JP2002213402A - Pressure-reducing valve and torque controller for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep functions of a change pump by preventing lowering of the flow of the pressure oil discharged from the charge pump, even if the output pressure of a pressure reducing valve is lowered when a rotating speed of an engine exceeds a fixed value. SOLUTION: When the delivery of the charge pump exceeds a fixed value, the front and back pressure difference, Pin-PR, of a restrictor 16 exceeds a fixed value, and the pressure-reducing valve 2 is switched from a position 2b to a position 2c. When the pressure-reducing valve 2 is located on the position 2c, an oil passage 15a at an input side of the pressure-reducing valve 2 is closed. By closing the input side oil passage 15a, an output pressure Pc of the pressure- reducing valve 2 is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a torque control device for a pressure reducing valve or an engine. More specifically, the present invention relates to a pressure reducing valve capable of limiting the output pressure of the pressure reducing valve so as not to exceed a fixed value, or a torque control device for limiting the engine torque by limiting the output pressure by the pressure reducing valve.

[0002]

2. Description of the Related Art HST circuits are incorporated in vehicles such as bulldozers. Here, the HST (Hydro Static Transmission) circuit is a hydraulic circuit that forms a closed circuit with a hydraulic pump driven by an engine and a hydraulic motor driven by hydraulic oil discharged from the hydraulic pump. is there.

[0003] In the HST circuit, the discharge flow rate per rotation of the hydraulic pump, that is, the capacity of the hydraulic pump is controlled in accordance with the number of rotations of the engine.

That is, when the engine speed increases,
Control is performed to increase the capacity of the hydraulic pump in accordance with the increase in the engine speed. By performing this control, an absorption horsepower corresponding to the output horsepower of the engine is obtained by the hydraulic pump.

FIG. 3 shows a hydraulic circuit of a conventional control device. FIG. 3 shows the invention described in JP-A-10-122363.

The charge pump 1 shown in FIG. 3 is driven by an engine.

The pressure oil discharged from the charge pump 1 is output to a pump discharge oil passage 15. The discharge pressure of the charge pump 1 is defined as a charge pressure. A throttle 16 is provided on the pump discharge oil passage 15. The pressure of the pressure oil on the inlet side of the throttle 16, that is, the charge pressure, is Pin, and the pressure of the pressure oil on the outlet side of the throttle 16 is PR. Pump discharge oil passage 15 is oil passage 1
It branches to 5a and 15b. Oil passage 15a is provided with a pressure reducing valve 2 '.
Connected to the entrance. The oil passage 15b is connected to the inlet of the relief valve 13. The outlet of relief valve 13 is tank 1
It communicates with 4.

The pressure reducing valve 2 'has two positions, a position 2a and a position 2b, and changes continuously between these two positions. The outlet of the pressure reducing valve 2 ′ is connected to the oil passage 21. The capacity of the hydraulic pump of the HST circuit is controlled according to the pressure Pc of the pressure oil output to the oil passage 21. That is, as the output pressure Pc of the oil passage 21 increases, the capacity of the hydraulic pump of the HST circuit increases.

The oil passage 21 branches into an oil passage 21b. A control valve 50 is provided on the oil passage 21b. Control valve 5
The outlet of “0” communicates with the tank 14.

The control valve 50 has two positions 50a and 50b.
Have a position. When the control valve 50 moves to the position 50a side, the pressure oil in the oil passage 21 is discharged to the tank 14 and the output pressure P
c (pressure downstream of the orifice) decreases. On the other hand, when the control valve 50 moves to the position 50b side, the pressure oil in the oil passage 21 is not discharged to the tank 14, and the output pressure Pc does not decrease.

The oil passage 15 branches into a pilot oil passage 17. The pilot oil passage 17 is connected to one pressure receiving surface 2e of the pressure reducing valve 2 '. That is, the pressure Pin of the pressure oil on the inlet side of the throttle 16 is applied to the pressure receiving surface 2e of the pressure reducing valve 2 'as the pilot pressure P'in. A spring S3 is provided on the same side of the pressure reducing valve 2 'as the pressure receiving surface 2e. Let K3 be the spring force of the spring S3.

The oil passage 15 b branches to a pilot oil passage 18. The pilot oil passage 18 is connected to the other pressure receiving surface 2d of the pressure reducing valve 2 '. That is, the pressure receiving surface 2d of the pressure reducing valve 2 '
The pressure PR of the pressure oil on the outlet side of the throttle 16 is applied as the pilot pressure P'R. A spring S2 is provided on the same side of the pressure reducing valve 2 'as the pressure receiving surface 2d. Let K2 be the spring force of the spring S2. The spring S2 is connected to the inching lever 20. The inching lever 20 is a lever operated by an external signal or a human operation, and is provided to change the output pressure Pc of the pressure reducing valve 2 '.

