JP3734639B2 - Absorption control device for variable displacement axial piston motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an absorption control device that controls the speed of a variable displacement axial piston motor that is mainly used for vehicle travel, such as a wheel shovel.
[0002]
[Prior art]
Conventionally, a variable displacement axial piston motor has been used for traveling of a wheel shovel or the like, and when the load pressure of the motor is small, the absorption amount of the motor is reduced to increase its speed (number of rotations). In general, it is controlled by an absorption control device. A specific example is as shown in FIGS. 1 and 2, and slides in a bore d formed in a casing c of the motor a on a cylinder block b integral with the output shaft v of the variable displacement axial piston motor a. A control piston g for adjusting the amount of absorption of the cylinder block b having large and small pressure receiving surfaces e and f on which the operating circuit pressure of the motor acts is connected.
[0003]
As shown in FIG. 3, the operating circuit pressure is guided to the large-diameter pressure receiving surface e through an introducing circuit h, and a control surface i on which the operating circuit pressure acts is applied to the introducing circuit h. A servo valve k having a spool j having the following: a force of an adjustable adjustment spring l and a force of a feedback spring m provided on the piston facing the large pressure receiving surface; Acting in the same direction, the introduction of the operating circuit pressure to the introduction circuit h and the connection of the introduction circuit h to the tank s are controlled by the servo valve k. The movement distance of the control piston g in the direction of the large diameter pressure receiving surface is limited by movement control means n including a plunger provided to face the large diameter pressure receiving surface.
[0004]
The motor a is connected to a variable displacement hydraulic pump (not shown) that is rotated by a traveling engine via an operation circuit o, p with a counter balance valve q interposed therebetween. Extracted from the shuttle valve r provided between the operation circuits o and p through the extraction circuit t.
[0005]
When fluid is supplied from the hydraulic pump to the operating circuit o, the counter balance valve q is switched to the position I. In this case, when the operating circuit pressure extracted from the shuttle valve r is large, the spool j of the servo valve k flexes and moves the feedback spring m by the operating circuit pressure acting on the control surface i. Is introduced into the large pressure receiving surface e through the introduction circuit h, the control piston g moves so as to increase the amount of absorption of the cylinder block b. As a result, the motor a rotates at a low speed. The piston g stops moving at a position where the force generated on the control surface i and the force generated on the large pressure receiving surface e are balanced.
[0006]
Further, when the extracted operating circuit pressure is small, the spool j is pushed by the force of the adjustment spring l and moves to the position shown in the figure, and the introduction circuit h is connected to the tank s, so that the large pressure receiving surface. The force generated in e disappears, and the control piston g is moved by the force of the feedback spring m to reduce the amount of absorption of the cylinder block b.
[0007]
When the motor a is used for vehicle travel, when the vehicle having a large operating circuit pressure is started, the output shaft v of the motor a is rotated at a low speed and a large torque by the control operation of the absorption amount control device. When the operating circuit pressure is reduced, the motor a rotates at a high speed and a low torque, so that the vehicle speed can be automatically controlled according to the acceleration state. Usually, the output shaft v is connected to a traveling device via a speed reducer w. Furthermore, as travel control, it is preferable to make the engine brake easier to operate during deceleration without affecting the acceleration, and for this purpose, a piston opposed to the large pressure receiving surface e of the control piston g with an appropriate interval. The retarder stroke limiter u is provided, and the counter pressure from the counter pressure circuit x is applied to the limiter u to increase the absorption amount of the motor a. As the counter pressure, a pressure generated in the operating circuit by deceleration is used. In the illustrated example, a pressure generated between the operating circuit p on the outflow side of the motor a and the counter balance valve q is used. Also, if the limiter u is activated when the reduction gear w has a large reduction ratio (1st speed), the engine brake is too effective and the vehicle has a large shock when the vehicle is decelerating. 4), an on-off valve y that opens and closes according to the reduction ratio is interposed in the counter pressure introducing circuit x so as to operate the limiter u, and the rotation characteristic of the output shaft as shown in FIG. 4 is obtained.
[0008]
[Problems to be solved by the invention]
The absorption amount control device for the motor a is provided with a piston-like retarder stroke limiter u on the control piston g to receive the counter pressure in order to perform the deceleration control of the rotation. There is a disadvantage that a case is required, the number of parts is large, assembly is complicated, and the cost is high. Further, the limiter u is required to have a length for reliably giving a stroke to the control piston g and strong enough to withstand the counter pressure, and is relatively large in size, so that it protrudes from one side of the casing c. The motor a is generally mounted on the bottom of a vehicle such as a wheel shovel with its output shaft v level, and since it is close to the ground, it easily collides with projections such as rough terrain, and the protruding limiter If u is damaged, the vehicle travels undesirably.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide an absorption amount control device for a variable displacement axial piston motor that has a small number of parts, has a simple structure, does not protrude from a casing, and is not easily damaged.
