JPS59714B2 - Discharge amount control circuit of variable displacement hydraulic pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit that controls the discharge amount of a variable displacement expansion hydraulic pump in accordance with the viscosity of hydraulic oil.

When starting a hydraulic system in a low temperature state such as in winter or in a cold region, a warm-up operation is generally performed to raise the oil temperature.

Since it is undesirable to rapidly flow hot hydraulic oil into cold hydraulic equipment, the actuator of the hydraulic circuit may be moved to flow pressure oil during this warm-up operation.

As described above, when operating a hydraulic pump in a state where the oil temperature is low, cavitation often occurs in the hydraulic pump, causing damage to the pump and having a negative impact on its life.

An object of the present invention is to provide a discharge amount control circuit that prevents cavitation of a variable displacement expansion hydraulic pump during warm-up operation.

This invention detects the viscosity of the hydraulic oil and regulates the amount of tilting of the variable displacement expansion hydraulic pump according to the detected value, thereby preventing the flow velocity of the hydraulic oil from exceeding the limit of cavitation occurrence. .

First, a method for detecting hydraulic fluid will be described with reference to FIG. 1a.

Pressure oil is supplied from one end at a constant pressure P, and the other end is open to the atmosphere or maintained at a constant pressure lower than Pl. and.

Here, when the pipeline is open to the atmosphere,
Consider the relationship between the pressure P2 between the orifice O and the choke C and the viscosity of the hydraulic oil.

If the flow rate of the hydraulic oil flowing through the orifice O is Ql, then it can be determined by the equation (Q, variable).

Qt=α°~rA71Y[Σ...(1) where α: flow coefficient (generally about 0.6) A opening area of the niorifice g: acceleration of gravity r: specific weight.

Further, the flow rate Q2 of the hydraulic oil flowing through the choke C is determined by equation (2).

π・d4・P Q2−□ ・・・・・・(2)128
・μ・t Where d: Diameter of choke with circular cross section t=Length of choke μ: Viscosity of hydraulic oil.

In this case, since Qt and Q2 are the flow rates of the same pipe, Ql = Q2.

Therefore, we transform equations (1) and (2) by assuming that they are equal,
If we set the constants together as K, we obtain equation (3).

1. , =, (3) "-"° C. The relationship between viscosity and pressure P2 is calculated from equation (3) and shown in a graph as shown in Figure 1b.

That is, a change in viscosity can be detected as a change in pressure.

Note that one end of the conduit is open to atmospheric pressure, and Pl
Even if the pressure is maintained at a constant pressure P3 lower than
) and a similar relationship is established.

Next, one embodiment of the present invention will be explained with reference to FIG.

The suction sides of a variable displacement pump (hereinafter referred to as main hydraulic pump) 1 that supplies pressure oil to an actuator (not shown) and an auxiliary hydraulic pump 2 that supplies pressure oil to the control device 7 are introduced into the same oil tank 22. The discharge pressure of the auxiliary hydraulic pump 2 is kept constant by the pressure control valve 8.

The discharge amount control device 7 of the variable displacement pump consists of a piston 4, a cylinder 3 containing a spring 6, and a directional control valve 5.
The piston 4 is connected to a tilting device of the main hydraulic pump 1.

Pressure oil from the auxiliary hydraulic pump 2 is guided into either the left or right chamber of the cylinder 3 to increase or decrease the discharge amount of the main hydraulic pump 1.

In this embodiment, when pressure oil is introduced into the left chamber of the cylinder 3, the discharge amount of the main hydraulic pump increases.

At this time, the main hydraulic pump 1 is tilted in the direction of arrow I.

Among the circuits between the cylinder 3 and the directional switching valve 5, a directional switching valve 12 as a control device is provided in the middle of the circuit that increases the discharge amount of the main hydraulic pump 1, and the directional switching valve 12 is provided as a control device. The side pipe has an orifice 9 and a choke 10.
A viscosity detection circuit 13 having a viscosity detection circuit 13 is connected thereto.

The other end of the viscosity detection circuit 13 is open to the oil tank.

Pressure oil between the orifice 9 and the choke 10 is guided to one end of a directional valve 12, and a spring 11 is provided at the other end of the directional valve 12.

The relationship between the force of the spring 11 and the pressure P2 introduced from between the orifice 9 and the choke 10 to the directional control valve 12 is such that when P2 is larger than a predetermined value, the directional control valve 12 is switched to the right position, and the pressure P2 is set to the predetermined value. When it is smaller, the directional control valve 12 is set to the left position a (the state shown in the figure).

When the hydraulic circuit is operated at a low temperature, the pressure P2 of the viscosity detection circuit 13 increases, and when the directional control valve 12 overcomes the spring 11 and is switched to position b, the left chamber of the cylinder 3 communicates with the oil tank. The piston 6 is moved to the left by the spring 6, and the discharge amount of the main hydraulic pump 1 is reduced.

At this time, the pressure oil from the directional valve 5 is blocked by the directional valve 12, so as long as the viscosity of the hydraulic oil is higher than a predetermined value, the main hydraulic pump 1 is operated regardless of the position of the directional valve 5. , it is operated with a small amount of tilting to prevent cavitation from occurring.

