Power plants – Motor operated by expansion and/or contraction of a unit of... – Unit of mass is a gas which is heated or cooled in one of a...
Reexamination Certificate
2001-09-26
2002-12-03
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Unit of mass is a gas which is heated or cooled in one of a...
C060S525000, C092S031000, C092S129000, C417S222100
Reexamination Certificate
active
06487858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to systems for converting between reciprocal and rotary motion. In another aspect, the invention concerns barrel-type engines having an elongated drive shaft that is rotated by a plurality of pistons symmetrically spaced around the shaft and reciprocating generally parallel to the axis of rotation of the shaft. In still another aspect, the invention concerns engines employing a non-hydrocarbon-based fluid as a piston lubricant. In a further aspect, the invention relates to parallel, double-acting Stirling engines employing an expandable and contractible working fluid to drive double-ended pistons. In a still further aspect, the invention concerns Stirling engines which employ heat exchangers that are integral with the cylinder assemblies that house the pistons. In a yet further aspect, the invention concerns systems for varying the power output of Stirling engines.
2. Discussion of Prior Art
Many conventional mechanical devices require reciprocal motion to be converted to rotary motion (e.g., engines) or rotary motion to be converted to reciprocal motion (e.g., pumps). An often-employed system for converting between rotary and reciprocal motion involves the use of a crank arm having a first end coupled to a linearly reciprocating piston and a second end coupled to a rotating crank shaft at a location eccentric to the axis of rotation of the crank shaft. Such an arrangement can be inefficient and can produce excessive vibration and noise. Further, such a system can impart a bending moment on the rotating crank shaft, thereby requiring a larger crank shaft in order to minimize the risk of failure due to fatigue.
As an alternative to systems using crank arms to convert between rotary and reciprocal motion, several crankless systems have been developed. These crankless systems typically employ a swash plate/roller arrangement. In such a arrangement the swash plate is coupled to a drive shaft for rotation therewith and the roller contacts at least one curved cam surface of the swash plate. The roller is coupled to a linearly reciprocating piston so that when the swash plate is rotated, the roller rolls on the curved cam surface, thereby causing the piston to move linearly. Alternatively, when the piston reciprocates linearly, the roller presses on the curve cam surface, thereby causing the swash plate and the drive shaft to rotate. Such prior art swash plate/roller systems, however, typically cause bending stresses on the drive shaft. Further, such systems have typically produced excessive noise and vibration due to their lack of dynamic balance.
Stirling engines (i.e., external combustion engines) have existed for years but have not been widely commercially implemented. Stirling engines typically operate by heating and cooling an expandable and contractible working fluid in a working fluid chamber to thereby drive reciprocating pistons. A potentially very efficient Stirling engine is known as a “parallel” form of the Franchot engine, described and illustrated in
Principles and Applications of Stirling Engines,
by C. D. West, 1986, pp 64-65, the disclosure of which is incorporated herein by reference. In such a “parallel” Stirling engine, an expansion (i.e., hot) cylinder and a compression (i.e., cold) cylinder, both containing respective double-ended pistons, cooperate with the compressible working fluid to drive the double-ended pistons. One significant advantage of the parallel Stirling arrangement is that the entire expansion cylinder (including both ends of the cylinder) is heated while the entire compression cylinder is cooled. This results in the virtual elimination of thermal shuttle losses typically experienced in serially connected Stirling engines comprising individual cylinders which each have a hot end and a cold end. However, a significant disadvantage of prior art parallel Stirling engines is the difficultly in maintaining a proper working fluid seal when a reciprocating piston rod coupled to the piston extends through an end portion of the cylinder wall that defines the working fluid chamber.
Stirling engines typically employ non-lubricated teflon piston rings to prevent the escape of the working fluid from the working fluid chambers. The main reason teflon rings are used rather than more conventional metallic piston rings is that metallic rings require conventional hydrocarbon-based lubricants to ensure efficient extended operation of the engine. However, using a conventional hydrocarbon-based lubricant in conjunction with a metallic piston ring will inevitably result in some lubricant passing from the lubricant holding chamber on one side of the piston into the working fluid chamber on the other side of the piston. The presence of even trace amounts of conventional hydrocarbon-based engine lubricants in the working fluid chamber of a Stirling engine is highly undesirable because these lubricants, when entrained in the working fluid, can irreversibly contaminate the regenerator of the Stirling engine. Thus, conventional engine lubricants can not be effectively employed to lubricate the pistons of a conventional Stirling engine. However, the solution of employing non-lubricated teflon piston rings in a Stirling engine has its own drawbacks. In particular, the physical properties of teflon (particularly its low melting point) place an upper temperature limit at which the piston cylinder can be maintained without damaging the teflon ring. This problem is especially pronounced in parallel Stirling engines employing double-ended pistons because the piston ring must be located proximal the working fluid chambers at each end of the pistons. Thus, a significant disadvantage of using teflon piston rings in a parallel Stirling engine is that the working fluid can not be heated to its optimum temperature without damaging the teflon piston rings.
A further disadvantage of prior art Stirling engines is the inefficiency of locating the heat exchangers remotely from the expanding and compression cylinders. Although spacing the heat exchangers from the expansion and compression cylinders allows for adequate heat exchange between the working fluid and the heat transfer fluid (i.e., the heating or cooling source), such a configuration does not allow for heat to be conducted directly from the physical structure of the heat exchanger to the physical structure of the cylinder assembly.
A still further disadvantage of prior art Stirling engines is their inability to rapidly vary the power output of the engine.
OBJECTS AND SUMMARY OF THE INVENTION
Responsive to these and other problems, it is an object of the present invention to provide an apparatus for converting between rotary and reciprocal motion without imparting a significant bending moment on a rotating drive shaft of the apparatus.
A further object of the present invention is to provide a dynamically balanced apparatus for converting between rotary and reciprocal motion.
A still further object of the present invention is to provide an apparatus for converting between rotary and reciprocal motion that has a more compact and robust construction than prior art devices.
An even further object of the present invention is to provide a parallel Stirling engine which employs a unique piston rod arrangement wherein the piston rod does not extend through a wall that defines the working fluid chamber.
Still a further object of the present invention is to provide a Stirling engine having a heat exchanger which is integral with the cylinder assembly to thereby allow heat to be directly conducted from the physical structure of the heat exchanger to the physical structure of the cylinder assembly.
Another object of the present invention is to provide a system which lubricates the pistons of a Stirling engine without causing contamination of the regenerator.
Still another object of the present invention is to provide a Stirling engine having the ability to rapidly vary the power output of the engine.
It should be noted that the above-listed objects
Hovey & Williams, LLP
Nguyen Hoang
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