JPH068641B2 - Hydraulic circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit provided in a construction machine such as a hydraulic shovel, and more particularly to a center bypass type directional control valve having a plurality of directional control valves. The present invention relates to a hydraulic circuit having a low pressure generating means for operating a regulator so that the discharge amount of a variable displacement hydraulic pump is reduced when all the valves are in a neutral state.

<Prior Art> FIG. 4 is a circuit diagram showing a conventional hydraulic circuit of this type, which is disclosed in Japanese Patent Publication No. 47-3927.

This conventional hydraulic circuit includes a variable displacement hydraulic pump 1 and a main relief valve R.V. which regulates the discharge amount of the variable displacement hydraulic pump 1. V, an actuator driven by the pressure oil discharged from the variable displacement hydraulic pump 1, that is, the operating devices 12a and 12b, the variable displacement hydraulic pump 1 and the operating device 1.
2a, 12b, and is arranged between the actuators 12a, 12
The composite switching valve 11 including a plurality of center bypass type directional switching valves 11a and 11b for controlling the drive of b, a reguulator for controlling the discharge amount of the variable displacement hydraulic pump 1, that is, a control cylinder 18, and the control cylinder 18. A connectable pilot pump, ie a control pump 16;
A low pressure that is provided downstream of the direction switching valves 11a and 11b and operates the control cylinder 18 so that the discharge amount of the variable displacement hydraulic pump 1 is reduced when the direction switching valves 11a and 11b are all in a neutral state. The low pressure generating means for generating, that is, the orifice 13, and this orifice 13
Between the pipe 40 communicating with the upstream side of the control cylinder 18 and the control cylinder 18, the cylinder 39, the power piston 38, the spool 26, the input limiting control valve 17 having the spring 34 for urging the spool 26, and the variable capacity. A prime mover 7 for driving the hydraulic pump 1 and the control pump 16 is provided.

The state shown in FIG. 4 shows an idling state in which the switching valves 11a and 11b of the composite switching valve 11 are both in the neutral position. At this time, the pressure oil discharged from the pump 1 is at the center of the composite switching valve 11. Through the bypass, tank 1
It is discharged to 0. So this pressure oil
The pressure is decreased by the pressure drop, and the pressure drop causes a pressure in the center bypass on the upstream side of the orifice 13. This pressure is guided to the cylinder 39 through the pipe 40, and the cylinder 3
9, the power piston 38 moves the spool 26 rightward against the repulsive force of the spring 34, and connects the inflow port 23 from the control pump 16 to the second outflow port 259. Then, the pressure oil is supplied to the rod end side of the control cylinder 18, the piston 19 of the control cylinder 18 is pushed near the left limit, and the cam plate 5 is positioned almost in the neutral position to reduce the discharge amount of the pump 1. , The discharge pressure is reduced.

Also, for example, the switching valve 1 for operating the actuator 12a
When 1a is switched from the neutral position, the center bypass of the composite switching valve 11 is cut off and the supply of pressure oil to the orifice 13 is cut off. Therefore, the pressure on the upstream side of the orifice 13 decreases. Therefore, the pressure in the cylinder 39 decreases,
The force of the power piston 38 to the right disappears, and the repulsive force of the spring 34 causes the spool 26 to move to the left, connecting the inflow port 23 of the input limiting control valve 17 to the first outflow port 24. The pressure oil of the control pump 16 is sent to the head end side of the control cylinder 18, resists the repulsive force of the spring 21, moves the piston 19 to the right, and tilts the cam plate 5 via the connecting rod 20 and the like. On the other hand, the oil on the rod end side of the control cylinder 18 is increased to the second outflow port 25.
Is discharged to the tank 10 through a pipeline indicated by a dotted line. Thereupon, the pump 1 increases the discharge amount, and this pressure oil is sent to the right chamber of the actuating device 12a via the switching valve 11a, causing the piston to move to the left.

<Problems to be Solved by the Invention> In the conventional hydraulic circuit configured as described above, the driving pressure of the operating devices 12a and 12b, that is, the pressure of the pressure oil discharged from the variable displacement hydraulic pump 1 is the main pressure. Relief valve R. Since it is uniquely limited by the set value of V, and the discharge amount of the variable displacement hydraulic pump 1 is also uniquely determined by the inclination of the cam plate 5 accompanying the switching operation of the switching valves 11a and 11b. There is.

