JP3483345B2 - Hydraulic control device for hydraulic drive circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive circuit for an actuator for a construction machine or the like, and more particularly to a hydraulic control device capable of improving operational stability and safety when driving a large load in this type of circuit. It is about.

[0002]

2. Description of the Related Art Generally, since a hydraulic drive circuit of this kind operates a plurality of actuators having different loads at the same time, it is preferably constructed as a load-sensing control type hydraulic drive circuit excellent in so-called combined operability. .

That is, a load sensing control type hydraulic drive circuit (hereinafter simply referred to as a conventional hydraulic drive circuit)
4, the discharge line 14 of the variable displacement pump 12 equipped with the negative flow rate control type discharge flow rate control means 10
In addition, a plurality (two in the illustrated example) of the actuator operation lines 16 and 18 and the bypass line 20 are connected in parallel, and the operation lines 16 and 18 are connected to the closed center type switching valves 22 and 24 and the actuator 2 respectively.
6 and 28 are connected, and the individual and / or maximum load pressures of the actuators when the switching valves 22 and 24 are operated to drive the actuators 26 and 28 individually or simultaneously, respectively. It is arranged to detect via the selection means 34 and the highest load signal line 36.

On the other hand, the bypass line 20 is connected to the flow control valve 38 with pressure compensation and the pressure generating means 40, and the control pressure is supplied from the upstream side line 39 of the pressure generating means 40 (that is, between the control valve 38). 42, and the control pressure 42 is applied to the discharge flow rate control means 10 of the variable displacement pump 12 via its signal line 42, and the flow rate control valve 38 with pressure compensation is changed in its opening direction. The displacement pump discharge pressure 44 (the signal line 4
4) and the maximum load pressure in the closing direction is 3
6 (via its signal line 36) and a load spring 46
Are applied respectively.

The load detection lines 30 and 32 are returned to the return lines 48 and 5 at the neutral positions of the switching valves 22 and 24.
It is connected to the tank 52 via 0, and also the bypass line 2
The downstream of 0 is also connected to the tank 52 via the return line 54.

Therefore, this type of hydraulic drive circuit operates as follows. That is, first, when both switching valves 22 and 24 are in the neutral position, both switching valves 22 and 24 are shut off,
Since both load detection lines 30 and 32 are connected to the return lines 44 and 46 as described above, the pressure oil from the variable displacement pump 12 flows only to the bypass line 20 and the pressure of the maximum load detection line 36. Is held at a low pressure. Therefore, in the system of the bypass line 20, the pump discharge pressure oil passes through the pressure compensating flow control valve 38 (the control valve 38 operates via the signal line 44 thereof so that the pump discharge pressure 44 acts on the load spring 46). And the pressure control means 40 is reached, and the control pressure 42 of the upstream side line 39 has its characteristic (that is, the characteristic of increasing the control pressure Pp according to the bypass oil amount q) [ [See FIG. 5]. Therefore, the variable displacement pump 12 changes the pump discharge flow rate Qp to the negative flow rate control characteristic (that is, the discharge flow rate by applying the boosted control pressure 42 from the signal line 42 to the discharge flow rate control means 10). Qp decreases according to the control pressure 42) [see FIG. 7],
Holds to a minimum.

Therefore, next, in the above state, for example, one of the switching valves 22 is operated by a predetermined amount and the actuator 26 is operated.
Assuming the case of driving the engine, in this case, the load detection line 30 (and the maximum load detection line 36) is connected to the actuator operation line 16 via the in-valve throttle 22a. The pressure rises to a pressure approximately equal to the pressure of 14 (ie, the bypass line 20).

Accordingly, the flow rate control valve 38 with pressure compensation has its opening reduced to reduce the bypass oil amount q, the pressure control means 40 lowers the upstream side control pressure 42 thereof, and the discharge flow rate control means 10 is reduced. The discharge flow rate Qp of the pump 12 is increased, and as a result, the actuator 26 is driven in a predetermined state (that is, according to the operation amount of the switching valve 22). In this case, it is obvious that the above operation is adapted to the high load actuator side when both the switching valves 22 and 24 are operated to simultaneously drive the two actuators 26 and 28. As described above, according to this type of hydraulic drive circuit, a plurality of actuators having different loads can be favorably combined and operated.

