JP2001304408A - Capacity control device for oil hydraulic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent mixing of air in suction oil of a sensing pump, also make bleeding of air easily performable even by mixing air in the suction oil of the sensing pump. SOLUTION: A charge pump 10 delivering pressure oil to suction oil paths 11, 19, 15R (or suction oil paths 11, 19, 15F) of a sensing pump 2 is provided. The pressure oil delivered from the charge pump 10 is sucked by the sensing pump 2 through the suction oil paths 11, 19, 15R (or suction oil paths 11, 19, 15F).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydraulic motor displacement control device for controlling the displacement of a hydraulic motor. More specifically, the present invention relates to a displacement control device for a hydraulic motor that prevents air from being mixed into suction oil of a sensing pump and that can easily release air even if air is mixed into suction oil of a sensing pump. Also, the present invention relates to a displacement control device for a hydraulic motor that can prevent frequent shifts when the vehicle is traveling at a speed near a vehicle speed range where the speed changes from a low speed to a high speed.

[0002]

2. Description of the Related Art In a vehicle such as a wheel loader, a wheel or a crawler belt is rotated by rotation of a hydraulic motor, and the vehicle speed is changed. The speed of the hydraulic motor is changed by changing the rotation speed of the hydraulic motor by changing the capacity of the hydraulic motor. As the capacity of the hydraulic motor increases, the rotational speed of the hydraulic motor decreases. Also, as the capacity of the hydraulic motor decreases, the rotation speed of the hydraulic motor increases.
In such shift control of the hydraulic motor, a pump called a sensing pump for detecting the rotation speed of the hydraulic motor may be used.

This sensing pump sucks pressure oil corresponding to the number of rotations of a hydraulic motor from a suction oil passage, and discharges the pressure oil sucked from the suction oil passage to a discharge oil passage.

[0004] Various inventions related to shift control of a hydraulic motor have already been known by filing various patent applications.

[0005] For example, the present applicant has disclosed in
In JP-A-33, two hydraulic motors, a low-speed hydraulic motor and a high-speed hydraulic motor, are provided to control the engagement of a clutch provided between the low-speed hydraulic motor and the drive shaft, The invention discloses that the shift is performed by combining the control of the displacement of the hydraulic motor and the control of the displacement of the low-speed hydraulic motor.

[0006]

In the sensing pump described above, suction oil may be sucked from a tank.

When suction oil is sucked from the tank, air may be mixed into the suction oil for various reasons.

Therefore, when the sensing pump sucks suction oil from the tank, air may enter the oil passage of the control circuit.

If air enters the oil passage of the control circuit, there is a problem that it is difficult to release air.

A first object of the present invention is to prevent air from being mixed into suction oil of a sensing pump and to easily release air even if air is mixed into suction oil of a sensing pump. I do.

By the way, when the vehicle is running at a speed near the vehicle speed range where the speed changes from a low speed to a high speed, the vehicle speed frequently changes, and hunting may occur in the shift control of the hydraulic motor.

[0012] When such hunting occurs, the ride comfort of the vehicle deteriorates and the life of the vehicle is shortened.

A second object of the present invention is to prevent the vehicle speed from being frequently changed when the vehicle is traveling at a speed near a vehicle speed range where the speed changes from a low speed to a high speed.

[0014]

Means and Effects for Solving the Problems The first aspect of the present invention.
In order to achieve the first object, the present invention provides a variable displacement hydraulic motor (1, 50) whose displacement changes by inputting a displacement control signal, a discharge oil passage and a suction oil passage, The number of rotations of the variable displacement hydraulic motor (1, 50) is detected, and pressure oil corresponding to the detected number of rotations is sucked from the suction oil passage, and the pressure oil sucked from the suction oil passage is sucked out of the suction oil passage. A sensing pump (2) for discharging to a discharge oil passage, wherein the capacity control is performed according to pressure oil sucked from the suction oil passage by the sensing pump (2) and pressure oil discharged to the discharge oil passage. A signal is input to the variable displacement hydraulic motor (1, 50) to control the displacement of the variable displacement hydraulic motor (1, 50). In the displacement control device for the hydraulic motor, pressure oil is discharged to the suction oil passage. Charge pump ( 0) is provided, characterized in that the pressure oil discharged from the charge pump (10) and to inhale through the suction oil passage by said sensing pump (2).

The first invention will be specifically described with reference to FIG.

According to the first invention, the suction oil passages 11, 19, 15R of the sensing pump 2 (or the suction oil passages 11, 1 and 15R) are provided.
9, 15F) is provided with a charge pump 10 for discharging pressure oil. The pressure oil discharged from the charge pump 10 is supplied to the suction oil passages 11, 19, and 15R by the sensing pump 2.
(Or the suction oil passages 11, 19, and 15F).

According to the first aspect of the present invention, the pressure oil discharged from the charge pump 10 is sucked by the sensing pump 2 as suction oil instead of the pressure oil in the tank. 19, 15R
(Or suction oil passages 11, 19, and 15F) can be prevented from being mixed with air. Further, even if air is mixed into the suction oil of the sensing pump 2, the suction oil passage 11, the suction oil passage 15R, or the suction oil passage 15F can be opened to easily release the air.

