JP2001193701A - Hydraulic control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic control device capable of suppressing energy loss when all of selector valves are at a neutral position. SOLUTION: In a supply flow passage 3, closed center type selector valves A-C, a first flow rate control valve 27 for supplying a constant flow rate to a power steering mechanism PS, and a second flow rate control valve 9 for controlling supply pressure of oil depending on load pressure of an actuator are connected in parallel with each other. Pressure on the upstream side of an orifice 31 is led to one pilot chamber 27a of the first flow rate control valve 27, and load pressure of the power steering mechanism PS is led to the other pilot chamber 27b. On the other hand, the second flow rate control valve 9 leads the supply pressure to one pilot chamber 9a, and leads the load pressure of the power steering mechanism PS to the other pilot chamber 9b. Control pressure ΔP2 of the second flow rate control valve 9 is larger than control pressure ΔP1 of the first flow rate control valve 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for supplying a constant control flow rate to a power steering mechanism side preferentially among flow rates discharged from a pump and supplying an excess flow rate to another actuator side. .

[0002]

2. Description of the Related Art The prior art shown in FIG. 2 is a hydraulic control device used for a forklift equipped with a power steering mechanism PS. A first flow control valve 1 of a bypass type is connected to the pump P. The first flow control valve 1 is connected to a priority flow path 2 and a supply flow path 3, and discharges oil from the pump P to the priority flow path 2 and the supply flow path 3 in accordance with the switching position. I try to sort them. A power steering mechanism PS is connected to the priority flow path 2 and an orifice 7 is provided upstream of the power steering mechanism PS. Then, the pressure on the upstream side of the orifice 7 is guided to one pilot chamber 1a of the first flow control valve 1, and the pressure on the downstream side of the orifice 7 is guided to the other pilot chamber 1b provided with the spring 8. ing.

[0003] The first flow control valve 1 controls the flow to be distributed to the power steering mechanism PS so that the differential pressure across the orifice 7 corresponds to the spring force of the spring 8. In other words, the differential pressure across the orifice 7 is maintained at Δp 1 by the first flow control valve 1 so that a constant control flow is always supplied to the power steering mechanism PS.

An excess flow rate equal to or higher than the control flow rate distributed by the first flow control valve 1 is guided to the supply flow path 3, which is connected to the closed center via parallel flow paths 4 to 6. Type switching valves A to C are connected. And, by these switching valves A to C, a lift cylinder,
The tilt cylinder and the attachment cylinder are individually controlled.

A second flow control valve 9 is connected upstream of the switching valves A to C. This second flow control valve 9
Are connected in series to the first flow control valve 1.
Then, one pilot chamber 9 of the second flow control valve 9
The supply flow path 3 is connected to a, and the load pressure line 11 is connected to the other pilot chamber 9 b provided with the spring 10. The load pressure line 11 includes load pressure lines 15 to 17 connected to the switching valves A to C and shuttle valves 12 to 14.
Accordingly, the highest load pressure of the actuator selected to be high pressure is guided to the other pilot chamber 9b of the second flow control valve 9.

Although the second flow control valve 9 as described above is closed in the normal state shown in the figure, the supply pressure guided from the supply flow path 3 is made smaller by the spring force of the spring 10 than the maximum load pressure of the actuator. The opening is controlled so as to increase by the corresponding pressure Δp2. By keeping the supply pressure higher than the maximum load pressure by Δp2, the operation speed of the actuator is stabilized. Note that the pressure Δp2 is the control pressure of the second flow control valve 9.

Further, a branch flow path 18 is connected to the supply flow path 3 upstream of the second flow control valve 9, and a flow control valve 19 is provided in the branch flow path 18. A fixed throttle 20 is provided on the downstream side of the flow control valve 19, the pressure on the upstream side is guided to one pilot chamber 19 a of the flow control valve 19, and the pressure on the downstream side is supplied to the other pilot chamber provided with a spring 21. It leads to the room 19b. The opening of the flow control valve 19 is controlled so that the differential pressure across the fixed throttle 20 is maintained at a pressure Δpr corresponding to the spring force of the spring 21. Then, a constant flow rate is supplied to the branch channel 18. The flow control valve 1
The pressure Δpr generated by the second flow control valve 9
Of the flow control valve 1
Pressure oil is preferentially supplied to the 9th side.

A relief valve 22 is connected to the downstream side of the branch flow path 18 so that the pressure on the upstream side of the relief valve 22 is maintained at the set pressure. Then, a pressure obtained by adding the differential pressure across the fixed throttle 7 to the set pressure of the relief valve 22 is used as a pilot pressure from a pilot line 23 connected upstream of the fixed throttle 20 to each of the switching valves A to C.
To the pilot's room. Further, the pilot line 23 is connected to the load pressure line 11 via the shuttle valve 12. When the maximum load pressure of the actuator becomes lower than the pilot pressure, the pilot pressure is changed to the pilot chamber 9b of the second flow control valve 9.
To lead to.

