JPH11182674A - Device and method for controlling forward/backward switching of hydraulic driven vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly change the forward/backward switching in the travel without any shift shock by providing a timer to make a delay for the prescribed time according to the vehicle speed until the switching control signal is outputted after the vehicle speed signal from a vehicle speed sensor is inputted and the switching command is inputted by a controller. SOLUTION: When a controller 10 receives the vehicle speed signal detected by a vehicle speed sensor 13 and an FR switching command from a forward/backward switching command means 9, the controller 10 outputs the FR switching control signal after the delay time according to the vehicle speed. The back pressure control hydraulic pressure of a back pressure valve 6 is reduced according to the back pressure correction command from the controller 10 by a back pressure correction control valve 15, and the hydraulic pressure from a pressure reducing valve 17 is reduced according to the motor volume correction command from the controller 10 by a solenoid pressure reducing valve 20. The vehicle speed is judged, and the back pressure valve 6 and a motor volume control valve 19 can be operated to meet the operation of a direction changing valve 8 at an appropriate timing, and the shift shock in the forward/backward switching in the travel can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forward / backward switching control device and control method for a hydraulically driven vehicle.

[0002]

2. Description of the Related Art A first prior art will be described with reference to FIG. The hydraulic motor 6 is driven by supplying pressure oil discharged from the hydraulic pump 2 to the hydraulic motor 6 through the direction switching valve 4 and returning oil returned from the hydraulic motor 6 to the tank 7. When a switching signal of a forward / reverse switching lever (hereinafter, referred to as an FR lever) 9 is input to the controller 10, the controller 10
Then, for the purpose of shockless, the electric signal or the hydraulic signal is delayed for a predetermined time and output to the pilot valve 8. Therefore, the direction switching valve 4 switches to F or R according to the pilot pressure from the pilot valve 8 delayed from the operation of the FR lever. With this configuration, the shift shock at the time of switching by the FR lever, and at the same time, cavitation generated at the time of stopping from high-speed rotation and at the time of reverse rotation are reduced.

FIG. 7 shows that the second prior art (Japanese Patent Application No. Hei 8-
No. 155986). A hydraulic drive circuit that supplies hydraulic pressure oil discharged from the hydraulic pump 2 to the hydraulic motor 6 via the direction switching valve 4, and when braking is applied by the hydraulic motor 6,
This is a hydraulic drive device that throttles return oil from the hydraulic motor 6 and discharge pressure oil of the hydraulic pump 2 with the throttle valve 11 to prevent cavitation of the hydraulic motor 6 via the suction valves 35a and 35b. The pressure on the drive side of the hydraulic motor 6 is taken out as a signal in synchronization with the pilot pressure for switching the direction switching valve 4 and supplied to the pilot pressure receiving portion 11a of the throttle valve 11.
A pilot valve 8 that is switched by a forward / reverse switching lever (hereinafter, referred to as an FR lever) 9, and a pressure of return oil (hereinafter, referred to as a “return oil”) that returns to the tank from the direction switching valve 4 by receiving the pressure on the hydraulic motor drive side by the pilot pressure receiving portion 11 a. And a variable throttle valve 11 for switching the pressure (called back pressure) to a low pressure or a high pressure. With this configuration, the loss of the driving horsepower caused by the back pressure of the return oil is reduced, and at the same time, the cavitation generated at the time of stopping from high-speed rotation and at the time of reverse rotation is suppressed.

[0004]

(1) However, in the first prior art, when an electric delay means such as a timer or a pilot pressure orifice is added for the purpose of shocklessness, a time lag from the time of operation of the FR lever is increased. Since it is determined uniformly, the responsiveness of the operation is reduced when a time lag is not required as when the vehicle speed is slow, and when a large time lag is required as when the vehicle speed is fast,
There was a problem that could not solve the forward / reverse switching shock.

