Hydraulic drive system

Abstract

To provide a hydraulic drive system that can control the two-speed switching mechanism, braking mechanism, and flushing mechanism of a hydraulic pump with low cost and a small number of valves. [Solution] When the hydraulic motor 20 is rotating, the pressure selection valve 30 supplies high-pressure hydraulic fluid from the first oil passage 11 or the second oil passage 12, which forms a closed circuit with the main pump 10, to the two-speed switching valve 40, and supplies low-pressure hydraulic fluid from the second oil passage 11 or the first oil passage 12 to the flushing mechanism 80 and the brake mechanism 60. When the hydraulic motor is stopped, the pressure selection valve 30 shuts off the supply of hydraulic fluid 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.

Description

Technical Field

[0001] The present invention relates to a hydraulic drive device for a closed circuit including a hydraulic motor used in industrial machines, construction machines, agricultural machines, and the like.

Background Art

[0002] Conventionally, a hydraulic drive device for a closed circuit has been used as a drive device. This hydraulic drive device is a device that rotates a hydraulic motor by hydraulic oil from a main pump.

[0003] Such a hydraulic drive device includes a two-speed switching mechanism that switches between high and low speeds of the hydraulic motor rotation speed by switching the inclination angle of a swash plate for variable capacity. It also includes a flushing mechanism that circulates hydraulic oil inside the hydraulic motor to cool the hydraulic motor, and a brake mechanism that is of a negative brake type and is released by pilot pressure (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional hydraulic drive device, it is necessary to use many valves, and many pipes and corresponding electromagnetic switching valves are also required. Therefore, there is a problem that the piping work man-hours and piping component costs increase.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a hydraulic drive device for a closed circuit that can reduce piping components without using high-cost components.

Means for Solving the Problems

[0007] (1) To solve the above problems, the hydraulic drive system includes a hydraulic motor connected to the main pump in a closed circuit via first and second oil passages, driven by the relatively high-pressure hydraulic fluid discharged from the main pump, and returning the relatively low-pressure hydraulic fluid after driving to the main pump; a pressure selection valve connected to the first and second oil passages and supplying the high-pressure and low-pressure hydraulic fluids to each part; a two-speed switching valve connected to the pressure selection valve via an oil passage; a two-speed switching mechanism controlled by the two-speed switching valve and controlling the tilt angle of the swash plate of the hydraulic motor; a brake mechanism connected to the pressure selection valve via an oil passage and performing brake operation of the hydraulic motor; and the brake mechanism The hydraulic motor includes a brake oil drain passage having an orifice for draining the hydraulic fluid to the outside of the closed circuit, and a flushing mechanism for flushing the hydraulic motor using a portion of the low-pressure hydraulic fluid. When the hydraulic motor is rotating, the pressure selection valve supplies the high-pressure hydraulic fluid from the first or second oil passage to the two-speed switching valve, and supplies the low-pressure hydraulic fluid from the second or first oil passage to the flushing mechanism and the brake mechanism. When the hydraulic motor is stopped, the pressure selection valve is configured to shut off the supply of hydraulic fluid from the first and second oil passages to the two-speed switching valve, the flushing mechanism, and the brake mechanism. (2) The brake mechanism is a mechanism that operates the brake by bringing the axial tip of a brake piston provided inside the housing of the hydraulic motor into contact with the brake disc by the biasing force of a spring, and releases the brake by separating the brake piston from the brake disc with the pressure of the low-pressure hydraulic fluid supplied to the pressure chamber, wherein the brake oil drain passage is formed inside the brake piston and opens at the axial base end, communicating the pressure chamber and the internal space of the housing, and when the brake is operated the brake oil drain passage is opened when the axial base end of the brake piston moves away from the inner end surface of the housing, and when the brake is released the brake oil drain passage is closed when the axial base end of the brake piston comes into contact with the inner end surface of the housing. (3) In a configuration in which a brake oil drain passage is provided in the brake piston, the pressure selection valve may be configured such that it has first and second input ports connected to the first and second oil passages, respectively, a first output port connected to the two-speed switching valve, a second output port connected to the flushing mechanism and the brake mechanism, and first and second pilot input ports connected to the first and second oil passages, respectively, and when the high-pressure side hydraulic fluid is introduced into the first pilot input port, it enters a first state in which the first and second input ports and the first and second output ports are in communication, respectively, and when the high-pressure side hydraulic fluid is introduced into the second pilot input port, it enters a second state in which the second and first input ports and the first and second output ports are in communication, respectively, and when the high-pressure side hydraulic fluid is not introduced into either the first or second pilot input port, it enters a neutral state in which each communication is stopped. (4) The brake oil drain passage may be connected to the pressure selection valve and, when the hydraulic motor is stopped, shut off the supply of hydraulic fluid from the first oil passage and the second oil passage to the two-speed switching valve, the flushing mechanism and the brake mechanism, while also connecting the oil passage to the brake mechanism to the brake oil drain passage. (5) In a configuration having a brake oil drain passage connected to the pressure selection valve, the pressure selection valve may have first and second input ports connected to the first and second oil passages, respectively, a first output port connected to the two-speed switching valve, a second output port connected to the flushing mechanism and the brake mechanism, a return output port connected to the brake oil drain passage, and first and second pilot input ports connected to the first and second oil passages, respectively, wherein when the high-pressure hydraulic fluid is introduced into the first pilot input port, the first and second input ports and the first and second output ports are connected to each other, respectively, entering a first state; when the high-pressure hydraulic fluid is introduced into the second pilot input port, the second and first input ports and the first and second output ports are connected to each other, respectively, entering a second state; and when the high-pressure hydraulic fluid is not introduced into either of the first and second pilot input ports, the communication is stopped and the second output port and the return output port are connected, entering a neutral state. (6) The two-speed switching valve may be a hydraulic pilot valve that is controlled to open and close using a portion of the hydraulic fluid supplied to the closed circuit from a charge pump driven by the engine. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a hydraulic drive device for closed circuits that can reduce the number of piping components without using high-cost parts. [Brief explanation of the drawing]