Reference numeral 24 in the figure denotes a solenoid valve 24 for energy saving. This solenoid valve 24
Normally, the closed state is maintained by excitation. However, when the pilot pressure is not required, it is opened to return the pressure oil from the branch flow path 18 to the tank. If the pressure oil is returned to the tank T via the solenoid valve 24 as described above,
Since pressure loss does not occur in the relief valve 22, energy loss when pilot pressure is not required can be reduced. Reference numeral 25 is a main relief valve for determining the maximum pressure in the circuit, and reference numeral 26 is a relief valve for the power steering mechanism PS.

[0010] The conventional apparatus as described above employs a pump P
Is supplied to the power steering mechanism PS preferentially by the first flow control valve 1. By doing so, the operation of the power steering mechanism PS is stabilized. Then, by stabilizing the operation of the power steering mechanism PS, safety during running of the vehicle is maintained.

[0011] Further, since the excess flow path equal to or larger than the control flow rate supplied to the power steering mechanism PS is led to the switching valves A to C through the supply flow path 3, any of the switching valves A to C is provided.
When C is switched, the actuator connected to the switching valve operates. At this time, the maximum load pressure of the actuator is guided to the pilot chamber 9b of the second flow control valve 9 via the load pressure line 11, so that the supply pressure is maintained higher than the maximum load pressure of the actuator by Δp2. . By keeping the supply pressure higher than the load pressure in this way, the operation of the actuator is stabilized.

On the other hand, when all of the switching valves A to C are maintained at the neutral position, the excess flow rate distributed to the supply flow path 3 is transmitted through the second flow rate control valve 9 and the flow rate control valve 19. Will be returned to the tank. However, the above flow control valve 1
The flow rate passing through 9 is very small because it is only for generating the pilot pressure. Therefore, most of the surplus flow rate allocated to the supply flow path 3 is returned to the tank via the second flow rate control valve 9.

[0013]

In the above conventional example, the first
Since the flow control valve 1 and the second flow control valve 9 are connected in series, there is a problem that the pressure loss increases when all of the closed center type switching valves A to C are maintained at the neutral position. there were. The reason is as follows. That is, when the switching valves A to C are in the neutral position, most of the surplus flow allocated to the supply flow path 3 must be returned to the tank T via the second flow control valve 9. Also, regardless of whether the switching valves A to C are in the neutral position, a constant flow rate must always be supplied to the power steering mechanism PS.

At this time, the discharge pressure of the pump P is controlled by connecting the first flow control valve 1 and the second flow control valve 9 in series, so that at least the first and second flow control valves 1 and 9 are operated. Must be maintained at the sum of the pressures required to achieve this. That is, the pump discharge pressure becomes a pressure Δp1 + Δp2 obtained by adding the control pressure Δp1 of the first flow control valve 1 and the control pressure Δp2 of the second flow control valve. However, as described above, the fact that all the switching valves A to C are at the neutral position is a state where the actuator is not operated. Since the pump discharge pressure must be maintained at Δp1 + Δp2 even though the actuator is not operated, there is a problem that the energy loss increases accordingly. An object of the present invention is to provide a hydraulic control device capable of suppressing an energy loss when all the switching valves are set to a neutral position.

[0015]

According to a first aspect of the present invention, a closed center type switching valve for controlling an actuator and a first flow rate control valve for supplying a constant flow rate to a power steering mechanism are provided in a supply flow path connected to a pump. And a second flow control valve for controlling the supply pressure in accordance with the load pressure of the actuator are connected in parallel to each other, and the first flow control valve is connected to an orifice provided on the downstream side in one of the pilot chambers. The pressure on the upstream side is led, and the load pressure of the power steering mechanism is led to the other pilot chamber provided with the spring.

On the other hand, the second flow control valve guides the supply pressure to one pilot chamber, and guides the load pressure of the power steering mechanism to the other pilot chamber provided with a spring. Is set to be larger than the control pressure ΔP1 of the first flow control valve. Then, a constant control flow rate is preferentially supplied to the power steering mechanism via the first flow control valve.

According to a second aspect, in the first aspect,
A differential pressure generating valve is provided upstream of the switching valve, the supply pressure is guided to one pilot chamber of the differential pressure generating valve, and the load pressure of the power steering mechanism is guided to the other pilot chamber provided with a spring. The control pressure ΔP3 of the generating valve is
It is characterized in that the control pressure is larger than the control pressure ΔP1 of the first flow control valve and smaller than the control pressure ΔP2 of the second flow control valve.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment shown in FIG. 1 is different from the embodiment shown in FIG. 1 in that a supply flow path 3 is directly connected to a pump P and a priority flow path 2 is branched from the supply flow path 3. It is characterized in that the first flow control valve 27 is provided and the differential pressure generating valves 28 to 30 are provided in the parallel flow paths 4 to 6, respectively, and other configurations, for example, the second flow control valve 9 and switching valve A
Since C to C are the same as those in the conventional example, the same components are denoted by the same reference numerals and detailed description thereof will be omitted.