(2) In the second prior art, the pilot pressure supplied to the pilot pressure receiving portion 11a of the throttle valve 11 by the pilot valve 8 is the pressure on the driving side of the hydraulic motor 6, so that, for example, When the pilot valve 8 is switched from forward to reverse by the switching lever 9, the direction switching valve 4
There is a period in which the vehicle speed remains at F even if the spool stroke of F changes from F to R. That is, since the directional control valve is moving backward while the vehicle is moving forward, a high braking pressure is generated and the driving pressure is on the reverse side. The control of the back pressure by the throttle valve 11 is switched to a low pressure when the driving pressure becomes high, so that not only a shift shock acts but also cavitation occurs. In addition, despite the fact that back pressure is not necessary during acceleration and constant speed running, the back pressure acts when the driving pressure is low, such as during normal running at a constant speed, and the running efficiency is reduced. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and by simply adding it to the conventional structure, forward / reverse switching during traveling can be performed smoothly without a shift shock, and deceleration can be achieved. It is an object of the present invention to provide a forward / backward switching control device for a hydraulically driven vehicle which minimizes back pressure to improve running efficiency and minimizes cavitation of a hydraulic motor during deceleration.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, a forward / reverse switching control apparatus for a hydraulically driven vehicle according to a first aspect of the present invention includes a hydraulic pump driven by an engine, a hydraulic pump, A hydraulic motor driven by the pump, a direction switching valve that supplies oil discharged from the hydraulic pump to one port of the hydraulic motor, and returns oil from the other port of the hydraulic motor to the tank; and a pilot pressure that switches the direction switching valve. Direction switching solenoid valve for controlling the direction switching solenoid valve, forward / reverse switching command means for outputting pilot pressure for forward or backward of the vehicle to the direction switching solenoid valve; A controller that outputs a switching control signal and a back pressure control oil pressure that is interposed between the direction switching valve and the tank and that is applied to the pilot pressure receiving portion, and applies a back pressure to the return oil from the direction switching valve. That a back pressure valve, receives the motor volume control oil pressure to the pilot pressure receiving portion, the discharge capacity of the hydraulic motor (cc /
rev) to control the forward / backward switching of a hydraulically driven vehicle having a motor displacement control valve and a vehicle speed sensor for detecting a vehicle speed, and after inputting a vehicle speed signal from the vehicle speed sensor and inputting a switch command by the controller. Until a switching control signal is output, a timer that delays by a predetermined time according to the vehicle speed, and a back pressure correction command from the controller that outputs the vehicle speed signal to the controller are input, and the control oil pressure for controlling the back pressure valve is reduced. A back pressure correction control valve that corrects to increase the back pressure, and a motor volume correction command from the controller is input, the motor volume control oil pressure that controls the motor discharge volume control valve is increased, and the motor discharge volume ( (cc / rev) with an electromagnetic pressure reducing valve that corrects the maximum discharge with hydraulic control only so as to reduce it to an arbitrary discharge volume required for deceleration.

According to the first aspect of the present invention, the time from the input of the switching command to the output of the switching control signal is delayed by a predetermined time according to the vehicle speed. Is improved, and when the vehicle speed is high, increasing the delay time reduces the forward / reverse switching shock. Further, when the back pressure correction control valve inputs a back pressure correction command from the controller, the control oil pressure of the back pressure valve is reduced, and the pressure of the return oil to the tank is increased by the back pressure valve. For this reason, the braking force acts on the hydraulic motor during deceleration, and the suction port of the hydraulic motor, which tends to run out of oil, tends to replenish the return oil to the tank raised by the back pressure valve from the suction valve, preventing cavitation. You. Further, when the electromagnetic pressure reducing valve inputs a correction command from the controller, the motor displacement hydraulic pressure is increased, and the discharge volume (cc / rev) of the motor is reduced. For this reason, the amount of oil in the suction port of the hydraulic motor, which tends to be insufficient during deceleration, is reduced, and the flow rate of supply to the hydraulic motor is reduced, thereby preventing cavitation.

Therefore, the cost can be reduced because of the simple structure in which the back pressure correction control valve and the electromagnetic pressure reducing valve are simply added to the conventional structure. In addition, by judging the vehicle speed and operating the directional control valve at the appropriate timing, the back pressure valve and the motor volume control valve are operated to compensate for the control in the area where self-pressure control alone is not complete, Shift shock during forward / reverse switching is reduced, smooth forward / reverse switching can be performed, and a correction command from the controller minimizes back pressure except during deceleration to improve running efficiency. And cavitation of the hydraulic motor can be reliably prevented. In this way, equipment damage is prevented by reducing shift shocks and reliably preventing cavitation.In addition, shuttle operation is possible even at a predetermined speed or higher, improving operability, and ensuring reliable forward movement even on cliffs. It is possible to change between reverse and reverse, and safety is improved, and reliability and durability are improved.

