JPS60129402A - Hydraulic circuit of construction machine - Google Patents

Abstract

PURPOSE:To prevent generation of cavitation at the time of speed reduction of a hydraulic motor by providing a relief valve in the vicinity of the end portion of a return oil path leading from a changeover valve to a tank. CONSTITUTION:A relief valve 13 is provided on a return oil path 8 leading from a changeover valve 3 through a tank 7 and the pilot oil path 15 of the relief valve 13 is connected to the discharge side oil path 4 of a hydraulic pump 2. And the return oil path 8 is connected to a hydraulic motor 1 through check valves 11, 12. Then, oil can directly be supplied from the return oil path 8 even when oil supply to the hydraulic motor 1 is decreased at the time of speed reduction of the hydraulic motor 1, and generation of cavitation in the hydraulic motor 1 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic circuit for construction machinery, and more particularly to a hydraulic circuit for preventing cavitation of a hydraulic motor.

BACKGROUND ART Conventionally, in construction work vehicles, a method of using a counterbalance valve with a cross relief valve has been generally used for the purpose of preventing runaway due to idle rotation of a hydraulic motor. However, this method has the disadvantage that shock and hunting occur during deceleration, which is contrary to the operator's intention.

For this reason, recently, as shown in Figure 1, a back pressure valve is installed in the return oil path leading from the switching valve that operates the hydraulic motor to the tank, and the oil path is run directly from upstream of the back pressure valve to the hydraulic motor. A check valve is provided in the oil passage to allow return oil from the switching valve to flow back to the hydraulic motor through the check valve. Alternatively, the hydraulic motor is provided with a spool valve so that the oil can be drawn into the hydraulic motor through a large-diameter oil path from the return circuit.

However, even with this type of circuit, if the distance from the switching valve to the hydraulic motor is long, or if the diameter of the oil pipe is small, piping resistance will be large, and cavitation may occur if a sufficient amount of oil is not supplied to the hydraulic motor. It's easy to do. Furthermore, if the back pressure is increased to supply a sufficient amount of oil to the hydraulic motor, the efficiency will deteriorate during acceleration. Furthermore, when a suction valve is attached to a hydraulic motor, there is a problem of space for the suction valve and its piping, which also causes an increase in cost.

The present invention was invented in view of the above points, and aims to prevent cavitation during deceleration of a hydraulic motor, and in particular, improves controllability and efficiency in a high-speed, large-flow hydraulic motor circuit. The aim is to have an anti-cavitation effect.

The configuration of the present invention is to provide a low-pressure IJ valve in the return side oil passage of a switching valve that controls the hydraulic motor of a construction work vehicle, and to connect the pilot oil passage not only from the inflow side oil passage but also to control the hydraulic motor. It is also derived from the discharge side oil passage of the operating hydraulic pump.

When the hydraulic motor decelerates, the pressure of the low pressure relief valve is set high enough to prevent the hydraulic motor from causing cavitation, so it is possible to prevent the vehicle from running away.

Hereinafter, the present invention will be described in detail with reference to embodiments thereof.

Reference numeral 1 denotes a hydraulic motor for driving the construction machine, 2 a hydraulic pump that supplies pressure oil to the hydraulic motor 1, 3 a switching valve that controls the hydraulic motor 1, and an oil path 4 from the hydraulic pump 2 to the switching valve 3.
An oil path 5. is connected from the switching valve 3 to the hydraulic motor 1.
6 is in communication, and a return oil passage 8 from the switching valve 3 to the tank 7 is also in communication. 9.10 is an oil passage that bypasses the switching valve 3 from the oil passage 5.6 leading to the hydraulic motor 1 to the return oil passage 8, and check that oil flows only toward the hydraulic motor 1 in the oil passage 9.1O. A valve 11.12 is installed in each case. 13 is an IJ installed near the end of the return oil passage 8.
This is a J-f valve and is for applying some pressure to the return oil path 8. The relief valve 13 is connected not only to the pilot oil passage 14 from its upstream side but also to the discharge side oil passage 4 of the hydraulic pump 2.
Also pyro.

Bokuyou Road 15 is connected to it. Therefore, not only can the return oil passage 8 be maintained at a constant oil pressure as a normal relief valve, but also the relief valve 13 can be controlled by changes in the discharge oil pressure of the hydraulic pump 2, and the oil pressure of the return oil passage 8 can be controlled. . 16 is a bypass mm of the relief valve 13 provided in the return oil passage 8, and the oil passage 16 is provided with a throttle 17.

The figure shows the structure of the IJ valve 13, where 18 is the valve body, 19. is a piston valve, 2o is a spring,
A valve portion 21 at the front of the piston valve 19 is in contact with a valve seat 24 between an inflow path 22 and an outflow path 23.

25 is a small diameter piston, the tip of which is in contact with the tip of the valve portion 21 of the piston valve 19. Therefore, 1 piston valve 1
9 is actuated not only by the oil pressure of the inlet 22 communicating with the return oil passage 8, but also by the small diameter piston 25 which is actuated by the oil pressure of the pilot oil passage 14.

