Patent Application
20100229717
The present invention relates to a linear compressor, comprising a piston housing and a compressor piston movable back and forth therein along an axis, wherein the compressor piston is supported in the piston housing by means of a housing wall having openings and by means of a gas flowing through the openings; to a refrigeration device; to a method for producing a linear compressor and to a gas pressure bearing which includes a rotatable and/or displaceable body and a bearing element, wherein the body is supported in the bearing element by means of a bearing wall having openings and by means of a fluid flowing through the openings.
With oil-free linear compressors it is known to separate a compressor piston from the cylinder wall by a cushion of gaseous refrigerant which flows inwardly into the cylinder through micro-bores through a cylinder wall. For an oil-free bearing of this type, the so-called gas pressure bearing, a continuous supply of gas is required in order to maintain the cushion. If the gas cushion is too thin or inhomogeneous, friction occurs through contact of the compressor piston with the cylinder wall. The friction leads to wear and loss of performance of the linear compressor.
Known solutions provide a multiplicity of micro-bores formed in the cylinder wall in order to form the gas cushion. As is known from U.S. Pat. No. 6,575,716, a peripheral groove with a central supply bore may also be provided in the cylinder wall. As compared to the micro-bores, the central peripheral groove has the disadvantage of uneven support capacity over the circumference and higher gas consumption. On the other hand, the micro-bores suffer an increased danger of blockage by impurities and require an upstream filter for the gas.
It is therefore an object of the present invention to provide a linear compressor and a refrigeration device with which reliable operation even over a long period can be achieved at low cost.
It is further an object of the present invention to specify a method for producing a linear compressor or a refrigeration device with a linear compressor, whereby a linear compressor or a refrigeration device can be produced at low cost in a simple manner, so that reliable operation even over a long period is made possible. In addition, it is an object of the invention to specify a method for cooling merchandise which allows especially rapid, reliable and energy-saving cooling of merchandise.
It is further an object of the invention to provide a gas pressure bearing which can be produced economically, operates reliably and is not susceptible to malfunctions.
These objects are achieved according to the invention by the linear compressor, by the refrigeration device, by the gas pressure bearing, by the method for producing the linear compressor, by the method for cooling merchandise and by the refrigeration device, as specified in the respective independent claims. Further advantageous configurations, in isolation or combined with one another in any desired manner, are the subject matter of the respective dependent claims.
The linear compressor according to the invention comprises a piston housing and a compressor piston movable back and forth therein along an axis, the compressor piston being supported in the piston housing by means of a housing wall having openings and by means of a gas flowing through the openings, and the housing wall being porous.
The compressor piston is supported in the piston housing by a gas cushion built up by the gas flow between the compressor piston and the piston housing. For this purpose gas is forced through the openings of a housing wall which serves as a bearing surface for the compressor piston. The openings enable gas to be supplied and therefore a bearing support to be provided at the locations where contact of the compressor piston with the piston housing would otherwise lead to wear. In order to build up the gas flow, the housing wall is porous.
In this context the term “porous” means that, unlike the known bore-holes, which pass through the housing wall in a substantially rectilinear manner and allow a gas flow only along the bore direction, the openings can also receive a lateral gas flow. Through the porosity, the gas inside the housing wall can flow in different, in particular more than two, directions. In particular, the gas can also flow parallel to a surface of the housing wall. The gas flow through the porous housing wall may be diffusive, i.e. the direction of the flowing gas changes locally from pore to pore and does not remain substantially unchanged, as in the case of a bore-hole in which a tubular flow forms. The porosity of the housing wall may be produced, in particular, by a granular structure of the housing wall. The porosity of the housing wall may be produced through bonding of a multiplicity of granules which are baked or sintered to one another.
The advantage of this porosity is that, in the event of blockage of a pore, a multiplicity of neighboring pores are available, into which the local gas flow can be diverted. Unlike the case with the known drilled openings, a local blockage of a single pore does not lead to blockage of the whole channel over the whole thickness of the housing wall, but only to blockage at the local site within the housing wall. As a result, the gas pressure bearing is far less susceptible to malfunction through contamination. An upstream filter for the gas can be dispensed with. Through a suitable choice of the porosity, the gas flow through the housing wall can be predefined very uniformly, whereby uniform bearing forces are produced. Uniform bearing forces provide good guidance in the bearing, and the magnitude of the gas flow required for adequate bearing support can be reduced.
The housing wall advantageously has open pores. Because of the open porosity, the gas can flow within the housing wall transversely to the main flow direction of the gas in an especially simple manner, if an opening at one location is blocked. Through the property of the housing wall of also permitting a lateral gas flow, the effective total number of flow channels available to the gas flow is considerably increased.
In a particular configuration the housing wall is sintered.
Through a suitable choice of the relevant parameters during sintering, the porosity, and therefore the flow behavior, for example the flow resistance, of the housing wall can be precisely tailored to the particular requirements of supporting the cylinder piston in the piston housing.
The local flow resistance through the housing wall advantageously changes along the axis of the piston housing. Through adaptation of the porosity along the axis, the bearing forces at a given location, which may vary in dependence on the position of the compressor piston, can be taken into account. In particular in zones where high bearing forces are required, a comparatively low through-flow resistance is to be selected, while a correspondingly higher local through-flow resistance can be specified in zones where only low bearing forces arise. By means of profiling of the flow resistance through the housing wall, the gas cushion can be adapted. The gas consumption required for adequate bearing support can thereby be minimized.