The oil passage 21 branches into a pilot oil passage 19. The pilot oil passage 19 is connected to the pressure receiving surface 2d of the pressure reducing valve 2 '. That is, the output pressure Pc of the pressure reducing valve 2 'is applied to the pressure receiving surface 2d of the pressure reducing valve 2' as the pilot pressure P'c.

Therefore, the pressure reducing valve 2 ′ is connected to the differential pressure P across the throttle 16.
in-PR and spring force K2-K3 change to balance,
Both are positioned at a position where they are balanced.

When the pressure reducing valve 2 'is located at the position 2a, the oil passage 2
1 communicates with the tank 14 and the oil passage 15a is shut off. Therefore, the output pressure Pc of the pressure reducing valve 2 'decreases. When the pressure reducing valve 2 'is located at the position 2b, the oil passage 21
5a and the communication between the oil pressure 21 and the tank 14 is cut off. Therefore, the output pressure Pc of the pressure reducing valve 2 'increases. When the pressure reducing valve 2 'is at a position intermediate between the position 2a and the position 2b, the oil passage 21 communicates with the tank 14 and communicates with the oil passage 15a. Let PT be the pressure in the tank 14.

The operation of the hydraulic circuit shown in FIG. 3 will be described below.

When the engine is driven, pressure oil having a flow rate corresponding to the engine speed is output from the charge pump 1 and passes through the throttle 16. Therefore, the differential pressure Pin-P across the throttle 16
R increases as the engine speed N increases.

The pressure reducing valve 2 'has a differential pressure Pin-P across the throttle 16.
R and the spring force K2-K3 change so as to be balanced, and are positioned at a position where both are balanced.

When the engine speed is low, the throttle 1
6, the pressure difference Pin-PR becomes smaller, and the pressure reducing valve 2 'moves toward the position 2a. Therefore, the oil passage 15a is shut off, and the oil passage 21 communicates with the tank 14. As a result, the output pressure Pc of the pressure reducing valve 2 'decreases. The output pressure Pc of the pressure reducing valve 2 ′ decreases at least to the tank pressure PT in the tank 14.
When the output pressure Pc of the pressure reducing valve 2 'decreases, the capacity of the hydraulic pump of the HST circuit decreases. This reduces the absorption torque of the hydraulic pump.

As described above, as the engine speed decreases, the absorption torque of the hydraulic pump can be reduced.

However, when the engine speed is idle, the output torque of the engine cannot be sufficiently absorbed by the hydraulic pump. Therefore, when the engine speed is in the idle state, the inching lever 20 is operated and the spring S
The second spring force K2 decreases. Therefore, the pressure reducing valve 2 ′ is set at the position 2
Move to b side. When the pressure reducing valve 2 'is located at the position 2b,
The oil passage 21 communicates with the oil passage 15a, and the throttle 16
The pressure oil at the outlet side of is input. As a result, the output pressure Pc of the pressure reducing valve 2 'increases. The output pressure Pc of the pressure reducing valve 2 ′ increases up to the pressure PR on the outlet side of the throttle 16. When the output pressure Pc of the pressure reducing valve 2 'increases, the capacity of the hydraulic pump of the HST circuit increases. This increases the absorption torque of the hydraulic pump.

As described above, when the engine speed is in the idle state, the output torque of the engine can be sufficiently absorbed by the hydraulic pump.

When the engine speed is high, the throttle 1
6, the pressure difference Pin-PR of the front and rear becomes large, and the pressure reducing valve 2 'moves to the position 2b side. Therefore, the oil passage 21 communicates with the oil passage 15a. As a result, the output pressure Pc of the pressure reducing valve 2 'increases. The output pressure Pc of the pressure reducing valve 2 'rises up to the pressure PR on the outlet side of the throttle 16 at the maximum. The maximum pressure PR on the outlet side of the throttle 16 is limited by the relief valve 13. Therefore, the output pressure Pc is output from the pressure reducing valve 2 'with the upper limit of the relief pressure of the relief valve 13 being substantially the upper limit.

When the output pressure Pc of the pressure reducing valve 2 'rises, H
The capacity of the hydraulic pump in the ST circuit increases. This increases the absorption torque of the hydraulic pump.

As described above, as the engine speed increases, the absorption torque of the hydraulic pump can be increased.

When the hydraulic circuit shown in FIG. 3 is mounted on a vehicle, the wheels or crawler tracks of the vehicle are rotated by the hydraulic motor of the HST circuit.

When the vehicle descends a hill, the vehicle exceeds the maximum speed and becomes overrun. That is, the load applied to the hydraulic motor of the HST circuit is reduced when the vehicle descends on a slope, and the hydraulic motor of the HST circuit receives a driving force from the load, and performs a pumping operation of discharging high-pressure oil by the driving force. On the other hand, the hydraulic pump of the HST circuit performs a motor function driven by sucking high-pressure oil. Thus, the vehicle is overrun above the maximum speed.

As a result, the engine speed N reaches the allowable maximum speed or more, and the output pressure Pc of the pressure reducing valve 2 ′ finally increases to the relief pressure of the relief valve 13.

