JPH0417281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic drive system for a variable displacement hydraulic pump having a backup device in case of failure.

[Conventional technology]

In work vehicles such as hydraulic excavators, when the pressure in the hydraulic circuit decreases, a large flow of pressure oil is supplied to increase the operating speed of the actuator, and conversely, when the pressure in the hydraulic circuit increases, the flow rate of pressure oil is reduced. In order to prevent the output of the pump from becoming larger than the output of the engine, a variable displacement hydraulic pump is used as the hydraulic pump.

FIG. 5 shows the basic structure of a conventionally known electro-hydraulic servo hydraulic drive device for a variable displacement hydraulic pump.

In this figure, 1 is a variable displacement hydraulic pump, 2
Reference numeral 3 indicates a variable displacement mechanism of the variable displacement hydraulic pump 1, which is composed of a swash plate or an oblique shaft, 3 is a servo piston that drives the variable displacement mechanism 2, and 4 is a servo cylinder that accommodates the servo piston 3.
4a and 4b are a left chamber and a right chamber of the servo cylinder 4 separated by the servo piston 3, and the cross-sectional area D of the left chamber 4a is larger than the cross-sectional area d of the right chamber 4b.

5 is a hydraulic source that supplies pressure oil to the servo cylinder 4; 6 is an oil tank that stores hydraulic oil for this hydraulic circuit; and 7 is a hydraulic source 5 and the servo cylinder 4.
A pipe line 8 communicates with the left side chamber 4a of the servo cylinder 4, a pipe line 8 connects the hydraulic power source 5 with the right side chamber 4b of the servo cylinder 4, and a return pipe 9 connects the pipe lines 7, 8 with the oil tank 6. 10 is a pipe 7 connecting the hydraulic power source 5 and the left chamber 4a of the servo cylinder 4.
11 is a solenoid valve installed in the return pipe 9. These solenoid valves 10, 11
is a normally closed solenoid valve (a function that returns to the closed state when no electricity is applied), and is switched by a signal from a discharge amount control device to be described later.

12 is a displacement meter connected to the variable displacement mechanism 2 or the servo piston 3, which detects the displacement of the variable displacement mechanism of the variable displacement hydraulic pump 1 and outputs a discharge amount signal Qp proportional to the amount of displacement. It's becoming like that.

13 is a discharge pipe line of the variable displacement hydraulic pump 1; 14
indicates an actuator disposed in this discharge pipe 13, and 15 indicates a load applied to this actuator 14.

Reference numeral 16 denotes a pressure detector provided in the discharge pipe line 13 of the variable displacement hydraulic pump 1, which detects the pressure of the pressure oil discharged from the variable displacement hydraulic pump 1 and outputs a pressure signal P. There is.

Reference numeral 17 is an operating lever for changing the tilt angle of the variable displacement hydraulic pump 1, and is designed to output a target discharge amount signal Qo.

Reference numeral 18 denotes a discharge amount control device composed of a microcomputer, and as shown in FIG. amplifiers 18c and 18d, a memory 18e that stores a control procedure program, a discharge amount control signal Qp output from the displacement meter 12, a pressure signal P output from the pressure detector 16, and an operating lever 17. The A/D converter 18f converts the target discharge amount signal Qo outputted from the target discharge amount signal Qo into a digital signal.

This discharge amount control device 18 includes the displacement meter 1
2, the pressure signal P output from the pressure detector 16, and the target discharge amount signal Qo output from the operating lever 17, a control procedure program stored in the memory 12e is generated. The drive command value of the variable displacement hydraulic pump 1 is calculated based on the
and output the discharge amount signal which is the output of the displacement meter 5.
The position of the servo piston 3 is controlled by an on/off servo using an electro-hydraulic servo so that Qp becomes equal to the command signal Qo'.

Reference numeral 19 indicates a power source for this discharge amount control device 18.

