Motors: expansible chamber type – Cyclically operable – Working member controlled inlet or exhaust port
Reexamination Certificate
2000-07-10
2001-05-15
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Cyclically operable
Working member controlled inlet or exhaust port
C092S240000
Reexamination Certificate
active
06230605
ABSTRACT:
BACKGROUND OF THE INVENTION
In the design of pneumatic engines, there has existed an historic problem of releasing “back pressure” caused by a return stroke of the engine piston after a firing or compression stroke has occurred. This problem has caused engine designers to employ complicated exhaust valves or to leave a clearance between the piston diameter and the cylinder diameter, so pressurized air could escape during the return stroke.
The mechanics of the pneumatic engine are very simple. When the piston is moving from the intake valve, it is in the compression stroke. When the piston is furthest away from the intake valve it exhausts any pressure left from the compression cycle. When the moving towards the intake valve, it is in the return cycle. This return cycle is where the piston's movement back to the firing position is critical; no pressure buildup should occur. In all designs only the inertia of the rotating components force the piston down during this cycle.
In the prior art, there exist pneumatic engines without a seal on the piston. These designs do not create back-pressure but are very inefficient during the compression stroke because of air loss between the piston and the cylinder wall. If an O-ring type seal, or any seal that seals in both direction, is used between the piston diameter and the cylinder diameter, the compression stroke becomes very inefficient since any compressed air would then exhaust at the top of the stroke. However, when the piston is returning to its firing position it can create up to 5 five atmospheres of back-pressure before the firing sequence begins again. This effect slows down the rotational speed of the rotating components. Thus more inertia and heavier parts such as flywheels are needed to compensate. These effects in other engines that create back-pressure requires an exhaust valve to vent this pressure. If no exhaust valve is used, such seals significantly lower the performance of the engine, and in some cases cause the engine not to function.
The present invention is therefore directed to an engine seal adapted to seal against the piston wall only during the compression stroke, but not during the return stroke, thereby obviating the need for either an exhaust valve or higher mass engine components.
SUMMARY OF THE INVENTION
Within a piston cylinder of a pneumatic engine, the inventive system comprises a piston proportioned for complemental travel within said piston cylinder, said piston having a radial compression surface thereof and means for effecting the axial reciprocation of said piston within said piston housing. The system further includes a piston seal including means for securement to said compression surface of said piston and an integrally dependent resilient annular skirt normally biased inwardly toward a longitudinal system axis, said skirt, in combination with said securement means, defining a radius of less than that from said system axis to interior walls of said cylinder during low pressure (return stroke) phases of a work cycle of the pneumatic engine and, during high pressure (compression stroke) phases thereof, defining a radius equal to that from the system axis to said inner wall of said cylinder. Therein, said inward bias of said skirt is overcome thereby causing axial and radial lifting of the skirt against inner walls of the cylinder, to effect a piston seal of a high integrity during high pressure phases of the engine work cycle. During low pressure phases, no seal is effected since the skirt has not yet expanded.
The piston seal more particularly includes a hollow cylindrical segment having an interior diameter complemental with an outside diameter of the piston to be sealed oppositely to the compression region of the engine cylinder. An upper base of the hollow cylindrical segment defines, in part, a surface which is complemental to lower annular surfaces of said piston which are radially inward from the inside diameter of the cylinder. The inventive includes, radially outwardly from said upper base of said cylindrical segment, an integrally dependent resilient annular umbrella-like skirt having a radial extent, when measured from the system axis, which is normally less than the radius from said axis to the outside diameter of the piston. Therein, the annular skirt in normally biased inwardly toward the system axis and radially away from the cylinder wall in which interface. Therefore sealing of said skirt against the cylindrical wall will occur only in the presence of elevated fluid pressure beneath the skirt which causes an axial lifting, and thereby radial expansion, of said skirt bringing the periphery thereof into fluid tight deformable contact with said wall of said cylinder during high pressure phases of the work cycle of the pneumatic engine.
It is accordingly an object of the present invention to provide an improved compression seal for a cylinder of a pneumatic engine.
It is another object to provide an improved piston-cylinder system, inclusive of a pneumatic piston seal, which will provide improved fluid integrity at the piston-cylinder interface during compression strokes of the engine.
It is a further object of the invention to provide a method of unsealing of a piston of a pneumatic engine during return strokes thereof.
It is a still further object to provide a piston seal for a pneumatic engine of a type particularly adapted for use with toy vehicles.
It is a further object to provide a piston seal of the above type which does not require manufacture thereof integrally with the manufacture of the piston of such an engine and does not require use of a return valve or high mass engine components.
The above and yet other objects and advantages of the present invention will become apparent from the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and Claims appended herewith.
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Lopez F. Daniel
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