JPH06280802A - Unloading valve - Google Patents

Abstract

PURPOSE:To switchover a main valve, which opens and closes ports of both a pump and a tank, slowly from unload to on-load by opening the main valve by virtue of pump port pressure, closing it by virtue of a main spring and the pressure inside a back pressure chamber and communicating the back pressure chamber to a load pressure introduction passage through an orifice. CONSTITUTION:A main valve 60 is held in the position where a pump port 62 and a tank port 63 are closed by means of a main spring 61. Pressure oil is supplied to an actuator by switching over an operating valve from the condition of the operating valve in a neutral position, the main valve 60 in an opened position (unload condition) and discharging pressure oil of an hydraulic pump in an unload condition. Load pressure inside the load introduction passage raises and flows into a back pressure chamber 64 for the unloading valve but load pressure flows into the back pressure chamber 64 through a small hole 65. Therefore, pressure oil raising inside the back pressure chamber 64 becomes slow and the main valve 60 is pushed slowly to the closing position (on-load condition). Thus pressure oil flow to the actuator does not increase suddenly and the actuator operates smoothly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unload valve used in a hydraulic circuit for supplying pressurized oil discharged from a hydraulic pump to a plurality of actuators by a plurality of closed center type operation valves.

[0002]

2. Description of the Related Art As shown in FIG. 1, a plurality of closed center type operation valves 2 are arranged in a discharge passage 1a of a hydraulic pump 1, and a pressure compensating valve 5 is connected to a connection circuit 4 between the operation valve 2 and an actuator 3. Is provided, the maximum pressure in the load pressure of each actuator 4 is detected by the shuttle valve 6, and the load pressure is supplied to the spring chamber 5a of each pressure compensating valve 5 to obtain a set pressure corresponding to the load pressure. It has been known.

With such a hydraulic circuit, a plurality of operating valves 2
The pressure compensating valve 5 is set by the maximum pressure among the load pressures of the plurality of actuators 3 when they are simultaneously operated. it can.

In such a hydraulic circuit, an unload valve 7 is provided in the discharge passage 1a of the hydraulic pump 1 and a relief valve 9 is provided in the load pressure introducing passage 8 so that the unload valve 7 is placed below the load pressure P _LS. When the pump discharge pressure P ₁ becomes higher than the set pressure, unloading is performed, and when the load pressure P _LS of the load pressure introducing passage 8 becomes equal to or higher than the set pressure of the relief valve 9, the relief valve 9 is relieved and the load pressure P _When a part of the _LS flows out into the tank and the load pressure P _LS decreases and the differential pressure from the pump discharge pressure P ₁ becomes equal to or higher than the set pressure, the unload valve 7 unloads and the pump discharge pressure P ₁ increases. It is proposed that a part of it can flow out to the tank to limit the maximum pump discharge pressure.

The unload valve 7 shown in FIG. 2 has been proposed. That is, the main valve 11 is provided in the valve body 10, and the main valve 11 is pushed by the pressure (load pressure P _LS ) in the main spring 12 and the back pressure chamber 13 in the direction to close the pump port 14 and the tank port 15 to push the pump port. 1
4 is pushed in the opening direction by the pressure of 4 (pump discharge pressure P ₁ ), and the pump port 14 becomes the discharge passage 1
The tank port 15 communicates with the tank passage 16 and the back pressure chamber 13 communicates with the load pressure introducing passage 8.

Since the main valve 11 of the unload valve 7 is held in the closed position (that is, the on-load state) by the spring force of the main spring 12, the pump discharge pressure P ₁ of the main spring 12 is higher than the load pressure P _LS . When the pressure corresponding to the spring force increases and the pressure difference between the pump discharge pressure P ₁ and the load pressure P _LS becomes greater than that, the main valve 11 is pushed to the open position against the main spring 12 and the pump is unloaded. The pressure oil of the port 14 flows out to the tank port 15, whereby the pump discharge pressure P ₁ is constantly maintained higher than the load pressure P _LS by the set pressure.