According to a second aspect of the present invention, there is provided a variable displacement hydraulic motor (1, 50) having a displacement that changes by inputting a displacement control signal, wherein the variable displacement hydraulic motor is provided. A control valve (3) for outputting a displacement control signal for controlling the displacement of the variable displacement hydraulic motor (1, 50) according to the number of revolutions of the motor (1, 50); A sensing pressure (Ps) corresponding to the number of rotations of the variable displacement hydraulic motor (1, 50) and a charging pressure (Ps) smaller than the sensing pressure (Ps)
c) and a pressure receiving surface (3e) on which the charge pressure (Pc) acts, and the valve position is set according to the pressure acting on these pressure receiving surfaces (3e, 3f). A low speed range position (3a) corresponding to a low rotation speed range of the variable displacement hydraulic motor (1, 50) or a high speed range position (3b) corresponding to a high rotation speed range of the variable displacement hydraulic motor (1, 50). The control valve (3) is configured to switch to
When the sensing pressure (Ps) becomes lower than the sensing pressure (Ps) when switching from the low speed range position (3a) to the high speed range position (3b), the valve position of the control valve (3) is changed. The high-speed range position (3b) is switched to the low-speed range position (3a).

The second invention will be specifically described with reference to FIG.

According to the second aspect of the present invention, the control valve 3 is provided with the pressure receiving surface 3f on which the sensing pressure Ps corresponding to the rotation speed of the hydraulic motor 1 and the charge pressure Pc smaller than the sensing pressure Ps act.
And a pressure receiving surface 3e on which the charge pressure Pc acts, and a valve position corresponding to the low rotation speed region of the hydraulic motors 1 and 50 or a hydraulic pressure position 3a corresponding to the pressure acting on the pressure receiving surfaces 3e and 3f. It is configured to switch to the high-speed range position 3b corresponding to the high rotation speed range of the motors 1 and 50.

Here, the sensing pressure Ps is set at the low speed range position 3a.
Pressure P when switching to high speed range position 3b from
When it becomes lower than s, the valve position of the control valve 3 switches from the high speed range position 3b to the low speed range position 3a.

According to the second aspect, unless the sensing pressure Ps is lower than the sensing pressure Ps when the sensing pressure Ps is switched from the low speed range position 3a to the high speed range position 3b, the control valve 3 is moved from the high speed range position 3b to the low speed range. Since the vehicle is not switched to the range position 3a, it is possible to prevent the vehicle speed from frequently changing when the vehicle is traveling at a speed near the vehicle speed range where the vehicle switches from a low speed to a high speed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic motor displacement control apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a hydraulic circuit diagram of the present embodiment.

As shown in FIG. 1, in this embodiment, the hydraulic pump 7 and the hydraulic motors 1 and 50 form a closed circuit. In the present embodiment, a case is assumed in which the vehicle is run by rotating wheels or crawler tracks by the hydraulic motors 1 and 50. The description will be made on the assumption that the hydraulic pump 7 and the hydraulic motors 1 and 50 use a swash plate type hydraulic pump and hydraulic motor. Instead of the swash plate type, a swash shaft type hydraulic pump or hydraulic motor may be used.

The hydraulic pump 7 is a variable displacement hydraulic pump. The hydraulic pump 7 is a swing type hydraulic pump having two ports 7b and 7c and capable of reversing the flow of pressure oil.

The hydraulic pump 7 is connected to a motor (not shown) via a rotating shaft 9. When the prime mover operates, the rotating shaft 9 rotates and the hydraulic oil is discharged from the hydraulic pump 7. As the inclination angle of the swash plate 7a of the hydraulic pump 7 changes, the capacity (displacement volume) of the hydraulic pump 7 changes. The swash plate 7a of the hydraulic pump 7 is connected to the piston 36. When the piston 36 operates, the capacity of the hydraulic pump 7 changes. Pressure oil having a pressure Pp (hereinafter referred to as discharge pressure Pp) is discharged from the port 7b or the port 7c of the hydraulic pump 7. The ports 7b and 7c of the hydraulic pump 7 are connected to the ports 1b and 1c of the hydraulic motor 1 through oil passages 8F and 8R, respectively.
Connected to The oil passage 8F branches to an oil passage 57.
The oil passage 8R is branched to an oil passage 58.

The charge pump 10 is a fixed displacement hydraulic pump. The charge pump 10 is connected to the prime mover via the rotating shaft 9. When the prime mover operates, the rotating shaft 9 rotates and the pressure oil is discharged from the charge pump 10. The discharge port 10 a of the charge pump 10 is connected to the charge pump discharge oil passage 11. A relief valve 12 is connected to the charge pump discharge oil passage 11. The relief valve 12 constantly fixes the pressure in the charge pump discharge oil passage 11 to the relief pressure Pc during the operation of the prime mover.

