Hydraulic drive device

Abstract

Provided is a hydraulic drive device capable of controlling a two-speed switching mechanism, a brake mechanism, and a flushing mechanism of a hydraulic pump with low cost and a small number of valves. When a hydraulic motor (20) is rotationally driven, a pressure selection valve (30) supplies high-pressure-side hydraulic oil in a first oil passage (11) or a second oil passage (12) to a two-speed switching valve (40), and supplies low-pressure-side hydraulic oil in the second oil passage (12) or the first oil passage (11) to a flushing mechanism (80) and a brake mechanism (60), and when the hydraulic motor is stopped, the pressure selection valve (30) supplies the high-pressure-side hydraulic oil in the first oil passage (11) or the second oil passage (12) to the two-speed switching valve (40). The pressure selection valve (30) cuts off the supply of hydraulic oil from the first oil passage (11) and the second oil passage (12) to the two-speed switching valve (40), the flushing mechanism (80), and the brake mechanism (60), and a closed circuit is formed between the first oil passage (11) or the second oil passage (12) and the main pump (10).

Description

Technical Field

[0001] This invention relates to a closed-loop hydraulic drive device with a hydraulic motor used in industrial machinery, construction machinery, and agricultural machinery. Background Technology

[0002] Traditionally, closed-loop hydraulic drive devices were used as driving units. These hydraulic drive devices rotated hydraulic motors using working oil from a main pump.

[0003] Such a hydraulic drive unit has a dual-speed switching mechanism that switches the rotational speed of the hydraulic motor between high and low speeds by changing the tilt angle of the swashplate used for variable capacity. The hydraulic drive unit also includes a flushing mechanism and a braking mechanism (e.g., Patent Document 1). The flushing mechanism circulates working oil within the hydraulic motor to cool it. The braking mechanism is a negative braking type and is released by pilot pressure.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-223256 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, conventional hydraulic drive systems require more valves, more piping, and corresponding solenoid switching valves. Therefore, conventional hydraulic drive systems suffer from increased piping work time and increased piping component costs.

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a hydraulic drive device for reducing the number of piping components in a closed loop even without using high-cost components.

[0010] Solution for solving the problem

[0011] (1) To solve the above-mentioned problem, the hydraulic drive device is configured to include: a hydraulic motor, which is connected in a closed loop to a main pump via a first oil circuit and a second oil circuit, driven by high-pressure side working oil with relatively high pressure discharged from the main pump, and causing low-pressure side working oil with relatively low pressure to return to the main pump after being driven; a pressure selection valve, which is connected to the first oil circuit and the second oil circuit, and supplies the high-pressure side working oil and the low-pressure side working oil to each part; a dual-speed switching valve, which is connected to the pressure selection valve via an oil circuit; a dual-speed switching mechanism, which is controlled by the dual-speed switching valve and controls the tilt angle of the swashplate of the hydraulic motor; and a braking mechanism, which is connected to the pressure selection valve via an oil circuit and performs braking on the hydraulic motor. Braking action; a brake drain line for discharging working oil from the braking mechanism to the outside of the closed circuit, and having a throttle orifice; and a flushing mechanism that uses a portion of the low-pressure side working oil to flush the hydraulic motor. When the hydraulic motor is driven to rotate, the pressure selection valve supplies the high-pressure side working oil from the first or second oil circuit to the dual-speed switching valve, and supplies the low-pressure side working oil from the second or first oil circuit to the flushing mechanism and the braking mechanism. When the hydraulic motor stops, the pressure selection valve cuts off the supply of working oil from the first and second oil circuits to the dual-speed switching valve, the flushing mechanism, and the braking mechanism.

[0012] (2) Alternatively, the braking mechanism causes the front end of the brake piston located inside the housing of the hydraulic motor to abut against the brake disc under the action of a spring to perform a braking action, and releases the brake by causing the brake piston to leave the brake disc through the pressure of the low-pressure side working oil supplied to the pressure chamber. The brake drain passage is formed inside the brake piston, with an opening at the base end relative to the front end, and communicates the pressure chamber with the internal space of the housing. During the braking action, the axial base end of the brake piston moves away from the inner end face of the housing, thereby opening the brake drain passage. When the brake is released, the base end of the brake piston abuts against the inner end face of the housing, thereby closing the brake drain passage.

[0013] (3) In the structure in which the brake piston is provided with a brake oil discharge passage, the pressure selection valve may also have: a first input port and a second input port, which are respectively connected to the first oil passage and the second oil passage; a first output port, which is connected to the dual-speed switching valve; a second output port, which is connected to the flushing mechanism and the braking mechanism; and a first pilot input port and a second pilot input port, which are respectively connected to the first oil passage and the second oil passage. When the high-pressure side working oil is introduced into the first pilot input port, it becomes a first state in which the first input port and the second input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is introduced into the second pilot input port, it becomes a second state in which the second input port and the first input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is not introduced into either the first pilot input port or the second pilot input port, it becomes a neutral state in which all connections are stopped.

[0014] (4) Alternatively, the brake drain circuit is connected to the pressure selection valve. When the hydraulic motor stops, the pressure selection valve cuts off the supply of working oil from the first oil circuit and the second oil circuit to the dual-speed switching valve, the flushing mechanism and the braking mechanism, and connects the oil circuit leading to the braking mechanism to the brake drain circuit.

[0015] (5) In a structure having a brake drain circuit connected to the pressure selection valve, the pressure selection valve may also have: a first input port and a second input port, which are respectively connected to the first oil circuit and the second oil circuit; a first output port, which is connected to the dual-speed switching valve; a second output port, which is connected to the flushing mechanism and the braking mechanism; a return output port, which is connected to the brake drain circuit; and a first pilot input port and a second pilot input port, which are respectively connected to the first oil circuit and the second oil circuit. When the high-pressure side working oil is introduced into the first pilot input port, it becomes a first state in which the first input port and the second input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is introduced into the second pilot input port, it becomes a second state in which the second input port and the first input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is not introduced into either the first pilot input port or the second pilot input port, it becomes a neutral state in which all connections are stopped and the second output port is connected to the return output port.

[0016] (6) Alternatively, the dual-speed switching valve may be a hydraulic pilot valve, which uses a portion of the working oil supplied from the oil supply pump to the first oil circuit or the second oil circuit for opening and closing control.

[0017] Invention Effects

[0018] According to the present invention, a hydraulic drive device for closed-loop piping components can be provided that reduces the number of piping components even without using high-cost components. Attached Figure Description

[0019] Figure 1 (a) is a hydraulic circuit diagram showing the neutral state of the pressure selection valve of the hydraulic drive device of the first embodiment, and (b) is a detailed view of part A thereto.