As a result, the hydraulic motor, the hydraulic pump or the engine may exceed the designed rotational speed, and the equipment may be damaged.

Therefore, in the hydraulic circuit of FIG. 3, when the engine speed exceeds the allowable maximum speed and the hydraulic pump of the HST circuit performs a motor operation, the control valve 50 is moved to the position 50a.
Is switched to

When the control valve 50 moves to the position 50a,
The pressure oil in the oil passage 21 is discharged to the tank 14, and the output pressure Pc of the pressure reducing valve 2 'decreases. When the output pressure Pc of the pressure reducing valve 2 'decreases, the capacity of the hydraulic pump of the HST circuit decreases. Therefore, a hydraulic brake pressure is generated on the suction side of the hydraulic pump, thereby preventing the hydraulic motor from overrunning.

In this manner, it is possible to prevent the rotational speed of the hydraulic motor, the hydraulic pump or the engine from exceeding the design allowable speed.

[0033]

However, in the hydraulic circuit shown in FIG. 3, when the vehicle is overrun, the control valve 50 is moved to the position 5.
0a, a part of the pressure oil discharged from the charge pump 1 is transferred to the tank 14 via the control valve 50.
It is discharged to.

Therefore, when the vehicle is overrun, the flow rate of the pressure oil discharged from the charge pump 1 (hereinafter referred to as charge flow rate) decreases.

On the other hand, when the oil pressure in the oil passage of the HST circuit decreases and the flow rate becomes insufficient, the charge pump 1
It is provided for the purpose of replenishing pressure oil in the oil passage of the circuit to prevent cavitation.

Therefore, when the charge flow rate discharged from the charge pump 1 is reduced, a sufficient flow rate of pressure oil cannot be supplied to the oil passage of the HST circuit, and cavitation cannot be effectively prevented.

According to the present invention, even if the output pressure of the pressure reducing valve is reduced when the engine speed exceeds a certain value, the flow rate of the pressure oil discharged from the charge pump 1 is not reduced, so that the charge pump 1 It is an object of the present invention to maintain the cavitation preventing function and to realize the cavitation preventing function with a simple configuration.

[0038]

According to a first aspect of the present invention, a pressure oil discharged from a charge pump (1) is input via an input-side oil passage (15a), and the charge pump (1) is provided. In the pressure reducing valve (2) that outputs the pressure oil through the output side oil passage (21) so that the output pressure increases in accordance with the increase in the discharge flow rate in 1), the discharge flow rate of the charge pump (1) is constant. If the value exceeds the value, the input side oil passage (15
valve position (2c) for shutting down a) and reducing the output pressure
Is provided in the pressure reducing valve (2).

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

According to the first invention, when the discharge flow rate of the charge pump 1 exceeds a certain value, the differential pressure Pin-P
When R exceeds a certain value, the pressure reducing valve 2 is switched from the position 2b to the position 2c. When the pressure reducing valve 2 is located at the position 2c, the oil passage 21 communicates with the tank 14 and the oil passage 15a on the input side of the pressure reducing valve 2 is shut off. The output pressure Pc of the pressure-reducing valve 2 is reduced by shutting off the input-side oil passage 15a.

As described above, according to the first aspect, the output pressure Pc of the pressure reducing valve 2 can be limited to a certain value or less.

On the other hand, when the pressure reducing valve 2 is located at the position 2c, the input side oil passage 15a is shut off, so that the pressure oil discharged from the charge pump 1 is supplied to the input side oil passage 15a,
It is not discharged to the tank 14 via the output side oil passage 21.

Therefore, even if the output pressure Pc of the pressure reducing valve 2 is limited to a predetermined value or less, the charge flow rate of the pressure oil discharged from the charge pump 1 does not decrease.

As described above, according to the first aspect of the present invention, even if the output pressure Pc of the pressure reducing valve 2 is reduced, the flow rate of the pressure oil discharged from the charge pump 1 does not decrease.
Cavitation prevention function can be maintained.

According to a second aspect, in the first aspect, the maximum pressure of the pressure oil output from the pressure reducing valve (2) is determined by a set relief pressure of the relief valve (13).

According to the second invention, the maximum pressure of the pressure oil output from the pressure reducing valve 2 is determined by the set relief of the relief valve 13.

According to a third aspect of the present invention, there is provided a hydraulic pump (5) driven by an engine (3) and the hydraulic pump (5).
A hydraulic motor (7) driven in accordance with pressure oil discharged from the engine, a rotation speed detecting means (16) for detecting a rotation speed of the engine (3), and a pressure oil discharged from the charge pump (1). A pressure reducing valve (2) for controlling a capacity of the hydraulic pump (5) in accordance with pressure oil input through an input-side oil passage (15a) and output through an output-side oil passage (21); The pressure reducing valve (2) outputs an output pressure for increasing the capacity of the hydraulic pump (5) in response to an increase in the engine speed detected by the speed detecting means (16). In the engine torque control device provided with the pressure reducing valve operating means (17, 18) for operating the engine (3), when the rotational speed of the engine (3) detected by the rotational speed detecting means (16) exceeds a certain value. The output pressure for lowering the capacity of the hydraulic pump (5) is As output from the serial pressure reducing valve (2), the valve position to cut off the input side oil path (15a) (2c), characterized in that provided in the pressure reducing valve (2).

