Hydraulic circuit structure, hydraulic actuator unit, and work machine

Abstract

Provided is a hydraulic circuit structure configured to be capable of preventing heat shock.　A hydraulic circuit structure (1) comprises: a hydraulic circuit for supplying hydraulic oil from a control valve (V1) to a hydraulic actuator (M); and warm-up oil passages (34a, 34b, 35, L4a, L4b). When the control valve is in a neutral position (PO) for bringing the hydraulic actuator into a neutral state, back-pressure oil, which is the hydraulic oil to which back pressure from the control valve is added and flowing into the hydraulic circuit, is discharged to a low-pressure region having a lower pressure than the back pressure via the warm-up oil passages.

Description

Hydraulic Circuit Structure, Hydraulic Actuator Unit, and Working Machine

[0001] The present invention relates to a hydraulic circuit structure provided with a hydraulic circuit for driving a hydraulic actuator, a hydraulic actuator unit including the hydraulic circuit structure and a hydraulic actuator, and a working machine provided with the hydraulic circuit structure and the hydraulic actuator.

[0002] For example, as described in Patent Document 1, a technique for constructing a hydraulic circuit including a counterbalance valve, an anti-cavitation valve, etc. for preventing runaway on a downhill slope in a valve block (center section) to which a hydraulic motor is attached is known.

[0003] Japanese Patent Publication "JP-A-2019-11835"

[0004] Regarding a working machine or the like provided with a traveling motor unit or the like formed by combining a valve block having a hydraulic circuit structure as described above and a hydraulic motor, even in a low-temperature outside air, the hydraulic motor, valve, and other hydraulic system-related devices included in the motor unit, and further, the working machine including the motor unit, etc. It is preferable to circulate the hydraulic oil in a somewhat high-temperature state through the hydraulic system so that the devices can operate efficiently and smoothly.

[0005] However, for example, in a low-temperature environment, when the hydraulic oil supplied from the hydraulic source to the control valve is warmed by warm-up and then the control valve is switched to start driving the hydraulic motor, the counterbalance valve in the valve block that has been cold in a neutral state until then suddenly has high-temperature hydraulic oil supplied from the control valve to the spool, and a heat shock state such as the spool locally expanding and becoming difficult to operate may occur.

[0006] In order to avoid such a situation, in the conventional technology, in a low-temperature environment, the temperature rise of the hydraulic oil due to warm-up on the control valve side is limited to a temperature lower than the desired temperature in terms of the reactivity of the hydraulic system-related devices, etc., and the current situation is that the best reactivity, etc. of the devices, etc. cannot be obtained.

[0007] The object of the present invention is to provide a hydraulic circuit structure configured to suppress thermal shock, a hydraulic actuator unit including the same, and a work machine equipped therewith.

[0008] A hydraulic circuit structure according to one aspect of the present invention comprises a hydraulic circuit for supplying hydraulic fluid from a control valve to a hydraulic actuator, and a warm-up oil passage, wherein when the control valve is in a neutral position for neutralizing the hydraulic actuator, the back-pressure oil, which is hydraulic fluid with back pressure added from the control valve that flows into the hydraulic circuit, is discharged through the warm-up oil passage to a low-pressure region lower than the back pressure.

[0009] A hydraulic actuator unit according to one aspect of the present invention comprises the hydraulic circuit structure and the hydraulic actuator.

[0010] A work machine according to one aspect of the present invention comprises the hydraulic circuit structure and the hydraulic actuator.

[0011] The hydraulic circuit structure is designed so that while the hydraulic actuator is in a neutral state, back pressure oil is discharged into the low-pressure region via a warm-up oil passage. This back pressure oil flow warms the hydraulic structure itself, preventing thermal shock (malfunction) of valve spools and other components within the hydraulic circuit structure, even when high-temperature hydraulic fluid flows in at the start of operation of the hydraulic actuator in a cold environment.

[0012] Furthermore, by incorporating such a hydraulic circuit structure, hydraulic actuator units and work machines can avoid the risk of thermal shock even when high-temperature hydraulic fluid is supplied to the hydraulic circuit structure from the control valve in cold regions. This allows the hydraulic actuators to be driven with hydraulic fluid heated to a desired level in terms of valve responsiveness and other factors, thereby maximizing their performance.

[0013] This is a hydraulic circuit diagram of a work machine equipped with a hydraulic circuit structure including a counterbalance valve equipped with a warm-up oil passage according to the first embodiment. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the first embodiment in the hydraulic circuit structure. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the first embodiment when the spool is in the neutral position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the first embodiment when the spool is in the process of moving from the neutral position to the first direction drive position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the first embodiment when the spool is in the first direction drive position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the second embodiment in the hydraulic circuit structure when the spool is in the neutral position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the second embodiment when the spool has started moving from the neutral position to the first direction drive position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the second embodiment when the spool is in the minimum stroke state in the first direction drive position. This is a cross-sectional view of the counterbalance valve equipped with a warm-up oil passage according to the second embodiment when the spool is in the full stroke state in the first direction drive position. This is a cross-sectional view of a counterbalance valve equipped with a warm-up oil passage according to the third embodiment in the hydraulic circuit structure when the spool is in the neutral position. This is a cross-sectional view of a counterbalance valve equipped with a warm-up oil passage according to the third embodiment when the spool starts moving from the neutral position to the first direction drive position. This is a cross-sectional view of a counterbalance valve equipped with a warm-up oil passage according to the third embodiment when the spool is about to enter the first direction drive position. This is a cross-sectional view of a counterbalance valve equipped with a warm-up oil passage according to the third embodiment when the spool is in the full stroke state in second direction drive position. This is a hydraulic circuit diagram of a work machine equipped with a hydraulic circuit structure having a warm-up oil passage according to the fourth embodiment. This is a hydraulic circuit diagram of a work machine equipped with a hydraulic circuit structure having a warm-up oil passage according to a modified example of the fourth embodiment. This is a hydraulic circuit diagram of a work machine equipped with a hydraulic circuit structure having a warm-up oil passage according to the fifth embodiment.This is a hydraulic circuit diagram of a work machine equipped with a hydraulic circuit structure having a warm-up oil passage according to the sixth embodiment.

[0014] Figures 1 to 7 illustrate the hydraulic circuit structure, hydraulic actuator unit, and work machine having a counterbalance valve with a warm-up oil passage.

[0015] Figure 1 is a hydraulic circuit diagram of a work machine 100 equipped with a hydraulic circuit structure 1 including a counterbalance valve V2a with a warm-up oil passage according to the first embodiment. Figure 2A is a cross-sectional view of the counterbalance valve V2a with a warm-up oil passage according to the first embodiment in the hydraulic circuit structure 1. Figure 2B is a cross-sectional view of the counterbalance valve V2a with a warm-up oil passage according to the first embodiment when the spool 3 is in the neutral position P10. Figure 2C is a cross-sectional view of the counterbalance valve V2a with a warm-up oil passage according to the first embodiment when the spool 3 is in the process of moving from the neutral position P10 to the first direction drive position P11. Figure 2D is a cross-sectional view of the counterbalance valve V2a with a warm-up oil passage according to the first embodiment when the spool 3 is in the first direction drive position P11.

[0016] Figure 3A is a cross-sectional view of the counterbalance valve V2b with a warm-up oil passage according to the second embodiment in the hydraulic circuit structure 1 when the spool 3 is in the neutral position P10. Figure 3B is a cross-sectional view of the counterbalance valve V2b with a warm-up oil passage according to the second embodiment when the spool 3 starts moving from the neutral position P10 to the first direction drive position P11. Figure 3C is a cross-sectional view of the counterbalance valve V2b with a warm-up oil passage according to the second embodiment when the spool 3 is in the minimum stroke state at the first direction drive position P11. Figure 3D is a cross-sectional view of the counterbalance valve V2b with a warm-up oil passage according to the second embodiment when the spool 3 is in the full stroke state at the first direction drive position P11.