The above-mentioned relief valve 9 is constructed as shown in FIG. That is, the valve body 10 is provided with a poppet 19 that opens and closes the inlet port 17 and the outlet port 18, and the poppet 19 is pushed in the closing direction by the spring 20. When the pressure in the inlet port 17 exceeds the set pressure, the poppet 19 is opened. The inlet port 17 and the outlet port 18 are communicated with each other by being pushed by, and the inlet port 19 communicates with the load pressure introducing passage 8 and the outlet port 18 communicates with the tank passage 16.

In the relief valve 9 described above, when the load pressure P _LS flowing into the inlet port 17 rises and becomes higher than the set pressure, the poppet 19 is pushed and a part of the load pressure P _LS is discharged from the outlet port 18. Outflow to the tank passage 16 and load pressure P _LS
Can be maintained at the set pressure. On the other hand, the load pressure P _LS acts on the pressure receiving portion 21a of the control valve 21 that controls the angle of the swash plate 20 of the hydraulic pump 1 to control the swash plate angle, as shown in FIG.

[0009]

The above-mentioned unloading valve 7
Therefore, when the operating valve 2 is in the neutral position, the pump port 14
However, the load pressure P _LS of the back pressure chamber 13 hardly rises, so that the main valve 11 is pushed against the main spring 12 to be in the unloading state and flowed into the pump port 14. Pump discharge pressure is outlet port 1
5 and flows out into the tank passage 16 and the pump discharge pressure P ₁ becomes a pressure commensurate with the spring force of the main spring 12.

When the operating valve 2 is switched from the above-mentioned state and pressure oil is supplied to the actuator 3, the load pressure P _{LS in} the load pressure introducing passage 8 rises sharply and the pressure in the back pressure chamber 13 also rises sharply. The main valve 11 is suddenly pushed to the closed position, that is, the on-road state. As a result, the pressure oil discharged from the hydraulic pump 1 that has been unloaded into the tank is rapidly supplied to the actuator 3, the supply flow rate to the actuator 3 is suddenly increased, and the actuator 3 is suddenly operated to smoothly operate the actuator 3. Can not work.

That is, the relationship between the operation valve stroke and the pump discharge pressure, the load pressure, the unload valve unload flow rate, and the actuator flow rate is shown in FIGS. 3 (a), (b), (c), and FIG.
As shown in (d), the actuator flow rate rapidly increases at the beginning of the operation valve stroke as shown by A, and the actuator pops out.

Therefore, an object of the present invention is to provide an unloading valve which can solve the above-mentioned problems.

[0013]

Means for Solving the Problems Discharge passage 1 of hydraulic pump 1
The main valve 60 that opens and closes the pump port 61 that communicates with a and the tank port 62 that communicates with the tank passage 56 is pushed in the opening direction by the pressure of the pump port 61, and the spring force of the main spring 63 and the back pressure chamber 64 An unload valve in which the back pressure chamber 64 is configured to be pushed in the closing direction by pressure and communicated with the load pressure introducing passage 8 through an orifice.

[0014]

[Operation] Since the load pressure in the load pressure introducing passage 8 flows into the back pressure chamber 64 through the orifice, the pressure in the back pressure chamber 64 rises slowly and the main valve 60 slowly closes. When pushed, the unload valve slowly changes from the unload state to the on-load state, and the pump discharge pressure oil supplied to the actuator increases slowly and smoothly without sudden increase, so the pump discharge pressure oil is supplied to the actuator. When the operating valve is switched from the neutral position, the pump discharge pressure oil is slowly supplied to the actuator, and the actuator operates slowly and smoothly.

