JPH06249339A - Hst hydraulic traveling driving device - Google Patents

Abstract

PURPOSE:To carry out smooth inertial running by providing a logic valve, which is provided with a master valve opening/closing a by-pass pipeline on the basis of a difference between pressure of a pair of main pipelines and a pilot pressure and a pilot pressure controlling part, which selects one of the pressure between the pressure of a pair of a main pipeline as a pilot pressure of the master valve part, in a by-pass pipeline. CONSTITUTION:A directional control valve 121 of a logic valve 100 is switched to an F position and a pressure Pa of a main pipeline 3 is selected as a pilot pressure Pc of a master valve part 110. When an accelerator pedal is stepped down in this condition, a discharging amount of an oil pressure pump 2 is increased and the pressure Pa of the main pipeline 3 becomes higher than the pressure Pb of the main pipeline 4, so that the by-pass pipeline 20 is closed. Reversely, when the accelerator pedal is released, the pressure Pb becomes higher than the pressure Pa, so that a poppet 111 is moved so as to open the by-pass pipeline 20. In this way, discharged oil from an oil pressure motor 5 to the main pipeline 4 is returned to the main pipeline 3 via the by-pass pipeline 20, so that no containment pressure is generated on a discharging side of the oil pressure motor 5 and inertial running can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an HST hydraulic traveling drive system used in a work vehicle such as a wheel loader.

[0002]

2. Description of the Related Art As a hydraulic traveling drive system for a work vehicle such as a wheel loader, for example, as disclosed in Japanese Utility Model Laid-Open No. 3-12659, a variable displacement hydraulic pump driven by a prime mover and a pair of main pipes are used to control the hydraulic pressure. The pump is equipped with a hydraulic motor connected in a closed circuit, and the discharge rate of the hydraulic pump is changed by increasing or decreasing the rotation speed of the prime mover by operating the accelerator pedal in the driver's seat, and the rotation speed of the hydraulic motor is changed according to this pump discharge quantity. HST that changes the running speed of the vehicle by changing the
Hydraulic drive devices are known. In the device described in the above publication, an on-off valve that is switch-controlled by a switch in the driver's seat is provided in a bypass line connecting a pair of main pipes. When the opening / closing valve is switched to the closed position to close the bypass line, a closing pressure is generated on the discharge side of the hydraulic motor by loosening the accelerator pedal, and the vehicle is decelerated. When the on-off valve is switched to the open position and the bypass line is opened, the discharge oil of the hydraulic motor returns to the suction side through the bypass line, so even if the accelerator pedal is loosened, the discharge side of the hydraulic motor is not discharged. The vehicle runs inertially without generating the closing pressure.

Here, when the accelerator pedal is depressed during inertial traveling, the discharge oil of the hydraulic pump escapes from the bypass conduit to the discharge side of the hydraulic motor if the bypass conduit is left open, and the rotational speed of the hydraulic motor. Does not rise. Therefore, in the device described in the publication, the discharge pressure of the charge pump driven by the prime mover is monitored, and when the accelerator pedal is depressed and the discharge pressure of the charge pump exceeds a predetermined value, the on-off valve is once returned to the closed position and bypassed. The pipeline is blocked.

[0004]

However, the discharge pressure of the charge pump changes due to various factors such as a change in the rotational speed of the prime mover due to the operation of the accelerator pedal, as well as a load change in the charge piping system. Moreover, since the charge pump and the hydraulic motor driving pump have different capacities, the pressure change characteristics with respect to the operation of the accelerator pedal also differ. For this reason, if the bypass pipeline is opened / closed according to the change in the discharge pressure of the charge pump, it is difficult to synchronize the change in the discharge amount of the hydraulic motor drive pump with the opening / closing of the bypass pipeline, and smooth inertial running is ensured. It's hard to realize.