[0017] Figure 4A is a cross-sectional view showing the state of the counterbalance valve V2c with the warm-up oil passage according to the third embodiment in the hydraulic circuit structure 1 when the spool 3 is in the neutral position P10. Figure 4B is a cross-sectional view of the counterbalance valve V2c with the warm-up oil passage according to the third embodiment when the spool 3 begins to move from the neutral position P10 to the first direction drive position P11. Figure 4C is a cross-sectional view of the counterbalance valve V2c with the warm-up oil passage according to the third embodiment when the spool 3 is about to enter the first direction drive position P11. Figure 4D is a cross-sectional view of the counterbalance valve V2c with the warm-up oil passage according to the third embodiment when the spool 3 is in the full stroke state at the first direction drive position P11. Figure 4E is a cross-sectional view of the counterbalance valve V2c with the warm-up oil passage according to the third embodiment when the spool 3 is in the full stroke state at the second direction drive position P12.

[0018] Figure 5A is a hydraulic circuit diagram of a work machine 100 equipped with a hydraulic circuit structure 1 having a warm-up oil passage according to the fourth embodiment. Figure 5B is a hydraulic circuit diagram of a work machine 100 equipped with a hydraulic circuit structure 1 having a warm-up oil passage according to a modified example of the fourth embodiment. Figure 6 is a hydraulic circuit diagram of a work machine 100 equipped with a hydraulic circuit structure 1 having a warm-up oil passage according to the fifth embodiment. Figure 7 is a hydraulic circuit diagram of a work machine 100 equipped with a hydraulic circuit structure 1 having a warm-up oil passage according to the sixth embodiment.

[0019] The work machine 100 shown in Figure 1 includes a hydraulic motor unit 10 which is a combination of a hydraulic motor M for driving, which is an example of a hydraulic actuator, and a hydraulic circuit structure 1 that has a hydraulic circuit for controlling the drive of the hydraulic motor M.

[0020] Furthermore, the hydraulic circuit structure 1 provided in the work machine 100 and the hydraulic actuator such as the hydraulic motor M controlled by the hydraulic circuit provided therein do not necessarily have to be combined as a unit.

[0021] Examples of work machines 100 include tractors, combine harvesters, backhoes, truck loaders, skid steer loaders, etc., but any construction machinery, agricultural machinery, industrial machinery, vehicle, etc. that is to which the hydraulic circuit structure 1 can be applied, which has a hydraulic actuator such as a hydraulic motor M for driving and a hydraulic circuit to control it, is acceptable.

[0022] The work machine 100 is equipped with a prime mover (not shown) and a hydraulic pump driven by the prime mover that discharges hydraulic fluid, and is equipped with a control valve V1 that receives the hydraulic fluid discharged by the hydraulic pump and can supply the hydraulic fluid to the hydraulic motor M.

[0023] The hydraulic motor M has a first port Ma and a second port Mb for supplying and discharging hydraulic fluid. The hydraulic motor M rotates in a first direction (for example, the forward direction) at a rotational speed corresponding to the flow rate of the hydraulic fluid that passes through the hydraulic motor M from the first port Ma to the second port Mb. The hydraulic motor M also rotates in a second direction (for example, the reverse direction) at a rotational speed corresponding to the flow rate of the hydraulic fluid that passes through the hydraulic motor M from the second port Mb to the first port Ma.

[0024] The control valve V1 is equipped with a first port V1a and a second port V1b for supplying and discharging hydraulic fluid. A pair of oil passages L1 and L2 for supplying and discharging hydraulic fluid are interposed between the control valve V1 and the hydraulic motor M. Oil passage L1 is a hydraulic fluid supply and discharge passage connecting the first port V1a of the control valve V1 and the first port Ma of the hydraulic motor M, and oil passage L2 is a hydraulic fluid supply and discharge passage connecting the second port V1b of the control valve V1 and the second port Mb of the hydraulic motor M.

[0025] The hydraulic circuit structure 1 included in the hydraulic motor unit 10 includes a valve case 2 and a hydraulic circuit provided inside or on the outer surface of the valve case 2. The hydraulic circuit of the valve case 2 includes at least a portion of a pair of oil passages L1 and L2.

[0026] At least one oil flow control valve is provided inside the valve case 2. In this embodiment, a counterbalance valve V2 and an anti-cavitation valve V3 are provided inside the valve case 2 as oil flow control valves.

[0027] In the following description, the counterbalance valve V2 (see Figure 5A) is a general term for valves having the basic structure and function of a counterbalance valve, and the counterbalance valves V2a to V2c (see Figures 1 to 4E) equipped with spools 3 that constitute the warm-up oil passage according to the first to third embodiments described later are included in the counterbalance valve V2.

[0028] Furthermore, in the following description, the anti-cavitation valve V3 (see Figure 1) is a general term for valves having the basic structure and function of an anti-cavitation valve (which may be a spool valve or a poppet valve), and the anti-cavitation valves V3a and V3b (see Figures 5A to 7) configured in relation to the warm-up oil passages according to the fourth to sixth embodiments described later are included in the anti-cavitation valve V3.

[0029] Within the valve case 2, a counterbalance valve V2 is interposed in the middle of a pair of oil passages L1 and L2, dividing oil passage L1 into oil passage L1a on the control valve V1 side and oil passage L1b on the hydraulic motor M side, and dividing oil passage L2 into oil passage L2a on the control valve V1 side and oil passage L2b on the hydraulic motor M side.

[0030] In other words, at least a portion of each of the oil passages L1a and L2a between the control valve V1 and the counterbalance valve V2, and the oil passages L1b and L2b between the hydraulic motor M and the counterbalance valve V2, are configured within the valve case 2.

[0031] Furthermore, the oil passages L1a and L2a, other than those formed within the valve case 2, can be constructed, for example, by a hose interposed between the control valve V1 and the valve case 2 within the work machine 100.

[0032] Furthermore, it is conceivable to connect the oil passages L1b and L2b configured within the valve case 2 to, for example, kidney port-shaped first port Ma and second port Mb formed on the mounting surface of the cylinder block of the hydraulic motor M on the outer surface of the valve case 2 that constitutes the hydraulic motor unit 10.

[0033] The control valve V1 is switchable between a neutral position P0, a first-direction (forward direction, etc.) drive position P1, and a second-direction (reverse direction, etc.) drive position P2.

[0034] When the control valve V1 is in the neutral position P0, no hydraulic fluid is supplied to the hydraulic motor M from either the first port V1a or the second port V1b. However, in this case, both the first port V1a and the second port V1b are in communication with the back pressure chamber of the control valve V1, and back pressure from the control valve V1 is applied to the oil passages L1a and L2a on the control valve V1 side.

[0035] When the control valve V1 is in the first direction drive position P1, hydraulic fluid is supplied from the first port V1a of the control valve V1 to the first port Ma of the hydraulic motor M via the oil passage L1, and hydraulic fluid is discharged from the second port Mb of the hydraulic motor M to the second port V1b of the control valve V1 via the oil passage L2. As a result, hydraulic fluid flows in the hydraulic motor M in the first direction from the first port Ma to the second port Mb.

[0036] At this time, the counterbalance valve V2 inside the valve case 2 of the hydraulic circuit structure 1 connects oil passage L1a and oil passage L1b, allowing oil flow from oil passage L1a to oil passage L1b, and connects oil passage L2a and oil passage L2b, allowing oil flow from oil passage L2b to oil passage L2a.

[0037] When the control valve V1 is in the second direction drive position P2, hydraulic fluid is supplied from the second port V1b of the control valve V1 to the second port Mb of the hydraulic motor M via the oil passage L2, and hydraulic fluid is discharged from the first port Ma of the hydraulic motor M to the first port V1a of the control valve V1 via the oil passage L1. As a result, hydraulic fluid flows in the hydraulic motor M in the second direction, from the second port Mb to the first port Ma.

[0038] At this time, the counterbalance valve V2 inside the valve case 2 connects oil passage L2a and oil passage L2b, allowing oil to flow from oil passage L2a to oil passage L2b, and connects oil passage L1a and oil passage L1b, allowing oil to flow from oil passage L1b to oil passage L1a.

[0039] Furthermore, the first-direction drive position P1 and the second-direction drive position P2 each have a certain range within which the operation amount of the control valve V1 can be increased or decreased. That is, the control valve V1 can be shifted from a state where the operation amount from the neutral position P0 is minimum to a state where the operation amount is maximum at each of the first-direction drive position P1 and the second-direction drive position P2, and in response to the change in this operation amount, the flow rate of the hydraulic oil flowing between the control valve V1 and the hydraulic motor M changes.