In such an on-off servo, when the solenoid valve 10 is excited and switched to the switching position B, the left chamber 4a of the servo cylinder 4 communicates with the hydraulic power source 8, and the left chamber 4a
Due to the area difference between the right chamber 4a and the servo piston 3
moves to the right in Figure 5. In addition, the solenoid valve 10
When the solenoid valve 11 is demagnetized and both return to the switching position A, the oil passage of the left chamber 4a is cut off.
The servo piston 3 is held stationary at that position. Further, when the solenoid valve 11 is excited and switched to the switching position B, the left chamber 4a and the oil tank 6
The pressure in the left chamber 4a decreases, and the servo piston 3 is moved to the left in FIG. 5 by the pressure in the right chamber 4b.

In such a hydraulic drive system, if the discharge amount control device 18, displacement meter 12, pressure detector 16, or operating lever 17 breaks down, it becomes impossible to control on/off of the solenoid valves 10 and 11, and the servo piston 3 The variable displacement hydraulic pump 1 moves to a position corresponding to the end face of the left chamber 4a or the right chamber 4b, and the tilt angle of the variable displacement hydraulic pump 1 becomes the maximum discharge amount or the minimum discharge amount.

That is, if a command signal Qo' for switching the solenoid valve 11 is continuously output from the discharge amount control device 18 due to a failure of these devices, the servo piston 3
moves until it abuts against the left end surface of the left chamber 4a of the servo cylinder 4, and the tilting angle of the variable displacement hydraulic pump 1 becomes maximum.

Further, when the command signal Qo' for switching the solenoid valve 10 is continuously outputted from the discharge amount control device 18, the servo piston 3 moves until it collides with the right end surface of the right chamber 4b of the servo cylinder 4, and The tilting angle of the displacement hydraulic pump 1 is minimized.

By the way, in work vehicles powered by variable displacement hydraulic pumps, in order to improve the operating speed of the actuator at low pressure, the rating is usually more than twice the output of the installed prime mover (maximum discharge x maximum A variable displacement hydraulic pump with pressure) is used. Therefore, due to a failure, the variable displacement hydraulic pump 1
When the tilting angle becomes the maximum and the discharge amount becomes the maximum, the load exceeds the prime mover output and the prime mover cannot be operated, making it impossible to operate the work vehicle.

On the other hand, in order to prevent energy loss caused by the activation of a relief valve (not shown) provided in the hydraulic circuit when the pressure is high, the minimum discharge amount of the variable displacement hydraulic pump 1 mounted on the hydraulic excavator is ,
It is set to a value almost zero. Therefore, if the tilting angle of the variable displacement hydraulic pump 1 becomes the minimum due to a failure and the discharge amount becomes the minimum, even if the variable displacement hydraulic pump 1 is driven, the minimum hydraulic pressure required to operate the work vehicle will not be reached. In this case as well, it becomes impossible to drive the work vehicle.

[Problem to be solved by the invention]

By the way, work vehicles are generally large and heavy, so if they become impossible to drive and fail at a factory site, it takes a lot of effort and time to move them, causing inconveniences such as delaying construction work. For this reason, work vehicles must be configured so that they can be operated under any circumstances and can be quickly moved from a construction site or the like.

The present invention has been made to solve such problems, and its purpose is to increase the displacement of the variable displacement hydraulic pump even if the discharge rate control device, displacement gauge, pressure detector, operating lever, etc. are out of order. It is an object of the present invention to provide a hydraulic drive circuit that can ensure the operation of a servo cylinder that drives a variable mechanism and enables the operation of a work vehicle.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a variable displacement hydraulic pump equipped with a variable displacement mechanism;
an actuator driven by pressure oil discharged from the pump; a servo cylinder housing a piston for driving the variable displacement mechanism; a hydraulic source supplying pressure oil to the servo cylinder; an oil tank for accumulating hydraulic oil to be supplied to the servo cylinder; and an oil tank for controlling the supply of hydraulic pressure from the hydraulic pressure source to the servo cylinder and the return of pressure oil from the servo cylinder to the oil tank; In a hydraulic drive device for a variable displacement hydraulic pump that includes a solenoid valve that controls the tilt angle of a variable displacement mechanism and a control means for the solenoid valve, when a failure occurs,
A changeover switch for switching the solenoid valve to a closed state via the control means is attached to the control means, and when the solenoid valve is switched to the closed state, the pressure oil of the hydraulic source is switched to the left side of the front servo cylinder. A pipe that communicates between the left and right chambers of the servo cylinder through a pipeline that supplies at least one of the chamber and the right chamber, and an oil passage that is opened and closed in the servo cylinder and that is opened and closed by the piston. A passageway was provided in the hydraulic circuit for driving the servo cylinder.