[0009] [Figure 1] (a) is a hydraulic circuit diagram showing the neutral state of the pressure selector valve of the hydraulic drive device according to the first embodiment, and (b) is a detailed view of part A thereof. [Figure 2] A hydraulic circuit diagram of a hydraulic drive device according to a first embodiment, wherein (a) is a diagram showing a first state, (b) is a detailed view of part B thereof, (c) is a diagram showing a second state, and (d) is a detailed view of part C thereof. [Figure 3](a) is a schematic cross-sectional view showing the brake mechanism and brake oil drain passage in the hydraulic drive system of Figure 1, and (b) is an enlarged view of section D in (a). [Figure 4] (a) is a hydraulic circuit diagram showing the neutral state of the pressure selection valve of the hydraulic drive device according to the second embodiment, and (b) is a detailed view of section E thereof. [Figure 5] Figure 4 is a schematic cross-sectional view showing the brake mechanism and brake oil drain passage in a hydraulic drive system. [Figure 6] (a) is a hydraulic circuit diagram showing the neutral state of the pressure selection valve of the hydraulic drive device according to the third embodiment, and (b) is a detailed view of section F thereof. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. (First Embodiment) Figure 1(a) is a hydraulic circuit diagram of the hydraulic drive device 100 according to the first embodiment, showing the neutral state of the pressure selector valve 30, and Figure 1(b) is a detailed view of part A thereof (collectively referred to simply as "Figure 1"; the same applies to the following figures). Figure 2(a) shows the first state of the pressure selector valve 30, Figure 2(b) is a detailed view of part B thereof, Figure 2(c) shows the second state of the pressure selector valve 30, and Figure 2(d) is a detailed view of part C thereof. The hydraulic drive device 100 of this embodiment includes a main pump 10, a hydraulic motor 20, a pressure selector valve 30, a two-speed switching valve 40, a two-speed switching mechanism 50, a brake mechanism 60, a brake oil drain passage 70, and a flushing mechanism 80.

[0011] The main pump 10 is, for example, a swashplate type variable displacement pump driven by an engine 110, and has two hydraulic fluid inlets and outlets, drawing in hydraulic fluid from one inlet and discharging it from the other. The direction of oil delivery, i.e., the inlet and outlet for intake and discharge, is switched by switching the tilt direction of the swashplate 13.

[0012] The hydraulic motor 20 is connected to the main pump 10 in a closed circuit via a first oil passage 11 and a second oil passage 12. As described above, depending on the discharge direction of the main pump 10, high-pressure hydraulic fluid flows through one of the first oil passage 11 and the second oil passage 12, and low-pressure hydraulic fluid flows through the other. In other words, the hydraulic motor 20 is driven by the high-pressure hydraulic fluid discharged from the main pump 10 and also recirculates the low-pressure hydraulic fluid back to the main pump 10 after being driven. The output shaft of the hydraulic motor 20 rotates, for example, the wheels of a work vehicle. This hydraulic motor 20 is a swashplate type variable displacement motor with two hydraulic fluid inlets and outlets, through which hydraulic fluid flows in and out. The rotation direction of the hydraulic motor 20 switches when the oil supply direction from the main pump is switched, and the rotation speed is switched by switching the tilt angle of the swashplate 22.

[0013] A pressure selector valve 30 is connected to the first oil passage 11 and the second oil passage 12. The pressure selector valve 30 is a valve that supplies high-pressure and low-pressure hydraulic fluids flowing through the first oil passage 11 and the second oil passage 12 to each part. The pressure selector valve 30 is a three-position control valve and operates using the high-pressure hydraulic fluid of either the first oil passage 11 or the second oil passage 12 as the pilot pressure. For example, as shown in Figure 1, when there is no pressure difference between the first oil passage 11 and the second oil passage 12 (i.e., when there is no discharge of hydraulic fluid from the main pump 10 and the hydraulic motor is stopped), it is in the neutral position. In this case, the pressure selector valve 30 shuts off the supply of hydraulic fluid from the first oil passage 11 and the second oil passage 12 to the two-speed control valve 40, the flushing mechanism 80, and the brake mechanism 60.

[0014] Furthermore, when high-pressure hydraulic fluid flows through the first oil passage 11, the pressure selection valve 30 is switched to connect the first oil passage 11 to the two-speed switching valve 40, and the second oil passage 12 to the flushing mechanism 80 and the brake mechanism 60, as shown in Figures 2(a) and 2(b). In other words, the pressure selection valve 30 supplies the high-pressure hydraulic fluid in the first oil passage 11 to the two-speed switching valve 40, and supplies the low-pressure hydraulic fluid in the second oil passage 12 to the flushing mechanism 80 and the brake mechanism 60.

[0015] Also, when the high-pressure side hydraulic oil flows through the second oil passage 12, as shown in FIGS. 2(c) and 2(d), the pressure selection valve 30 is switched to connect the second oil passage 12 and the two-speed switching valve 40, and at the same time, connect the first oil passage 11 with the flushing mechanism 80 and the brake mechanism 60. That is, the pressure selection valve 30 supplies the high-pressure side hydraulic oil in the second oil passage 12 to the two-speed switching valve 40, and supplies the low-pressure side hydraulic oil in the first oil passage 11 to the flushing mechanism 80 and the brake mechanism 60. Details of the structure of the pressure selection valve 30 will be described later.

[0016] The two-speed switching valve 40 connected to the pressure selection valve 30 via an oil passage is, as shown in FIG. 1, a 3-port valve that switches the supply of the high-pressure side hydraulic oil supplied from the pressure selection valve 30 to the two-speed switching mechanism 50 and the oil discharge from the two-speed switching mechanism 50. The two-speed switching valve 40 is a hydraulic pilot valve, and is controlled to open and close by switching the charge pressure of the hydraulic oil replenished from the charge pump 90 driven by the engine 110 to the first oil passage 11 and the second oil passage 12 by the 3-port solenoid valve 42. The oil passage 91 for the replenishing hydraulic oil from this charge pump 90 branches midway and is connected to the first oil passage 11 and the second oil passage 12 that respectively pass through the check valves 92a and 92b to form a closed circuit. Thereby, it is configured to supply the replenishing hydraulic oil to the lower pressure side oil passage of either the first oil passage 11 or the second oil passage are. The pilot oil passage 41 to the two-speed switching valve 40 is an oil passage branched from the oil passage 91 before branching to the check valves 92a and 92b, and is connected to the pilot input port 40d of the two-speed switching valve 40 by energizing and switching the control 3-port solenoid valve 42. Details of the structure of the two-speed switching valve 40 will be described later.

