JPH04136504A - Hydraulic circuit - Google Patents

Abstract

PURPOSE:To enhance the responsiveness of a hydraulic circuit by connecting the hydraulic circuit for leading loaded pressure oil to a switching valve, which controls the hydraulic pump capacity in the direction of decrease by pump discharge pressure and in the direction of increase by load pressure, to the tank through a bleed-off valve which shuts off the oil by control valve switching-over pressure and allows to pass through by spring force. CONSTITUTION:A branch circuit 26 is connected to a hydraulic circuit 23 for connecting a shuttle valve 21 to a pressure receiving portion 14a of a switching valve 14 and a bypass circuit 27 is connected to a discharge line 10a for a hydraulic pump 10. These circuits 26 and 27 are connected to and shut off from a tank 29 through a bleed-off valve 28. The bleed-off valve 28 at a connecting position A connects the branch circuit 26 to the tank 29 through a restriction 31 by a spring 30, and the bypass line 27 to the tank 29, at a middle position B, shuts off the branch circuit 26 by a pressure at the pressure receiving portion 32 and, at a shutting position C, the circuits 26 and 27 shut off. Thus, the responsiveness of the circuit can be enhanced since the loaded pressure oil does not flow out into the tank 29.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit that supplies pressure oil discharged from one hydraulic pump to a plurality of hydraulic actuators.

[Conventional technology]

In order to supply pressure oil discharged from one hydraulic pump to multiple hydraulic actuators, it is sufficient to provide multiple operating valves in the discharge path of the hydraulic pump and supply pressure oil to each hydraulic actuator by switching the operating valves. However, in this case, when pressure oil is supplied to a plurality of hydraulic actuators at the same time, pressure oil is supplied only to the hydraulic actuators with a small load, and no pressure oil is supplied to the hydraulic actuators with a large load.

As a hydraulic circuit that solves this problem, for example, JP-A-59
The one shown in Japanese Patent No. 197803 has been proposed.

Such a hydraulic circuit is schematically shown in FIG. 6.

In other words, the discharge path 1ai of the hydraulic pump l: the plurality of operating valves 2
A pressure compensating valve 5 is provided in each circuit 4 connecting each operating valve 2 and each hydraulic actuator 3, and the pressure in each circuit 4, that is, the highest pressure in the load pressure is detected by a shuttle valve 6. The load pressure applied to each pressure compensation valve 5 is set to a pressure commensurate with the load pressure, and when the outlet side pressure of each operation valve 2 is equalized and each operation valve 2 is operated simultaneously, the opening area of each operation valve is This allows pressure oil to be supplied to each hydraulic actuator 3 at a branching ratio proportional to .

With such a hydraulic circuit, the function of the pressure compensating valve 5 makes it possible to distribute the flow rate in proportion to the opening area of the operating valve 2, regardless of the magnitude of the load on each hydraulic actuator 3. It can be supplied to each hydraulic actuator 3 in proportion to the amount of operation of the operation valve 2.

However, the capacity (discharge flow rate per rotation) of the hydraulic pump 1 is controlled by the pump pressure and load pressure so that the capacity becomes smaller when the pump pressure increases and becomes larger when the load pressure decreases. In the neutral position, discharge path 1
A and circuit 4 are cut off, circuit 4 is blocked, and load pressure remains, and the pump capacity does not decrease until the load pressure decreases due to leaks from various parts.

For this reason, the capacity of the hydraulic pump 1 increases for a predetermined period of time after the operator returns the operating valve 2 to the neutral position, producing hydraulic pump drive noise, giving the operator a sense of discomfort.

Therefore, the applicant first connected the circuit that introduces load pressure to the switching valve that controls the capacity of the hydraulic pump to the tank through a throttle, and when the operating valve is set to the neutral position, the load pressure in the circuit immediately drops. We proposed a hydraulic circuit designed to do this.

This hydraulic circuit is specifically constructed as shown in FIG.

That is, the hydraulic pump 10 is a variable displacement hydraulic pump in which the displacement, that is, the discharge flow rate per rotation, is changed by changing the angle of the swash plate 11, and the swash plate 11 is tilted in the direction of decreasing capacity by the large diameter piston 12. Then, the small diameter piston 13 tilts in the direction of increasing capacity.

The pressure receiving chamber 12a of the large diameter piston 12 is communicated with and cut off from the discharge passage 10a of the hydraulic pump 10 by a switching valve 14, and the pressure receiving chamber 13a of the small diameter piston 13 is connected to the discharge passage 10g.

