Compressor having a piston received on a gas bearing

The present invention relates to a compressor having a gas-bearing piston, in particular for use as a refrigerant compressor in a domestic refrigerator.

Compressors with rotary-driven lifting pistons and oil lubrication are conventionally used in domestic appliances. Owing to the rotary drive, during the course of its lifting movement in a working chamber the piston in such a compressor is also exposed to forces transverse to the lifting direction which push the piston against the wall of the working chamber. To protect the compressor against frictional wear there must be a continuous film of oil between piston and chamber wall. The viscosity of the oil must be high enough to prevent the oil from being displaced between wall and piston under the influence of a transverse force. The greater the transverse forces are, the more viscous the oil must be and the friction losses are all the greater owing to the viscosity of the oil.

To improve the efficiency of the compressors increased efforts have recently been made to develop compressors with a linear motor drive. A linear motor of this kind exerts smaller transverse forces on the piston so lower viscosity lubricants can be used, through to bearing of the piston by the gas that is itself to be compressed. With a compressor of this kind with gas bearing, openings are formed in a wall of the working chamber covered by the piston and communicate with an outlet connection of the compressor, so a small portion of the compressed medium can flow from the outlet connection, via the openings and back into the working chamber and in the process generates a gas cushion between piston and wall which ideally allows movement of the piston without any contact with the wall at all and therefore without any frictional wear either.

These ideal conditions prove to be difficult to implement, however. In practice it has been found that the linear compressor frequently fails after a relatively short service life owing to the frictional wear between piston and chamber wall.

It is therefore the object of the invention to create a compressor with gas bearing which allows such frictional wear to be reliably prevented.

The object is achieved by a compressor comprising an inlet connection and an outlet connection for a gas to be compressed, and a working chamber in which a piston for compressing the gas can be displaced, openings communicating with the outlet connection being configured in a wall of the working chamber covered by the piston, said compressor being characterized by a particle filter arranged in a flow path of the gas through the compressor between the inlet connection and the outlet connection.

More detailed examinations of the failed compressors have shown that contaminants found therein could be attributed not only to abrasion of the piston and chamber wall, but were in some cases introduced from other areas of the refrigerant circuit as well, and it is assumed that even if the quantity and particle size of these contaminants, which are alien to the compressor, is not sufficient per se to affect the mobility of the piston in the compressor, they initially block several of the wall openings if they circulate with the flow of refrigerant, so the gas cushion protecting the piston becomes incomplete. Contact between piston and wall can no longer be reliably prevented in the region of these holes, so the abrasion resulting from contact quickly destroys the compressor.

The inventive particle filter remedies this by preventing these foreign bodies from reaching the wall openings.

A particle filter of this kind may be provided at various sites in the compressor. According to a first configuration the particle filter is arranged between the inlet connection and the working chamber. A particle filter of this kind has the advantage that foreign bodies can be prevented from reaching the working chamber from the outset. This is particularly desirable in the case of coarse foreign bodies which can cause damage solely by virtue of their presence in the working chamber.

One drawback of such placement of the particle filter however is that the filtering of the entire gas flow passing through the compressor that it brings about requires considerable driving power and as a result affects the efficiency of the compressor. Additionally, the drop in pressure at a particle filter of this kind can never be greater than the pressure at the inlet connection itself, so to achieve a sufficient throughput a high conductance and therefore a large filter cross-section may be necessary. In particular when using the compressor in a refrigerating machine it is important that the particle filter does not build up excessive dynamic pressure as this would impair evaporation of the refrigerant in the evaporator located upstream of the filter.

According to a second embodiment the particle filter is arranged in a pipe, connecting an egress of the working chamber to the outlet connection, between the egress and a branch pipe leading to the openings. This arrangement of the filter does not lead to an undesirable increase in pressure at the inlet connection of the compressor. In addition a greater drop in pressure can be built up at such a filter arranged on the pressure side of the compressor than at the inlet-side filter described above, so sufficient throughput can also be achieved in a compact filter although such a high drop in pressure does in turn affect the efficiency of the compressor.

According to a third, particularly preferred embodiment a branch pipe leading to the openings branches off from a pressure pipe connecting an egress of the working chamber to the outlet connection, and the particle filter is arranged in the branch pipe. As a particle filter of this kind only acts on the fraction of the gas throughput which is required for generating the gas cushion, the driving power that has to be applied for filtering is low, even if the drop in pressure at the particle filter is the same as that according to the second embodiment.

While the filter arranged in the branch pipe does not prevent foreign bodies from passing through the compressor from the start, it does collect them during the course of compressor operation as soon as they pass into the branch pipe.