When pressure oil is discharged from the charge pump 10, charge pressure oil having a pressure Pc (hereinafter referred to as charge pressure Pc) is output to the charge pump discharge oil passage 11. The charge pump discharge oil passage 11 is connected to the motor displacement control unit 4.

The hydraulic motor 1 is a variable displacement type hydraulic motor. One port 1b of the hydraulic motor 1 is connected to an oil passage 8F. The other port 1c of the hydraulic motor 1 is connected to an oil passage 8
Connected to R. Assuming that the flow rate of the pressure oil discharged from the hydraulic pump 7 is constant, the displacement (displacement volume) of the hydraulic motor 1 changes due to the change of the swash plate 1a of the hydraulic motor 1, and the shift of the hydraulic motor 1 is performed. Will be When the swash plate 1a changes to the side where the capacity of the hydraulic motor 1 increases, the rotation speed of the hydraulic motor 1 decreases. Further, when the swash plate 1a changes to the side where the capacity of the hydraulic motor 1 decreases, the rotation speed of the hydraulic motor 1 increases.

The swash plate 1 a of the hydraulic motor 1 is connected to the piston 6. When the piston 6 operates, the capacity of the hydraulic motor 1 changes. The position of the piston 6 is the transmission valve 5
Is controlled by The piston 6 is housed in a cylinder 33.

The rotary shaft 13 of the hydraulic motor 1 is connected to a speed reducer 14. The drive shaft 59 is connected to the speed reducer 14. The drive shaft 59 is connected to wheels or crawler tracks. When the rotary shaft 13 of the hydraulic motor 1 rotates, the drive shaft 59 rotates via the speed reducer 14, and the wheels or crawler tracks rotate. Therefore, the speed of the vehicle changes.

The rotary shaft 13 of the hydraulic motor 1 is
4 is connected to the vehicle speed sensing pump 2. The rotation shaft 13 may be directly connected to the vehicle speed sensing pump 2. The vehicle speed sensing pump 2 is a fixed displacement hydraulic pump. Vehicle speed sensing pump 2 has two ports 2
a and 2b. The ports 2a and 2b of the vehicle speed sensing pump 2 are connected to oil passages 15F and 15R, respectively. The oil passages 15F and 15R are connected to the motor displacement control unit 4, respectively. The vehicle speed sensing pump 2 sucks pressure oil discharged from the charge pump 10 as suction oil instead of the pressure oil in the tank 40.

When the pressure oil is discharged from the port 7b of the hydraulic pump 7, the vehicle moves forward, and when the pressure oil is discharged from the port 7c of the hydraulic pump 7, the vehicle moves backward.

When the piston 36 moves from the neutral position to the side for moving the vehicle forward, the swash plate 7a of the hydraulic pump 7 tilts forward and the discharge pressure P from one port 7b of the hydraulic pump 7 moves.
The pressure oil of p is discharged to the oil passage 8F. The pressure oil discharged to the oil passage 8F is supplied to the port 1b of the hydraulic motor 1. When the pressure oil is supplied to the port 1b of the hydraulic motor 1, the hydraulic motor 1 operates, the drive shaft 59 rotates in the forward direction, and the vehicle moves forward.

Similarly, the vehicle moves backward.

When the rotating shaft 13 of the hydraulic motor 1 rotates in the forward direction, the vehicle speed sensing pump 2 rotates in accordance with the number of rotations of the rotating shaft 13, and the pressure oil of the pressure Ps (hereinafter referred to as sensing pressure Ps) flows from the port 2a. To the oil passage 15F. The sensing pressure Ps of the oil passage 15F has a magnitude corresponding to the rotation speed of the hydraulic motor 1. Conversely, when the rotation shaft 13 of the hydraulic motor 1 rotates in the reverse direction, the vehicle speed sensing pump 2 rotates according to the rotation speed of the rotation shaft 13 and discharges the pressure oil of the sensing pressure Ps from the port 2b to the oil passage 15R. . The sensing pressure Ps of the oil passage 15R has a magnitude corresponding to the rotation speed of the hydraulic motor 1.

The hydraulic motor 50 is similar to the hydraulic motor 1.
Is also a variable displacement hydraulic motor. One port 50 b of the hydraulic motor 50 is connected to an oil passage 57. The other port 50 c of the hydraulic motor 50 is connected to the oil passage 58. Assuming that the flow rate of the hydraulic oil discharged from the hydraulic pump 7 is constant, the displacement (displacement volume) of the hydraulic motor 50 changes due to the change of the swash plate 50a of the hydraulic motor 50, and the hydraulic motor 50 shifts. Will be Hydraulic motor 50
When the swash plate 50a changes to the side where the capacity of the hydraulic motor 50 increases, the rotation speed of the hydraulic motor 50 decreases. The hydraulic motor 50
When the swash plate 50a changes to the side where the capacity of the hydraulic motor 50 decreases, the rotation speed of the hydraulic motor 50 increases.

The swash plate 50a of the hydraulic motor 50 is
5a. When the piston 55a operates, the capacity of the hydraulic motor 50 changes. Piston 55
The position of “a” is controlled by the servo valve 56. The servo valve 56 is connected between the oil passage 54 and the tank 40. The piston 55a is housed in the cylinder 55.