[0017] The two-speed switching mechanism 50 controlled by the two-speed switching valve 40 includes a control cylinder 51 that switches the tilt angle of the swash plate 22 to switch the rotational speed of the hydraulic motor 20. This control cylinder 51 is a single-acting cylinder that operates with high-pressure side hydraulic oil. When this control cylinder 51 is not operating (when high-pressure side hydraulic oil is not supplied), the tilt of the swash plate 22 is set to the low-speed position by the biasing force of a spring (not shown). Also, when the control cylinder 51 is operating (when high-pressure side hydraulic oil is supplied), the tilt of the swash plate 22 is set to the high-speed position by the operating force of this control cylinder 51 against the biasing force of a spring (not shown). That is, the two-speed switching mechanism 50 controls the tilt angle (switching between low speed and high speed) of the swash plate 22 of the hydraulic motor 20. <000009​​​​​​​​​​A first stepped portion 202 is provided adjacent to the opening side (opposite side of the bottom surface 201) of the first housing portion 210. The first stepped portion 202 extends away from the central axis of the housing 21, with the boundary with the first housing portion 210 as its base end. The first stepped portion 202 is substantially parallel to the bottom surface 201 and substantially perpendicular to the rotation axis 23 of the hydraulic motor 20. The brake disc 63 of the brake mechanism 60 is provided so as to be aligned with this first stepped portion 202.

[0021] Furthermore, the housing 21 includes a first stepped portion 202, and a second housing portion 220 is provided adjacent to the first housing portion 210 with the first stepped portion 202 as the boundary. The second housing portion 220 has a larger diameter than the first housing portion 210. Also, there is a second stepped portion 203 adjacent to the opening side (opposite side from the first housing portion 210) end of the second housing portion 220. The second stepped portion 203 is formed parallel to the first stepped portion 202 and extends in a direction away from the central axis of the housing 21 with the boundary with the second housing portion 220 as its base end. Furthermore, the housing 21 includes a second stepped portion 203, and a third housing portion 230 is provided adjacent to the second housing portion 220 with the second stepped portion 203 as the boundary. The third housing portion 230 has a larger diameter than the second housing portion 220. In other words, inside the housing 21, the first housing section 210, the second housing section 220, and the third housing section 230 are formed in order from the bottom surface 201 side, such that their inner diameters increase in order by the first stepped section 202 and the second stepped section 203.

[0022] The housing 21 is divided into a recessed member (right side in the figure) that houses the hydraulic motor 20 and the rotating shaft 23, and a cover member (left side in the figure) that is provided to close the opening of the recessed member. The portion of the cover member of the housing 21 that faces the brake piston 61 is designated as the inner end face 21b.

[0023] The rotating shaft 23 of the hydraulic motor 20 is located on the central axis side of the housing 21, and a cylinder block or the like (not shown) that rotates integrally with the rotating shaft 23 is provided around it. Furthermore, a brake mechanism 60 is arranged around the cylinder block or the like. The brake piston 61 has a roughly stepped annular shape. The brake piston 61 is positioned between the first stepped portion 202 and the inner end face 21b of the housing 21 that is opposite to the first stepped portion 202. That is, the brake piston 61 is positioned on the outer circumference of the hydraulic motor 20 in the second housing portion 220 and the third housing portion 230. The side of the brake piston 61 that faces the brake disc 63 positioned along the first stepped portion 202 becomes the axial tip portion 61a, and the side opposite to this becomes the axial base portion 61b. The brake piston 61 is provided to be movable between a brake operating position in which its axial tip 61a abuts against the brake disc 63 and a brake release position in which its axial base 61b abuts against the inner end face 21b of the housing 21.

[0024] In the example shown in Figure 3(a), the inner end of the axial tip portion 61a is larger in the radial direction (vertical direction in Figure 3(a)) than the inner diameter of the first stepped portion 202. The outer end of the axial tip portion 61a extends to the side surface (inner circumferential surface) of the second housing portion 220 of the housing 21. Furthermore, the outer surface of the brake piston 61 that faces the side surface of the second housing portion 220 extends beyond the second housing portion 220 to the third housing portion 230 of the housing 21.

[0025] The brake piston 61 has a stepped portion facing the second stepped portion 203, and its diameter expands from the side surface of the second housing portion 220 through the second stepped portion 203 to the side surface of the third housing portion 230. That is, in the axial direction, the outer diameter of the brake piston 61 is larger at the axial base portion 61b than at the axial tip portion 61a due to this stepped portion. The surface of this stepped portion becomes the opposing surface 64 on the brake piston 61 side that faces the second stepped portion 203. There is also a gap between this opposing surface 64 and the second stepped portion 203, which is called the pressure chamber P. The pressure chamber P is an annular space.

[0026] Furthermore, in the axial direction of the rotating shaft 23, a small-diameter portion smaller than the diameter of the first housing portion 210 is formed on a part of the inner circumferential surface of the brake piston 61. The small-diameter portion is formed for a predetermined length from the axial tip portion 61a to the axial base portion 61b, and is formed for a length slightly shorter than the axial length of the second housing portion 220. Furthermore, at the axial base portion 61b, the brake piston 61 is formed to have a large-diameter portion with an inner diameter larger than the small-diameter portion. On the inner circumferential side of the brake piston 61, the large-diameter portion of the brake piston 61 becomes the housing portion for the spring 62.

[0027] The spring 62 biases the brake piston 61 in a direction that brings it into contact with the brake disc 63. The spring 62 is made of, for example, a coil spring.