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

According to the third aspect, when the rotation speed of the engine 3 exceeds a certain value, the discharge flow rate of the charge pump 1 driven by the engine 3 exceeds the certain value. Therefore, the pressure difference Pin-PR across the throttle 16 exceeds a certain value, and the pressure reducing valve 2 is switched from the position 2b to the position 2c. When the pressure reducing valve 2 is located at the position 2c, the input side oil passage 15a is shut off. The output pressure Pc of the pressure-reducing valve 2 is reduced by shutting off the input-side oil passage 15a. When the output pressure Pc of the pressure reducing valve 2 'decreases, the capacity of the hydraulic pump 5 of the HST circuit decreases. For this reason, the hydraulic brake torque of the HST circuit can be increased, and overrun of the hydraulic motor can be prevented. In this way, it is possible to eliminate problems such as damage to equipment caused when the hydraulic motor, the hydraulic pump, or the engine exceeds the design allowable rotation speed.

On the other hand, when the pressure reducing valve 2 is located at the position 2c, the input side oil passage 15a is shut off, so that the pressure oil discharged from the charge pump 1 is supplied to the input side oil passage 15a, as in the prior art.
It is not discharged to the tank 14 via the output side oil passage 21.

Therefore, the charge flow rate of the pressure oil discharged from the charge pump 1 during the overrun of the vehicle does not decrease.

Accordingly, a sufficient amount of pressure oil can be supplied from the charge pump 1 into the oil passages 6F and 6R of the HST circuit, and cavitation can be effectively prevented.

As described above, according to the third aspect, the engine 3
Output pressure Pc of the pressure reducing valve 2 when the number of revolutions of
Even if the capacity of the hydraulic pump 5 is reduced by lowering the pressure, the flow rate of the pressure oil discharged from the charge pump 1 does not decrease, so that the cavitation preventing function of the charge pump 1 can be maintained.

According to a fourth aspect of the present invention, there is provided a hydraulic pump (5) driven by an engine (3) and the hydraulic pump (5).
A hydraulic motor (7) driven in accordance with pressure oil discharged from the engine, a rotation speed detecting means (16) for detecting a rotation speed of the engine (3), and a pressure oil discharged from the charge pump (1). A pressure reducing valve (2) that controls the capacity of the hydraulic motor (7) in accordance with the pressure oil input through the input side oil passage (15a) and output through the output side oil passage (21); The pressure reducing valve (2) outputs an output pressure for decreasing the capacity of the hydraulic motor (7) in response to an increase in the engine speed detected by the speed detecting means (16). In the engine torque control device provided with the pressure reducing valve operating means (17, 18) for operating the engine (3), when the rotational speed of the engine (3) detected by the rotational speed detecting means (16) exceeds a certain value. The output pressure for increasing the capacity of the hydraulic motor (7) is As output from the serial pressure reducing valve (2), the valve position to cut off the input side oil path (15a) (2c), characterized in that provided in the pressure reducing valve (2).

The fourth invention is characterized in that control for increasing the capacity of the hydraulic motor 7 is performed instead of control for reducing the capacity of the hydraulic pump 5.

According to the fourth aspect, the same effect as the third aspect can be obtained.

[0057]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pressure reducing valve and an engine torque control device according to the present invention will be described below with reference to the drawings.

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

As shown in FIG. 1, the apparatus of this embodiment includes:
An HST circuit of a closed circuit configured by connecting the hydraulic pump 5 and the hydraulic motor 7 via oil paths 6F and 6R is provided.

In the present embodiment, it is assumed that the vehicle runs by rotating the wheels or crawler belts by the hydraulic motor 7.

The hydraulic pump 5 is a variable displacement hydraulic pump. The hydraulic pump 5 is a swing type hydraulic pump having two ports 5b and 5c and capable of reversing the flow of pressure oil.

