JP2006183727A - Load sensing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load sensing circuit capable of miniaturizing an unloading valve. <P>SOLUTION: The unloading valve 13 can switch an operating position for guiding a maximum pressure selecting line 8 to another chamber of a regulator 1, and an unloading position for guiding a pressure at an upstream side of switch valves 2, 3 to the maximum pressure selecting line 8. When the unloading valve 13 is located at the unloading position, the regulator 1 is operated by the action of high pressure of the maximum pressure selecting line to control a capacity of a variable discharge pump P to the minimum, and pressures of both pilot chambers of flow dividing valves 6, 7 are equalized to keep the flow dividing valves 6, 7 at a totally-enclosed position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a load sensing circuit having an unload function.

A load sensing circuit described in Patent Document 1 is conventionally known as this type. This conventional load sensing circuit has a structure in which a switching valve is provided upstream of the pressure compensation valve, and the actuator cannot be stopped unless the switching valve is returned to the neutral position.
JP-A-5-172108

Therefore, in the conventional load sensing circuit as described above, when the switching valve is stuck and cannot be returned to the neutral position, or the switching valve is inadvertently switched, the actuator operates. Will continue. In other words, in the conventional load sensing circuit, there is a problem that the actuator is activated although it is desired to stop or keep the actuator stopped.
An object of the present invention is to provide a load sensing circuit in which an actuator is not inadvertently operated by operating an unload valve.

  A first invention is provided with a variable discharge pump, a regulator for guiding the discharge pressure of the variable discharge pump to one chamber, a plurality of switching valves connected in parallel to the variable discharge pump, and a downstream side of the switching valve. A diversion valve and an actuator provided on the downstream side of the diversion valve. The pressure on the downstream side of the switching valve is introduced into one pilot chamber of the diversion valve, and the maximum pressure of each actuator is provided in the other pilot chamber. The pressure of the maximum pressure selection line is selected and the spring force of the spring is applied, and the shunt valve is configured to maintain the differential pressure before and after the opening of the switching valve at an amount corresponding to the spring force of the spring. Assumes a load sensing circuit.

  Based on the above circuit, the first invention provides an operating position for guiding the maximum pressure selection line to the other chamber of the regulator and an unloading position for guiding the pressure upstream of the switching valve to the maximum pressure selection line. When equipped with an unloading valve that can be switched, and when this unloading valve is in the unloading position, the regulator is operated by the high pressure of the maximum pressure selection line to control the tilt angle of the variable discharge pump and pump discharge The feature is that the amount is controlled to the minimum, and both the pilot chambers of the flow dividing valve are set to the same pressure to keep the flow dividing valve in the fully closed position.

  According to the first aspect of the invention, as long as the unloading valve is kept at the unloading position, the diversion valve keeps the fully closed position, so that the pressure fluid on the variable discharge pump side is inadvertently supplied to the actuator side. There is no danger.

  In the first embodiment shown in FIG. 1, a plurality of switching valves 2 and 3 are connected in parallel to a variable discharge pump P including a regulator 1. The actuators 4 and 5 are connected to the downstream side of the switching valves 2 and 3, and the diversion valves 6 and 7 are connected between the switching valves 2 and 3 and the actuators 4 and 5. The diversion valves 6 and 7 connect one of the pilot chambers 6a and 7a to the downstream side of the switching valves 2 and 3, connect the other pilot chamber 6b and 7b to the maximum pressure selection line 8, and The spring force of the springs 9 and 10 is applied to the pilot chambers 6b and 7b. The maximum pressure selection line 8 is used to guide the maximum load pressure selected between the plurality of actuators 4 and 5.

  The flow dividing valves 6 and 7 configured as described above control so that the required flow rate of the actuators 4 and 5 determined by the opening degree of the switching valves 2 and 3 is always constant regardless of the fluctuation of the load pressure. That is, the differential pressure before and after the switching valves 2 and 3 is controlled to be equivalent to the spring force of the spring 9. However, when the pressures in the pilot chambers 6a, 7a and 6b, 7b become the same, the diverter valves 6, 7 maintain the illustrated position by the spring force of the springs 9, 10, and the variable discharge pump P and the actuators 4, 5 Block communication with. In the figure, reference numerals 11 and 12 are check valves that allow only the flow from the switching valves 2 and 3 to the maximum pressure selection line 8.