[Effect]

As mentioned above, if the discharge amount control device, displacement gauge, pressure detector, control lever, etc. malfunctions while the solenoid valve is open, pressure oil from the hydraulic source will flow into either the left or right chamber of the servo cylinder. The piston moves to either the left or right end and becomes inoperable.

In this state, when the changeover switch is operated to switch the solenoid valve to the closed state, pressure oil from the hydraulic source is supplied to the left side chamber or the right side chamber of the servo cylinder via a conduit connected to the hydraulic source. Further, the pressure oil is also supplied to the other side chamber via a conduit connected to the oil passage of the servo cylinder. As a result, pressure oil flows from the high-pressure side chamber to the low-pressure side chamber, and the piston, which was biased toward the low-pressure side, moves toward the center of the servo cylinder. Then, when the oil passage opened in the servo cylinder is closed by the piston, the flow of pressure oil from the high-pressure side chamber to the low-pressure side chamber is stopped.

Even after this state is reached, pressure oil from the hydraulic source continues to be supplied to the left or right chamber of the servo cylinder, so the piston moves to the low pressure side, but when the oil passage is reopened, the same as above occurs. Pressure oil then flows from the high-pressure side chamber to the low-pressure side chamber, and the pressure in the low-pressure side chamber increases, causing the piston to return in the opposite direction. In this way, the piston is placed near the opening position of the oil passage while swinging slightly from side to side.

Therefore, in the event of a failure, it is necessary to adjust the oil pressure so that the piston is fixed at a position where the tilting angle of the variable displacement hydraulic pump can be adjusted so that the prime mover can operate and a discharge amount sufficient to drive the work vehicle is obtained. By setting the opening position of the passage, it is possible to ensure the operable state in the event of a failure.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, in which similar members to those shown in FIG. 5 are designated by the same reference numerals.

In this figure, 20 is a servo piston, 21
is a servo cylinder. Servo piston 20
has a large diameter at one end and a small diameter at the other end, and an escape groove 20c is formed between the large diameter portion 20a and the small diameter portion 20b. 21a is the left chamber of the servo cylinder 21 formed with a large diameter; 21b
is the right chamber of the servo cylinder 21 formed to have a small diameter. 21c, 21d, and 21e indicate oil passages opened in the servo cylinder 21. Of these, the oil passage 21c is connected to the servo piston 2 in the event of a failure.
The position to which the end face of the small diameter portion 20b of 0 is to be moved, that is, by the movement of the servo piston 20,
The tilting angle of the variable displacement hydraulic pump is set at a position where the tilting angle of the variable displacement hydraulic pump can be adjusted so that the prime mover can operate and a discharge amount sufficient to drive the work vehicle can be obtained.
Further, the oil passage 21d is opened at a position separated from the oil passage 21c by a length L of the small diameter portion 20b of the servo piston 20. The oil passage 21e connects the small diameter portion 20b of the servo piston 20 to the oil passage 21c,
21d, it is opened at a position communicating with the relief groove 20c. Reference numeral 22 denotes a backup electromagnetic valve, which is interposed in a conduit 23 that communicates the oil passages 21c and 21d with the conduit 7 that communicates the hydraulic power source 5 and the left chamber 21a of the servo cylinder 21. This solenoid valve 22 is connected to the discharge amount control device 1
It is connected to the power source 19 of No. 8 via a changeover switch 24, and conducts through the conduit 23 when the power is turned on.

