COMPRESSOR, IN PARTICULAR A RADIAL PISTON COMPRESSOR FOR CARBON DIOXIDE AS A REFRIGERANT

Abstract

A compressor, in particular a radial piston compressor, further in particular a compressor for CO2 as a refrigerant, including a compressor unit for compressing refrigerant and a drive shaft for driving the compressor unit and a motor chamber bounded substantially by a motor housing, wherein the motor chamber has a fluid connection to a suction gas side, in particular a suction gas chamber, of the compressor by means of a fluid connection formed at least partially in the drive shaft, wherein at least one device for accumulating oil is arranged in the fluid connection.

Description

The present invention relates to a compressor, in particular a radial piston compressor, more particularly a compressor for CO₂ as refrigerant, as per the preamble of patent claim 1.

Compressors, in particular compressors for refrigerant such as for example R134a, R404A, R507, R407c, R22 or R744 (CO₂), have become indispensible in this day and age and are used inter alia in the field of mobile cooling and air conditioning, such as for example the air-conditioning of passenger motor vehicles and utility vehicles, the air-conditioning of buses and trains and in-transit cooling, and also in the static cooling of foodstuffs, in refrigerated warehouses or in the field of medical technology. Such compressors are nowadays essential also in the field of air conditioning for buildings.

Examples of compressors which are used in some of the fields mentioned are known from the applicant's semi-hermetics catalog. In particular, reciprocating piston compressors having two, four, six and eight cylinders, which have swept volumes of approximately 62 cm³-3,215 cm³, are known from said catalog.

Furthermore, DE 103 56 373 A1 discloses a compressor in the form of a radial piston compressor which comprises a compressor unit for compressing refrigerant and comprises a drive shaft for driving the compressor unit. In the compressor according to DE 103 56 373 A1, the central points of the pistons are arranged in a common plane through which the drive shaft extends perpendicularly, or to which a central axis extending in the longitudinal direction of the drive shaft is perpendicular.

Also known from the prior art are compressors, in particular radial piston compressors, whose drive shaft is operatively connected to an electric motor, the motor being delimited substantially by a motor housing which in its interior defines a motor chamber, the motor chamber being fluidically connected via a bore in the drive shaft to a suction gas chamber from which the refrigerant to be compressed is sucked. To cool the motor, a partial mass flow of the suction gas from the suction gas chamber is supplied to the motor chamber via a duct and is supplied to the suction gas volume again via the abovementioned bore in the drive shaft. On account of the flow conditions, the partial mass flow conducted back to the suction gas volume contains oil. Said oil is used for lubricating bearings or the like. Depending on the operating state of the compressor, however, a situation may arise (for example at low rotational speeds) in which optimum lubrication does not take place.

Taking the prior art discussed above as a starting point, it is an object of the present invention to specify a compressor in which good lubrication is ensured for wide operating ranges.

Said object is achieved by means of a compressor having the features of patent claim 1, wherein further features and advantages of the invention may be gathered from the following description of the figures and from the subclaims.

The invention will be described by way of example below with reference to the appended drawings on the basis of possible embodiments. In the drawings:

FIG. 1 shows a first embodiment of a compressor according to the invention in a partially sectional illustration in a horizontal installation situation;

FIG. 2 shows the embodiment as per FIG. 1 in a vertical installation situation;

FIG. 3 shows a detailed illustration of a detail from FIGS. 1 and 2;

FIG. 4 shows a detailed illustration of a second possible embodiment of a compressor according to the invention, similar to the illustration in FIG. 3; and

FIG. 5 shows a detailed illustration of a third possible embodiment of a compressor according to the invention, similar to the illustration in FIG. 3.