[0040] Also, the counterbalance valve V2 slides the spool 3 with the hydraulic pressure of the pilot pressure oil obtained by extracting a part of the hydraulic oil in the high-pressure-side oil passage among the oil passages L1a and L2a. Therefore, as described above, as the flow rate of the hydraulic oil in the high-pressure-side oil passage among the oil passages L1a and L2a changes in response to the change in the operation amount of the control valve V, the sliding amount of the spool 3 changes.

[0041] Referring to FIG. 2A and the like, the basic configuration of the counterbalance valve V2 will be described. The counterbalance valve V2 is composed of a combination of a valve case 2 and a spool 3. In the valve case 2, a spool chamber 20 and a pair of opposed pilot pressure oil chambers 21c and P2c sandwiching the spool chamber 20 are formed.

[0042] Note that the openings of the pilot pressure oil chambers 21c and P2c of the valve case 2 to the outside are plugged by plugs 7. The plugs 7 define the sliding amount (stroke) of the spool 3.

[0043] At least a part of each of the aforementioned oil passages L1a, L1b, L2a, and L2b is formed in the valve case 2.

[0044] Furthermore, within the valve case 2, a throttled pilot pressure oil passage L1c branched from the oil passage L1a is connected to the pilot pressure oil chamber 21c, and a throttled pilot pressure oil passage L2c branched from the oil passage L2a is connected to the pilot pressure oil chamber 22c.

[0045] The spool 3 that is slidably fitted in the spool chamber 20 has its first end 3a, which is one end in the longitudinal (axial) direction, inserted into the pilot pressure oil chamber 21c as a pressure-receiving part for receiving the pilot pressure in the pilot pressure oil chamber 21c, and its second end 3b, which is the other end in the longitudinal (axial) direction, inserted into the pilot pressure oil chamber 22c as a pressure-receiving part for receiving the pilot pressure in the pilot pressure oil chamber 22c.

[0046] Around the communication ports of the pilot pressure oil chambers 21c and 22c with the spool chamber 20, annular spring stoppers 6 are provided, and a spring 5 is interposed between the plug 7 and the spring stopper 6. On the outer peripheral part of the spool 3, a shoulder 3c corresponding to the spring stopper 6 in the pilot pressure oil chamber 21c is formed near the first end 3a, and a shoulder 3d corresponding to the spring stopper 6 in the pilot pressure oil chamber 22c is formed near the second end 3b.

[0047] The spool 3 is biased such that the first end 3a is biased toward the second end 3b by the spring 5 in the pilot pressure oil chamber 21c, and the second end 3b is biased toward the first end 3a by the spring 5 in the pilot pressure oil chamber 22c. The spool 3 is biased to the neutral position P10 by these two springs 5. When the spool 3 is in the neutral position P10, both shoulders 3c and 3d are in contact with the corresponding spring stoppers 6.

[0048] When the control valve V1 is in the neutral position P0, only the back pressure in the control valve V1 is applied to the hydraulic oil in the oil paths L1 and L2, and there is no hydraulic pressure sufficient to move the spool 3 against the spring 5 in either of the pilot pressure oil chambers 21c and 22c. Therefore, the counterbalance valve V2 (spool 3) is in the neutral position P10.

[0049] When the control valve V1 is switched from the neutral position P0 to the first-direction drive position P1, hydraulic oil is discharged from the first port V1a into the oil path L1a, and a part of it flows into the pilot pressure oil chamber 21 through the pilot pressure oil path L1c. As a result, the increased hydraulic pressure (pilot pressure) in the pilot pressure oil chamber 21 presses the first end 3a of the spool 3 toward the second end 3b side.

[0050] Meanwhile, at this time, the hydraulic pressure in oil passage L2a becomes negative relative to the hydraulic pressure in oil passage L1a, and an amount of hydraulic fluid from the pilot pressure oil chamber 22 corresponding to the pilot pressure applied from the pilot pressure oil chamber 21 is released through the spool 3 into oil passage L2a via the pilot pressure oil passage L2c.

[0051] As a result, the spool 3 slides in a direction that reduces the degree of penetration of the first end 3a into the pilot pressure oil chamber 21 and increases the degree of penetration of the second end 3b into the pilot pressure oil chamber 22. In other words, the spool 3 shifts from a neutral position P10 corresponding to the neutral position P0 of the control valve V1 to a first directional drive position P11 corresponding to the first directional drive position P1 of the control valve V1.

[0052] Within the first directional drive position P1, as the amount of operation (stroke) of the control valve V1, which is a proportional valve, increases from its neutral position, the amount of sliding movement (stroke) of the spool 3 from its neutral position P10 increases, and the degree to which the second end 3b of the spool 3 penetrates the pilot pressure oil chamber 22c increases. The amount of sliding movement (stroke) of the spool 3 from the neutral position P10 can be increased until the second end 3b of the spool 3 contacts the plug 7 that is blocking the pilot pressure oil chamber 22c. In other words, when the second end 3b contacts the plug 7, the stroke of the spool 3 in the first directional drive position P1 reaches its full stroke.

[0053] As a result of this sliding motion, the shoulder portion 3c on the first end 3a side detaches from the spring stopper 6 in the pilot pressure oil chamber 21c, while the spring stopper 6 in the pilot pressure oil chamber 22c remains in contact with the shoulder portion 3d on the second end 3b side and is pushed by the spool 3 against the spring 5, entering deeper into the pilot pressure oil chamber 22 together with the second end 3b of the spool 3.

[0054] When the control valve V1 switches from the neutral position P0 to the second directional drive position P2, the pilot pressure in the pilot pressure oil chamber 22c causes the spool 3 to slide in a direction that increases the degree of penetration of the first end 3a into the pilot pressure oil chamber 21c and decreases the degree of penetration of the second end 3b into the pilot pressure oil chamber 22c. In other words, the spool 3 shifts from the neutral position P10, which corresponds to the neutral position P0 of the control valve V1, to the second directional drive position P12, which corresponds to the second directional drive position P2 of the control valve V1.

[0055] In the second directional drive position P12, the amount of sliding movement (stroke) of the spool 3 from the neutral position P10 can be increased until the first end 3a of the spool 3 contacts the plug 7 that is blocking the pilot pressure oil chamber 21c and reaches the maximum amount of sliding movement (full stroke).

[0056] The flow of hydraulic fluid in the oil passages L1a, L2a and pilot pressure oil passages L1c and L2c, as well as the operation of the shoulders 3c and 3d, are the same as described above, and a detailed explanation will be omitted.

[0057] Furthermore, in the following description of the counterbalance valve V2, the flow of hydraulic fluid within the spool 3 when the control valve V1 switches from the neutral position P0 to the first direction drive position P1 will be described in detail by referring to the state of the spool 3 shown in Figures 2B to 2D. On the other hand, when the control valve V1 switches from the neutral position P0 to the second direction drive position P2, this is omitted in Figures 2B to 2D, and the illustrations and explanations for when the control valve V1 switches to the first direction drive position P1 should be used as a reference, and a detailed explanation may be omitted.

[0058] On the inner circumferential surface of the valve case 2 facing the portion of the spool chamber 20 closer to the pilot pressure oil chamber 21c than the longitudinal center, a pair of ports 21a and 21b are provided in parallel along the longitudinal direction of the spool chamber 20. The first port 21a, closer to the longitudinal center of the spool chamber 20, is connected to the oil passage L1a, and the second port 21b, closer to the pilot pressure oil chamber 21c, is connected to the oil passage L1b.

[0059] On the other hand, a pair of ports 31a and 31b are provided parallel to the longitudinal (axial) direction of the spool 3 at the portion of the spool 3 closer to the first end 3a than to the longitudinal (axial) center of the spool 3. The first port 31a, closer to the longitudinal (axial) center of the spool 3, is opened on the outer circumferential surface of the spool 3 to correspond to the first port 21a of the valve case 2, and the second port 31b, closer to the first end 3a, is opened on the outer circumferential surface of the spool 3 to correspond to the second port 21b of the valve case 2.

[0060] An axial hole is formed inside the portion of the spool 3 that is on the side of the first end 3a from the longitudinal (axial) center, connecting the first port 31a and the second port 31b. This axial hole serves as a communication passage 31c that allows oil flow to be transmitted between the first port 31a and the second port 31b.

[0061] Furthermore, a check valve 4 is fitted into the portion of the axial core hole, which serves as the communication passage 31c, on the side of the first end 3a, and is biased from the first end 3a toward the longitudinal center of the spool 3.