The hydraulic pump 5 is connected to the engine 3 via the rotary shaft 4. When the engine 3 rotates, the rotating shaft 4 rotates and the hydraulic pump 5 rotates. Swash plate 5 of hydraulic pump 5
As the value a changes, the capacity (displacement volume) of the hydraulic pump 5 changes. The swash plate 5 a of the hydraulic pump 5 is connected to the piston 8. When the piston 8 operates, the capacity of the hydraulic pump 5 changes. The pump discharge pressure oil is output from the port 5b or the port 5c of the hydraulic pump 5. The ports 5b and 5c of the hydraulic pump 5 are connected to the ports 7b and 7c of the hydraulic motor 7 through oil passages 6F and 6R, respectively.
Connected to

The charge pump 1 is a fixed displacement hydraulic pump. The charge pump 1 is connected to an engine 3 via a rotating shaft 4. When the engine 3 rotates, the rotating shaft 4
Rotates, and the charge pump 1 rotates. The discharge port 1 a of the charge pump 1 is connected to a pump discharge oil passage 15. A throttle 16 is provided in the pump discharge oil passage 15. The pump discharge oil passage 15 branches into an oil passage 15a and an oil passage 15b. The relief valve 13 is connected to the oil passage 15b. The relief valve 13 limits the pressure PR in the oil passage 15b to the relief pressure or less.

When the charge pump 1 rotates, charge pressure oil having a pressure Pin (hereinafter referred to as charge pressure Pin) is output to the pump discharge oil passage 15.

The hydraulic motor 7 is a fixed displacement type hydraulic motor. The hydraulic motor 7 is a swing type hydraulic motor having two ports 7b and 7c and capable of reversing the flow of pressure oil. One port 7b of the hydraulic motor 7 is connected to an oil passage 6F.
Connected to The other port 7c of the hydraulic motor 7 is connected to the oil passage 6R.

The rotating shaft of the hydraulic motor 7 is connected to wheels or crawler tracks of the vehicle. When the hydraulic motor 7 rotates, the wheels or crawler belts rotate. Therefore, the speed of the vehicle changes.

The swash plate 5 a of the hydraulic pump 5 is connected to the piston 8. When the piston 8 operates, the capacity of the hydraulic pump 5 changes.

The operating lever device 9 is provided for operating the piston 8. The operating lever device 9 is a piston 1
0 and 11 and pressure reducing valves 12 and 13 respectively corresponding to the pistons 10 and 11 are mainly configured. The operation lever device 9 operates when an operation lever (not shown) is operated.

That is, when the operation lever is operated in the forward direction, the piston 10 is displaced downward, and when the operation lever is operated in the reverse direction, the piston 11 is displaced downward. When the pistons 10, 11 are displaced downward, the pressure reducing valve 12,
The output pressure of each of the thirteen increases.

Pressure oil having a pressure Pc (hereinafter, the output pressure of the pressure reducing valve 2 is referred to as Pc) is supplied from the pressure reducing valve 2 to the pressure reducing valves 12 and 13 of the operation lever device 9 via the oil passage 21. The pressure oil of the pressure Pc supplied from the oil passage 21 to the pressure reducing valves 12 and 13 is reduced by the pressure reducing valves 12 and 13 to a set pressure corresponding to the operation amount of the operation lever.

The outlet of the pressure reducing valve 12 communicates with one of the pressure receiving chambers 8 a of the piston 8 via an oil passage 22. The outlet of the pressure reducing valve 13 communicates with the other pressure receiving chamber 8 b of the piston 8 via the oil passage 23. Therefore, when the operation lever of the operation lever device 9 is operated to the forward side, pressure oil having a pressure corresponding to the operation amount is supplied to the forward side pressure receiving chamber 8 a of the piston 8 via the pressure reducing valve 12 and the oil passage 22. As a result, the piston 8 moves from the neutral position to the forward position. With the movement of the piston 8 to the forward position, the swash plate 5a of the hydraulic pump 5 tilts forward and the hydraulic oil is discharged from one port 5b of the hydraulic pump 5. Similarly, when the operation lever of the operation lever device 9 is operated in the reverse direction, pressure oil having a pressure corresponding to the operation amount is released from the pressure reducing valve 1.
3. The piston 8 is supplied to the reverse pressure receiving chamber 8b via the oil passage 23. Thereby, the piston 8 moves from the neutral position to the reverse position. With the movement of the piston 8 to the reverse position, the swash plate 5a of the hydraulic pump 5 tilts to the reverse side, and pressure oil is discharged from the other port 5c of the hydraulic pump 5.

Thus, the hydraulic pump 5 changes its capacity according to the operation amount of the operation lever of the operation lever device 9.

As described above, the operation lever device 9 operates when the output pressure Pc of the pressure reducing valve 2 is supplied. Therefore, as the supply pressure Pc to the operation lever device 9 increases, the capacity of the hydraulic pump 5 increases.

Next, the configuration of the pressure reducing valve 2 will be described.

The oil passage 15a is connected to the inlet of the pressure reducing valve 2.

The pressure reducing valve 2 is located at positions 2a, 2b and 2c.
There are three positions. Pressure reducing valve 2 is located at position 2a and position 2b
And the position 2b and the position 2c are selectively switched without a continuous change. The outlet of the pressure reducing valve 2 is connected to the oil passage 21. The output pressure Pc supplied to the operation lever device 9 changes in accordance with the pressure Pc of the pressure oil output from the pressure reducing valve 2 to the oil passage 21, and the capacity of the hydraulic pump 5 of the HST circuit is controlled. That is, the pressure reducing valve 2
When the output pressure Pc increases, the hydraulic pump 5 of the HST circuit
Of the swash plate 5a tilts toward the side where the capacity is increased.