[0010]
[Means for Solving the Problems]
In the present invention, the cylinder block of the variable displacement axial piston motor is provided with a large-diameter and small-diameter pressure receiving surface that slides in a bore formed in the casing of the motor and on which the operating circuit pressure of the motor acts. A control piston for adjusting the amount of absorption of the block is connected, and a servo valve provided with a spool having a control surface on which the operating circuit pressure is applied is provided in an introduction circuit that guides the operating circuit pressure to the large-diameter pressure receiving surface, An adjustment spring force that can be adjusted in opposition to the force generated on the control surface and a feedback spring force provided on the piston in opposition to the large-diameter pressure receiving surface are applied to the spool. Movement control for controlling the movement distance in the direction of the pressure receiving surface of the large diameter of the control piston by controlling the introduction of the operation circuit pressure to the introduction circuit and the connection of the introduction circuit to the tank by a valve In the absorption amount control device provided with a step, an annular concave groove is provided on the peripheral surface of the large-diameter end portion forming the large-diameter pressure receiving surface of the control piston, continuous with the bore of the control piston and the large A control chamber is formed in which the end of the diameter protrudes and the concave groove is opened and closed, and the counter pressure of the motor is guided to the tank through the check valve, the first throttle, and the second throttle that is sufficiently smaller than the first throttle. A counter pressure introducing circuit is provided to introduce an intermediate pressure between the first and second throttles into the concave groove, and the control piston moves toward the pressure receiving surface of the small diameter which increases the absorption amount of the axial piston motor. When the absorption amount moves to the middle between the maximum and minimum, the connection between the concave groove and the control chamber is cut off, thereby achieving the above object. It is advantageous to provide an on-off valve in the counter pressure introduction circuit from the counter pressure extraction point to the concave groove.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. In FIGS. 5 and 6, reference numeral 1 denotes a variable displacement axial piston motor, and the motor 1 has one end of an output shaft 3 extending in and out of a casing 2. A drive plate 4 provided in the cylinder, a cylinder block 6 in which a plurality of pistons 5 fitted to the head of the drive plate 4 are projected and retracted, and a control piston 7 for inclining the cylinder block 6 with respect to the output shaft 3. And a lens-like control plate 9 slidable along an arcuate groove 8 formed on the inner surface of the casing 2 and in contact with the rear end of the cylinder block 6, the piston 7 and the plate 9 are The pins 10 are connected to each other, and the piston 7 moves in the casing 2 to change the angle between the output shaft 3 and the cylinder block 6, that is, the tilt angle. By changing the tilt angle, the absorption amount of the cylinder block 6, that is, the absorption amount of the motor 1 is changed.
[0012]
As shown in FIG. 7, the cylinder block 6 is provided with a counter balance valve 15, a direction control valve, a relief valve and other control devices from a variable displacement hydraulic pump 12 driven by an engine 11 of the vehicle. The working fluid is supplied through one of two ports (not shown) of the control plate 9 connected to the circuits 13 and 14. The piston 5 is pushed out of the cylinder block 6 by the pressure of the working fluid to rotate the output shaft 3, and the working fluid that has finished its work returns from the other port to the tank 16 through the working circuit 14.
[0013]
The control piston 7 includes a large diameter pressure receiving surface 17 and a small diameter pressure receiving surface 18 on which the operating circuit pressure of the motor 1 extracted via the shuttle valve 37 acts. The introduction circuit 19 for guiding the operation circuit pressure is provided with a servo valve 22 having a spool 21 having a control surface 20 on which the operation circuit pressure is applied, and is opposed to the force generated by the operation circuit pressure on the control surface 20. The force of the adjustable adjustment spring 35 and the force of the feedback spring 23 provided so as to face the large-diameter pressure receiving surface 17 of the piston 7 are applied to the spool 21, and the servo valve 22 is actuated to operate the introduction circuit. Control is made as to whether the operating circuit pressure is introduced to 19 or the introduction circuit 19 is connected to the tank 16 via the tank circuit 36, and the control piston 7 and the cylinder block 6 are moved. Controlling, absorption of the motor 1 is controlled.
