Fluid handling – Systems – Supply and exhaust
Reexamination Certificate
1999-06-10
2001-01-23
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Supply and exhaust
C091S420000, C091S451000
Reexamination Certificate
active
06176261
ABSTRACT:
The invention relates to a hydraulic control device.
In hydraulic applications for extreme high pressures (working pressures between about 450 and about 800 bar) different from high pressure hydraulic applications (working pressures up to about 400 bars) frequently only pumps with relatively small delivery volume or multi-stage pumping systems with one pump stage having a small delivery volume of e.g. only 1.0 l/min, are used for achieving said maximum working pressure. This is for example useful in portable devices having an integrated pressure supply system, such as power screwdrivers, riveting devices, building moving devices, etc. In a hydraulic control device for extreme high working pressures however, then a leakage cannot be tolerated as it might be tolerable for high pressure hydraulic application. The reason is that the leakage with increasing pressure progressively is growing leading to the fact that the maximum working pressure cannot be reached or cannot be maintained since said increasing leakage cannot be compensated with such small delivery volumes as mentioned.
In high pressure hydraulic applications (brochure D 7470 B published by Heilmeier und Weinlein, DE, pages 1 and 3) for the directional control of hydro-motors directional seated valves are provided which due to their seated valve design are operating leakage-free. On page 3 of said brochure, example K, for a bi-directional actuable consumer two 3/2 directional seated valves with solenoid actuation are provided between the consumer lines and the pressure and return lines. The consumer lines additionally are supervised by load holding-blocking valves designed with a seated valve function. In hydraulic control devices for high pressure hydraulic application upstream of said solenoid actuated directional seated valves a 2/2 switch valve having a seated valve design is provided between the pressure line or pump line and the return line. Said switching valve is actuated by a solenoid in case that no consumer pressure is needed. Additionally a pressure limiting valve is responding when the maximum system pressure is reached. Another possibility employed in practice uses a pressure sensor connected to the pump line with which pressure sensor an electric switch is coupled to switch on and switch off the pump. As soon as the adjusted pressure is reached, the pump is switched off. Said principle is not useful for hydraulic applications with extremely high working pressures because said principle needs sophisticated control electronic circuitry and leads to extremely high loads for the pressure medium. Furthermore, directional control valves with a piston slide design as widely useful for high pressure hydraulic applications cannot be used for such extreme high working pressures as mentioned, due to the design depending unavoidable leakage and due to potential jamming danger of the piston slides under such extremely high working pressures.
Further prior art is contained in: U.S. Pat. No. 4,145,958, EP-A-0 718 504, U.S. Pat. No. 4,835,966, EP-A-0 823 559, U.S. Pat. Nos. 4,722,359, 4,506,517, 5,290,007, 5,464,330, 5,243,761.
It is a task of the invention to provide a hydraulic control device for the direction control of at least one hydro-motor of hydraulic applications with extremely high working pressures which hydraulic control device should be able to meet the particular requirements of hydraulic applications for extremely high working pressures with simple structural design, which is reliable and which avoids undesirable high loads of the pump or the pumping system.
Said task can be achieved by the features of the invention.
In said hydraulic control device customised for hydraulic applications for extremely high working pressures leakages reliably are avoided since the seated valve design with closure elements and valve seats made for example from hardened steel are absolutely leakage-free in the closure positions. Thanks to the leakage-free operation even extremely high working pressures can be reached with relatively small delivery volumes of the pump and, moreover, can be maintained reliably. Since the load pressure of the hydro-motor is backed up by the load holding blocking valve, in the basic position the system can be pressure relieved upstream of the load holding blocking valve in order to relieve the pump and the pressure medium. Important is that for said pressure relief of the system (idling or shunting condition) no electric signals have to be generated and no hydraulic pressures have to be derived electrically, but that said 2/2-idling-directional seated valve automatically switches into its open position so that the pump then can deliver the pressure medium counter to an extremely low counter-pressure into the return line and does not need to be switched off. In the region between the hydraulic actuation of said directional seated valve and the return line any leakage is avoided with technically simple efforts such that no pressure medium can leak from the pilot line into the return line. Particularly advantageous the pressure signal representing a pressure medium demand and present in the section of the consumer line between said black/white-directional seated valve and the load holding-blocking valve is used which pressure signal practically is available independent from the load pressure. The pressure signal is used to switch said 2/2-shunt directional seated valve leakage-free by means of its hydraulic actuation into the locking position. The idling pressure and the flow resistance in idling condition are extremely low and desirable for the pump. Said pressure signal results from the co-operation between the respective black/white-directional seated valve, the load holding blocking valve associated thereto, and the load pressure maintaining said blocking valve in its locking position. As core of the invention for hydraulic applications with extremely working pressures the leakage freedom of seated valves switching even under said extreme high pressures without jamming danger is combined with the pressure signal resulting from the piping structure in order to achieve an idling or shunting condition which is depending on demand, is reliable, simple in view to control technique and produces no or only negligible losses. A black/white directional seated valve is characterised by fully open and fully closed positions only (black/white) and no intermediate positions where the valve would be only partially open or partially closed.
In a very simple fashion said pressure signal for switching into the idling or shunting-condition is generated by a combination of black/white-directional seated valves and a load holding-blocking valve. Then said pressure signal (a pressure drop) for the switching action into the idling or shunting condition is generated by relieving the system via a second black/white-directional seated valve in the branch from the consumer line towards the return line.
Advantageously for a double-sided actuable hydro-motor alternatively two pressure signals are brought to said hydraulic actuation. Said hydraulic actuation is relieved via said black/white-directional seated valve to the return line for switching the valve into the idling position.
In another embodiment both load holding-blocking valves are hydraulically pilot operated opened by the pressure in the respective other consumer line, and particularly in strict dependency from the directional control pressure in said respective other consumer line. The pilot lines or the pressure signals, respectively, for opening said load holding blocking valves additionally can be used to operate said idling or shunting circuit.
Basically also further hydro-motors can be controlled with the same pressure source and with the help of a common idling or shunting system. By means of the chain of changeover valves the respective highest load pressure is brought into said hydraulic actuation, said hydraulic actuation, however, permanently is leakage free towards the return side.
In another embodiment said black/white directional seated valves are
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Heilmeier & Weinlein Fabrik F. Oel-Hydraulik GmbH & Co. KG
Michalsky Gerald A.
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