JP2690353B2 - Make-up device for hydraulic circuit using load sensing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a makeup device for a hydraulic circuit using a load sensing system suitable for use in a hydraulic excavator or the like.

B. Conventional Technology FIG. 4 shows an example of a hydraulic circuit of a conventional hydraulically driven vehicle using a load sensing system. This hydraulic circuit
A traveling hydraulic circuit TC for driving the hydraulic traveling motor 4A,
An excavation hydraulic circuit DC for driving the hydraulic cylinder 4B is provided, and each circuit is provided with control valves 2A, 2B.

In the load sensing system, the pressure across the control valves 2A and 2B, that is, the differential pressure between the inlet pressure (pump pressure) and the outlet pressure of the control valve (the load pressure of the hydraulic actuator, called load sensing pressure) becomes a constant value. Thus, the discharge volume of the variable displacement hydraulic pump 1 (hereinafter referred to as the tilt angle) is controlled.

Therefore, a load sensing regulator 11 that switches according to the differential pressure between the pump pressure and the load sensing pressure is provided, and the differential pressure between the pump pressure and the load sensing pressure is provided by the spring 11.
When the pressure becomes equal to or higher than the pressure set in a, the load sensing regulator 11 switches to the direction of the position A according to the pressure. In this position, the pump pressure is guided to the servo cylinder 12, the pump tilt angle is reduced, and the pump discharge flow rate is reduced. On the contrary, when the differential pressure becomes less than the pressure set by the spring 11a, the load sensing regulator 11 is switched to the position of B and the servo cylinder 12 is connected to the tank. As a result, the pump tilt angle increases and the pump discharge flow rate increases.

The load sensing pressure is the load sensing line.
It is taken out from one of the circuits via a high pressure selection valve 17 provided in 18 and guided to a load sensing regulator 11. Further, in FIG. 4, 19A and 19B are circuits TC,
A pressure compensating valve for independently compensating the DC load pressure, 15 is an unloading valve, which opens when the differential pressure between the load sensing pressure and the discharge pressure of the variable displacement hydraulic pump 1 becomes a predetermined value or more and opens. Guide the discharged oil to the tank.

By the above operation, in the load sensing system,
The pump tilt angle is controlled so that the pump discharge flow rate becomes the required flow rate of the control valve 2A or 2B, the excess flow rate is not discharged, and waste due to throttling loss is eliminated, improving fuel efficiency and operability is also good. .

The direction and flow rate of the pressure oil discharged from the variable displacement hydraulic pump 1 controlled by such a load sensing system are controlled by the hydraulic pilot type control valves 2A and 2B. For example, in the traveling hydraulic circuit TC, when the forward / reverse switching valve 8 is switched to the forward (F position) and the pedal 6a of the pilot valve 6 is operated, the oil discharged from the hydraulic pump 5 is discharged from the pilot control valve.
It is guided to the pilot port 2a of 2a, and this control valve 2a is switched by the stroke amount according to the pilot oil pressure. As a result, the oil discharged from the variable displacement hydraulic pump 1 is supplied to the hydraulic motor 4A via the counter balance valve 3 and the vehicle runs. The speed of the vehicle depends on the amount of depression of the pilot valve 6.

When the pedal 6a is released during traveling, the pilot valve 6 shuts off the pressure oil, and the outlet port thereof communicates with the tank 10. As a result, the pressure oil acting on the pilot port 2a returns to the tank 10 via the forward / reverse switching valve 8, the slow return valve 7, and the pilot valve 6. At this time, the return oil is throttled by the throttle 7a of the slow return valve valve 7, the pilot control valve 2A is gradually switched to the neutral position, and the vehicle is decelerated.

During such deceleration, the hydraulic pump 1 to the main pipelines 13A, 13
The hydraulic oil is no longer supplied to B, the hydraulic motor 4A acts as a pump, and the oil circulates in the hydraulic motor 4A, the control valve 2A, and the main pipelines 13A, 13B. However, due to pressure loss in the circuit, leakage, drainage, or the like, the amount of oil flowing into the hydraulic motor 4A may be insufficient and cavitation may occur.

