Brakes – Internal-resistance motion retarder – With means for locking parts together temporarily
Reexamination Certificate
1999-09-17
2001-10-02
Oberleitner, Robert J. (Department: 3613)
Brakes
Internal-resistance motion retarder
With means for locking parts together temporarily
C267S064120
Reexamination Certificate
active
06296089
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a locking device of the type in which a cylinder defining a chamber that is filled with a working fluid receives a piston on a piston rod that divides the chamber into two working sections and a flow connection between the working sections is controlled by a first valve and a second valve arranged in series.
U.S. Pat. No. 5,450,933 describes and shows a locking piston/cylinder device, for example, for use with doors, in which a flow connection through the piston has two throttle points in series to allow fluid flow between two working sections, one on each side of the piston. The flow at each throttle point is controlled by a valve that has a valve body arranged in step fashion that is biased in the closing direction by a spring. A small pin on both valve bodies seals a flow connection between the two throttle points or working sections. An annular shoulder on the valve bodies provides a pressure-affected surface for the one flow direction, and the projected end face of the pin provides a pressure-affected surface for the other flow direction. The opening motion of both valves and therefore the securing force of the locking device is determined by the springs of the two valve bodies, since both valves must be open when the working medium flows. Very strict relationships are, therefore, imposed on the design of the securing forces in relation to the opening forces, which can lead to the opening forces being too great or too small. The object of the two valves connected in series lies, among other things, in that a slightly greater force is required for opening the valve and a smaller force is required for keeping the valve open, wherein one valve would be completely sufficient for one through-flow direction. If the intent is to realize this operational behavior for both flow directions, then two valves must be used. For reasons of installation space economy, the two valves are arranged in a flow connection and must, therefore, inevitably be open at the same time.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the above-described relationship between the opening and locking forces.
According to the invention, the foregoing object is attained by a locking device that includes a cylinder defining a chamber that is filled with a working fluid, a piston dividing the chamber into two working sections, and a flow connection between the working sections which is controlled by a first valve and a second valve arranged in parallel. The second valve is arranged to open only when the first valve opens in response to dynamic pressure of working fluid passing through the first valve from one working section. The second valve, once open, is kept open by a pressure in a bypass from the said one working section past the first valve, regardless of the state of the first valve.
The essential advantage of the present invention is that with an already open second valve, the state or the throttle action of the first valve does not exert any influence on the operational behavior of the second valve. Consequently, the two valves can be designed exactly for the respective technical tasks.
In an advantageous embodiment, the second valve is a gate valve that opens or closes the bypass to the first valve. If a gate valve has its flow direction radial to the direction of movement of the piston, then even small adjusting forces on the locking device move the gate valve between its open and closed positions.
With regard to the simplest and shortest flow paths, the working medium that has flowed from the first valve and the working medium flowing from the bypass are combined in an accumulation chamber.
A locking device, according to the present invention, may have a valve tappet associated with one of the two valves that is functionally connected to an opening device, the opening device being controlled independently of the pressure conditions of the working medium acting on the two valves. As a result, the locking device can be brought into the unlocked condition at a predetermined point along the operating stroke.
The opening device may include a securing device which secures the valve tappet during a sliding motion of the piston and, therefore, opens the one of the two valves independently of the state of the other valve.
The function of keeping one of the two valves open is limited to one stroke length by virtue of the fact that the securing device includes a spring element which keeps the valve tappet open for one stroke length counter to the force of the spring of the associated valve. Then, the opening device disengages and is thereafter inactive. At a new stop of the locking device motion, the opening device is inoperative.
Consequently, the securing device is designed for a defined stroke position of the piston, which corresponds to the fully retracted position of the piston. In vehicle doors, which must be opened from the closed position, there is frequently an unfavorable lever arm length when the door is closed so that relatively high manual forces would be required for an opening motion of one of the two valves. This particular embodiment counteracts the above-described effect and enables the door to be opened with a low force.
The spring element, together with the valve tappet, can be allowed to cooperate with a cylinder-end stop, wherein the stop determines the defined stroke position. A simple bead in the cylinder can be used as the stop.
REFERENCES:
patent: 3414134 (1968-12-01), Nealis
patent: 5450933 (1995-09-01), Schüttler
patent: 5560456 (1996-10-01), Koch et al.
patent: 5799759 (1998-09-01), Koch
patent: 3413815 (1985-10-01), None
patent: 4239172 (1993-12-01), None
patent: 1161859 (1969-08-01), None
Koch Klaus
Sauer Rainer
Schuttler Oliver
Baker & Botts L.L.P.
Lipka Pamela J.
Oberleitner Robert J.
Stabilus GmbH
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