Now, one of the displacement gauge 12, pressure detector 16, and discharge rate control device 18 has failed, and the servo piston 20 is caused to collide with the end face of the left chamber 21a by the output signal from the discharge rate control device 18. Suppose you move until

When the operator switches the changeover switch 24 from the discharge rate control device 18 side to the backup solenoid valve 22 side, the solenoid valves 10 and 11 connected to the discharge rate control device 18 return to switching position A, and the backup solenoid valve 22 is switched to the switching position B, and the conduit 23 is opened.

When the pipe line 23 is opened, the servo cylinder 21
Pressure oil in the right chamber 21b of the servo cylinder 21 flows into the left chamber 21a of the servo cylinder 21 via the oil passage 21c, the electromagnetic valve 22, the pipe line 23, and the pipe line 7. , servo piston 2
0 moves to the right on Figure 1.

When the servo piston 20 moves to the right and the small diameter portion 20b of the servo piston 20 comes to the position where it closes the oil passage 21c, the oil flows from the right chamber 21b to the left chamber 21.
The flow of pressure oil to the left side chamber 21a is stopped, and the oil pressure from the oil pressure source 5 is applied directly to the small diameter portion 20b of the servo piston 20. On the other hand, the oil passage 21d is opened, so that the pressure oil in the left side chamber 21a is transferred to the pipe line 7. , pipe line 23, backup solenoid valve 22, oil passage 21d, relief groove 20
c, it is returned to the oil tank 6 via the oil passage 21e, and the servo piston 20 starts moving leftward.

When the servo piston 20 moves to the left and the small diameter portion 20b of the servo piston 20 closes the oil passage 21d and opens the oil passage 21c, the right chamber 2
1b flows into the left chamber 21a of the servo cylinder 21 via the oil passage 21c, the backup electromagnetic valve 22, the pipe line 23, and the pipe line 7, and due to the difference in area between both ends of the servo piston 20, the servo piston 2
0 starts moving to the right again.

By repeating the above operations, the piston 20
is held at the opening position of the oil passage 21c.

On the other hand, assume that the servo piston 20 moves until it abuts against the end surface of the right chamber 21b due to failure of the displacement gauge 12, pressure detector 16, and discharge amount control device 18.

In this case, when the operator switches the changeover switch 24, the oil passage 21c is connected to the servo piston 2.
0, the hydraulic pressure from the hydraulic source 5 is applied to the small side chamber 20b of the servo piston 20,
On the other hand, since the oil passage 21d is open, the pressure oil in the left chamber 21a flows through the pipe line 7, the pipe line 23, the backup solenoid valve 24, the oil passage 21d, and the relief groove 21e.
is returned to the oil tank 6 via the servo piston 20, and the servo piston 20 moves to the left.

The small diameter portion 20b of the servo piston 20 is the oil passage 2
When 1d is closed, the flow of pressure oil from the left chamber 21a to the oil tank 6 is stopped. At the same time, the oil passage 21c is opened, and the pressure oil in the right side chamber 21b is transferred to the oil passage 21c, the backup solenoid valve 22, and the pipe line 2.
3. The oil flows into the left chamber 21a of the servo cylinder 21 through the pipe 7, and due to the difference in area between the two ends of the servo piston 20, the servo piston 20 moves to the right, and the small diameter part 20b of the servo piston 20 is filled with oil. The passage 21c is closed and the oil passage 21d is opened.

By repeating the above operations, the servo piston 20 is held at the opening position of the oil passage 21c, as in the above case.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and the same members as shown in FIG. 1 are designated by the same reference numerals.

