REFRIGERATION COMPRESSOR AND A METHOD FOR ASSEMBLING SUCH A REFRIGERATION COMPRESSOR

Abstract

This refrigeration compressor includes an electric motor having a stator and a rotor provided with an axial through passage, a compression unit adapted for compressing refrigerant, and a drive shaft adapted for driving the compression unit, the drive shaft extending into the axial through passage of the rotor. The rotor is slide-fitted on the drive shaft.

Description

FIELD OF THE INVENTION

The present invention relates to a refrigeration compressor, and in particular to a scroll-type refrigeration compressor.

BACKGROUND OF THE INVENTION

As known, a scroll-type refrigeration compressor comprises:

• • an electric motor having a stator and a rotor, the rotor being provided with an axial through passage,
  • a scroll compression unit adapted for compressing refrigerant and including an orbiting scroll member and a fixed scroll member, and
  • a drive shaft adapted for driving the orbiting scroll member of the compression unit, the drive shaft extending into the axial through passage of the rotor and being tightly fixed to the rotor for example by press-fitting or heat shrink fitting the rotor to the drive shaft.

During start-up of the compressor electric motor, the rotor has a tendency to slightly axially move in the direction of the compression unit, which leads to a corresponding axial movement of the drive shaft and of the orbiting scroll member due to the fact that the rotor is fixed to the drive shaft. Such a movement of the orbiting scroll member could create excessive forces between the fixed and orbiting scroll members, and thus damage the orbiting and fixed scroll members or the sealing element disposed between the spiral wrap of the orbiting scroll member and the end plate of the fixe scroll member.

Further, in operation of such a refrigeration compressor, deformations of the drive shaft, and more particularly flexions of the drive shaft, may be transferred to the rotor and then damage the latter.

Furthermore, in operation of such a refrigeration compressor, torque variations occuring in the motor generate vibrations which are transferred to the shaft and to the scroll compression unit, which could damage some elements of the scroll compression unit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved refrigeration compressor which can overcome the drawbacks encountered in conventional refrigeration compressors.

Another object of the present invention is to provide a refrigeration compressor which is reliable.

According to the invention such a refrigeration compressor comprises:

• • an electric motor having a stator and a rotor, the rotor being provided with an axial through passage,
  • a compression unit adapted for compressing refrigerant,
  • a drive shaft adapted for driving the compression unit (8), the drive shaft extending into the axial through passage of the rotor and being connected to the rotor, the drive shaft extending, in use, substantially vertically, and
  • a positioning element secured on the drive shaft, the positioning element having an axial stop surface on which rests a lower end portion of the rotor, the axial stop surface being arranged to slidably co-operate with a lower end portion of the rotor,
  • wherein the connection between the rotor and the drive shaft is arranged to allow limited relative movements between the rotor and the drive shaft during start and normal operations of the refrigeration compressor.

Such a mounting of the rotor allows, during operations of the refrigeration compressor, small angular movements of the rotor in relation to the stator, which avoids transfer of mechanical tensions from the drive shaft to the rotor and damps vibrations generated by torque variations occuring in the motor. Such a vibrations damping leads to a reduction of the noise level of the compressor and to a reduction of the vibrations transmitted to the piping connected to the compressor.

Further such a mounting of the rotor allows small axial movements of the rotor in relation to the drive shaft during start-up of the compressor electric motor, which reduces the impact of the orbiting scroll member on the fixed scroll member.

As a result, any damage of the rotor and of the compression unit can be prevented during operation of the refrigeration compressor according to the invention.

According to an embodiment of the invention, the fit interference between the rotor and the drive shaft is less than 0,0003, said fit interference being calculated with the following formula: FI=(D_DS−D_R)/D_R, where FI is the fit interference between the rotor and the drive shaft, D_DS is the outer diameter of the portion of the drive shaft extending through the axial through passage of the rotor, and D_R is the inner diameter of the rotor. The fit interference may be negative, in such a case there is a clearance between the rotor and the drive shaft. For example, the interference may be between −0,005 and +0.0003.

According to an embodiment of the invention, the rotor is slide-fitted on the drive shaft, which means that the maximal fit interference is 0.

Such a mounting of the rotor, i.e. without applying constraint to the rotor, allows small angular and axial movements of the rotor in relation to the stator.

Furthermore such a mounting of the rotor avoids to secure the rotor to the drive shaft by heat shrink fitting, and thus to expose the rotor to high temperatures. Therefore, the present invention allows the use of IPM (Interior Permanent Magnet) rotor comprising permanent magnets which lose their magnet properties when expose to high temperatures.

According to an embodiment of the invention, the rotor is slide-fitted on the drive shaft in a slide-fit relationship arranged to allow limited relative angular and/or axial sliding movements between the rotor and the drive shaft. In other words, the rotor is fitted on the drive shaft with an axial and/or angular clearance.