The rotating shaft 52 of the hydraulic motor 50 is
1 is connected to the speed reducer 14. The clutch 51 is connected to a clutch control oil passage 53. When the tank pressure is output to the clutch control oil passage 53, the clutch 51 is connected. When the charge pressure Pc is output to the clutch control oil passage 53, the clutch 51 enters the disconnected state.

When the clutch 51 is in the connected state, the rotating shaft 52 of the hydraulic motor 50 rotates together with the rotating shaft 13 of the hydraulic motor 1, the driving shaft 59 rotates through the speed reducer 14, and the wheels or crawler belts rotate. I do. Therefore, the speed of the vehicle changes.

On the other hand, when the clutch 51 is in the disengaged state, the rotation shaft 52 of the hydraulic motor 50 stops, and the rotation of only the rotation shaft 13 of the hydraulic motor 1 rotates the drive shaft 59 to rotate the wheels or the crawler belt. .

The rotary shaft 52 of the hydraulic motor 50 is
Is connected to the vehicle speed sensing pump 2 via the

The swash plate 7a of the hydraulic pump 7 is tilted forward, and pressure oil having a discharge pressure Pp is discharged from one port 7b of the hydraulic pump 7 to the oil passage 8F. The pressure oil discharged to the oil passage 8F is diverted to the oil passage 57 and supplied to the port 50b of the hydraulic motor 50. When the pressure oil is supplied to the port 50b of the hydraulic motor 50, the hydraulic motor 50 operates, and when the clutch 51 is in the connected state, the rotating shaft 52 rotates in the forward direction and the vehicle moves forward.

Similarly, the vehicle moves backward.

When the rotation shaft 52 of the hydraulic motor 50 rotates in the forward direction, the vehicle speed sensing pump 2 rotates according to the rotation speed of the rotation shaft 52 and discharges the pressure oil of the sensing pressure Ps from the port 2a to the oil passage 15F. I do. The sensing pressure Ps of the oil passage 15F has a magnitude corresponding to the rotation speed of the hydraulic motor 50. Conversely, when the rotation shaft 52 of the hydraulic motor 50 rotates in the reverse direction, the vehicle speed sensing pump 2 rotates according to the rotation speed of the rotation shaft 52 and discharges the pressure oil of the sensing pressure Ps from the port 2b to the oil passage 15R. . Sensing pressure P of oil passage 15R
s has a size corresponding to the rotation speed of the hydraulic motor 50. The motor displacement control section 4 includes a switching valve 16, a throttle valve 21, and the control valve 3.

The switching valve 16 is a two-position switching valve having a position 16a and a position 16b.

The oil passages 15F and 15R are connected to the switching valve 16. The oil passage 15F branches to an oil passage 17a. The oil passage 17a is connected to one pressure receiving surface 16c of the switching valve 16. The oil passage 15R is branched to an oil passage 17b. Oil passage 17
“b” is connected to the other pressure receiving surface 16 d of the switching valve 16.
The output side of the switching valve 16 is connected to oil passages 18 and 19.
The oil passage 19 is connected to the charge pump discharge oil passage 11. Therefore, the pressure in the oil passage 19 becomes the charge pressure Pc.

When the hydraulic motor 1 is rotating forward, the vehicle speed sensing pump 2 discharges pressure oil to the oil passage 15F. At this time, the sensing pressure Ps acts on the pressure receiving surface 16c of the switching valve 16 via the oil passage 17a. Therefore, the switching valve 16 is switched to the position 16a. Therefore, oil passage 15F
Communicates with the oil passage 18 and the pressure in the oil passage 18 is the sensing pressure P
s. At this time, the oil passage 15R communicates with the oil passage 19, and the pressure of the oil pressure 15R is the charge pressure P which is the pressure in the oil passage 19.
becomes c.

Similarly, when the hydraulic motor 1 is rotating backward, the switching valve 16 is switched to the position 16b. Therefore, the pressure of the oil passage 18 becomes the sensing pressure Ps,
The pressure in the oil passage 15R becomes the charge pressure Pc.

As described above, the pressure in the oil passage 18 is equal to the sensing pressure Ps regardless of whether the hydraulic motor 1 is rotating in the forward or backward rotation direction.

A throttle valve 21 for controlling the flow rate Q of the pressure oil flowing through the oil passage 18 is provided on the oil passage 18. The throttle valve 21 has two positions, a position 21a and a position 21b.

When the throttle valve 21 moves toward the position 21a, the aperture area A of the throttle of the throttle valve 21 decreases. Throttle valve 21
Moves to the position 21b side, the opening area A of the throttle of the throttle valve 21 increases. The opening area A changes continuously between the position 21a and the position 21b.

