator (decreased responsiveness).

[0147] In this embodiment, the bleed circuit 45 allows a portion of the hydraulic oil to flow into the hydraulic oil tank T upstream of the conduit restriction 43, so there is no pressure loss in the conduit restriction 43 due to the flow of a portion of the hydraulic oil into the hydraulic oil tank T, and the provision of the bleed circuit 45 does not cause a decrease in the speed or responsiveness of the hydraulic actuator due to pressure loss in the conduit restriction 43.

[0148] Furthermore, as a method for transmitting the highest load pressure among the load pressures of multiple hydraulic actuators to the regulator 20, there is a multistage shuttle valve method in which two load pressures are sequentially compared to finally obtain the highest load pressure. This multistage shuttle valve method first selects the higher load pressure of a first hydraulic actuator or a second hydraulic actuator among the multiple hydraulic actuators as the first load pressure using a first shuttle valve, then selects the higher load pressure between the selected first load pressure and the load pressure of a third hydraulic actuator, which is another hydraulic actuator, as the second load pressure using a second shuttle valve, and then selects the higher load pressure between the selected second load pressure and the load pressure of a fourth hydraulic actuator, which is yet another hydraulic actuator, as the third load pressure using a third shuttle valve, in this manner, to finally obtain the highest load pressure.

[0149] In a hydraulic system that obtains the maximum load pressure using the above-described multistage shuttle valve system, if, for example, a portion of the hydraulic oil upstream of the pipe restriction 43 is allowed to leak into the hydraulic oil tank T, pressure loss will occur in each shuttle valve, and this pressure loss will result in a decrease in the speed and responsiveness of the hydraulic actuator.

[0150] In this embodiment, the load pressures of the first hydraulic actuator and the second hydraulic actuator are input to the load pressure selection valve V15, and the load pressure selection valve V15 outputs the maximum load pressure, which is the higher of the load pressures of the first hydraulic actuator and the second hydraulic actuator. In other words, the first relief circuit 41 is connected to the first line w1 that transmits the load pressure from the first hydraulic actuator, and the second relief circuit 42 is connected to the second line w2 that transmits the load pressure from the second hydraulic actuator. Because this is a system in which the maximum load pressure of the first hydraulic actuator and the second hydraulic actuator is output by the load pressure selection valve V15 downstream of the connection point of the relief circuit 42, only one shuttle valve is provided in the load signal pressure transmission circuit (PLS signal pressure transmission circuit) that transmits the maximum load pressure of the hydraulic actuator to the regulator 20, and even if a bleed circuit 45 is connected to the pipe (section pipe 44) downstream of the load pressure selection valve V15 and part of the hydraulic oil is leaked into the hydraulic oil tank T by this bleed circuit 45, the warm-up effect can be improved with the pressure loss effect of only one load pressure selection valve V15.

[0151] As described above, in this embodiment, by providing the bleed circuit 45 that leaks a portion of the hydraulic oil in the section conduit 44 between the load pressure selection valve V15 and the conduit restriction 43 (bleeding it to a discharge destination (hydraulic oil tank T) different from the regulator 20), the warm-up effect can be improved without the influence of pressure loss in the conduit restriction 43 and with the influence of pressure loss in only one load pressure selection valve V15 (shuttle valve). In other words, a sufficient warm-up effect can be obtained while minimizing the influence of speed reduction due to pressure loss in each part of the PLS signal pressure transmission circuit.

[0152] A preferred embodiment of the present invention provides a work machine 1 as described in the following items.

[0153] (Item 1) A hydraulic pressure control device including a first discharge port P1 and a second discharge port P2 for discharging hydraulic oil, a plurality of first hydraulic actuators A1 to which the hydraulic oil discharged from the first discharge port P1 can be supplied, a plurality of second hydraulic actuators A2 to which the hydraulic oil discharged from the second discharge port P2 can be supplied, and a load pressure selector that receives the load pressures of the first hydraulic actuators A1 and the second hydraulic actuators A2 and outputs a maximum load pressure that is the higher of the load pressures of the first hydraulic actuators A1 and the second hydraulic actuators A2. a regulator 20 that receives the maximum load pressure output from the load pressure selection valve V15 and controls the discharge rates of the first discharge port P1 and the second discharge port P2 in accordance with the input maximum load pressure; a line restriction 43 that is provided in a load pressure transmission line x3 between the regulator 20 and the load pressure selection valve V15; and a bleed circuit 45 that releases a portion of the hydraulic oil in a section line 44 in the load pressure transmission line x3 between the load pressure selection valve V15 and the line restriction 43 to a discharge destination different from the regulator 20.

[0154] According to the work machine 1 relating to this item 1, a flow of hydraulic oil is generated in the section pipe 44 by using the bleed circuit 45 to release a portion of the hydraulic oil in the section pipe 44 between the load pressure selection valve V15 and the pipe restriction 43 to a discharge destination other than the regulator 20, thereby improving the warm-up performance of the pipe restriction 43. In addition, a flow of hydraulic oil is also generated in the load pressure selection valve V15 by using the bleed circuit 45 to release a portion of the hydraulic oil to a discharge destination other than the regulator 20, thereby improving the warm-up performance of the load pressure selection valve V15. As a result, responsiveness (load pressure transmission responsiveness) at low temperatures can be improved.

