Power plants – Pressure fluid source and motor – Condition responsive control of or by input to input pump...
Reexamination Certificate
1999-10-14
2001-05-01
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of or by input to input pump...
C091S001000, C091S517000
Reexamination Certificate
active
06223530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention in general relates to a control device for hydraulic power cylinders, and, more particularly, to power cylinders for a tailgate of a truck, with a motor driven hydraulic medium pump which may be connected to a medium supply and, by way of pump branch conduits and associated control valves, to a chamber of the power cylinder.
2. The State of the Prior Art
When working with hitherto known control devices of this kind (U.S. Pat. No. 5,305,680), tilting moments pose a problem in that they subject the lifting arms and closing cylinders of the tailgate to increased tension or pressure forces when a load has been improperly positioned on a tailgate. This may, for instance, result in a five-fold increase of the permissible forces which may cause damage to, or destroy, the lifting arms and/or closing cylinder.
OBJECT OF THE INVENTION
The invention aims at providing a device of the kind referred to supra which alleviates the mentioned hazards.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the invention an adjustable electric pressure gauge and switching device provided with a computer for entering threshold pressure values is connected to the chamber or the corresponding pump branch conduit. When a predetermined pressure value is exceeded, the measuring and switching device switches off the pump motor and actuates a signal generator. Furthermore, a safety valve set at a lower opening pressure than the mentioned threshold pressure is connected to the chamber or corresponding pump branch conduit opened by a solenoid valve when the device is in an idle state.
The invention provides a simple structure which prevents, for instance, overloading of lifting arms or closing cylinder of a tailgate while generating a warning signal at the same time. The safety valve which is opened in the idle state of the device prevents overload indications when the pressure gauge and switching device is actuated as a result of the hydraulic circuit warming up as may happen when the vehicle is exposed in an idle state to the sun for an extended period, for such increased temperatures may lead to pressure increases of 10 bar/° C.
In accordance with the invention, the pressure gauge and switching device preferably is only connected to a source of electricity when the tailgate is in an open condition, or some other implement, for instance a crane, is in a loaded state, within an angle of inclination of ±15°.
Preferably, the electric pressure gauge and switching device actuates a counter for counting the number of times pressure has been exceeded.
REFERENCES:
patent: 3788076 (1974-01-01), Lansky et al.
patent: 5255517 (1993-10-01), Weber
patent: 5305680 (1994-04-01), Weber
patent: 5317870 (1994-06-01), Ingawa
patent: 5687567 (1997-11-01), Hansson et al.
patent: 5944159 (1999-08-01), Scheneider et al.
patent: 36 30 850 (1988-03-01), None
Hormann Karl
Ryznic John E.
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