The oil passage 18 is connected to the oil passage 20 on the input side of the throttle valve 21.
Has branched to. The oil passage 20 is a pressure receiving surface 21c of the throttle valve 21.
Connected to Therefore, the throttle valve 21 has the sensing pressure Ps
Is pushed in the direction of the position 21c. The oil passage 18 branches to an oil passage 22 on the output side of the throttle valve 21. The oil passage 22 is connected to the other pressure receiving surface 21 d of the throttle valve 21. A spring 21e is provided on the pressure receiving surface 21d of the throttle valve 21. The oil passage 22 is connected to the oil passage 19. Accordingly, the throttle valve 21 is moved to the position 21 by the charge pressure Pc and the spring 21e.
It is pushed in the direction of a.

Next, the sensing pressure Ps will be described.

The sensing pressure Ps is designed to increase as the rotational speed of the hydraulic motor 1 increases.

When the pressure difference between the pressures P1 and P2 before and after the throttle valve 21 is ΔP, the flow rate Q flowing through the oil passage 18 and the pressure difference ΔP
And the aperture area A of the throttle of the throttle valve 21, the following relationship is established.

Q = c · A√ (ΔP) (1) where c is a flow coefficient.

FIG. 3 shows the relationship between the flow rate Q and the differential pressure ΔP. The characteristic L indicated by a solid line in FIG. 3 is the flow rate Q and the differential pressure Δ when the throttle valve 21 operates and moves between the positions 21a and 21b.
The relationship with P is shown.

As shown in FIG. 3, the characteristic L1 switches to the characteristic L2 as the flow rate Q increases.

When the rotation speed of the hydraulic motor 1 increases, the input pressure P1 of the throttle valve 21 increases, so that a large pressure acts on the pressure receiving surface 21c of the throttle valve 21. Therefore, the throttle valve 21 is located at the position 21b. Therefore, the opening area A of the throttle valve 21 increases. Therefore, when the rotation speed of the hydraulic motor 1 is high, the flow rate Q and the differential pressure ΔP change according to the characteristic L2 shown in FIG.

Next, the control valve 3 will be described.

The control valve 3 has two positions, a position 3a in a low speed range and a position 3b in a high speed range.

Here, the low speed range means that the speed V of the vehicle is 0 km /
It is a speed range from h to V1. The high-speed range is a speed range in which the speed V of the vehicle is higher than V1 and equal to or lower than the speed V2 allowed by the vehicle.

The input port 3 g of the control valve 3 is connected to the charge pump discharge oil passage 11. The control valve 3 is constantly supplied with pressure oil having a charge pressure Pc. On the input side of the control valve 3, the charge pump discharge oil passage 11 branches to a pilot oil passage 23. The pilot oil passage 23 is connected to the pressure receiving surface 3 e of the control valve 3. Therefore, the charge pressure Pc acts as a pilot pressure on the pressure receiving surface 3e of the control valve 3. The pressure receiving surface 3e of the control valve 3 is provided with a spring 3d. The control valve 3 is pushed in the direction of the position 3a by the charge pressure Pc and the spring 3d.

The tank port 3h of the control valve 3 is connected to the tank 40
Is in communication with

The port 3m of the control valve 3 is connected to the pilot oil passage 2
4 is connected. The pilot oil passage 24 is connected to the other pressure receiving surface 3f of the control valve 3. Therefore, the pressure in the pilot oil passage 24 acts on the pressure receiving surface 3f of the control valve 3 as the pilot pressure.

On the input side of the throttle valve 21, the oil passage 18 branches to a pilot oil passage 25. The pilot oil passage 25 further branches into a pilot oil passage 25a. The pilot oil passage 25a is connected to the pressure receiving surface 3f of the control valve 3. Therefore, the sensing pressure P of the oil passage 18 is applied to the pressure receiving surface 3f of the control valve 3.
s acts as pilot pressure. The position of the control valve 3 is determined by the pressure of the pilot oil passage 24 and the sensing pressure Ps.
It is pushed in the directions of b and 3c.

The pilot oil passage 25 is connected to port 3 of the control valve 3.
r.

The output port 3j of the control valve 3 is connected to the oil passage 26. The port 3n of the control valve 3 is connected to the clutch control oil passage 53.

When the control valve 3 is in the low speed range position 3a, the input port 3g communicates with the port 3m and the output port 3j. Therefore, the charge pump discharge oil passage 11 and the pilot oil passage 24
Communicates through the pilot oil passage 24 to charge pressure P
c acts on the pressure receiving surface 3f of the control valve 3. The charge pump discharge oil passage 11 and the oil passage 26 communicate with each other, and the charge pressure Pc is output to the oil passage 26 via the control valve 3. Further, the tank port 3h communicates with the port 3n. Therefore, the tank 40 communicates with the oil passage 53, and the tank pressure is output to the clutch control oil passage 53 via the control valve 3.

When the control valve 3 is in the high speed range position 3b, the input port 3g communicates with the port 3n. Therefore, the charge pump discharge oil passage 11 and the oil passage 53 communicate with each other, and the charge pressure Pc is output to the clutch control oil passage 53 via the control valve 3. The tank port 3h and the output port 3j communicate. Therefore, the tank 40 and the oil passage 26 communicate with each other, and the tank pressure is output to the oil passage 26 via the control valve 3. The port 3r and the port 3m communicate with each other, and the sensing pressure Ps (P1) acts on the pressure receiving surface 3f of the control valve 3 via the pilot oil passage 24.