[0062] When the spool 3 is in the first directional drive position P11 (see Figure 2D, etc.), the check valve 4 opens due to the hydraulic pressure of the hydraulic fluid from port V1a of the control valve V1 flowing into the oil passage L1a and the first port 31a connected to the first port 21a, which are on the high-pressure side, and the communication passage 31c, thereby opening the communication passage 31c and allowing the high-pressure oil flow to pass through the oil passage L1b and the second port 31b connected to the second port 21b. Otherwise, the check valve 4 is closed, blocking the oil flow between the first port 31a and the second port 31b via the communication passage 31c.

[0063] Furthermore, a pair of ports 22a and 22b are provided on the inner circumferential surface of the valve case 2 facing the portion of the spool chamber 20 closer to the pilot pressure oil chamber 22c than the longitudinal center of the spool chamber 20, so as to be parallel to the longitudinal direction of the spool chamber 20. The third port 22a, closer to the longitudinal center of the spool chamber 20, is connected to the oil passage L2a, and the fourth port 22b, closer to the pilot pressure oil chamber 22c, is connected to the oil passage L2b.

[0064] On the other hand, a pair of ports 32a and 32b are provided parallel to the longitudinal (axial) direction of the spool 3 on the side of the second end 3b rather than the longitudinal (axial) center of the spool 3. The third port 32a, closer to the longitudinal (axial) center of the spool 3, is opened on the outer circumferential surface of the spool 3 to correspond to the third port 22a of the valve case 2, and the fourth port 32b, closer to the second end 3b, is opened on the outer circumferential surface of the spool 3 to correspond to the fourth port 22b of the valve case 2.

[0065] An axial hole is formed inside the portion of the spool 3 from the center in the longitudinal (axial) direction toward the second end 3b, extending along the axis of the spool 3 to connect the third port 32a and the fourth port 32b. This axial hole serves as a communication passage 32c that allows oil flow to be established between the third port 32a and the fourth port 32b.

[0066] Furthermore, a check valve 4 is fitted into the portion of the axial core hole, which serves as the communication passage 32c, on the side of the second end 3b, and is biased from the second end 3b toward the longitudinal center of the spool 3.

[0067] When the spool 3 is in the second direction drive position P12 (see Figures 2D and 4E, etc.), the check valve 4 opens due to the hydraulic pressure of the hydraulic fluid flowing from port V1b of the control valve V1 into the oil passage L2a, the third port 32a connected to the third port 22a, and the communication passage 32c, which are on the high-pressure side. This opens the communication passage 32c, allowing the high-pressure oil flow to pass through the oil passage L2b to the fourth port 32b, which is connected to the fourth port 22b. Otherwise, the check valve 4 is closed, blocking the oil flow between the third port 32a and the fourth port 32b via the communication passage 32c.

[0068] Furthermore, a tank port 23 is provided on the inner circumferential surface of the valve case 2 facing the longitudinal central portion of the spool chamber 20 between the first port 21a and the third port 22a. Meanwhile, an anticavitation valve V3, which is a spool valve as shown in Figure 1, is provided inside the valve case 2, and the tank port 23 and the anticavitation valve V3 are connected via an anticavitation oil passage L5.

[0069] Referring to Figure 1, etc., the spool 8 of the anti-cavitation valve V3 is switched between a neutral position P20 corresponding to the neutral position P0 of the control valve V1, a first directional drive position P21 corresponding to the first directional drive position P1 of the control valve V1, and a second directional drive position P22 corresponding to the second directional drive position P2 of the control valve V1.

[0070] The anti-cavitation valve V3 closes in the neutral position P20, discharges a portion of the hydraulic fluid in the high-pressure oil passage L1a to the anti-cavitation oil passage L5 in the first directional drive position P21, and discharges a portion of the hydraulic fluid in the high-pressure oil passage L2a to the anti-cavitation oil passage L5 in the second directional drive position P22.

[0071] Furthermore, the tank port 23 communicates with the communication passage 31c inside the spool 3 of the counterbalance valve V2 at the first directional drive position P11, bypassing the check valve 4 on the first end 3a side, and is capable of receiving a portion of the hydraulic fluid in the high-pressure oil passage L1a even through the communication passage 31c inside the spool 3.

[0072] Furthermore, the tank port 23 is connected to the communication passage 32c inside the spool 3 of the counterbalance valve V2 at the second direction drive position P12, bypassing the check valve 4 on the second end 3b side, and is capable of receiving a portion of the hydraulic fluid in the high-pressure oil passage L2a via the communication passage 32c inside the spool 3.

[0073] Furthermore, referring to Figure 5B, the counterbalance valve V2 in the neutral position P10 may be configured such that the hydraulic fluid in the tank port 23 passes through the spool 3 and is discharged to the hydraulic fluid tank T.

[0074] Also, referring to Figure 5B, the hydraulic fluid in the anti-cavitation oil passage L5 may be supplied to the hydraulic cylinder, which is a hydraulic actuator 103 for switching the brake 102 on and off, provided on the output shaft of the hydraulic motor M, via the throttled actuator oil passage L5a.

[0075] Referring to Figure 5B, the output shaft of the hydraulic motor M for travel is driven and connected to the drive wheels (tires, or crawler drive wheels, etc.) of the work machine 100. It may be directly connected to the drive wheels, or it may be connected to the drive wheels via a reduction mechanism 101 as shown in the figure, without being directly connected to the drive wheels. Possible reduction mechanisms 101 include gear-type transmission mechanisms and endless belt (belt, chain, etc.) type transmission mechanisms.

[0076] The flow of hydraulic fluid in oil passages L1 and L2 using the counterbalance valve V2 having the basic configuration described above will be explained.

[0077] Referring to Figures 2B, 3A, and 4A, when the spool 3 is in the neutral position P10 corresponding to the neutral position P0 of the control valve V1, the first port 31a is in communication with the first port 21a, the second port 31b is in communication with the second port 21b, the third port 32a is in communication with the third port 22a, and the fourth port 32b is in communication with the fourth port 22b. At this time, back pressure oil, which is the hydraulic fluid with back pressure from the control valve V1, flows into the first port 31a and the third port 32a, but both check valves 4 close against the hydraulic pressure (back pressure) of this back pressure oil, blocking the communication passages 31c and 32c, and the counterbalance valve V2 is in a state of dividing the oil passages L1 and L2.

[0078] Referring to Figures 2D, 3C, and 4D, when the spool 3 is in the first directional drive position P11 (full stroke) corresponding to the first directional drive position P1 of the control valve V1, with respect to the high-pressure oil passage L1, the first port 31a of the spool 3 communicates with the first port 21a, and the second port 31b communicates with the second port 21b. The check valve 4 on the first end 3a side opens due to the hydraulic pressure of the high-pressure hydraulic fluid flowing from the oil passage L1a to the first port 31a, so that the hydraulic fluid flows from the oil passage L1a to the oil passage L1b via the communication passage 31c inside the spool 3 and flows into port Ma of the hydraulic motor M.

[0079] On the other hand, with respect to the low-pressure oil passage L2, the fourth port 32b of the spool 3 is positioned further towards the pilot pressure oil chamber 22c than the fourth port 22b, but the third port 32a communicates with both the third port 22a and the fourth port 22b. As a result, the hydraulic fluid that flows from port Mb of the hydraulic motor M to the fourth port 22b via oil passage L2b flows through the third port 32a along the outer circumference of the spool 3 to the third port 22a and oil passage L2a, bypassing the check valve 4 on the second end 3b side, and is returned to port V1b of the control valve V1.

[0080] Furthermore, a barrier is formed in the third port 32a that acts as an obstacle to the oil flow from the fourth port 22b to the third port 22a. This reduces the flow velocity of the oil flow in the low-pressure oil passage L2, thereby preventing runaway of work equipment and other devices that are driven by the rotation of the hydraulic motor M on downhill slopes.

[0081] Referring to Figure 4E, when the spool 3 is in the second direction drive position P12 (full stroke), which corresponds to the second direction drive position P2 of the control valve V1, the third port 32a of the spool 3 communicates with the third port 22a and the fourth port 32b communicates with the fourth port 22b with respect to the high-pressure oil passage L2. The check valve 4 on the second end 3b side opens due to the hydraulic pressure of the high-pressure hydraulic fluid flowing from the oil passage L2a to the third port 32a. As a result, hydraulic fluid flows from the oil passage L2a to the oil passage L2b via the communication passage 32c inside the spool 3 and flows into port Mb of the hydraulic motor M.