The forward / backward switching control apparatus for a hydraulically driven vehicle according to a second aspect of the present invention is the first aspect, wherein the motor driving pressure of the hydraulic motor is controlled by a pilot valve of the back pressure valve as a back pressure control hydraulic pressure via a direction switching solenoid valve. Acts on the pressure receiving part, and after the higher oil pressure of one port and the other port of the hydraulic motor is selected by the shuttle valve, it is reduced to a predetermined pressure by the pressure reducing valve and acts as input pressure to the electromagnetic pressure reducing valve. It is characterized by doing.

According to the second aspect, when the direction switching solenoid valve is operated forward or backward, the motor driving pressure of the hydraulic motor acts on the pilot pressure receiving portion of the back pressure valve. Also, the higher oil pressure of one of the ports and the other port of the hydraulic motor is input to the electromagnetic pressure reducing valve via the shuttle valve and the pressure reducing valve. Therefore, there is no need to separately provide a back pressure control hydraulic source acting on the pilot pressure receiving portion of the back pressure valve and a hydraulic source input to the electromagnetic pressure reducing valve, so that the configuration is simplified and the cost is reduced.

According to a third aspect of the present invention, there is provided a forward / reverse switching control apparatus for a hydraulically driven vehicle according to the first aspect, wherein the pilot pressure receiving section receives pump volume control hydraulic pressure to control the discharge volume (cc / rev) of the hydraulic pump. The pump displacement control valve is provided, and the motor displacement control oil pressure is increased by an electromagnetic pressure reducing valve, so that the pump displacement (cc / rev) is corrected so as to increase.

According to the third aspect of the invention, the pump displacement control valve receives the pump displacement control oil pressure from the electromagnetic pressure reducing valve to the pilot pressure receiving portion, and is corrected so as to increase the pump displacement (cc / rev). For this reason, the oil amount of the suction port of the hydraulic motor, which tends to be insufficient during deceleration, is replenished by the increased pump discharge oil, and cavitation is reliably prevented.

According to a fourth aspect of the present invention, there is provided a method for controlling forward / reverse switching of a hydraulically driven vehicle, wherein the hydraulic pump increases the discharge volume (cc / rev) and the hydraulic motor increases the discharge volume (cc / rev) by increasing the engine speed. In a hydraulic drive device having an open hydraulic drive circuit that controls the back pressure of the oil returning to the tank with a back pressure valve to prevent cavitation, the hydraulic drive device reduces the vehicle from a forward position through a neutral position to a reverse position,
Alternatively, when switching from the reverse position to the forward position through the neutral position, the directional control valve is held at the neutral position to decelerate to the first predetermined speed, and the back pressure is increased by the back pressure valve to return the oil to the tank. To the main circuit connected to the entrance and exit of the hydraulic motor, and between the first predetermined vehicle speed or lower and the second predetermined vehicle speed or higher, the back pressure is increased by the back pressure valve to supply return oil to the tank to the motor circuit. In addition, it is characterized in that holding or maximizing the volume of the motor is reduced to an arbitrary discharge volume.

According to the fourth aspect of the invention, when the vehicle is to be switched from the forward position to the reverse position via the neutral position or from the reverse position to the forward position via the neutral position, the vehicle can be held by holding the directional control valve at the neutral position. When the speed is reduced to the first predetermined speed, and the back pressure is increased by the back pressure valve to supply the return oil to the tank to the main circuit connected to the inlet of the hydraulic motor,
Cavitation is prevented by replenishing the pressure oil of the main circuit connected to the inlet of the motor. When the vehicle is decelerated and becomes lower than the first predetermined vehicle speed and higher than the second predetermined vehicle speed, the volume of the motor is maintained or reduced, so that the rotation speed of the motor is maintained or maintained even when the engine is decelerated during forward / reverse shifting. The vehicle speed is maintained because of the increase. Further, the pressure oil raised by the back pressure valve is supplied to the motor circuit, and the amount of suction oil of the hydraulic motor, which is likely to be insufficient, is reduced by holding or reducing the volume of the motor, so that cavitation is reliably prevented.

According to a fifth aspect of the present invention, there is provided a method for controlling the forward / reverse switching of a hydraulically driven vehicle according to the fourth aspect, wherein the back pressure valve is returned when the vehicle speed is equal to or lower than a second predetermined vehicle speed, thereby reducing the back pressure of the return oil to the tank. In addition, the capacity of the motor is increased.