[0009]

However, the conventional hydraulic drive circuit described above still has the following drawbacks.

That is, in the conventional hydraulic drive circuit, the actuator is driven in accordance with the operation amount of the switching valve, as described above. That is, in FIG. 7, the oil supply amount QA to the actuator is uniquely set (that is, via one QA-St line) only by the operation amount St of the switching valve regardless of the load pressure of the actuator. To be done. However, this is often pointed out as an inconvenience particularly in an actuator hydraulic drive circuit of a construction machine or the like that drives a large load, and its improvement has been strongly demanded.

That is, at the time of driving the heavy load, from the viewpoint of stability and safety of the operation, a relatively low speed operation (in other words, in the heavy load driving, the same operation of the switching valve is performed as compared with the light load driving. Regarding the amount St, it is desired to set the actuator supply oil amount QA small, and conversely, for the same actuator supply oil amount QA, set the switching valve operation amount St large. However, in the conventional hydraulic drive circuit, as is apparent from the above description (that is, the actuator supply oil amount QA is uniquely set only by the switching valve operation amount St), the above-mentioned demand is achieved. Was impossible.

Therefore, an object of the present invention is to provide a hydraulic control device for a hydraulic drive circuit which can set the amount of oil supplied to the actuator relating to the operation amount of the switching valve to a smaller value when driving a large load as compared to when driving a small load. To provide.

[0013]

In order to achieve the above object, a hydraulic control device for a hydraulic drive circuit according to the present invention includes a plurality of discharge lines of a variable displacement pump equipped with a negative flow control type discharge flow control means. When the actuator operation line and the bypass line are connected in parallel, a closed center type switching valve and an actuator are connected to the operation line respectively, and the switching valve is operated to drive the actuators individually or simultaneously. Detecting the individual and / or maximum load pressure of the actuator, connecting the flow control valve with pressure compensation and the pressure generating means to the bypass line, and detecting the control pressure from the upstream side of the pressure generating means, While applying the control pressure to the discharge flow rate control means of the variable displacement pump, In the hydraulic drive circuit configured to apply the variable displacement pump discharge pressure to the compensating flow control valve in the opening direction and to apply the maximum load pressure and the load of the load spring in the closing direction, the pressure compensation is performed. A load control device configured to reduce the load of the load spring in response to an increase in the discharge pressure of the variable displacement pump is provided in the load spring of the attached flow control valve.

In this case, the load control device can be composed of a differential pressure piston cylinder device having a control spring pressure chamber and a pump discharge pressure oil chamber on both sides.

[0015]

According to the present invention, the control pressure applied to the pump discharge flow rate control means of the load sensing control type hydraulic drive circuit is the load of the load spring of the pressure compensating flow control valve for controlling the control pressure. By configuring the control device to reduce the discharge pressure of the variable displacement pump according to the rise in the discharge pressure, the amount of oil supplied to the actuator related to the operation amount of the switching valve can be made smaller when driving a large load than when driving a small load. It becomes possible to set.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic control system for a hydraulic drive circuit according to the present invention will be described in detail below with reference to the accompanying drawings. For convenience of explanation, the same components as those of the conventional structure shown in FIGS. 4 to 7 are designated by the same reference numerals, and detailed description thereof will be omitted.

First of all, the construction and operation of the hydraulic drive circuit itself of the present invention is basically the same as the conventional one (FIG. 4). Therefore, this basic configuration and operation is fully understood by re-describing some of the conventional operations described above. That is, the basic operation of the hydraulic drive circuit of the present invention is as follows. In FIG. 1, for example, when the switching valve 22 is operated to drive the actuator 26, the load detection line 30 (and the maximum load detection line 36) is the valve. Since it is connected to the actuator operation line 16 via the inner throttle 22a, its pressure is increased to a pressure substantially equal to the pressure of the pump discharge line 14 (that is, the bypass line 20).