A plurality of operation valves 1 are provided in the discharge passage 10a of the hydraulic pump 10.
5 are provided, each operating valve unit 5 and hydraulic actuator 1
A pressure compensation valve 18 is provided in each of the circuits 17 connecting 6, and the pressure compensation valves 18 are pushed to the low pressure set side by the pressure oil of the first pressure receiving part 19, and are pushed to the high pressure set side by the pressure oil of the second pressure receiving part 20. The first pressure receiving part 19 is connected to the outlet side of the operation valve 15 and is supplied with outlet side pressure, and the second
The pressure receiving section 20 is connected to each circuit 17 via a shuttle valve 21 and is supplied with the highest load pressure.

The switching valve 14 is pushed in the communication direction by the pressure in the discharge passage 10a, and pushed in the drain direction by the spring 22 and the load pressure, so that when the discharge pressure P1 increases, the discharge pressure is applied to the pressure receiving chamber 12g of the large diameter piston 12. When the discharge pressure P1 becomes low, the pressure-receiving material 12a of the large-diameter piston 12 flows out to the tank side, and the swash plate 11 is tilted in the direction of increasing capacity.

A circuit 23 that supplies the load pressure to the pressure receiving section 14g of the switching valve 14, that is, a circuit 23 that connects the pressure receiving section 14a and the output side of the shuttle valve 21, is connected to the tank 25 through a throttle 24.

In such a hydraulic circuit, the operation valve 15 is moved to the pressure oil supply position I.
Then, as in the conventional case, the discharge pressure oil of the hydraulic pump 10 is supplied to the hydraulic actuator 16, and the load pressure is supplied from the shuttle valve 21 and the circuit 23 to the pressure receiving part 14a of the switching valve 14.

At this time, the pressure oil flowing into the circuit 23 passes through the throttle 24 to the tank 2.
However, since pressure oil always flows in, the pressure on the upstream side of the throttle 24 is maintained and supplied to the pressure receiving part 14a of the switching valve 14 as a load pressure.

When the operation valve 15 is set to the neutral position N from the above-mentioned state, the discharge passage 10g and the circuit 17 are blocked, but the pressure oil in the circuit 23 flows out from the throttle 24 to the tank 25, and the load pressure in the circuit 23 rapidly increases. The pressure receiving chamber 12a of the large-diameter piston 12 communicates with the discharge passage 10a, and the capacity of the hydraulic pump 10 immediately becomes the minimum.The discharge flow rate of the hydraulic pump 10 decreases and the pump pressure decreases, so that the drive of the hydraulic pump 10 decreases. The sound becomes quieter.

[Problem to be solved by the invention]

However, in the previously proposed hydraulic circuit, the circuit 23 that supplies the load pressure to the pressure receiving part 14a of the switching valve 14 is always connected to the tank 25 via the throttle 24, so the operating valve 15 is moved to the neutral position N. When operating from the pressure oil supply position to the pressure oil supply position, there is a delay in increasing the load pressure, resulting in poor response.

Therefore, an object of the present invention is to provide a hydraulic circuit that can solve the above-mentioned problems.

[Means and actions for solving the problem] A circuit that supplies load pressure to the pressure receiving part of the switching valve is connected to the tank through a bleed-off valve, and the bleed-off valve is set to the cutoff position by the operating valve switching pressure, and the spring force When the control valve is in the neutral position, the bleed-off valve is in the cutoff position and the load pressure flows out to the tank, and when the control valve is in the pressure oil supply position, the bleed-off valve is in the cutoff position. This prevents the load pressure from flowing into the tank.

〔Example〕

As shown in FIG. 1, a branch circuit 26 is connected to the circuit 23 connecting the shuttle valve 21 and the pressure receiving part 14a of the switching valve 14, and a bypass circuit 27 is connected to the discharge path 10a of the hydraulic pump 10. 27 and the branch circuit 26 are communicated with and cut off from the tank 29 by a bleed-off valve 28.

The bleed-off valve 28 is held at the communication position A by a spring 30, connects the branch circuit 26 to the tank 29 through the throttle 31, and connects the bypass passage 27 to the tank 29, and is moved to the intermediate position B by the pressure of the pressure receiving part 32.

They are sequentially pushed to the cutoff position C, and when the intermediate position B is reached, the branch circuit 26 is cut off and the bypass circuit 27 is communicated with the tank 29 via the throttle 33, and when the cutoff position C is reached, both circuits are cut off.

The pressure receiving part 32 of the bleed-off valve 28 is supplied with the highest pressure among the output pressures of a plurality of pilot control valves 34 for switching the operation valve 15 by a shuttle valve 35, and the pilot control valve 34 is operated by a lever 36. .

Therefore, when the lever 36 of the pilot control valve 34 is set to the neutral position and the operating valve 15 is set to the neutral position N, the hydraulic pump 1
A discharge pressure of 0 is supplied to the pressure receiving chamber 12a of the large-diameter piston 12, the swash plate 11 is at its minimum angle, and the pump capacity is minimized.Furthermore, the bleed-off valve 28 is in the communication position A, and the pump's small discharge flow rate is reduced. is the tank 2 from the bypass circuit 27.
9, and the circuit 23 communicates with a tank 29 via a branch circuit 26 and a throttle 31.

