Expansible chamber devices – With guide or seal on cylinder end portion for piston or...
Patent
1997-11-06
1999-06-29
Ryznic, John E.
Expansible chamber devices
With guide or seal on cylinder end portion for piston or...
92168, 92DIG2, 384 1, F16J 1518, F16C 3200
Patent
active
059163500
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a bearing assembly for a piston rod of a linearly reciprocating piston type engine.
The type of linearly reciprocating piston engine with which the invention is concerned has a cylinder, a piston movable axially in said cylinder, a piston rod secured to and projecting from each side of the piston, said piston rod extending axially of the piston and being movable with the piston in a fixed plane parallel to the axis of the cylinder, a cover assembly at one end of the cylinder and facing said one side of the piston, and an opening formed in said cover assembly through which the piston rod extends.
Usually, the piston will have a pair of piston rods, each extending axially outwardly of a respective one of the opposed working faces of the piston.
The invention has been developed primarily in connection with a reciprocating piston type compressor having a "floating" piston (in which the piston does not rely upon contact with the wall of the cylinder to guide its linear reciprocation). However, it should be understood that the invention may be applied to other forms of reciprocating piston type engine which require mechanical power input in order to do mechanical work e.g. to pressurise a working fluid as in a pump or compressor, or which are energised by a pressurised working fluid in order to generate mechanical power e.g. an air motor.
There are many applications in industry in which a supply of compressed air is required e.g. to operate pneumatic tools in an assembly line, or in a textile mill, and in recent years rotary compressors (screw compressors, vane compressors or centrifugal compressors) have been considered to be the sole practical and reliable way of supplying compressed air.
The invention seeks to reverse this trend, and to overcome perceived drawbacks to the use of linearly reciprocating piston type compressors.
It is of course known to mount a linearly displaceable shaft in a bearing assembly, in which the shaft is taken through a circular central aperture of a ball bearing, and the balls engage the outer periphery of the shaft and each ball rotates about its own axis as the shaft moves back and forwards relative to the ball bearing during each cycle of operation.
The balls are arranged in an annular array between two coaxial annular surfaces, in which the inner annular surface is formed by the cylindrical periphery of the shaft and the outer annular surface is formed by a fixed sleeve or bush which is normally rigidly secured against the internal wall of the opening in which the bearing is mounted.
Grease or oil is normally contained within the annular space in which the balls are arranged, and lubricate the rotation of the balls. While the balls are rotating, a film of lubricant builds-up at the interfaces between the instantaneous surfaces of contact of the balls and the inner and outer annular surfaces. However, each time the shaft reverses its linear movement, there is a "dwell period" in which the rotation of the balls is arrested (prior to rotation in a reverse direction) and this tends to break down the lubricant film and allow direct metal to metal contact which is a source of wear which, over a period of time, results in unacceptable wear and breakdown, and generation of undesired clearances caused by wear.
Therefore, while it would be particularly suitable for a "floating piston" type of compressor to provide rigid guidance for the movement of the piston rod in an end cover of the cylinder via a bearing assembly, (known for other uses in guiding linear movement as described above), this would not be suitable for such a use because of wear problems in the balls, and the need to provide rigid guidance by the bearing assembly to the piston/piston rod assembly.
Accordingly, in one aspect the invention seeks, by simple means, to improve the lubrication of the bearings in the bearing assembly for a piston rod of a reciprocating piston type of engine of the type defined above.
According to one aspect of the invention there is provided a linearly reciprocating pisto
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Carding Specialist Limited
Ryznic John E.
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