In this figure, 30 is a servo piston, 31
is a servo cylinder. Servo piston 30
has a large diameter at one end and a small diameter at the other end, and a narrow protrusion 30c is formed slightly inside the tip of the small diameter portion 30b. 30d is an escape groove formed between the large diameter portion 30a of the servo piston 30 and the protrusion 30c. 31a is the left chamber of the servo cylinder 31 formed with a large diameter; 31b
is the right side chamber of the servo cylinder 31 formed to have a small diameter. 31c and 31d are oil passages opened in the servo cylinder 31. Among these, the oil passage 31c is formed to have a smaller diameter than the width t of the protrusion 30c formed on the servo piston 30,
The position to which the protrusion 30c of the servo piston 30 is to be moved in the event of a failure, that is, the tilting angle of the variable displacement hydraulic pump 1 can be changed by moving the servo piston 30 so that the prime mover can be started and the work vehicle can be driven. It is opened at a position that can be adjusted so that a sufficient discharge amount can be obtained. Further, the oil passage 31d connects the protrusion 30c of the servo piston 30 to the oil passage 31c.
When the relief groove 30 is positioned so as to close the
It will be established in a location that communicates with d. 31e is a pipe line that communicates this oil passage 31d and the oil tank 6. 32 is a solenoid valve for backup;
It is interposed in a pipe line 7 that communicates the hydraulic power source 5 and the left chamber 31a of the servo cylinder 31, and a pipe line 33 that communicates the oil passage 31c. This backup solenoid valve 32 is connected to the power source 19 of the discharge amount control device 18.
It is connected via a changeover switch 24, and conducts through the conduit 33 when energized.

Now, one of the displacement gauge 12, pressure detector 16, and discharge rate control device 18 has failed, and the servo piston 30 is brought into contact with the end face of the left chamber 31a by the output signal from the discharge rate control device 18. Suppose you move until

In this state, the operator operates the changeover switch 24 from the discharge amount control device 18 side to the back-up solenoid valve 3.
When switched to the second side, the solenoid valves 10 and 11 connected to the discharge amount control device 18 return to the switching position A, and the backup solenoid valve 32 returns to the switching position B.
Then, the pipe line 33 is opened.

When the pipe line 33 is opened, since the oil passage 31c is open, the oil pressure source 5 is connected to the servo cylinder 3.
The pressure oil supplied to the right side chamber 31b of the oil passage 3
1c, the left side chamber 31a of the servo cylinder 31 via the backup solenoid valve 32, the pipe line 33, and the pipe line 7.
The servo piston 30 moves to the right due to the difference in area between both ends of the servo piston 30.

The protrusion 30c of the servo piston 30 is shown in FIG.
When the oil passage 31c moves to the right, the oil passage 3
1c and the escape groove 30d communicate with each other, and the pressure oil in the left chamber 31a of the servo cylinder 30 is transferred to the pipe line 7, the pipe line 33, the backup solenoid valve 32, and the oil passage 31.
c. The servo piston 30 is returned to the oil tank 6 via the relief groove 30d and is caused by the pressure of the hydraulic source 5 acting on the small diameter portion 30b of the servo piston 30.
starts moving to the left.

By repeating the above operations, the piston 30
is held at the opening position of the oil passage 31c.

On the other hand, assume that the servo piston 30 moves until it collides with the end surface of the right chamber 31b due to a failure in any one of the displacement gauge 12, the pressure detector 16, and the discharge amount control device 18.

In this case, when the operator switches the changeover switch 24, the left side chamber 3 of the servo cylinder 31
The pressure oil in 1a flows through the pipe line 7, the pipe line 33, the backup solenoid valve 32, the oil passage 31c, the relief groove 30d,
The pressure from the hydraulic source 5 returns to the oil tank 6 via the oil passage 31d and acts on the right side chamber 30b.
The servo piston 30 moves to the left.

The protrusion 30c of the servo piston 30 is the oil passage 31
When c is closed, the flow of pressure oil from the left chamber 31a is stopped, and the servo piston 30 moves to the right due to the difference in area between both ends of the servo piston 30.

Thereafter, by repeating the same operation, the servo piston 30 is held at the opening position of the oil passage 31c.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention, in which similar members to those shown in FIGS. 1 and 2 are designated by the same reference numerals.