[0020] Figure 2 This is a hydraulic circuit diagram of the hydraulic drive device according to the first embodiment, wherein (a) is a diagram showing the first state, (b) is a detailed view of its B part, (c) is a diagram showing the second state, and (d) is a detailed view of its C part.

[0021] Figure 3 (a) is shown Figure 1 (a) is a schematic cross-sectional view of the braking mechanism and brake drain circuit in the hydraulic drive device, and (b) is an enlarged view of part D of (a).

[0022] Figure 4 (a) is a hydraulic circuit diagram showing the neutral state of the pressure selection valve of the hydraulic drive device of the second embodiment, and (b) is a detailed view of its E section.

[0023] Figure 5 It is shown Figure 4 A schematic cross-sectional view of the braking mechanism and brake drain circuit in a hydraulic drive unit.

[0024] Figure 6 (a) is a hydraulic circuit diagram showing the neutral state of the pressure selection valve of the hydraulic drive device of the third embodiment, and (b) is a detailed view of its F part.

[0025] Explanation of reference numerals in the attached figures

[0026] 10 Main Pump

[0027] 11 First oil route

[0028] 12 Second oil line

[0029] 13 Sloping plate

[0030] 20 Hydraulic motors

[0031] 21. Shell

[0032] 21b Inner end face

[0033] 22 Sloping plate

[0034] 23 Rotation axis

[0035] 24 Interior Space

[0036] 30, 130 pressure selector valve

[0037] 31a First Input Port

[0038] 31b Second Input Port

[0039] 32a First Output Port

[0040] 32b Second Output Port

[0041] 33 Return to output port

[0042] 34a First pilot input port

[0043] 34b Second Pilot Input Port

[0044] 40, 140 Dual-Speed ​​Switching Valve

[0045] 40a Input Port

[0046] 40b Output Port

[0047] 40c Return to output port

[0048] 40d pilot input port

[0049] 41 Pilot oil circuit

[0050] 42 Three-way solenoid valve

[0051] 50 Dual-speed switching mechanism

[0052] 51 Control cylinder

[0053] 60 Braking mechanism

[0054] 61 Brake piston

[0055] 61a Front end

[0056] 61b base end

[0057] 61c Step surface

[0058] 62 Springs

[0059] 63 Brake disc

[0060] 64 Opposite surfaces

[0061] 70, 70a Brake Oil Discharge Circuit

[0062] 80 Flushing Mechanism

[0063] 81. Flushing relief valve

[0064] 82 Oil drain line

[0065] 90 oil supply pump

[0066] 91. Oil lines for replenishing working fluid.

[0067] 92a, 92b check valves

[0068] 100, 200, 300 hydraulic drive units

[0069] 110 engine

[0070] 201 Bottom

[0071] 202 First Step Section

[0072] 203 Second Step Section

[0073] 210 First Containment Department

[0074] 220 Second Containment Department

[0075] 230 Third Containment Department

[0076] P pressure chamber. Detailed Implementation

[0077] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings.

[0078] (First Implementation)

[0079] Figure 1 (a) is a hydraulic circuit diagram of the hydraulic drive device 100 of the first embodiment, which shows the neutral state of the pressure selection valve 30. Figure 1 (b) is a detailed drawing of its A section (also referred to as "the overall drawing"). Figure 1 (The same applies to the following diagrams). Figure 2 (a) is a diagram showing the first state of the pressure selection valve 30. Figure 2 (b) is a detailed diagram of its B section. Figure 2 (c) is a diagram showing the second state of the pressure selection valve 30. Figure 2 (d) is a detailed view of its C section. The hydraulic drive device 100 of this embodiment includes a main pump 10, a hydraulic motor 20, a pressure selection valve 30, a dual-speed switching valve 40, a dual-speed switching mechanism 50, a braking mechanism 60, a brake drain line 70, and a flushing mechanism 80.

[0080] The main pump 10 is, for example, a swashplate-type variable-capacity pump driven by the engine 110. The main pump 10 has two working oil inlets and outlets, drawing in working oil from one inlet and discharging it from the other. It is configured such that the oil delivery direction of the main pump 10, i.e., the intake / discharge inlet and outlet, is switched by changing the tilt direction of the swashplate 13.

[0081] The hydraulic motor 20 is connected to the main pump 10 in a closed loop via the first oil passage 11 and the second oil passage 12. As described above, depending on the discharge direction of the main pump 10, the high-pressure side working oil (relatively high pressure) flows to one of the first oil passage 11 and the second oil passage 12. Conversely, the low-pressure side working oil (relatively low pressure) flows to the other side. That is, the hydraulic motor 20 is driven by the high-pressure side working oil discharged from the main pump 10. Furthermore, the hydraulic motor 20 is a motor that returns the driven low-pressure side working oil to the main pump 10. The output shaft of the hydraulic motor 20, for example, drives the wheels of a work vehicle to rotate. This hydraulic motor 20 is a swashplate-type variable capacity motor. The hydraulic motor 20 has two working oil inlets and outlets; working oil flows in from one inlet and out from the other. The rotation direction of the hydraulic motor 20 changes accordingly to the oil delivery direction from the main pump 10. Additionally, the rotation speed of the hydraulic motor 20 is changed by changing the tilt angle of the swashplate 22.

[0082] A pressure selection valve 30 is connected to the first oil passage 11 and the second oil passage 12. The pressure selection valve 30 supplies the high-pressure side working oil and the low-pressure side working oil flowing in the first oil passage 11 and the second oil passage 12 to various parts. The pressure selection valve 30 is a three-position switching valve, operating with the high-pressure side working oil from either the first oil passage 11 or the second oil passage 12 as the pilot pressure. For example, as... Figure 1 As shown, the system is in a neutral state when there is no pressure difference between the first oil passage 11 and the second oil passage 12. This absence of a pressure difference means that the hydraulic motor stops when there is no discharge of working oil from the main pump 10. In this case, the pressure selection valve 30 cuts off the supply of working oil from both the first oil passage 11 and the second oil passage 12 to the dual-speed switching valve 40, the flushing mechanism 80, and the braking mechanism 60.

[0083] In addition, regarding the flow of high-pressure side working oil in the first oil circuit 11, Figure 2 (a) and Figure 2 As shown in (b), in this case, the pressure selection valve 30 is switched, and the dual-speed switching valve 40 is connected to the first oil circuit 11. Along with this connection, the flushing mechanism 80 and the braking mechanism 60 are connected to the second oil circuit 12. That is, the pressure selection valve 30 supplies high-pressure side working oil from the first oil circuit 11 to the dual-speed switching valve 40. Along with this supply, the pressure selection valve 30 supplies low-pressure side working oil from the second oil circuit 12 to the flushing mechanism 80 and the braking mechanism 60.

