JP2677880B2 - Load sensing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a load sensing circuit using a variable discharge pump, and in particular, a pilot relief valve that regulates the maximum pressure and a peak cut valve that absorbs a surge of load side hydraulic pressure. The present invention relates to an improvement of a load sensing circuit provided with.

[Conventional technology]

Conventionally, there is a load sensing circuit of this type as shown in FIG.

This load sensing circuit supplies the discharge oil from a variable discharge pump (hereinafter simply referred to as “pump”) 1 to a load device 7 via an electromagnetic flow control valve 2, and the pump side hydraulic pressure P _S of this flow control valve 2 is supplied. The discharge amount of the pump 1 is controlled by the load sensing valve 3 that operates according to the pressure difference between the load side hydraulic pressure P _L and the load side hydraulic pressure P _L.

Furthermore, a pilot relief 4 for releasing the discharge oil of the pump 1 when the pump side hydraulic pressure P _S reaches a set value, and a pressure control for detecting the flow to the pilot relief valve 4 and controlling the discharge amount of the pump 1. A valve 5 and a peak cut valve 6 that absorbs the surge of the load side oil pressure P _L are provided, and its vent line 13 is introduced to the inlet side of the pilot relief valve 4 via a load sensing line 14 to adjust the peak cut pressure. I have to. In addition, 8 is a tank.

The load sensing valve 3 introduces the pump side hydraulic pressure of the flow rate control valve 2, that is, the hydraulic pressure P _S of the discharge line 10 and the load side hydraulic pressure, that is, the hydraulic pressure P _L of the output line 11 as pilot pressure, and the differential pressure ΔP = P _L -P _{When S} is smaller than a predetermined value, the ports a and b conduct as shown in the drawing, and the oil in the control cylinder 1a of the pump 1 is drained to the tank 8 through the line 12 to increase the discharge amount.

On the contrary, when the differential pressure ΔP becomes larger than the predetermined value, the spool overcomes the spring 3a and moves, and the ports a and c are brought into conduction, and the pump side hydraulic pressure P _S is passed through the line 12 to the control cylinder 1a of the pump 1. Introduce control hydraulic pressure by
Reduce the discharge rate.

When the differential pressure ΔP is near a predetermined value, the balance between the offset pressure and the differential pressure by the spring 3a causes the ports a and b to be balanced.
And c are made to conduct little by little, and the control hydraulic pressure is introduced into the control cylinder 1a of the pump 1 while partly escaping to the tank 8.
The discharge flow rate is controlled to be substantially constant.

The peak cut valve 6 does not open during normal pressure control by the pilot relief valve 4, and the pilot relief valve 4 does not open.
A large amount of flow is generated in the output line 11, and the peak pressure is generated in the output line 11 to increase the amount of oil flowing to the orifice 6a of the peak cut valve 6, and the cracking pressure is applied to the spring 6b so that it opens when the differential pressure across it increases. It is set higher than usual.

When the load 7 is, for example, an injection cylinder of an injection molding machine, when the speed control process by the flow rate control ends and the pressure control process appears, the peak cut valve 6 operates in the conversion process, and the set value of the pilot relief valve 4 is changed. Suppress the peak amount.

At the pressure control step, the value is controlled by the pilot relief valve 4.

[Problems to be solved by the invention]

However, in such a conventional load sensing circuit, the hydraulic pressure of the discharge line 10 during the pressure control described above.
Since P _S is controlled by the total pressure of the pressure control valve 5 and the pilot relief valve 4, there is a problem that the value cannot be reduced sufficiently.

For example, if the minimum pressure of the pilot relief valve 4 is 4k and the differential pressure generated in the orifice 5a of the pressure control valve 5 is 6k, the hydraulic pressure P _S of the discharge line 10 is 10k.

Since hardly entail the flow rate control valve 2 at the time of pressure control, the minimum value of P _S = P _L, and the hydraulic pressure P _L of the output line 11 becomes 10k. This is not low enough.