In this figure, 40 is a servo piston, 41
is a servo cylinder. The servo piston 40 has one end with a large diameter and the other end with a small diameter. 4
1a is a left chamber of the servo cylinder formed with a large diameter, 41b is a right chamber of the servo cylinder formed with a small diameter, and 41c is an escape groove formed between the servo piston 40 and the servo cylinder 41. 41d, 41e, 41f are servo cylinders 4
1 shows the oil passage opened. Among these, the oil passage 41d is located at a position where the end face of the large diameter portion 40a of the servo piston 40 is to be moved in the event of a failure, that is, the tilting angle of the variable displacement hydraulic pump 1 is controlled by the movement of the servo piston 40. , is located at a position that allows the prime mover to be started and is adjusted so that a discharge amount sufficient to drive the work vehicle is obtained. Further, the oil passage 41e is opened at the end surface of the large diameter portion of the servo cylinder 41. The oil passage 41f connects the end face of the large diameter portion 40a of the servo piston 40 to the oil passage 4.
1d, it is opened at a position that communicates with the relief groove 41c. Reference numeral 42 indicates a pipe line that communicates the hydraulic pressure source 5 and the oil passage 41e, and reference numeral 43 indicates a throttle provided in this pipe line 42. Reference numeral 44 indicates a pipe line that communicates the oil passage 41d and the oil tank 6, and 45 indicates a pipe line that communicates the oil passage 41f and the oil tank 6. Reference numeral 46 is a blind stopper that normally closes the oil passages 41d and 41e, and if any of the displacement gauge 12, pressure detector 16, and discharge rate control device 18 fails, the pipes 43, 44 are connected as described above.

Now, one of the displacement gauge 12, the pressure detector 16, and the discharge rate control device 18 has failed, and the servo piston 40 collides with the end face of the left chamber 41a according to the output signal from the discharge rate control device 18. Suppose you move until

If such a failure occurs, the operator must first
Switch 24 is disconnected and solenoid valves 10 and 11 are switched to switching position A.

Next, the operator removes the blind stopper 46 from the oil passages 41d and 41e, and
When the pipes 43 and 44 are connected to e, pressure oil from the hydraulic source 5 is supplied to the left chamber 41a of the servo cylinder 41 via the pipe 7, the pipe 42, and the oil passage 41e, and both ends of the servo piston 40 are connected to the pipes 43 and 44. The servo piston 40 moves to the right due to the area difference.

The large diameter portion 40a of the servo piston 40 is the oil passage 4.
When moved to the right of 1d, the left side chamber 41a and the oil tank 6 are communicated with each other, and the pressure oil in the left side chamber 41a is transferred to the oil tank 6 through the oil passage 41d and the pipe line 44.
, the pressure in the left chamber 41a decreases, and the servo piston 40 moves to the left due to the pressure of the pressure oil supplied from the hydraulic source 5 to the right chamber 41b.

The servo cylinder 40 moves to the left and the oil passage 4
1d, the flow of pressure oil from the left chamber 40a to the oil tank 6 is stopped, and the left chamber 40a and the right chamber 40b are each supplied with pressure oil from the hydraulic source 5. , the servo piston 40 moves to the right.

By repeating the above operations, the piston 40
is held at the opening position of the oil passage 41d.

On the other hand, assume that the servo piston 40 moves until it collides with the end surface of the right chamber 41b due to a failure in any one of the displacement gauge 12, the pressure detector 16, and the discharge amount control device 18.

In this case, the operator disconnects the switch 24 and switches the solenoid valves 10 and 11 to the switching position A, and also removes the blind stopper 46 from the oil passages 41d and 41e.
Remove the pipes 43 and 41 from the oil passages 41d and 41e.
44 is connected, the pressure oil in the left chamber 41a is returned to the oil tank 6 via the oil passage 41d and the pipe 44, the pressure in the left chamber 41a is reduced, and the pressure oil is supplied from the hydraulic source 5 to the right chamber 41b. The servo piston 40 moves to the left due to the pressure of the pressure oil.

The servo piston 40 moves to the left and the oil passage 4
When 1f is closed, the flow of pressure oil is stopped, and the pressure oil from the hydraulic source 5 flows into the left chamber 4 of the servo cylinder 41.
1a and the right chamber 41b, and the servo piston 40 moves to the right due to the difference in area between both ends of the servo piston 40.