[0014]
Such a configuration is also provided with a conventional absorption amount control device, but in the present invention, in order to control the absorption amount as necessary, a large-diameter end formed with a large-diameter pressure receiving surface 17 of the control piston 7. An annular concave groove 25 is provided around the portion 24, the large diameter end portion 24 protrudes and protrudes in the same area as the cross-sectional area of the large diameter pressure receiving surface 17 and is continuous with the bore 26 in which the piston 7 slides. A control chamber 27 in which the concave groove 25 was opened and closed was formed. A counter pressure introducing circuit 30 is provided for guiding the counter pressure of the motor 1 to the tank 16 through the check valve 31, the first throttle 28, and the second throttle 29 having a sufficiently small throttle area than the first throttle, An intermediate pressure between the first and second throttles 28 and 29 is applied to the large-diameter pressure receiving surface 17. When the control piston 7 moves in the direction of decreasing absorption and the connection between the concave groove 25 and the control chamber 27 is closed, the counter pressure does not enter the control chamber 27 and the control piston 7 stops.
[0015]
When the fluid from the hydraulic pump 12 is supplied to the operation circuit 13 in FIG. 7, the counter pressure is generated by the counter balance valve 15 in the operation circuit 14, so that the counter pressure is recessed from the operation circuit 14 via the check valve 31. The counter pressure was guided to the groove 25. An opening / closing valve 32 is interposed in the counter pressure introducing circuit 30 from the counter pressure extraction point of the operating circuit 14 to the control chamber 27, and the output shaft 3 of the motor 1 is connected to traveling means 34 such as a wheel via a speed reducer 33. When connected, the on-off valve 32 can be opened and closed in conjunction with the selection of the reduction ratio of the reduction gear 33.
[0016]
The operation of the illustrated embodiment applied to vehicle travel will be described. When the working fluid is supplied from the hydraulic pump 12 to the working circuit 13, the hydraulic motor 1 is rotated to return the working fluid from the working circuit 14 to the tank 16. . The rotation of the hydraulic motor 1 is transmitted to the travel means 34 via the speed reducer 33, and the vehicle travels. A relatively large operating circuit pressure is generated in the operating circuit 13 when the vehicle is started and when the vehicle is running at a low speed, and the force generated on the control surface 20 of the servo valve 22 by the action of the operating circuit pressure is larger than the force of the adjustment spring 35. Then, the spool 21 moves to introduce the operating circuit pressure into the introducing circuit 19, and the operating circuit pressure acts on the large pressure receiving surface 17 of the control piston 7. The operating circuit pressure also acts on the small pressure receiving surface 18 of the control piston 7 so that the control piston 7 increases the amount of absorption of the cylinder block 6 by the thrust generated by the area difference between the pressure receiving surfaces 17 and 18. Move to. Thereby, the motor 1 rotates at a low speed and a large torque according to the running state of the vehicle. The spool 21 of the servo valve 22 is pushed back to the balanced position by the force of the feedback spring 23 that transmits the movement of the control piston 7.
[0017]
When the vehicle is accelerated and the operating circuit pressure decreases, the spool 21 of the servo valve 22 is pushed by the adjustment spring 35 to connect the introduction circuit 19 to the tank 16, so that the large pressure receiving surface 17 has a tank pressure. The control piston 7 moves so as to enter the control chamber 27 so as to reduce the amount of absorption of the cylinder block 6 by the operating circuit pressure acting on the small diameter pressure receiving surface 18. As a result, the motor 1 rotates at high speed and low torque, and the vehicle speed increases.
[0018]
When the speed reducer of the vehicle is set to the second speed (low reduction ratio), the on-off valve 32 is opened, and the counter pressure is prepared to be guided to the concave groove 25 of the control piston 7. When the concave groove 25 is open, when the accelerator pedal is released, the flow rate from the hydraulic pump 12 decreases, the pressure of the operating circuit 14 becomes higher than that of the operating circuit 13, and a counter pressure is generated. Since the concave groove 25 is open to the control chamber 25, the counter pressure acts on the large pressure receiving surface 17 via the check valve 31, so that the control piston 7 is forced to increase the amount of absorption, It stops at the position where the concave groove 25 and the control chamber 27 are closed, the absorption amount is between the maximum and the minimum, the absorption torque of the motor 1 is increased, and the engine brake is easily used. The diaphragm 28 is sufficiently larger than the diaphragm 29 so as not to prevent the control piston 7 from being pushed in the direction of increasing the absorption amount of the motor 1. When the speed reducer is set to the first speed (large reduction ratio), the counter pressure from the check valve 31 is not introduced into the large pressure receiving surface 17 by closing the on-off valve 32. Is not increased, and there is no shock due to excessive braking of the engine at low speed. The relationship between the absorption amount of the motor 1 and the motor inlet pressure is almost the same as the conventional one shown in FIG.