In addition, 26 is a return oil path when the switching valve 3 is in neutral.

The present invention is constructed as described in Section 2 below, and the case where it actually operates will be explained.

When operating the hydraulic motor l, the switching valve 3 is switched to the right or left. The oil discharged from the hydraulic pump 2 is delivered through an oil path 4,
The return oil reaches the hydraulic motor 1 through the switching valve 3 and the oil passage 5, and the return oil passes through the oil passage 6, the switching valve 3, and the return oil passage 8 before reaching the relief valve 13.
However, due to the resistance of the hydraulic motor 1, the discharge oil pressure of the hydraulic pump 2 rises by 200 ft, and the relief valve 13 is relieved via the pilot oil passage 15. That is, the small diameter piston 25 pushes the piston valve 19 to the right by the pyrostatic pressure, opens the inflow oil passage 22 and the outflow oil passage 23, and the return oil passage 8 communicates with the tank 7. Therefore, while the hydraulic motor 1 is in operation, the relief valve 13 is completely open.

Next, when the hydraulic motor 1 is to be stopped, the switching valve 3 is of course returned to the neutral position. The area is reduced, and the amount of oil flowing to the hydraulic motor 1 through the switching valve 3 rapidly decreases just before it is shut off. On the other hand, since the hydraulic motor 1 has inertia, its rotational speed cannot be suddenly reduced, and it continues to rotate.

For this reason, the oil passage 5 or 6 on the inflow side leading to the hydraulic motor 1 lacks the amount of oil, and the hydraulic motor 1 tends to cause cavitation. However, since the switching valve 3 has been returned to near the neutral position, the return oil passage at the neutral position is opened, and part of the oil discharged from the hydraulic pump 2 flows through the oil passage 26 to the tank 7, increasing the oil pressure. Since the discharge oil pressure of the pump 2 has decreased, the hydraulic pressure acting on the IJ-F valve 13 through the pilot oil path 15 has decreased, and the pilot pressure from the oil path 15 no longer acts on the relief valve 13. , the relief valve 13 functions only as a normal relief valve having a pilot oil passage 14.

Since the pilot oil pressure from the pilot oil passage 14 is set to a low pressure, the return oil passage 8 is maintained at a low pressure. As described above, since the return oil passage 8 has a constant but low pressure, if the supply of oil to the inlet side oil passage of the hydraulic motor 1 is insufficient and the pressure decreases, the check valve 11, to oil path 5 via oil path 9, or check valve 12, oil path 1
Oil flows to the oil path 6 through 0. Therefore, even if the port through which the pressure oil flows becomes smaller just before the switching valve 3 is returned to the neutral position, and the oil supply becomes insufficient, the hydraulic motor 1 is refilled with oil from the return oil path 8. It operates smoothly without causing cavitation.

As described above, the present invention provides a low-pressure IJ valve in the return circuit of the switching valve that controls the hydraulic motor, and uses the pilot oil passage not only as the oil passage on the inflow side but also to operate the hydraulic motor. It is also guided from the discharge side oil path of the hydraulic pump.
And check from the return oil route.

Since the oil passage is connected directly to the hydraulic motor through the valve,
Even if oil supply to the hydraulic motor decreases during deceleration of the hydraulic motor, cavitation will not occur in the hydraulic motor because oil can be directly supplied from the return oil path.

Additionally, when the hydraulic motor is operating under load, pilot pressure acts directly from the hydraulic pump to open the relief valve, eliminating return side pressure (back pressure) and improving the operating efficiency of the hydraulic motor. .

In addition, since the relief valve only needs to be provided at the end of the return oil path, even if there are many switching valves, only one
Only one counterbalance valve is required, which is very economical and reduces costs compared to the conventional method in which each actuator circuit is provided with a counterbalance valve.

[Brief explanation of the drawing]

FIG. 1 is a conventional hydraulic motor circuit diagram, FIG. 2 is a hydraulic motor circuit diagram of the present invention, and FIG. 3 is a longitudinal sectional view showing the configuration of the IJ IJ-7 valve of FIG. 2. 1---=-Hydraulic motor 2-----1 Hydraulic pump 3-----All changeover valve 8-----1 Return oil path 9-----1--Double path 10---- -tt ll--+----Chetta valve 12-------u 13--, -m-relief valve 14-----Pilot oil line 15-------- The above patent applications Representative of Hitoyutani Heavy Industries Co., Ltd. Tadayoshi Otsuka

Claims (1)

[Claims] (1) In a hydraulic circuit in which an oil path is formed from the hydraulic pump to the hydraulic motor via the switching valve, and a bypass oil path for the switching valve is formed from the return oil path leading from the switching valve to the tank to the hydraulic motor via the check valve, A relief valve is provided near the end of the return oil path leading from the switching valve to the tank, and the pilot oil path is connected to the return oil path on the inflow side of the relief valve, and the other is connected to the oil on the discharge port side of the hydraulic pump. A hydraulic circuit for construction machinery, characterized in that it is connected to the road.