By the way, in the case of a construction machine equipped with such a hydraulic circuit, for example, a hydraulic shovel, in addition to excavation work which is usually performed, when booms and arms are raised and lowered to suspend loads, that is, crane work. However, this crane work generally requires a high pump discharge pressure for obtaining a large lifting force, and a relatively small pump discharge amount that gives a slow working speed in consideration of safety.

However, in the above-mentioned conventional hydraulic circuit, a constant discharge pressure and discharge flow rate are always supplied to the operating devices 12a and 12b, so it is difficult to handle such crane work, that is, the pump discharge pressure is insufficient. There is a concern that work load may be reduced due to insufficient lifting force of the load due to the above, and rapid lifting of the arm and the like due to a large pump discharge flow rate.

The present invention has been made in view of the above-mentioned actual situation in the prior art, and an object thereof is to provide a hydraulic circuit capable of changing the pump discharge amount and the pump discharge pressure as necessary.

<Means for Solving Problems> To achieve this object, the present invention provides a variable displacement hydraulic pump, a main relief valve that regulates the pressure of the discharge oil of the variable displacement hydraulic pump, and a variable displacement hydraulic pump. An actuator driven by discharge oil, a plurality of center bypass type directional control valves arranged between the variable displacement hydraulic pump and the actuator and controlling the drive of the actuator, and the discharge amount of the variable displacement hydraulic pump. A regulator to be controlled, a pilot pump that can be connected to the regulator, and a directional control valve are provided downstream of the directional control valve so that when the directional control valves are all in the neutral state, the discharge amount of the variable displacement hydraulic pump is reduced. In a device provided with a low pressure generating means for generating a low pressure for operating the regu- lator, the pressure supplied via the pilot pump is controlled. , The upstream of the low pressure generating means including the low pressure generated by the low pressure generating means while setting the regurator at a controllable pressure so that the discharge amount of the variable displacement hydraulic pump is smaller than the maximum flow rate normally supplied by a predetermined amount. And a pressure supply means including, for example, a shuttle valve, capable of selectively supplying either of the pressure of the pressure regulator and the pressure supplied via the pilot pump to the regulator.
Switching means provided between the pressure supply means and the pilot pump, for switching whether or not the pressure supplied through the pilot pump is guided to the pressure supply means, for example, a switching valve or the like, and switching of the pressure supply means. For example, a pressure changing unit that changes the discharge pressure of the variable displacement hydraulic pump to increase in conjunction with the operation is provided with a pressure changing unit including a plurality of main relief valves and pressure reducing valves.

<Operation> Since the present invention is configured as described above, when the directional control valves are all in the neutral state, the low pressure generated by the low pressure generating means is supplied to the regurator via the pressure supply means, and Therefore, the discharge amount of the variable displacement hydraulic pump is reduced, and during normal work when the directional control valve is switched, it is limited by the set pressure of the normal main relief valve via the pressure changing means. In order to perform the normal work by supplying the pump discharge pressure to the actuator, and for crane work in a hydraulic shovel, the pressure related to the pilot pump is supplied to the regurator via the pressure supply means via the switching means, This regulator is operated to reduce the maximum flow rate of the pump, and the discharge pressure of the variable displacement hydraulic pump is increased in conjunction with the switching operation of the switching means. It is possible to supply these high pump discharge pressure and relatively small pump discharge amount.

<Example> Hereinafter, the hydraulic circuit of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In this figure, 51 is a variable displacement hydraulic pump, and 52, 53.
Is a main relief valve that regulates the pressure of the pressure oil discharged from the variable displacement hydraulic pump 51, and the set pressure of the main relief valve 52 is set to be higher than the set pressure of the main relief valve 53. Reference numerals 54 and 55 are center bypass type directional control valves that control the drive of an actuator (not shown), and 56 is a regulator that controls the discharge amount of the variable displacement hydraulic pump 51. 57 is arranged downstream of the direction switching valve 55, and when all of the direction switching 54, 55 are in a neutral state, a low pressure is generated to operate the regulator 56 so that the discharge amount of the variable displacement hydraulic pump 51 is reduced. The means, eg a low pressure relief valve, 58 is a tank.

