JPH0681374A - Hydraulic control equipment for construction machinery - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a hydraulic control device capable of supplying a suitable amount of pressure oil to the hydraulic actuator according to the type of the front. [Structure] The pilot line 13 of the regulator 12 of the hydraulic pump 1 is connected to the shuttle valve 30, and the shuttle valve 30
The pressure Pa of the hydraulic oil introduced from the control valve 2 to the primary side of the throttle 10 is introduced into one of the input ports. When the manual switching valve 31 and the pilot control valve 32 are in the A position, the output pressure Pc of the pressure adjusting valve 33 is guided to the other input port of the shuttle valve 30. The pressure Pc is set higher than the minimum pressure of the primary side pressure Pa of the throttle 10, and the minimum pressure of the pilot line 13 is switched between the two stages of the tank pressure and the pressure Pc according to the switching position of the manual switching valve 31. The upper limit of the discharge capacity of the pump 1 is changed.

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 which replaces a front surface and performs various works.

[0002]

2. Description of the Related Art An example of a hydraulic control device used in a hydraulic excavator is shown in FIG. In the figure, 1 is a variable displacement hydraulic pump driven by a prime mover (not shown), 2 is a control valve for distributing the discharge oil of the hydraulic pump 1 to hydraulic actuators provided at various places of the hydraulic excavator,
The control valve 2 incorporates a plurality (three in the figure) of spools 3, 4, and 5. Reference numeral 6 is a remote control valve for switching the position of the first spool 3, and its operating lever 6s
Is operated in the A direction or the B direction, the oil discharged from the pilot hydraulic pump 7 is discharged from either one of the pilot valves 6a and 6b, and the operation amount of the operation lever 6a is changed to one of the pilot conduits 8a and 8b. The corresponding pressure rises. The first spool 3 moves from the neutral position to the A position or the B position according to the pressure difference between the pipelines 8a and 8b at this time, and the discharge oil of the hydraulic pump 1 is moved to the port by the flow rate corresponding to the moving amount of the spool 3. It is led to P1 or P2. Port P
The pressure oil guided to either 1 or P2 is supplied to either one of the oil chambers 9a and 9b of the hydraulic cylinder 9 that drives the front (not shown), and the operation direction and operation amount of the operation lever 6s of the remote control valve 6 are controlled. According to the rod 9c of the hydraulic cylinder 9
Expands and contracts.

When the operating lever 6s of the remote control valve 6 is in the neutral position, the first spool 3 is also in the neutral position, and the discharge oil of the hydraulic pump 1 is not supplied to the hydraulic cylinder 9 and the second and third spools 4 are not supplied. , 5 side is led. When the second and third spools 4 and 5 move from the neutral position to the A position or the B position, the discharge oil of the hydraulic pump 1 is supplied to the ports P3 to P6 by the flow rate corresponding to the moving amount, and the ports P3 to P are supplied.
The operation of the hydraulic actuator connected to 6 is controlled.

The hydraulic oil that has passed through the control valve 2 without being guided to the ports P1 to P6 is discharged to the tank line 11 via the throttle 10, and the pressure Pa on the primary side of the throttle 10 is the discharge capacity of the hydraulic pump 1. It is guided to the pilot line 13 of the regulator 12 that controls. Regulator 1
Reference numeral 2 reduces the tilt angle of the hydraulic pump 1 as the pressure in the pilot line 13 increases, thereby reducing the discharge capacity of the hydraulic pump 1. The pressure in the pilot line 13 increases as the flow rate of the hydraulic oil introduced to the primary side of the throttle 10 increases. Therefore, when all the spools 3 to 5 of the control valve 2 are in the neutral position, the pressure in the pilot line 13 becomes maximum and the discharge capacity of the hydraulic pump 1 becomes minimum,
As the spools 3 to 5 move toward the A position or the B position, the pressure in the pilot pipe line 13 decreases and the hydraulic pump 1
Discharge capacity increases. In the figure, 14 to 19 are relief valves that regulate the pressure of the hydraulic oil discharged from the ports P1 to P6.

[0005]

In the above-mentioned device, a plurality of fronts are selectively used according to the work purpose. However, since the rated flow rates of the hydraulic actuators driving these fronts are different from each other, the ports P1 and P2 are different. It is necessary to adjust the maximum flow rate of the pressure oil that is introduced to each front replacement. In order to limit the maximum flow rate to the ports P1 and P2, the movement amount from the neutral position of the first spool 3 to the A position or the B position is limited, or the prime mover rotational speed is lowered to reduce the discharge flow rate of the hydraulic pump 1 itself. Can be reduced.
However, according to the former, since the pressure oil is bypassed to the spools 4 and 5 side even when the first spool 3 is moved to the maximum, the output pressure of the ports P1 and P2 is reduced.
The set pressures of 4 and 15 may not be reached and the front rated output may not be obtained. In the case of the latter, there are different problems depending on whether the prime mover rotation speed is reduced only when the front is operating, or whether the prime mover rotation speed is reduced regardless of the front operation. If it is lowered only when the front is operating, the number of rotations of the prime mover will increase and decrease frequently, and noise will be annoying. Also,
It is also necessary to improve the responsiveness of the prime mover, and it is difficult to handle this with a turbocharged engine. If the prime mover speed is reduced regardless of the front operation, the rated horsepower of the prime mover cannot be obtained, and the front output is reduced.