[0028] The aforementioned pressure chamber P is configured to allow the introduction of low-pressure hydraulic fluid from the pressure selection valve 30 through a through-hole in the housing 21. When low-pressure hydraulic fluid is introduced into the pressure chamber P, the opposing surface 64 of the brake piston 61 is pressed away from the second stepped portion 203 of the housing 21, in opposition to the pressing force of the spring 62. As a result, the axial tip 61a of the brake piston 61 moves away from the brake disc 63.

[0029] The brake disc 63 is located inside the housing 21 on the rotating side of the hydraulic motor 20 and rotates integrally with the rotation axis 23 of the hydraulic motor 20. When the axial tip 61a of the brake piston 61 contacts the brake disc 63 due to the biasing force of the spring 62, the brake disc 63 is sandwiched between the axial tip 61a and the first stepped portion 202 of the housing 21. As a result, the brake of the hydraulic motor 20 is activated by frictional force, rendering the hydraulic motor 20 unable to rotate. On the other hand, when low-pressure hydraulic fluid is supplied to the pressure chamber P, the pressure of the low-pressure hydraulic fluid causes the brake piston 61 to move away from the brake disc 63 against the spring 62, releasing the brake and allowing the hydraulic motor 20 to rotate again.

[0030] As shown in Figure 3(b), in this embodiment, a brake oil drain passage 70 is provided so as to partially penetrate the annular brake piston 61. That is, the brake oil drain passage 70 is formed as a through hole that penetrates a part of the brake piston 61, for example, from a part of the axial base end 61b to the opposing surface 64 along the direction of expansion and contraction of the spring 62. An orifice is also provided in a part of the brake oil drain passage 70. The brake oil drain passage 70 connects the pressure chamber P and the internal space 24 of the housing 21.

[0031] When the brakes are applied, the axial base end 61b of the brake piston 61 separates from the inner end face 21b of the housing 21, thereby opening the brake oil drain passage 70. Conversely, when the brakes are released, the axial base end 61b of the brake piston 61 contacts the inner end face 21b of the housing 21, thereby closing the brake oil drain passage 70.

[0032] The internal space 24 of the housing 21 is a space that is cooled by flushing, and an oil drain passage 82 is connected to it that drains the hydraulic fluid after flushing to the drain DR. The pressure in this internal space 24 is below the set pressure of the flushing relief valve 81 (see Figure 1) and is lower than the pressure of the low-pressure hydraulic fluid in the pressure chamber P, so when the brake oil drain passage 70 is opened, the low-pressure hydraulic fluid in the pressure chamber P is drained through this internal space 24.

[0033] The flushing mechanism 80, as shown in Figure 1, includes an oil passage branching off from the oil passage from the pressure selection valve 30 to the brake mechanism 60 and leading to the hydraulic motor 20, and a flushing relief valve 81 provided in this oil passage. The flushing mechanism 80 is a mechanism that flushes and cools the hydraulic motor 20 to prevent the temperature of the hydraulic motor 20 and the hydraulic fluid from rising. In a closed circuit, the flushing mechanism 80 causes a portion of the low-pressure hydraulic fluid that is returned from the hydraulic motor 20 to the main pump 10 to flow into the internal space 24 (see Figure 3) of the housing 21 of the hydraulic motor 20, after the hydraulic motor 20 has been cooled. The hydraulic fluid is then discharged to the drain DR through the drain passage 82.

[0034] Next, the details of the pressure selector valve 30 will be described. As mentioned above, the pressure selector valve 30 is a three-position switching valve. The pressure selector 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 connected to the first oil passage 11 and the second oil passage 12, respectively. The first output port 32a is connected to the two-speed switching valve 40, and the second output port 32b is connected to the flushing mechanism 80 and the brake mechanism 60. The pressure selector valve 30 also has a first pilot input port 34a and a second pilot input port 34b, which are connected to the first oil passage 11 and the second oil passage 12, respectively.

[0035] In the illustrated example, the oil passage to the two-speed switching valve 40 is connected to two physical ports on the pressure selection valve 30: a first output port 32a that can be connected to the first input port 31a, and a first output port 32a that can be connected to the second input port 31b. In this specification, although both of these physical ports are connected to the two-speed switching valve 40, for the sake of explanation, both will be referred to as "first output port 32a".

[0036] The pressure selection valve 30 switches between the following three states depending on the pilot input status to the first pilot input port 34a and the second pilot input port 34b. (1) When high-pressure hydraulic fluid is introduced into the first pilot input port 34a, the system transitions to a first state in which the first input port 31a communicates with the first output port 32a and the second input port 31b communicates with the second output port 32b (see Figures 2(a) and 2(b)). (2) When high-pressure hydraulic fluid is introduced into the second pilot input port 34b, the second input port 31b communicates with the first output port 32a, and the system transitions to a second state in which the first input port 31a communicates with the second output port 32b (see Figures 2(c) and 2(d)). (3) If high-pressure hydraulic fluid 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 shut off, resulting in a neutral state where communication is stopped (see Figure 1).

[0037] In this embodiment, the high-pressure and low-pressure sides of the hydraulic fluid flowing through the first oil passage 11 and the second oil passage 12 are changed by switching the direction of oil discharge by the main pump 10. Accordingly, the first and second states of the pressure selection valve 30 are switched by the above configuration. As a result, the high-pressure hydraulic fluid is output from the first output port 32a and supplied to the two-speed switching valve 40, and the low-pressure hydraulic fluid is output from the second output port 32b and supplied to the brake mechanism 60 and the flushing mechanism 80. When the discharge of oil from the main pump 10 stops and the circulation of hydraulic fluid stops and the pressure difference between the first oil passage 11 and the second oil passage 12 disappears, the pressure selection valve 30 returns to the neutral state by the force of the spring.

[0038] Next, the details of the two-speed switching valve 40 will be described with reference to Figure 1. The two-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 by an oil passage to the first output port 32a of the pressure selection valve 30, the output port 40b is connected to the two-speed switching mechanism 50, and the return output port 40c is connected to the oil passage downstream of the flushing relief valve 81 of the flushing mechanism 80. This oil passage downstream of the flushing relief valve 81 is used as an oil drain passage.