The present invention has been made to solve such a problem, and in the load sensing circuit as described above, by using a peak cut valve capable of sufficiently lowering the cracking pressure, it is possible to obtain a higher pressure than conventional pressure control. The purpose is to enable low pressure control.

[Means for solving the problem]

In order to achieve the above object, the present invention, in the load sensing circuit as described above, sets the cracking pressure of the peak cut valve to a sufficiently low level and installs it in the outlet line of the flow control valve, and at the same time, switches it to the inlet side of the pilot relief valve. Is provided, the vent line of the peak cut valve is branched into two, one of the branch lines is guided to one port of the switching valve via a hydraulic resistor and a load sensing line, and the other branch line is switched to the above. By introducing this to the other port of the valve, the switching valve switches the inlet side of the pilot relief valve to the load sensing line during the load sensing operation, and to the vent line of the peak cut valve during the peak cut pressure control.

(Operation)

The load sensing circuit according to the present invention operates similarly to the conventional load sensing circuit during the load sensing operation in which the inlet side of the pilot relief valve is connected to the load sensing line by the switching valve.

During peak cut pressure control in which the inlet side of the pilot relief valve is connected to the vent line of the peak cut valve by the switching valve, the cracking pressure of the peak cut valve is set low, and the flow rate to the pilot relief valve also changes from the orifice of the peak cut valve. Since there is only the flow rate, the minimum pressure of the pilot relief valve also drops, and the oil pressure in the output line can be made extremely low.

At this time, the flow rate control by the load sensing valve is also effective, and the pressure control can be performed while controlling the flow rate.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a load sensing circuit according to a first embodiment of the present invention. The same parts as those in the conventional example shown in FIG. 3 are designated by the same reference numerals, and their description will be omitted. To do.

This embodiment differs from the load sensing circuit shown in FIG. 3 in that the peak cut valve 20 connected to the output line 11 which is the outlet line of the flow control valve 2 has a sufficiently low cracking pressure due to the spring 20b. , For example 2
It is set to k.

Further, an electromagnetic switching valve 21 is provided on the inlet side of the pilot relief valve 4, the vent line 13 of the peak cut valve 20 is branched into two, and one branch line 13a thereof is connected to the check valve 2
3 is led to one port A of the switching valve 21 via the hydraulic resistor 22 and the load sensing line 14 constituted by the throttle 24, and the other branch line 13b is led to the other port B of the switching valve 21. ing.

The switching valve 21 switches the inlet side of the pilot relief valve 4 to the load sensing line 14 during the load sensing operation and to the vent line 13 of the peak cut valve 20 during the peak cut pressure control.

According to this embodiment, the cracking pressure of the peak cut valve 20 is reduced (for example, 4k from the peak cut valve 6 in FIG. 3).
The decrease) is achieved by setting the resistance value of the resistor 22 to the pressure value (for example, 4k) corresponding to the decrease.

Therefore, in the illustrated state in which the switching valve 21 is OFF, that is, in the load sensing operation, the same operation as the conventional example shown in FIG. 3 is performed.

Next, when the switching valve 21 is turned on, the load sensing line 14 is shut off and the branch line 13b from the vent line 13 of the peak cut valve 20 is connected to the pilot relief valve 4.

At this time, the cracking pressure of the peak cut valve 20 is set sufficiently low (for example, 2k) as described above,
The flow rate to the pilot relief valve 4 is the sum of the flow rates from both the orifice 6a of the peak cut valve 6 and the orifice 5a of the pressure control valve 5 in the example of FIG. Since it is only the flow rate of the orifice 20a, it is about half.

Therefore, the minimum pressure of the pilot relief valve 4 is
In the example of FIG. 3, it was 4k, but in this embodiment it is 2k, for example.
And the minimum pressure of the output line 11 becomes 2k + 2K = 4k, which is much lower than 10k in the example of FIG.

