JPH08260522A - Hydraulic control device for hydraulic shovel - Google Patents

Abstract

PURPOSE: To improve working property by providing such a constitution as supplying a necessary pressure to an actuator even at the low speed operation of an engine in a hydraulic shovel in which a plurality of actuators are operated by one pump a control valve with bleed-off function. CONSTITUTION: When an engine 13 is generally operated, the pressure of a pilot pump 10 energizes spool stroke switching pistons 6, 6,... forward and regulates the strokes of spools 4, 4,... up to a prescribed position close to full stroke. When the spools 4, 4,... are switched to a state 4a and becomes situated in the prescribed position, a pump port P and a tank port T are laid in the state opened by a prescribed bleed-of quantity. When the speed of the engine 13 is low, the spool stroke switching pistons 6, 6,... are retreated, and the spools 4, 4,... are displaced to the full stroke.

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 hydraulic excavator, and more particularly to a hydraulic control device for a hydraulic excavator that operates a plurality of actuators with a single pump.

[0002]

2. Description of the Related Art A conventional hydraulic control device for a hydraulic excavator of this type will be described with reference to FIGS. As shown in FIG. 3, the plurality of actuators 1, 1, ... Is operated by one pump 3 via the control valve 2. In the control valve 2, a plurality of spools 4, 4, ... Corresponding to the plurality of actuators 1, 1 ,. In such a configuration in which one pump operates a plurality of actuators, when the maximum discharge amount of the pump is set in accordance with a certain one actuator, the speeds of other actuators may become too fast. Therefore, the control valve 2 has an oil passage for bypassing the hydraulic oil from the pump 3 to the tank 5 and bleeding off for each spool 4, 4 ... (The lower left pump port P and the upper left tank port T of the spool in the figure are connected. Oil passage, which will be referred to as "P-T oil passage" hereinafter).

When an equivalent circuit is drawn for each spool 4 by using a variable throttle symbol, an actuator inflow throttle portion P-C, an actuator outflow throttle portion CT and a pump are shown as shown in FIG.・ Throttle part for tank bypass P
-T (corresponding to the PT oil passage) and three throttle parts P-
It is composed of C, C-T, and P-T. Then, these throttle parts P-C, C-T, and P-T are opened and closed in association with each other according to the displacement of the spool 4. Therefore,
The throttle parts P-C, C-T, with respect to the displacement position of the spool 4,
The relationship between the P-T opening areas is shown in FIG. As shown by the chain double-dashed line in the figure, in the throttle portion P-T (P-T oil passage) for pump / tank bypass, the spool 4 has a full stroke with a scale of "8" (in FIG.
A constant amount (bleed-off amount) is opened even in the state of being located at a). Thus, the spools 4, 4 ...
Are switched to 4a, 4a, ..., the surplus of the hydraulic oil pressure-fed from the pump 3 to the actuators 1, 1 ... Passes through the P-T oil passage having the constant opening area and is short-circuited to the tank 5. Because it is circulated, actuators 1, 1
Will be optimally speed controlled.

[0004]

The supply pressure to the actuator is determined by the pump flow rate and the opening area of the P-T oil passage. So, when designing these hydraulic circuits,
The bleed-off amount required to obtain the optimum speed of the actuator, that is, the PT oil passage opening area when the spool is in full stroke, is set based on the time when the pump flow rate is maximized. Therefore, in such a hydraulic excavator, the bleed-off effectively functions when the engine is operating at high speed, but when the pump flow rate is very small, the hydraulic oil leaks more than necessary from the P-T oil passage, and the hydraulic pressure of the actuator is reduced. The pressure stops rising. Therefore, when the engine is operating at a low speed, the hydraulic excavator may not be able to be jacked up or may have insufficient power.

