SU466678A3 - Hydraulic drive - Google Patents

Description

(54) HYDRAULIC DRIVE

The invention relates to a hydraulic drive with a closed circulation circuit and, in particular, a hydraulic drive with an adjustable pump, equipped with a servo drive for changing the working volume, consisting of an actuating hydraulic cylinder and a follower hydraulic distributor, with which the master cylinder is connected.

In the known hydraulic drives with an adjustable pump, in order to limit the increase in pressure in the pressure line with a sharp increase in the external load or productivity, the pumps provide for the action of a moving element of the follow-up valve controlled by pressure in the pressure line.

The proposed hydraulic drive for this purpose uses the characteristic for hydraulic drives with a closed circulation loop the pressure drop in the low pressure line with a sharp increase in external load or pump performance, caused mainly by the limited performance of the feed pump.

To use this pressure drop, the cavity of the servo master cylinder is in communication with the low pressure line of the closed loop of the hydraulic drive through a check valve. As a result of the pressure drop, the fluid from the cavity of the master cylinder is displaced by the piston through the specified check valve. There is a shift of the following control valve to reduce the pump displacement.

The cavity of the actuating hydraulic cylinder can be connected to the low pressure line through a non-return valve.

The cavity of the master cylinder can be communicated with the discharge line of the auxiliary pump, the pressure in which is maintained using a control throttle somewhat less than in the low pressure line of the hydraulic drive, or with the discharge line of the feed pump through a check valve and adjustable throttle.

A variant is possible with a master cylinder connected to a mechanical permutation device (M.

FIG. Figures 1 and 2 depict hydraulic circuit diagrams (versions with and without an additional pump).

The described hydraulic drive comprises an adjustable pump 1 communicated with an actuating hydraulic motor (not shown) by the high pressure line 2 and the low pressure line 3.

The pressurizing line 4 of the pump of the pump 5 is connected to the lines 2 and 3 through check valves 6.

Overflow valve 7 is connected to line 4 and maintains the set pressure in the low pressure line 3. Pump 1 is equipped with a servo drive containing an actuating hydraulic cylinder 8 connected by a gear 9 with a regulating body of the pump 1, a follower valve 10 and a setting hydraulic cylinder 11, the rod of which can be connected to the valve 10 by means of the lever 12.

The valve 10 is read from line 4 of the make-up pump 5. The cavity of the master cylinder C is communicated with the low pressure line 3 via a non-return valve 13. The cavity of the actuating cylinder 8 can also be communicated with the line 3 via a back valve 14. The piston of the master cylinder 11 is loaded with a return spring 15.

To control the movement of the piston of the master cylinder I, and, consequently, of the hydraulic distributor 10 and the piston of the hydraulic cylinder, an additional pump 16 can be provided (see Fig. 1) with a safety valve 17 and an adjustable throttle 18.

The magnitude of the opening of the throttle 18 determines the pressure in the cavity of the hydraulic cylinder 11 and, thus, the position of the piston of the latter. The pump 16 may be communicated with the line 4 of the pump 5 through the check valve 19.

In the absence of an additional pump (see Fig. 2), the cavity of the hydraulic cylinder I communicates with line 4 through a check valve 20 and an adjustable throttle 21. In this embodiment, the master hydraulic cylinder is connected to a shifting lever 22.

When the hydraulic drive operates at steady state or with smooth changes in the external load, the pressure in line 3 is maintained at the level determined by the setting of valve 7.

In the case of a sharp increase in external load, a decrease in pressure occurs in line 3. In the cavity of the master cylinder 11, the pressure also drops. As a result, the piston of this hydraulic cylinder is moved by the action of the spring 15, the lever 12 and the movable element of the hydraulic distributor 10. The pressure also drops in the cavity of the hydraulic cylinder 8 and its piston moves to the right.

The movement of the latter through the transmission 9 is transmitted to the regulator of the pump 1, reducing its working volume. This reduces the pressure drop in line 2. When pressure in line 3 is restored, the position of the pistons of hydraulic cylinders 11 and 8 is restored and the pump displacement increases without a significant increase in pressure in line 2.

A similar picture also occurs when

a sharp increase in the speed of rotation of the shaft of the nose 1 and with a sharp closure of the throttles 18 (see Fig. 1) or a sharp shift of the lever 22 (see Fig. 2).

In all cases, there is a reduction in the rate of increase in pressure in line 2.

Subject invention

Claims (6)

1. A closed-loop hydraulic actuator that contains an adjustable main pump, communicated with a low pressure line of a closed circuit, a feed pump and a transfer valve, and a servo drive to change the displacement of the main pump, consisting of an actuating hydraulic cylinder and fed from an injection line feed pump of a follow-up valve controlled by means of a master cylinder, characterized in that, in order to limit the increase in pressure in the pressure line of a closed loop during an abrupt increasing the external load or capacity of the main pump due to the automatic reduction of the pump displacement using a closed circuit for this pressure drop in the low pressure line, the working cavity of the servo master cylinder communicates with the low pressure line of the closed loop through a non-return valve. 2. The hydraulic actuator according to claim 1, characterized in that the working cavity of the actuating cylinder of the servo drive is also communicated with drain line through an additional check valve. 3. The hydraulic actuator on PP. 1 and 2, characterized in that the piston of the master cylinder is loaded with a return spring, the force of which corresponds to a pressure lower than the pressure in the low pressure line, under steady state operation of the hydraulic drive. 4. The hydraulic actuator on PP. 1-3, characterized in that an additional pump is provided for supplying the master cylinder, with a discharge line in parallel with a safety valve and an adjustable choke. 5. The hydraulic actuator according to claim 1, characterized in that the discharge line of the additional throttle is communicated through a non-return valve with the discharge line of the pump feed. 6. The hydraulic actuator according to claim 3, which is different the fact that the master cylinder is rigidly connected to the mechanical permutation device, and its cavity is in communication with the discharge line of the feed pump through a check valve and an adjustable choke.