[0084] In addition, regarding the flow of high-pressure side working oil in the second oil circuit 12, Figure 2 (c) and Figure 2As shown in (d), in this case, the pressure selection valve 30 is switched, and the dual-speed switching valve 40 is connected to the second oil circuit 12. Along with this connection, the flushing mechanism 80 and the braking mechanism 60 are connected to the first oil circuit 11. That is, the pressure selection valve 30 supplies high-pressure side working oil from the second oil circuit 12 to the dual-speed switching valve 40. Along with this supply, the pressure selection valve 30 supplies low-pressure side working oil from the first oil circuit 11 to the flushing mechanism 80 and the braking mechanism 60. It should be noted that detailed information regarding the structure of the pressure selection valve 30 will be described later.

[0085] The dual-speed switching valve 40 is a three-way valve connected to the pressure selection valve 30 via an oil circuit. For example... Figure 1 As shown, the dual-speed switching valve 40 switches between a state where high-pressure working oil supplied from the pressure selection valve 30 is supplied to the dual-speed switching mechanism 50 and a state where oil is discharged from the dual-speed switching mechanism 50. The dual-speed switching valve 40 is a hydraulic pilot valve, controlled by a three-way solenoid valve 42. That is, when the engine 110 drives the fuel pump 90, working oil is supplied from the fuel pump 90 to the first fuel line 11 and the second fuel line 12. The opening and closing of the dual-speed switching valve 40 is controlled by switching the supply pressure using the three-way solenoid valve 42. The fuel line 91 for supplementing working oil from the fuel pump 90 branches midway, passing through check valves 92a and 92b respectively. Thus, the fuel line 91 is connected to the first fuel line 11 and the second fuel line 12, forming a closed loop. This configuration supplies supplementary working oil to the low-pressure side of either the first fuel line 11 or the second fuel line 12. The pilot oil passage 41 leading to the dual-speed switching valve 40 is a branch of the oil passage 91 before branching to check valves 92a and 92b. Switching is achieved by energizing the three-way solenoid valve 42 for control, and oil passage 41 is connected to the pilot input port 40d of the dual-speed switching valve 40. It should be noted that the detailed structure of the dual-speed switching valve 40 will be described later.

[0086] The dual-speed switching mechanism 50 is controlled by the dual-speed switching valve 40. The dual-speed switching mechanism 50 includes a control cylinder 51. The control cylinder 51 switches the tilt angle of the swashplate 22 to switch the rotational speed of the hydraulic motor 20. This control cylinder 51 is a single-acting cylinder operating with high-pressure side working oil. When the control cylinder 51 is not operating (when high-pressure side working oil is not supplied), the tilt angle of the swashplate 22 is set to a low-speed position by the force of a spring (not shown). Conversely, when the control cylinder 51 is operating (when high-pressure side working oil is supplied), the tilt angle of the swashplate 22 is set to a high-speed position by the working force of the control cylinder 51 overcoming the force of the spring (not shown). In other words, the dual-speed switching mechanism 50 controls the tilt angle of the swashplate 22 of the hydraulic motor 20 (switching between first and second speeds).

[0087] Figure 3 (a) is a schematic cross-sectional view of the braking mechanism 60. Figure 3 (b) is Figure 3 Enlarged view of part D in (a). The braking mechanism 60 is connected to the pressure selection valve 30 via an oil passage. The braking mechanism 60 performs braking action under normal conditions (when no hydraulic pressure is supplied), and releases the brake when working oil is supplied (when hydraulic pressure is supplied). That is, the braking mechanism 60 is a negative braking type. The braking mechanism 60 includes a brake piston 61, a spring 62, and a brake disc 63.

[0088] The brake piston 61 is disposed inside the housing 21 of the hydraulic motor 20, and is arranged in a manner that allows it to move axially within the hydraulic motor 20. Regarding the interior of the housing 21... Figure 3 An example is shown below. The housing 21 has a stepped inner circumferential surface. For example, the inner circumferential surface of the housing 21 is formed in a stepped shape such that the diameter gradually increases from the bottom surface 201 side. On the bottom surface 201 side of the housing 21 ( Figure 3 (a) On the right side, a first receiving portion 210 with the smallest diameter is provided. A recess is provided on the central side of the bottom surface 201 in the first receiving portion 210, and a bearing is supported thereon. The bearing supports the rotating shaft 23 of the hydraulic motor 20 so that it can rotate.

[0089] The first stepped portion 202 is disposed adjacent to the end of the opening side (opposite to the bottom surface 201) of the first receiving portion 210. The first stepped portion 202 is disposed extending away from the central axis of the housing 21 with the boundary of the first receiving portion 210 as its base end. In addition, the first stepped portion 202 is formed to be parallel to the bottom surface 201 and orthogonal to the rotation axis 23 of the hydraulic motor 20. Furthermore, the brake disc 63 of the braking mechanism 60 is disposed along the first stepped portion 202.

[0090] Furthermore, the housing 21 includes a first stepped portion 202. A second receiving portion 220 is provided in the housing 21, adjacent to the first receiving portion 210 and bounded by the first stepped portion 202. The diameter of the second receiving portion 220 is larger than the diameter of the first receiving portion 210. Additionally, a second stepped portion 203 is provided adjacent to the end of the opening side (the side opposite to the first receiving portion 210) of the second receiving portion 220. The second stepped portion 203 is formed parallel to the first stepped portion 202. Furthermore, the second stepped portion 203 is provided extending away from the central axis of the housing 21, with its base end at the boundary of the second receiving portion 220. The housing 21 also includes the second stepped portion 203. A third receiving portion 230 is provided in the housing 21, adjacent to the second receiving portion 220 and bounded by the second stepped portion 203. The diameter of the third receiving portion 230 is larger than the diameter of the second receiving portion 220. That is, starting from the bottom surface 201 side, the inner diameters of the first receiving part 210, the second receiving part 220 and the third receiving part 230 increase sequentially via the first step part 202 and the second step part 203.

[0091] The housing 21 is divided into a concave side member (right side of the figure) that houses the hydraulic motor 20 and the rotating shaft 23, and a cover side member (left side of the figure) that is provided to block the opening of the concave side member. In the cover side member of the housing 21, the part facing the brake piston 61 is designated as the inner end face 21b.