The pump oil passage 15 is connected to the pilot oil passage 17
Has branched to. The pilot oil passage 17 is connected to one pressure receiving surface 2 e of the pressure reducing valve 2. That is, the charge pressure Pin of the charge pressure oil on the inlet side of the throttle 16 is applied to the pressure receiving surface 2e of the pressure reducing valve 2 as the pilot pressure P'in. Pressure reducing valve 2
A spring S2 is provided on the same side as the pressure receiving surface 2e.
Let K2 be the spring force of the spring S2. The spring S2 is connected to the inching lever 20. This inching lever 2
Reference numeral 0 denotes a lever that operates in conjunction with the accelerator pedal 12 of the engine 3, and is provided to change the output pressure Pc of the pressure reducing valve 2.

A spring S is provided on the same side of the pressure reducing valve 2 as the pressure receiving surface 2e.
3 has been granted. Let K3 be the spring force of the spring S3.

The oil passage 15 b branches to the pilot oil passage 18. The pilot oil passage 18 is connected to the other pressure receiving surface 2 d of the pressure reducing valve 2. That is, the pressure PR of the pressure oil on the outlet side of the throttle 16 is applied to the pressure receiving surface 2d of the pressure reducing valve 2 by the pilot pressure P'R.
Added as A spring S1 is provided on the same side of the pressure reducing valve 2 as the pressure receiving surface 2d. Let K1 be the spring force of the spring S1.

The oil passage 21 branches to the pilot oil passage 19. The pilot oil passage 19 is connected to a pressure receiving surface 2 d of the pressure reducing valve 2. That is, the pressure reducing valve 2 is provided on the pressure receiving surface 2d of the pressure reducing valve 2.
Is applied as a pilot pressure P'c.

Therefore, the pressure reducing valve 2 is provided with a differential pressure Pin across the throttle 16.
-PR and the spring force K1-K2-K3 change so as to be balanced, and are positioned at a position where both are balanced.

When the pressure reducing valve 2 is located at the position 2a, the oil passage 21
Communicates with the tank 14 and the oil passage 15a is shut off. Therefore, the output pressure Pc of the pressure reducing valve 2 decreases. When the pressure reducing valve 2 is located at the position 2b, the oil passage 21 communicates with the oil passage 15a and the communication between the oil passage 21 and the tank 14 is cut off. Therefore, the output pressure Pc of the pressure reducing valve 2 increases. When the pressure reducing valve 2 is at a position intermediate between the position 2a and the position 2b, the oil passage 21 communicates with the tank 14 and communicates with the oil passage 15a. Let PT be the pressure in the tank 14.

When the pressure reducing valve 2 is located at the position 2c, the oil passage 21 communicates with the tank 14 and the oil passage 15a is shut off. Therefore, the output pressure Pc of the pressure reducing valve 2 decreases.

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

When the engine 3 is driven, pressure oil having a flow rate corresponding to the rotation speed N of the engine 3 is output from the charge pump 1 and passes through the throttle 16. For this reason, the differential pressure Pin-PR of the throttle 16 increases as the rotational speed N of the engine 3 increases.

The pressure reducing valve 2 is provided with a differential pressure Pin-PR across the throttle 16.
And the spring forces K 1 -K 2 -K 3 change so as to be balanced, and are positioned at a position where both are balanced.

When the rotational speed N of the engine 3 is small, the differential pressure Pin-PR of the throttle 16 becomes small, and the pressure reducing valve 2 moves to the position 2a. Therefore, the oil passage 15a is shut off, and the oil passage 21 communicates with the tank 14. As a result, the output pressure Pc of the pressure reducing valve 2 decreases. Output pressure Pc of pressure reducing valve 2
Decreases to the tank pressure PT in the tank 14 at least. When the output pressure Pc of the pressure reducing valve 2 decreases, the supply pressure Pc to the operation lever device 9 decreases. Therefore, the capacity of the hydraulic pump 5 of the HST circuit is reduced. Thereby, the absorption torque of the hydraulic pump 5 decreases.

As described above, when the rotation speed N of the engine 3 decreases, the absorption torque of the hydraulic pump 5 can be reduced.

However, when the rotation speed N of the engine 3 is in an idle state, the output torque of the engine 3 cannot be sufficiently absorbed by the hydraulic pump 5. Then, when the accelerator pedal 12 of the engine 3 is positioned at the idle state, the inching lever 20 operates and the spring force K2 of the spring S2 increases. When the spring force K2 of the spring S2 increases, the pressure reducing valve 2 moves to the position 2b. For this reason, the oil passage 21 communicates with the oil passage 15 a and the pressure oil on the outlet side of the throttle 16 is input to the pressure reducing valve 2.
As a result, the output pressure Pc of the pressure reducing valve 2 increases. The output pressure Pc of the pressure reducing valve 2 increases up to the pressure PR on the outlet side of the throttle 16 at the maximum. When the output pressure Pc of the pressure reducing valve 2 increases, the supply pressure Pc to the operation lever device 9 increases. Therefore HST
The capacity of the hydraulic pump 5 in the circuit increases. Thereby, the absorption torque of the hydraulic pump 5 increases.