An object of the present invention is to provide an HST hydraulic traveling drive system capable of smooth inertia traveling.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1 which is an embodiment. In the present invention, the variable displacement hydraulic pump 2 driven by a prime mover 1 and a pair of main pipelines 3, 3.
4 is applied to the variable displacement hydraulic pump 2 in a closed circuit, and is applied to an HST hydraulic traveling drive device including a hydraulic motor 5 driven by oil discharged from the variable displacement hydraulic pump 2. The above-described object is to provide the bypass conduit 20 connecting the pair of main conduits 3 and 4 with the pair of main conduits 3 and 4.
Of the parent valve portion 110 that opens and closes the bypass pipeline 20 based on the difference between the pressures Pa and Pb of the main pipelines and the pilot pressure Pc, and the parent valve portion 110 that controls either one of the pair of main pipelines 3 and 4.
It is achieved by providing a logic valve 100 having a pilot pressure control section 120 which is selected as the pilot pressure Pc.

[0007]

In the HST hydraulic traveling drive system of the present invention, by selecting either one of the pair of main pipelines 3 and 4 as the pilot pressure Pc, the magnitude relationship between the discharge side pressure and the suction side pressure of the hydraulic motor 5 is determined. it can. Then, for example, the pressure of the main pipeline on the suction side of the hydraulic motor 5 is set to the pilot pressure Pc.
When the accelerator pedal is depressed, the pilot pressure Pc increases if the pressure on the suction side of the hydraulic motor 5 rises, and if the pressure on the discharge side of the hydraulic motor 5 rises by loosening the accelerator pedal, the pilot pressure Pc rises. Since Pc becomes low, the parent valve 11
By adjusting so that 0 opens and closes, the bypass pipeline 20 opens and closes in conjunction with the pressure change of the main pipelines 3 and 4.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

【Example】

-First Embodiment- Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows a first embodiment of the present invention. In the figure, reference numeral 1 is a prime mover (for example, a diesel engine) of a wheel loader, and a variable displacement hydraulic pump 5 driven by the prime mover 1 is connected to a variable displacement hydraulic motor 5 by a pair of main pipe lines 3 and 4 in a closed circuit. Has been done.
The tilt amount of the variable displacement hydraulic pump 2 is controlled by a fixed displacement charge pump 6 that discharges pressure oil at a flow rate according to the rotation speed of the prime mover 1. That is, a part of the oil discharged from the charge pump 6 is guided to the forward / reverse switching valve 8 via the throttle 7, while the rest is directly guided to the forward / reverse switching valve 8 without passing through the throttle 7, and These discharged oils are guided to the oil chambers 9a and 9b of the tilt cylinder 9 according to the switching position of the forward / reverse switching valve 8. The pressure difference between the upstream side and the downstream side of the throttle 7 changes according to the discharge amount of the charge pump 6, and the tilt cylinder 9 is driven by this pressure difference, and the tilt amount of the hydraulic pump 2 changes. The relationship between the switching position of the forward / reverse switching valve 8, the pressure oil discharge direction of the hydraulic pump 2, and the traveling direction of the wheel loader is such that pressure oil is discharged to the main pipe line 3 side when the forward / reverse switching valve 8 is in the F position. As a result, the wheel loader moves forward, and when the forward / reverse switching valve 8 is in the R position, the main pipe line 4
The pressure load is discharged to the side and the wheel loader moves backward. The forward / reverse selector valve 8 is switched by a forward / rearward selector switch (not shown) in the cab.

The output shaft 5a of the hydraulic motor 5 is connected to a transmission 10 for changing its output speed.
Output is propeller shaft 11 and axle shaft 12
Is transmitted to the left and right drive wheels 13 via. Transmission 10
Is to selectively connect two hydraulic clutches to switch the meshing of gears attached to these hydraulic clutches between a high speed stage and a low speed stage. The switching of the hydraulic clutch is performed by a shift switch (not shown) provided in the driver's cab.