Further, when the lever 36 is operated to supply pilot pressure from the pilot control valve 34 to the operation valve 15 to set the pressure oil supply position I, the discharge pressure oil of the hydraulic pump 10 passes through the pressure compensation valve 18 to the hydraulic actuator 16. The output pressure of the pilot control valve 34 is supplied to the pressure receiving part 32 of the bleed-off valve 28.
Therefore, when the stroke of the lever 36 is small and the output pressure is low, the bleed-off valve 28 is in the intermediate position B, and when the lever 36 is at full stroke, the output pressure is high and the bleed-off valve 28 is in the cutoff position C.

Therefore, when the operation valve 15 is operated from the neutral position N to the pressure oil supply position I, the bleed-off valve 28 changes from the communication position A to the intermediate position MB to the cutoff position C, so that the circuit 23 does not communicate with the tank 29, resulting in responsiveness. is secured and the operation valve 15
When the is operated from the pressure oil supply position I to the neutral position N, the bleed-off valve 28 changes from the cutoff position C to the intermediate position B5 and the communication position A, and the circuit 23 passes through the throttle 31 and communicates with the tank 29, resulting in a decrease in load pressure. Since the pump pressure decreases quickly and the pump pressure does not drop quickly, there is no discomfort.

Further, in the embodiment, the pressure oil discharged from the hydraulic pump 10 is communicated with and cut off from the tank 29 by the bleed-off valve 28, so that the following effects are obtained.

That is, when the operation valve 15 is in the neutral position N, the bleed-off valve 28 is in the communication position A, and the pressure oil discharged from the hydraulic pump 10 flows to the tank side. Furthermore, when the operation valve 15 is set to the first and second pressure oil supply positions, the bleed-off valve 28 is set to the cutoff position C, and the pressure oil discharged from the hydraulic pump 10 is transferred to the tank side. It stops flowing.

Therefore, not only can the static stability of the hydraulic actuator 16 be improved when the operating valve 15 is suddenly operated, but also the static stability of the hydraulic actuator 16 can be improved.
It is possible to increase the discharge flow rate of the hydraulic pump 10 when the hydraulic pump 10 is at the neutral position to improve responsiveness, and when supplying pressure oil to the hydraulic actuator 16, pressure compensation can be performed in the same way as in the conventional case.

FIG. 2 shows a second embodiment, in which the load pressure is detected from the output side of the pressure compensation valve 18.

3 and 4 show modified examples of the bleed-off valve 28,
A throttle 31 is provided on the inlet side and the outlet side of the branch circuit 26.

〔Effect of the invention〕

Discharge path 10a1 circuit 17 with operating valve 15 at neutral position N
When the bleed-off valve 28 is closed, the pressure oil in the circuit 23 that introduces load pressure flows into the tank 29, and the pressure in the circuit 23, that is, the load pressure, decreases rapidly. As soon as the operation valve 15 is set to the neutral position N, the capacity of the hydraulic pump 10 becomes the minimum, and the driving noise of the hydraulic pump 10 is not generated, so that the operator does not feel uncomfortable.

Furthermore, when the operating valve 15 is moved from the neutral position to the pressure oil supply position, the bleed-off valve 28 is in the cutoff position and the pressure in the circuit 23, that is, the load pressure, does not flow out to the tank 29.
Responsiveness can be improved.

[Brief explanation of drawings]

Figures 1 and 2 are hydraulic circuit diagrams showing the first and second embodiments of the present invention, Figures 3 and 4 are explanatory diagrams showing modifications of the bleed-off valve, and Figure 5 is an illustration of a modification of the bleed-off valve. FIG. 6 is a conventional hydraulic circuit diagram. 10 is a hydraulic pump, 10a is a discharge path, 14 is a switching valve, 1
5 is an operating valve, 16 is a hydraulic actuator, 17 is a circuit,
18 is a pressure compensation valve, 23 is a circuit, 28 is a bleed-off valve, and 29 is a tank.

Claims (1)

[Claims] A plurality of operation valves 15 are provided in the discharge path 10a of the hydraulic pump 10, and a pressure compensation valve 18 is provided in the connection circuit between each operation valve 15 and each hydraulic actuator 16, and each pressure compensation valve 1
8 is set at the highest pressure among the load pressures of each hydraulic actuator 16, the switching valve 14 for controlling the capacity of the hydraulic pump 10 is operated in the direction of reducing the capacity by the pump discharge pressure, and the load pressure The circuit 23, which operates in the direction of increasing capacity and leads the load pressure to the switching valve 14, is connected to the tank 29 via the bleed-off valve 28, and the bleed-off valve 28 is brought to the cutoff position by the operating valve switching pressure, and is closed by the spring force. A hydraulic circuit characterized by being in a communicating position.