[0092] A rotating shaft 23 of a hydraulic motor 20 is located on the central axis side of the housing 21, and a cylinder or similar component (not shown) that rotates integrally with the rotating shaft 23 is arranged around it. A braking mechanism 60 is disposed around this cylinder or similar component. The brake piston 61 is generally annular with a stepped shape. The brake piston 61 is disposed between the first stepped portion 202 and the inner end face 21b of the housing 21 opposite to the first stepped portion 202. That is, the brake piston 61 is disposed in the second receiving portion 220 and the third receiving portion 230 on the outer periphery of the hydraulic motor 20. The axially extending front end portion 61a (face) of the brake piston 61 faces the brake disc 63 disposed along the first stepped portion 202. The side of the brake piston 61 opposite to the front end portion 61a in the axial direction will be described as the base end portion 61b. The brake piston 61 is in the braking position by abutting against the brake disc 63 through the front end portion 61a. Furthermore, the brake piston 61 is in the brake release position when it abuts against the inner end face 21b of the housing 21 via its base end 61b. In other words, the brake piston 61 is configured to move between the brake action position and the brake release position.

[0093] Regarding the front end 61a, Figure 3 Example (a) will be used for illustration. The inner end of the front end 61a is radially ( Figure 3 The diameter of (a) in the vertical direction is larger than the inner diameter of the first step portion 202. In addition, the outer end of the front end portion 61a reaches the side (inner circumferential surface) of the second receiving portion 220 of the housing 21. Furthermore, the outer side of the brake piston 61, which is opposite to the side of the second receiving portion 220, passes over the second receiving portion 220 and reaches the third receiving portion 230 of the housing 21.

[0094] The brake piston 61 has a stepped portion opposite the second stepped portion 203, and its diameter increases from the side of the second receiving portion 220, through the second stepped portion 203, along the side of the third receiving portion 230. That is, by providing this stepped portion, the outer diameter of the base end portion 61b of the brake piston 61 is larger than the outer diameter of the front end portion 61a in the axial direction. The surface of this stepped portion becomes the opposing surface 64 of the brake piston 61 side facing the second stepped portion 203. Furthermore, a gap exists between this opposing surface 64 and the second stepped portion 203, and this gap is designated as a pressure chamber P. The pressure chamber P is an annular space.

[0095] Furthermore, along the axial direction of the rotating shaft 23, a small-diameter portion smaller than the diameter of the first receiving portion 210 is formed on a portion of the inner circumferential surface of the brake piston 61. This small-diameter portion extends from the front end portion 61a towards the base end portion 61b with a predetermined length. This predetermined length is, for example, slightly shorter than the axial length of the second receiving portion 220 described above. On the base end portion 61b side, the brake piston 61 is formed with an inner diameter larger than the small-diameter portion. For ease of explanation, this is referred to as the large-diameter portion. The inner circumferential side of the brake piston 61, i.e., the large-diameter portion of the brake piston 61, becomes the receiving portion of the spring 62.

[0096] Spring 62 applies force in the direction that causes brake piston 61 to abut against brake disc 63. Spring 62 is, for example, a coil spring.

[0097] Low-pressure side working oil can be introduced into the aforementioned pressure chamber P through the through hole in the housing 21 via the pressure selection valve 30. By introducing the low-pressure side working oil, the opposing surface 64 of the brake piston 61 overcomes the pressing force of the spring 62 and is pressed away from the second step 203 of the housing 21. As a result, the front end 61a of the brake piston 61 moves away from the brake disc 63.

[0098] The brake disc 63 is disposed inside the housing 21 on the rotating side of the hydraulic motor 20 and rotates integrally with the rotating shaft 23 of the hydraulic motor 20. The front end 61a of the brake piston 61 abuts against the brake disc 63 by the force of the spring 62. As a result, the brake disc 63 is clamped between the front end 61a and the first step 202 of the housing 21. Consequently, under the action of friction, the hydraulic motor 20 brakes and becomes unable to rotate. On the other hand, when low-pressure working oil is supplied to the pressure chamber P, under the pressure of the low-pressure working oil, the brake piston 61 overcomes the spring 62 and moves away from the brake disc 63. As a result, the brake is released, and the hydraulic motor 20 can rotate.

[0099] like Figure 3 As shown in (b), in this embodiment, a brake drain passage 70 is provided as a partially through-hole in the form of a circular brake piston 61. That is, the brake drain passage 70 is formed as a through hole extending from a portion of the base end 61b, for example, along the extension / retraction direction of the spring 62 to the opposing surface 64. In addition, a throttling orifice is provided in a portion of the brake drain passage 70. The brake drain passage 70 connects the pressure chamber P to the internal space 24 of the housing 21.

[0100] During braking, the base end 61b of the brake piston 61 moves away from the inner end face 21b of the housing 21, thereby opening the brake drain passage 70. Conversely, when the brake is released, the base end 61b of the brake piston 61 abuts against the inner end face 21b of the housing 21, thereby closing the brake drain passage 70.

[0101] The internal space 24 of the housing 21 is a space cooled by flushing. An oil drain line 82 is connected to the internal space 24. The flushed working oil is discharged to the discharge section DR via the oil drain line 82. The pressure of this internal space 24 is controlled by the flushing relief valve 81 (see reference). Figure 1 The pressure is below the set pressure of the brake oil and is lower than the pressure of the low-pressure side working oil in pressure chamber P. Therefore, when the brake drain line 70 is opened, the low-pressure side working oil in pressure chamber P is discharged through the internal space 24.

[0102] exist Figure 1 The flushing mechanism 80 includes an oil passage branching from the pressure selection valve 30 to the braking mechanism 60 and reaching the hydraulic motor 20, and a flushing relief valve 81 disposed in this oil passage. The flushing mechanism 80 is a mechanism for flushing and cooling the hydraulic motor 20 to prevent the temperature of the hydraulic motor 20 and the working oil from rising. The flushing mechanism 80 reduces the pressure of a portion of the low-pressure side working oil flowing back from the hydraulic motor 20 to the main pump 10 in the closed circuit via the flushing relief valve 81, allowing it to flow into the internal space 24 of the housing 21 of the hydraulic motor 20 (see reference). Figure 3 The working oil of the hydraulic motor 20 after cooling is discharged to the discharge section DR through the oil drain passage 82.

[0103] Next, the details of the pressure selection valve 30 will be described. As mentioned earlier, the pressure selection valve 30 is a three-position switching valve. The pressure selection valve 30 has a first input port 31a, a second input port 31b, a first output port 32a, and a second output port 32b. The first input port 31a and the second input port 31b are respectively connected to the first oil passage 11 and the second oil passage 12. The first output port 32a is connected to the dual-speed switching valve 40. The second output port 32b is connected to the flushing mechanism 80 and the braking mechanism 60. In addition, the pressure selection valve 30, connected to the first oil passage 11 and the second oil passage 12 respectively, has a first pilot input port 34a and a second pilot input port 34b.

