JPS60250131A - Oil pressure control circuit - Google Patents

Abstract

PURPOSE:To raise the inching characteristics of a boom by a method in which the pilot pressures of a pilot pressure-powered boom and other control valves are directed through a shuttle valve to the switch valve of the bleed-off circuit of an oil-pressure pump for control. CONSTITUTION:An oil-pressure pump P is connected in parallel to a slewing control valve, an arm control valve and boom control valves 13, 14 and 15 and connected through a switch valve 33 to a tank T for bleeding-off. Control valves 13-15 are each connected to pilot pressure type control levers 19-21, and the pilot pressures of the arm and slewing control operating levers 19 and 20 are led to a shuttle valve 25. The pilot pressure of the operating lever 22 for controlling the boom and the shuttle valve 25 are connected to a shuttle valve 26 which controllably switches the switch valve 33. The control characteristics of the switch valve are, therefore, varied when the boom is in operation or not in operation, and the inching characteristics of the boom can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic control circuit in which a plurality of center-closed switching valves are connected, and inching characteristics can be obtained in accordance with the function of an actuator connected to each of these switching valves.

(Industrial Field of Application) The present invention is most suitable, for example, as a hydraulic control circuit for a construction vehicle such as a power shovel in which a traveling motor, a packet cylinder, a boom cylinder, etc. are operated by one pump.

(Prior Art) FIG. 4 shows a control circuit used in a conventional construction vehicle, in which a parallel feeder 12 is connected to a main passage 11 connected to a variable displacement pump P.

The parallel feeder 12 has a traveling motor 1.
A switching valve 13 for controlling the cylinder 6, a switching valve 14 for controlling the packet cylinder 17, and a switching valve 15 for controlling the boom cylinder 18 are connected, and each of these switching valves 13 to 15 is of a center closed type.

Pilot operating mechanisms 19 to 21 that generate pilot pressure proportional to the amount of operation are connected to the pilot chambers of each of the switching valves 13 to 15 as described above.

Therefore, by operating the predetermined pilot operating mechanism,
A switching valve corresponding to the operating mechanism is switched in proportion to the operating amount. And the pilot operating mechanism 19-2
The pilot pressure generated by operating the shuttle valve 22
~24 and 25.28, the highest pressure among them is selected, and the regulator 2 of the variable displacement pump P
7 and the pilot chamber 28a of the bypass valve 28.

When the pilot pressure is introduced to the pressure regulator 27 as described above, the discharge amount of the variable displacement pump P is controlled in accordance with this pilot pressure.

In addition, the /hay pass valve 28 has its pilot chamber 28
A spring 29 is applied on the side opposite to a, and normally the fully open position shown in the figure is maintained. When the bypass valve 28 is held at the fully open position, the bypass passage 30 connected to the main passage 11 is communicated with the tank T. In this state, when the pilot pressure from the shuttle valve 26 acts on the pilot chamber 28a, the bypass valve 2 is switched against the spring 29. Therefore, if the pilot pressure is low, the bypass valve 28 will remain open for a while, but if the pilot pressure exceeds the set pressure,
The bypass valve 28 is completely closed.

Therefore, when each of the switching valves 13 to 15 is held at the illustrated neutral position, in other words, when none of the pilot operating mechanisms 18 to 21 is operated, the bypass valve 1
8 holds the fully open position shown, so that the variable displacement pump P
The lowest discharge amount is returned to the tank T via this bypass valve 28.

Then, in order to switch one of the switching valves from the above state, when the pilot operation mechanism corresponding to the switching valve is operated, the bypass valve is switched by the action of the pilot pressure at that time, but the bypass valve at that time is The opening degree of the valve is determined according to the pilot pressure.

For example, when the pilot operating mechanism is slightly operated to perform an inching operation on a certain actuator, the pilot pressure at that time is not so high, so the bypass valve 28
It remains in a certain state for some time. When the bypass valve 28 remains l/X for a certain period of time, a portion of the discharge amount of the variable displacement pump P is bled off to the tank T depending on its opening degree, so that the inching operability of the actuator is improved. get well.

In addition, the reference numeral 31 in the figure is a pyro pump that supplies pressure oil to each of the pilot operating mechanisms 19 to 21, and the supply pressure is kept constant by the action of a constant pressure relief valve 32. There is.