[0155] (Item 2) The work machine 1 according to Item 1 includes a hydraulic oil tank T that stores the hydraulic oil, and the bleed circuit 45 has a bleed pipe 45a having one end connected to the section pipe 44 and the other end communicating with the hydraulic oil tank T, and a bleed throttle 45b provided in the bleed pipe 45a.

[0156] According to the work machine 1 relating to this item 2, a bleed circuit 45 can be easily constructed to release a portion of the hydraulic oil in the section pipe 44 to a discharge destination other than the regulator 20 .

[0157] (Item 3) The work machine 1 according to Item 2, wherein one end of the bleed pipe 45 a is connected to the section pipe 44 in the vicinity of the pipe restriction 43 .

[0158] According to the work machine 1 of item 3, it is possible to efficiently improve the warm-up performance of the conduit restriction 43. Furthermore, for example, if a portion of the hydraulic oil were to flow downstream of the conduit restriction 43 to the hydraulic oil tank T, a flow of hydraulic oil due to leakage would occur in the conduit restriction 43, causing a pressure loss that would adversely affect the speed (responsiveness) of the hydraulic actuator, but in this embodiment, the bleed circuit 45 is used to cause a portion of the hydraulic oil to flow to the hydraulic oil tank T upstream of the conduit restriction 43, so there is no pressure loss in the conduit restriction 43 due to flowing a portion of the hydraulic oil to the hydraulic oil tank T, and the provision of the bleed circuit 45 does not cause a decrease in the speed or responsiveness of the hydraulic actuator due to pressure loss in the conduit restriction 43.

[0159] (Item 4) A hydraulic oil tank T for storing the hydraulic oil, a first line w1 connected to one input port 29 of the load pressure selection valve V15, a second line w2 connected to the other input port 30 of the load pressure selection valve V15, and a plurality of first load transmission oil passages y1 provided for each of the plurality of first hydraulic actuators A1 and transmitting the load of the corresponding first hydraulic actuator A1, the plurality of first load transmission oil passages y1 connected to the first line w1, and a second line w2 provided for each of the plurality of second hydraulic actuators A2. the second hydraulic actuator A2 is connected to a first line w2, the second load transmission oil passages y2 are connected to a second line w2, a first relief circuit 41 is connected to the first line w1 and releases a portion of the hydraulic oil in the first line w1 to the hydraulic oil tank T on the upstream side of the load pressure selection valve V15, and a second relief circuit 42 is connected to the second line w2 and releases a portion of the hydraulic oil in the second line w2 to the hydraulic oil tank T on the upstream side of the load pressure selection valve V15.

[0160] In the work machine 1 of this item 4, a first relief circuit 41 is provided that relieves a portion of the hydraulic oil in the first line w1 that transmits the load pressure from the first hydraulic actuator A1 on the upstream side of the load pressure selection valve V15, and a second relief circuit 42 is provided that relieves a portion of the hydraulic oil in the second line w2 that transmits the load pressure from the second hydraulic actuator A2 on the upstream side of the load pressure selection valve V15, and the first hydraulic actuator A1 and the second hydraulic actuator A2 are relieved by the load pressure selection valve V15 on the downstream side of the connection part 41c of the first relief circuit 41 in the first line w1 and the connection part 42c of the second relief circuit 42 in the second line w2. Since this is a system in which the maximum load pressure of the two hydraulic actuators A1, A2 is output, only one shuttle valve is provided in the load signal transmission circuit that transmits the maximum load pressure of the load pressures of the operated hydraulic actuators A1, A2 as a load signal pressure to the regulator 20, and even if a bleed circuit 45 is connected downstream of the load pressure selection valve V15 and part of the hydraulic oil is allowed to escape to a discharge destination other than the regulator 20 by the bleed circuit 45 (for example, leaking into the hydraulic oil tank T), the warm-up effect can be improved with the pressure loss effect of only one load pressure selection valve V15.

[0161] (Item 5) The work machine 1 according to any one of items 1 to 4, comprising: a plurality of first control valves VA1 provided corresponding to the plurality of first hydraulic actuators A1 and controlling the flow of hydraulic oil to the first hydraulic actuators A1; a plurality of second control valves VA2 provided corresponding to the plurality of second hydraulic actuators A2 and controlling the flow of hydraulic oil to the second hydraulic actuators A2; and a control valve CV incorporating the plurality of first control valves VA1, the plurality of second control valves VA2, the load pressure selection valve V15, and the conduit restriction 43, wherein a conduit between the control valve CV and the regulator 20 in the load pressure transmission conduit x3 is constituted by a hydraulic hose 46.

