Expansible chamber devices – With lubricating means – Portion of expansible chamber device includes solid...
Patent
1996-07-10
1998-10-27
Lopez, F. Daniel
Expansible chamber devices
With lubricating means
Portion of expansible chamber device includes solid...
92167, 921711, 92259, 267161, F01B 310
Patent
active
058264914
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a sealing arrangement on a piston-cylinder unit with a piston longitudinally movable in a cylinder. The cylinder has a liner extending in the direction of a central axis of the cylinder, with a piston casing and a contact-free gap seal between cylinder liner and piston casing for sealing a liquid or gaseous medium under excess pressure.
Sealing arrangements of this type are used in known manner in compressors, servo motors, measuring pistons or Stirling free-piston motors, which cooperate with a gaseous or, in the case of servo motors or measuring pistons, potentially also liquid medium. Special problems occur wherever the piston-cylinder unit is to be operated free of friction as well as also free of lubricants. This is the case for example with oxygen compressors, or compressors for the food industry. Known compressors of this type include a piston-cylinder unit in which the seal between piston and cylinder is formed by a labyrinth seal. Therein the piston must be guided as centrally as possible in the cylinder in order to avoid contact of the piston casing on the cylinder wall and to prevent corresponding damage or erosion. In order to meet these guidance conditions the piston is provided with a piston rod which is supported and guided in a crosshead. This crosshead is, in turn, driven in known manner via a connecting rod by a rotating crank shaft. In this way, the necessary oscillating motions of the piston are generated wherein the desired guidance of the piston in the cylinder is ensured through the crosshead. Corresponding compressors are described in the technical work "Kolbenverdichter {piston compressors}" by K. H. Kuttner, Springer Verlag 1991, pages 236 and in the following. A disadvantage of this implementation resides in that it is not possible to provide very narrow gaps between the piston casing and the cylinder wall but rather a relatively large play is necessary. This is due to the running play of the crosshead guidance, and to the fact that oilfree compressors require a significantly longer construction than oil-lubricated piston compressors. In a long cylinder, the excursions or the deviations of the piston from the central axis become increasingly greater and the free play or the gap between piston and cylinder must therefore be subsequently also correspondingly large. This requires subsequently also the use of labyrinth seals in order to attain the desired sealing between the pressure side of the piston and the pressure-free side. Since during the translational motions in the direction of the central axis the piston cannot be maintained precisely on this axis, the sealing gap between piston casing and cylinder wall does not have an annular cross section but rather the cross section is most often sickle-shaped. The consequence is that the width of the gap on one side can be nearly doubled that on an opposite side and accordingly the sealing tightness in this region is considerably reduced. This asymmetry of the sealing gap leads to considerable problems and is undesirable; however, it cannot be avoided in compressors of this type. The leakage losses in the region of the seal are also correspondly large.
From DE-B 19 33 159 a piston-cylinder unit for a Stirling piston machine is known in which the centering of the piston and the sealing between piston and cylinder is implemented via O-rings. However, this arrangement in practice has only a very short service life, since the seal rings in a lubrication-free operation are very rapidly worn and centering and sealing are no longer ensured. In addition, abrasion particles from the seals become entrained in the circulation of the pressure medium, which normally is not permissible and can also lead to considerable disturbance. Therefore with this solution and for a lubricant-free operation the precise guidance of the piston on the central axis and for long-term operation can not be achieved.
SUMMARY OF THE INVENTION
It is therefore the task of the present invention to describe
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