In this example, the pump 1 is controlled by the load sensing valve 3, and the hydraulic pressure P _S of the discharge line 10 thereof corresponds to the set pressure of the load sensing valve 3, for example, 6 k is the hydraulic pressure P _{L of the} output line 11.
The flow rate is normally controlled by the flow rate control valve 2.

Therefore, during this pressure control, the flow rate can be made sufficiently low, that is, the flow rate to the peak cut valve 20 can be reduced, and the control pressure can be further decreased.

The check function of the check valve 23 of the resistor 22 prevents the pressure oil from the discharge line 10 from joining the branch line 13b via the orifice 5a of the pressure control valve 5.

By the way, the hydraulic unit is normally stably operated at 40 to 50 ° C., but at the time of warming up when restarting the operation after being stopped for a long time, the peak cut valve 20 can also be used as a temperature raising relief valve. The oil temperature of the unit can be raised in a short time.

FIG. 2 is a hydraulic circuit diagram showing a load sensing circuit of a second embodiment of the present invention. The same parts as those of the first embodiment shown in FIG. Is omitted.

The second embodiment differs from the first embodiment described above in that a sequence valve 25 having a predetermined cracking pressure is used as a hydraulic resistor.

Since the response of the peak cut valve 20 changes somewhat depending on the capacity of the pilot relief valve 4, when the capacity of the pilot relief valve 4 is large (a large amount of flow can be made to flow with a small override), the sequence valve as in the second embodiment is used.
The response of the peak cut valve 20 becomes faster when 25 is used.

The hydraulic resistor may be composed of a sequence valve and a throttle.

〔The invention's effect〕

As described above, according to the present invention, it is possible to perform the minimum pressure control which cannot be realized by the conventional load sensing circuit.

Further, the pressure control can be performed while the flow rate is controlled, the peak cut function is excellent, and the peak cut valve can also perform the relief function when the temperature is raised.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a hydraulic circuit diagram of a conventional load sensing circuit. 1 ... Variable discharge pump, 2 ... Flow control valve 3 ... Load sensing valve 4 ... Pilot relief valve 5 ... Pressure control valve, 6,20 ... Peak cut valve 7 ... Load device, 8 ... Tank , 10 ...... Discharge line 11 …… Output line, 13 …… Vent line 14 …… Load sensing line 21 …… Switching valve, 22 …… Hydraulic resistor 23 …… Check valve, 24 …… Throttle 25 …… Sequence Valve (hydraulic resistor)

Claims (4)

(57) [Claims] Claim: What is claimed is: 1. Discharge oil from a variable displacement pump is supplied to a load via a flow control valve, and the pump is driven by a load sensing valve that operates according to the differential pressure between the pump side hydraulic pressure and the load side hydraulic pressure of the flow control valve. The discharge amount of the pump is controlled, and the discharge amount of the pump is detected by detecting the flow to the pilot relief valve for releasing the discharge oil of the pump when the hydraulic pressure on the pump side reaches a set value. In a load sensing circuit provided with a pressure control valve to control and a peak cut valve that absorbs the surge of the load side hydraulic pressure, the cracking pressure of the peak cut valve is set to a sufficiently low level and is provided in the outlet line of the flow control valve. A switching valve is provided on the inlet side of the pilot relief valve, and the vent line of the peak cut valve is branched into two. Through a hydraulic resistor and a load sensing line to one port of the directional control valve, and the other branch line to the other port of the directional control valve, through which the pilot relief valve The load sensing circuit is characterized in that the inlet side is switched to the load sensing line during a load sensing operation and to the vent line of the peak cut valve during pressure control by the peak cut valve. 2. The load sensing circuit according to claim 1, wherein the hydraulic resistor is constituted by a check valve and a throttle. 3. The load sensing circuit according to claim 1, wherein the hydraulic resistor is a sequence valve. 4. The load sensing circuit according to claim 1, wherein the hydraulic resistor comprises a sequence valve and a throttle.