The maximum pressure selection line 8 is connected to an unload valve 13, and the unload valve 13 is provided with a first port 13a, a second port 13b, and a third port 13c. The highest selection line 8 is connected to the first port 13a. The second port 13b is connected in parallel to one chamber of the regulator 1 and the tank T, and a communication process communicating with the second port 13b and the regulator 1, and a communication process communicating with the tank T, respectively. Are provided with orifices 14 and 15. The third port 13c is connected to the upstream side of the switching valves 2 and 3 and directly communicates with the variable discharge pump P.
The other chamber of the regulator 1 communicates with the upstream side of the switching valves 2 and 3.

  When the unload valve 13 as described above is in a non-excited state, the first port 13a and the third port 13c communicate with each other while maintaining the right position in the drawing, and the first port 13c communicates with the maximum pressure selection line 8. Then, the second port 13b is closed, and the third port 13c communicates with the upstream side of the switching valves 2 and 3. Therefore, when the unload valve 13 is in the right position shown in the figure, the variable discharge pump P communicates with the maximum pressure selection line 8.

  Further, when the unload valve 13 is in an excited state and switches to the left position in the drawing, the first and second ports 13a and 13b communicate with each other, and the first port 13a communicates with the maximum pressure selection line 8. The second port 13b communicates with one chamber of the regulator 1 and the tank T. The other chamber of the regulator is adapted to guide the discharge pressure of the variable discharge pump P. When the maximum pressure of the circuit from the maximum pressure selection line 8 is led to one chamber of the regulator 1 in this way, the regulator 1 causes the discharge pressure of the variable discharge pump P to be equal to the set pressure than the maximum pressure. The variable discharge pump P is controlled so as to increase.

Next, the operation of the first embodiment will be described.
When the actuators 4 and 5 are normally operated, the unload valve 13 is kept in an excited state, and the first port 13a and the second port 13b are kept in communication with each other. When the variable discharge pump P is driven in this state, the hydraulic oil discharged from the pump first flows into the pilot chambers 6a and 7a of the diversion valves 6 and 7 via the switching valves 2 and 3, respectively. Accordingly, the diversion valves 6 and 7 instantaneously switch to the fully open position, which is the right side position in the drawing, and supply the working fluid to the actuators 4 and 5.

When pressure fluid is supplied to the actuators 4 and 5, the maximum pressure selection line 8 generates a maximum pressure corresponding to the load at that time, and the pressure is applied to one chamber of the regulator 1 and the flow dividing valves 6 and 7. Guided to the other pilot chamber 6b, 7b.
Therefore, the variable discharge pump P discharges the working fluid that is higher than the maximum pressure by the set pressure as described above. Further, the diversion valves 6 and 7 are controlled so that the required flow rate of the actuators 4 and 5 determined by the opening degree of the switching valves 2 and 3 as described above is always constant regardless of the fluctuation of the load pressure.

  When the unloading valve 13 is de-energized from the above state and switched to the unloading position on the right side of the drawing, the second port 13b of the unloading valve 13 is closed. Kept. Therefore, the discharge amount of the variable discharge pump P is kept to a minimum. Moreover, in this state, the first port 13a and the third port 13c communicate with each other, so that the highest pressure selection line 8 is upstream of the switching valves 2 and 3 via the first and third ports 13a and 13c, that is, The variable discharge pump P communicates directly.

  Therefore, the pilot chambers 6a, 7a and 6b, 7b of the diversion valves 6, 7 have the same pressure. When the pilot chambers 6a, 7a and 6b, 7b are at the same pressure, the diversion valves 6 and 7 are switched to the closed position shown in the figure by the action of the springs 9 and 10, and fluid supply to the actuators 4 and 5 is blocked. Will be unloaded.

  When the unload valve 13 is energized and switched to the normal operation position on the left side of the drawing, the first port 13a and the second port 13b communicate with each other and the maximum pressure in the maximum pressure selection line 8 is guided to the regulator 1. At the same time, the third port 13c is closed, and the communication between the variable discharge pump P and the maximum pressure selection line 8 is blocked. Therefore, the regulator 1 controls the variable discharge pump P so that the discharge pressure of the variable discharge pump P is higher than the maximum pressure of the maximum pressure selection line 8 by a set pressure. In this state, the diversion valves 6 and 7 function so that the supply flow rate to the actuators 4 and 5 is constant regardless of the load pressure fluctuation.