[0082] On the other hand, with respect to the low-pressure oil passage L1, the second port 31b of the spool 3 is positioned further towards the pilot pressure oil chamber 21c than the second port 21b, but the first port 31a communicates with both the first port 21a and the second port 21b. As a result, the hydraulic fluid that flows from port Ma of the hydraulic motor M to the second port 21b via oil passage L1b flows into the first port 21a and oil passage L1a via the first port 31a along the outer circumference of the spool 3, bypassing the check valve 4 on the first end 3a side, and is returned to port V1a of the control valve V1.

[0083] Furthermore, a barrier is formed in the first port 31a that acts as an obstacle to the oil flow from the second port 21b to the first port 21a. This reduces the flow velocity of the oil in the low-pressure oil passage L1, thereby preventing runaway of work equipment and other devices that are driven by the rotation of the hydraulic motor M on downhill slopes.

[0084] As variations of the counterbalance valve V2 having the basic configuration described above, counterbalance valves V2a, V2b, and V2c, which have a warm-up oil passage in the spool 3, will be described.

[0085] First, as a common configuration for counterbalance valves V2a, V2b, and V2c, the tank port 23 is formed circumferentially at the longitudinal (axial) center of the spool chamber 20 within the valve case 2. A hydraulic oil tank (reservoir tank) T is provided inside or outside the hydraulic motor unit 10, and at least a portion of the tank oil passage L3 connected to the hydraulic oil tank T is configured inside the valve case 2 and connected to the tank port 23. In this way, the counterbalance valves V2 (V2a to V2c) are capable of discharging the hydraulic oil that flows into the tank port 23 to the hydraulic oil tank T via the tank oil passage L3.

[0086] Furthermore, the tank oil passage L3 does not need to reach the hydraulic oil tank T, but only needs to reach a low-pressure region that is lower than the back pressure of the control valve V1, which is the hydraulic pressure of the back pressure oil flowing into the tank port 23.

[0087] The counterbalance valve V2a shown in Figures 1 and 2A to 2D will now be described. A pair of tank ports 33a and 33b are provided in the longitudinal (axial) center of the spool 3, corresponding to the tank port 23 of the valve case 2. The tank ports 33a and 33b are arranged in parallel in the longitudinal direction of the spool 3, with tank port 33a located on the first end 3a side and tank port 33b located on the second end 3b side.

[0088] A pair of warm-up oil passages 34a and 34b, which are orifices, are provided inside the spool 3. The warm-up oil passage 34a connects the communication passage 31c, which is the axial hole in the first end 3a side portion of the spool 3, to the tank port 33a on the second end 3b side, and the warm-up oil passage 34b connects the communication passage 32c, which is the axial hole in the second end 3b side portion of the spool 3, to the tank port 33b on the first end 3a side.

[0089] Referring to Figures 2A and 2B, when the spool 3 is in the neutral position P10 corresponding to the neutral position P0 of the control valve V1, the tank port 33b on the first end 3a (oil passage L1) side communicates with the portion of the tank port 23 on the pilot pressure oil chamber 21c side, and the tank port 33a on the second end 3b (oil passage L2) side communicates with the portion of the tank port 23 on the pilot pressure oil chamber 22c side.

[0090] Therefore, of the back pressure oil from the control valve V1 that flows into the spool 3 in the neutral position P10, the portion that flows into the first port 31a gradually flows out to the tank port 23 via the communication passage 31c, the warm-up oil passage 34a, and the tank port 33a, while the portion that flows into the third port 32a gradually flows out to the tank port 23 via the communication passage 32c, the warm-up oil passage 34b, and the tank port 33b.

[0091] Then, the back pressure oil, which has already been heated on the control valve V1 side, is partially discharged through the warming oil passages 34a and 34b, which are orifices. This acts as a priming agent, causing the entire back pressure oil in the oil passages L1a and L2a to flow slowly into the spool 3, transferring its heat to the spool 3, and further transferring it to the valve case 2 via the spool 3. As a result, even if the hydraulic motor M of the hydraulic motor unit 10 is held in a neutral state for a long time in a cold environment, the spool 3 and valve case 2 included in the hydraulic circuit structure 1 are warmed by the heat of the back pressure oil during that time. This prevents the occurrence of a heat shock within the hydraulic circuit structure 1 when high-temperature, high-pressure hydraulic oil flows into the spool 3 to start driving the hydraulic motor M.

[0092] Furthermore, the warm-up oil passage 34a connects the communication passage 31c on the first end 3a side to the tank port 33a on the second end 3b side, rather than the tank port 33b on the first end 3a side, and the warm-up oil passage 34b connects the communication passage 32c on the second end 3b side to the tank port 33b on the first end 3a side, rather than the tank port 33a on the second end 3b side. As a result, the warm-up oil passages 34a and 34b are long enough to ensure that the heat of the back pressure oil passing through them is reliably transferred to the spool 3 as a warm-up effect.

[0093] Furthermore, since the warm-up oil passage 34a connects the communication passage 31c on the first end 3a side to the tank port 33a on the second end 3b side, and the warm-up oil passage 34b connects the communication passage 32c on the second end 3b side to the tank port 33b on the first end 3a side, as soon as the spool 3 starts to shift from the neutral position P10 to the first direction drive position P11 or the second direction drive position P12, the tank port 33a or 33b, which is connected to the high-pressure oil passage L1a or L2a via the warm-up oil passage 34a or 34b, separates from the tank port 23. This prevents the hydraulic fluid from the high-pressure oil passage L1a or L2a flowing into the first port 31a or the third port 32a from flowing out to the tank port 23, thereby allowing the hydraulic motor M to be supplied with the target flow rate of hydraulic fluid without leakage.

[0094] For example, referring to Figure 2C, when the control valve V1 switches from the neutral position P0 to the first direction drive position P1, the moment the spool 3 begins to move from the neutral position P10 to the first direction drive position P11 on the second end 3b side (pilot pressure oil chamber 22c side), the tank port 33a on the second end 3b side, which was in communication with the pilot pressure oil chamber 22c side portion of the tank port 23, separates from the tank port 23, and the oil flow from the tank port 33a to the tank port 23, which is connected via the high-pressure oil passage L1a and the warm-up oil passage 34a, is cut off.

[0095] On the other hand, the tank port 33a or 33b, which is connected to the low-pressure side (which supplies hydraulic fluid from the hydraulic motor M to the control valve V1) via the warm-up oil passage 34a or 34b, is in communication with the tank port 23 from the moment the spool 3 starts moving from the neutral position P10 until it passes between one end and the other end of the tank port 23 in the longitudinal direction of the spool 3.

[0096] For example, referring to Figure 2C, when the control valve V1 switches from the neutral position P0 to the first direction drive position P1, the tank port 33b, which is connected to the low-pressure oil passage L2a via the warm-up oil passage 34b, is in communication with the tank port 23 from the time the spool 3 starts moving from the neutral position P10 until it passes between one end and the other end of the tank port 23 in the longitudinal direction of the spool 3.

[0097] Thus, with respect to the hydraulic fluid in the low-pressure oil passage L1a or L2a, it is acceptable for a portion of it to leak to the tank port 23 and tank oil passage L3 via the warm-up oil passage 34a or 34b and the tank port 33a or 33b for a while. In other words, the configuration in which the warm-up oil passage 34a connects the communication passage 31c on the first end 3a side to the tank port 33a on the second end 3b side, and the warm-up oil passage 34b connects the communication passage 32c on the second end 3b side to the tank port 33b on the first end 3a side, does not cause any problems with the low-pressure oil passage L1 or L2 when the spool 3 starts shifting from the neutral position P10 to the first direction drive position P11 or the second direction drive position P12.

[0098] In the embodiment shown in Figure 1, the tank port 23 is connected to the hydraulic oil tank T via the tank oil passage L3. Because the hydraulic pressure in the hydraulic oil tank T is lower than the back pressure of the control valve V1, the back pressure oil flowing from the warm-up oil passages 34a and 34b into the tank port 23 is discharged to the hydraulic oil tank T via the tank oil passage L3. However, the back pressure oil after passing through the warm-up oil passages 34a and 34b only needs to be discharged into a low-pressure region that is lower than the said back pressure, and the hydraulic oil tank T is included in this low-pressure region.

