A piston guide means for a compressor

Abstract

 A piston guide means for use in a swash plate compressor comprises a piston (10) with a piston head (12) at one end and a foot portion (14) at its other end. The piston head (12) can reciprocate in a cylinder (18) and foot portion (14) accommodates a bearing (16) for a swash or wobble plate arrangement (17) of the compressor. A piston rod (11) extends between the piston head (12) and the foot portion (14) and passes through a plate (20) or similar arrangement. In this way compression of the rod (11) is reduced and wear of the piston (10) caused by axial forces acting thereon as a result of the swash plate arrangement is thereby mitigated.

Description

[0001] The present invention relates to a piston guide means for use in a swash or wobble plate compressor, in particular a CO₂ compressor, for a vehicle air-conditioning system and to a compressor incorporating such a guide means.

[0002] Compressors are often constructed as reciprocating piston compressors, in particular in the field of vehicle air-conditioning systems, because such compressors are compact and their output can be continuously controlled by adjustment of the angle of a swash or wobble plate arrangement which is used to drive the pistons. Compressors employing a swash or wobble plate arrangement do not need a connecting rod, the driving force for each piston being transmitted from the swash or wobble plate arrangement to the piston by bearings comprising sliding shoes or blocks.

[0003] As illustrated diagrammatically in Fig. 3, a conventional swash plate compressor comprises a piston 1 with a piston head 2 at one end which reciprocates in a cylinder 3. The end 4 of the piston 1 opposite the piston head 2 extends out of the cylinder 3 and is provided with a recess 5 in which is mounted a pair of sliding shoes 6. A swash or wobble plate arrangement 7, which is rotatably driven by a drive shaft (not shown) of the compressor, is located between the shoes 6 so that drive forces are transmitted from the arrangement 7 via the shoes 6 to the piston 1. As the swash or wobble plate arrangement is inclined with respect to the longitudinal axis 8 of the drive shaft, the forces transmitted to the piston 1 are not exclusively axial forces but comprise a substantial radial component F₁, which is dependent on the angle of inclination of the plate arrangement 7. The radial component F₁ results in forces of reaction F₂ and F₃, of which F₂ is the greater and acts at the edge 9 of the cylinder 3, as shown in the enlarged scrap view in Fig. 3. Despite radiussing of the edge 9 as at R, line contact between the piston 2 and the edge 9 occurs with a consequent substantial compression of the piston 1 that increases wear.

[0004] To prevent or mitigate such wear, particularly in compressors to be used with a high pressure refrigerant such as CO₂, various measures may required such as the following.

• The use of pistons made from steel rather than aluminium, which has been hitherto used for pistons in compressors for vehicle air-conditioning systems. The use of steel pistons would also mean the abandonment of the use of lightweight pistons, which are otherwise advantageous in producing a good dynamic performance of the compressor with good controllability.
• Coating of the pistons with a material which will increase their durability. However, this has the disadvantages of being labor-intensive and expensive.
• Machining of the pistons, again to increase their durability. This also has the disadvantage of being labor-intensive.

[0005] The object of the present invention is to provide a piston guide means for use in a swash plate compressor which overcomes or substantially mitigates the aforementioned disadvantages.

[0006] According to a first aspect of the present invention there is provided a piston guide means for use in a swash or wobble plate compressor comprising a piston with a piston head at one end and a foot portion at its other end, which foot portion accommodates a bearing for a swash or wobble plate arrangement of the compressor, and a cylinder in which the piston head can be reciprocated, and characterised in that the piston comprises a piston rod that extends out of the cylinder between the piston head and the foot portion through a plate or similar arrangement.

[0007] Preferably, the plate covers the end of the cylinder.

[0008] Preferably also, the piston rod passes through a bush which is mounted in the plate.

[0009] Preferably also, the outer surface of the bush defines a domed or hemispherical profile so that it is capable of rotation with respect to the plate.

[0010] Advantageously, the bush is resiliently mounted in the plate, preferably by being embedded in a resilient material or by being spring mounted in the plate.

