JPH0687701U - Load sensing hydraulic circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent hunting of the unload valve at a minute flow rate in the load sensing hydraulic circuit of construction machinery. [Structure] A throttle 18 and a relief valve 19 are provided in parallel on the secondary side of the unload valve 10 and connected to the tank 11. The primary pressure of the throttle 18 is applied to the closing side port 10b of the unload valve 10.
The secondary pressure of the throttle 18 is led to the opening side port 10a.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a hydraulic circuit of a construction machine, and more particularly to a load sensing hydraulic circuit that controls pump discharge pressure in response to load pressure fluctuations.

[0002]

[Prior art]

 A conventional load sensing hydraulic circuit of this type is shown in FIG. An actuator 6 is connected to a discharge oil passage 2 of a variable displacement hydraulic pump 1 via a direction control valve 3, a pressure compensation valve 4, and a load pressure switching valve 5. The load pressure detection oil passage 7 is branched from the front stage of the load pressure switching valve 5 and connected to the pump regulator 8. Further, an oil passage 9 is branched from the discharge oil passage 2, an unload valve 10 is provided in the oil passage 9 and connected to a tank 11.

Thus, the load pressure of the actuator 6 is led to the pump regulator 8 via the load pressure detection oil passage 7, and the discharge pressure of the hydraulic pump 1 is controlled according to the change of the load pressure. Further, the discharge pressure of the hydraulic pump 1 is derived to the open side port 10a of the unload valve 10, the spring 12 is installed in the close side port 10b of the unload valve 10, and the load pressure from the load pressure detection oil passage 7 is applied. Derive. Therefore, when the load pressure of the actuator 6 becomes extremely small, the unload valve 10 is opened and the oil passage 9 communicates with the tank 11 to be in the unload state.

[0004]

[Problems to be solved by the device]

 In the load sensing hydraulic circuit equipped with the unload valve 10, when the directional control valve 3 is opened, the discharge oil of the hydraulic pump 1 is discharged to the actuator 6 via the directional control valve 3 and the oil passage 9. The flow is divided into the portion discharged to the unload valve 10. Here, in the conventional hydraulic circuit, the unload valve 10 needs to be configured to flow at a flow rate higher than the minimum flow rate of the hydraulic pump, and it may not operate smoothly at a minute flow rate.

In that case, hunting occurs in the unload valve 10 and the operability deteriorates. In particular, when the directional control valve 3 is suddenly operated, hunting is likely to occur in the unload valve 10, which in turn causes the hydraulic pump 1 to hunt, which causes operator fatigue. Therefore, there is a technical problem to be solved in order to prevent pressure hunting at a minute flow rate of the unload valve, hydraulic pump, etc. and to make the operation of the load sensing hydraulic circuit smooth. The purpose is to solve.

[0006]

[Means for Solving the Problems]

 The present invention has been proposed in order to achieve the above-mentioned object, and an actuator is connected to a discharge oil passage of a hydraulic pump via a directional control valve so that a load pressure of the actuator is led to a pump regulator to discharge the discharge oil. An unload valve is provided by branching the oil passage from the passage, the discharge pressure of the hydraulic pump is derived to the opening side port of the unload valve, a spring is installed at the closing side port of the unload valve, and the load pressure of the actuator is In the load-sensing hydraulic circuit formed so as to derive the above, the throttle valve and the relief valve are provided in parallel on the secondary side of the unload valve and connected to the tank, and the primary pressure of the throttle valve is applied to the closing side of the unload valve. The present invention provides a load sensing hydraulic circuit in which the secondary pressure of the throttle is led to the opening side port of the unload valve.

[0007]

[Action]

 When the directional control valve is in the open state, the discharge oil of the hydraulic pump is divided into the directional control valve and the unload valve, and the pump discharge pressure is led to the open side port of the unload valve. The closing port of the unload valve receives the load pressure of the actuator along with the spring pressure, and in normal operation, the unload valve is closed due to the spring pressure.

When the load pressure of the actuator becomes small, the pump discharge pressure becomes larger than the sum of the load pressure and the spring pressure, and the unload valve is opened. The oil that has passed through the unload valve is throttled and returned to the tank, and the primary pressure of the throttle is discharged to the closing port of the unload valve. Therefore, the unload valve acts in the closing direction to prevent the flow rate of the unload valve from rapidly increasing. When the unloading flow rate gradually increases and the primary pressure of the throttle increases to a predetermined pressure, the relief valve opens and the unloading state occurs.

[0009]

【Example】

 An embodiment of the present invention will be described below in detail with reference to FIGS. For convenience of explanation, the same reference numerals are used for the same components as those of the conventional technique. As shown in FIG. 1, an actuator 6 is connected to a discharge oil passage 2 of a variable displacement hydraulic pump 1 via a directional control valve 3, a pressure compensating valve 4, and a load pressure switching valve 5. The load pressure detection oil passage 7 and the load pressure release oil passage 13 are branched from the preceding stage of the load pressure switching valve 5.

A load pressure release valve 14 is provided in the load pressure release oil passage 13 to connect to the tank 11, and the load pressure detection oil passage 7 is connected to one inlet of the shuttle valve 15. A load pressure detection oil passage (not shown) of another actuator is connected to the other inlet of the shuttle valve 15, and the load pressure of either one of the actuators is selected as a high pressure and pumped through the maximum load pressure oil passage 16. It is led to the regulator 8. If there is only one actuator, the shuttle valve 15 is not provided and the load pressure detection oil passage 7 is directly connected to the pump regulator 8.