Therefore, the oil discharged from the pilot hydraulic pump 5 is guided to the main pipelines 13A and 13B connecting the hydraulic motor 4A and the control valve 2A via the makeup pipeline 20 and the double check valves 21a and 21b to prevent cavitation.

C. Problem to be Solved by the Invention However, in order to secure a sufficient makeup flow rate, it is necessary to sufficiently increase the capacity of the pilot hydraulic pump 5, resulting in an increase in cost. Further, when the vehicle restarts after deceleration, if the discharge oil of the pilot hydraulic pump 5 flows to the makeup line 20 side, the flow rate to the control valve 2A side tends to be insufficient, and the pilot pressure acting on the control valve 2A is delayed. . This phenomenon becomes particularly noticeable when descending a slope, which adversely affects the driving feeling.

There is also a method of performing makeup by directly connecting the double check valves 21a and 21b to the tank instead of the makeup of oil from the pilot hydraulic pump 5, but if the tank back pressure is low, the makeup flow rate will be insufficient, In particular, cavitation is likely to occur during deceleration during downhill travel, which adversely affects the life of hydraulic equipment. If the set pressure of the tank low pressure relief valve (not shown) is increased to increase the tank back pressure, the effective pressure of the hydraulic motor decreases, which is not preferable. Furthermore, pressurizing the tank with air increases the cost.

A technical problem of the present invention is to improve makeup efficiency in a hydraulic circuit using a load sensing system without increasing costs and without affecting other hydraulic equipment.

D. Means for Solving the Problems 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.
Of the variable displacement hydraulic pump 1, the hydraulic motor 4A that is driven by the pressure oil discharged from the variable displacement hydraulic pump 1 to drive the inertial load, the control valve 2A that controls the pressure oil flowing to the hydraulic motor 4A, and the variable displacement hydraulic pump 1. Make-up of a hydraulic circuit using a load sensing system including a load sensing regulator 11 for controlling the discharge volume of the variable displacement hydraulic pump 1 so as to keep the discharge pressure higher than the load pressure of the hydraulic motor 4A by a predetermined value. Applies to equipment.

 Then, the above technical problem is solved by the following configuration.

A rotation detecting means 35 for detecting that the hydraulic motor 4A is rotating, a valve position detecting means 37 for detecting that the control valve 2A is in the neutral position, and a main conduit connecting the hydraulic motor 4A and the control valve 2A. 13A and 13B are the discharge lines 31 of the variable displacement hydraulic pump 1.
The makeup pipes 32a, 32b connected to and the makeup pipes 32a, 32b are arranged, and the detection means 35, 37 detect that the hydraulic motor 4A is rotating and the control valve 2A is in the neutral position. And a makeup valve 34 that opens the makeup lines 32a and 32b.

An unload valve 15 that opens when the pressure difference between the discharge pressure of the variable displacement hydraulic pump 1 and the load pressure of the hydraulic motor 4A exceeds a predetermined value to allow the discharge pressure of the variable displacement hydraulic pump 1 to escape to the low pressure line 15
May be provided.

E. Action For example, when the inertia traveling state is detected by the rotation detecting means 35 and the valve position detecting means 37, the makeup valve 34 is opened and the oil discharged from the variable displacement hydraulic pump 1 is made up by the makeup pipeline 32a,
It is supplied to the main pipelines 13A and 13B connected to the input / output port of the hydraulic motor 4A through 32b. As a result, makeup is applied. Since the discharge volume (tilt angle) of the variable displacement hydraulic pump 1 is controlled by the load sensing regulator 11, the pump tilt angle is controlled according to the required makeup flow rate, and makeup oil can be sufficiently supplied to the hydraulic motor 4A. .

Also, the discharge pressure of the variable displacement hydraulic pump 1 and the hydraulic motor
Unload valve where the pressure difference from the load pressure of 4 A is more than a specified value
Even if 15 is opened and the makeup flow rate increases, the makeup pressure does not become higher than the above differential pressure, and there is no effect on the durability of each device that constitutes the makeup circuit.