Next, the transmission valve 5 will be described.

The shift valve 5 has a position 5a and a position 5b.

The pressure receiving surface 5d of the transmission valve 5 is provided with pilot ports 5f and 5g. The other pressure receiving surface 5c of the transmission valve 5 is provided with a spring 5e.

The pilot port 5f of the transmission valve 5 is connected to the oil passage 2
It communicates with 6. Therefore, the pressure of the pressure oil output from the control valve 3 acts on the pilot port 5f of the transmission valve 5 as the pilot pressure.

The pilot port 5g of the transmission valve 5 is connected to the oil passage 3
It communicates with 1. The oil passage 31 is connected to the oil passage 36. The oil passages 8R and 8F are connected to check valves 27 and 28 via oil passages 29 and 30, respectively. Check valve 2
7 and 28 are connected to an oil passage 36.

The check valve 27 allows pressure oil to pass only in the direction from the oil passage 29 to the oil passage 36. Check valve 2
8 allows the pressure oil to pass only in the direction from the oil passage 30 to the oil passage 36. For this reason, the higher pressure of the oil passages 8R and 8F is led to the oil passage 36. Therefore, the pressure in the oil passage 8F or the oil passage 8R
Of the pressures acts as pilot pressure.
That is, the discharge pressure Pp of the hydraulic pump 7 acts as a pilot pressure on the pilot port 5g of the transmission valve 5.

The oil passage 31 is connected to the oil passage 32. The oil passage 32 branches to an oil passage 34. The oil passage 34 is connected to the transmission valve 5. The oil passage 32 communicates with the cylinder chamber 33 b on the small diameter side of the piston 6.

The large-diameter cylinder chamber 33 a of the piston 6 communicates with the oil passage 35. The oil passage 35 is connected to the transmission valve 5. The transmission valve 5 is connected to the tank 40.

When the transmission valve 5 is located at the position 5a, the oil passage 34 and the oil passage 35 communicate with each other via the transmission valve 5. Therefore, the pressure in the cylinder chamber 33a on the large-diameter side of the piston 6
It becomes the same magnitude as the pressure of 2. Also, the pressure in the cylinder chamber 33 b on the small diameter side of the piston 6 becomes the same as the pressure in the oil passage 32. Therefore, the piston 6 moves in the direction of compressing the cylinder chamber 33b on the small diameter side due to the difference in the pressure receiving area of the piston 6. Therefore, the swash plate 1a of the hydraulic motor 1 tilts to the side where the capacity is increased.

When the transmission valve 5 is located at the position 5b, the oil passage 35 communicates with the tank 40 via the transmission valve 5. Therefore, the pressure in the cylinder chamber 33a on the large diameter side of the piston 6 becomes the tank pressure. Also, the cylinder chamber 33 on the small diameter side of the piston 6
The pressure of b is the same as the pressure of the oil passage 32. Therefore, the piston 6 moves in a direction to compress the large-diameter cylinder chamber 33a. Therefore, the swash plate 1a of the hydraulic motor 1 tilts to the side where the capacity becomes smaller. The transmission valve 5 changes to a position where the force according to the pilot pressure acting on the pilot ports 5f and 5g and the spring force of the spring 5e are balanced.

Hereinafter, the operation of the hydraulic circuit of FIG. 1 will be described.

The following control contents are the same for both the case where the vehicle is moving forward and the case where the vehicle is moving backward, so that the case where the vehicle is moving forward will be described as a representative. I do.

When the vehicle is moving forward, the pump discharge pressure oil in the oil passage 8F is supplied to the port 1b of the hydraulic motor 1
And the pressure oil is discharged from the port 1c of the hydraulic motor 1 to the oil passage 8R.

The vehicle speed sensing pump 2 discharges a flow rate corresponding to the rotation speed of the hydraulic motor 1 to the oil passage 15F.

Therefore, the switching valve 16 is located at the position 16a, and the oil passage 15F communicates with the oil passage 18. The pressure in the oil passage 18 has a magnitude corresponding to the rotation speed of the hydraulic motor 1.

When the control valve 3 is located at the low speed range position 3a, the input port 3g and the output port 3j communicate. Therefore, the charge pump discharge oil passage 11 and the oil passage 26 communicate with each other, and the charge pressure Pc is output to the oil passage 26 via the control valve 3.

FIG. 2A shows the position of the transmission valve 5 when the control valve 3 is located at the low speed range position 3a.

As shown in FIG. 2A, a charge pressure Pc is applied as a pilot pressure to the pilot port 5f of the transmission valve 5 through the oil passage 26. On the other hand, the pressure in the oil passage 31 is applied to the pilot port 5g of the transmission valve 5 as pilot pressure. Therefore, the shift valve 5 moves in a direction to compress the spring 5e, and the shift valve 5 is located at the position 5a. Transmission valve 5
Is located at the position 5a, the oil passage 34 and the oil passage 35 communicate with each other via the transmission valve 5. Therefore, the pressure in the cylinder chamber 33 a on the large diameter side of the piston 6 becomes the pressure in the oil passage 32. The pressure in the cylinder chamber 33b on the small diameter side of the piston 6 is
2 pressure. Due to the difference in the pressure receiving area of the piston 6, the piston 6 moves in a direction to compress the cylinder chamber 33b on the small diameter side. Therefore, the swash plate 1a of the hydraulic motor 1 tilts to the side where the capacity is increased.