A bypass pipe 20 is provided between the main pipes 3 and 4 connecting the hydraulic motor 5 and the hydraulic pump 2, and a logic valve 100 is connected to the bypass pipe 20. The logic valve 100 includes a parent valve unit 110 that opens and closes the bypass conduit 20 and a pilot pressure control unit 120 that controls the pilot pressure Pc to the parent valve unit 110. As shown in more detail in FIG. 2, the parent valve portion 1
10 is the pressure P of the main pipe lines 3 and 4 acting on the first and second pressure receiving surfaces 111a and 111b on one end side of the poppet 111.
a, Pb and the third pressure receiving surface 11 on the other end side of the poppet 111
The bypass line 20 is opened and closed based on the difference from the pilot pressure Pc acting on 1c. Specifically, the force of pushing the poppet 111 to the left in the figure by the pressures Pa and Pb of the main pipelines 3, 4 is the force of pushing the poppet 111 to the right in the figure by the pilot pressure Pc and the force Fs of the spring 112. When the resultant force is exceeded, the bypass pipeline 20 is opened to connect the main pipelines 3 and 4.

As shown in FIG. 1, the pilot pressure controller 1
20 is a two-position type directional control valve 121 and a high pressure selection valve 12
2 and. When the directional control valve 121 is in the F position, only the pressure Pa in the main pipeline 3 is guided to the high pressure selection valve 122 and selected as the pilot pressure Pc. When the directional control valve 121 is in the R position, the pressure in the main pipelines 3 and 4 is selected. Pa and Pb are guided to the high pressure selection valve 122, and the higher pressure is selected as the pilot pressure Pc. Reference numeral 123 in the drawing is a throttle for restricting the moving speed of the poppet 111 when switching the directional control valve 121 to prevent a shock when switching the directional control valve 121.

Directional control valve 1 of pilot pressure control unit 120
Reference numeral 21 is switch-controlled by a change-over switch 30. This changeover switch 30 is changed over in conjunction with the change-over position of the forward / reverse change-over valve 8, and is turned on when the forward-reverse change-over valve 8 is in the F position, and turned off in the R position and the neutral position. When the changeover switch 30 is turned on, a drive current is supplied from the power supply 31 to the solenoid portion 121s of the directional control valve 121 to switch the directional control valve 121 to the F position, and when the changeover switch 30 is turned off, the supply of the drive current is stopped. Then, the directional control valve 121 returns to the R position.

In the figure, reference numeral 14 is an overload relief valve that regulates the maximum pressure in the main pipes 3, 4, 15 is a charge check valve for supplying pressure oil from the charge pump 6 to the main pipes 3, 4, and 16 is a charge check valve. It is a charge relief valve that regulates the maximum pressure of the charge system.

Next, the operation of the HST hydraulic traveling drive system constructed as above will be described. When the forward / reverse switching valve 8 is switched to the F position to move forward, the changeover switch 30 is turned on and the directional control valve 121 of the logic valve 100 is switched to the F position, so that the main conduit 3 of the main pipe line 3 is closed as shown in FIG. The pressure Pa is introduced as the pilot pressure Pc of the parent valve portion 110. If the accelerator pedal is depressed in this state, the hydraulic pump 2
And the pressure Pa of the main pipeline 3 becomes higher than the pressure Pb of the main pipeline 4. At this time, the magnitude relation of the forces acting on the poppet 111 is as follows.
Assuming that the area of 11c is Aa to Ac, Ac · Pc + Fs = (Aa + Ab) · Pa + Fs> Aa · Pa + Ab · Pb (1), the bypass pipe 20 is blocked. Therefore, the hydraulic motor 5 is driven at a speed according to its capacity and the discharge amount of the hydraulic pump 2, and the vehicle moves forward.

When the accelerator pedal is loosened in the state shown in FIG. 2A, the discharge amount of the hydraulic pump 2 decreases and the pressure Pb of the main pipe line 4 on the discharge side of the hydraulic motor 5 is the pressure Pa of the main pipe line 3. Since it becomes higher, the magnitude relation of the expression (1) is not established, and when Ab · Pa + Fs <Ab · Pb (2), the poppet 111 is moved and the bypass line 20 is opened. As a result, the oil discharged from the hydraulic motor 5 to the main pipe line 4 returns to the main pipe line 3 via the bypass pipe line 20, so that the vehicle runs inertially without generating a closing pressure on the discharge side of the hydraulic motor 5. Here, the spring force Fs
Is negligibly small compared with the forces generated by the pressures Pa and Pb of the main pipelines 3 and 4, so that the bypass pipeline 20 opens almost at the same time when the discharge pressure of the hydraulic motor 5 exceeds the suction pressure.