Reference numeral 59 is a pilot pump, and 60 is a relief valve that regulates the pilot pressure of the pilot pump 59. The relief valve 60 normally supplies the pilot pressure of the pilot pump 59 with the discharge amount of the variable displacement hydraulic pump 51. The regulator 56 is set to a pressure at which it can be controlled by a predetermined amount less than the maximum flow rate. Again 6
Reference numeral 1 denotes a pressure supply means capable of selectively supplying either the pressure upstream of the low pressure relief valve 57 including the low pressure generated by the low pressure relief valve 57 or the pilot pressure of the pilot pump 59 to the reguulator 56, for example, a shuttle valve. ,
It is connected to the upstream side of the low pressure relief valve 57 via a line 62, to the regulator 56 via a line 63, and to a line 64 capable of supplying the pilot pressure of the pilot pump 59. The pressure of either 62 or 64 is supplied to the reguulator 56 via the conduit 63.

65 connects the line 64 to the pilot pump 59, or
Alternatively, an electromagnetic switching valve for connecting or switching to the tank 58 can be switched to the right position in the figure against the spring, that is, the position communicating with the pipe line 64, by inputting a signal from the switch 66. The switch 66, the electromagnetic switching valve 65, and the pipe 64 described above are connected to the pilot pump 5.
A switching means for switching whether or not the pilot pressure 9 is introduced to the shuttle valve 61 is configured. Reference numeral 67 is an open / close valve that is switched to a closed position according to the pressure in the pipe 64, and is connected to the drive unit of the main relief valve 53 via a pipe 68. The on-off valve 67, the main relief valve 53, and the main relief valve 52 described above interlock with the switching operation of the electromagnetic switching valve 65 that connects the pilot pump 59 and the pipeline 64, and the discharge pressure of the variable displacement hydraulic pump is increased. A pressure changing means for changing the pressure to be higher is configured.

In the hydraulic circuit configured as described above, as shown in FIG. 1, the switch 66 is OFF and the electromagnetic switching valve 65 is turned off.
Is switched to the left position, the pipe line 64 is connected to the tank 58 via the electromagnetic switching valve 65 so that the pilot pressure of the pilot pump 59 is not guided to the shuttle valve 61. The on-off valve 67 is in the communicating position as shown in FIG. 1 because the tank pressure is in the passage 64, and accordingly, the drive portion of the main relief valve 53 has the conduit 6
8, and communicates with the tank 58 via the open / close valve 67. As shown in FIG. 1, when both of the direction switching valves 54 and 55 are in the neutral state, the pressure oil discharged from the variable displacement hydraulic pump 51 is the direction switching valves 54 and 55 and the low pressure relief valve 57. The low pressure generated upstream of the low pressure relief valve 57 is led to the shuttle valve 61 via the pipe 62 and further to the reguulator 56 via the pipe 63. Then, the regu- lator 56 is controlled to reduce the tilt angle of the variable displacement hydraulic pump 51, and the discharge amount of the variable displacement hydraulic pump 51 is controlled to be almost zero. At this time, the drive unit of the main relief valve 53, which has a smaller set pressure than the set pressure of the main relief valve 52, communicates with the tank 58 via the pipe line 68 and the opening / closing valve 67, and therefore the variable displacement hydraulic pump 51. Is limited to the set pressure of the main relief valve 53.

When the switch 66 is in the OFF state as described above and the direction switching valves 54 and 55 are appropriately switched from the neutral position, the pressure oil of the variable displacement hydraulic pump 51 stops flowing upstream of the low pressure relief valve 57, Therefore, the pressure upstream of the low-pressure relief valve 57 decreases and becomes, for example, the tank pressure, and this tank pressure is supplied to the reguulator 56 via the pipe line 62, the shuttle valve 61, and the pipe line 63. Then, the regulator 56 or the variable displacement hydraulic pump 51 is controlled so as to increase the tilt angle, the maximum displacement is discharged from the variable displacement hydraulic pump 51, and the discharge pressure limited by the main relief valve 53 and the above-mentioned discharge. The quantity is supplied to the actuator (not shown) via the corresponding directional control valves 54, 55, so that normal operation by the actuator, for example oil It is possible to perform digging work or the like in Shiyoberu.