According to the fifth invention, the speed is further reduced and the second
When the vehicle speed is lower than the specified vehicle speed, the hydraulic oil in the main circuit connected to the inlet of the hydraulic motor does not run out and cavitation does not occur, so the back pressure is reduced to reduce the return oil to the tank and the back pressure loss is reduced. By reducing the speed and increasing the discharge volume of the motor to reduce the speed, the switching shock is reduced by smoothly switching from neutral to forward or from neutral to reverse.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a forward / reverse switching control apparatus for a hydraulically driven vehicle according to the present invention will be described in detail below with reference to FIGS.

The configuration of the first embodiment will be described with reference to FIG. The engine 1 drives a variable displacement hydraulic pump 2 and a fixed displacement control pump 3. The oil discharged from the hydraulic pump 2 is supplied from the first main circuit 5a to the variable displacement hydraulic motor 6 via the forward (hereinafter referred to as F) position of the direction switching valve 4.
And the oil discharged from the other port 6b of the hydraulic motor 6 is returned from the second main circuit 5b to the tank 7 via the F position of the direction switching valve 4 so that the hydraulic motor 6 It is driven forward. Similarly, hydraulic pump 2
Is supplied from the second main circuit 5b to the other port 6b of the hydraulic motor 6 via the reverse (hereinafter, referred to as R) position of the directional control valve 4, and the one port 6a of the hydraulic motor 6
Is returned from the first main circuit 5a to the tank 7 via the R position of the direction switching valve 4, whereby the hydraulic motor 6 is driven backward. The directional control valve 4 is a three-position directional control valve having a neutral (hereinafter, referred to as N) position between the F position and the R position, and restricts return oil from the directional control valve 4 between the directional control valve 4 and the tank 7. Back pressure valve 11 for applying back pressure to return oil
Is interposed.

When a vehicle speed signal detected by the vehicle speed sensor 13 and an FR switching command for switching to F or R from forward / reverse switching command means (hereinafter referred to as an FR lever) 9 are input to the controller 10, the controller 10 outputs the FR signal. An FR switching control signal is output to the direction switching electromagnetic valve 8 after a delay time (see FIG. 3) corresponding to the vehicle speed from the input of the switching command. At the F position of the direction switching solenoid valve 8, the direction switching valve 4 is switched to the F position by the hydraulic pressure of the first main circuit 5 a, and acts on the pilot pressure receiving portion 11 a of the back pressure valve 11 via the pilot line 12. Reduce pressure. Similarly, at the R position of the direction switching solenoid valve 8, the hydraulic pressure of the second main circuit 5b causes
The directional control valve 4 is switched to the R position, and the pilot pressure receiving portion 1 of the back pressure valve 11 is
Acts on 1a to reduce back pressure.

A back pressure correction control valve 15 for controlling the hydraulic pressure of the pilot line 12 is provided between the pilot line 12 and the tank 7, and a back pressure correction control valve 15 is provided from the controller 10 to the solenoid control unit 15a of the back pressure correction control valve 15. When a pressure correction command is input, the back pressure correction control valve 15 reduces the back pressure control oil pressure of the back pressure valve 6 according to the back pressure correction command. At the N position of the direction switching solenoid valve 8, the pilot does not act on the direction switching valve 4, so that the direction switching valve 4 is at the N position and the control pressure line 3 a of the control pump 3 and the pilot pressure receiving portion 11 a of the back pressure valve 11. Is drained to the tank 7.

A relief valve 36a and a suction valve 35b, and a relief valve 36b and a suction valve 35a are provided between the main circuits 5a and 5b.
The return oil from the direction switching valve 4 and the hydraulic pump 2 to which the back pressure has been applied by the back pressure valve 11 is
The back pressure is supplied to the first main circuit 5a or the second main circuit 5b from the back pressure line 11b through suction valves 35a and 35b provided between the first main circuit 5a and the second main circuit 5b to prevent cavitation. Also, among the hydraulic pressures of the main circuits 5a and 5b,
The higher one is input to the pressure reducing valve 17 through the first shuttle valve 16, and the hydraulic pressure reduced by the pressure reducing valve 17 and the main circuits 5 a and 5 b supplied through the F position or the R position of the direction switching solenoid valve 8. The higher the motor drive pressure is selected by the second shuttle valve 18, and the motor drive pressure of the hydraulic motor 6
9 is supplied as the control source pressure. On the other hand, the hydraulic pressure reduced by the pressure reducing valve 17 is reduced by the electromagnetic pressure reducing valve 20, supplied to the downstream of the check valve 22 provided in the control pressure line 3 a of the control pump 3, and supplied to the pump volume control valve 23. The control pressure is supplied to the pilot pressure receiving portion 23 a and the pilot pressure receiving portion 19 a of the motor volume control valve 19. From the controller 10 to the solenoid control unit 20 of the electromagnetic pressure reducing valve 20
When the motor volume correction command is input to the control valve a, the electromagnetic pressure reducing valve 2
0 reduces the oil pressure from the pressure reducing valve 17 according to the motor volume correction command.