When the forward / reverse switching valve 8 is switched to the R position to move backward, the selector switch 30 is turned off and the logic valve 1 is turned on.
The directional control valve 121 of 00 is switched to the R position, and the higher pressure of the pressures Pa and Pb in the main pipelines 3 and 4 is introduced to the pilot pressure Pc of the parent valve portion 110. When the pressure Pb of the main pipe line 4 on the suction side of the hydraulic motor 5 becomes higher than the pressure Pa of the main pipe line 3 by depressing the accelerator pedal, the pressure Pb of the main pipe line 4 is increased as shown in FIG. 2 (B). Since the magnitude relation of the forces acting on the poppet 111 due to the pilot pressure Pc is Ac · Pc + Fs = (Aa + Ab) · Pb + Fs> Aa · Pa + Ab · Pb (3), the bypass conduit 20 is blocked. . Therefore, the hydraulic motor 5 is driven by the oil discharged from the hydraulic pump 2 and the vehicle moves backward.

On the other hand, when the pressure Pa of the main conduit 3 on the discharge side of the hydraulic motor 5 becomes higher than the pressure Pb of the main conduit 4 by loosening the accelerator pedal, as shown in FIG. The pressure Pa of No. 3 is guided to the pilot pressure Pc, and the magnitude relation of the force acting on the poppet 111 becomes as shown in the equation (1). Therefore, the bypass line 20 is closed and the hydraulic motor 5
The closing pressure is generated in the main pipe line 3 on the discharge side of the vehicle, and the vehicle is decelerated.

As described above, in the device of this embodiment, the bypass line 20 opens and closes according to the pressure change in the main lines 3 and 4 due to the operation of the accelerator pedal, so that the discharge pressure of the charge pump 6 changes according to the change. Compared with the conventional example in which the bypass pipeline 20 is opened and closed, the followability of the opening and closing operation of the bypass pipeline 20 with respect to changes in the discharge amount of the hydraulic pump 2 is improved, and smooth inertial traveling is realized.

Further, in the present embodiment, when increasing the flow rate of the bypass conduit 20, it is sufficient to increase only the flow rate of the parent valve section 110, and the pilot pressure control section 120 merely guides the pressure, so it is necessary to increase it. Absent. Therefore, it is possible to increase the flow rate of the bypass conduit 20 and perform full-scale inertial traveling while preventing the device from increasing in size.
Incidentally, in the conventional example in which the electromagnetic switching valve is switched to open / close the bypass pipe, the entire electromagnetic switching valve needs to be enlarged to cope with an increase in the flow rate, so that the device becomes considerably large. Moreover, when the electromagnetic switching valve is enlarged, the force for switching the electromagnetic switching valve also increases, and a large switching shock is inevitable. However, in the case of the embodiment, the pressures Pa and Pb in the main pipelines 3 and 4 are irrespective of the flow rate. Difference between the pilot pressure Pc and the pilot pressure Pc
There is almost no switching shock because it only moves. Directional control valve 1 included in pilot pressure control unit 120
Since 21 is also small, switching shock is small.

In this embodiment, the high pressure selection valve 122 is arranged on the downstream side of the directional control valve 121, but the present invention is not limited to this. For example, as shown in FIG. You may use the pilot pressure control part 130 arrange | positioned upstream of the control valve 131. In this case, the directional control valve 131 is switched to the F position at the time of forward movement to guide the pressure Pa of the main pipe line 3 to the pilot pressure Pc of the parent valve section 110, and the directional control valve 131 is switched to the R position at the time of reverse movement to switch the high pressure selection valve. The higher one of the pressures Pa, Pb of the main pipelines 3, 4 selected at 122 is introduced as the pilot pressure Pc.

