JPS5824671Y2 - Hydraulic circuit of hydraulic drive - Google Patents

Description

[Detailed Description of the Invention] This invention mainly relates to a hydraulic circuit for a hydraulic drive device for driving a construction vehicle.

Conventionally, hydraulic drive devices that drive construction machinery, etc.
It is formed as shown in FIG.

That is, the discharge pressure from a variable displacement hydraulic pump b driven by an engine a is supplied to a fixed displacement hydraulic motor d via a closed circuit C, and this hydraulic motor d drives the suspension of the construction machine. The output shaft rotation speed of the hydraulic motor d is determined by the pump capacity of the hydraulic pump b and the motor capacity of the hydraulic motor d.

Therefore, the output shaft rotation speed cannot be increased beyond the rotation speed obtained from the pump capacity.

Furthermore, if you want to further increase the vehicle speed when the load on the construction machine is small, the vehicle speed range is limited to within the pump capacity even though engine a has a margin of output, resulting in poor work efficiency and engine a. There were some problems, such as the output could not be used effectively.

This invention was made with the aim of improving this problem, and provides a hydraulic circuit for a hydraulic drive device that can achieve a higher vehicle speed by merging the hydraulic pressures of the working machine hydraulic circuits as necessary. The aim is to improve work efficiency and make effective use of engine output.

This invention will be described in detail below with reference to an embodiment shown in FIG.

In the figure, 1 is an engine installed in a construction machine (not shown), and this engine 1 is used to drive a variable capacity hydraulic pump 2.
, two working machine pumps 3 and 4 having different capacities, a control pump 5, and a charge pump 6 are driven simultaneously.

Hydraulic pressure discharged from the hydraulic pump 2 is supplied to a hydraulic motor 9 via closed circuits 7 and 8, and this hydraulic motor 9 drives the undercarriage of construction machinery and the like. Out of the pumps 3 and 4, the discharge pressure of the pump 3, which has a smaller capacity, is regulated by the relief valve 9, and then the discharge pressure is transferred to the pipe line 1.
0 to the working machine circuit 11, and the discharge pressure of the large-capacity pump 4 is regulated by the relief valve 12, and then flows to the pipe line 10 via the pilot switching valve 13.
The power is supplied to the working machine circuit 11.

In addition, the discharge pressure of the control pump 5 is regulated by the IJ IJ valve 14 and then supplied to the servo cylinder 16 via the forward/reverse and speed control valve 15. At the same time, the discharge pressure of the charge pump 6 is regulated by the relief valve 17 and then supplied to the closed circuits 7 and 8 via the check valves 18 and 19 to replenish the insufficient oil.

On the other hand, between the closed circuits 7 and 8, when one of the closed circuits 7 and 8 becomes high pressure, the position 7 is set to A, and the conduit 20
The discharge pressure of the work equipment pump 4 introduced via the switching valve 13 is merged with the discharge pressure of the charge pump 6 into the high pressure side closed circuit 7, and when the other closed circuit 7, 8 becomes high pressure, the position is set. B becomes work equipment hydraulic pump 4
A shuttle valve 21 is connected thereto, which causes the discharge pressure of the charge pump 6 to join the discharge pressure of the charge pump 6 into the high-pressure side closed circuit 8 .

Further, a filter 22 and a check valve 23 are interposed in the middle of the pipe line 20 that introduces the discharge pressure of the work equipment pump 4, and from the middle of the pipe line 20 that connects the filter 22 and the check valve 23, A pilot pipe line 24 is branched, and this pilot pipe line 24 is connected to one end side of the pilot switching valve 13 via a switching valve 26 and a throttle 27 that operate in conjunction with the forward/reverse and speed control valve 15. With,
A control pump 5 is connected to the other end of the pilot switching valve 13 and is introduced from the forward/reverse and speed control valve 15 through a conduit 2.8.
A part of the discharge pressure is supplied.

The hydraulic motor 9 is rotated by the discharge pressure driven by the engine 1 and the vehicle travels, and the vehicle speed can be arbitrarily set by operating the longitudinal control valve 15.

Next, while the vehicle is running at maximum speed with a small load on the hydraulic motor 9, in order to further increase the vehicle speed, the switching valve 26, which is linked to the forward/reverse and speed control valve 15, is moved to position A.
, the pressure on the discharge side of the speed control valve 15 further increases and is supplied to the left side of the pilot switching valve 13, and at the same time, part of the hydraulic pressure on the high pressure side of the closed circuits 7 and 8 is transferred to the pipe line 2.
0 and 24 to the right side of the pilot switching valve 27 via the switching valve 24 and the throttle 27.

As a result, the pilot switching valve 13 is
The hydraulic motor 9 is switched to It is rotated by the discharge pressure of the hydraulic pump 2 and the work equipment pump 4, and a faster vehicle speed can be obtained.