[0104] It should be noted that, in the illustrated example, the oil passage leading to the dual-speed switching valve 40 is connected to two physical ports. One of these physical ports is a first output port 32a, which can be connected to the first input port 31a in the pressure selection valve 30, and the other is a first output port 32a, which can be connected to the second input port 31b in the pressure selection valve 30. In this specification, these two physical ports are connected to the dual-speed switching valve 40 respectively, but for ease of explanation, both are referred to as "first output port 32a".

[0105] The pressure selection valve 30 switches to one of three states based on the pilot input conditions to the first pilot input port 34a and the second pilot input port 34b.

[0106] (1) When high-pressure side working oil is introduced into the first pilot input port 34a, the first input port 31a is connected to the first output port 32a. Additionally, the second input port 31b transitions to a first state connected to the second output port 32b (see [reference]). Figure 2 of (a) Figure 2 (b)

[0107] (2) When high-pressure side working oil is introduced into the second pilot input port 34b, the second input port 31b is connected to the first output port 32a. Additionally, the first input port 31a transitions to a second state connected to the second output port 32b (see [reference]). Figure 2 (c) Figure 2 (d)

[0108] (3) When high-pressure side working oil is not introduced into either the first pilot input port 34a or the second pilot input port 34b, the first input port 31a and the second input port 31b, and the first output port 32a and the second output port 32b are all disconnected. This results in a neutral state where all connections are stopped (see reference). Figure 1 ).

[0109] In this embodiment, the high-pressure side / low-pressure side of the working oil flowing to the first oil passage 11 and the second oil passage 12 is changed by switching the discharge direction of the oil from the main pump 10. Correspondingly, according to the above structure, the first state and the second state of the pressure selection valve 30 are switched. Therefore, high-pressure side working oil is output from the first output port 32a and supplied to the dual-speed switching valve 40, while low-pressure side working oil is output from the second output port 32b and supplied to the braking mechanism 60 and the flushing mechanism 80. When there is no discharge of oil from the main pump 10, the circulation of the working oil stops, and the pressure difference between the first oil passage 11 and the second oil passage 12 disappears, the pressure selection valve 30 becomes neutral due to the force of the spring.

[0110] Next, refer to Figure 1 The dual-speed switching valve 40 is described in detail below. The dual-speed switching valve 40 has an input port 40a, an output port 40b, and a return output port 40c. The input port 40a is connected via an oil passage to the first output port 32a of the pressure selection valve 30. The output port 40b is connected to the dual-speed switching mechanism 50. The return output port 40c is connected to the oil passage downstream of the flushing relief valve 81 of the flushing mechanism 80. The oil passage downstream of the flushing relief valve 81 serves as a drain line.

[0111] As described above, the pilot oil passage 41 leading to the dual-speed switching valve 40 is connected to the pilot input port 40d of the dual-speed switching valve 40 via a three-way solenoid valve 42 for control. When no pilot oil is supplied to the pilot input port 40d, it is in a drain state. In the drain state, the output port 40b of the dual-speed switching valve 40 is connected to the return output port 40c, and oil is drained from the dual-speed switching mechanism 50. Conversely, when pilot oil is supplied to the pilot input port 40d, it is in a supply state. In the supply state, the input port 40a and output port 40b of the dual-speed switching valve 40 are connected, and high-pressure side working oil is supplied to the dual-speed switching mechanism 50. Thus, the supply / stop of pilot oil to the dual-speed switching valve 40 is switched via the three-way solenoid valve 42. With this structure, it is possible to switch between the supply state (supply of high-pressure side working oil from the dual-speed switching valve 40 to the dual-speed switching mechanism 50) and the drain state (drainage from the dual-speed switching mechanism 50).

[0112] Next, refer to Figure 1 , Figure 2 The operation of the hydraulic drive device 100 of this embodiment, configured as described above, will be explained. When no oil is discharged from the main pump 10 to either the first oil passage 11 or the second oil passage 12, there is no pressure difference between the first oil passage 11 and the second oil passage 12. In other words, the swashplate 13 is in a zero-tilt state with no tilt, as... Figure 1 As shown, pressure selection valve 30 is in a neutral state. Therefore, no working oil is supplied to the dual-speed switching mechanism 50, and the swashplate 22 of the hydraulic motor 20 is in the low-speed side. No working oil is supplied to the braking mechanism 60, and braking action is performed. No working oil is supplied to the flushing mechanism 80, and flushing stops.

[0113] At this time, Figure 3 In the braking mechanism 60 shown in (a), no working oil is supplied to the pressure chamber P. At this time, the front end 61a of the brake piston 61 abuts against the brake disc 63 by the force of the spring 62, and the braking action is performed. In addition, the base end 61b of the brake piston 61 moves away from the inner end face 21b of the housing 21, thereby opening the brake oil discharge passage 70. Therefore, the working oil in the pressure chamber P is discharged through the internal space 24 of the housing 21.

[0114] exist Figure 1 In this configuration, the swashplate 13 of the main pump 10 is tilted to one side, for example, by external operation. This allows the main pump 10 to discharge working oil into either the first oil passage 11 or the second oil passage 12. For example, it draws in oil from the inlet / outlet on the second oil passage 12 side and discharges it from the inlet / outlet on the first oil passage 11 side. Thus, the first oil passage 11 becomes the high-pressure side, and the second oil passage 12 becomes the low-pressure side. It should be noted that the oil supply pump 90 is also rotated and discharges oil via the engine 110. Therefore, the low-pressure side is also replenished by the working oil from the oil supply pump 90, thus becoming the set pressure of the flushing relief valve.

[0115] As a result, the high-pressure side working oil is introduced into the first pilot input port 34a of the pressure selection valve 30 connected to the first oil circuit 11. Thus, the state of the pressure selection valve 30 becomes... Figure 2 of (a) Figure 2 The first state is shown in (b). That is, the first input port 31a and the second input port 31b are connected to the first output port 32a and the second output port 32b, respectively. Therefore, the high-pressure side working oil introduced into the first input port 31a is supplied to the dual-speed switching valve 40 connected to the first output port 32a. In addition, the low-pressure side working oil introduced into the second input port 31b is supplied to the flushing mechanism 80 and the braking mechanism 60 connected to the second output port 32b. As a result, the flushing mechanism 80 operates and flushes the hydraulic motor 20, and the braking mechanism 60 operates, the brake drain line 70 is closed, and the brake is released under the pressure of the pressure chamber P. As a result, the hydraulic motor 20 is driven to rotate in one direction by the high-pressure side working oil discharged from the main pump 10. For example, when the hydraulic motor 20 is driven to rotate, the driving wheels of the work vehicle are driven to rotate in the forward direction and enter a low-speed driving state. It should be noted that the low-speed driving state refers to a relatively low-speed state during the speed switching of the dual-speed switching mechanism 50. Similarly, the high-speed driving state described later refers to a state of relative high speed. Hereinafter, "high speed" and "low speed" also refer to the difference between relative high speed and relative low speed based on the dual-speed switching mechanism 50.

