JPH0874805A - Oil pressure control device for construction machine - Google Patents

Abstract

PURPOSE: To improve minute operatability and compound operatability by generating a pailot pressure which is changed according to rotating speed of an engine by an engine sensing valve, and leading the pilot pressure to a load sensing valve. CONSTITUTION: A variable pump 1 and a control pump 2 are rotating driven, and discharging pressure of the variable pump 1 is supplied from a pipe passage 3 to an actuator 6 such as a working mechine cylinder through a pressure compensation valve 4 and a main operating valve 5. An engine sensing valve 12 is provided so as to operate by discharging pressure of the control pump 2 which is changed according to rotating speed of the engine, pilot pressure which is changed according to rotation of the engine is generated by the valve 12, and pilot pressure is led into a load sensing valve 14. It is thus possible to improve minute operatability and compound operatability by controlling the discharging capacity of the variable pump 1 according to a load and engine rotating speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a construction machine such as a rough terrain crane.

[0002]

2. Description of the Related Art A construction machine having a conventional working machine is often operated while finely operating the working machine.
Therefore, various proposals have been made to facilitate fine operation of the working machine.

For example, in Japanese Unexamined Patent Publication No. Hei 2-261902, a construction machine equipped with at least one closed center switching valve and a load sensing system for varying the discharge oil amount of a pump according to the operation amount of the switching valve is disclosed. , The discharge capacity of the pump is changed by changing the additional force used for switching the switching valve that operates by the pump discharge pressure, the load pressure of the actuator, and the additional force of the spring. There has been proposed a hydraulic control device in which the fine control curve is made variable within the range of (1), the rotational speed of the engine is detected, and the discharge capacity of the pump is controlled according to the rotational speed of the engine.

According to the above hydraulic control device, even in one pump of the variable circuit of the discharge volume of the pump in the closed center load sensing system, the flow rate flowing to the actuator within the range of the fine control curve with respect to the stroke of the operating lever. The stroke is variable, and fine operation is possible when you want to move a little.
Further, even in the case of the maximum discharge amount of one pump, the discharge amount can be varied according to the fluctuation of the engine, so that the rotation of the pump is lowered in the engine even in the case of an actuator whose required flow rate is smaller than the maximum discharge amount of the pump. The turning speed changes accordingly and it matches the human sense, making the machine easier to use. Furthermore, since one pump and one valve can be used, the structure is simplified, and the space and space can be reduced, and the cost can be reduced.

[0005]

However, in the case of a construction machine, such as a rough terrain crane, which requires fine operability and combined operability of the working machine in the range of low idle to high idle of the engine, the above-mentioned conventional method is used. As with the hydraulic control device described in (1), it is difficult to perform fine operation while moving the working machine quickly, and the combined operability at low idle is inferior. is there.

That is, FIG. 1 is a diagram showing the relationship between the operating lever for operating the work implement operating valve, the stroke, and the work implement speed. Li indicates low idle, Hi indicates high idle, and during stroke S ₁ . Since the speed of the working machine cannot be controlled by accelerator work, the combined operation of the working machine must be performed within the shaded area in the figure, and there is a problem that the combined operability is poor.

Further, in the above-mentioned conventional hydraulic control device, the engine rotation speed is detected, and the discharge capacity of the pump is controlled according to the engine rotation speed. Therefore, the engine sensor for detecting the engine rotation speed. In addition, a controller for electrically controlling the discharge capacity of the pump in accordance with the detected rotation speed is required, resulting in a problem that the configuration is complicated and expensive. The present invention has been made in order to solve such a problem, and an object thereof is to provide a hydraulic control device for a construction machine, which has improved fine operability and combined operability, with a simple structure and at low cost.

