Piston Assembly for a Stirling Engine

Abstract

A piston assembly for a double-acting engine such as a double-acting Stirling engine. A pair of sealing rings located on opposite sides of a land ring are positioned between a base section and a dome section of a piston head. These sealing rings are alternatively urged into sealing engagement with the cylinder bore as the piston reciprocates. The ring assembly further features selected rings with radial gaps used with annular non-split rings. An expander ring is further provided to radially bias the sealing rings with radial gaps. The piston assembly further features assembly features and component configurations providing excellent piston gas sealing and durability performance.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims priority to provisional patent application No. 61 / 151,783 filed Feb. 11, 2009.FIELD OF THE INVENTION[0002]This invention is related to a heat engine and particularly to an improved Stirling cycle engine incorporating numerous refinements and design features intended to enhance engine performance, manufacturability, and reliability.BACKGROUND AND SUMMARY OF THE INVENTIONS[0003]The basic concept of a Stirling engine dates back to a patent registered by Robert Stirling in 1817. Since that time, this engine has been the subject of intense scrutiny and evaluation. Various Stirling engine systems have been prototyped and put into limited operation throughout the world. One potential application area for Stirling engines is for automobiles as a prime mover or engine power unit for hybrid electric applications. Other fields of potential use of a Stirling engine such as stationary auxiliary power units, marine applications a...

AI Technical Summary

Benefits of technology

[0007]The Stirling engine in accordance with the present invention has a so-called “modular” construction. The major components of the engine, comprising the drive case and cylinder block, are bolted together along mating surfaces. Piston rod seals for the pistons traverse this mating plane. A sliding rod seal can be used which is mounted either to the drive case or cylinder block. The rod seal controls leakage of the high pressure engine working gas at one end of the piston connecting rod to atmosphere.

[0010]The combustion exhaust gases after passing through the heater head of the engine still contain useful heat. It is well known to use an air preheater to use this additional heat to heat incoming combustion air as a means of enhancing thermal efficiency. In accordance with this invention, an air preheater is described which provides a compact configuration with high thermal efficiency.

[0013]A critical component in the Stirling engine of the type described previously involves providing highly reliable seals between the high pressure displacer pistons and the low pressure drive case of the machine. Separating these two volumes is a piston rod seal assembly. Each piston connecting rod reciprocates through a piston rod seal which needs to reliably seal against the piston rod to maintain a low loss rate of working gas to the atmosphere. Absolute sealing of gas leakage through this area is likely not achievable. However, the piston rod seal assembly in accordance with the present invention provides low levels of leakage and reduces contamination of the working gas through “pumping” of lubricating oil in the drive case region.

[0014]Another critical design feature for enhancing efficiency of the Stirling engine comes from the design of the piston assembly. The displacer piston separates the hot and cold fluid spaces of the engine and reacts against gas pressures in these areas to deliver mechanical power. Thermal conduction losses across the piston between the hot and cold spaces need to be minimized to enhance efficiency. Moreover, a highly reliable sliding gas seal is required between the piston rings and the cylinder bore. In addition to constituting a thermal loss, such leakage across the piston seals further results in a net mass exchange of working gases between the individual cycle volumes of the Stirling engine. Significant differences in leakage across the piston seals can result in rapidly changing gas volumes in the cycle volumes. Although means are provided in accordance with this invention for reducing such imbalances, it is desirable to reduce the rate at which these imbalances occur.

Problems solved by technology

Since that time, this engine has been the subject of intense scrutiny and evaluation.

Various Stirling engine systems have been prototyped and put into limited operation throughout the world.

In many past designs of Stirling engines, a large volume of the engine housing is exposed to the high working pressures of the working gas.

Upon the occurrence of a component failure causing leakage, a significant imbalance could result which could have a destructive effect on the engine.

Absolute sealing of gas leakage through this area is likely not achievable.

In addition to constituting a thermal loss, such leakage across the piston seals further results in a net mass exchange of working gases between the individual cycle volumes of the Stirling engine.

Significant differences in leakage across the piston seals can result in rapidly changing gas volumes in the cycle volumes.

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