Further, the pump discharge pressure detection oil passage 17 and the oil passage 9 are branched from the vicinity of the discharge port of the hydraulic pump 1, the pump discharge pressure detection oil passage 17 is connected to the pump regulator 8, and the oil passage 9 is unloaded. A valve 10 is provided. Further, a throttle valve 18 and a relief valve 19 are provided in parallel on the secondary side of the unload valve 10 and connected to the tank 11, and a signal pressure oil passage 20 is branched from the primary side of the throttle valve 18 and the relief valve 19 to disconnect the unload valve 10. It is connected to the closing side port 10b of the load valve 10, and the oil passage 21 is branched from the secondary side of the throttle 18 and the relief valve 19 to be connected to the opening side port 10a of the unload valve 10.

When the directional control valve 3 is in the open state, the load pressure switching valve 5 is opened so that the oil discharged from the hydraulic pump 1 is discharged from the directional control valve 3, the pressure compensating valve 4, and the load pressure switching valve 5. And the actuator 6 is driven. At that time, the load pressure of the actuator 6 passes through the load pressure detecting oil passage 7, is selected as a high pressure by the shuttle valve 15, and is led to the pump regulator 8 via the maximum load pressure oil passage 16. At the same time, the pump discharge pressure is led to the pump regulator 8 via the pump discharge pressure detection oil passage 17, and the pump discharge pressure is controlled by the action of the pump regulator 8 according to the fluctuation of the maximum load pressure.

Further, the discharge oil of the hydraulic pump 1 is also branched to the oil passage 9 and is discharged to the primary side of the unload valve 10 and a part of the pump discharge pressure is discharged to the open side port 10 a of the unload valve 10. To be done. The pump discharge pressure P _P and the tank pressure P _{T of the} oil passage 21 act on the open side port 10a of the unload valve 10, and the maximum load pressure P _LS is applied to the close side port 10b of the unload valve 10. The pressure P _{k of the} spring 12 and the pressure P _S of the signal pressure oil passage 20 act. That is, the pressure balance expressed by the following equation is obtained.

[0014]

[Equation 1]

In normal operation, the pressure difference between the pump discharge pressure and the maximum load pressure (P_P-P_LS) Is the pressure P of the spring 12 due to the action of the pump regulator 8._kSince it is set as follows, the unload valve 10 is in the closed state and will not be unloaded. The load pressure of the actuator 6 becomes small, and the differential pressure (P _P -P_LS) Is the pressure P of the spring 12_kWhen it exceeds, as shown in the graph of FIG. 2, the unload valve 10 is opened to start unloading. The differential pressure (P_P-P_LS) Becomes larger, the unloading flow rate Q gradually increases, but part of the oil that has passed through the unloading valve 10 passes through the signal pressure oil passage 20 to the closing side port 10b of the unloading valve 10. Derived. That is, since the primary pressure of the throttle 18 acts in the direction of closing the unload valve 10, an unnecessary increase in the unload flow rate Q is suppressed, and hunting of the unload valve 10 at a minute flow rate is prevented.

When the pressure P _S of the signal pressure oil passage 20, that is, the primary pressure of the throttle 18 rises to the set pressure of the relief valve 19, the relief valve 19 opens and the oil passing through the unload valve 10 is throttled. It returns to the tank 11 via 18 and the relief valve 19. The set pressure of the relief valve 19 is set so that the opening pressure of the unload valve 10 becomes almost the same as the conventional one. Then, after the relief valve 19 is open, the differential pressure _(P P -P _LS) is unloaded state while maintaining the substantially constant value.

The present invention can be variously modified without departing from the spirit of the present invention, and it goes without saying that the present invention extends to the modified one.

[0018]

[Effect of device]

 As described in detail in the above one embodiment, the present invention controls the opening of the unloading valve by the throttle and the relief valve provided on the secondary side of the unloading valve, so that unnecessary unloading at a minute flow rate is performed. The increase in load flow rate is suppressed. Therefore, the unloading valve is prevented from opening rapidly and pressure hunting is prevented, and the operation of the load sensing hydraulic circuit is smoothly performed.

Thus, the operability of the operator is improved, the fatigue of the operator is reduced, and the like, and the invention has various practical values.

[Brief description of drawings]

FIG. 1 is a load sensing hydraulic circuit diagram of an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the differential pressure between the pump discharge pressure and the maximum load pressure, and the unload flow rate.

FIG. 3 is a conventional load sensing hydraulic circuit.

[Explanation of symbols]

1 Hydraulic Pump 2 Discharge Oil Path 6 Actuator 9 Oil Path 10 Unload Valve 10a Open Port 10b Closing Port 11 Tank 12 Spring 18 Throttling 19 Relief Valve P _P Pump Discharge Pressure P _LS Actuator Maximum Load Pressure P _S Signal Pressure Oil Line pressure P _T Tank pressure P _k Spring pressure

Claims (1)

[Scope of utility model registration request] 1. An actuator is connected to a discharge oil passage of a hydraulic pump via a directional control valve, a load pressure of the actuator is led to a pump regulator, and the oil passage is branched from the discharge oil passage to form an unload valve. In the load sensing hydraulic circuit, which is provided so that the discharge pressure of the hydraulic pump is derived to the open side port of the unload valve, the spring is installed at the close side port of the unload valve, and the load pressure of the actuator is derived. And a throttle valve and a relief valve are provided in parallel on the secondary side of the unload valve and connected to the tank, the primary pressure of the throttle is led to the closing side port of the unload valve, and the secondary pressure of the throttle is unloaded. A load sensing hydraulic circuit characterized by being led to the open side port of the load valve.