The operation of the first embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing a temporal change at the time of FR switching, FIG. 4 is a diagram showing a relationship between a vehicle speed V and a delay time Tδ of an FR switching control signal, and FIG. 5 is a control flowchart of a forward / reverse switching control device. It is.

FIG. 3 will be described with reference to FIG.
In each of (A) to (H), the elapsed time is shown on the abscissa, and (A) is the ordinate on the FR lever 9 from the controller 1.
A switching command output to 0, (B) is a switching control signal output from the controller 10 to the direction switching solenoid valve 8, (C)
Is the spool stroke of the direction switching valve 4, (D) is the vehicle speed,
(E) is the back pressure of the back pressure valve 11, (F) is the pump capacity of the hydraulic pump 2, (G) is the motor capacity of the hydraulic motor 6, (H)
Is the ON / OF of the back pressure correction control valve 15 and the electromagnetic pressure reducing valve 20
The F state is shown. In (A), the FR lever 9 is switched from F to R via N at time t1. In (B), when the controller 10 inputs the switching command from the FR lever 9 shown in (A), the controller 10 outputs the time t.
After holding N for a predetermined delay time Tδ from 1 to t2a, a switching control signal for switching to R is output to the direction switching solenoid valve 8. The broken line indicates the switching control signal when there is no delay time Tδ. In (C), the pilot pressure according to the switching control signal shown in (B) is applied from the direction switching solenoid valve 8 to the direction switching valve 4.
, The spool stroke of the directional control valve 4 is controlled from F to N from time t1 to t2 and continuously from N to R. The broken line indicates the delay time T in FIG.
A spool stroke corresponding to the case where there is no δ (shown by a broken line) is shown.

In (D), the spool stroke of the directional control valve 4 shown in (C) is reduced, and from time t1 to t2, the hydraulic pump 2 switches to the F port of the directional control valve 4, the first main circuit 5a, and the hydraulic motor. 6. The amount of oil circulating from the second main circuit 5b to the F port of the direction switching valve 4 decreases, and the vehicle speed decreases. On the other hand, the amount of oil drained from the back pressure valve 11 from the hydraulic pump 2 through the F port of the direction switching valve 4 increases. After the time t2, the spool stroke of the directional control valve 4 becomes R
Therefore, the discharge oil of the hydraulic pump 2
It is supplied to the second main circuit 5b via the port. For this reason,
The pressure in the second main circuit 5b of the hydraulic motor 6 becomes high due to the pressure oil being discharged to the second main circuit 5b, and the relief valve 3
6b to the first main circuit 5a from the suction valve 35a.
, And is drained from the R position of the direction switching valve 4 via the back pressure valve 11. At this time, although the vehicle speed is F, since the spool stroke of the direction switching valve 4 and the direction switching solenoid valve 8 are at the R position, the high-pressure hydraulic pressure of the second main circuit 5b passes through the R position of the direction switching solenoid valve 8. The pressure is supplied to the pilot pressure receiving portion 11 a of the back pressure valve 11. For this reason, the back pressure of the back pressure valve 11 decreases, and it becomes difficult to replenish the pressure oil of the first main circuit 5a, which tends to become negative pressure, via the back pressure line 11b and the suction valve 35a, and cavitation easily occurs. .