[0015]

[Example] As shown in FIG. 4, the shaft hole 3 of the valve body 30
1, the sleeve 33 is fitted and inserted, and the main valve 60 is fitted inside the one end of the sleeve 33.
Is held at the position where the main spring 61 closes the pump port 62 and the tank port 63, that is, the on-road state,
The back pressure chamber 64 on the side of the main spring 61 has a fine hole (orifice) 6 formed in a piston 47 of a relief valve 9 described later.
5 communicates with the annular groove 51, opens into the load pressure introducing passage 8 as will be described later, the load pressure P _LS flows in, and the pump discharge pressure P ₁ flowing into the pump port 62 is larger than the load pressure P _LS than the main spring. When the pressure becomes higher than the pressure corresponding to 61, the main valve 60 is pushed and the pump port 62 communicates with the tank port 63 to be in the unloading state, whereby the pump discharge pressure P ₁ is higher than the load pressure P _LS. The unload valve 7 that maintains a slightly high pressure corresponding to the spring force of the spring 61 is configured. The tank port 63 has a tank passage 56.
Is in communication with.

Because of this, the operation valve 2 is switched from the state where the discharge pressure oil of the hydraulic pump 1 is unloaded with the operation valve 2 in the neutral position and the main valve 60 in the open position (unloaded state). 3, the load pressure P _LS in the load pressure introducing passage 8 rises, and the load pressure P _LS flows into the back pressure chamber 64 of the unload valve 7, but this load pressure P _LS is small. Since it flows into the back pressure chamber 64 through the hole 65, the pressure rise in the back pressure chamber 64 becomes gentle, and the main valve 60 is slowly pushed to the closed position (on-load state).

Therefore, the discharge pressure oil of the hydraulic pump 1 that has been unloaded is not slowly unloaded and is sequentially supplied to the actuator 3, and the flow rate of the actuator 3 slowly increases without rapidly increasing, The actuator 3 operates smoothly. The relationship among the operation valve stroke, the pump discharge pressure, the load pressure, the unload flow rate, and the actuator flow rate at this time is shown in FIG. 5 (a), (b), (c),
5D, the load pressure in the back pressure chamber 63 of the unload valve 7 becomes as shown in B of FIG. 5B, and the actuator flow rate gradually increases as shown in C of FIG. 5D. .

[0018]

Since the load pressure in the load pressure introducing passage 8 flows into the back pressure chamber 64 through the orifice, the pressure in the back pressure chamber 64 slowly rises and the main valve 60 slowly closes. The unload valve is slowly pushed into the on-load state from the unload state, and the pump discharge pressure oil supplied to the actuator increases slowly and smoothly without sudden increase. The pump discharge pressure oil is slowly supplied to the actuator when the operation valve for supplying the pressure is switched from the neutral position, and the actuator operates slowly and smoothly.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram including a closed center type operation valve.

FIG. 2 is a sectional view showing an example of an unload valve.

FIG. 3 is a chart showing operation valve stroke, pump discharge pressure, load pressure, unload flow rate, and actuator flow rate.

FIG. 4 is a sectional view of an unload valve showing an embodiment of the present invention.

FIG. 5 is a chart showing operation valve stroke, pump discharge pressure, load pressure, unload flow rate, and actuator flow rate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydraulic pump, 1a ... Discharge path, 2 ... Operation valve, 3 ... Actuator, 7 ... Unload valve, 8 ... Load pressure introduction path, 5
6 ... Tank passage, 60 ... Main valve, 61 ... Pump port, 62 ... Tank port, 63 ... Main spring, 64 ...
Back pressure chamber, 65 ... Pore.

Claims (1)

[Claims] 1. A main valve 60 for opening and closing a pump port 61 communicating with a discharge passage 1a of a hydraulic pump 1 and a tank port 62 communicating with a tank passage 56 is pushed in the opening direction by the pressure of the pump port 61, and a main spring is used. An unloading valve characterized in that the spring force of 63 and the pressure in the back pressure chamber 64 are pushed in the closing direction, and the back pressure chamber 64 is connected to the load pressure introducing passage 8 via an orifice.