The refrigeration compressor can further comprise a locking element adapted to rotatably couple the drive shaft to the rotor. For example, the locking element can be made of non-magnetic material. According to an embodiment of the invention, the locking element is adapted to allow limited relative angular sliding movements between the rotor and the drive shaft.

According to an embodiment of the invention, an outer surface of the drive shaft has a first longitudinal recess, and an inner surface of the rotor has a second longitudinal recess, the first and second longitudinal recesses being circumferentially aligned and the locking element extending into the first and second longitudinal recesses.

According to an aspect of the invention, the locking element is slide-fitted into at least one of the first and second longitudinal recesses.

According to an aspect of the invention, the section dimensions of the locking element and of the first and second longitudinal recesses are adapted to allow limited relative axial sliding movements between the rotor and the drive shaft.

According to an aspect of the invention, the section dimensions of the locking element and of the first and second longitudinal recesses are adapted to allow limited relative angular sliding movements between the rotor and the drive shaft.

The second longitudinal recess provided on the rotor can extend substantially along the entire length of the rotor.

According to an embodiment of the invention, the positioning element is a positioning ring secured to the drive shaft.

According to an embodiment of the invention, the positioning element is heat shrink fitted to the drive shaft. For example, the positioning element can be made of non-magnetic material.

According to an aspect of the invention, the refrigeration compressor further comprises a first axial abutment surface provided on the rotor and a second axial abutment surface provided on the drive shaft, a predetermined axial gap being provided between the first and second axial abutment surfaces in order to allow limited relative axial movements between the drive shaft and the rotor. For example, the predetermined axial gap is between 0,005 and 1 mm, and preferably between 0,5 and 1 mm.

According to an embodiment of the invention, the drive shaft has a radial step delimiting the second axial abutment surface.

According to an embodiment of the invention, the first and second axial abutment surfaces are arranged to prevent the rotor from axially moving beyond a predetermined position towards the compression unit.

The first axial abutment surface can be provided on an end face of the rotor facing the compression unit.

According to an embodiment of the invention, the refrigeration compressor is a scroll-type refrigeration compressor.

According to an aspect of the invention, the drive shaft has a first end adapted to drive a moving part of the compression unit.

According to an embodiment of the invention, the rotor is an IPM rotor.

The present invention also relates to a method for assembling a refrigeration compressor according to the invention, comprising the steps of:

• • connecting the rotor to the drive shaft so as to allow limited relative movements between the rotor and the drive shaft during start and normal operations of the refrigeration compressor, and
  • securing the positioning element to the drive shaft so that the lower end portion of the rotor rests on the axial stop surface of the positioning element.

According to an aspect of the invention, the connecting step consists in slide-fitting the rotor to the drive shaft.

The method can further comprise the steps of:

• • pushing the rotor along the drive shaft towards the compression unit until the first annular abutment surface provided on the rotor bears against the second annular abutment surface provided on the drive shaft,
  • securing the positioning element to the drive shaft at an axial distance from the rotor corresponding to the predetermined axial gap.

According to an alternative aspect of the invention, the method can further comprise the steps of:

• • pushing the rotor along the drive shaft towards the compression unit until the first annular abutment surface provided on the rotor bears against the second annular abutment surface provided on the drive shaft,
  • securing the positioning element to the drive shaft so that the axial stop surface of the positioning element bears against the lower end portion of the rotor.

According to an aspect of the invention, the securing step includes the step of heat shrink fitting the positioning element to the drive shaft.

The method can further comprise the steps of:

• • aligning the first and second longitudinal recesses,
  • inserting the locking element into the first and second longitudinal recesses.

According to an aspect of the invention, the inserting step includes the steps of slide-fitting the locking element into at least one of the first and second longitudinal recesses.

These and other advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting example, one embodiment of the refrigeration compressor according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of embodiment of the invention is better understood when read in conjunction with the appended drawings being understood, however, that the invention is not limited to the specific embodiment disclosed.

FIG. 1 is a longitudinal section view of a scroll-type refrigeration compressor according to the invention.

FIG. 2 is an enlarged view of a detail of FIG. 1.

FIG. 3 is an enlarged view of a detail of FIG. 2.

FIG. 4 is an exploded perspective view of a detail of the refrigeration compressor of FIG. 1.

FIG. 5 is a perspective view of the different elements shown in FIG. 4.

FIG. 5 is an exploded perspective view of a detail of the refrigeration compressor of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a scroll-type refrigeration compressor 2 occupying a vertical position. However, the refrigeration compressor 2 according to the invention could occupy an inclined position, or a horizontal position, without significant modification to its structure.

The refrigeration compressor 2 shown in FIG. 1 comprises a closed casing 3 defined by a shell 4 whose top and bottom ends are respectively closed by cap 5 and a base 6.