F. Embodiment -First Embodiment- A first embodiment of the present invention will be described with reference to FIG. The same parts as those in FIG. 4 will be described with the same reference numerals.

The device according to the present embodiment supplies makeup oil to the traveling hydraulic circuit TC by the discharge oil of the variable displacement hydraulic pump 1, and the discharge pipe line 31 of the hydraulic pump 1 and the double check valve 21a,
Makeup lines 32a, 32b, check valve 33 between 21b
Also, a makeup circuit MC formed by makeup valve 34 is provided.

The make-up valve 34 is controlled by the pressure difference between the load sensing pressure and the discharge pressure of the pilot hydraulic pump 5, and is switched between the m position for communicating the make-up pipelines 32a and 32b and the closed l position. Only when traveling, the discharge pressure of the pilot hydraulic pump 5 is one pilot port 34a of the makeup valve 34.
A travel detection valve 35 is disposed between the pilot hydraulic pump 5 and one pilot port 34a of the makeup valve 34 so as to be guided to. The traveling detection valve 35 is a three-position switching valve, and at the neutral position N, one pilot port 34a of the makeup valve 34 is connected to the tank via a pipe line 36b.
At the operating positions L and M, the pilot port 34a and the pilot hydraulic pump 5 are connected via the pipelines 36a and 36b. The other pilot port 34a of the makeup valve 34 is connected to the load sensing pipe 18 by a pipe 37. Further, a relief valve 38 is provided in the makeup line 32b.

In addition, 45 is a swivel joint installed at the connecting portion between the upper swing body and the lower traveling body.

In the above configuration, the travel detection valve 35 constitutes rotation detection means, and the conduit 37 connected to the load sensing line 18 constitutes valve position detection means.

 The operation of the hydraulic circuit thus configured will be described.

When the traveling pedal 6a is released during normal traveling to start decelerating traveling, the control valve 2A is gradually switched to the neutral position. for that reason,
For example, the line 13B becomes high pressure and the line 13A becomes low pressure, and the travel detection valve 35 is switched to the M position. As a result, the discharge pressure of the pilot hydraulic pump 5 is guided to one pilot port 34a of the makeup valve 34. On the other hand, during this deceleration operation, the control valve 2A is switched to the neutral position, so that the load sensing pressure becomes zero, and as a result, the makeup valve 34 is switched to the m position, and the makeup pipe lines 32a and 32b are connected.
Therefore, the oil discharged from the variable displacement hydraulic pump 1 is guided through the make-up circuit MC from the double check valves 21a, 21b to the main pipelines 13A, 13B of the travel motor 4A to be made up.

Here, since the tilt angle of the variable displacement hydraulic pump 1 is controlled by the load sensing regulator 11, when the make-up required flow rate increases and the pressure in the pump discharge pipe line 31 decreases, the tilt angle of the pump 1 is correspondingly increased. The angle increases and the discharge flow rate increases, making it possible to sufficiently supply makeup oil.
Further, when the differential pressure between the load sensing pressure and the load pressure of the hydraulic motor 4A exceeds a predetermined value, the unload valve 15 opens and the discharge pressure of the variable displacement hydraulic pump 1 escapes to the low pressure line. Even if a sufficient amount of makeup is applied, the makeup pressure is prevented from rising undesirably.

-Second Embodiment- A second embodiment of the present invention will be described with reference to FIG. The same parts as those in FIG. 1 are described with the same reference numerals.

The pilot hydraulic make-up valve 34 is an electromagnetic switching make-up valve 134, and when the inertia traveling state is detected, the makeup valve 134 is electrically switched to supply makeup oil to the traveling hydraulic circuit TC.

The inertial traveling can be detected by whether or not the control valve 2A is neutral and high pressure is generated in either one of the main pipelines 13A and 13B. Therefore, the travel detection valve 35 is controlled by the pressure difference between the main pipelines 13A and 13B.
Is switched to guide the discharge pressure of the pilot hydraulic pump 5 to the pressure sensor 41. On the other hand, since the load sensing pressure is zero when the control valve 2A is in the neutral position, the pressure sensor 42 detects the load sensing pressure.
Guide the load sensing pressure to. The detection outputs of the pressure sensors 41 and 42 are input to the controller 43, and the controller 43 determines inertial traveling.