[0011] Preferably also, the piston rod defines a non-spherical transverse cross-sectional profile so that it cannot rotate with respect to the plate. Alternatively, the piston rod is eccentrically mounted to the piston head so that the piston cannot rotate with respect to the plate.

[0012] Preferably also, the piston rod comprises a hollow tube which is swaged to the piston head and to the foot portion. Whilst the piston rod may be made of steel, preferably the piston head and the foot portion are made of aluminium.

[0013] Preferably also, the plate defines at least one bore to provide for gas and/or oil balancing within the cylinder as the piston head reciprocates therein. Alternatively, a gap is provided between the plate and the end of the cylinder.

[0014] According to a second aspect of the present invention there is provided a swash or wobble plate compressor comprising a piston guide means according to the first aspect of the present invention.

[0015] According to a third aspect of the present invention there is provided a compressor for a vehicle air conditioning system comprising a drive shaft, a swash or wobble plate arrangement operatively connected to the drive shaft, a piston with a piston head at one end and a foot portion at its other end, a cylinder in which the piston head can be reciprocated, and a bearing accommodated in the foot portion that cooperates with the swash or wobble plate arrangement to reciprocate the piston as the drive shaft rotates, and characterised in that the piston comprises a piston rod that extends out of the cylinder between the piston head and the foot portion through a plate or similar arrangement.

[0016] The present invention will now be described by way of example with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic, part longitudinal cross-sectional view of a piston guide means according to the invention for use as part of a driving mechanism of a swash plate compressor;

Fig. 2 is a view to an enlarged scale of the area enclosed within the dashed line II; and

Fig. 3 is a view similar to Fig. 1 but of a conventional guide means as described above.

[0017] In a piston guide means as shown in Figs. 1 and 2, a piston 10 comprises a piston rod 11 with a head portion 12 comprising piston rings 13 at one end, and a foot portion 14 at its other end. The foot portion 14 defines a recess 15 which accommodates a bearing 16 for a swash or wobble plate arrangement 17 that is connected to a drive shaft (not shown) of the compressor for driving the piston 10 with a reciprocating motion.

[0018] The piston rod 11 may be made of a solid material, such as steel, the size of the rod being such that making it of a solid material does not increase the overall weight of the piston 11 excessively. However, preferably the rod 11 comprises a hollow tube and is connected to the head portion 12 and to the foot portion 14 by swaging or other method.

[0019] The head portion 12 of piston 10 reciprocates within a cylinder 18 of the compressor, the piston rod 11 extending out of the cylinder 18 through a bush 19 that is mounted in a plate 20 which covers the end of the cylinder 18. Bores 21 are provided in the plate 20 adjacent the bush 19 to provide for gas and oil balancing within the cylinder 18 as the piston head 12 reciprocates. Alternatively, the plate 20 may be mounted some distance from the end of the cylinder 18 to provide a gap for gas and oil balancing.

[0020] The rod 11 reciprocates within the central bore of the bush 19. The outer surface of the bush 19 preferably defines a domed or hemispherical profile, as shown in Fig. 3, so that it is capable of rotation with respect to the plate 20. The force F₂, as described above, thereby acts over the internal surface of the bush 19 against the rod 11. Hence, the combination of the piston rod 11 with the arrangement of the plate 20 and bush 19 enables the F₂ force component to be spread over a larger area than in the prior art, which thereby reduces compression of the rod 11 as a result. Wear of the piston rod 11 is thereby mitigated. Also, whilst the piston rod 11 may be made from steel, the piston head 12 and the foot portion 14 can be made of a more lightweight material such as aluminium.

[0021] In a modification (not shown), the bush 19 is not necessarily domed but is able to twist or rotate slightly by being resiliently mounted in the plate 20, for example by being embedded in a resilient material such as an elastomer or by being spring mounted, for example by being suspended on a metal spring which allows some tipping movement.