[0099] Next, the counterbalance valve V2b shown in Figures 3A to 3D will be described. Note that parts with the same configuration and reference numerals as the counterbalance valve V2a shown in Figures 1 and 2A to 2D, as well as parts with the same functions and operations, may be omitted from the explanation. In addition, the state of the spool 3 when switching to the second direction drive position P12 may be explained by referring to the state of the spool 3 when switching to the first direction drive position P11 in Figures 3B to 3D.

[0100] In the counterbalance valve V2b, a single tank port 33 is provided in the longitudinal (axial) center of the spool 3, corresponding to the tank port 23 of the valve case 2. In other words, the pair of tank ports 33a and 33b in the counterbalance valve V2a are integrated into a single tank port 33 in the counterbalance valve V2b. This single tank port 33 is connected to the communication passage 31c on the oil passage L1a side via the warm-up oil passage 34a within the spool 3, and to the communication passage 32c on the oil passage L2a side via the warm-up oil passage 34b.

[0101] Referring to Figure 3A, when the spool 3 is in the neutral position P10 corresponding to the neutral position P0 of the control valve V1, the tank port 33 communicates with the central portion of the tank port 23 in the longitudinal direction of the spool chamber 20.

[0102] As a result, the back pressure oil in the first port 31a and third port 32a of the spool 3 in the neutral position P10 is gradually discharged to the tank port 33 and tank port 23 via the warming oil passage 34a and warming oil passage 34b. This causes the back pressure oil in the oil passages L1a and L2a to flow slowly into the first port 31a and third port 32a, thereby transferring the heat of the back pressure oil to the spool 3.

[0103] Thus, even when the spool 3 is in the neutral position P10 and is connected to one tank port 33 located at a position that communicates with the central part of the tank port 23 in the longitudinal direction of the spool chamber 20, warm-up oil passages 34a and 34b of sufficient length to reduce the flow velocity of the back pressure oil discharged in order to gradually transfer the heat of the back pressure oil to the spool 3 can be configured within the spool 3.

[0104] When the spool 3 is in the neutral position P10, the tank port 33, which communicates with the central part of the tank port 23, is at a slight distance from both the end of the tank port 23 on the pilot pressure oil chamber 21c side and the end of the tank port 23 on the pilot pressure oil chamber 22c side, in the longitudinal (axial) direction of the spool 3.

[0105] Therefore, referring to Figure 3B, when the spool 3 begins to shift from the neutral position P10 to, for example, the first direction drive position P11, communication between the tank port 33 and the tank port 23 is maintained as long as the amount of sliding of the spool 3 is less than the said distance, and leakage of hydraulic fluid from the high-pressure oil passage L1a or L2a through the warm-up oil passage 34a or 34b continues during this time.

[0106] However, since this distance is approximately half the distance between the ends of the tank port 23 in the longitudinal direction of the spool chamber 20, the period from when the counterbalance valve V2b starts shifting the spool 3 from the neutral position P10 to when the tank port 33 is in communication with the tank port 23 can be made shorter than the period from when the counterbalance valve V2a starts shifting the spool 3 from the neutral position P10 to when the tank port 33a or 33b, which is in communication with the low-pressure oil passage L1a or L2a via the warm-up oil passage 34a or 34b, is in communication with the tank port 23.

[0107] Referring to Figure 3C, the moment the sliding amount of the spool 3 from the neutral position P10 exceeds the aforementioned distance (i.e., when the minimum stroke is operated in the first direction drive position P11 or the second direction drive position P12), the tank port 33 separates from the tank port 23, and the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L1 or L2a, and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L1 or L2a, are carried out without leakage to the tank port 23 via the warm-up oil passages 34a and 34b.

[0108] Referring to Figure 3D, in the spool 3 during full-stroke operation at the first direction drive position P11 or the second direction drive position P12, the tank port 33 is not in communication with the tank port 23. As described above, the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L1 or L2, and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L1 or L2, are performed without leakage to the tank port 23 via the warm-up oil passages 34a and 34b.

[0109] Furthermore, in the case of the counterbalance valve V2b, if only one of the warm-up oil passages 34a and 34b is provided, and the inflow of back-pressure oil through only one of the oil passages L1a and L2a is sufficient to transfer enough heat from the back-pressure oil to the spool 3 to suppress thermal shock, then only one of them may be provided on the spool 3.

[0110] Next, the counterbalance valve V2c shown in Figures 4A to 4E will be described. Note that parts with the same configuration and the same reference numerals as the counterbalance valves V2a and V2b shown in Figures 1 to 3D, as well as parts with the same functions and operations, may be omitted from the explanation. In addition, the state of the spool 3 when switching to the second direction drive position P12 may be explained by referring to the state of the spool 3 when switching to the first direction drive position P11 in Figures 4B and 4C.

[0111] In the counterbalance valve V2c, a labyrinth port 35, where oil flow tends to accumulate, is provided as a warm-up oil passage at the longitudinal (axial) center of the spool 3, corresponding to the tank port 23 of the valve case 2. Furthermore, one of the axial holes, which serves as a communication passage 31c in the first end 3a side of the spool 3 and the axial hole, which serves as a communication passage 32c in the second end 3b side of the spool 3, is extended further toward the longitudinal center of the spool 3 and connected to the labyrinth port 35.

[0112] In the counterbalance valve V2c shown in Figures 4A to 4E, the axial hole serving as the communication passage 31c in the first end 3a portion of the spool 3, which is on the oil passage L1 side, is extended to the longitudinal center of the spool 3 and serves as the communication passage 31d connected to the labyrinth port 35. Alternatively, the axial hole serving as the communication passage 32c in the second end 3b portion of the spool 3, which is on the oil passage L2 side, may be extended to the longitudinal center of the spool 3 and connected to the labyrinth port 35.

[0113] The following describes the state of the counterbalance valve V2c at the neutral position P10, the first direction drive position P11, and the second direction drive position P12, assuming that the communication passage 31c on the first end 3a side of the spool 3 is extended to become the communication passage 31d.

[0114] Referring to Figure 4A, when the spool 3 is in the neutral position P10 corresponding to the neutral position P0 of the control valve V1, the labyrinth port 35 communicates with the central part of the tank port 23 in the longitudinal direction of the spool chamber 20.

[0115] As a result, the back pressure oil at the first port 31a of the spool 3 in the neutral position P10 flows out to the labyrinth port 35 and the tank port 23 via the connecting passage 31d. At the labyrinth port 35, the flow velocity of the back pressure oil flowing out to the tank port 23 is reduced, causing the back pressure oil in the oil passage L1a to flow slowly into the first port 31a, and its heat is transferred to the spool 3.

[0116] When the spool 3 is in the neutral position P10, the labyrinth port 35, which communicates with the central part of the tank port 23, is at a slight distance from both the end of the tank port 23 on the pilot pressure oil chamber 21c side and the end of the tank port 23 on the pilot pressure oil chamber 22c side, in the longitudinal (axial) direction of the spool 3.

[0117] Therefore, referring to Figure 4B, when the spool 3 begins to shift from the neutral position P10 to the first direction drive position P11, as long as the amount of sliding of the spool 3 is less than the distance to the end of the tank port 23 on the pilot pressure oil chamber 22c side, communication between the labyrinth port 35 and the tank port 23 is maintained, and leakage continues from the first port 31a, which is connected to the oil passage L1a that is on the higher pressure side than the oil passage L2a, to the tank port 23 via the communication passage 31c and the labyrinth port 35.

[0118] Similarly, when the spool 3 begins to shift from the neutral position P10 to the second direction drive position P12, as long as the amount of sliding of the spool 3 is less than the distance to the end of the tank port 23 on the pilot pressure oil chamber 21c side, communication between the labyrinth port 35 and the tank port 23 is maintained, and leakage continues from the first port 31a, which is connected to the oil passage L1a that is at a lower pressure than the oil passage L2a, to the tank port 23 via the communication passage 31c and the labyrinth port 35.

[0119] Referring to Figure 4C, as soon as the amount of sliding of the spool 3 during switching from the neutral position P10 to the first direction drive position P11 exceeds the aforementioned distance (i.e., as soon as it enters the first direction drive position P11), the labyrinth port 35 separates from the tank port 23, and without causing leakage from the first port 31a to the tank port 23 via the communication passage 31c and the labyrinth port 35, the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L1 and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L2 are performed.