Hereinafter, in the same manner as above, the servo piston 40
The end face of the large diameter portion 40a is held at the position of the oil passage 41d.

FIG. 4 shows a fourth example of the backup device according to the present invention.
1 to 3 are circuit diagrams showing an embodiment of
Components similar to those shown in the figures are designated by the same reference numerals.

In this figure, 50 is a servo piston, 51
is a servo cylinder in which this servo piston 50 is housed. Both ends of the servo piston 50 are formed to have the same diameter, and protrusions 50a and 50b are circumferentially provided slightly inside the both ends. 50c is
This is an escape groove formed between the protrusions 50a and 50b. 51a is the left chamber of the servo cylinder 51;
51b is the right chamber of the servo cylinder 51, 51c,
51d and 51e indicate oil passages opened in the servo cylinder 51. Among these oil passages, oil passage 5
1c and 51d are the positions to which the protrusions 50a and 50b of the servo piston 50 are to be moved in the event of a failure, that is, the tilting angle of the variable displacement hydraulic pump 1 can be changed by the movement of the servo piston 50, and the prime mover can be operated. It is located at a position where it can be adjusted to obtain a discharge amount sufficient to drive a work vehicle. The oil passage 51e is opened approximately at the center of the servo cylinder 51.

Reference numeral 52 denotes a switching valve for backup in the event of a failure, and is interposed in a pipe line 53 that connects the oil passages 51c and 51d opened in the servo cylinder 51.

Reference numerals 54, 55, 56, and 57 are electromagnetic valves controlled by control signals from the discharge amount control device 18. Among these, the solenoid valve 54 is a normally open solenoid valve (a function that returns to the communicating state when the power is not energized), and is installed in a conduit 58 that connects the hydraulic power source 5 and the left chamber 51a of the servo cylinder 51. be done. Further, the solenoid valve 55 is a normally closed solenoid valve (a function that returns to the closed state when no electricity is applied), and is provided in a return pipe 59 that connects the pipe 58 and the oil tank 6 . The solenoid valve 56 is a normally open solenoid valve, and is interposed in a conduit 60 that communicates the hydraulic power source 5 and the right chamber 51b of the servo cylinder 51. The solenoid valve 57 is a normally closed solenoid valve, and is provided in a return pipe 61 that connects the pipe 60 and the oil tank 6 .

Reference numeral 62 indicates a throttle provided in the pipe line 58, and reference numeral 63 indicates a throttle provided in the pipe line 60.

Now, one of the displacement gauge 12, the pressure detector 16, and the discharge amount control device 18 has failed, and the servo piston 50 is brought into contact with the end surface of the left chamber 51a by the output signal from the discharge amount control device 18. Suppose you move until

When the operator disconnects the switch 24, the power to the discharge amount control device 18 is disconnected, and the solenoid valves 54, 5 are disconnected.
6 returns to the conducting position, and the solenoid valves 55, 5
7 returns to the closed position.

Here, switch the backup switching valve 52 to position B.
When switching to , the right chamber 5 of the servo cylinder 51
The pressure oil in 1b flows through the oil passage 51d, the pipe line 53, the backup switching valve 52, the oil passage 51c, and the relief groove 5.
0c, the oil is returned to the oil tank 6 via the oil passage 51e, the pressure in the right chamber 51b decreases, and the oil pressure source 5
The servo piston 50 is moved to the right by the pressure of the pressure oil supplied to the left chamber 51a through the conduit 58, the electromagnetic valve 54, and the throttle 62.

When the protrusions 50a and 50b of the servo piston 50 close the oil passages 51c and 51d, the right chamber 51b
The movement of pressure oil from the servo cylinder 50 to the left chamber 51a is stopped, the pressures at both ends of the servo cylinder 50 are equalized, and the servo piston 50 is held at that position.