Therefore, in a hydraulic excavator in which a plurality of actuators are operated by a single pump via a control valve having a bleed-off function, the required pressure is supplied to the actuators even when the engine is operating at a low speed. Therefore, a technical problem to be solved in order to improve workability arises, and an object of the present invention is to solve the problem.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned problems. A plurality of actuators are operated by one pump via a control valve, and the control valve is Hydraulic control of a hydraulic excavator in which a plurality of spools corresponding to each of the plurality of actuators are provided in parallel, and a pump / tank bypass oil passage for bleed-off is provided for each spool. In the device, the control valve is provided with spool stroke restricting means, and the spool stroke restricting means restricts the spool stroke to a predetermined position near the full stroke only when the engine speed exceeds a predetermined value. In addition, when the spool is located at the predetermined position, the pump / tank bypass oil passage is Is opened by the lead-off amount, whereas,
A hydraulic control device for a hydraulic excavator in which the pump / tank bypass oil passage is closed when the spool is in the full stroke position.

[0007]

When the engine speed exceeds the predetermined value, the stroke of the spool is restricted by the spool stroke restriction means, and the spool can be displaced only to a predetermined position near the full stroke. When the spool is in the predetermined position, the P-T oil passage is open, so the hydraulic fluid is bleed off and the actuator speed is optimally controlled. On the other hand, when the engine speed becomes equal to or lower than the predetermined value, the regulation is released, so that the spool can reach the full stroke. When the spool is in the full stroke, the P-T oil passage is closed, so that bleed-off is not performed and the hydraulic fluid pressure-fed from the pump is fed to the actuator. Therefore, even if the pump flow rate is low because the engine speed is low, the pressure of the actuator can rise to the relief pressure. Thus, the lack of force of the hydraulic excavator during low speed operation is resolved and workability is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. For convenience of explanation, elements that are the same as those of the conventional example will be assigned the same reference numerals and explanation thereof will be omitted.

As shown in FIG. 1, the control valve 2 is provided with spool stroke switching pistons 6, 6 ... At one end of each spool 4, 4. Pilot oil passage 7 is provided in the spool stroke switching pistons 6, 6 ...
The solenoid valve 8 is extended through the. Normally, since the solenoid valve 8 is biased by the spring 9, the pressure of the pilot pump 10 is transmitted through the solenoid valve 8 to the spool stroke switching pistons 6 and 6.
Acting on ... Therefore, the spool stroke switching pistons 6, 6, ... Are urged forward and the spools 4, 4 ,.
2 is restricted to a predetermined position near a full stroke described later in FIG.

Further, a controller 11 is extended from the solenoid valve 8, and the controller 1 is further provided.
1, a rotation speed detector 12 is extended. The rotation speed detector 12 is mounted on an engine 13 of a hydraulic excavator,
The controller 1 detects the rotational speed of the engine 13
It outputs to 1. Then, the controller 11 is configured to excite the solenoid valve 8 to switch the direction when the rotation speed becomes equal to or lower than a predetermined value. The predetermined value is a value calculated in advance as the upper limit value of the engine speed at which the pressure of the actuators 1, 1 ... Does not rise to the relief pressure when the hydraulic oil is continuously bleed off.

When the direction of the solenoid valve 8 is switched, the pressure of the pilot pump 10 is shut off and the spool stroke switching pistons 6, 6 ... Retreat,
The stroke regulation of the spools 4, 4, ... Is released.

FIG. 2 shows the spools 4, 4 ... According to this embodiment.
Actuator inflow throttle P- with respect to the displacement position of
3 illustrates the relationship between the opening areas of C, the actuator outflow throttle portion CT, and the pump / tank bypass throttle portion PT (PT oil passage). The horizontal axis scale "8 (right end in the figure)" in the figure is a full stroke, and "7 (broken line in the figure)"
Is a predetermined position where the spools 4, 4, ... Can be displaced by the maximum amount when the strokes of the spools 4, 4 ,. As shown in the figure, the pump / tank bypass throttle portion P-T (P-T oil passage) has spool displacement positions "0 to 7".
The section is substantially the same as the conventional state, and at the displacement position "7", the actuators 1, 1 ... Are opened by a predetermined bleed-off amount B required for optimal control. On the other hand, when the displacement position exceeds "7", the opening area of the pump / tank bypass throttle portion P-T (P-T oil passage) sharply decreases and is completely closed at the full stroke "8". There is.

