Hydraulic control system

#The invention relates to a hydraulic control system with a hydraulic motor, which is connected with a control valve via two working lines, the control valve being connected with a low-pressure connection and, via a compensation valve, with a high-pressure connection.

#In dependence of the desired operation direction of the motor on existing control valves, the control valve releases flow paths, from the high-pressure connection to a working line on the one side and from the other working line to the low-pressure connection on the other side. This release, however, occurs in a more or less throttled manner, the height of the throttling resistance depending on the operating stroke (or another corresponding operating movement) of the control valve. In this connection, the compensation valve serves as pressure control valve. In some cases, it is also called pressure balance. It ensures that the pressure over the slide of the control valve is practically always the same. Expediently, the compensation valve exists in the form of a slide, which is acted upon on the one side by a return spring and the load pressure and on the other side by the pressure in a line section between the compensation valve and the control valve.

#Usually, such control valves work reliably. Problems occur, when the motor is working with the so-called negative loads. Such negative loads occur, for example, when the motor is activated by an external weight, for example a load hanging in a crane hook. Another example is a vehicle's own weight, which drives on a sloping surface or has to be braked from a certain speed. In this case, the hydraulic system of the control device may tend to oscillate.

#FIG. 1 is a schematic view of the hydraulic control system of this invention;

#FIG. 2 is a schematic view of nominal hydraulic lines; and

#FIG. 3 is a schematic view of a second embodiment of a hydraulic control system of this invention.

#A control device 1 has a proportional valve 2 as control valve, which is merely shown schematically in FIG. 1. The proportional valve 2 has two adjustable throttles A, B, which can be adjusted by means of an operating handle 3, which is also only shown schematically. The proportional valve 2 is connected with a high-pressure connection P and a low-pressure connection T. In the connection to the high-pressure connection P is arranged a compensation valve 4, which has a return spring 5 prestressing the compensation valve 4 in the opening direction. For this purpose, the compensation valve 4 can, for example, have a slide, which is loaded by the return spring 5 in the opening direction. In the closing direction, the slide can be acted upon via the line 6 by a pressure at a point 7 between the compensation valve 4 and the throttle A. When the throttle A is closed, the pressure at the point 7 increases to a level, which closes the compensation valve 4. When the throttle A is opened, the pressure at the point 7 is reduced, and the return spring 5 can open the compensation valve 4 further. For this reason, the compensation valve 4 can also be called pressure control valve or pressure balance valve.

#The proportional valve 2 is connected with a motor 10 via working lines 8, 9. In the present case, the motor 10 consists of two part drives, both acting upon the wheels of a vehicle. The motor 10 is provided with a brake 11, which can be released via a control line 12. In the control line, the pressure rules behind the throttle A. As, in a manner not shown in detail, the proportional valve 2 can also lead the pressure from the high-pressure connection P via the throttle B to the motor 10, a shuttle valve 13 is provided, which uses the highest pressure between the throttles A, B for releasing the brake 11.

#Additionally, the compensation valve 4 is acted upon by a load sensing pressure LS in the opening direction, that is, the load sensing pressure LS acts in the same direction as the return spring 5. The return spring 5 produces a force, which, for example, corresponds to a pressure of 7 bars.