As shown in FIG. 1, the priority flow path 2 branched from the supply flow path 3 is provided with a first flow control valve 27 of a series type.
Is provided. The first flow control valve 27 is connected to the supply flow path 3
Are connected in parallel with the second flow control valve 9.
Also, one pilot chamber 2 of the first flow control valve 27 is provided.
The pressure on the upstream side of the orifice 31 provided on the downstream side is guided to 7a, and the pressure on the downstream side of the orifice 31, that is, the load pressure of the power steering mechanism PS is supplied to the other pilot chamber 27b provided with the spring 32. I try to guide.

The first flow control valve 27 controls the flow supplied to the power steering mechanism PS such that the differential pressure across the orifice 31 corresponds to the spring force of the spring 32. In other words, the first flow control valve 27
Thereby, the differential pressure across the orifice 31 is maintained at ΔP1, and the control flow rate to the power steering mechanism PS is kept constant. Note that the differential pressure ΔP1 is the control pressure of the first flow control valve of the present invention.

A load pressure line 33 is connected to the priority flow path 2 downstream of the orifice 31, and the load pressure line 11 is connected to the load pressure line 33 via a shuttle valve 34. Then, the load pressure of the power steering mechanism PS derived from the load pressure line 33 and the load pressure line 1
The highest one of the maximum load pressures of the actuators derived from 1 is selected by the shuttle valve 34 and guided to the pilot chamber 9b of the second flow control valve 9.

On the other hand, supply pressure is supplied from the supply passage 3 to one of the pilot chambers 28a-30a of the differential pressure generating valves 28-30 provided in the parallel passages 4-6, and the springs 35-3
7, the higher pressure of the power steering mechanism PS or the maximum load pressure of the actuator is guided to the other pilot chamber 28b-30b through the load pressure line 38. The differential pressure generating valve 2 thus configured
8 to 30 are closed in the illustrated normal state, but the supply pressure is higher than the maximum load pressure of the actuator or the load pressure of the power steering mechanism PS by a pressure ΔP3 corresponding to the spring force of the springs 35 to 37. Is controlled in such a manner.

The control pressure ΔP3 of the differential pressure generating valves 28 to 30 is changed to the control pressure ΔP of the first flow control valve 27.
It is set larger than P1 and smaller than the control pressure ΔP2 of the second flow control valve 9. In addition, the flow control valve 1
9, the control pressure Δpr of the first flow rate control valve 27 is equal to or lower than the control pressure ΔP1. That is, the control pressure is Δp
The relationship is r ≦ ΔP1 <ΔP3 <ΔP2.

Next, the operation of this embodiment will be described. The pressure oil supplied from the pump P to the supply flow path 3 is preferentially supplied to the first flow control valve 27 and the flow control valve 19 having small control pressures. Therefore, as before, a constant control flow rate is preferentially supplied to the power steering mechanism PS,
A predetermined pilot pressure is led to a pilot line 23.

The surplus flow rate, which is obtained by subtracting the control flow rate and the pilot flow rate from the discharge rate of the pump P, is equal to the switching valves A to C.
Supplied to Therefore, when the switching valves A to C are switched, the actuator connected to the switching valve operates. Further, the maximum load pressure of the actuator generated at this time is guided to the shuttle valve 34 via the load pressure line 11. If the maximum load pressure is higher than the load pressure of the power steering mechanism PS, the maximum load pressure of the actuator is guided to the pilot chamber 9b of the second flow control valve 9. Therefore, the supply pressure is kept higher than the maximum load pressure of the actuator by the control pressure ΔP2 by the second flow control valve 9, and the operation speed of the actuator is stabilized.

On the other hand, when all the switching valves A to C are in the neutral position, the entire amount of the excess flow is returned from the second flow control valve 9 to the tank. And the first flow control valve 27 are connected in parallel with each other. Therefore, the discharge pressure of the pump P is maintained at the higher one of the control pressures of the first flow control valve 27 and the second flow control valve 9. That is, in this embodiment, the control pressure ΔP2 of the second flow control valve 9
Since the control pressure ΔP1 of the flow control valve 27 is higher than the control pressure ΔP1, the discharge pressure of the pump P is maintained at the control pressure ΔP2 of the second flow control valve 9.