(Problems to be Solved by the Present Invention) In the conventional control circuit as described above, no matter which actuator is operated, if the pressure at that time is the same, the opening degree of the high pass valve is constant. , the inching characteristics of each actuator are the same.

However, there are those such as packet cylinders that do not place much importance on inching characteristics, and those such as boom cylinders that do not place much importance on inching characteristics.
．． In a power shovel that places importance on inching characteristics, there is a drawback that if the inching characteristics for all actuators are the same, as in the above-mentioned conventional type, the operability becomes poor.

Therefore, the present invention has been developed to solve the following problems when operating an actuator that emphasizes inching characteristics, such as a boom cylinder.
When another actuator, such as a packet cylinder, in which inching characteristics are not important, is operated, the control characteristics of the bypass valve are changed to obtain inching characteristics suitable for the actuator.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a plurality of center-closed type switching valves, and connects each of these switching valves to a variable displacement pump via a parallel feeder. on the other hand,
This variable displacement pump is also communicated with the tank via the Novei Pass valve, and when each of the switching valves is held in the neutral position, the Novei Pass valve is fully opened and the discharge amount of the variable displacement pump is returned to the tank. , when any of the above switching valves is switched, the bypass valve is switched in the direction of closing, and the opening degree of this bypass valve is adjusted according to the pilot pressure at this time to control the flow rate to be bleed off at that time. In a hydraulic control circuit that operates a specific actuator, the pilot pressure when operating a specific actuator acts on the bypass valve, and the pilot pressure when operating another actuator acts on this bypass valve. The configuration is such that the control characteristics are different.

(Operation of the present invention) Since the present invention is configured as described above, when a specific actuator, for example, a boom cylinder in a power shovel is actuated, and when another actuator, such as a packet cylinder, is actuated, Since the control characteristics of the bypass valves are made different, it is possible to obtain operability suitable for the actuator concerned.

(Embodiment of the present invention) The first embodiment shown in FIG. 1 is different from the conventional structure in the structure of the bypass valve 33, and the other structure is the same as the conventional structure. Therefore, common elements will be described with the same reference numerals as in FIG. 3.

Thus, the bypass valve 33 of the first embodiment has pilot chambers 33b and 33c4 provided at both ends of the spool portion 33a, and the pressure receiving area in the other pilot chamber 33c is 11 for the pressure receiving area in the pilot chamber 33b. The area is reduced, and a spring 34 is applied to the other reduced pilot chamber 33c.

One pilot chamber 33b of the bypass valve 33 configured as described above is connected to the shuttle valve 26 as in the prior art, while the other pilot chamber 33c is connected to the shuttle valve 24. Since this shuttle valve 24 is connected to the pilot operating mechanism 21, the boom cylinder 1
When the switching valve 15 is switched to operate the valve 8, the pilot pressure acts on the other pilot chamber 33c.

Now, if pilot pressure is not acting on either of the pilot chambers 33b and 33c, this bypass valve 3
3 is held in the fully open position shown in the figure by the action of a spring 34.

Then, when the seven actuators other than the boom cylinder 1 are operated, the pilot pressure at that time acts on one pilot chamber 33b, but no pressure acts on the other pilot chamber 33c.

Therefore, at this time, the opening degree of the bypass valve 33 is determined by the pilot pressure and the spring force of the spring 34, as in the prior art.

On the other hand, when the boom cylinder 18 is operated, pilot pressure is guided to both pilot chambers 33b and 33c of the bypass valve 33, regardless of whether other actuators are operated or not.

The acting force of the pilot pressure in the pilot chamber 33c is:
Coupled with the spring force of the spring 34, the pilot chamber 33
In this case, the sensitivity of the bypass valve 33 is reduced because it opposes the acting force at e. therefore,
Even with the same pilot pressure, the opening degree of the bypass valve 33 is different when the boom cylinder 18 is operated and when another actuator is operated, and the boom cylinder 18
When the bypass valve 33 is operated, the opening degree of the bypass valve 33 becomes larger.

FIG. 2 shows the relationship between the opening area of the bypass valve 33 and the pilot pressure acting on the pilot chamber 33b. In FIG. 2, the solid line a shows the characteristics when actuators other than the boom cylinder 18 are actuated, and the dotted line a shows the characteristics when the boom cylinder 18 is actuated.