[0039] As mentioned above, the pilot oil passage 41 to the two-speed switching valve 40 is connected to the pilot input port 40d of the two-speed switching valve 40 via a control 3-port solenoid valve 42. When no pilot oil is supplied to the pilot input port 40d, the output port 40b and return output port 40c of the two-speed switching valve 40 are connected, and oil is discharged from the two-speed switching mechanism 50 (oil discharge state). When pilot oil is supplied to the pilot input port 40d, the input port 40a and output port 40b of the two-speed switching valve 40 are connected, and high-pressure hydraulic oil is supplied to the two-speed switching mechanism 50 (supply state). In this way, by switching the supply and stop of pilot oil to the two-speed switching valve 40 with the 3-port solenoid valve 42, the supply state of high-pressure hydraulic oil to the two-speed switching mechanism 50 by the two-speed switching valve 40 and the oil discharge state from the two-speed switching mechanism 50 can be switched.

[0040] Next, the operation of the hydraulic drive unit 100 of this embodiment, configured as described above, will be explained with reference to Figures 1 and 2. When oil is not discharged from the main pump 10 to either the first oil passage 11 or the second oil passage 12 (zero tilt state with no tilt of the swash plate 13), there is no pressure difference between the first oil passage 11 and the second oil passage 12, so as shown in Figure 1, the pressure selection valve 30 is in the neutral state. For this reason, no hydraulic fluid is supplied to the two-speed switching mechanism 50, the swash plate 22 of the hydraulic motor 20 is in the low-speed position, no hydraulic fluid is supplied to the brake mechanism 60 and the brakes are activated, and no hydraulic fluid is supplied to the flushing mechanism 80 and flushing is stopped.

[0041] In this case, within the brake mechanism 60 shown in Figure 3(a), no hydraulic fluid is supplied to the pressure chamber P, and the axial tip 61a of the brake piston 61 is in contact with the brake disc 63 due to the biasing force of the spring 62, thereby operating the brake. Furthermore, the axial base end 61b of the brake piston 61 is separated from the inner end face 21b of the housing 21, and the brake oil drain passage 70 is open. As a result, the hydraulic fluid in the pressure chamber P is drained through the internal space 24 of the housing 21.

[0042] In Figure 1, when the swash plate 13 of the main pump 10 is tilted to one side, for example by external operation, the main pump 10 discharges hydraulic fluid into the first oil passage 11 or the second oil passage 12. For example, if fluid is drawn in from the inlet / outlet on the second oil passage 12 side and discharged from the inlet / outlet on the first oil passage 11 side, the first oil passage 11 becomes the high-pressure side and the second oil passage 12 becomes the low-pressure side. Since the charge pump 90 is also rotated and discharged by the engine 110, the low-pressure side also reaches the set pressure of the flushing relief valve by replenishing hydraulic fluid from the charge pump 90.

[0043] As a result, high-pressure hydraulic fluid is introduced into the first pilot input port 34a of the pressure selection valve 30 connected to the first oil passage 11, so the state of the pressure selection valve 30 becomes the first state shown in Figures 2(a) and 2(b). That is, the first input port 31a and the second input port 31b communicate with the first output port 32a and the second output port 32b, respectively. Therefore, the high-pressure hydraulic fluid introduced into the first input port 31a is supplied to the two-speed switching valve 40 connected to the first output port 32a. In addition, the low-pressure hydraulic fluid introduced into the second input port 31b is supplied to the flushing mechanism 80 and the brake mechanism 60 connected to the second output port 32b. As a result, the flushing mechanism 80 is activated to flush the hydraulic motor 20, and the brake mechanism 60 is activated, the brake oil drain passage 70 is closed, and the brake is released by the pressure in the pressure chamber P. As a result, the hydraulic motor 20 is rotated in one direction by the high-pressure hydraulic fluid discharged from the main pump 10, and for example, it rotates the wheels of a work vehicle in the forward direction, resulting in a low-speed travel state. The low-speed travel state refers to the relatively low speed among the speed settings of the two-speed switching mechanism 50. Similarly, the high-speed travel state, which will be described later, refers to the relatively high speed. Hereafter, "high speed" and "low speed" will similarly refer to the difference between the relative high speed and the relative low speed determined by the two-speed switching mechanism 50.

[0044] At this time, within the brake mechanism 60 shown in Figure 3, low-pressure hydraulic fluid is supplied to the pressure chamber P, and the brake piston 61 receives the pressure from the pressure chamber P on the stepped surface 61c. As a result, the axial tip 61a separates from the brake disc 63 against the biasing force of the spring 62, and the brake is released. At this time, the axial base end 61b of the brake piston 61 comes into contact with the inner end surface 21b of the housing 21, so the brake oil drain passage 70 is closed.

[0045] On the other hand, in Figure 1, when the swash plate 13 of the main pump 10 is tilted to the other side, the main pump 10 circulates the hydraulic fluid in the reverse direction, so the second oil passage 12 becomes the high-pressure side and the first oil passage 11 becomes the low-pressure side. Therefore, as shown in Figures 2(c) and 2(d), high-pressure hydraulic fluid is introduced into the second pilot input port 34b of the pressure selection valve 30 connected to the second oil passage 12, and the state of the pressure selection valve 30 becomes the second state. At this time, the second input port 31b and the first input port 31a communicate with the first output port 32a and the second output port 32b, respectively. As a result, high-pressure hydraulic fluid is supplied to the two-speed switching valve 40, and low-pressure hydraulic fluid is supplied to the brake mechanism 60 and the flushing mechanism 80. This causes the hydraulic motor 20 to flush and the brake to be released. As a result, the hydraulic motor 20 is rotated in the other direction, for example, by rotating the wheels of a work vehicle in the reverse direction to achieve a low-speed driving state. This configuration allows for the omission of brake piping compared to conventional designs.