Accordingly, the pressure-compensated flow control valve 38 (via the previously boosted maximum deep pressure applied in the closing direction):
The opening degree decreases, the bypass oil amount q decreases (see FIG. 5), the pressure control unit 40 decreases the upstream control pressure 42, and the discharge flow rate control unit 10 controls the discharge flow rate Qp of the pump 12. As a result, the actuator 26 is driven in a predetermined state (according to the operation amount of the switching valve 22). That is, in FIG. 7, the oil supply amount QA to the actuator is set uniquely (that is, by one QA-St characteristic) only by the operation amount St of the switching valve regardless of the load pressure of the actuator. Is configured.

However, in the present invention, in the above configuration (or operation), the flow control valve 38 with pressure compensation is used.
The load spring 46 is provided with a load control device 60 that controls the load (spring force) Ff (see FIG. 2). That is,
The load control device 60 is formed by a cylinder device 70 having a control spring pressure chamber 64 having a control spring 62 and a differential pressure piston 68 having a pump discharge pressure oil chamber 66 on both sides. Then, the pump discharge pressure Pd is introduced into the pump discharge pressure oil chamber 66 via a signal line 72, and
The piston 68 is configured to act on the load spring 46 of the flow control valve 38 with pressure compensation.

In this case, the spring force of the control spring 62 is set to be larger than the spring force of the load spring 46 so that the pressure in the pump discharge pressure oil chamber 66 (pump discharge pressure) Pd is relatively large. While the pressure is low, the piston 68 is brought into contact with the right end of the oil chamber 66 so as to hold the load spring 46 in the maximum compressed state. That is, in FIG. 2, the stroke amount Sc of the differential pressure piston 68 and the spring force (load) F of the load spring 46 with respect to the pump discharge pressure Pd.
The relationship of f is shown in the Pd-Sc and Pd-Ff characteristic diagrams, respectively.

Therefore, the hydraulic control system of the present invention operates as follows. That is, referring to FIG. 2, first, when the pump discharge pressure Pd is relatively low, the load spring 46 is compressed to the maximum and a high spring force Ff1 is applied, so the flow control valve with pressure compensation 38. For the switching valve 22
The pressure oil is supplied to the actuator 26 until the pressure of the maximum load detection line 36 is reduced to a pressure corresponding to the high spring force Ff1 or less as compared with the pump discharge pressure Pd by operating the.

However, the spring force Ff of the load spring 46 is
When the pump discharge pressure Pd is applied to (in the pump discharge pressure oil chamber 66 of) the load control device 60, the load control device 60 decreases to a low spring force Ff2. The amount of oil passing through the throttle 22a of 22 decreases slightly, and the sum of the pressure of the maximum load detection line 36 and the spring force Ff of the load spring 46 becomes lower than the pump discharge pressure Pd and passes through the control valve 38. Bypass oil amount q increases.

As a result, as shown in FIG. 3 (corresponding to FIG. 8 described above), the amount QA of oil supplied to the actuator with respect to the switching valve operation amount St is corresponding to each St-. QA characteristic diagram (St1-QA2 and St1-
QA1 characteristic diagram). That is, the actuator supply oil amount QA is set to be small (QA2) for a large load and large (QA1) for a small load even if the operation amount of the switching valve is the same St1.

As described above, in the present invention, the amount of oil supplied to the actuator relating to the manipulated variable of the switching valve can be set smaller when driving a large load than when driving a small load. In the heavy-duty hydraulic drive circuit described above, it is possible to effectively eliminate the feeling of strangeness in operation. Therefore, according to the present invention, the operability and safety in this type of hydraulic drive circuit can be greatly improved. Further, the hydraulic control device of the present invention has an advantage that it can be easily applied to this type of hydraulic drive circuit.

Next, the opening / closing shutoff valve 80, which is indicated by a chain line in FIG. 1 for convenience, shows another embodiment of the present invention. That is, the opening / closing cutoff valve 80 is provided on the signal line (pressure oil supply line) 72 to the load control device 60, and is configured to be opened / closed by the external signal 82.

Therefore, this embodiment has the advantage that the load control device 60 can be operated as required.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and many design changes can be made without departing from the spirit of the present invention.