As can be seen for example from FIGS. 1 and 2, the first embodiment of a compressor 10 according to the invention has a compressor unit 12 and a motor unit 14. The motor unit 14 has a motor housing 16 which, in the first embodiment, delimits not only a motor chamber 18 but also, in part, the compressor unit 12. Arranged in the motor chamber 18 in addition to an electric motor is a drive shaft 22 via which the motor 20 is operatively connected to the compressor unit 12. In the described first embodiment, the compressor unit 12 has six pistons 24 which are arranged in the radial direction. The pistons 24 are arranged in a common plane spanned by the piston longitudinal axes which extend in the piston longitudinal direction, which plane is perpendicular to the drive shaft 22. It is pointed out at this juncture that a different number of pistons 24 is self-evidently also conceivable, wherein the number of pistons is determined in particular by the technical requirements of the user of the compressor 10 (swept volume and desired compression power).

The compressor unit 12 is provided for the compression of refrigerants, wherein common refrigerants such as for example R134a, R404A, R507, R407c, R22 or preferably R744 (CO₂) are conceivable as refrigerant. The refrigerant passes, on a suction gas side, via a suction gas chamber 26 arranged at the suction gas side into cylinder bores 28 (which are formed in the radial direction) of the compressor 10, in which cylinder bores the pistons 24 are arranged in a reciprocating fashion. The compression of the refrigerant is realized by means of a movement of the pistons 24 in the radial direction. When the piston 24 has arrived in an upper position in the cylinder bore 28, that is to say the piston 24 has arrived in a radially outwardly facing position, the refrigerant which is then compressed is discharged into a compressed-gas chamber 30 which is arranged at the high-pressure side and from which the compressed refrigerant is provided to a refrigerant circuit assigned to the compressor 10.

The compressor 10 also has, in addition to the compressor unit 12 and the motor unit 14, an electrical terminal box 32 which is fastened to the motor housing 16 of the compressor 10 by means of fastening elements for example in the form of screws. The stator of the electric motor 20 is positioned in the motor housing 16 and may be fixed to the latter for example by means of screws.

The electrical terminals for the compressor 10, in particular the terminals for the current or voltage supply to the electric motor 20, are arranged in the terminal box 32. Also contained in the terminal box 32 are electronic motor protection components to which components such as for example a heat protection thermostat 38 can also be connected. For a supply of electricity, the terminal box 32 has a plurality of cable inlets 36 which, as illustrated in FIG. 1, may be closed off when not being used, for example by means of closure elements. The cable inlets 36 illustrated are preferably pre-punched, originally closed cutouts which are first opened by being pushed in. Therefore, no separate components are required; these are rather regions of the outer contour of the terminal box 32 which have been pre-punched such that they can be opened more easily.

On account of the high pressures of the refrigerant (for example CO₂), a heat protection thermostat 38 is preferably not arranged so as to be in direct contact with the refrigerant but rather arranged in the motor housing 16 so as to be separate from the refrigerant. In this way, the heat protection thermostat 38 has only an indirect thermal connection to the refrigerant. The heat protection thermostat 38 may be connected to elements in the terminal box 32 by means of a cable 39, for example through a cable inlet 36.

For the lubrication of the compressor 10, lubricant in the form of oil 41 is situated in the compressor 10. The oil 41 is stored in the motor chamber 18, wherein the oil 41 is used not only for lubricating parts of the compressor 10 arranged in the motor chamber 18 but rather also for lubricating parts of the compressor 10 arranged outside the motor chamber 18. In the region of the motor chamber 18, it is necessary to lubricate bearings 40, 42, 44 (front bearing bush 42, rear bearing bush 44 and bearing 40 for mounting the drive shaft 22 in the motor housing 16). Outside the motor chamber 18, the movable parts of the compressor unit 12, in particular the pistons 24, require corresponding lubrication.

The compressor 10 has a fluid connection 45 between the motor chamber 18 and the suction gas side (suction gas chamber 26), which fluid connection, aside from returning the partial mass flow which cools the motor, also serves for the lubrication of the bearings 40, 42, 44. The fluid connection 45 is formed to a large extent in the drive shaft 22 and consists inter alia of an axial cutout formed in the drive shaft 22 in the manner of a bore 46 extending in the axial direction. Furthermore, the fluid connection 45 comprises four radial cutouts arranged in the radial direction in the drive shaft 22, said radial cutouts taking the form of a first, a second, a third and a fourth radial bore 48, 50, 52, 54 which are fluidically connected to the bore 46. The first radial bore 48, which extends through the entire drive shaft 22 so as to have two openings to the motor chamber 18, serves for receiving the partial mass flow which also contains oil or oil mist. The second, third and fourth radial bores 50, 52, 54 are provided for the lubrication of the bearings 40, 42, 44. Oil 41 can emerge through said bores in the radial direction into the bearing points to be lubricated. The outflow of the oil 41 in the radial direction is assisted by the rotational movement of the drive shaft 22 and the resulting centrifugal forces generated.