However, in (E), during (t) from time t2 to t3 when the spool stroke of the directional control valve 4 becomes R when the vehicle advances in (D), the solenoid control unit 15a of the back pressure correction control valve 15 causes the controller 10a to operate. It is excited by the back pressure correction command from. Therefore, the amount of oil drained from the pilot line 12 increases, and the pilot pressure receiving portion 11a of the back pressure valve 11
The back pressure by the back pressure valve 11, the pressure of which has been reduced and the pressure drop is suppressed, replenishes the first main circuit 5a from the suction valve 35a via the back pressure line 11b to prevent cavitation. In (F), at time (t) in (A), a switching command for the FR lever 9 is output to the controller 10, and at the same time, the solenoid control section 20a of the electromagnetic pressure reducing valve 20 is excited by a motor volume correction command from the controller 10. You. For this reason, the high pressure selected by the shuttle valve in the first and second main circuits 5a and 5b is reduced by the pressure reducing valve 17 and further reduced by the electromagnetic pressure reducing valve 20 to the motor control unit 19a and the pump control unit 23a. Supplied. Thus, the hydraulic pump 6
Discharge volume D increases to Dp compared to when the electromagnetic pressure reducing valve 20 is not installed (shown by a broken line).

In (G), similarly to (F), the discharge volume D of the hydraulic motor 6 is reduced to Dm as compared to when the electromagnetic pressure reducing valve 20 is not installed (shown by a broken line). As described above, when the discharge volume D of the hydraulic motor 6 decreases and the discharge volume D of the hydraulic pump 6 increases, the amount of oil required to replenish the first main circuit 5a decreases. Cavitation is prevented. Further, when the engine 1 is decelerated by releasing the accelerator pedal during the FR shift, the rotational speed of the control pump 3 decreases and the hydraulic pressure of the control pressure line 3a decreases. When the control valve 23 and the motor displacement control valve 19 are controlled, the pump displacement is reduced and the motor displacement is increased, so that a sufficient vehicle speed cannot be obtained. However, the hydraulic pressure of one of the main circuits 5a, 5b having a high pressure is selected by the first shuttle valve 16, and the pressure is reduced by the pressure reducing valve 17 and the electromagnetic pressure reducing valve 20, so that the pump volume control valve 23 and the motor volume control valve 1
9, the pump volume increases and the motor volume decreases, and a sufficient vehicle speed can be obtained. Further, if the motor volume is made constant like Dm and the braking torque is made constant, the braking force can be stabilized and shift shock can be prevented.
In (H), as shown in (E), during the time t2 to t3, the solenoid control unit 15a of the back pressure correction control valve 15 is set to O.
N (excitation), and as shown in (F) and (G), at time t
During the period from 1 to t3, the electromagnetic pressure reducing valve 20 is turned on. In addition,
Although the switching control from F to R has been described with reference to FIG. 3, the switching control from F to R is the same, and the description is omitted.

Referring to FIG. The horizontal axis shows the vehicle speed V, and the vertical axis shows the delay time Tδ of the FR switching control signal. In the low speed range of the vehicle speed V1 from the stop, the delay time Tδ is eliminated, and the FR switching command is output to the direction switching solenoid valve 8 simultaneously with the operation of the FR lever 9, thereby improving the responsiveness of the operation. In addition, the delay time T is applied to the vehicle speed V1 to V2.
When the vehicle speed becomes equal to or lower than V2, the delay time Tδ is increased when the vehicle speed V is fast to reduce the forward / reverse switching shock. In this embodiment, the delay time Tδ is increased stepwise according to the increase of the vehicle speed V, but may be increased continuously as shown by a broken line.

Referring to FIG. 5 and FIGS.
A flow of forward / reverse switching control of the embodiment will be described. In step S1, an FR switching command is input from the FR lever 9 to the controller 10. In step S2, a shuttle switching operation is performed to switch from the F position to the R position via the N position or the R position to the F position via the N position (ie, from the F position to the F position via the N position or the R position). (It is not a switching operation to the R position via the N position).
In step S3, it is determined whether or not the vehicle speed is equal to or higher than 12 km / h.
Then, the FR solenoids 8a and 8b of the direction switching electromagnetic valve 8 are not excited, and the direction switching electromagnetic valve 8 keeps the N position.
Returning to step S3 without shifting, the direction switching solenoid valve 8 is decelerated because of the N position and loops through S3 and S4 until the vehicle speed becomes less than 12 km / h. Step S
In a step S5, it is determined whether or not the vehicle speed is equal to or higher than 12 km / h.
As shown in (D), the direction switching solenoid valve 8 is set to N for 0.3 seconds.
The position is maintained, and after the spool stroke of the direction switching valve 4 becomes substantially the N position, the position is switched to the R position (or the F position). At the same time, at step S7, the solenoid control unit of the back pressure correction control valve 15 is switched. 15a ON (electromagnetic pressure reducing valve 2
0 solenoid control unit 20a is ON) and the back pressure valve 1
Then, the vehicle decelerates while maintaining the back pressure of 1 to prevent cavitation, returns to the step before S5, and repeats the loop of S5 to S7 until the vehicle speed becomes less than 1 km / h.

