Valves and valve actuation – Fluid actuated or retarded – With mechanical movement between actuator and valve
Reexamination Certificate
1997-11-19
2001-03-13
Lopez, F. Daniel (Department: 3745)
Valves and valve actuation
Fluid actuated or retarded
With mechanical movement between actuator and valve
C091S394000, C092S16200R
Reexamination Certificate
active
06199822
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fluid-operated actuator in which a piston is arranged for reciprocal motion in a cylinder between two end positions.
BACKGROUND OF THE INVENTION
The need for hydraulic or compressed air-operated actuators exists in many technical areas. Traditional actuators have a piston arranged for reciprocal motion within a cylinder, with the piston cooperating with an actuator rod connected to a component, the relative position of which is to be changed. Typically, the piston is provided with at least one piston ring to ensure no leakage of the operating fluid past the piston. In many applications, the piston rings are made of a soft, elastic material such as rubber or a plastics material. In working environments in which an actuator may be subjected to high temperatures, however, it is not possible to use materials having a low melting point. In such cases it has hitherto been necessary to employ piston rings made of, for example, spring steel.
Nevertheless, even spring steel has limitations as regards temperatures to which it may be subjected. For example, unless special precautions are taken, it is not possible to use such an actuator in the vicinity of the exhaust manifold of an internal combustion engine.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a fluid-operated actuator suitable for use in harsh environments, which actuator is simpler than traditional actuators.
This object is achieved by a fluid-operated actuator comprising:
a housing defining a cylinder having a cylinder wall extending about a longitudinal axis;
a piston arranged for reciprocal motion in said cylinder along said longitudinal axis between a first end position and a second end position;
an actuator rod cooperating with said piston for displacement substantially along said longitudinal axis, and
first sealing means in said housing for establishing a sealing contact with a first region of said piston in said first end position and second sealing means in said housing for establishing a sealing contact with a second region of said piston in said second end position to thereby prevent leakage of operating fluid past said piston when said piston is in said first end position and said second end position;
wherein said piston and said housing are arranged such that when said piston is between said first end position and said second end position, operating fluid is permitted to leak between said piston and said cylinder wall.
The present invention is based on the insight that many actuators are required only to effect displacement of a component between two predetermined end positions. A typical application of such an actuator is for operating an on/off valve, i.e. the valve is either fully open or fully closed. With such valves, movement of the piston between the two end positions takes place very rapidly. As such, the need for high quality sealing exists only in the end positions because any leakage which takes place during the displacement of the piston will be low in volume due to the short time which the piston takes to travel from one end position to the other.
In a preferred embodiment of the invention, the actuator rod cooperates with the piston via a flexible coupling, the flexible coupling being arranged to permit axial displacement of the actuator rod relative the piston. In this manner, sealing relationship is ensured even if the actuator rod be subjected to vibrations.
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Lerner David Littenberg Krumholz & Mentlik LLP
Lopez F. Daniel
Volvo Lastvagnar AB
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