At this time, since the discharge pressure of the small-capacity work implement pump 3 is applied to the work implement circuit 11, there is no problem with fine operation of the work implement.

Next, for some reason, such as pitching, the hydraulic motor 9
When the load increases, the pressure in one of the closed circuits 7 and 8, for example 7, increases, and at the same time, the pressure in the conduit 20 also increases.

When the pressure in the pipe line 20 exceeds a certain value P2, this pressure plus the force of the return spring 13a overcomes the pressure from the control pump 5 introduced on the left side of the pilot switching valve 13, and the switching valve 13 is placed in the N position. Therefore, the discharge pressure of the work equipment pump 4 is cut off from joining the discharge pressure of the hydraulic pump 2, and the hydraulic motor 9 is rotated only by the discharge pressure of the hydraulic pump 2, and the work equipment pump 4
The discharge pressure is supplied to the working machine circuit 11.

The above operation is performed with some delay due to the throttle 27 provided in the conduit 20.

Furthermore, when the load on the hydraulic motor 9 becomes smaller, the pilot switching valve 13 becomes the A position again, and the discharge pressure of the work implement pump 4 joins the discharge pressure of the hydraulic pump 2.

That is, the pilot switching valve 13 constantly detects the load applied to the hydraulic motor 19 and connects or cuts off the discharge pressure of the work equipment pump 4, thereby preventing the hydraulic motor 9 from being destroyed due to overload. When the pilot switching valve 13 is in the N position, the discharge pressure of the work implement pump 4 can be merged with the discharge pressure of the work implement pump 3 to operate the work implement.

Note that in the above embodiment, the circuit in which one hydraulic motor 9 is rotated by one hydraulic pump 2 has been described.
Of course, the present invention can also be applied to a two-pump, two-motor circuit in which the left and right suspensions are driven by independent hydraulic pumps and hydraulic motors.

In this case, two work equipment pumps 4 are provided to merge the discharge pressure of the left and right hydraulic pumps 2, but one work equipment pump 20
The discharge pressure of the hydraulic pump 2 may be divided by a distribution valve and merged with the discharge pressure of the left and right hydraulic pumps 2.

As explained in detail above, this invention allows the discharge pressure of the work machine pump when loading snacks to be merged with the discharge pressure of the hydraulic pump, which makes it possible to obtain faster vehicle speed, improve work efficiency, and improve work efficiency. Engine output can be used effectively.

In addition, even when the discharge pressure of the work equipment pump is merging with the delivery pressure of the hydraulic pump, fine control of the work equipment is possible using a separate work equipment pump, so there is no problem with work and the hydraulic motor By detecting the load and controlling the discharge pressures of the work equipment pumps to merge or shut off, it is possible to reliably prevent damage to the hydraulic motor and the suspension driven by it due to overload. be able to.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional hydraulic circuit, and FIG. 2 is a circuit diagram of a hydraulic circuit according to an embodiment of this invention. 1 is an engine, 2 is a hydraulic pump, 3 and 4 are working machine pumps, 7 and 8 are closed circuits, 9 is a hydraulic motor, 13 is a pilot switching valve, 15 is a forward/reverse movement and speed control valve, 20 is a pipe, 21 is a shuttle valve, and 26 is a switching valve.

Claims (2)

[Scope of utility model registration request] (1) The discharge pressure of the hydraulic pump 2 driven by the engine 1 is supplied to the hydraulic motor 9 via the closed circuits 7 and 8, and the hydraulic motor 9 drives the suspension and rotates the hydraulic pump 2. Work equipment pumps 3 and 4 driven by the engine 1 are provided, the direction and speed of which are controlled by the forward/reverse and speed control valves 15, and the discharge circuit of one of the work equipment pumps 4 is connected to the forward/reverse and speed control valves 15. Rapid feed rate control valve 1
A pilot switching valve 13 operated by the control pressure of 5 is provided to allow the discharge pressure of the work equipment pump 4 to flow into the pipe line 20, and the pipe line 20 is provided between the closed circuits 7 and 8, and these are closed. Hydraulic drive is achieved by connecting the circuits 7 and 8 to the closed circuits 7 and 8 via a shuttle valve 21 that operates based on the differential pressure between the circuits 7 and 8, thereby merging the discharge pressure of the work equipment pump 4 into the high-pressure side closed circuits 7 and 8. Hydraulic circuit of the device. (2) The high pressure side pressure of the closed circuits 7 and 8 is introduced as one pilot pressure of the pilot switching valve 13 via the switching valve 26 which is linked with the forward/reverse and speed control valve 15, and the high pressure side pressure is set to a value P1 In the hydraulic drive system according to claim 1, in which the flow of the discharge pressure of the work equipment pump 4 into the closed circuit 7.8 is interrupted by switching the pilot switching valve 13. Hydraulic circuit.