As described above, when the rotation speed N of the engine 3 is in the idle state, the absorption torque of the hydraulic pump 5 can be increased to a level that can sufficiently absorb the output torque of the engine 3.

When the rotational speed N of the engine 3 is high, the differential pressure Pin-PR of the throttle 16 becomes large, and the pressure reducing valve 2 moves to the position 2b. Therefore, the oil passage 21 is connected to the oil passage 15a.
Communicate with As a result, the output pressure Pc of the pressure reducing valve 2 increases. The output pressure Pc of the pressure reducing valve 2 increases up to the pressure PR on the outlet side of the throttle 16 at the maximum. The maximum pressure PR on the outlet side of the throttle 16 is limited by the relief valve 13. Therefore, the pressure reducing valve 2 outputs an output pressure Pc having the relief pressure of the relief valve 13 as an upper limit.

When the output pressure Pc of the pressure reducing valve 2 increases, the supply pressure Pc to the operation lever device 9 increases. For this reason HS
The capacity of the hydraulic pump 5 of the T circuit increases. Thereby, the absorption torque of the hydraulic pump 5 increases.

As described above, when the rotation speed N of the engine 3 increases, the absorption torque of the hydraulic pump 5 can be increased.

When the vehicle descends the hill, the vehicle goes over the maximum speed and becomes overrun. That is, the load applied to the hydraulic motor 7 of the HST circuit is reduced when the vehicle descends on a slope, and the hydraulic motor 7 of the HST circuit receives a driving force from the load in reverse, and performs a pump action of discharging high-pressure hydraulic oil by the driving force. On the other hand, the hydraulic pump 5 of the HST circuit performs a motor function driven by sucking high pressure oil. Thus, the vehicle is overrun above the maximum speed.

Therefore, the number of revolutions N of the engine 3 increases to the maximum permissible number of revolutions or more, and the output pressure Pc of the pressure reducing valve 2 finally increases to the relief pressure of the relief valve 13.

Therefore, the hydraulic motor 7 or the hydraulic pump 5
Or, if the engine speed exceeds the design allowable speed,
There is a possibility that a malfunction that the equipment is damaged may occur.

Therefore, in the hydraulic circuit shown in FIG. 1, when the rotational speed N of the engine 3 exceeds a certain rotational speed, a control to reduce the capacity of the hydraulic pump 5 is performed.

That is, when the rotation speed N of the engine 3 exceeds a certain rotation speed, the pressure difference Pin-PR across the throttle 16 exceeds a certain value, so that the pressure reducing valve 2 is switched to the position 2c. Therefore, the oil passage 15a is shut off and the oil passage 21 communicates with the tank 14. As a result, the output pressure Pc of the pressure reducing valve 2 decreases. The output pressure Pc of the pressure reducing valve 2 decreases to the tank pressure PT in the tank 14. When the output pressure Pc of the pressure reducing valve 2 decreases, the supply pressure Pc to the operation lever device 9 decreases. For this reason, the capacity of the hydraulic pump 5 of the HST circuit decreases. Accordingly, the hydraulic brake pressure increases, so that overrun can be prevented.

FIG. 2 shows the relationship between the engine speed N and the output pressure Pc of the pressure reducing valve 2. The engine speed N and the output pressure Pc change according to the characteristic L shown in FIG.

When the pressure reducing valve 2 is switched to the position 2c, the increase in the rotation speed N of the engine 3 is suppressed and the output pressure Pc is reduced. The input torque from the hydraulic pump 5 is balanced.

As described above, according to the embodiment, the hydraulic motor 7, the hydraulic pump 5, the engine 3
Can be controlled to be equal to or less than the design allowable rotational speed.

On the other hand, when the pressure reducing valve 2 is located at the position 2c, the oil passage 15a on the input side of the pressure reducing valve 2 is shut off, so that the pressure oil discharged from the charge pump 1 is supplied to the oil passage 15a on the input side as in the prior art. Is not discharged to the tank 14 via the oil passage 21 on the output side of the pressure reducing valve 2.

Therefore, the charge flow rate of the charge pressure oil discharged from the charge pump 1 during the overrun of the vehicle does not decrease.

Therefore, a sufficient amount of pressure oil can be supplied from the charge pump 1 into the oil passages 6F and 6R of the HST circuit, and cavitation can be effectively prevented.