If the vehicle speed becomes less than 1 km / h in step S5, the solenoid control unit 15a of the back pressure correction control valve 15 and the solenoid control unit 20a of the electromagnetic pressure reducing valve 20 change to the state shown in FIG. As shown, when the excitation is continued for 0.5 seconds, the control pressures of the pump volume control valve 23 and the motor volume control valve 19 are increased, so that the discharge volume of the hydraulic pump increases and the discharge volume of the hydraulic motor decreases. Decrease. Therefore, a sufficient vehicle speed can be maintained even when the accelerator pedal is loosened and the engine 1 is decelerated during the FR shift, and the amount of oil required to replenish the first main circuit 5a is reduced. Cavitation is prevented. At the same time, the back pressure of the back pressure valve 11 is increased because the pilot pressure of the pilot line 12 is reduced by the back pressure correction control valve 15, and cavitation on the low pressure side of the first main circuit 5a and the hydraulic motor 6 is reliably prevented. . In this way, as shown in FIG. 3D, when the vehicle is almost stopped, the solenoid control units 15a and 20a of the back pressure correction control valve 15 and the electromagnetic pressure reducing valve 20 are demagnetized.
The R switching control ends.

The configuration of the second embodiment will be described with reference to FIG. A back pressure control hydraulic source 25 different from FIG. 1 is installed in the pilot line 12 of the back pressure valve 11, and the control pump 3 shown in FIG.
, Another control pump 24 was installed. Check valve 3
The first shuttle valve 16 and the pressure reducing valve 17 shown in FIG. 1 are connected to the motor control line 26 connecting the control pump 24 and the motor displacement control valve 19 via the electromagnetic pressure reducing valve 20 via the electromagnetic pressure reducing valve 20. A motor volume control hydraulic source 28 was provided. Further, a pump volume correcting hydraulic source 29 is provided via a pump electromagnetic pressure reducing valve 30 in a pump control line 27 connecting the control pump 24 and the pump volume control valve 23 via a check valve 34. The solenoid control unit 20a of the electromagnetic pressure reducing valve 20 controls the motor volume correction oil pressure according to the motor volume correction command from the controller 10. Also, the electromagnetic pressure reducing valve 3 for the pump
The 0 solenoid control unit 30a inputs a pump volume correction command from the controller 10 and controls the pump volume correction hydraulic pressure. Other configurations are the same as those in FIG. 1, and thus the same reference numerals are given and description thereof is omitted.

The operation of the second embodiment will be described. Since the control pump 24, the back pressure control hydraulic pressure source 25, the motor volume control hydraulic pressure source 28, and the pump electromagnetic pressure reducing valve 30 are installed separately from the engine drive, they can be controlled separately from the engine control. Other operations are the same as those in FIG.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a change over time during FR switching of the forward / reverse switching control device according to the present invention.

FIG. 4 is a diagram illustrating a relationship between a vehicle speed V and a delay time Tδ of an FR switching control signal according to the present invention.

FIG. 5 is a diagram showing a control flowchart of a forward / reverse switching control device according to the present invention.

FIG. 6 is a diagram showing a first conventional technique.

FIG. 7 is a diagram showing a second conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... hydraulic pump, 3, 24 ... control pump, 4 ... directional switching valve, 5a ... 1st main circuit, 5b ... 2nd main circuit, 6 ... hydraulic motor, 7 ... tank, 8 ... directional switching electromagnetic Valve: 9: FR lever (forward / backward switching command means), 10: Controller, 11: Back pressure valve, 11a: Pilot pressure receiving unit, 12: Pilot line, 13: Vehicle speed sensor, 15:
Back pressure correction control valve, 16: first shuttle valve, 17: pressure reducing valve, 18: second shuttle valve, 19: motor displacement control valve,
20: electromagnetic pressure reducing valve, 21: control hydraulic line, 22: check valve, 23: pump volume control valve, 25: back pressure control hydraulic source, 26: motor control line, 27: pump control line, 2
Reference numeral 8: hydraulic pressure source for controlling the motor volume, 29: hydraulic pressure source for correcting the pump volume, 30: electromagnetic pressure reducing valve for the pump, 33, 34: check valve.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F16H 59:44