[0022] In a preferred embodiment, the piston rod 11 has a non-spherical transverse cross-sectional profile, for example it may have an elliptical transverse profile, so that it cannot rotate within the bush 19. This has the significant advantage that the piston 10 is also prevented from rotating within the cylinder 18 without other more expensive means having to be provided for the same purpose. Such means have the disadvantage that they usually result in additional frictional losses within the compressor. A similar result can be achieved by an eccentric mounting of the piston rod 11 to the piston head 12. In addition, the present invention has the advantage that it does not require any labor-intensive machining operations to be carried out on the piston 10, nor coating of the piston 10 with wear resistant material.

Claims

1. A piston guide means for use in a swash or wobble plate compressor comprising a piston (10) with a piston head (12) at one end and a foot portion (14) at its other end, which foot portion (14) accommodates a bearing (16) for a swash or wobble plate arrangement (17) of the compressor, and a cylinder (18) in which the piston head (12) can be reciprocated, and
characterised in that
the piston (10) comprises a piston rod (11) that extends out of the cylinder (18) between the piston head (12) and the foot portion (14) through a plate (20) or similar arrangement.

2. A guide means as claimed in Claim 1,
characterised in that
the plate (20) covers the end of the cylinder (18).

3. A guide means as claimed in Claim 1 or Claim 2,
characterised in that
the piston rod (11) passes through a bush (19) which is mounted in the plate (20).

4. A guide means as claimed in any one of Claims 1 to 3,
characterised in that
the outer surface of the bush (19) defines a domed or hemispherical profile so that it is capable of rotation with respect to the plate (20).

5. A guide means as claimed in any one of Claims 1 to 4,
characterised in that
the bush (19) is resiliently mounted in the plate (20).

6. A guide means as claimed in Claim 5,
characterised in that
the bush (19) is resiliently mounted in the plate (20) by being embedded in a resilient material.

7. A guide means as claimed in Claim 5,
characterised in that
the bush (19) is spring mounted in the plate (20).

8. A guide means as claimed in any one of Claims 1 to 7,
characterised in that
the piston rod (11) defines a non-spherical transverse cross-sectional profile so that it cannot rotate with respect to the plate (20).

9. A guide means as claimed in any one of Claims 1 to 7,
characterised in that
the piston rod (11) is eccentrically mounted to the piston head (12) so that the piston (10) cannot rotate with respect to the plate (20).

10. A guide means as claimed in any one of Claims 1 to 9,
characterised in that
the piston rod (11) comprises a hollow tube.

10. A guide means as claimed in any one of Claims 1 to 9,
characterised in that
the piston rod (11) is made of steel.

12. A guide means as claimed in any one of Claims 1 to 11,
characterised in that
the piston head (12) and/or the foot portion (14) are made of aluminium.

13. A guide means as claimed in any one of Claims 1 to 12,
characterised in that
the piston rod (11) is swaged to the piston head (12) and to the foot portion (14).

14. A guide means as claimed in any one of Claims 1 to 13,
characterised in that
the plate (20) defines at least one bore (21) to provide for gas and/or oil balancing within the cylinder (18) as the piston head (12) reciprocates therein.

15. A guide means as claimed in any one of Claims 1 to 13,
characterised in that
the plate (20) is mounted some distance from the end of the cylinder (18) to define a gap which provides for gas and/or oil balancing within the cylinder (18) as the piston head (12) reciprocates therein.

16. A swash or wobble plate compressor
characterised in that
it comprises a piston guide means as claimed in any one of Claims 1 to 15.

17. A compressor for a vehicle air conditioning system comprising a drive shaft, a swash or wobble plate arrangement (17) operatively connected to the drive shaft, a piston (10) with a piston head (12) at one end and a foot portion (14) at its other end, a cylinder (18) in which the piston head (12) can be reciprocated, and a bearing (16) accommodated in the foot portion (14) that cooperates with the swash or wobble plate arrangement (17) to reciprocate the piston (10) as the drive shaft rotates, and
characterised in that
the piston (10) comprises a piston rod (11) that extends out of the cylinder (18) between the piston head (12) and the foot portion (14) through a plate (20) or similar arrangement.

Drawing