As means for changing the flow rate of pressure oil to the front hydraulic actuator, as shown in FIGS. 7 and 8, two systems from the hydraulic pump 1 to the tank line 11 via the control valve 2 are prepared. , The pressure oil output from the control valve 2 of each system is supplied to the hydraulic cylinder 9A for the standard bucket, and the pressure oil output from the control valve 2 of one system is supplied to the hydraulic cylinder 9B having a small rated flow rate. Sometimes only oil is supplied. However, this means is effective only when the cylinder diameter of the hydraulic cylinder 9B is approximately half that of the hydraulic cylinder 9A, and cannot be applied to other cases.

An object of the present invention is to change the flow rate of the pressure oil supplied to the hydraulic actuator according to the type of the front without changing the flow rate of the pressure oil on the control valve side or adjusting the rotational speed of the prime mover. It is to provide a hydraulic control device capable of supplying a suitable amount of pressure oil to the hydraulic actuator.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1 showing an embodiment. The present invention relates to a variable displacement hydraulic pump 1 driven by a prime mover, and a hydraulic pressure for driving the hydraulic pump 1 to the front. A control valve 2 for controlling the supply of pressure oil to the actuator 9, and a pilot line in which the maximum pressure is generated when the control valve 2 is in the neutral position and the pressure decreases toward the minimum pressure as the neutral position is switched. It is applied to a hydraulic control device for a construction machine, which is provided with 13 and a pump displacement control means 12 that increases the discharge displacement of the hydraulic pump 1 based on the pressure in the pilot line 13 as the pressure decreases. The above-mentioned object is achieved by providing the pilot minimum pressure switching means 30 and 31 for switching the minimum pressure of the pilot line 13 in at least two stages.

[0009]

The minimum pressure of the pilot line 13 is set low when a hydraulic actuator having a large rated flow rate is installed, and the minimum pressure of the pilot line 13 is set high when a hydraulic actuator having a small rated flow rate is installed.
When the minimum pressure of the pilot line 13 increases, the upper limit value of the discharge capacity of the hydraulic pump 1 decreases, and the maximum flow rate of the pressure oil supplied to the hydraulic actuator decreases.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The same parts as those in the example shown in FIG. 6 described above are designated by the same reference numerals, and the description thereof will be omitted. This embodiment is intended for a hydraulic excavator in which a standard bucket and a front for dismantling a high place can be exchanged. FIG. 5 shows a state in which the front for dismantling a high place is attached. In the figure, reference numeral 100 is an upper revolving structure of a hydraulic excavator, and a front dismantling front 101 is attached to the front part thereof. Front 10 for dismantling high places
A boom 102, arms 103 and 104, and a gripper 105 are rotatably connected to each other. A hydraulic actuator (not shown) incorporated in the gripper 105 while controlling the attitude of the gripper 105 with hydraulic cylinders 106a to 106d. Then, the fingers 105a and 105b are opened and closed to grasp the wall of the building or the like, and the dismantling work is performed.

1 and 2 show a hydraulic circuit of this embodiment. In this embodiment, the pilot line 13 of the regulator 12 of the hydraulic pump 1 is connected to the output side of the shuttle valve 30. Shuttle valve 30 selects the larger pressure of primary pressure Pa of throttle 10 introduced to its input port and output pressure Pb of manual switching valve 31 and outputs it to pilot line 13. The manual switching valve 31 is manually switched by the operating lever 31a, and its output pressure Pb changes based on the switching positions of the manual operating valve 31 and the pilot control valve 32. When both the manually operated valve 31 and the pilot control valve 32 are in the B position (see FIG. 2), the pressure Pc of the hydraulic oil discharged from the hydraulic pump 7 and reduced by the pressure adjusting valve 33 is supplied from the manual switching valve 31. Is output. When either the manually operated valve 31 or the pilot control valve 32 is switched to the A position, the manual switching valve 3
The output side of 1 is opened to the tank, and the output pressure Pb becomes equal to the tank pressure.