[0019]
The structure in which the annular concave groove 25 is formed around the large-diameter end portion 24 of the control piston 7 and the check valve 31 and the first and second throttles 28 and 29 are provided in the counter pressure introducing circuit 30 is a complicated conventional structure. Compared to the structure having a piston-shaped retarder stroke limiter having a structure, the length of the device in the direction of the large-diameter end can be shortened so as not to protrude from the casing 2, and the motor 1 is placed at the bottom of the vehicle. Even if it is attached, the inconvenience that the absorption control device collides with the rough terrain and is damaged hardly occurs.
[0020]
In a specific example, when the diameter of the large diameter end 24 is set to 28 mm, the diameter of the first throttle 28 is set to 1.4 mm and the diameter of the second throttle 29 is set to 1 mm. The control piston 7 can be moved to an intermediate position of its stroke with a pressure intermediate between the generated pressures, and there is no hindrance to the operation of reducing the amount of absorption and increasing the vehicle speed.
[0021]
【The invention's effect】
As described above, according to the present invention, an annular groove is provided on the peripheral surface of the large-diameter end portion of the control piston constituting the absorption amount control device of the variable displacement axial piston motor, and is continuous with the bore of the piston. A control chamber in which the large-diameter end portion protrudes and retracts to open and close the concave groove is formed, and an intermediate pressure between the first and second throttles provided in a counter pressure introducing circuit that guides the counter pressure of the motor to the tank Since it is introduced into the concave groove, the piston can be moved to a position between the maximum and the minimum absorption amount with a simple configuration having a small size and a small number of parts, and a component member for controlling the movement of the piston can be provided. Since it can be accommodated in the casing of the motor and can be prevented from projecting to the outside, the control device can be prevented from being damaged by collision with the motor, and the control device can be assembled easily and inexpensively.
[Brief description of the drawings]
FIG. 1 is a cut-away side view of a conventional variable displacement axial piston motor absorption control device. FIG. 2 is a left side view of FIG. 1. FIG. 3 is a diagram of a control circuit using the absorption control device of FIG. FIG. 4 is a relationship diagram of absorption amount and motor inlet pressure. FIG. 5 is a cutaway side view showing an embodiment of the present invention. FIG. 6 is a right side view of FIG. Diagram of the control circuit used [Explanation of symbols]
1 Variable displacement axial piston pump, 2 casing, 3 output shaft, 5 piston, 6 cylinder block, 7 control piston, 13/14 operating circuit, 16 tank, 17 large diameter pressure receiving surface, 18 small diameter pressure receiving surface, 19 introduction Circuit, 20 control valve, 21 spool, 22 servo valve, 23 feedback spring, 24 large-diameter end, 25 concave groove, 26 bore, 27 control chamber, 28 first throttle, 29 second throttle, 30 counter pressure introduction circuit, 31 Check valve, 32 Open / close valve, 35 Adjustment spring, 36 Tank circuit,

Claims (2)

Absorption amount of the cylinder block having a large-diameter and small-diameter pressure receiving surface that slides in a bore formed in the casing of the motor on the cylinder block of the variable displacement axial piston motor and on which the operating circuit pressure of the motor acts. A servo valve having a spool having a control surface on which the operating circuit pressure is applied is provided in an introduction circuit for connecting a control piston for adjusting the pressure and introducing the operating circuit pressure to the large-diameter pressure receiving surface. The force of the adjustment spring that can be adjusted to oppose the generated force and the force of the feedback spring provided on the piston to oppose the large-diameter pressure-receiving surface act on the spool, and the introduction is performed by the servo valve. Provided with a movement control means for controlling the introduction of the operating circuit pressure to the circuit and the connection of the introduction circuit to the tank and controlling the movement distance of the control piston in the direction of the large pressure receiving surface In the yield control device, an annular concave groove is provided on the peripheral surface of the large diameter end portion that forms the large diameter pressure receiving surface of the control piston, and the large diameter end portion is continuous with the bore of the control piston. And a counter pressure introduction circuit for forming a control chamber in which the groove is opened and closed, and for introducing the counter pressure of the motor to the tank through the check valve, the first throttle and the second throttle which is sufficiently smaller than the first throttle. An intermediate pressure between the first and second throttles is introduced into the concave groove, and the control piston moves toward the pressure receiving surface of the small diameter which increases the amount of absorption of the axial piston motor. When the actuator moves to the minimum intermediate position, the connection between the concave groove and the control chamber is cut off. 2. An absorption amount control device for a variable displacement axial piston motor according to claim 1, wherein an opening / closing valve is provided in a counter pressure circuit from the counter pressure extraction point to the concave groove.

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