The refrigeration compressor 2 also comprises a support frame 7 fixed in the closed casing 3, the closed casing 3 and the support frame 7 defining a low pressure volume underneath the support frame 7 and a high pressure volume above the support frame 7.

The refrigeration compressor 2 further comprises a scroll compression unit 8 disposed above the support frame 7, i.e. in the high pressure volume. The scroll compression unit 8 has a fixed scroll member 9 and an orbiting scroll member 11 interfitting with each other. In particular the orbiting scroll member 11 is supported by and in slidable contact with an upper face of the support frame 7, and the fixed scroll member 11 is fixed in relation to the closed casing 3. The fixed scroll member 11 could for example be fixed to the support frame 7.

As known, the fixed scroll member 9 has an end plate 12 and a spiral wrap 13 projecting from the end plate 12 towards the orbiting scroll member 11, and the orbiting scroll member 11 has an end plate 14 and a spiral wrap 15 projecting from the end plate 14 towards the fixed scroll member 9. The spiral wrap 15 of the orbiting scroll member 11 meshes with the spiral wrap 13 of the fixed scroll member 9 to form a plurality of compression chambers 16 between them. The compression chambers 16 have a variable volume which decreases from the outside towards the inside, when the orbiting scroll member 11 is driven to orbit relative to the fixed scroll member 9. The refrigerant compressed in the compression chambers 16 escapes from the centre of the fixed and orbiting scroll members 9, 11 through an opening 17 in the fixed scroll member 9 leading to a high-pressure chamber 18, from which the compressed refrigerant is discharged by a discharge port 19.

The refrigeration compressor 2 further comprises an electric motor disposed below the support frame 7. The electric motor has a rotor 21 provided with an axial through passage 22, and a stator 23 disposed around the rotor 21. For example, the electric motor may be a variable-speed electric motor, and the rotor 21 may be an IPM rotor.

Furthermore the refrigeration compressor 2 comprises a drive shaft 24 adapted for driving the orbiting scroll member 11 in an orbital movement. The drive shaft 24 extends into the axial through passage 22 of the rotor 21 and is rotatably coupled to the rotor 21 so that the drive shaft 24 is driven to rotate by the rotor 21 about a rotational axis.

The drive shaft 24 comprises, at its top end, an eccentric pin 25 which is off-centered from the center of the drive shaft 24, and which is inserted in a connecting sleeve part 26 of the orbiting scroll member 11 so as to cause the orbiting scroll member 11 to be driven in an orbital movement relative to the fixed scroll member 9 when the electric motor is operated.

The bottom end of the drive shaft 24 drives an oil pump 27 which supplies oil from a sump defined by the closed casing 3 to a lubrication passage 30 formed inside the central part of the drive shaft 24.

According to the invention, the rotor 21 is slide-fitted to the drive shaft 24.

As shown in FIG. 2, the refrigeration compressor 2 includes a first annular axial abutment surface 28 provided on the rotor 21 and a second annular axial abutment surface 29 provided on the drive shaft 24. As particularly shown in FIG. 3, a predetermined axial gap is provided between the first and second axial abutment surfaces 28, 29 in order to allow relative axial sliding movements between the rotor 21 and the drive shaft 24. For example, the predetermined axial gap is between 0,5 and 1 mm.

Particularly, the first annular axial abutment surface 28 is provided on the upper end face of the rotor 21, and the drive shaft 24 has a radial step delimiting the second annular axial abutment surface 29. The first and second annular axial abutment surfaces 28, 29 are arranged to prevent the rotor 21 from axially moving relative to the drive shaft 24 beyond a predetermined position towards the compression unit 8.

The refrigeration compressor 2 further includes a positioning ring 31 secured to the drive shaft 24. For example, the positioning ring 31 is heat shrink fitted to the drive shaft 24. Advantageously the positioning ring 31 is made of non-magnetic material.

The positioning ring 31 has an axial stop surface 32 on which rests a lower end portion of the rotor 21, and more precisely a radial abutment surface 33 provided on the lower end portion of the rotor 21. Thus the positioning ring 31 is arranged to axially position the rotor 21.

The refrigeration compressor 2 further comprises a locking pin 34 adapted to rotatably couple the drive shaft 24 to the rotor 21. For example the locking pin 34 is made of non-magnetic material.

The locking pin 34 extends respectively into a first longitudinal recess 35 provided on the outer surface of the drive shaft 24 and into a second longitudinal recess 36 provided on the inner surface of the rotor 21, the first and second longitudinal recesses 35, 36 being circumferentially aligned. The section dimensions of the locking pin 34 and of the first and second longitudinal recesses 35, 36 are adapted to allow relative axial and angular sliding movements between the rotor 21 and the drive shaft 24. According to the embodiment shown on the figures, the locking pin 34 is slightly larger than the first longitudinal recesses 35 so that the locking pin 34 is press fitted into the first longitudinal recess 35, and the locking pin 34 is slide-fitted into the second longitudinal recess 36. However, the locking pin 34 may be slide-fitted into the first and second longitudinal recesses 35, 36.