In an advantageous configuration the porosity, in particular the material content, of the housing wall changes along the axis. In this case the mean pore sizes, the distribution of pore sizes, the ratio of open pores to closed pores and the proportion of material to free spaces, i.e. the material content, among other parameters, can be changed. The material content may be from 70% to 99%, in particular from 80% to 90%. The porosity can be influenced, for example, by the selection of the grains to be bonded to one another in the sintering process, or by the temperature profile over time during the sintering process.
It is also advantageous to vary the thickness of the housing wall. The local through-flow resistance can also be influenced, or the profile of the bearing forces acting on the compressor piston can be influenced or predefined, via the thickness of the housing wall.
In a particular configuration the flow resistance, in particular the thickness of the housing wall, varies over the length of the piston housing within a range from 1.5 to 6, in particular within a range from 2 to 4.
The length of the piston housing should be understood to mean the length corresponding to the stroke of the compressor piston in the piston housing, that is, the length over which support for the compressor piston in the piston housing is required.
For example, the local through-flow resistance increases along the axis in the direction of retraction of the compressor piston from the piston housing. This adaptation of the local through-flow resistance is suitable for cases in which the bearing forces required for the compressor piston in the retracted state of the compressor piston from the piston housing are smaller than in the “telescoped” state, i.e. when the compressor piston is fully inserted in the piston housing.
The housing wall may be configured as a cylinder liner. In this case the cylinder liner may be inserted in the piston housing in such a manner that an annular cavity, which may be charged with the gas through a gas connection, is formed between the piston housing and the cylinder liner.
The housing wall may be made from a metal or from a ceramic material.
The compressor piston may be supported in an oil-free manner in the piston housing.
The housing wall has pores the mean diameter of which is within the range from 0.005 mm to 0.100 mm, in particular in a range from 0.01 mm to 0.06 mm, preferably in a range from 0.02 mm to 0.04 mm.
Through such dimensioning of the pore sizes an especially uniform gas flow through the housing wall can be effected, contributing to a uniform and reliable gas bearing whereby wear on the compressor piston and/or the housing wall is reduced.
In a configuration, the maximum diameter of the pores is less than 0.13 mm, in particular less than 0.08 mm, preferably less than 0.05 mm.
The refrigeration device according to invention includes the linear compressor according to the invention. Because of the operating reliability, non-susceptibility to malfunction and simple manufacturability of the linear compressor, the refrigeration device, for example a refrigerator, a freezer or an air-conditioning system, in particular an air-conditioning system for motor vehicles, operates in an especially malfunction-proof and reliable manner and can also be simply produced. In particular, because of the particular characteristics of the linear compressor according to the invention, no pre-filter for the gas is required, further reducing the manufacturing cost of the refrigeration device.
The gas pressure bearing according to the invention comprises a rotatable and/or displaceable body and a bearing element, the body being supported in the bearing element by means of a bearing wall having openings and by means of a fluid flowing through the openings, and the bearing wall being porous.
As already described above with reference to the linear compressor comprising the compressor piston, the piston housing and the housing wall, the gas pressure bearing comprising the body, the bearing element and the bearing wall has especially advantageous properties with regard to improved non-susceptibility to malfunction, and with regard to uniform support of the rotatable and/or displaceable body in the bearing element. In addition, a consumption of gas for producing the gas cushion for the bearing can be reduced.
Through the diffusive character of the gas flow through the bearing wall, which also permits a gas flow transverse to the main flow direction and allows zonally spontaneous variation of a flow path, an especially low susceptibility to malfunction of the bearing, and therefore high reliability, are achieved.
The bearing wall may be open-pored. The bearing wall is advantageously sintered.
Through the specification of suitable parameters of the sintering process, the porosity, in particular the size of the pores and the distribution thereof, or the ratio of the number of open pores to closed pores, can be adapted to the particular application of the bearing. In particular, it is possible to produce bearing elements with almost any desired form in a simple and low-English cost manner. The bearing wall may be made of a metal or of a ceramic material.
The bearing wall has pores the mean diameter of which is within the range from 0.005 mm to 0.200 mm, in particular in a range from 0.01 to 0.06 mm, preferably in a range from 0.02 mm to 0.04 mm. The maximum diameter of the pores may be less than 0.13 mm, in particular less than 0.08 mm, preferably less than 0.05 mm.
The porosity of the bearing surface may vary along a direction; in particular the material content, the pore sizes and other parameters may be varied as described.
The method according to the invention for producing a linear compressor or for producing a refrigeration device including a linear compressor, the linear compressor comprising a piston housing and a compressor piston movable back and forth therein along an axis, and the compressor piston being supported in the piston housing by means of a housing wall having openings and by means of a gas flowing through the openings, comprises the following process steps:
Unlike the prior art, which entailed comparatively complex and costly manufacture of the linear compressor, since the individual openings in the housing wall had to be produced individually, according to the present invention the housing wall is produced block-wise in a simple manner substantially by one sintering process step. The manufacturing cost is thereby considerably reduced.
The method according to the invention for cooling merchandise utilizes the refrigeration device according to the invention. It is able to cool and keep cool merchandise, in particular foodstuffs, in a rapid, reliable and energy-saving manner.
Further advantages and particular developments are explained in more detail with reference to the following drawing, which is intended not to restrict the invention but merely to illustrate it in an exemplary manner. In the drawing:
As the flowing gas, the coolant utilized in the refrigeration device is advantageously used.
The invention relates to a linear compressor 1 and to a method for production thereof, comprising a piston housing 2 and a compressor piston 3 movable back and forth therein along an axis 4, the compressor piston 3 being supported in the piston housing 2 by means of a housing wall 5 having openings 6 and by means of a gas flowing through the openings 6, the housing wall 5 being porous, in particular sintered, characterized by high reliability in operation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 009 268.6 | Feb 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/050537 | 1/19/2007 | WO | 00 | 2/25/2010 |