On the other hand, when the control valve 3 is located at the low speed range position 3a, the tank port 3h and the port 3n communicate. Therefore, the tank 40 communicates with the clutch control oil passage 53, and the tank pressure is output to the clutch control oil passage 53 via the control valve 3. As a result, the clutch 51 enters the connected state.

The pressure oil of the tank pressure output to the clutch control oil passage 53 is diverted to the oil passage 54 and supplied to the servo valve 56. Then, the piston 55a is operated by the servo valve 56.
Is controlled, and the swash plate 50a of the hydraulic motor 50 tilts to the side where the capacity is increased.

As described above, when the rotational speeds of the hydraulic motors 1 and 50 are small, that is, when the input pressure P1 of the throttle valve 21 is small, the capacity of the hydraulic motors 1 and 50 increases.

When the rotation speed of the hydraulic motor 1 increases and the pressure Ps in the oil passage 18 increases, the control valve 3
Move in the direction of b.

When the control valve 3 is located at the high speed range position 3b,
The tank port 3h communicates with the output port 3j. Therefore, the tank 40 communicates with the oil passage 26, and the tank pressure is output to the oil passage 26 via the control valve 3.

FIG. 2B shows the position of the transmission valve 5 when the control valve 3 is located at the high speed range position 3b.

The pilot port 5f of the transmission valve 5 is at the tank pressure P. On the other hand, the pilot port 5 of the transmission valve 5
The pressure in the oil passage 32 is applied to g through the oil passage 31 as a pilot pressure. Therefore, the transmission valve 5 moves in the direction in which the spring 5e extends, and the transmission valve 5 is located at the position 5b. When the transmission valve 5 is located at the position 5b, the oil passage 34
And the tank 40 communicate with each other. Therefore, the pressure in the cylinder chamber 33a on the large diameter side of the piston 6 becomes the tank pressure (low pressure). The pressure in the cylinder chamber 33b on the small diameter side of the piston 6 becomes the pressure (high pressure) in the oil passage 32. Accordingly, the piston 6 moves in a direction to compress the large-diameter cylinder chamber 33a. Therefore, the swash plate 1a of the hydraulic motor 1 tilts to the side where the capacity becomes smaller.

On the other hand, when the control valve 3 is located at the high speed range position 3b, the input port 3g and the port 3n communicate with each other. For this reason, the charge pump discharge oil passage 11 and the clutch control oil passage 53
And the charge pressure Pc is output to the clutch control oil passage 53 via the control valve 3. As a result, the clutch 51 enters the disconnected state.

The pressure oil of the charge pressure Pc output to the clutch control oil passage 53 is diverted to the oil passage 54 and
6. The position of the piston 55a is controlled by the servo valve 56, and the swash plate 50a of the hydraulic motor 50 is controlled.
Tilts to the side where the capacity becomes smaller.

As described above, when the rotational speeds of the hydraulic motors 1 and 50 are large and the pressure Ps in the oil passage 18 is large, the capacity of the hydraulic motors 1 and 50 becomes small.

The pressure applied to the pilot port 5g of the transmission valve 5 changes according to the load applied to the wheels or the crawler belt. That is, when the load applied to the wheels or crawler belt increases, the pressure applied to the pilot port 5g of the transmission valve 5 via the oil passage 8F or 8R increases, and the transmission valve 5 moves from the position 5b to the position 5a. Therefore, the hydraulic motor 1
Of the swash plate 1a tilts toward the side where the capacity is increased. As described above, when the load applied to the wheels or the crawler belt increases, the capacity of the hydraulic motor 1 increases, and a torque corresponding to the load applied to the wheels or the crawler belt is generated in the hydraulic motor 1.

The control valve 3 is provided with hysteresis when switching from the low speed region position 3a to the high speed region position 3b and conversely when switching from the high speed region position 3b to the low speed region position 3a. The reason why the hysteresis is provided is to prevent frequent shifts when the vehicle is traveling near the allowable speed V2. Hereinafter, the hysteresis will be described.

When the control valve 3 is located at the low speed range position 3a, the charge pressure Pc acts on the pressure receiving surface 3e of the control valve 3, and the charge pressure Pc acts on each pilot port of the pressure receiving surface 3f.
c and the sensing pressure Ps are acting respectively.

On the other hand, when the control valve 3 is located at the high speed range position 3b, the charge pressure Pc acts on the pressure receiving surface 3e of the control valve 3, and the sensing pressure Ps acts on each pilot port of the pressure receiving surface 3f. ing.

Since the sensing pressure Ps is higher than the charge pressure Pc, the pressure of the control valve 3 is higher when the control valve 3 is located at the high speed range position 3b than when the control valve 3 is positioned at the low speed range position 3a. The force acting on the surface 3f increases.