[0008]

In order to achieve the above object, the present invention provides a variable pump and a control pump driven by an engine and an actuator operation by supplying the discharge pressure of the variable pump to the actuator. It operates by the main operating valve to be controlled and the differential pressure between the load pressure of the actuator and the discharge pressure of the variable pump, and controls the discharge capacity of the variable pump so that a flow rate according to the manipulated variable is discharged regardless of the load. In a hydraulic control device for a construction machine equipped with a load sensing valve, an engine sensing valve that operates according to the discharge pressure of a control pump that changes according to the engine speed is provided. Generate a changing pilot pressure, and this pilot pressure is used for the load sensing. By introducing into, but which is adapted to control the discharge capacity of the variable pump load and according to the engine speed.

A differential pressure valve is provided on the discharge side of the control pump to generate a differential pressure according to the engine speed,
The engine sensing valve is operated by this differential pressure.

[0010]

With the above structure, the pilot pressure corresponding to the engine speed acts on the load sensing valve to reduce the apparent flow gain in the low speed region of the engine, thereby improving the fine operability. Also, since the speed of the working machine can be controlled by the accelerator work over the entire stroke of the operation lever that operates the main operation valve, the combined operability is also improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings shown in FIG. FIG. 2 is a circuit diagram of a hydraulic control device mounted on a construction machine such as a rough terrain crane, in which 1 is a variable pump and 2 is a control pump. These variable pump 1 and control pump 2
Is rotated by an engine (not shown),
The discharge pressure PP of the variable pump 1 is the pressure compensation valve 4 from the line 3.
Also, it is supplied to the actuator 6 such as a working machine cylinder via the main operation valve 5.

Further, the discharge pressure of the control pump 2 is supplied to a pilot valve (not shown) via a differential pressure valve 8 and a relief valve 9 by a conduit 7, and the differential pressure valve 8 is also provided.
The differential pressure generated before and after is introduced to both ends of the spool 12a of the engine sensing valve 12 by the pilot lines 10 and 11, and the hydraulic pressure on the downstream side of the differential pressure valve 8 is set to the line 13
Accordingly, the discharge pressure PP of the variable pump 1 is introduced to the right end side of the spool 14a of the load sensing valve 14 via the engine sensing valve 12. The discharge pressure PP of the variable pump 1 is also introduced to the left end side of the servo cylinder 16 that controls the swash plate angle of the variable pump 1 and to the right end side of the servo cylinder 16 through the load sensing valve 14 by the conduit 17. At the same time, the load pressure PLS of the actuator 6 is introduced to the left end side of the spool 14a of the load sensing valve 14 through the conduit 18.

Next, the operation of the hydraulic control device configured as described above will be described with reference to the diagrams shown in FIGS. 3 and 4. The discharge pressure PP of the variable pump 1 driven by the engine is supplied to the main operating valve 5 via the pressure compensating valve 4, and the variable pump 1 is controlled by switching the main operating valve 5 by a pilot valve (not shown). Discharge pressure PP flows into the actuator 6 via the main operation valve 5, and the actuator 6 operates a working machine (not shown).

Further, the load pressure PLS of the actuator 6,
The discharge pressure PP of the variable pump 1 is the load sensing valve 14
The spool 14a of the load sensing valve 14 is switched by the pressure difference between the spool 14a of the variable pump 1 and the spool 14a of the load sensing valve 14 is switched by the servo cylinder 16 so that the required flow rate on the load side is discharged from the variable pump 1. The plate angle is controlled.

On the other hand, the discharge pressure of the control pump 2 is supplied to a pilot valve (not shown) via a differential pressure valve 8 and a relief valve 9, but the differential pressure generated before and after the differential pressure valve 8 is the pilot conduits 10, 11. Is introduced into both ends of the spool 12a of the engine sensing valve 12, and the spool 12a is switched as follows due to the differential pressure.

That is, when the engine speed increases and the discharge pressure of the control pump 2 increases, the differential pressure before and after the differential pressure valve 8 increases, and the spool 12a of the engine sensing valve 12 is moved to the left and the pipe The passage 13 is narrowed, and conversely, when the engine speed decreases, the spool 12a of the engine sensing valve 12 is moved to the right and the pipe passage 13 is opened. As a result, as shown in FIG. 3, the output pressure PSIG, which is inversely proportional to the engine speed, is supplied to the right side of the spool 14a of the load sensing valve 14 from the pipe line 13, so that the load sensing valve 14 discharges the variable pump 1. Output pressure PS from engine sensing valve 12 to pressure PP
The pressure difference between the pressure added with IG and the load pressure PLS (PP + PSI
The spool 14a is operated by (G-PLS), and the apparent flow gain at low engine speed is reduced.