When the switch 66 is turned on from such a state, the electromagnetic switching valve 65 is switched to the right position in FIG. 1, whereby the pilot pressure defined by the relief valve 60 from the pilot pump 59 is changed to the electromagnetic switching. Valve 65, line 6
4 to the shuttle valve 61. In this case, when the direction switching valves 54 and 55 are in the neutral state, the low pressure generated upstream of the low pressure relief valve 57 as described above is applied to the conduit 62.
The low pressure is larger than the pilot pressure described above, and the low pressure is supplied to the reguulator 56, so that the tilt angle of the variable displacement hydraulic pump 51 is the discharge amount. Is controlled so as to be close to zero. Then, in such a state, when the direction switching valves 54 and 55 are switched from their neutral positions, the pressure upstream of the low pressure relief valve 57 decreases, but this time, the above pilot pressure is changed to the shuttle valve 61. Is supplied to the regu- lator 56 via the pipe 63, whereby the variable displacement hydraulic pump 51 discharges a relatively small flow rate slightly cut off from the maximum flow rate.

Further, when the pilot pressure is introduced into the conduit 64 as described above, the opening / closing valve 67 shown in FIG. 1 is switched to the right position, whereby the conduit 68 connected to the drive portion of the main relief valve 53. Is blocked. Therefore, when the pressure of the pressure oil discharged from the variable displacement hydraulic pump 51 becomes higher than the set pressure of the main relief valve 53, this pressure is now restricted by the high pressure defined by the main relief valve 52. It That is, as described above, when the switch 66 is turned on and the direction switching valves 54 and 55 are switched from the neutral position,
Pressure oil having a relatively small discharge amount and a high discharge pressure as compared with the time of normal work is supplied to the corresponding actuator via the directional control valves 54, 55, whereby special work by the actuator, for example, hydraulic shovel. It is possible to perform excavation work, etc.

In the first embodiment configured as described above, the pump discharge amount and the pump discharge pressure can be changed as necessary, and thus, the optimum actuator operation corresponding to the type of work can be realized. You can

For example, with a hydraulic shovel, excavation work that normally moves the arm or the like relatively quickly can be performed, and a large lifting force can be obtained during crane work, and the arm and the like can be moved relatively slowly to perform work. You can be safe.

2 and 3 are circuit diagrams showing second and third embodiments of the present invention, respectively.

In the second embodiment shown in FIG. 2, the low pressure generating means is replaced by a throttle 69 instead of the low pressure relief valve shown in FIG.
Is provided. The other structure is the same as that of the first embodiment shown in FIG. Even when the diaphragm 69 is provided in this way,
When the directional control valves 54, 55 are in the neutral state, a low pressure is generated upstream of the throttle 69, and this low pressure is guided to the regu- lator 56 via the pipe line 62, the shuttle valve 61, and the pipe line 63, and the variable displacement hydraulic pump. The discharge amount of 51 decreases to near zero. Then, as in the first embodiment, the O of the switch 66 is
By the switching operation of N and the direction switching valves 54 and 55, it is possible to supply a pressure oil having a smaller discharge amount and a higher discharge pressure to an actuator (not shown), and the same effect as the first embodiment is obtained.

In the third embodiment of the present invention shown in FIG. 3, two variable displacement hydraulic pumps 51a corresponding to two systems of hydraulic circuits each including a plurality of center bypass type directional control valves are provided.
51b is provided, and the discharge pressure of each self-pump is given to the regulators 56b and 56a of the other pump,
Full horsepower control is possible. In addition, when the directional control valves of the same system are all neutral, the low pressure relief valves 57a and 57b are
Of low pressure generated upstream of the switch 66 is supplied to the shuttle valves 61a and 61b through the conduits 62a and 62b, and the switch 66 is turned off.
When set to N, the pilot pressure of the pilot pump 59 is reduced by the pressure reducing valve 70 and can be supplied to the shuttle valves 61a and 61b via the electromagnetic switching valve 65. The pressures selected by the shuttle valves 61a and 61b are Regulator 56
a, 56b.