In the first embodiment as described above, since the unload valve 13 only needs to control the flow of the maximum pressure selection line 8, the unload valve 13 may be a small valve. In addition, since the diversion valve 6.7 maintains the fully closed position in the unloaded state, the problem that the actuators 4 and 5 move carelessly does not occur.
Further, as long as the unloading valve is kept at the unloading position, the flow dividing valves 6 and 7 are kept at the closed position, so that the problem that the actuators g4 and 5 are inadvertently operated does not occur.

  In the second embodiment shown in FIG. 2, a standby flow rate unload valve 16 is provided on a line connecting the upstream side of the switching valves 2 and 3 and the second port 13b of the unload valve 13, and the other configurations are as follows. This is the same as in the first embodiment. The standby flow rate unload valve 16 communicates one pilot chamber 16 a upstream of the switching valves 2, 3, that is, the variable discharge pump P, and connects the other pilot chamber 16 b to the tank T and the unload valve 13. It communicates with the 2 port 13b.

  When the main unload valve 13 is kept at the unload position shown in the figure, the variable discharge pump P communicates with the maximum pressure selection line 8 and the pump discharge pressure is one pilot chamber 16a of the standby flow rate unload valve 16. Act on. Further, since the second port 13b of the main unload valve 13 is closed, the other pilot chamber 16b of the standby flow rate unload valve 16 communicates only with the tank T. Accordingly, the standby flow rate unloading valve 16 switches to the unloading position which is the right side of the drawing against the spring 17 and unloads the discharge fluid of the variable discharge pump P to the tank T. Therefore, the standby flow rate can be returned to the tank T, and the energy loss can be reduced.

  Further, when the main unload valve 13 is kept at the normal operation position, the second port 13b of the unload valve 13 communicates with the maximum pressure selection line 8 via the first port 13a. The pressure of the highest pressure selection line 8 is guided to the other pilot chamber 16b. At this time, the pump discharge pressure is guided to one pilot chamber 16a of the standby flow rate unload valve 16, but the spring force of the spring 17 is added to the other pilot chamber 16b. The load valve 16 maintains a closed position which is a left position in the drawing. Accordingly, the discharge fluid of the variable discharge pump P is not returned to the tank T, but is in a normal operation state where it is supplied to the actuators 4 and 5.

It is a circuit diagram of a 1st embodiment. It is a circuit diagram of a 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Regulator P Variable discharge pump 2,3 Switching valve 5,6 Split flow valve 6a, 7a One pilot chamber 6b, 7b The other pilot chamber 8 Maximum pressure selection line 9,10 Spring 13 Unload valve 16 Standby flow unload valve

Claims (2)

  A variable discharge pump; a regulator for guiding the discharge pressure of the variable discharge pump to one chamber; a plurality of switching valves connected in parallel to the variable discharge pump; a diversion valve provided downstream of the switching valve; An actuator provided on the downstream side of the diversion valve, and the highest pressure selection that guides the pressure on the downstream side of the switching valve to one pilot chamber of the diversion valve and selects the highest pressure of each actuator in the other pilot chamber In the load sensing circuit configured to guide the pressure of the line and apply the spring force of the spring, and the diversion valve maintains the differential pressure before and after the opening of the switching valve to the amount corresponding to the spring force of the spring. An unloading position that enables switching between an operating position that leads the highest pressure selection line to the other chamber of the regulator and an unloading position that leads the pressure upstream of the switching valve to the highest pressure selection line. When the unload valve is in the unload position, the regulator is operated by the high pressure of the maximum pressure selection line to control the pump discharge to a minimum, and both pilot chambers of the shunt valve Load sensing circuit configured to maintain the shunt valve in the fully closed position with the same pressure.   When the unloading valve is in the unloading position, a standby flow rate unloading valve for unloading the standby flow rate communicating with the tank is provided in a passage communicating the unloading valve at the unloading position and the upstream side of the switching valve. Item 1. The load sensing circuit according to Item 1.

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