Claims (5)

[Claims] A hydraulic pump (2) driven by an engine (1) and a hydraulic motor driven by a hydraulic pump (2)
(6) and the oil discharged from the hydraulic pump (2) is supplied to one port (6a) of the hydraulic motor (6), and the oil from the other port (6b) of the hydraulic motor (6) is supplied to the tank (7). Direction switching valve (4)
A directional control solenoid valve (8) for controlling pilot pressure for switching the directional control valve (4), and a forward / reverse switching command means (9) for outputting pilot pressure for vehicle forward or backward to the directional control solenoid valve (8) And a controller (10) for inputting the switching command of the forward / reverse switching command means (9) and outputting a switching control signal to the direction switching solenoid valve (8), and between the direction switching valve (4) and the tank (7). A back pressure valve (11), which receives back pressure control oil pressure at the pilot pressure receiving portion (11a) and applies back pressure to return oil from the directional control valve (4), and a motor displacement at the pilot pressure receiving portion (19a) A forward-reverse switching control device for a hydraulically driven vehicle having a motor displacement control valve (19) for controlling a discharge volume (cc / rev) of a hydraulic motor (6) in response to a control oil pressure; 13) and the vehicle speed signal from the vehicle speed sensor (13), and after the controller (10) inputs the switching command, A timer that delays until a control signal is output for a predetermined time according to the vehicle speed, and a controller
A back pressure correction control valve (15) for inputting a back pressure correction command from (10) and lowering the control oil pressure for controlling the back pressure valve (11) to increase the back pressure, and a controller (10 ) From the motor discharge volume control valve (1
9) has an electromagnetic pressure reducing valve (20) that raises the motor volume control oil pressure to control and corrects the maximum discharge volume (cc / rev) of the motor so as to reduce it to an arbitrary discharge volume. A forward / reverse switching control device for a hydraulically driven vehicle. 2. The system according to claim 1, wherein the motor driving pressure of the hydraulic motor (6) acts on the pilot pressure receiving portion (11a) of the back pressure valve (11) as back pressure control oil pressure via the direction switching solenoid valve (8). And one port (6a) of the hydraulic motor (6) and the other port
After the higher oil pressure of (6b) is selected by the shuttle valve (16), it is reduced to a predetermined pressure by the pressure reducing valve (17) and acts as an input pressure on the electromagnetic pressure reducing valve (20). Forward / backward switching control device for a hydraulically driven vehicle. 3. The pilot pressure receiving section (2) according to claim 1,
3a) is provided with a pump volume control valve (23) that receives the pump volume control hydraulic pressure and controls the discharge volume (cc / rev) of the hydraulic pump (2), and the motor volume control hydraulic pressure is controlled by an electromagnetic pressure reducing valve (20). A forward / backward switching control device for a hydraulically driven vehicle, which raises and corrects so as to increase the discharge volume (cc / rev) of a pump. 4. A hydraulic drive system in which the hydraulic pump increases the discharge volume (cc / rev) by increasing the engine speed and the hydraulic motor reduces the discharge volume (cc / rev). In a hydraulic drive vehicle having an open hydraulic drive circuit that controls cavitation by controlling with a back pressure valve, when the vehicle is switched from a forward position to a reverse position through a neutral position, or from a reverse position to a forward position through a neutral position, The directional control valve is held at the neutral position to reduce the speed to a first predetermined speed, and the back pressure valve is operated to supply the return oil to the tank to a main circuit connected to the inlet / outlet of the hydraulic motor. Between the vehicle speed and the second predetermined vehicle speed or more, the back pressure valve is operated to supply the return oil to the tank to the motor circuit, and the discharge of the motor to maintain or maximize the volume is arbitrary. The forward-reverse switching control method of a hydraulic driving vehicle, characterized in that to reduce the volume. 5. The hydraulically driven vehicle according to claim 6, wherein when the vehicle speed is equal to or lower than a second predetermined vehicle speed, the back pressure valve is returned to reduce the back pressure of the return oil to the tank and increase the volume of the motor. Forward and backward switching control method.