JP2846532B2 - Hydraulic control device for construction machinery - 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 control device for a construction machine which performs various operations by replacing a front.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a hydraulic control device used for a hydraulic excavator. In the figure, reference numeral 1 denotes a variable displacement hydraulic pump driven by a prime mover (not shown), and 2 denotes a control valve for distributing the discharge oil of the hydraulic pump 1 to hydraulic actuators provided at various parts of a hydraulic shovel,
The control valve 2 incorporates a plurality (three in the figure) of spools 3, 4, and 5. Reference numeral 6 denotes a remote control valve for switching the position of the first spool 3, and its operation lever 6s
Is operated in the A direction or the B direction, the discharge oil of the pilot hydraulic pump 7 is discharged from one of the pilot valves 6a and 6b, and the operation amount of the operation lever 6a is transferred to one of the pilot lines 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 ported by a flow rate corresponding to the movement amount of the spool 3. It is led to P1 or P2. Port P
The pressure oil guided to one of P1 and P2 is supplied to one of oil chambers 9a and 9b of a hydraulic cylinder 9 for driving a front (not shown), and the operation direction and operation amount of the operation lever 6s of the remote control valve 6 are controlled. Rod 9c of the hydraulic cylinder 9 according to
Expands and contracts.

When the operation lever 6s of the remote control valve 6 is at the neutral position, the first spool 3 is also at the neutral position, and the discharge oil of the hydraulic pump 1 is not supplied to the hydraulic cylinder 9 without being supplied to the hydraulic cylinder 9. , 5 side. 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 a flow rate corresponding to the movement amount, and the ports P3 to P6
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 through the throttle 10, and the pressure Pa on the primary side of the throttle 10 determines the discharge capacity of the hydraulic pump 1. It is led to a pilot line 13 of a regulator 12 to be controlled. Regulator 1
2 reduces the displacement angle of the hydraulic pump 1 by decreasing the tilt angle of the hydraulic pump 1 as the pressure in the pilot line 13 increases. The pressure in the pilot line 13 increases as the flow rate of the hydraulic oil guided to the primary side of the throttle 10 increases. Therefore, when all of 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 line 13 decreases and the hydraulic pump 1
Discharge capacity increases. In the figure, reference numerals 14 to 19 denote relief valves for regulating the pressure of the hydraulic oil discharged from the ports P1 to P6.

[0005]

In the above-described apparatus, a plurality of fronts are selectively used in accordance with the work purpose. However, since the rated flow rates of hydraulic actuators for driving the fronts are different from each other, ports P1 and P2 are used. It is necessary to adjust the maximum flow rate of pressurized oil to the front every time the front is replaced. In order to limit the maximum flow rate to the ports P1 and P2, the amount of movement of the first spool 3 from the neutral position to the A position or the B position is limited, or the discharge flow rate of the hydraulic pump 1 is reduced by reducing the rotation speed of the prime mover. Can be reduced.
However, according to the former, even when the first spool 3 is moved to the maximum, the pressure oil is bypassed to the spools 4 and 5, so that the output pressure of the ports P1 and P2 is reduced by the relief valve 1
There is a case where the rated output of the front cannot be obtained because the pressure does not rise to the set pressure of 4 or 15. In the latter case, there is a different problem depending on whether the rotation speed of the prime mover is reduced only during the operation of the front or the rotation speed of the prime mover regardless of the operation of the front. If the speed is reduced only during the operation of the front, the number of revolutions of the prime mover frequently increases and decreases, so that the noise becomes harsh. Also,
It is necessary to improve the responsiveness of the prime mover, and it is difficult for a turbocharged engine to respond. If the rotation speed of the prime mover is reduced irrespective of the operation of the front, the rated output of the prime mover cannot be obtained, so that the front output decreases.

As means for changing the pressure oil flow rate 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 hydraulic oil output from the control valve 2 of each system is supplied to the hydraulic cylinder 9A for the standard bucket, and the hydraulic 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 almost half of that of the hydraulic cylinder 9A, and cannot be applied to other cases.