[0116] At this time, Figure 3 In the braking mechanism 60 shown, low-pressure working oil is supplied to the pressure chamber P, and the brake piston 61 is subjected to pressure from the pressure chamber P on the stepped surface 61c. Therefore, the front end 61a overcomes the force of the spring 62 and moves away from the brake disc 63, thereby releasing the brake. At this time, the base end 61b of the brake piston 61 abuts against the inner end face 21b of the housing 21, thus closing the brake oil discharge passage 70.

[0117] On the other hand, Figure 1 In this configuration, when the swashplate 13 of the main pump 10 is tilted to the other side, the main pump 10 causes the working oil to circulate in the opposite direction. Therefore, the second oil passage 12 becomes the high-pressure side, and the first oil passage 11 becomes the low-pressure side. Thus, as... Figure 2 (c) Figure 2As shown in (d), high-pressure side working oil is introduced into the second pilot input port 34b of the pressure selection valve 30 connected to the second oil circuit 12, and the pressure selection valve 30 enters the second state. At this time, the second input port 31b and the first input port 31a are connected to the first output port 32a and the second output port 32b, respectively. Therefore, high-pressure side working oil is supplied to the dual-speed switching valve 40, and low-pressure side working oil is supplied to the braking mechanism 60 and the flushing mechanism 80. This performs flushing and brake release of the hydraulic motor 20. As a result, the hydraulic motor 20 is driven to rotate in the other direction. For example, by driving the hydraulic motor 20 to rotate, the driving wheels of the work vehicle are driven to rotate in the reverse direction and enter a low-speed driving state. With this structure, the brake piping can be omitted compared to the past.

[0118] exist Figure 2 (a) and Figure 2 (b) or Figure 2 (c) and Figure 2 In step (d), the three-way solenoid valve 42, which provides pilot control for the dual-speed switching valve 40, is further energized. When energized, it switches to a pilot oil supply state. At this time, the dual-speed switching valve 40 is in the aforementioned supply state (illustration omitted). Consequently, high-pressure side working oil is supplied to the control cylinder 51 of the dual-speed switching mechanism 50. As a result, the control cylinder 51 operates, and the swashplate 22 of the hydraulic motor 20 switches to a high-speed position. For example, the hydraulic motor 20 and the traveling wheels rotate at high speed, thereby putting the work vehicle into a high-speed driving state.

[0119] When the energization of the three-way solenoid valve 42 is set to OFF, it switches to the pilot oil discharge state. In the pilot oil discharge state, the dual-speed switching valve 40 is in the discharge state, and the working oil from the control cylinder 51 of the dual-speed switching mechanism 50 is discharged to the discharge section DR via the flushing oil circuit. As a result, the operation of the control cylinder 51 stops, and the swashplate 22 of the hydraulic motor 20 returns to the low-speed position. In this way, for example, the rotation of the hydraulic motor 20 and the travel wheels returns to low speed, and the work vehicle enters a low-speed travel state.

[0120] Furthermore, when the swashplate 13 of the main pump 10 returns to the neutral position, the pressure difference between the first oil passage 11 and the second oil passage 12 disappears. Therefore, high-pressure side working oil is no longer introduced into either the first pilot input port 34a connected to the first oil passage 11 or the second pilot input port 34b connected to the second oil passage 12. Thus, the pressure selection valve 30 becomes neutral (see reference). Figure 1As a result, the supply of high-pressure working oil to the dual-speed switching valve 40 stops, and the supply of low-pressure working oil to the flushing mechanism 80 and the braking mechanism 60 also stops. Therefore, flushing stops, the braking mechanism 60 operates, and the hydraulic motor 20 stops. As an example, when the hydraulic motor 20 stops, the driving wheels rotate, and the movement of the work vehicle stops.

[0121] At this time, Figure 3 In the braking mechanism 60 shown in (a), no working oil is supplied to the pressure chamber P. Therefore, the front end 61a of the brake piston 61 abuts against the brake disc 63 by the force of the spring 62. That is, braking action is performed. At this time, the base end 61b of the brake piston 61 is away from the inner end face 21b of the housing 21. Therefore, the brake drain passage 70 is opened. When the brake drain passage 70 is opened, the working oil in the pressure chamber P is discharged through the internal space 24 of the housing 21. It should be noted that the discharge of the working oil through the brake drain passage 70 is carried out gradually by throttling through the throttle orifice, so the braking action is also carried out gradually. This prevents shock and damage caused by sudden braking action.

[0122] According to this embodiment, the supply control of working oil from the hydraulic motor 20 to the dual-speed switching mechanism 50, the flushing mechanism 80, and the braking mechanism 60 can be achieved using only two valves: the pressure selection valve 30 and the dual-speed switching valve 40. Therefore, a hydraulic drive device 100 that can control these mechanisms with a low cost and a small number of valves can be realized.

[0123] In closed-loop hydraulic drive systems using numerous valves such as dual-speed switching valves, high-pressure selector valves, solenoid valves for piloting dual-speed switching valves, solenoid valves for driving brake release cylinders, and low-pressure switching valves, the brake release cylinder and the dual-speed switching valve (hydraulic pilot valve) are each driven by pilot oil. Therefore, two pilot pipes are required, along with two solenoid switching valves for supplying / stopping the pilot oil to these pilot pipes. Compared to such hydraulic drive systems that require pipe fittings and hydraulic hoses to guide each pilot oil, this embodiment reduces piping operation time and piping component costs through the aforementioned structure.

[0124] Additionally, there exists a hydraulic drive unit comprising: a high-pressure selector valve supplying high-pressure side working oil to a dual-speed switching valve; an electromagnetic proportional valve controlling a brake release actuator; and a low-pressure selector valve supplying low-pressure side working oil to the electromagnetic proportional valve and a flushing relief valve. In this unit, the two pilot pipes for brake release and dual-speed switching can be omitted. However, this requires multiple valves, including a dual-speed switching valve, a high-pressure selector valve, an electromagnetic proportional valve, and a low-pressure selector valve, and uses an advanced electromagnetic proportional valve instead of a simple electromagnetic switching valve. Furthermore, it requires an expensive electronic control device to control the costly electromagnetic proportional valve and its current value. In contrast, in this embodiment, the above-described structure reduces piping operation time and piping component costs even without using the electromagnetic proportional valve and the expensive electronic control device. When the hydraulic drive unit is used as the motor of a work vehicle, mud and water immersion become problems, and the use of the electromagnetic proportional valve itself becomes problematic; however, in this embodiment, the aforementioned structure is unnecessary.