On the other hand, if the servo piston 50 moves until it collides with the end face of the right chamber 51b due to a failure in any one of the displacement gauge 12, pressure detector 16, and discharge amount control device 18, the servo piston 50 The pressure oil in the left chamber 51a of the cylinder 51 is
c, the oil is returned to the oil tank 6 via the pipe line 53, the backup switching valve 52, the oil passage 51d, the relief groove 50c, and the oil passage 51e, the pressure in the left chamber 51a decreases, and the oil is removed from the hydraulic source 5 to the pipe line 60. , solenoid valve 56,
The pressure of the pressure oil supplied to the right chamber 51b through the throttle 63 moves the servo piston 50 to the right.

When the ridges 50a, 50b of the servo piston 50 close the oil passages 51c, 51d, the pressures at both ends of the servo piston 50 equalize in the same manner as described above, and the servo piston 50 is held at that position.

In each of the above embodiments, only the case where the backup mechanism in the event of a failure is applied to a device that controls the variable displacement mechanism of a variable displacement hydraulic pump by electro-hydraulic servo control has been described.
The gist of the present invention is not limited to this,
The present invention can also be applied to a device in which the variable displacement mechanism of a variable displacement hydraulic pump is controlled by other control methods.

〔Effect of the invention〕

The backup device of the present invention returns the tilting angle of the variable displacement hydraulic pump to a predetermined position in the event of a failure by operating the hydraulic actuator that drives the variable displacement mechanism of the variable displacement hydraulic pump. Therefore, even if any member constituting the servo control device, such as the displacement gauge, pressure detector, or discharge amount control device, breaks down, the work vehicle can continue to work. Therefore, it is possible to avoid disadvantages such as the failure of these members, which causes the work vehicle to fail and the construction work to be delayed, as in the past.

Further, the backup device of the present invention requires only a conduit for supplying pressure oil from the hydraulic source to the hydraulic actuator in the event of a failure, so the structure is simple, highly reliable, and can be implemented at low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention,
Fig. 2 is a circuit diagram showing the second embodiment, Fig. 3 is a circuit diagram showing the third embodiment, Fig. 4 is a circuit diagram showing the fourth embodiment, and Fig. 5 is a conventional hydraulic drive. 6 is a block diagram showing the basic structure of a discharge amount control device provided in the hydraulic drive device shown in FIG. 5. FIG. 1: Variable displacement hydraulic pump, 2: Variable displacement mechanism, 3: Servo piston, 4: Servo cylinder, 5: Hydraulic source, 6: Oil tank, 7, 8: Pipe line, 9: Return pipe line, 10, 11 : Solenoid valve, 12:
Displacement meter, 16: Pressure detector, 17: Operation lever,
18: Discharge amount control device, 20, 30, 40, 5
0: Servo piston, 21, 31, 41, 51:
servo cylinder.

Claims (1)

[Claims] 1. A variable displacement hydraulic pump equipped with a variable displacement mechanism, an actuator driven by pressure oil discharged from the pump, and a piston that drives the variable displacement mechanism are housed. A servo cylinder, a hydraulic source for supplying pressure oil to the servo cylinder, an oil tank for accumulating hydraulic oil to be supplied to the servo cylinder, and a hydraulic oil source for supplying pressure oil from the hydraulic source to the servo cylinder. A variable displacement hydraulic pump comprising: a solenoid valve that controls supply and return of pressure oil from the servo cylinder to the oil tank to control a tilting angle of the variable displacement mechanism; and a control means for the solenoid valve. In the hydraulic drive device, a changeover switch is attached to the control means to switch the solenoid valve to a closed state via the control means in the event of a failure, and when the solenoid valve is switched to the closed state, the pressure of the hydraulic source is A pipeline for supplying oil to at least one of a left chamber and a right chamber of the servo cylinder, and an oil passage opened and closed in the servo cylinder and opened and closed by the piston to the left chamber of the servo cylinder. 1. A hydraulic drive device for a variable displacement hydraulic pump having a backup mechanism, characterized in that a pipeline for communicating with a right side chamber is provided in the hydraulic circuit for driving the servo cylinder.