SUMMARY OF THE INVENTION It is an object of the present invention to change the flow rate of pressure oil supplied to a hydraulic actuator by the amount of pressure oil bypass on the control valve side or to adjust the rotation speed of the prime mover according to the type of front. It is another object of the present invention to provide a hydraulic control device capable of supplying an appropriate flow rate of pressure oil to the hydraulic actuator.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 showing one embodiment, the present invention relates to a variable displacement hydraulic pump 1 driven by a prime mover, and a hydraulic pump 1 for driving a front drive. A control valve 2 for controlling the supply of pressure oil to the actuator 9; and a discharge displacement control pressure having a maximum value when the control valve 2 is at a neutral position, and a pressure decreasing toward a minimum value as the control valve 2 is switched from the neutral position. And a pressure compensation higher than the minimum value and lower than the maximum value of the discharge volume control pressure specified by the discharge volume control pressure generation circuit. Limiting pressure generating circuits 7 and 33 for generating the limiting pressure, selecting means 31 for selecting to use the limiting pressure, and a discharge capacity control pressure generating circuit when the selecting means selects the use of the limiting pressure. From the limiting pressure generation circuit Based on any large pressure of force, the pressure by providing a pump displacement control means 12 for increasing the discharge capacity of the hydraulic pump as drops, the above objects can be achieved.

[0009]

When a hydraulic actuator having a large rated flow rate is mounted, the selecting means 31 does not use the limiting pressure, and the minimum pressure of the discharge displacement control pressure is set low. When a hydraulic actuator having a small rated flow rate is mounted, the selecting means 31 uses the limiting pressure, and the minimum pressure of the discharge displacement control pressure is limited by the limiting pressure and set high. When the minimum value of the discharge displacement control pressure increases, the upper limit of the discharge displacement of the hydraulic pump 1 decreases, and the maximum flow rate of the pressure oil supplied to the hydraulic actuator decreases. In addition, since the limiting pressure is pressure-compensated, the limiting pressure becomes constant regardless of fluctuations in the rotation speed of the prime mover, and the maximum flow rate when a hydraulic actuator having a small rated flow rate is attached can be appropriately limited.

[0010] In the means and means for solving the above problems which explain the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. However, the present invention is not limited to this.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Parts common to the example shown in FIG. 6 described above are denoted by the same reference numerals, and description thereof is omitted. This embodiment is directed to a hydraulic excavator in which a standard bucket and a front for dismantling high places can be exchanged, and FIG. 5 shows a state where the front for dismantling high places is attached. In the figure, reference numeral 100 denotes an upper swing body of a hydraulic excavator, and a high-dismantling front 101 is attached to a front portion thereof. Front 10 for high-level dismantling
Reference numeral 1 denotes a boom 102, arms 103 and 104, and a gripper 105 that are rotatably connected to each other. A hydraulic actuator (not shown) built in the gripper 105 while controlling the attitude of the gripper 105 by hydraulic cylinders 106a to 106d. The fingers 105a and 105b are opened and closed to grip a wall or the like of a building, and dismantling work is performed.

FIGS. 1 and 2 show a hydraulic circuit according to 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. The shuttle valve 30 selects a larger pressure among the primary pressure Pa of the throttle 10 guided to the input port and the output pressure Pb of the manual switching valve 31 and outputs the selected pressure to the pilot line 13. The manual switching valve 31 is manually switched by the operation lever 31a, and the output pressure Pb changes based on the switching positions of the manual operation valve 31 and the pilot control valve 32. When both the manually operated valve 31 and the pilot control valve 32 are at the position B (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 transmitted from the manual switching valve 31 to the manual switching valve 31. Is output. When either one of the manually operated valve 31 and the pilot control valve 32 is switched to the position A, the manual switching valve 3
1 is opened to the tank, and the output pressure Pb becomes equal to the tank pressure.