[0120] The same applies when the counterbalance valve V2c switches from the neutral position P10 to the second direction drive position P12. As soon as the sliding amount of the spool 3 exceeds the aforementioned distance (i.e., when it enters the second direction drive position P12), the labyrinth port 35 separates from the tank port 23, and without causing leakage from the first port 31a to the tank port 23 via the communication passage 31c and the labyrinth port 35, the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L2 and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L1 are performed.

[0121] Referring to Figure 4D, in the spool 3 during full stroke operation at the first directional drive position P11, the labyrinth port 35 is not in communication with the tank port 23. As described above, without leakage from the first port 31a to the tank port 23 via the communication passage 31c and the labyrinth port 35, the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L1, and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L2 are performed.

[0122] Referring to Figure 4E, in the spool 3 during full stroke operation at the second direction drive position P12, the labyrinth port 35 is not in communication with the tank port 23. As described above, without leakage from the first port 31a to the tank port 23 via the communication passage 31c and the labyrinth port 35, the transfer of hydraulic fluid from the control valve V1 side to the hydraulic motor M side via the spool 3 in the high-pressure oil passage L2, and the transfer of hydraulic fluid from the hydraulic motor M side to the control valve V1 side via the spool 3 in the low-pressure oil passage L1 are performed.

[0123] Next, with reference to Figures 5A to 7, an embodiment of the hydraulic circuit structure 1 in which a warm-up oil passage is provided in a portion of the counterbalance valve V2 other than the spool 3 will be described.

[0124] In the hydraulic circuit structure 1 shown in Figure 5A, a spool valve having a spool 8 as an anti-cavitation valve V3a is provided inside the valve case 2. Also, a pair of restricting oil passages (orifices) connected to the anti-cavitation valve V3a are provided inside the valve case 2 as warm-up oil passages L4a and L4b.

[0125] The spool 8 of the anti-cavitation valve V3a has connecting passages 8a and 8b that open when the control valve V1 is in a neutral position P20, which corresponds to the neutral position P0. When the control valve V1 is in the neutral position P0 and the counterbalance valve V2 is in the neutral position P10, the back pressure oil in the oil passage L1a flows into the warm-up oil passage L4a via the connecting passage 8a, and the back pressure oil in the oil passage L2a flows into the warm-up oil passage L4b via the connecting passage 8b.

[0126] As the back pressure oil is discharged to the hydraulic oil tank T via the warm-up oil passages L4a and L4b, which are orifices, the back pressure oil in the oil passages L1a and L2a flows slowly, and as it passes through the connecting passages 8a and 8b, the heat of the back pressure oil is transferred to the spool 8 of the anti-cavitation valve V3a. Furthermore, this heat is transferred to the valve case 2, which warms the valve case 2, and eventually the spool 3 of the counterbalance valve V2 inside the valve case 2 is also warmed.

[0127] In Figure 5A, the warm-up oil passages L4a and L4b are shown reaching the hydraulic oil tank T, but they do not need to reach the hydraulic oil tank T; any passage that reaches a pressure lower than the back pressure of the control valve V1, which is the hydraulic pressure of the back pressure oil, is acceptable. This also applies to the warm-up oil passages L4a and L4b in the embodiments shown in Figures 5B, 6, and 7.

[0128] Figure 5B shows an example of a modification of the hydraulic circuit structure 1 shown in Figure 5A. Specifically, the hydraulic circuit structure 1 in Figure 5B is configured to utilize the oil discharged from the anticavitation valve V3a to the anticavitation oil passage L5 as the hydraulic fluid for the hydraulic actuator 103 for the brake 102. Furthermore, the oil in the anticavitation oil passage L5 is either discharged to the hydraulic fluid tank T via the spool 3 of the counterbalance valve V2 in the neutral position P10, or merged with the oil flow in the high-pressure side communication passage 31c or 32c within the spool 3 in the first direction drive position P11 or the second direction drive position P12. These configurations have been described above and will not be described in detail here.

[0129] In the hydraulic circuit structure 1 shown in Figure 6, a pair of throttling oil passages (orifices) serving as warm-up oil passages L4a and L4b are provided within the valve case 2. Furthermore, a spool valve V4, separate from the counterbalance valve V2 and the anti-cavitation valve V3a (V3), is provided to introduce back pressure oil from oil passages L1a and L2a when the control valve V1 is in the neutral position P0 into the warm-up oil passages L4a and L4b.

[0130] The spool valve V4 includes a spool 9 that switches between a neutral position P20, a first-direction drive position P21, and a second-direction drive position P22 in response to the switching of the control valve V1 to a neutral position P0, a first-direction drive position P1, and a second-direction drive position P2. The spool 9 is provided with connecting passages 9a and 9b that open when the spool 9 is in the neutral position P20 and close when it is in the first-direction drive position P21 or the second-direction drive position P22.

[0131] When the control valve V1 is in the neutral position P0, the spool 3 of the counterbalance valve V2 is positioned in the neutral position P10, the spool 9 of the anticavitation valve V3a is positioned in the neutral position P20, and the spool 9 of the spool valve V4 is positioned in the neutral position P30. In this state, the back pressure oil in the oil passage L1a flows into the warm-up oil passage L4a via the connecting passage 8a of the spool 8 and the connecting passage 9a of the spool 9, and the back pressure oil in the oil passage L2a flows into the warm-up oil passage L4b via the connecting passage 8b of the spool 8 and the connecting passage 9b of the spool 9. As the back pressure oil is discharged through the warm-up oil passages L4a and L4b, which are orifices, the back pressure oil in the oil passages L1a and L2a flows slowly, transferring its heat to the spools 8 and 9 as it passes through them, and further transferring it to the valve case 2, thereby warming up the hydraulic circuit structure 1.

[0132] In the hydraulic circuit structure 1 shown in Figure 7, similar to the hydraulic circuit structure 1 in Figure 6, a counterbalance valve V2 having a spool 3, a pair of throttling oil passages (orifices) serving as warm-up oil passages L4a and L4b, and a spool valve V4 having a spool 9 connected to the warm-up oil passages L4a and L4b are provided inside the valve case 2.

[0133] On the other hand, in the hydraulic circuit structure 1 of Figure 7, a pair of poppet valves (check valves) V3b, each having a poppet 11, are provided in the valve case 2 as an anti-cavitation valve V3. The pair of poppet valves V3b are connected to oil passages L1a and L2a in the valve case 2, respectively. Of the oil passages L1a and L2a, the poppet valve V3b connected to the oil passage L1a or L2a that becomes high-pressure when the control valve V1 is switched to the first directional drive position P1 or the second directional drive position P2 opens, and a portion of the high-pressure oil in the oil passage L1a or L2a is discharged into the anti-cavitation oil passage L5.

[0134] When the control valve V1 is in the neutral position P0 and the counterbalance valve V2 is in the neutral position P10, the back pressure oil in oil passages L1a and L2a flows out through both poppet valves V3b, the oil passage from both poppet valves V3b to the anticavitation oil passage L5, and the anticavitation oil passage L5, bypassing the spool valve V4's spool 9, and flows into the warm-up oil passages L4a and L4b via the communication passages 9a and 9b. As the back pressure oil is discharged through the warm-up oil passages L4a and L4b, which are orifices, the back pressure oil in oil passages L1a and L2a flows slowly, transferring its heat to the spool 9 as it passes through it, and further transferring it to the valve case 2, thereby warming up the hydraulic circuit structure 1.

[0135] The specific configurations of the hydraulic circuit structure 1, hydraulic motor unit (hydraulic actuator unit) 10, and work machine 100 have been described above. Next, the effects of some of the configurations of the hydraulic circuit structure 1, hydraulic actuator unit 10, and work machine 100 will be explained.

[0136] (Item 1) A hydraulic circuit structure 1 comprising a hydraulic circuit for supplying hydraulic fluid from a control valve V1 to a hydraulic actuator M, and warm-up oil passages 34a, 34b, 35, L4a, L4b, wherein when the control valve V1 is in a neutral position P0 for neutralizing the hydraulic actuator M, the back-pressure oil, which is hydraulic fluid with back pressure added from the control valve V1 that flows into the hydraulic circuit, is discharged through the warm-up oil passages 34a, 34b, 35, L4a, L4b to a low-pressure region lower than the back pressure.