As described above, according to the present embodiment, even if the output pressure Pc of the pressure reducing valve 2 is reduced to reduce the capacity of the hydraulic pump 5 when the rotational speed N of the engine 3 exceeds a certain value, the charge pump Since the charge flow rate of the charge pressure oil discharged from the fuel pump 1 does not decrease, the function of preventing cavitation by the charge pump 1 can be maintained.

In the present embodiment, the hydraulic brake torque is applied to the HST circuit by reducing the capacity of the hydraulic pump 5 when the vehicle is overrun, thereby preventing the overrun.

However, the hydraulic motor 7 may be a variable displacement type hydraulic motor, and the hydraulic brake torque of the HST circuit may be increased by increasing the capacity of the hydraulic motor 7.
That is, by increasing the capacity of the hydraulic motor 7, the capacity of the hydraulic pump 5 is apparently reduced. Therefore, a hydraulic brake pressure is generated on the suction side of the hydraulic pump, and it is possible to prevent the hydraulic motor from overrunning.

In FIG. 2, the inching lever 20 is used.
, The characteristic L can be changed as shown by the arrow F and changed to the characteristic indicated by the dashed line.

The above embodiment has been described on the assumption that the hydraulic circuit of FIG. 1 is mounted on the vehicle. However, the present invention is not limited to controlling the speed of the vehicle. That is, the rotating body connected to the rotating shaft of the hydraulic motor 7 is not limited to wheels or crawler tracks.

Further, the embodiment has been described on the assumption that the torque of the engine 3 is controlled by the pressure reducing valve. However, the present invention is not limited to controlling the torque of the engine 3. That is, the object controlled by the output pressure Pc of the pressure reducing valve 2 is arbitrary.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of an embodiment.

FIG. 2 is a diagram showing a relationship between an engine speed and an output pressure.

FIG. 3 is a hydraulic circuit diagram using a conventional pressure reducing valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charge pump 2 Pressure reducing valve 3 Engine 5 Hydraulic pump 7 Hydraulic motor 15a Input side oil passage 16 Throttle 21 Output side oil passage

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F15B 11/04 HBF Term (Reference) 2D003 AB05 AB06 BB01 CA06 DA03 DB03 3H089 AA45 BB11 CC08 DA02 DA03 DA13 DB05 GG02 JJ01 3J053 AA02 AB01 AB46

Claims (4)

[Claims] 1. A pressure oil discharged from a charge pump (1) is input via an input-side oil passage (15a), and an output pressure increases in accordance with an increase in a discharge flow rate of the charge pump (1). A pressure reducing valve (2) that outputs pressure oil via an output-side oil passage (21). When the discharge flow rate of the charge pump (1) exceeds a certain value, the input-side oil passage (15a) A pressure reducing valve, wherein a valve position (2c) for shutting off and reducing the output pressure is provided in the pressure reducing valve (2). 2. The pressure reducing valve according to claim 1, wherein the maximum pressure of the pressure oil output from the pressure reducing valve is determined by a relief pressure set by a relief valve. 3. A hydraulic pump (5) driven by an engine (3), a hydraulic motor (7) driven according to pressure oil discharged from the hydraulic pump (5), and a hydraulic pump (5). Rotation speed detecting means for detecting the rotation speed (16)
And hydraulic oil discharged from the charge pump (1) through the input-side oil passage (15a) and the hydraulic pump (5) according to the pressure oil output through the output-side oil passage (21). ), And an output pressure that increases the capacity of the hydraulic pump (5) in response to an increase in the engine speed detected by the engine speed detection means (16). (2) a torque control device for an engine, comprising: a pressure reducing valve operating means (17, 18) for operating the pressure reducing valve (2) so as to be output from the engine (2). When the rotation speed of the engine (3) exceeds a certain value, the output pressure for lowering the capacity of the hydraulic pump (5) is increased by the pressure reducing valve (2).
A torque control device for an engine, wherein a valve position (2c) for shutting off the input side oil passage (15a) is provided in the pressure reducing valve (2) so as to be output from the engine. 4. A hydraulic pump (5) driven by an engine (3), a hydraulic motor (7) driven in accordance with pressure oil discharged from the hydraulic pump (5), and an engine (3). Rotation speed detecting means for detecting the rotation speed (16)
And the hydraulic motor (7) according to the pressure oil discharged from the charge pump (1) via the input side oil passage (15a) and the output from the output side oil passage (21). A pressure reducing valve for controlling the displacement of the hydraulic motor, and an output pressure for decreasing the displacement of the hydraulic motor in response to an increase in the engine speed detected by the speed detecting means. In a torque control device for an engine, comprising: a pressure reducing valve operating means (17, 18) for operating the pressure reducing valve (2) so as to be output from (2). When the number of revolutions of the engine (3) exceeds a certain value, the output pressure for increasing the capacity of the hydraulic motor (7) is increased by the pressure reducing valve (2).
An engine torque control device characterized in that a valve position (2c) for shutting off the input side oil passage (15a) is provided in the pressure reducing valve (2) so as to be output from the engine.