The pilot control valve 32 is switch-controlled according to the operation of the operation lever 6s of the remote control valve 6. When the operating lever 6s is operated and the pressure rises in either one of the pilot conduits 8a and 8b, this pressure is applied to the shuttle valve 3
4 is selected and guided to the pilot line 35, and the pilot control valve 32 is switched to the B position. When the operation lever 6s is in the neutral position, the pressure in the pilot pipe line 35 becomes the tank pressure, and the pilot control valve 32 is switched to the A position.

The pressure regulating valve 33 has its pilot line 3
When the pressure of 3a exceeds a certain value, passage of pressure oil from the hydraulic pump 7 to the pilot control valve 32 is blocked, and the output pressure Pc is limited to a certain value. The output pressure Pc is set to a value lower than the maximum value Pmax of the primary side pressure Pa of the throttle 10 when the prime mover is rotated at a predetermined work speed and higher than the tank pressure.

When the standard bucket is used in the hydraulic control device having the above construction, the manual switching valve 31 is switched to the A position. As a result, the output pressure Pb of the manual switching valve 31 becomes equal to the tank pressure, so that the pressure Pa on the primary side of the throttle 10 is always output from the shuttle valve 30 and guided to the pilot conduit 13. Therefore, the control valve 2
When all the spools 3 to 5 are in the neutral position, the pressure in the pilot conduit 13 becomes maximum and the discharge capacity of the hydraulic pump 1 becomes minimum, and the spools 3 to 5 move toward the A position or the B position. The pressure in the pilot line 13 decreases and the discharge capacity of the hydraulic pump 1 increases.

When the aerial dismantling front 101 is mounted and the hydraulic cylinder 9 connected to the ports P1 and P2 of the control valve 2 is changed to one having a small rated flow rate, the manual switching valve 31 is changed as shown in FIG. Switch to B position. When the remote control valve 6 is operated to operate the front in this state, the first spool 3 moves accordingly to the A position or B position side, and the hydraulic cylinder 9 connected to the ports P1 and P2 starts operating. . At the same time, the pilot control valve 32
Is switched to the B position, and the output pressure Pc of the pressure adjusting valve 33 is guided to the shuttle valve 30.

Here, as shown in FIG. 3, the primary side pressure Pa of the throttle 10 decreases as the moving amount of the spool 3 increases, and becomes the minimum pressure Pt (tank pressure) at the maximum moving amount Smax, and manual switching is performed. The output pressure Pb of the valve 31 is constant at the output pressure Pc of the pressure regulating valve 33. Therefore, the manual switching valve 31 is set to B
When in the position, the pilot line 13 pressure is
From the start of the movement until the movement amount reaches a predetermined value Sc, it decreases according to the primary pressure Pa of the throttle 10.
The constant pressure Pc is maintained until the moving amount exceeds Sc and reaches the maximum moving amount Smax. Therefore, the displacement of the hydraulic pump 1 increases or decreases according to the decrease in the pressure Pa until the movement amount of the spool 3 reaches Sc, and the movement amount of the spool 3 becomes S.
After exceeding c, it is maintained at a constant value according to the pressure Pc.

When the discharge capacity of the hydraulic pump 1 changes as described above, the relationship between the moving amount of the spool 3 and the flow rate of the pressure oil supplied to the hydraulic cylinder 9 is as shown in FIG.
In the figure, Q1 indicates that when the manual switching valve 31 is in the A position,
Q2 shows a change when the manual switching valve 31 is in the B position. When the manual switching valve 31 is in the A position, the spool 3
Increase in the discharge capacity of the hydraulic pump 1 with respect to the increase in the movement amount of the hydraulic pump 1 and the port P of the control valve 2 from the hydraulic pump 1.
When the flow rate of pressure oil to the hydraulic cylinder 9 increases due to the increase in the opening of the flow path leading to P1 and P2, and the movement amount of the spool 3 reaches the maximum value Smax (the spool 3 is in the A position or the B position). (When completely switched to), the maximum flow rate becomes Qmax.

When the manual switching valve 31 is in the B position, the manual switching valve 3 is operated until the moving amount of the spool 3 reaches Sc.
The pressure oil flow rate to the hydraulic cylinder 9 increases along the change curve Q1 when 1 is in the A position. When the movement amount of the spool 3 exceeds Sc, the discharge capacity of the hydraulic pump 1 is fixed to a constant value, so that the flow rate of pressure oil to the hydraulic cylinder 9 is a flow path from the hydraulic pump 1 to the ports P1 and P2 of the control valve 2. It increases or decreases depending on the opening degree of. Therefore, when the displacement of the spool 3 reaches the maximum value Smax, the pressure oil flow rate Qc to the hydraulic cylinder 9 becomes smaller than the maximum flow rate Qmax by the fixed discharge capacity of the hydraulic pump 1.