FIG. 3 is a flowchart for detecting the inertial traveling state.

In step S1, the traveling state signal P1 and the control valve position signal P2, which are the detection outputs of the pressure sensors 41 and 42, are read,
It is determined in S2 whether P1 is greater than or equal to the predetermined value R1, and in step S3 P2
Is determined to be zero. If both steps S2 and S3 are affirmed, the process proceeds to step S4, and the makeup valve 134 is switched to the m position. When either one of steps S2 and S3 is denied, the routine proceeds to step S5, where the makeup valve 134 is switched to the 1 position. After performing steps S4 and S5, the process returns to the beginning.

Even in the second embodiment as described above, the makeup similar to that in the first embodiment can be achieved.

In addition, the main pipeline 13 is used to detect whether or not the vehicle is actually traveling.
The differential pressure between A and 13B can be directly detected by a differential pressure gauge, or the rotation of the traveling drive shaft can be monitored. Further, the neutral state of the control valve 2A can be detected by various methods such as monitoring the discharge pressure of the pilot valve 6 or directly monitoring the depression amount of the traveling pedal 6a.

In the above, the make-up of the traveling hydraulic circuit has been described, but the present invention can be applied to a swing hydraulic circuit and a circuit having a hydraulic motor that drives other inertial bodies.

G. Effect of the Invention According to the present invention, in the hydraulic circuit using the load sensing system, when the hydraulic motor also detects the inertial driving state, the hydraulic motor is driven by the discharge oil of the variable displacement hydraulic pump for driving the hydraulic motor. Since makeup oil is supplied, the makeup efficiency can be improved without increasing the pump capacity for makeup. Also, when the differential pressure between the load sensing pressure and the load pressure of the hydraulic motor exceeds a specified value, the discharge line of the variable displacement hydraulic pump is made to communicate with the low pressure line. Even when makeup is applied, the makeup pressure is prevented from undesirably rising.

[Brief description of the drawings]

1 and 2 are circuit diagrams showing first and second embodiments of the present invention, FIG. 3 is a flow chart showing an example of a processing procedure of the second embodiment, and FIG. 4 is a circuit showing a conventional example. It is a figure. 1: Variable displacement hydraulic pump 2A, 2B: Pilot control valve 3: Counter balance valve, 4A: Hydraulic motor 5: Pilot hydraulic pump 6: Pilot valve, 7: Slow return valve 8: Forward / reverse switching valve 11: Load sensing regulator 12: Servo cylinder, 13A, 13B: Main line 15: Unload valve 32a, 32b: Make-up line 34: Make-up valve, 35: Travel detection valve 37: Line MC: Make-up circuit, TC: Travel hydraulic circuit

Claims (2)

(57) [Claims] 1. A variable displacement hydraulic pump driven by a prime mover, a hydraulic motor rotated by pressure oil discharged from the variable displacement hydraulic pump to drive an inertial load, and pressure oil flowing through the hydraulic motor is controlled. A load sensing system including a control valve and a load sensing regulator for controlling the discharge volume of the variable displacement hydraulic pump so as to maintain the discharge pressure of the variable displacement hydraulic pump higher than the load pressure of the hydraulic motor by a predetermined value. In a makeup device for a hydraulic circuit using, a rotation detecting unit that detects that the hydraulic motor is rotating, a valve position detecting unit that detects that the control valve is in a neutral position, and the hydraulic motor. A makeup line that connects a line communicating with a control valve to the discharge line of the variable displacement hydraulic pump; A makeup valve which is disposed in the pipeline and opens the makeup pipeline when the hydraulic motor is detected by both of the detecting means and the control valve is detected to be in the neutral position. Make-up device for hydraulic circuit using load sensing system. 2. An unload valve that opens when a pressure difference between the discharge pressure of the variable displacement hydraulic pump and the load pressure of the hydraulic motor exceeds a predetermined value to release the discharge pressure of the variable displacement hydraulic pump to a low pressure line. A make-up device for a hydraulic circuit using the load sensing system according to claim 1.