[0125] Furthermore, according to this embodiment, a brake drain passage 70 is provided inside the brake piston 61. The brake drain passage 70 is opened and closed by the brake piston 61 abutting against or separating from the inner end face 21b of the housing 21. As a result, a new valve is not required to control the opening and closing of the drain passage from the brake mechanism 60, thus reducing the number of valves and simplifying the piping.

[0126] (Second Implementation)

[0127] Figure 4 (a) is a hydraulic circuit diagram of the hydraulic drive device 200 according to the second embodiment of the present invention. Figure 4 (b) is its detailed drawing of part E (also referred to as "the overall drawing"). Figure 4 It should be noted that, in the following description, the structural designations that perform the same function as in the first embodiment are different from those in the first embodiment. Figures 1-3 The same reference numerals are used in the accompanying drawings, and repeated descriptions are omitted where appropriate. The hydraulic drive device 200 of this embodiment has a structure substantially the same as that of the hydraulic drive device 100, but the layout of the brake oil discharge passage is different. More specifically, in the hydraulic drive device 200, the brake piston 61 (see reference 600) is not... Figure 3 The internal brake drain line is set up, and the brake drain line 70a is connected to the pressure selection valve 130.

[0128] The pressure selection valve 130 has a structure substantially the same as that of the pressure selection valve 30 in the first embodiment. That is, the pressure selection valve 130 has a first input port 31a, a second input port 31b, a first output port 32a, and a second output port 32b. The first input port 31a and the second input port 31b are connected to the first oil passage 11 and the second oil passage 12, respectively. The first output port 32a is connected to the dual-speed switching valve 40. The second output port 32b is connected to the braking mechanism 60 and the flushing mechanism 80. Furthermore, the pressure selection valve 130 has a first pilot input port 34a and a second pilot input port 34b, respectively connected to the first oil passage 11 and the second oil passage 12. On the other hand, unlike the pressure selection valve 30, the pressure selection valve 130 also has a return output port 33 connected to the brake drain passage 70a.

[0129] Like pressure selector valve 30, pressure selector valve 130 switches between three states—first state, second state, and neutral state—based on the pilot input condition. The first and second states are the same as in the first embodiment. Figure 4 As shown, the neutral state of the pressure selection valve 130 is the same as that of the pressure selection valve 30 in the first embodiment. That is, the connections between the first input port 31a and the second input port 31b and the first output port 32a and the second output port 32b in the first and second states are disconnected. On the other hand, in the neutral state of the pressure selection valve 130, the second output port 32b connected to the braking mechanism 60 and the flushing mechanism 80 and the return output port 33 connected to the brake drain line 70a are connected.

[0130] Figure 5 This is a schematic cross-sectional view showing the braking mechanism 60 and the brake drain line 70a according to this embodiment. The upstream side of the brake drain line 70a is connected to the return output port 33 of the pressure selection valve 130. Meanwhile, the downstream side of the brake drain line 70a is connected to the housing 21 of the hydraulic motor 20 via a throttle orifice and communicates with its internal space 24. The internal space 24 of the housing 21 is a space cooled by flushing. A drain line 82 is connected to the internal space 24 to discharge the flushed working oil to the drain section DR. The pressure of this internal space 24 is controlled by the flushing relief valve 81 (see reference). Figure 4 The pressure is below the set pressure and lower than the pressure of the working oil on the low-pressure side of the pressure chamber P of the braking mechanism 60. Therefore, when the oil passage to the pressure chamber P is connected to the brake drain passage 70a through the pressure selection valve 130, the working oil of the pressure chamber P flows into the internal space 24 through the brake drain passage 70a. Furthermore, the working oil is discharged through the drain passage 82. It should be noted that the discharge of the working oil through the brake drain passage 70a is carried out gradually by throttling through a throttle orifice; therefore, the braking action is also gradual. This prevents shocks and damage caused by sudden braking actions.

[0131] The braking mechanism 60 of this embodiment is the same as the braking mechanism 60 of the first embodiment, except that the brake piston 61 does not have a brake oil discharge passage 70. Figure 1 and Figure 4 Although the representation of the braking mechanism 60 in the piping diagram is different, the only difference between the braking mechanism 60 in the first embodiment and the one in this embodiment is this.

[0132] The operation of the hydraulic drive device 200 of this embodiment, configured as described above, is the same as that of the hydraulic drive device of the first embodiment, except for the oil discharge operation from the brake mechanism 60.

[0133] According to this embodiment, the supply control of working oil from the hydraulic motor 20 to the dual-speed switching mechanism 50, the flushing mechanism 80, and the braking mechanism 60 can be achieved using only two valves: the pressure selection valve 30 and the dual-speed switching valve 40. Therefore, a hydraulic drive device capable of controlling these mechanisms with a low cost and a small number of valves can be realized.

[0134] Furthermore, according to this embodiment, the pressure selection valve 130 is configured to open and close the brake drain line 70a that drains oil from the brake mechanism 60. As a result, a new valve that does not require opening and closing control of the drain line draining oil from the brake mechanism 60 can be used, thereby reducing the number of valves and simplifying the piping.

[0135] (Third implementation method)

[0136] Figure 6 (a) is a hydraulic circuit diagram of the hydraulic drive device 300 according to the third embodiment of the present invention. Figure 6 (b) is a detailed view of its F section. In the hydraulic drive device 300 of this embodiment, a two-speed switching valve 140, which is a three-way solenoid switching valve, is used instead of a two-speed switching valve 40, which is a hydraulic pilot valve, thereby driving the control cylinder 5 of the two-speed switching mechanism 50. In the third embodiment, the structure is the same as that of the first embodiment, except for this.

[0137] The dual-speed switching valve 140, like the dual-speed switching valve 40 of the first embodiment, has an input port 40a, an output port 40b, and a return output port 40c. The input port 40a is connected to the first output port 32a of the pressure selection valve 30. The output port 40b is connected to the dual-speed switching mechanism 50. The return output port 40c is connected to the downstream oil passage of the flushing relief valve 81 of the flushing mechanism 80. When the dual-speed switching valve 140 is not energized, the output port 40b of the dual-speed switching valve 140 is connected to the return output port 40c, thereby putting the dual-speed switching mechanism 50 into an oil discharge state. Conversely, when the dual-speed switching valve 140 is energized, the input port 40a and output port 40b of the dual-speed switching valve 40 are connected, thereby supplying high-pressure side working oil to the dual-speed switching mechanism 50.