The ratio between the maximum flow rate Qmax and the flow rate Qc is made equal to the ratio of the rated flow rates of the hydraulic cylinder of the standard bucket and the hydraulic cylinder of the front for dismantling a high place by adjusting the set pressure Pc of the pressure adjusting valve 33. It For example, when the cylinder diameter of the hydraulic cylinder at the front for disassembling a high place is 40% of the cylinder diameter of the hydraulic cylinder of the standard bucket, the pressure Pc is set so that Qc becomes 40% of Qmax. Therefore, when the manual switching valve 31 is in the A position, the spool 3
When the amount of movement of the valve reaches the maximum value Smax, the pressure oil having a flow rate equal to the rated flow rate of the hydraulic cylinder for the standard bucket is discharged from the port P1 or P2, and when the manual switching valve 31 is at the B position, the port P1 or P2. The pressure oil is discharged at a flow rate equal to the rated flow rate of the hydraulic cylinder on the front for dismantling a high place.

As is apparent from the above, in this embodiment, the pilot conduit 13 is operated by the switching operation of the manual switching valve 31.
Changes the minimum pressure of the hydraulic pump 1 to change the upper limit value of the discharge capacity of the hydraulic pump 1, which increases or decreases the maximum flow rate of the pressure oil supplied to the hydraulic cylinder 9. Therefore, when the rated flow rate of the hydraulic cylinder 9 is small, the spool It is not necessary to regulate the moving amount of 3 or reduce the rotation speed of the prime mover. Therefore, the conventional drawbacks such as insufficient output at the front and noise due to fluctuations in the engine speed are eliminated.

In the present embodiment, the minimum pressure in the pilot line 13 can be switched between two stages of the tank pressure Pt and the set pressure Pc of the pressure adjusting valve 33, but the present invention is not limited to this, and three stages are possible. Alternatively, it may be changeable more than that. For this purpose, for example, the pressure adjusting valve 33 may be a variable type, and the set value may be changed according to the rated flow rate of the hydraulic cylinder.
Further, in the embodiment, the manual switching valve 31 is manually switched according to the change in the rated flow rate of the hydraulic cylinder 9, but the switching valve 31 may be switched in conjunction with the replacement of the front.

In the above embodiment, the regulator 12 constitutes the pump displacement control means, and the shuttle valve 30 and the manual switching valve 31 constitute the pilot minimum pressure switching means.

[0024]

As described above, according to the present invention, the minimum pressure of the pilot line for controlling the discharge capacity of the hydraulic pump is increased when the hydraulic actuator for driving the front is changed to one having a small rated flow rate. With this, the upper limit of the discharge capacity of the hydraulic pump decreases and the pressure oil flow rate to the hydraulic actuator is reduced.Therefore, the control valve side bypasses the hydraulic pump discharge oil and limits the pressure oil flow rate to the hydraulic actuator. It is not necessary to increase or decrease the prime mover speed according to the rated flow rate of the hydraulic actuator. For this reason,
The front output does not decrease, the noise problem due to frequent changes in the prime mover speed is eliminated, and the engine's blow-up characteristics are not a problem.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram according to an embodiment of the present invention.

2 is a schematic diagram of the hydraulic circuit diagram of FIG.
The figure which shows the state which was switched.

3 is a diagram showing a relationship between a movement amount of a spool 3 built in the control valve 2 of FIG. 1 and a pilot pressure of a regulator 12 of the hydraulic pump 1. FIG.

FIG. 4 is a diagram showing a relationship between a movement amount of a spool 3 built in the control valve 2 of FIG. 1 and a flow rate of pressure oil to a front drive hydraulic cylinder 9;

FIG. 5 is a view showing a state in which a front for dismantling a high place is attached to the hydraulic excavator.

FIG. 6 is a conventional hydraulic circuit diagram.

FIG. 7 is another conventional hydraulic circuit diagram.

8 is a diagram showing a state in which the hydraulic circuit of FIG. 7 copes with a decrease in the rated flow rate of a hydraulic cylinder.

[Explanation of symbols]

 1 Hydraulic Pump 2 Control Valve 9 Hydraulic Cylinder for Front Drive 12 Regulator 30 Shuttle Valve 31 Manual Switching Valve 32 Pilot Control Valve

Claims (1)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a control valve for controlling the supply of pressure oil from the hydraulic pump to a hydraulic actuator for driving the front, and when the control valve is in a neutral position. Indicates that the maximum pressure is generated and the pressure decreases toward the minimum pressure as the neutral position is switched, and based on the pressure in this pilot line, the discharge capacity of the hydraulic pump increases as the pressure decreases. A hydraulic control apparatus for a construction machine, comprising: a pump displacement control means, wherein a minimum pilot pressure switching means for switching the minimum pressure of the pilot line in at least two stages is provided.