The second longitudinal recess 36 provided on the rotor 21 can extend along the entire length of the rotor 21. Advantageously, the first longitudinal recess 35 extends only along a partial length of the drive shaft 24 and delimits an axial stop surface 37 for the upper end of the locking pin 34. Furthermore the axial stop surface 32 provided on the positioning ring 31 forms also an axial stop for the lower end of the locking pin 34.

The method for assembling the refrigeration compressor 2 according to the invention comprises at least the following steps:

• • tight fitting the locking pin 34 into the first longitudinal recess 35 so that the upper end face of the locking pin 34 bears against the axial stop surface 37 provided on the drive shaft 24,
  • engaging the rotor 21 around the drive shaft 24 from the lower end portion of the drive shaft 24,
  • aligning the second longitudinal recess 36 with the locking pin 34,
  • pushing the rotor 21 along the drive shaft 24 towards the compression unit 8 until the first annular abutment surface 28 provided on the rotor 21 bears against the second annular abutment surface 29 provided on the drive shaft 24,
  • heating the positioning ring 31,
  • engaging the positioning ring 31 around the drive shaft 24 from the lower end portion of the drive shaft 24,
  • positionning the support surface 32 of the positioning ring 31 at an axial distance from the radial abutment surface 33 provided on the rotor 21 corresponding to the predetermined axial gap, and
  • cooling down the positioning ring 31.

When assembled, the refrigeration compressor 2 is vertically positioned. As a consequence the rotor 21 slides axially by gravity along the drive shaft 24 until the radial abutment surface 33 provided on the rotor 21 bears against the support surface 32 of the positioning ring 31, and the predetermined axial gap between the first and second axial abutment surfaces 28, 29 is introduced.

It should be noted that the positionning step may consist in positionning the support surface 32 of the positioning ring 31 against the radial abutment surface 33 provided on the rotor 21. In such a case, a very small axial gap (few micrometers) is finally provided between the first and second axial abutment surfaces 28, 29 due to the cooling down of the positioning ring 31.

Of course, the invention is not restricted to the embodiment described above by way of non-limiting example, but on the contrary it encompasses all embodiments thereof.

Claims

1. A refrigeration compressor comprising:

an electric motor having a stator and a rotor, the rotor being provided with an axial through passage,

a compression unit adapted for compressing refrigerant,

a drive shaft shaft adapted for driving the compression unit, the drive shaft extending into the axial through passage of the rotor and being connected to the rotor, the drive shaft extending, in use, substantially vertically, and

a positioning element secured on the drive shaft, the positioning element having an axial stop surface on which rests a lower end portion of the rotor, the axial stop surface being arranged to slidably co-operate with a lower end portion of the rotor,

wherein the connection between the rotor and the drive shaft is arranged to allow limited relative movements between the rotor and the drive shaft during start and normal operations of the refrigeration compressor.

2. The refrigeration compressor according to claim 1, wherein the rotor is slide-fitted on the drive shaft.

3. The refrigeration compressor according to claim 1, further comprising a locking element adapted to rotatably couple the drive shaft to the rotor.

4. The refrigeration compressor according to claim 3, wherein an outer surface of the drive shaft has a first longitudinal recess, and an inner surface of the rotor has a second longitudinal recess, the first and second longitudinal recesses being circumferentially aligned and the locking element extending into the first and second longitudinal recesses.

5. The refrigeration compressor according to claim 3, wherein the locking element is adapted to allow limited relative angular sliding movements between the rotor and the drive shaft.

6. The refrigeration compressor according to claim 1, wherein the positioning element is a positioning ring secured to the drive shaft.

7. The refrigeration compressor according to claim 1, wherein the positioning element is heat shrink fitted to the drive shaft.

8. The refrigeration compressor according to claim 1, further comprising a first axial abutment surface provided on the rotor and a second axial abutment surface provided on the drive shaft, a predetermined axial gap being provided between the first and second axial abutment surfaces in order to allow limited relative axial movements between the drive shaft and the rotor.

9. The refrigeration compressor according to claim 8, wherein the first and second axial abutment surfaces are arranged to prevent the rotor from axially moving beyond a predetermined position towards the compression unit.

10. A method for assembling a refrigeration compressor according to claim 1, comprising the steps of:

connecting the rotor to the drive shaft so as to allow limited relative movements between the rotor and the drive shaft during start and normal operations of the refrigeration compressor, and

securing the positioning element to the drive shaft so that the lower end portion of the rotor rests on the axial stop surface of the positioning element.

11. The method according to claim 10, wherein the connecting step consists in slide-fitting the rotor to the drive shaft.