To permit cooling of the motor, the suction gas chamber 26, as already mentioned above, is connected to the motor chamber 18 by means of a fluid connection 45. The fluid connection 45 has inter alia the first radial bore 48, which serves as an inlet for the partial mass flow, and the bore 46 which is fluidically connected to said first radial bore. For the lubrication of the bearing 44 (second bearing bush), the fluid connection also has a radial bore 54 which is fluidically connected to the bore 46. The radial bore 54 is fluidically connected to a second axial cutout in the form of a second bore 56 which extends in the axial direction in the drive shaft 22, which second bore has a cross section smaller than the cross section of the bore 46 and which second bore is fluidically connected, at its end facing away from the motor chamber 18, to the suction gas chamber 26. Arranged at the suction-gas-side end of the bore 56 is a point of reduced cross section in the form of a nozzle 58 which limits and defines the inflow of oil into the suction gas chamber 26. According to requirements, the nozzle 58 is selected at the factory and the corresponding cross section or the corresponding throughflow rate is adapted to the design requirements.

It is additionally possible, in alternative embodiments of the invention, for the oil inflow to be regulated by means of the bore cross section of the radial bore 54 or of the axial bore 56, for example by means of the bore cross section itself or by means of a constriction arranged in the bore 54 or 56, or an orifice or a flap, in addition to the nozzle 58 or instead of the nozzle 58. The orifice or flap may be designed so as to be non-adjustable or adjustable, such that by means thereof, the oil flow or the lubrication via the suction gas chamber 26 can be controlled or regulated as a function of external parameters and if appropriate also as a function of parameters of the compressor itself. Furthermore, it is possible for the nozzle 58 to be provided with a variable nozzle cross section and/or an upstream valve which opens or closes on a predetermined or variable clock cycle such that the oil quantity supplied to the suction gas chamber 26 can be regulated or controlled.

The two axial cutouts 46 and 56 are formed in the drive shaft 22 preferably axially parallel to one another with a radial spacing, and preferably in the manner of axially parallel bores.

To ensure a reliable supply of oil in particular to the bearings 42, 44, a device for causing a build-up of oil, in the form of a tubular element or tube 60, is arranged in the fluid connection 45, which device serves to ensure that sufficient oil 41 is supplied to the nozzle 58 and to the radial bores 52, 54. Aside from the function of causing a build-up, the tube 60, on account of its being fluidically connected, at its side facing away from the motor chamber, to the suction gas volume, serves to ensure the return of the partial mass flow from the motor into the suction gas chamber. An oil overflow device in the form of a tube 61 which is pressed into the drive shaft 22 and which extends into the axial bore 46 serves for the discharge of excess built-up oil 41. It should however be noted that the tube 60 is provided not for the lubrication of the compressor unit 12 but rather merely as an oil overflow in the event that too large an oil quantity has built up. The device for causing a build-up of oil, in the form of the tube 60, is designed to cause a build-up of oil 41 while maintaining an uninterrupted fluid connection. It should be noted that the tube 60 has an outer diameter smaller than the diameter of the axial bore 46, and that the tube 60 is arranged concentrically with respect to the axial bore 46 and projects into the latter. As an alternative to this, a non-concentric, parallel arrangement with respect to the bore is also conceivable.

The compressor 10 illustrated in FIG. 1 is illustrated in a vertical installation situation in FIG. 2, wherein in this installation situation, the lubricant in the form of the oil 41 covers the radial cutout (radial bore 48). Operation is possible even with a covered radial cutout, wherein it would also be conceivable for the radial bore 48 to be arranged above the oil level, such that again, oil mist rather than oil 41 is sucked in.

