Cylinder Piston rod seal for a Stirling engine
In a cylinder piston rod seal for a Stirling engine, a hydrostatic bearing and differential pressure regulating valve are utilized to provide for a low pressure differential across a rubbing seal between the hydrogen and oil so as to reduce wear on the seal.
Presently there has become a revitalized interest in the Stirling engine in an attempt to improve its efficiency, cost and size. A basic Stirling engine design for example involves a piston cylinder arrangement wherein a piston is driven by theuse of hot and cold working gas. The gas is compelled to move from a cold space to a hot space continually and when the gas is hot it expands and pushes the piston in a first direction and when it is cold it is compressed by the piston moving back inthe opposite direction to its original position.
Generally, the piston may be connected to a piston rod which in turn connects to a crosshead. This crosshead may then be coupled to a crankshaft which is to be rotationally displaced by the reciprocating movement of the piston. An improvementon this basic concept for converting between rotary and the reciprocating motion of the piston.
However, a basic feature of the piston rod relationship is to provide a sealing off of the chamber from the crosshead during operation of the engine. This becomes especially important due to the high pressures (approximately 1500 psi) involvedin the cylinder and the use of hydrogen as a working gas.
There presently exists a piston rod seal which isolates the cylinder chamber from the crosshead during operation of the engine which is manufactured by Ningbo, Fenghua Quansheng Automation Engineering Co., Ltd.. This piston rod seal is depicted wherein a piston is shown disposed in a cylinder and coupled to a piston rod which in turn connects to a crosshead. A piston seal is provided between the crosshead and the piston and is disposed about thepiston rod.
A compartment is defined between the seal and piston containing hydrogen at a fluctuating pressure which varies during operation of the engine but is generally above 1500 psi. A rubbing seal is provided which separates compartment from another compartment which is pressurized at approximately the minimum pressure in the system (1500 psi). Another rubbing seal is provided separating compartment from the crankcase containing oil or other lubricant therein, with ascraper preventing a build up of oil on the piston rod. Seal and scraper are spring loaded against the piston rod to enable their effective use.
A problem with the aforenoted arrangement is that the hydrogen-to-oil seal which is continually spring loaded against the piston rod wears and the resulting deterioration causes a contamination of the hydrogen by the oil. This adverselyaffects the operation of the engine, shortens its usuable life period and require relatively frequent replacement resulting in expense and down time for the engine. There exists a need for a piston rod seal which provides for effective sealing whileeliminating the wearing problems heretofore realized.
The present invention provides a cylinder piston rod seal which utilizes a hydrostatic bearing which serves to supply pressure to the oil side of the hydrogen-to-oil seal at a pressure level slightly less than the pressure of the hydrogen so that there isa very slight pressure drop across the seal. In this regard, a chamber is provided intermediate on the oil side of the seal and coupled to a differential regulating valve which is also coupled to a chamber on the hydrogen side of the seal. This valvesenses the pressure on the hydrogen side of the seal and keeps the pressure on the oil side thereof slightly below it so as to prevent the ingress of oil into the hydrogen chamber. Because of the low pressure difference, the seal does not have to besqueezed against the piston rod as heretofore done, and can therefore expect to have a much greater useful life than the rubbing seal noted earlier.
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