The switching of the pilot control valve 32 is controlled in accordance with the operation of the operation lever 6s of the remote control valve 6. When the operating lever 6s is operated and pressure rises in one of the pilot lines 8a and 8b, this pressure is applied to the shuttle valve 3
The pilot control valve 32 is selected and guided to the pilot line 35, and the pilot control valve 32 is switched to the position B. When the operation lever 6s is at the neutral position, the pressure in the pilot line 35 becomes the tank pressure, and the pilot control valve 32 switches to the A position.

The pressure regulating valve 33 is connected to the pilot line 3
When the pressure 3a exceeds a certain value, the passage of pressure oil from the hydraulic pump 7 to the pilot control valve 32 is prevented, 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 pressure Pa of the throttle 10 when the prime mover is rotated at a predetermined operation speed and higher than the tank pressure.

When the standard bucket is used in the hydraulic control device having the above configuration, the manual switching valve 31 is switched to the position A. As a result, the output pressure Pb of the manual switching valve 31 becomes equal to the tank pressure. Therefore, the pressure Pa on the primary side of the throttle 10 is always output from the shuttle valve 30 and guided to the pilot line 13. Therefore, control valve 2
When all of the spools 3 to 5 are at the neutral position, the pressure in the pilot line 13 is maximized, the discharge capacity of the hydraulic pump 1 is minimized, and the more 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 hydraulic cylinder 9 connected to the ports P1 and P2 of the control valve 2 is changed to one having a smaller rated flow rate when the high-level disassembly front 101 is mounted, as shown in FIG. Switch to position B. When the remote control valve 6 is operated to operate the front in this state, the first spool 3 moves to the position A or the position B accordingly, 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 pressure Pa of the throttle 10 decreases as the moving amount of the spool 3 increases, and reaches the minimum pressure Pt (tank pressure) at the maximum moving amount Smax. The output pressure Pb of the valve 31 is constant at the output pressure Pc of the pressure regulating valve 33. For this reason, the manual switching valve 31
When in position, the pressure in pilot line 13 is
From the start of movement until the movement amount reaches a predetermined value Sc, the pressure 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 as the pressure Pa decreases until the displacement of the spool 3 reaches Sc.
After exceeding c, it is maintained at a constant value corresponding to the pressure Pc.

When the discharge capacity of the hydraulic pump 1 changes as described above, the relationship between the amount of movement 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 when the manual switching valve 31 is at the position A,
Q2 indicates a change when the manual switching valve 31 is at the B position. When the manual switching valve 31 is at the position A, the spool 3
The displacement of the hydraulic pump 1 with respect to the increase in the amount of movement of the hydraulic pump 1 and the port P of the control valve 2
1, when the flow rate of the hydraulic oil to the hydraulic cylinder 9 increases due to the increase in the degree of opening of the flow path leading to P2, and the amount of movement of the spool 3 reaches the maximum value Smax (when the spool 3 is in the A position or the B position). (When it is completely switched to) the maximum flow rate Qmax.

When the manual switching valve 31 is at the position B, the manual switching valve 3 is not 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 at the A position. When the displacement of the spool 3 exceeds Sc, the discharge capacity of the hydraulic pump 1 is fixed at a constant value. Therefore, the flow rate of the hydraulic 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. Increases or decreases depending on the degree of opening. Therefore, when the displacement of the spool 3 reaches the maximum value Smax, the hydraulic oil flow Qc to the hydraulic cylinder 9 becomes smaller than the maximum flow Qmax by the amount by which the discharge capacity of the hydraulic pump 1 is fixed.

The ratio between the maximum flow rate Qmax and the flow rate Qc is made equal to the ratio between the rated flow rate of the hydraulic cylinder of the standard bucket and the rated flow rate of the hydraulic cylinder of the high-level dismantling front by adjusting the set pressure Pc of the pressure regulating valve 33. You. For example, when the cylinder diameter of the hydraulic cylinder at the front of the high-level demolition cylinder is 40% of the cylinder diameter of the hydraulic cylinder of the standard bucket, the pressure Pc is determined so that Qc is 40% of Qmax. Therefore, when the manual switching valve 31 is at the position A, the spool 3
When the amount of movement of the hydraulic cylinder reaches the maximum value Smax, 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 position B, the port P1 or P2 Pressure oil is discharged at a flow rate equal to the rated flow rate of the hydraulic cylinder at the front of the high-level dismantling cylinder.