Additionally or alternatively to the tube 60 as a device for causing a build-up of oil, it is also conceivable for an orifice 62 (in this regard cf.

FIG. 4) arranged for example in the drive shaft 22, and/or reservoir-like or basin-like cutouts 64 (in this regard, cf. FIG. 5) which extend in the radial direction, to be provided in the fluid connection 45 between the motor chamber 18 and the suction gas side or suction gas chamber 26 in order to cause a build-up of oil 41. As illustrated in FIG. 5, the reservoir-like cutouts 64 are formed in the region of the radial bores 52, 54. It is self-evidently also conceivable for reservoir-like cutouts of said type to also be provided in the region of the further cutouts/bores arranged in the radial direction in the drive shaft. The centrifugal forces arising as the drive shaft 22 rotates ensure a reliable supply of oil to the cutouts 64.

Even though the invention has been described on the basis of embodiments with a certain combination of features, the invention however also encompasses further combinations as specified in particular but not exhaustively by the subclaims.

Claims

1. A compressor, in particular radial piston compressor, more particularly a compressor for CO2 as refrigerant, which compressor comprises a compressor unit for compressing refrigerant and comprises a drive shaft for driving the compressor unit and also comprises a motor chamber delimited substantially by a motor housing, the motor chamber being fluidically connected to a suction gas side, in particular suction gas chamber, of the compressor via at least one fluid connection formed at least partially in the drive shaft, wherein at least one device for causing a build-up of oil is arranged in the fluid connection.

2. The compressor as claimed in claim 1, wherein the at least one device for causing a build-up of oil is formed so as to maintain an uninterrupted fluid connection.

3. The compressor as claimed in claim 1, wherein the fluid connection comprises an in particular cylindrical first axial cutout which is formed in the axial direction in the drive shaft.

4. The compressor as claimed in claim 1, wherein the fluid connection is fluidically connected to at least one in particular cylindrical radial cutout which is formed in the radial direction in the drive shaft.

5. The compressor as claimed in claim 3, wherein the fluid connection has a tubular element whose outer diameter is smaller than the diameter of the axial cutout, wherein the tubular element is arranged parallel to or concentrically with respect to the axial cutout and projects at least partially into the latter.

6. The compressor as claimed in claim 5, wherein the tubular element is fluidically connected to the suction gas side, in particular suction gas chamber.

7. The compressor as claimed in claim 3, wherein the fluidic connection comprises a second, in particular cylindrical axial cutout which is formed in the axial direction in the drive shaft and whose cross section, in particular diameter, is smaller than that of the first axial cutout, and in that the second axial cutout is fluidically connected at one end thereof to the first axial cutout and which opens out at its second end into the suction gas side.

8. The compressor as claimed in claim 7, wherein the second axial cutout is fluidically connected at one end thereof to the first axial cutout by means of at least one radial cutout, preferably radial bore, which extends radially relative to said first axial cutout.

9. The compressor as claimed in claim 1, wherein the fluid connection has a point of reduced cross section.

10. The compressor as claimed in claim 9, wherein the point of reduced cross section comprises a nozzle or an orifice or a point of reduced material cutout or a flap.

11. The compressor as claimed in claim 9, wherein the point of reduced cross section is arranged in the second axial cutout and/or in the radial cutout.

12. The compressor as claimed in claim 9, wherein the point of reduced cross section has an adjustable, in particular controllable or regulable cross section.

13. The compressor as claimed in claim 1, wherein the fluid connection comprises at least one further in particular reservoir-like or basin-like cutout which is arranged in the drive shaft and which is designed to cause a build-up of the oil.

14. The compressor as claimed in claim 1, wherein an oil overflow is provided which determines the amount of oil built up or accumulated.

15. The compressor as claimed in claim 14, wherein the oil overflow comprises a tubular element which is arranged in a radial cutout in the drive shaft and which projects into the fluid connection between the motor chamber and the suction gas side.