[0137] The hydraulic circuit structure 1 related to item 1 discharges back pressure oil into the low-pressure region via warm-up oil passages 34a, 34b, 35, L4a, and L4b while the hydraulic actuator M is in a neutral state. This warms the hydraulic circuit structure 1 itself with the flow of back pressure oil, preventing heat shock (malfunction) of valve spools and other components in the hydraulic circuit structure 1 even when high-temperature hydraulic fluid flows in at the start of operation of the hydraulic actuator M in a cold environment.

[0138] (Item 2) The hydraulic circuit structure 1 according to Item 1, wherein the hydraulic circuit comprises at least one oil flow control valve V2, V3, V4, and the warm-up oil passages 34a, 34b, 35, L4a, L4b discharge the back pressure oil passing through the oil flow control valves V2, V3, V4 to the low-pressure region when the oil flow control valves V2, V3, V4 are in positions P10, P20 corresponding to the neutral position P0 of the control valve V1.

[0139] The hydraulic circuit structure 1 related to item 2 uses oil flow control valves V2, V3, and V4 as means for introducing back pressure oil from control valve V1 into warm-up oil passages 34a, 34b, 35, L4a, and L4b. This allows the back pressure oil to be smoothly guided into the warm-up oil passages 34a, 34b, 35, L4a, and L4b, enabling efficient warm-up.

[0140] (Item 3) The hydraulic circuit structure 1 according to Item 2, wherein the hydraulic circuit is equipped with a counterbalance valve V2 as the oil flow control valve, and the warm-up oil passages 34a, 34b, and 35 are provided on the spool 3 of the counterbalance valve V2.

[0141] The hydraulic circuit structure 1 related to item 3 is equipped with a spool 3 for a counterbalance valve V2 that is intended to prevent heat shock. Since the spool 3 is provided with warming oil passages 34a, 34b, and 35, the heat of the back pressure oil that flows into the spool 3, which is primed by the discharge of the warming oil passages 34a, 34b, and 35, is directly transferred to the spool 3, enabling efficient and highly effective warming. Furthermore, since no additional members are required, the compactness of the hydraulic circuit structure 1 can be maintained. In addition, the spool 3 equipped with the warming oil passages 34a, 34b, and 35 can be widely provided as a spool 3 that is less prone to heat shock.

[0142] (Item 4) The hydraulic circuit structure 1 according to Item 2, wherein the hydraulic circuit is equipped with an anti-cavitation valve V3 as the oil flow control valve, and when the anti-cavitation valve V3 is in position P20 corresponding to the neutral position P0 of the control valve V1, it allows the back pressure oil to pass through and discharges it to the warm-up oil passages L4a and L4b.

[0143] In the hydraulic circuit structure 1 related to item 4, the warm-up oil passages L4a and L4b can be constructed relatively easily by, for example, machining the valve case 2 that constitutes the hydraulic circuit, compared to constructing them by machining the spool 3, etc., and the existing anti-cavitation valve V3 can be used as a means of introducing back pressure oil into the warm-up oil passages L4a and L4b. Furthermore, if the anti-cavitation valve V3 is a spool valve, the back pressure oil can directly heat the spool as it passes through it. In this way, a hydraulic circuit structure 1 that is less prone to thermal shock can be provided economically.

[0144] (Item 5) The hydraulic circuit structure 1 according to Item 2, wherein the oil flow control valve V4 opens only when the control valve V1 is in the neutral position P0, and the back pressure oil flows out to the warm-up oil passages L4a and L4b.

[0145] The hydraulic circuit structure 1 relating to item 4 can use an oil flow control valve V4, which has a relatively simple structure in which the control valve V1 opens only when it is in the neutral position P0, as a means for introducing back pressure oil into the warm-up oil passages L4a and L4b, and thus can easily provide a hydraulic circuit structure 1 that is less prone to thermal shock.

[0146] (Item 6) The hydraulic circuit structure according to Item 5, wherein the hydraulic circuit comprises the oil flow control valve V4 in addition to the counterbalance valve V2 and the anticavitation valve V3.

[0147] The hydraulic circuit structure 1 related to item 6 can easily provide a means for introducing back pressure oil into warm-up oil passages L4a and L4b by simply adding another oil flow control valve V4 without requiring any special processing to the existing counterbalance valve V2 and anti-cavitation valve V3, thereby providing a hydraulic circuit structure 1 that is less prone to thermal shock.

[0148] (Item 7) A hydraulic actuator unit 10 comprising the hydraulic circuit structure 1 described in any one of items 1 to 6 and the hydraulic actuator M.

[0149] The hydraulic actuator unit 10 relating to item 7, by including the hydraulic circuit structure 1, eliminates the concern of thermal shock even when high-temperature hydraulic fluid is supplied to the hydraulic circuit structure 1 from the control valve V1 in cold regions. As a result, the hydraulic actuator can be driven with hydraulic fluid heated to a desired level in terms of the responsiveness of the valve, etc., and the hydraulic actuator unit 10 can be provided that can maximize the performance of the hydraulic actuator M.

[0150] (Item 8) A work machine 100 comprising the hydraulic circuit structure 1 described in any one of items 1 to 7 and the hydraulic actuator M.

[0151] The work machine 100 relating to item 8, by being equipped with the hydraulic circuit structure 1, eliminates the concern of thermal shock even when high-temperature hydraulic fluid is supplied to the hydraulic circuit structure 1 from the control valve V1 in cold regions. Therefore, the hydraulic equipment, including the hydraulic actuators, provided in the work machine 100 can be operated with hydraulic fluid heated to a desired level in terms of the responsiveness of the valves, etc., and the work machine 100 can be provided that can maximize the performance of the hydraulic equipment.

[0152] While embodiments of the present invention have been described above, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended to be included.

[0153] 1 Hydraulic circuit structure 2 Valve case 3 Spool (of counterbalance valve V2) 8 Spool (of anticavitation valve V3) 9 Spool (of spool valve V4) 34a Warm-up oil passage 34b Warm-up oil passage 35 Labyrinth port (warm-up oil passage) L4a Warm-up oil passage L4b Warm-up oil passage P0 Neutral position (of control valve V1) P10 Neutral position (of counterbalance valve V2) P20 Neutral position (of anticavitation valve V3) P30 Neutral position (of spool valve V4) V1 Control valve V2 Counterbalance valve (oil flow control valve) V2a Counterbalance valve (with warm-up oil passage on spool 3) V2b Counterbalance valve (with warm-up oil passage on spool 3) V2c Counterbalance valve (with warm-up oil passage on spool 3) V3 Anti-cavitation valve (oil flow control valve) V4 Spool valve (oil flow control valve)

Claims

1. A hydraulic circuit structure comprising a hydraulic circuit for supplying hydraulic fluid from a control valve to a hydraulic actuator, and a warm-up oil passage, wherein when the control valve is in a neutral position for neutralizing the hydraulic actuator, the back-pressure oil, which is hydraulic fluid with back pressure added from the control valve flowing into the hydraulic circuit, is discharged through the warm-up oil passage to a low-pressure region lower than the back pressure.

2. The hydraulic circuit structure according to claim 1, wherein the hydraulic circuit comprises at least one oil flow control valve, and the warm-up oil passage discharges the back pressure oil passing through the oil flow control valve to the low-pressure region when the oil flow control valve is in a position corresponding to the neutral position of the control valve.

3. The hydraulic circuit structure according to claim 2, wherein the hydraulic circuit is equipped with a counterbalance valve as the oil flow control valve, and the warm-up oil passage is provided on the spool of the counterbalance valve.

4. The hydraulic circuit structure according to claim 2, wherein the hydraulic circuit is equipped with an anti-cavitation valve as the oil flow control valve, and when the anti-cavitation valve is in a position corresponding to the neutral position of the control valve, it allows the back pressure oil to pass through and discharges it to the warm-up oil passage.

5. The hydraulic circuit structure according to claim 2, wherein the oil flow control valve opens only when the control valve is in the neutral position, thereby allowing the back pressure oil to flow out into the warm-up oil passage.

6. The hydraulic circuit structure according to claim 5, wherein the hydraulic circuit comprises the oil flow control valve in addition to the counterbalance valve and the anticavitation valve.

7. A hydraulic actuator unit comprising the hydraulic circuit structure according to any one of claims 1 to 6, and the hydraulic actuator.

8. A work machine comprising the hydraulic circuit structure according to any one of claims 1 to 6, and the hydraulic actuator.

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