[0138] Next, the operation of the hydraulic drive device 300 configured in this embodiment will be explained. When the hydraulic motor 20 is rotating at low speed, and the dual-speed switching valve 140, which functions as a three-way solenoid valve, is energized, the dual-speed switching valve 140 enters a supply state. In the supply state, high-pressure side working oil is supplied to the control cylinder 51 of the dual-speed switching mechanism 50. This causes the control cylinder 51 to operate, thereby switching the swashplate 22 of the hydraulic motor 20 to a high-speed position. The hydraulic motor 20 rotates at high speed. When, for example, the hydraulic motor 20 rotates at high speed, the work vehicle rotates its wheels at high speed, thus entering a high-speed driving state.

[0139] On the other hand, when the energization to the dual-speed switching valve 140 is set to OFF, the dual-speed switching valve 140 enters the oil discharge state, and the working oil from the control cylinder 51 is discharged to the discharge section DR via the oil passage downstream of the flushing relief valve 81. As a result, the operation of the control cylinder 51 stops, the swashplate 22 of the hydraulic motor 20 returns to the low-speed position, the rotation of the hydraulic motor 20 and the traveling wheels returns to low speed, and the work vehicle enters a low-speed driving state.

[0140] The hydraulic drive device 300 of this embodiment has a structure other than those described above and Figure 1 The hydraulic drive device 100 of the first embodiment shown is similar.

[0141] According to this structure, the pilot control of the dual-speed switching valve 40 does not require the three-way solenoid valve 42 or the pilot oil circuit 41. Therefore, a hydraulic drive device capable of controlling the supply and discharge of working oil from the hydraulic motor 20 to the dual-speed switching mechanism 50, the braking mechanism 60, and the flushing mechanism 80 can be realized with fewer valves and piping.

[0142] The embodiments of the present invention have been described above, but various design changes can be made to the present invention without departing from its spirit. For example, the dual-speed switching valve 140 can also be applied to the hydraulic drive device 200 of the second embodiment. In addition, in the second embodiment, the oil discharge passage from the braking mechanism 60 is configured to discharge oil to the discharge section DR via the housing 21 of the hydraulic motor 20 and the flushing oil discharge passage 82, but it is not limited to this. As long as the oil discharge passage from the braking mechanism 60 passes through the brake oil discharge passage 70a connected to the pressure selection valve 130, oil can be discharged via any path.

Claims

1. A hydraulic drive device, characterized in that, The hydraulic drive device includes: A hydraulic motor is connected to the main pump in a closed loop via a first oil circuit and a second oil circuit. It is driven by high-pressure side working oil with relatively high pressure discharged from the main pump, and the low-pressure side working oil with relatively low pressure after being driven flows back to the main pump. A pressure selection valve, which is connected to the first oil circuit and the second oil circuit, supplies the high-pressure side working oil and the low-pressure side working oil to each part. A dual-speed switching valve is connected to the pressure selection valve via an oil circuit; A dual-speed switching mechanism, controlled by the dual-speed switching valve, controls the tilt angle of the swashplate of the hydraulic motor. A braking mechanism, which is connected to the pressure selection valve via an oil circuit, performs the braking action of the hydraulic motor; A brake fluid discharge passage, used to discharge working fluid from the brake mechanism to the outside of the closed circuit, and having a throttle orifice; and The flushing mechanism uses a portion of the low-pressure side working oil to flush the hydraulic motor. When the hydraulic motor is driven to rotate, the pressure selection valve supplies the high-pressure side working oil from the first or second oil circuit to the dual-speed switching valve, and supplies the low-pressure side working oil from the second or first oil circuit to the flushing mechanism and the braking mechanism. When the hydraulic motor stops, the pressure selection valve cuts off the supply of working oil from the first oil circuit and the second oil circuit to the dual-speed switching valve, the flushing mechanism and the braking mechanism.

2. The hydraulic drive device according to claim 1, characterized in that, The braking mechanism causes the axially extending front end of a brake piston located inside the housing of the hydraulic motor to abut against a brake disc under the action of a spring, thereby performing a braking action. The brake is released by the pressure of the low-pressure working oil supplied to the pressure chamber, causing the brake piston to disengage from the brake disc. The brake oil drain passage is formed inside the brake piston, opens at the base end relative to the front end portion, and communicates with the internal space of the housing. During braking, the axial base end of the brake piston moves away from the inner end face of the housing, thereby opening the brake oil discharge passage. When the brake is released, the base end of the brake piston abuts against the inner end face of the housing, thereby closing the brake oil drain circuit.

3. The hydraulic drive device according to claim 2, characterized in that, The pressure selection valve has: a first input port and a second input port, which are respectively connected to the first oil circuit and the second oil circuit; and a first output port, which is connected to the dual-speed switching valve. A second output port is connected to the flushing mechanism and the braking mechanism; and a first pilot input port and a second pilot input port are respectively connected to the first oil circuit and the second oil circuit. When the high-pressure side working oil is introduced into the first pilot input port, it enters a first state where the first input port and the second input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is introduced into the second pilot input port, it enters a second state where the second input port and the first input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is not introduced into either the first pilot input port or the second pilot input port, it becomes a neutral state where all connections are stopped.

4. The hydraulic drive device according to claim 1, characterized in that, The brake drain line is connected to the pressure selector valve. When the hydraulic motor stops, the pressure selection valve cuts off the supply of working oil from the first oil circuit and the second oil circuit to the dual-speed switching valve, the flushing mechanism and the braking mechanism, and connects the oil circuit to the braking mechanism to the brake drain circuit.

5. The hydraulic drive device according to claim 4, characterized in that, The pressure selection valve has: a first input port and a second input port, which are respectively connected to the first oil circuit and the second oil circuit; and a first output port, which is connected to the dual-speed switching valve. The second output port is connected to the flushing mechanism and the braking mechanism; The return output port is connected to the brake oil drain circuit; and the first pilot input port and the second pilot input port are connected to the first oil circuit and the second oil circuit, respectively. When the high-pressure side working oil is introduced into the first pilot input port, it enters a first state where the first input port and the second input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is introduced into the second pilot input port, it enters a second state where the second input port and the first input port are respectively connected to the first output port and the second output port. When the high-pressure side working oil is not introduced into either the first pilot input port or the second pilot input port, it becomes a neutral state in which all connections are stopped and the second output port is connected to the return output port.

6. The hydraulic drive device according to claim 1, characterized in that, The dual-speed switching valve is a hydraulic pilot valve that uses a portion of the working oil supplied from the oil supply pump to the first or second oil circuit for opening and closing control.

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