This means that once the control valve 3 is switched from the low speed range position 3a to the high speed range position 3b, the sensing pressure Ps is lower than the sensing pressure Ps when switching from the low speed range position 3a to the high speed range position 3b. Otherwise, it means that the high-speed range position 3b is not switched to the low-speed range position 3a. That is, the rotational speed of the hydraulic motor 1 is set to the low speed range position 3
Unless the rotational speed is lower than the rotational speed at the time of switching from the position a to the high speed region position 3b, it is not possible to switch from the high speed region position 3b to the low speed region position 3a.

If the control valve 3 is replaced with the vehicle speed, the control valve 3 is switched from the high speed region position 3b to the low speed region position 3a unless the vehicle speed is lower than the vehicle speed at the time of switching from the low speed region position 3a to the high speed region position 3b. Absent.

As described above, according to the present embodiment,
Since the pressure oil discharged from the charge pump 10 is sucked as suction oil by the sensing pump 2 instead of the pressure oil in the tank 40, the suction oil passages 11, 19, and 15R of the sensing pump 2 (or the suction oil passage 11) are provided. , 1
9, 15F) can be prevented from being mixed with air.
Further, even if air is mixed into the suction oil of the sensing pump 2, the suction oil passage 11 is opened to easily release the air.

According to the present embodiment, the sensing pressure P
Unless s is lower than the sensing pressure Ps when switching from the low speed range position 3a to the high speed range position 3b, the valve position of the control valve 3 does not switch from the high speed range position 3b to the low speed range position 3a. When the vehicle is traveling at a speed near the vehicle speed range in which the vehicle speed is switched to a high speed, the vehicle speed can be prevented from frequently changing.

Instead of providing the throttle valve 21 in the oil passage 18 in FIG. 1, a fixed throttle having a constant opening area A may be provided. However, in this case, the pilot pressure acting on the control valve 3 via the pilot oil passage 25a greatly varies. To cope with this, the pressure receiving areas of the pressure receiving surfaces 3e and 3f of the control valve 3 and the spring force of the spring 3d may be appropriately changed.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of an embodiment of the present invention.

FIGS. 2A, 2B, and 2C are diagrams for explaining a state in which a hydraulic motor shifts speed.

FIG. 3 is a diagram showing a differential pressure ΔP across a throttle valve 21 shown in FIG. 1;
It is a figure which shows the relationship between the flow rate Q.

[Explanation of symbols]

 1, 50: Variable displacement hydraulic motor 2: Vehicle speed sensing pump 10: Charge pump

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2D003 AA01 AB01 AB07 BA02 BB02 BB03 CA04 DA03 DB03 3H082 AA13 BB08 CC02 EE01 3H089 AA32 BB10 BB24 CC09 DA02 DA03 DA13 DB43 FF04 FF16 GG02 JJ01 3J053 AA01 AB17 AB

Claims (2)

[Claims] 1. A variable displacement hydraulic motor (1, 50) having a variable displacement hydraulic motor (1, 50) whose displacement changes by inputting a displacement control signal, a discharge oil passage and a suction oil passage. ) Is detected, and pressure oil corresponding to the detected number of rotations is sucked from the suction oil passage.
A sensing pump (2) for discharging pressure oil sucked from the suction oil passage to the discharge oil passage; and a pressure oil sucked from the suction oil passage by the sensing pump (2) to the discharge oil passage. The displacement control signal is input to the variable displacement hydraulic motor (1, 50) in accordance with the discharged hydraulic oil, and the displacement of the variable displacement hydraulic motor (1, 50) is controlled. In the apparatus, a charge pump (10) for discharging pressure oil to the suction oil passage (10)
Wherein the pressure oil discharged from the charge pump (10) is sucked by the sensing pump (2) through the suction oil passage. 2. A variable displacement hydraulic motor (1 and 50) whose displacement changes by inputting a displacement control signal, and said variable displacement hydraulic motor (1 and 50) according to the number of rotations of said variable displacement hydraulic motor (1 and 50). A control valve (3) for outputting a capacity control signal for controlling the capacity of the hydraulic motor (1, 50), wherein the control valve (3) outputs a displacement control signal. Pressure receiving surface (3) on which the applied sensing pressure (Ps) and the charging pressure (Pc) smaller than the sensing pressure (Ps) act.
f) and the pressure receiving surface (3) on which the charge pressure (Pc) acts.
e), and the valve position is adjusted according to the pressure acting on these pressure receiving surfaces (3e, 3f) by the variable displacement hydraulic motor (1, 2).
The control valve is switched to a low speed range position (3a) corresponding to a low rotation speed range of 50) or a high speed range position (3b) corresponding to a high rotation speed range of the variable displacement hydraulic motor (1, 50). (3), the control is performed when the sensing pressure (Ps) becomes lower than the sensing pressure (Ps) when the low-speed position (3a) is switched to the high-speed position (3b). A displacement control device for a hydraulic motor, wherein the valve position of the valve (3) is switched from the high speed range position (3b) to the low speed range position (3a).