[0046] In Figures 2(a) and 2(b) or 2(c) and 2(d), when the 3-port solenoid valve 42 that pilot-controls the two-speed switching valve 40 is further energized, it transitions to a pilot oil supply state. At this time, the two-speed switching valve 40 enters the aforementioned supply state (not shown) and supplies high-pressure hydraulic fluid to the control cylinder 51 of the two-speed switching mechanism 50. As a result, the control cylinder 51 operates, switching the swash plate 22 of the hydraulic motor 20 to the high-speed position, causing the hydraulic motor 20 and the travel wheels to rotate at high speed, and the work vehicle enters a high-speed travel state.

[0047] When the power to the 3-port solenoid valve 42 is turned OFF and the system switches to the pilot oil drain state, the two-speed switching valve 40 enters the oil drain state, and the hydraulic fluid from the control cylinder 51 of the two-speed switching mechanism 50 is drained to the drain DR via the flushing oil passage. As a result, the operation of the control cylinder 51 stops, the swash plate 22 of the hydraulic motor 20 returns to the low-speed position, the rotation of the hydraulic motor 20 and the wheels returns to low speed, and the work vehicle enters a low-speed travel state.

[0048] Furthermore, when the swash plate 13 of the main pump 10 is returned to the neutral position, the pressure difference between the first oil passage 11 and the second oil passage 12 disappears. As a result, high-pressure hydraulic fluid is not 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, and the pressure selection valve 30 returns to the neutral position (see Figure 1). Consequently, the supply of high-pressure hydraulic fluid to the two-speed switching valve 40 is stopped, as is the supply of low-pressure hydraulic fluid to the flushing mechanism 80 and the brake mechanism 60. As a result, flushing stops, the brake mechanism 60 activates, the rotation of the hydraulic motor 20 and the travel wheels stops, and the movement of the work vehicle also stops.

[0049] At this time, in the brake mechanism 60 shown in Figure 3(a), no hydraulic fluid is supplied to the pressure chamber P. Therefore, the brake piston 61 is subjected to the biasing force of the spring 62, causing its axial tip 61a to contact the brake disc 63 and activate the brake. At this time, the axial base end 61b of the brake piston 61 separates from the inner end face 21b of the housing 21, and the brake oil drain passage 70 is opened. When the brake oil drain passage 70 is opened, the hydraulic fluid in the pressure chamber P is drained through the internal space 24 of the housing 21. The drainage of the hydraulic fluid through this brake oil drain passage 70 is restricted by the orifice and performed gradually, so the brake is also operated gradually. This prevents shocks and adverse effects caused by sudden brake operation.

[0050] According to this embodiment, the supply of hydraulic fluid to the two-speed switching mechanism 50, the flushing mechanism 80, and the brake mechanism 60 of the hydraulic motor 20 can be controlled by only two valves, the pressure selection valve 30 and the two-speed switching valve 40. Therefore, a hydraulic drive system 100 that can control these mechanisms at low cost and with a small number of valves can be realized. In a closed-circuit hydraulic drive system that uses many valves, such as a two-speed selector valve, a high-pressure selector valve, a solenoid valve for pilot driving the two-speed selector valve, a solenoid valve for driving the brake release cylinder, and a low-pressure selector valve, the brake release cylinder and the two-speed selector valve (hydraulic pilot valve) are each driven by pilot oil. Therefore, two pilot lines are required, and two solenoid selector valves are required to supply and stop the pilot oil in those pilot lines. Compared to such hydraulic drive systems that require pipe fittings and hydraulic hoses to guide each pilot oil, this embodiment reduces the amount of piping work and the cost of piping components with the above configuration. Furthermore, in a hydraulic drive system having a high-pressure selector valve that supplies high-pressure hydraulic fluid to the two-speed switching valve, an electromagnetic proportional valve that controls the brake release actuator, and a low-pressure selector valve that supplies low-pressure hydraulic fluid to the electromagnetic proportional valve and the flushing relief valve, the two pilot pipes for brake release and two-speed switching can be omitted. However, this requires the use of many valves, such as the two-speed switching valve, high-pressure selector valve, electromagnetic proportional valve, and low-pressure selector valve, and a highly functional electromagnetic proportional valve is used instead of a simple electromagnetic switching valve. In addition, an expensive electromagnetic proportional valve and an expensive electronic control device for controlling the current value are also required. In comparison, in this embodiment, the above configuration makes it possible to reduce piping work time and piping component costs without using an electromagnetic proportional valve or an expensive electronic control device. When a hydraulic drive system is used as a motor for a work vehicle, mud and water ingress can be a problem, and the use of an electromagnetic proportional valve itself may become problematic, but in this embodiment, it is not necessary to adopt such a configuration.

[0051] Furthermore, according to this embodiment, a brake oil drain passage 70 is provided inside the brake piston 61. The brake oil drain passage 70 is opened and closed when the brake piston 61 contacts and separates from the inner end face 21b of the housing 21. As a result, a new valve to control the opening and closing of the drain passage from the brake mechanism 60 is not required, and the number of valves can be reduced and the piping can be simplified.

[0052] (Second embodiment) Figure 4(a) is a hydraulic circuit diagram of a hydraulic drive device 200 according to a second embodiment of the present invention, and Figure 4(b) is a detailed view of section E thereof (collectively referred to simply as "Figure 4"). In the following description, components that perform the same functions as in the first embodiment are denoted by the same reference numerals as in Figures 1 to 3, and redundant explanations are omitted as appropriate. The hydraulic drive device 200 of this embodiment has substantially the same configuration as the hydraulic drive device 100, but the layout of the brake oil drain passage is different. More specifically, instead of providing a brake oil drain passage inside the brake piston 61 (see Figure 3), in the hydraulic drive device 200, the brake oil drain passage 70a is connected to the pressure selection valve 130.