[0162] Incidentally, if the conduit restriction 43 is not provided, when the load pressure output from the load pressure selection valve V15 enters the hydraulic hose 46, the hydraulic hose 46 expands, and this expansion increases the amount of hydraulic oil passing through, affecting the stability of response. However, in the embodiment according to item 5, by providing the conduit restriction 43, the flow rate of the hydraulic oil is restricted by the conduit restriction 43, and the conduit restriction 43 is effective to slow down the response in response to the increase in the amount of hydraulic oil passing through the hydraulic hose 46 due to the expansion, thereby making it possible to stabilize the response. Furthermore, even if the conduit restriction 43 is provided, a flow of hydraulic oil is generated by leaking a portion of the hydraulic oil through the bleed circuit 45, so that a decrease in response at low temperatures can be suppressed.

[0163] (Item 6) The work machine 1 according to item 5, which cites item 2 or 3, wherein the bleed restrictor 43 is attached directly or indirectly to the control valve CV.

[0164] (Item 7) The work machine 1 described in Item 5, which cites Item 2 or 3, wherein the bleed pipe 43 is incorporated in the control valve CV, one end is connected to the section pipe 44, and the other end is in communication with the hydraulic oil tank T via a drain oil passage g provided in the control valve CV.

[0165] According to the work machine 1 relating to this item 7, the flow rate of the hydraulic oil passing through the bleed restrictor 45b can be made more stable by the action of the exhaust pressure of the drain oil passage g.

[0166] Although one embodiment of the present invention has been described above, the embodiment disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0167] 1 Work machine 20 Regulator 29 Input port 30 Input port 41 First relief circuit 42 Second relief circuit 43 Pipe restriction 44 Section pipe 45 Bleed circuit 45a Bleed pipe 45a1 First bleed pipe 45a2 Second bleed pipe 45b Bleed restriction 46 Hydraulic hose 47 Discharge port A1 First hydraulic actuator A2 Second hydraulic actuator g Drain oil passage P1 First discharge port P2 Second discharge port T Hydraulic oil tank V15 Load pressure selection valve VA1 First control valve VA2 Second control valve x3 Load pressure transmission pipe y1 First load transmission oil passage y2 Second load transmission oil passage w1 First line w2 Second line

Claims

1. a first discharge port and a second discharge port for discharging hydraulic oil; a plurality of first hydraulic actuators to which the hydraulic oil discharged from the first discharge port can be supplied; a plurality of second hydraulic actuators to which the hydraulic oil discharged from the second discharge port can be supplied; a load pressure selection valve that receives the load pressures of the first hydraulic actuator and the second hydraulic actuator and outputs a maximum load pressure that is the higher of the load pressure of the first hydraulic actuator and the load pressure of the second hydraulic actuator; a regulator that receives the maximum load pressure output from the load pressure selection valve and controls the discharge rates of the first discharge port and the second discharge port in accordance with the received maximum load pressure; a line restriction provided in a load pressure transmission line between the regulator and the load pressure selection valve; a bleed circuit that releases a portion of the hydraulic oil in a section of the load pressure transmission pipe between the load pressure selection valve and the pipe restriction to a discharge destination other than the regulator; A work machine equipped with the above.

2. a hydraulic oil tank for storing the hydraulic oil; 2. The work machine according to claim 1, wherein the bleed circuit comprises a bleed pipe line having one end connected to the section pipe line and the other end communicating with the hydraulic oil tank, and a bleed restrictor provided in the bleed pipe line.

3. 3. The work machine according to claim 2, wherein one end of the bleed pipe is connected to the section pipe in the vicinity of the pipe restriction.

4. a hydraulic oil tank that stores the hydraulic oil; a first line connected to one input port of the load pressure selection valve; a second line connected to the other input port of the load pressure selection valve; A first hydraulic actuator is provided for each of the plurality of first hydraulic actuators. a plurality of first load transmission oil passages for transmitting loads of an actuator, the plurality of first load transmission oil passages being connected to the first line; a plurality of second load transmission oil passages provided for each of the plurality of second hydraulic actuators to transmit loads of the corresponding second hydraulic actuators, the plurality of second load transmission oil passages being connected to the second line; a first relief circuit located upstream of the load pressure selection valve for releasing a portion of the hydraulic oil in the first line to the hydraulic oil tank; a second relief circuit located upstream of the load pressure selection valve for releasing a portion of the hydraulic oil in the second line to the hydraulic oil tank; The work machine according to any one of claims 1 to 3, comprising:

5. a plurality of first control valves provided corresponding to the plurality of first hydraulic actuators and configured to control the flow of the hydraulic oil to the first hydraulic actuators; a plurality of second control valves provided corresponding to the plurality of second hydraulic actuators and configured to control the flow of the hydraulic oil to the second hydraulic actuators; a control valve incorporating the plurality of first control valves, the plurality of second control valves, the load pressure selection valve, and the pipe restriction; Equipped with 4. The work machine according to claim 1, wherein the load pressure transmission line between the control valve and the regulator is formed by a hydraulic hose.

6. 6. The work machine according to claim 5, wherein the bleed restrictor is attached directly or indirectly to the control valve.

7. The working machine according to claim 5, which cites claim 2 or 3, wherein the bleed pipe is incorporated into the control valve, one end of which is connected to the section pipe, and the other end of which is connected to the hydraulic oil tank via a drain oil passage provided within the control valve.

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