-Second Embodiment- Next, a second embodiment of the present invention will be described with reference to FIGS. The same components as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 4, the greatest difference between the HST hydraulic traveling drive system of this embodiment and that of the first embodiment is that the directional control valve 141 of the pilot pressure control unit 140 of the logic valve 102 is of the three-value type. It is in use.

When the directional control valve 141 is in the F position, FIG.
As shown in (A), only the pressure Pa of the main pipeline 3 is guided to the high pressure selection valve 122 and selected as the pilot pressure Pc,
At the R position, as shown in FIG. 2B, only the pressure Pb in the main conduit 4 is guided to the high pressure selection valve 122 and selected as the pilot pressure Pc. When the directional control valve 141 is in the neutral position, the pressures Pa and Pb in the main pipelines 3 and 4 are high pressure selection valves 122.
Whichever is higher is selected as the pilot pressure Pc.

The directional control valve 141 includes a manual mode selection switch 32 and a forward / reverse switching switch 33 provided in the driver's seat.
Is controlled by switching. When the mode selection switch 32 is turned on and the F side of the reverse switching valve 33 is turned on, the solenoid portion 141a is excited and switched to the F position,
When the R side of the forward / reverse selector switch 33 is turned on, the solenoid portion 141b is excited and switched to the R position. When the mode selection switch 32 is turned off, the solenoids 141a and 141b are deenergized and held in the neutral position. The forward / reverse changeover switch 33 controls the forward / reverse changeover valve 8 so that the forward / reverse changeover valve 8 is switched to the F position when the F side is turned on and to the R position when the R side is turned on.

In this embodiment, when the F side of the forward / rearward travel changeover switch 33 is turned on and the mode selection switch 32 is turned on, the directional control valve 141 is in the F position.
As shown in (A), since the pressure Pa of the main pipeline 3 is selected as the pilot pressure Pc, the directional control valve 1 in the first embodiment is selected.
Similarly to the case where 21 is switched to the F position, when the accelerator pedal is stepped on, the bypass pipe line 20 follows the formula (1).
Is closed and the hydraulic motor 5 is driven by the hydraulic pump 2,
When the accelerator pedal is released, the bypass line 20 is opened according to the equation (2), and the vehicle inertially travels.

On the other hand, when the R side of the forward / reverse selector switch 33 is turned on, the mode selection switch 32 is turned on, and the directional control valve 141 is switched to the R position, as shown in FIG. As shown, the pressure Pb in the main pipeline 4 is selected as the pilot pressure Pc. In this state, when the accelerator pedal is depressed and the pressure Pb in the main pipeline 4 becomes higher than the pressure Pa in the main pipeline 3, the bypass pipeline 20 is closed according to the equation (3), and the discharge oil of the hydraulic pump 2 is discharged. The hydraulic motor 5 is driven. When the accelerator pedal is loosened and the pressure Pa in the main pipeline 3 exceeds the pressure Pb in the main pipeline 4, the relationship of equation (3) is no longer established, and Aa · Pb + Fs <Aa · Pa (4) At some times, the poppet 111 moves to open the bypass line 20 and the vehicle inertially travels.

When the mode selection switch 32 is turned off and the directional control valve 141 is switched to the neutral position, as in the case of switching the directional control valve 121 to the R position in the first embodiment, the main pipe lines 3 and 4 are connected. Since the higher of the pressures Pa and Pb is selected as the pilot pressure Pc, the bypass line 20 is closed regardless of the operation of the accelerator pedal. When the mode selection switch 32 is turned off, the bypass conduit 20 is closed regardless of the switching state of the forward / reverse traveling changeover switch 33, so that HST traveling can be performed in either forward or reverse traveling.

As described above, also in this embodiment, since the poppet 111 is moved and the bypass conduit 20 is opened and closed according to the pressure change in the main conduits 3 and 4 due to the operation of the accelerator pedal, the smooth operation is smooth as in the first embodiment. Inertial traveling can be realized, the flow rate of the inertial traveling circuit can be increased while preventing the apparatus from becoming large, and switching shock can be prevented. In addition, in the present embodiment, the combination of the three-position type directional control valve 141 and the selection switch 32 makes it possible to select inertia traveling during reverse traveling and HST traveling during forward traveling, which has the advantage of expanding the selection range of traveling modes.