[0053] The pressure selector valve 130 has substantially the same structure as the pressure selector valve 30 of the first embodiment. That is, the pressure selector 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 two-speed switching valve 40, and the second output port 32b is connected to the brake mechanism 60 and the flushing mechanism 80. The pressure selector valve 130 also has a first pilot input port 34a and a second pilot input port 34b, which are connected to the first oil passage 11 and the second oil passage 12, respectively. On the other hand, unlike the pressure selector valve 30, the pressure selector valve 130 also has a return output port 33 connected to the brake oil drain passage 70a.

[0054] Similar to the pressure selector valve 30, the pressure selector valve 130 switches between three states—a first state, a second state, and a neutral state—depending on the pilot input status. Of these, the first and second states are the same as in the first embodiment. That is, as shown in Figure 4, in the neutral state of the pressure selector valve 130, similar to the pressure selector valve 30 in the first embodiment, 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 are disconnected in the first and second states. On the other hand, in the neutral state of the pressure selector valve 130, the second output port 32b, which is connected to the brake mechanism 60 and the flushing mechanism 80, is connected to the return output port 33, which is connected to the brake oil drain passage 70a.

[0055] Figure 5 is a schematic cross-sectional view showing the brake mechanism 60 and brake oil drain passage 70a of this embodiment. The brake oil drain passage 70a is connected upstream to the return output port 33 of the pressure selection valve 130, and downstream to the housing 21 of the hydraulic motor 20 via an orifice, communicating with its internal space 24. The internal space 24 of the housing 21 is a space cooled by flushing, and an oil drain passage 82 is connected to it for draining the hydraulic fluid after flushing to the drain DR. The pressure in this internal space 24 is below the set pressure of the flushing relief valve 81 (see Figure 4) and is lower than the pressure of the low-pressure side hydraulic fluid in the pressure chamber P of the brake mechanism 60. Therefore, when the oil passage to the pressure chamber P communicates with the brake oil drain passage 70a by the pressure selection valve 130, the hydraulic fluid in the pressure chamber P flows into the internal space 24 through the brake oil drain passage 70a and is drained through the oil drain passage 82. Furthermore, since the hydraulic fluid is gradually drained through the brake fluid drain passage 70a by being restricted by the orifice, the brakes are also operated gradually. This prevents shocks and adverse effects caused by sudden braking.

[0056] The brake mechanism 60 of this embodiment is the same as the brake mechanism 60 of the first embodiment, except that a brake oil drain passage 70 is not formed in the brake piston 61. Although the brake mechanism 60 is shown differently in the piping diagrams of Figures 1 and 4, this is the only difference between the brake mechanism 60 of the first embodiment and the brake mechanism 60 of this embodiment.

[0057] The operation of the hydraulic drive unit 200 of this embodiment, configured as described above, is the same as that of the hydraulic drive unit of the first embodiment, except for the oil discharge operation from the brake mechanism 60.

[0058] According to this embodiment, the supply of hydraulic fluid to the two-speed switching mechanism 50, the flushing mechanism 80, and the brake mechanism 60 of the hydraulic motor 20 can be controlled by only two valves, the pressure selection valve 30 and the two-speed switching valve 40. Therefore, a hydraulic drive system can be realized that controls each of the above mechanisms at low cost and with a small number of valves.

[0059] Furthermore, according to this embodiment, the pressure selection valve 130 is configured to open and close the brake oil drain passage 70a that drains oil from the brake mechanism 60. As a result, a new valve for controlling the opening and closing of the oil drain passage from the brake mechanism 60 is not required, and the number of valves can be reduced and the piping can be simplified.

[0060] (Third embodiment) Figure 6(a) is a hydraulic circuit diagram of a hydraulic drive device 300 according to a third embodiment of the present invention, and Figure 6(b) is a detailed view of section F. In this embodiment, the hydraulic drive device 300 uses a two-speed switching valve 140, which is a three-port electromagnetic switching valve, to drive the control cylinder 51 of the two-speed switching mechanism 50, instead of the two-speed switching valve 40, which is a hydraulic pilot valve. The rest of the configuration is the same as in the first embodiment.

[0061] The two-speed switching valve 140, like the two-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 two-speed switching mechanism 50, and the return output port 40c is connected to the oil passage downstream of the flushing relief valve 81 of the flushing mechanism 80. When the two-speed switching valve 140 is not energized, the output port 40b and the return output port 40c of the two-speed switching valve 140 are connected, and the two-speed switching mechanism 50 is in an oil discharge state. When the two-speed switching valve 140 is energized, the input port 40a and the output port 40b of the two-speed switching valve 40 are connected, and high-pressure hydraulic fluid is supplied to the two-speed switching mechanism 50.

[0062] Next, the operation of the hydraulic drive unit 300 of this embodiment, configured as described above, will be explained. When the hydraulic motor 20 is rotating at a low speed, energizing the two-speed switching valve 140, which is a three-port solenoid valve, causes the two-speed switching valve 140 to enter a supply state and supply high-pressure hydraulic fluid to the control cylinder 51 of the two-speed switching mechanism 50. As a result, the control cylinder 51 is activated, switching the swash plate 22 of the hydraulic motor 20 to the high-speed position, causing the hydraulic motor 20 and the wheels to rotate at high speed, and the work vehicle to enter a high-speed travel state.

[0063] On the other hand, when the power to the two-speed switching valve 140 is turned OFF, the two-speed switching valve 140 enters an oil-draining state, and the hydraulic fluid from the control cylinder 51 is drained to the drain DR via the oil passage downstream of the flushing relief valve 81. As a result, the operation of the control cylinder 51 stops, the swash plate 22 of the hydraulic motor 20 returns to the low-speed position, 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.

[0064] The other configurations of the hydraulic drive unit 300 in this embodiment are the same as those of the hydraulic drive unit 100 in the first embodiment shown in Figure 1. This configuration eliminates the need for a 3-port solenoid valve 42 and pilot oil passage 41 for pilot control of the two-speed switching valve 40. As a result, a hydraulic drive system can be realized that controls the supply and discharge of hydraulic fluid to the two-speed switching mechanism 50, brake mechanism 60, and flushing mechanism 80 of the hydraulic motor 20 with fewer valves and pipes.