For example, when finely operating a work machine such as a boom, the engine speed is reduced to low idle Li to adjust the flow rate supplied from the main operation valve 5 to the actuator 6. In the conventional operation, the main operation valve 5 is operated. Since the speed of the work machine is controlled according to the stroke of the operating lever,
The fine control of the work machine was not easy.

However, in the present invention, when the operation stroke of the main operation valve 5 is fixed to, for example, S ₂ as shown in FIG.
Rotate the engine by accelerator operation Low idle L
By controlling from i to high idle Hi, the speed of the work machine can be freely controlled. That is, the conventional hydraulic control device cannot control the speed of the working machine by the accelerator work during the stroke S ₁ of FIG. 1, but according to the present invention, the stroke S of FIG.
_In the range of _2, the work speed can be freely controlled by the accelerator work, so the work machine can be easily operated. Further, the combined operation of operating the work machine by simultaneously operating a plurality of actuators can be performed by the entire stroke of the operation lever for operating the main operation valve 5, so that the combined operability is also improved.

[0019]

As described above in detail, according to the present invention, since the speed of the working machine can be freely controlled by the accelerator work within the full stroke range of the operating lever for operating the main operating valve, the working machine is finely operated. In this case, the work machine can be finely operated by controlling the rotation of the engine with the accelerator work while the operation lever is fixed at an arbitrary position. As a result, the fine operability of the work implement is further improved, and the composite operability is also improved because the composite operation of operating the work implement by simultaneously operating a plurality of actuators can be performed with the entire stroke of the operation lever.

Further, the engine sensing valve is operated by the discharge pressure of the control pump, which changes according to the engine speed, to obtain the pilot pressure according to the engine speed, and the pilot pressure is introduced into the load sensing valve. Since the discharge capacity of the variable pump is controlled, the engine rotation sensor for controlling the conventional engine speed and the controller for electrically controlling the discharge capacity of the variable pump are not required. Since the whole structure is simple, it can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an operating lever stroke and a working machine speed in a conventional hydraulic control device for a construction machine.

FIG. 2 is a circuit diagram showing a hydraulic control device for a construction machine according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an engine speed and an output pressure of an engine sensing valve in a hydraulic control device for a construction machine according to an embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an operating lever stroke and a working machine speed in a hydraulic control device for a construction machine according to an embodiment of the present invention.

[Explanation of symbols]

 1 Variable Pump 2 Control Pump 5 Main Operating Valve 6 Actuator 8 Differential Pressure Valve 12 Engine Sensing Valve 14 Load Sensing Valve

Claims (2)

[Claims] 1. A variable pump 1 driven by an engine.
And a control pump 2, a main operation valve 5 that controls the operation of the actuator 6 by supplying the discharge pressure of the variable pump 1 to the actuator 6, and a difference between the load pressure of the actuator 6 and the discharge pressure of the variable pump 1. In a hydraulic control device for a construction machine, which includes a load sensing valve 14 which operates by pressure and discharges a flow rate according to a manipulated variable regardless of load, the engine rotation speed is increased. An engine sensing valve 12 that operates according to the discharge pressure of the control pump 2 that changes according to the number is provided, and this engine sensing valve 12 generates a pilot pressure that changes according to the number of revolutions of the engine. By introducing into the sensing valve 14, the discharge of the variable pump 1 according to the engine speed Hydraulic control system for a construction machine, characterized by controlling the amount. 2. The differential pressure valve 8 is provided on the discharge side of the control pump 2 to generate a differential pressure according to the engine speed, and the engine sensing valve 12 is operated by this differential pressure. Hydraulic control device.