In this embodiment, H
Although ST traveling can be selected, the neutral position of the directional control valve 141 may be omitted when only inertia traveling is sufficient for forward and backward traveling. In this case, the high pressure selection valve 122 is also unnecessary. When inertial traveling or HST traveling can be selected in either forward or reverse direction, it is not always necessary to use the ternary control valve 141. A modification thereof is shown in FIG.

The pilot pressure control unit 150 of the logic valve 103 shown in FIG. 5 is a two-value type directional control valve 151,15.
2 and the high pressure selection valve 122 are combined to enable selection between inertial traveling and HST traveling by moving forward and backward as in the second embodiment.
When the second directional control valve 152 is switched to the I position, when the first directional control valve 151 is at the F position, the pressure P of the main pipeline 3 is
When a is in the R position, the pressure Pb in the main pipeline 4 is guided from the pilot pipeline 153 to the parent valve section 110 via the second directional control valve 152. Therefore, by switching the first directional control valve 151 to the F position when the vehicle moves forward and to the R position when moving the vehicle backward, it is possible to open and close the bypass conduit 20 in accordance with the operation of the accelerator pedal for inertial traveling.
When the second directional control valve 152 is switched to the H position, the pressure selected by the high pressure selection valve 122 is guided to the parent valve portion 110, so the first directional control valve 151 is switched to the F position to select the high pressure. By guiding the pressures Pa and Pb of the main pipelines 3 and 4 to the valve 122, the higher pressure is selected as the pilot pressure Pc, and the bypass pipeline 20 is always closed regardless of the traveling direction of the vehicle.

As is clear from the above example, when the logic valve is used, the pressure of either one of the main pipes Pa and Pb of the main pipes 3 and 4 on the suction side of the hydraulic motor 5 is set to the pilot pressure Pc. If it is selected to, the bypass conduit 20 will be opened by loosening the accelerator pedal, and the main conduit 3,
If the higher one of the pressures Pa and Pb of 4 is always selected as the pilot pressure Pc, the bypass line 20 will be closed. As long as the pilot pressure can be selected in this way, the specific configuration of the pilot pressure control unit is Various changes may be made.

[0032]

As described above, in the HST hydraulic traveling drive system of the present invention, the bypass pipe opens and closes according to the pressure change in the main pipe due to the operation of the accelerator pedal, so that the discharge amount of the hydraulic pump can be changed. The followability of the opening / closing operation is improved, and smooth inertial running is realized. Moreover, since it is possible to cope with an increase in the flow rate of the inertial traveling circuit by enlarging only the parent valve portion, it is possible to realize full-scale inertial traveling with a large flow rate while preventing the apparatus from becoming large. Since the parent valve portion opens and closes due to the difference between the pilot pressure and the main pipeline pressure, a large switching shock does not occur with the opening and closing of the bypass pipeline.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an HST hydraulic traveling drive system according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of a parent valve portion of a logic valve.

FIG. 3 is a diagram showing a modification of the first embodiment of the present invention.

FIG. 4 is a diagram showing a circuit configuration of an HST hydraulic traveling drive system according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a modification of the second embodiment of the present invention.

[Explanation of symbols]

 1 prime mover 2 variable displacement hydraulic pump 3,4 main pipeline 5 hydraulic motor 20 bypass pipeline 100, 101, 102, 103 logic valve 110 parent valve section 120, 130, 140, 150 pilot pressure control section

Claims (1)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, and a hydraulic motor which is closed circuit connected to the variable displacement hydraulic pump by a pair of main pipes and is driven by oil discharged from the variable displacement hydraulic pump. In a HST hydraulic traveling drive device including: a parent valve unit that opens and closes a bypass pipeline connecting the pair of main pipelines based on the difference between the pressure of the main pipeline and the pilot pressure. An HST hydraulic traveling drive device comprising a logic valve including: a pilot pressure control unit that selects a pressure of one of the pair of main pipelines as a pilot pressure of the parent valve unit.