As is clear from this FIG. 2, the boom cylinder 18
When activated, the pressure range until the opening area closes becomes wider than when other actuators are activated. Therefore, when operating the boom cylinder 18, the sensitivity of the inching operation is reduced, and the operation becomes easier.

In the above case, if the pilot pressure from the shuttle valve 26 becomes higher and higher, both pilot chambers 33b and 3
Since the difference in the acting force on 3c becomes larger, the bypass valve 33 will eventually be switched to the fully closed position.

The second embodiment shown in FIG. 3 has a constant ratio pressure reducing valve 3 between the shuttle valve 2G and the pilot chamber 35a of the bypass valve 35.
6 is interposed.

This gravity ratio pressure reducing valve 36 has a first pilot chamber 3 on one side.
&a, and on the opposite side from this first pilot chamber Ha,
Second pilot chamber 3fib and third pilot chamber 36c
has been established.

The first pilot chamber 38a is connected to the shuttle valve 2B, the second pilot chamber 313b is connected to the shuttle valve 24, and the third pilot chamber 3Bc is connected to the secondary side of the gravity ratio pressure reducing valve 36. I'm trying to guide the pressure.

Therefore, when actuators other than the boom cylinder 1 are operated, pilot pressure is not guided to the second pilot chamber 313b, but pilot pressure from the shuttle valve 26 is guided to the first pilot chamber 38a.

When pilot pressure acts on the first pilot chamber 38a as described above, the gravity ratio pressure reducing valve 36 operates to generate pressure on its secondary side. This pressure generated on the secondary side acts on the third pilot chamber 3θC, and through interaction with the pilot pressure acting on the first pilot chamber 313a,
The pressure reduction ratio of the secondary side pressure is specified, and the secondary side pressure thus specified acts on the pilot pressure of the bypass valve 35; The pilot pressure passes through the shuttle valve 24 to the second
It acts on the pilot chamber 311b. When the pilot pressure acts on the second pilot chamber 36b in this way, the pressure reduction rate of the constant ratio pressure reducing valve 36 changes from when the actuator other than the boot cylinder 1 is operated, and the pressure on the secondary side thereof is reduced. make low.

Therefore, when the boom cylinder 18 is actuated,
The force acting on the pilot chamber 35a of the bypass valve 35 is different from when other actuators are operated. In other words, when operating the boom cylinder 18,
Since the sensitivity of the bypass valve 35 is substantially lowered, its inching characteristics are improved as in the first embodiment.

In this second embodiment, the secondary side of the gravity ratio pressure reducing valve is connected to the regulator 27, but it goes without saying that the shuttle valve 26 may be directly connected to the regulator 27.

(Effects of the Present Invention) According to the present invention, the sensitivity of the bypass valve can be varied depending on the specific actuator to be operated, so that inching characteristics can be obtained depending on the actuator.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the first embodiment of this invention, Figure 2 is a graph showing the correlation between the opening degree of the bypass valve and the pilot pressure, and Figure 3 is a circuit diagram of the second embodiment. FIG. 4 is a conventional circuit diagram. P...Variable displacement pump, 12...Parallel feeder, 13-15...Switching valve, 18-18...Travel motor as actuator, packet cylinder, boom cylinder, 33.35...Bypass valve , T...tank. Representative Patent Attorney Nobuyuki Shima

Claims (1)

[Claims] A plurality of center-closed type switching valves are provided, and each of these switching valves is connected to a variable displacement pump via a parallel feeder, and when this variable displacement pump is also connected to a tank via a bypass valve, each of the switching valves described above is connected to the variable displacement pump via a parallel feeder. When the valve is held in the neutral position, the bypass valve is fully opened and the discharge amount of the variable displacement pump is returned to the tank, and when any of the switching valves is switched, the bypass valve is switched in the direction of closing, In a hydraulic control circuit that adjusts the opening degree of this bypass valve according to the pilot pressure at this time and controls the flow rate that is bleed off at that time, when the pilot pressure that operates a specific actuator acts on the bypass valve. , a hydraulic control circuit that makes the sensitivity of this bypass valve different depending on when the pilot pressure that operates the other 7 actuators acts on this bypass valve.