When the oil groove rises and the viscosity decreases, the pressure P2 also decreases and the directional control valve 12 becomes the state shown (position a), so the discharge amount of the main hydraulic pump 1 is controlled by the directional control valve 5. .

FIG. 3 shows another embodiment of the present invention in which the discharge amount of the main hydraulic pump 1 is controlled by an external command pressure car (-ffiU). Represents the same thing or something equivalent.

In this embodiment, the variable displacement pump discharge amount control device 7 consists of a servo valve 14 and a hydraulic cylinder 3, and pressure oil from the auxiliary hydraulic pump 2 is supplied to the hydraulic cylinder 3 via the servo valve 14. It has become.

The servo valve 14 includes a sleeve 16, a spool 15 housed in the sleeve 16, and a spring 1 that presses one end of the spool 15.
8, and the sleeve 16 is connected to the piston 4 of the cylinder 3 via a link 17.

The command for the discharge amount is given to the servo valve 14 by pressure through the command line 23, and the pressure causes the spool 15 to spring 18.
is moved to a position where it balances the force of.

As a result, pressure oil from the auxiliary hydraulic pump 2 is supplied to the cylinder 3 through the servo valve 14, and the piston 4 is moved.

The amount of movement of the piston 4 is transmitted to the sleeve 16 by the link 17, and when the spool 15 moves to the position according to the command, the servo valve 140 circuit is closed and the piston 4 is stopped.

Orifice 9 and choke 10 in viscosity detection circuit 13
Pressure oil between the two is sent to the control device 12.

Control device 1: M: consists of a cylinder 19 containing a piston 20 and a spring 21, and the pressure oil is guided to a chamber on the side opposite to the spring of the cylinder 19.

One end of the piston 20 protrudes coaxially with the spool 15, and limits the distance that the spool 15 moves to the right when the piston 20 moves and compresses the spring 21 due to an increase in pressure P2.

When the hydraulic circuit is operated at a low temperature, the pressure P2 of the viscosity detection circuit 13 increases, and when the piston 20 overcomes the spring 21 and moves to the left, the end of the piston 20 touches the spool 15.
protrude to the side.

At this time, even if command pressure to increase the discharge amount is applied to the spool 15 from the outside through the command pipe and path 23, the spool 15
is restricted from moving to the right by the protruding end of the piston 20, and therefore the discharge amount of the main hydraulic pump 1 is equal to the pressure P2.
controlled by

That is, the discharge amount of the main hydraulic pump 1 does not exceed the discharge amount regulated by the viscosity of the pressure oil, and cavitation is prevented from occurring.

As the oil temperature increases and the viscosity decreases, the pressure P2 also decreases.
The piston 20 is pushed back by the spring 21, so the amount of movement of the spool 15 is not restricted in any way, and the discharge amount of the main hydraulic pump 1 is controlled by command pressure from the outside.

In the above embodiment, the viscosity detection circuit 13 is connected to the main hydraulic pump 1.
Although it was installed on the discharge side of the auxiliary hydraulic pump 2, which is the power source of the device that controls the discharge amount of The viscosity detection circuit 13 may also be provided for such a hydraulic pump.

Furthermore, in a so-called self-pressure-operated hydraulic pump that uses part of the pressure oil discharged by the pump as the power for the pump discharge amount control device, the pressure oil that moves the piston 4 is used as in the above-mentioned embodiment. A similar effect can be obtained by limiting or limiting the discharge amount command.

Note that the oil pressure P2 in the viscosity detection circuit 13 may be converted into other energy such as electricity, thereby controlling the discharge amount of the main hydraulic pump.

According to the invention described above, it is possible to prevent the occurrence of cavitation during low-temperature operation of the variable displacement cedar hydraulic pump, and to reduce damage caused by cavitation.

[Brief explanation of drawings]

FIG. 1a is an explanatory diagram showing a pressure oil viscosity detection circuit according to the present invention, FIG. 1b is a graph showing the relationship between pressure oil viscosity and pressure in the pressure oil detection circuit of FIG. 1a, and FIGS. The figure is a hydraulic circuit diagram showing a different embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Variable displacement cedar hydraulic pump, 2... Auxiliary hydraulic pump, 3... Cylinder, 4... Piston, 5... Directional switching valve, 6... Spring, 7... Control device , 8...
Pressure control valve, 9... Orifice, 10... Choke, 11... Spring, 12... Directional switching valve, 13...
Viscosity detection circuit, 14... Servo valve, 15... Spool, 16... Sleeve, 11... Link, 18...
・Spring, 19...Cylinder, 20...Piston, 2
1... Spring, 22... Oil tank, 23... Command pipe.

Claims (1)

[Claims] 1. In the discharge side circuit of a hydraulic pump that sucks hydraulic oil from the same oil suction side as the variable displacement expansion hydraulic pump to be controlled and discharges it at a constant pressure, a circuit with a constant pressure lower than the constant pressure is sequentially passed through an orifice and a choke. A discharge amount control circuit for a variable displacement expansion hydraulic pump, characterized in that a viscosity detection circuit communicating with the variable displacement hydraulic pump is provided, and the viscosity detection circuit is connected to a discharge 1tIJ control device for increasing or decreasing the discharge amount of the variable displacement expansion hydraulic pump.