[0028]

As described above, the hydraulic control device for the hydraulic drive circuit according to the present invention is, in summary, a load sensing control type equipped with a control device including a flow control valve with pressure compensation on a bypass line. In the hydraulic drive circuit, the load spring of the flow control valve with pressure compensation is provided with a load control device configured to reduce the load of the load spring in response to an increase in the discharge pressure of the variable displacement pump. As for the control pressure applied to the pump discharge flow rate control means of the hydraulic drive circuit, it is possible to set the amount of oil supplied to the actuator with respect to the operation amount of the switching valve to be smaller when driving a large load than when driving a small load. Become.

Therefore, according to the present invention, it is possible to effectively eliminate the uncomfortable feeling of operation especially in a heavy load hydraulic drive circuit of a construction machine or the like. That is, the operability and safety of this type of hydraulic drive circuit can be greatly improved. Further, the hydraulic control device of the present invention has a great advantage that it can be easily applied to this type of hydraulic drive circuit.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic control device for a hydraulic drive circuit according to the present invention.

FIG. 2 is a diagram showing a relationship between a stroke amount Sc of a differential pressure piston and a spring force (load) Ff of a load spring with respect to a pump discharge pressure Pd in the hydraulic control system shown in FIG.
It is a Pd-Ff characteristic diagram.

FIG. 3 is a St-QA (ST1-QA2 and St1-QA1) characteristic line showing the relationship between the switching valve operation amount St and the oil supply amount QA to the actuator in the hydraulic control device shown in FIG. It is a figure.

FIG. 4 is a hydraulic circuit diagram showing a general load sensing control hydraulic drive circuit.

5 is a q-PP characteristic diagram showing the relationship between the pump signal line pressure PP and the bypass oil amount q in the pressure generating means of the hydraulic drive circuit shown in FIG.

6 is a PP-QP characteristic diagram showing the relationship between the pump signal line pressure PP and the pump discharge flow rate QP in the variable displacement pump of the hydraulic drive circuit shown in FIG.

FIG. 7 is a St-QA characteristic diagram showing the relationship between the switching valve operation amount St and the oil supply amount QA to the actuator in the hydraulic drive circuit shown in FIG.

[Explanation of symbols]

10 Discharge flow rate control means 12 Variable displacement pump 14 Discharge line 16, 18 Actuator operation line 20, bypass line 22, 24 Closed center type switching valve 26, 28 actuator 30, 32 Load detection line 34 High voltage selection means 36 Maximum load detection line 38 Flow control valve with pressure compensation 39 Upstream pressure (line) 40 Pressure generating means 42 Pump control pressure (signal line) 44 signal line 46 load spring 48, 50, 52 Return line 52 tank 60 load control device 62 control spring 64 control spring pressure chamber 66 Pump discharge pressure oil chamber 68 Differential pressure piston 70 Differential pressure piston cylinder device 72 signal line 80 open / close shutoff valve 82 External signal line

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F15B 11/00 E02F 9/22

Claims (3)

(57) [Claims] 1. A plurality of actuator operation lines and a bypass line are connected in parallel to a discharge line of a variable displacement pump equipped with a negative flow rate control type discharge flow rate control means, and each of the operation lines has a closed center type switching valve and the same. An actuator is connected downstream, and the switching valve is operated to detect the individual and / or maximum load pressure of the actuator when the actuator is driven alone or simultaneously, and the bypass line has a flow control valve with pressure compensation. And the pressure generating means are connected, the control pressure is detected from the upstream side of the pressure generating means, the control pressure is applied to the discharge flow rate control means of the variable displacement pump, and the flow control valve with pressure compensation is also provided. Is applied with the variable displacement pump discharge pressure in the opening direction, and In a hydraulic drive circuit configured to apply the maximum load pressure and the load of the load spring, the load spring of the variable displacement pump is applied to the load spring of the flow control valve with pressure compensation according to the increase of the discharge pressure of the variable displacement pump. A hydraulic control device for a hydraulic drive circuit, wherein a load control device configured to reduce the load is provided. 2. The hydraulic control device for a hydraulic drive circuit according to claim 1, wherein the load control device comprises a differential pressure piston cylinder device having a control spring pressure chamber and a pump discharge pressure oil chamber on both sides. 3. The hydraulic control device for a hydraulic drive circuit according to claim 2, wherein the differential pressure piston cylinder device has an opening / closing cutoff valve on a pressure oil supply line to the pump discharge pressure oil chamber.