[0065] Although embodiments of the present invention have been described above, various design modifications can be made to the present invention without departing from its spirit. For example, the two-speed switching valve 140 may be applied to the hydraulic drive device 200 according to the second embodiment. In the second embodiment, the oil drain passage from the brake mechanism 60 is configured to drain oil to the drain DR via the housing 21 of the hydraulic motor 20 and the flushing oil drain passage 82, but the invention is not limited to this. The oil drain passage from the brake mechanism 60 can drain oil via any route as long as it passes through the brake oil drain passage 70a connected to the pressure selection valve 130. [Explanation of symbols]

[0066] 10 Main pump 11. The first oil channel 12. Second oil channel 13 Swash plate 20 Hydraulic motor 21 Housing 21b Inner end surface 22 Swash plate 23 Rotation axis 24 Interior space 30,130 Pressure Selector Valve 31a First input port 31b Second input port 32a First output port 32b Second output port 33 Return output ports 34a First pilot input port 34b Second pilot input port 40, 140 Two-speed switching valve 40a Input Port 40b Output Port 40c return output port 40d Pilot Input Port 41 Pilot oil channel 42 3-port solenoid valve 50 Two-speed switching mechanism 51 Control Cylinder 60 Brake mechanism 61 Brake piston 61a Axial tip 61b Axial proximal end 61c Step surface 62 Springs 63 Brake Disc 64 Opposing surfaces 70, 70a Brake oil drain channel 80 Flushing mechanism 81 Flushing relief valve 82 Oil drain path 90 Charge Pump 91 Oil passage for replenishment hydraulic fluid 92a, 92b Check valve 100, 200, 300 Hydraulic drive unit 110 engine 201 Bottom 202 First step section 203 Second step section 210 First Detention Unit 220 Second Detention Unit 230 Third Detention Unit P pressure chamber

Claims

1. A hydraulic motor is connected to the main pump in a closed circuit via first and second oil passages, driven by the relatively high-pressure hydraulic fluid discharged from the main pump, and returns the relatively low-pressure hydraulic fluid to the main pump after being driven. A pressure selection valve connected to the first and second oil passages, which supplies the high-pressure hydraulic fluid and the low-pressure hydraulic fluid to each part, A two-speed switching valve connected to the pressure selection valve via an oil passage, A two-speed switching mechanism controlled by the two-speed switching valve controls the tilt angle of the swash plate of the hydraulic motor, A brake mechanism connected to the pressure selection valve via an oil passage, which performs the brake operation of the hydraulic motor, A brake oil drain passage having an orifice for draining hydraulic fluid from the brake mechanism to the outside of the closed circuit, A flushing mechanism that flushes the hydraulic motor using a portion of the low-pressure hydraulic fluid, Includes, When the hydraulic motor is rotationally driven, the pressure selection valve supplies the high-pressure hydraulic fluid from the first or second oil passage to the two-speed switching valve, and supplies the low-pressure hydraulic fluid from the second or first oil passage to the flushing mechanism and the brake mechanism. A hydraulic drive system characterized in that, when the hydraulic motor is stopped, the pressure selection valve shuts off the supply of hydraulic fluid from the first oil passage and the second oil passage to the two-speed switching valve, the flushing mechanism, and the brake mechanism.

2. The aforementioned brake mechanism is a mechanism that operates the brake by bringing the axial tip of a brake piston, which is provided inside the housing of the hydraulic motor, into contact with the brake disc by the biasing force of a spring, and releases the brake by separating the brake piston from the brake disc with the pressure of the low-pressure hydraulic fluid supplied to the pressure chamber. The brake oil drain passage is formed inside the brake piston and opens at the axial base end, connecting the pressure chamber and the internal space of the housing. When the brakes are applied, the axial base end of the brake piston separates from the inner end face of the housing, thereby opening the brake oil drain passage. The hydraulic drive device according to claim 1, characterized in that when the brake is released, the axial base end of the brake piston abuts against the inner end surface of the housing, thereby closing the brake oil drain passage.

3. The pressure selection valve has first and second input ports connected to the first and second oil passages, respectively, a first output port connected to the two-speed switching valve, a second output port connected to the flushing mechanism and the brake mechanism, and first and second pilot input ports connected to the first and second oil passages, respectively. When the high-pressure hydraulic fluid is introduced into the first pilot input port, the first and second input ports and the first and second output ports are connected to each other, resulting in a first state. When the high-pressure hydraulic fluid is introduced into the second pilot input port, the second and first input ports and the first and second output ports are connected to each other, resulting in a second state. The hydraulic drive device according to claim 2, characterized in that if the high-pressure hydraulic fluid is not introduced into either of the first and second pilot input ports, the device enters a neutral state in which each communication is stopped.

4. The brake oil drain passage is connected to the pressure selection valve, The hydraulic drive device according to claim 1, characterized in that when the hydraulic motor is stopped, the pressure selection valve shuts off the supply of hydraulic fluid from the first oil passage and the second oil passage to the two-speed switching valve, the flushing mechanism and the brake mechanism, and connects the oil passage to the brake mechanism to the brake oil drain passage.

5. The pressure selection valve has first and second input ports connected to the first and second oil passages, respectively, a first output port connected to the two-speed switching valve, a second output port connected to the flushing mechanism and the brake mechanism, a return output port connected to the brake oil drain passage, and first and second pilot input ports connected to the first and second oil passages, respectively. When the high-pressure hydraulic fluid is introduced into the first pilot input port, the first and second input ports and the first and second output ports are connected to each other, resulting in a first state. When the high-pressure hydraulic fluid is introduced into the second pilot input port, the second and first input ports and the first and second output ports are connected to each other, resulting in a second state. The hydraulic drive device according to claim 4, characterized in that if the high-pressure hydraulic fluid is not introduced into either of the first and second pilot input ports, the communication between them is stopped, and the second output port and the return output port are connected to enter a neutral state.

6. The hydraulic drive device according to claim 1, characterized in that the two-speed switching valve is a hydraulic pilot valve and is controlled to open and close using a portion of the hydraulic fluid supplied from the charge pump to the first or second oil passage.

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