Also in the third embodiment configured as described above, when all the directional control valves included in the hydraulic pump 51a or the respective systems corresponding to the hydraulic pump 51b are in the neutral state, the low pressure relief valve 57a or the Low pressure is generated upstream of the low pressure relief valve 57b, and these low pressures are supplied to the regulator 56a or the regulator 56b through the shuttle valves 61a and 61b so that the discharge amounts of the variable displacement hydraulic pumps 51a and 51b are almost zero. You can Further, when the direction switching valve is switched from the neutral position with the switch 66 turned on, the pressure obtained by reducing the pilot pressure of the pilot pump 59 by the pressure reducing valve 70 causes the solenoid valve 65 to transfer the shuttle valve 61a or the shuttle valve 6 to the other side.
1b, and the pressure is regulated by the regulators 56a, 56a.
b, the discharge amounts of the variable displacement hydraulic pumps 51a, 51b are limited to be slightly smaller than the maximum flow rate during normal work, and the switching valve 67 is switched by switching the electromagnetic switching valve 65. From the set pressure of the main relief valve 53, the main relief pressure is changed to the main relief valve 52.
Therefore, the discharge pressure of the variable displacement hydraulic pumps 51a and 51b becomes high, and thus the work that requires a large discharge pressure, such as a crane work in a hydraulic shovel, does not require a large discharge amount. It can be carried out.

In the above embodiment, the switch 66, the electromagnetic switching valve 65, and the opening / closing valve 67 are separately provided to form an electric system. However, the present invention is not limited to this, and the electromagnetic switching valve 65 is used. It is also possible to incorporate the function of the on-off valve 67 into one switching valve block, provide a manually operated lever instead of the switch 66, and switch the switching valve block by this lever.

Further, in the above-described embodiment, the two main relief valves 5 having different set pressures are used as the pressure changing means.
2, 53 are provided, but the present invention is not limited to this, and one main relief valve is provided in place of the main relief valves 52, 53, and means for varying the spring force of the spring that determines the set pressure thereof. May be provided.

In the third embodiment, the pressure supplied from the pilot pump 59 to the shuttle valves 61a and 61b is uniquely determined by the pressure reducing valve 70, but the present invention is not limited to this. A configuration may be provided in which a means for varying the spring force of the spring that determines the secondary pressure of the valve 70 is provided.

<Effects of the Invention> Since the hydraulic circuit of the present invention is configured as described above, it is possible to change the pump discharge amount and the pump discharge pressure as needed, and it is performed in a construction machine equipped with the hydraulic circuit. There is an effect that the optimum actuator operation corresponding to the type of work can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a hydraulic circuit of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG.
FIG. 4 is a circuit diagram showing a third embodiment of the present invention, and FIG. 4 is a circuit diagram showing a conventional hydraulic circuit. 51 ... variable displacement hydraulic pump, 51a ... first variable displacement hydraulic pump, 51b ... second variable displacement hydraulic pump,
52, 53 ... Main relief valve, 54, 55 ... Direction switching valve, 56, 56a, 56b ... Regulator, 5
7, 57a, 57b ... Low-pressure relief valve (low-pressure generating means), 58 ... Tank, 59 ... Pilot pump, 6
0 ... Relief valve, 61, 61a, 61b ... Shuttle valve (pressure supply means), 62, 62a, 62b, 63, 6
3a, 63b, 64, 68 ... Pipe line, 65 ... Electromagnetic switching valve, 66 ... Switch, 67 ... Open / close valve, 69 ... Throttle (low pressure generating means), 70 ... Pressure reducing valve.

Claims (1)

[Claims] Claim: What is claimed is: 1. A variable displacement hydraulic pump, and a main relief valve that regulates the pressure of oil discharged from the variable displacement hydraulic pump.
An actuator driven by the discharge oil of the variable displacement hydraulic pump, a plurality of center bypass type directional control valves disposed between the variable displacement hydraulic pump and the actuator and controlling the drive of the actuator, and the variable displacement A regulator that controls the discharge amount of the hydraulic pump, a pilot pump that can communicate with the regulator, and a variable displacement hydraulic pump that is provided downstream of the directional switching valve and is in a neutral state. In a hydraulic circuit including a low pressure generating means for generating a low pressure for operating the regu- lator so that the discharge amount of the variable displacement hydraulic pump is usually the discharge amount of the variable displacement hydraulic pump. When the regulator is set to a controllable pressure so that it is reduced by a specified amount compared to the maximum flow rate supplied. A pressure supply means capable of selectively supplying either the pressure upstream of the low pressure generation means including the low pressure generated by the low pressure generation means or the pressure supplied via the pilot pump to the regulator, and Provided between the pressure supply means and the pilot pump,
Interlocked with the switching operation of the switching means for switching whether or not the pressure supplied through the pilot pump is guided to the pressure supply means, and the switching operation of the switching means for guiding the pressure supplied through the pilot pump to the pressure supply means. And a pressure changing means for changing the discharge pressure of the variable displacement hydraulic pump so as to be high.