As described above, in this embodiment, when all the switching valves A to C are at the neutral position, the pressure of the pump P may be maintained at the control pressure ΔP2 of the second flow control valve 9, so that The pump discharge pressure can be lower than in the conventional example. Therefore, the energy loss can be reduced by reducing the pump discharge pressure.

When all the switching valves A to C are set to the neutral position, the load pressure of the actuator becomes smaller than the load pressure of the power steering mechanism PS. In this case, the high pressure is selected by the shuttle valve 34. The load pressure of the power steering mechanism PS is guided to the pilot chamber 9b of the second flow control valve 9 and the pilot chambers 28b to 30b of the differential pressure generating valves 28 to 30. Therefore, the load pressure of the same power steering mechanism PS is led to the other pilot chambers 27b, 9b, 28b-30b of the first and second flow control valves 27 and the differential pressure generating valves 28-30.

By applying the same pressure to the first and second flow rate control valves 27 and 9 and the differential pressure generating valves 28 to 30 in this manner, these first and second flow rate control valves 27 and 9 and the differential pressure generating valves 28 to
Since the relationship between the control pressures 30 is ΔP1 <ΔP3ΔP2, the pressure oil discharged from the pump P is preferentially supplied to the first flow control valve 27 side. Therefore, in this embodiment, a constant control flow rate can always be preferentially supplied to the power steering mechanism PS.

If the differential pressure generating valves 28 to 30 are not provided, if the load pressure of the actuator becomes lower than the load pressure of the power steering mechanism PS, the pressure oil is preferentially supplied to the actuator side. In addition, there is a possibility that the flow rate of the power steering mechanism PS becomes insufficient. But,
According to this embodiment, as described above, the differential pressure generating valve 28
30 are provided on the upstream side of the switching valves A to C, and the control pressure ΔP3 thereof is made larger than the control pressure ΔP1 of the first flow control valve 27, so that such a problem does not occur.

[0031]

According to the first aspect of the present invention, the first flow control valve and the second flow control valve are connected in parallel with each other. Therefore, when all the switching valves of the closed center type are maintained at the neutral position, The discharge pressure may be kept equivalent to the control pressure of the second flow control valve having a high control pressure. Therefore, the first
Energy loss when the switching valve is in the neutral position can be reduced as compared with the conventional example in which the flow control valve and the second flow control valve are connected in series.

According to the second aspect, the differential pressure generating valve is provided upstream of the switching valve, and the pressure on the upstream side is made higher than the control pressure of the first flow control valve. Even if the load pressure of the power steering mechanism becomes smaller than the load pressure of the power steering mechanism, the control flow rate can be preferentially supplied to the power steering mechanism. Therefore, it is possible to prevent the power steering mechanism from running out of flow and to stabilize its operation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

 Reference Signs List 3 supply flow path 9 second flow control valve 9a one pilot chamber of second flow control valve 9b other pilot chamber of second flow control valve 10 spring provided in second flow control valve 27 first flow control valve 27a One pilot chamber of one flow control valve 27b The other pilot chamber of first flow control valve 28-30 Differential pressure generating valve 28a-30a One pilot chamber of differential pressure generating valve 28b-30b The other pilot of differential pressure generating valve Chamber 21 Orifice 32 Spring provided on first flow control valve 35-37 Spring of differential pressure generating valve

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D033 EB07 EB08 EB11 EC08 ED06 ED07 JB14 3H089 AA74 BB20 CC01 DA02 DB03 DB13 DB14 DB17 DB47 DB49 DB54 EE14 GG02 JJ09

Claims (2)

[Claims] 1. A closed center type switching valve for controlling an actuator in a supply passage connected to a pump, and a first valve for supplying a constant flow rate to a power steering mechanism.
A flow control valve and a second flow control valve for controlling the supply pressure in accordance with the load pressure of the actuator are connected in parallel with each other, and the first flow control valve is provided downstream of one of the pilot chambers. The second flow control valve guides the pressure on the upstream side of the orifice and guides the load pressure of the power steering mechanism to the other pilot chamber provided with a spring. The load pressure of the power steering mechanism is led to the other pilot chamber provided, and the control pressure ΔP2 of the second flow rate control valve is made larger than the control pressure ΔP1 of the first flow rate control valve so as to maintain a constant control flow rate. Is supplied to the power steering mechanism preferentially via the first flow control valve. 2. A differential pressure generating valve is provided upstream of the switching valve, a supply pressure is guided to one pilot chamber of the differential pressure generating valve, and a load pressure of the power steering mechanism is guided to the other pilot chamber provided with a spring. 2. The control pressure .DELTA.P3 of the differential pressure generating valve is made larger than the control pressure .DELTA.P1 of the first flow control valve and smaller than the control pressure .DELTA.P2 of the second flow control valve. The hydraulic control device as described.