As described above, when the engine speed exceeds the predetermined value (during normal operation), the spool stroke switching pistons 6, 6, ... Are urged forward, so that the spools 4, 4 ,. Are switched to the states of 4a, 4a ..., The spools 4, 4, ... Are restricted in the displacement range and remain at the position "7" near the full stroke. At this time, since the P-T oil passage is opened by the predetermined bleed-off amount B, the surplus portion of the hydraulic oil pressure-fed from the pump 3 to the actuators 1, 1 ... Is bleed-off to the tank 5. It will be short-circuited and recirculated. In this way, the actuators 1, 1 ... Are optimally speed-controlled.

When the engine speed falls below a predetermined value and the working oil flow rate becomes small, the spool stroke switching pistons 6, 6 ... Retreat and the spools 4, 4 ,.
The stroke restriction of is released. Then, the spools 4, 4, ... Will reach a full stroke in the state of the switching positions 4a, 4a. At this time, since the P-T oil passage is completely closed, the entire amount of hydraulic oil is supplied to the actuators 1, 1 ... Without bleeding off.
Therefore, the pressure of the actuators 1, 1 ... Can reach the relief pressure even if the flow rate of the hydraulic oil is small,
It is possible to jack up without falling short of power.
Thus, the workability of the hydraulic excavator is improved.

As another embodiment of the spool stroke regulating means, the controller 11 and the rotation speed detector 12 are provided.
Instead of using the limit switch, the limit switch is interposed between the solenoid valve 8 and the throttle lever of the hydraulic excavator, and the limit switch is turned on when the throttle lever is returned to a predetermined position on the low rotation side.
Therefore, the solenoid valve 8 may be switched. Further, 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.

[0016]

As described in detail in the above one embodiment, the present invention provides the control valve with the spool stroke regulating means so that the spool stroke is regulated to a predetermined position near the full stroke during the normal operation, and the spool stroke is regulated. Is in the predetermined position, the P-T oil passage is opened by a predetermined bleed-off amount, and the regulation is released during low speed operation so that the spool can reach the full stroke. In position, the P-T oil passage is configured to be closed. Therefore, in normal operation, the hydraulic fluid is bleed off and the actuator is controlled at the optimum speed, whereas in low speed operation, bleed-off is not performed and the hydraulic fluid is supplied to the actuator in full quantity, so that the actuator obtains the required pressure be able to. In this way, the insufficient force of the hydraulic excavator during low speed operation is resolved and workability is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an oil pressure and control of the embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the spool displacement position and the opening area of the spool throttle portion in FIG.

FIG. 3 is a hydraulic circuit diagram showing a conventional example.

FIG. 4 is a hydraulic circuit diagram in which spools are converted into equivalent circuits by variable throttle symbols for each actuator.

5 is a graph showing the relationship between the spool displacement position and the opening area of the spool throttle portion in FIG.

[Explanation of symbols]

 1 Actuator 2 Control valve 3 Pump 4 Spool 5 Tank 6 Spool stroke switching piston 7 Pilot oil passage 8 Solenoid valve 9 Spring 10 Pilot pump 11 Controller 12 Rotation speed detector 13 Engine P Bleed-off pump port T Bleed-off tank port B Bleed off amount

Claims (1)

[Claims] 1. A plurality of actuators are operated by one pump via a control valve, and
The control valve is provided with a plurality of spools corresponding to the plurality of actuators in a one-to-one correspondence, and a hydraulic excavator in which a bleed-off pump / tank bypass oil passage is provided for each spool. In this hydraulic control device, the control valve is provided with spool stroke restricting means, and the spool stroke restricting means changes the spool stroke to a predetermined position near the full stroke only when the engine speed exceeds a predetermined value. When the spool is located at the predetermined position, the pump / tank bypass oil passage is opened by a predetermined bleed-off amount, while when the spool is located at the full stroke, the pump / tank bypass oil passage is opened. A hydraulic control device for a hydraulic excavator, characterized in that the road is closed.