As is apparent from the above, in this embodiment, the switching operation of the manual switching valve 31 causes the pilot line 13
Is changed to change the upper limit value of the discharge capacity of the hydraulic pump 1, thereby increasing or decreasing the maximum flow rate of the pressure oil supplied to the hydraulic cylinder 9. There is no need to regulate the amount of movement of No. 3 or reduce the rotational speed of the prime mover. For this reason, the conventional disadvantages of insufficient output of the front and noise due to fluctuations in the rotation speed of the prime mover are eliminated.

In the present embodiment, the minimum pressure of the pilot line 13 can be switched between the tank pressure Pt and the set pressure Pc of the pressure regulating valve 33, but the present invention is not limited to this. Alternatively, it can be changed more. For this purpose, for example, the pressure regulating valve 33 may be made variable, 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 of 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 hydraulic pump 1, the control valves 3, 4, 5, the throttle 10, and the pipeline 11 constitute a discharge displacement control pressure generating circuit, and the hydraulic pump 7 and the pressure regulating valve 33 constitute a limiting pressure generating circuit. , The regulator 12 constitutes the pump displacement control means, and the manual switching valve 31 constitutes the selection means. The pressure Pc corresponds to the limiting pressure, and the pressure Pa corresponds to the discharge displacement control pressure.

[0024]

As described above, according to the present invention, when the front drive hydraulic actuator is changed to one having a smaller rated flow rate, the minimum value of the discharge displacement control pressure for controlling the discharge displacement of the hydraulic pump is obtained. By simply increasing the hydraulic pressure, the upper limit of the discharge capacity of the hydraulic pump is reduced and the hydraulic oil flow to the hydraulic actuator is reduced, so the hydraulic oil flow to the hydraulic actuator is bypassed by bypassing the hydraulic pump discharge oil on the control valve side. And it is not necessary to increase or decrease the rotation speed of the prime mover according to the rated flow rate of the hydraulic actuator. For this reason, the front output does not decrease, the noise problem caused by frequent changes in the rotation speed of the motor is eliminated, and the blow-up characteristic of the motor does not matter. Also, since the limiting pressure is pressure compensated, it becomes constant regardless of the rotation speed fluctuation of the prime mover, etc.
The maximum flow rate when a hydraulic actuator with a small rated flow rate is attached can be appropriately limited.

[Brief description of the drawings]

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

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

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

FIG. 5 is a diagram showing a state in which a front for high-level disassembly is attached to the hydraulic shovel.

FIG. 6 is a conventional hydraulic circuit diagram.

FIG. 7 is another hydraulic circuit diagram of the related art.

8 is a diagram showing a state in which a reduction in the rated flow rate of the hydraulic cylinder has been dealt with in the hydraulic circuit of FIG. 7;

[Explanation of symbols]

 DESCRIPTION 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)

(57) [Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a control valve for controlling supply of pressure oil from the hydraulic pump to a front drive hydraulic actuator, and when the control valve is in a neutral position. Is the maximum value, and the discharge volume control pressure generation circuit generates the discharge volume control pressure in which the pressure decreases toward the minimum value as the position is switched from the neutral position.
And the discharge capacity defined by the discharge capacity control pressure generation circuit
Pressure compensation higher than the minimum value of the control pressure and lower than the maximum value
A limiting pressure generating circuit for generating the limited pressure, a selecting means for selecting to use the limiting pressure, and when using the limiting pressure is selected by the selecting means ,
From the discharge capacity control pressure generation circuit and the limit pressure generation circuit
And a pump displacement control means for increasing the discharge displacement of the hydraulic pump as the pressure decreases, based on the larger one of the pressures .