US20140140867A1

US20140140867A1 - Variable speed scroll compressor

Info

Publication number: US20140140867A1
Application number: US14/084,152
Authority: US
Inventors: Patrice Bonnefoi; Gael Meldener
Original assignee: Danfoss Commercial Compressors SA
Current assignee: Danfoss Commercial Compressors SA
Priority date: 2012-11-19
Filing date: 2013-11-19
Publication date: 2014-05-22
Also published as: CN103821718A; DE102013019110A1; FR2998340A1

Abstract

This variable speed scroll compressor includes a closed casing including a low pressure volume and a high pressure volume, and an electric motor arranged in the low pressure volume and including a rotor and a stator, the rotor including permanent magnets, the stator including a stator core provided with a plurality of radially extending tooth portions and with a plurality of slots formed between the radially extending tooth portions, and stator windings each wound on the radially extending tooth portions. Each stator winding is wound around a respective tooth portion and includes winding portions extending respectively in the slots formed on each side of the respective tooth portion.

Description

FIELD OF THE INVENTION

The present invention relates to a variable speed scroll compressor.

BACKGROUND OF THE INVENTION

As known, a scroll-type compressor may comprise:

- a closed casing comprising a low pressure volume and a high pressure volume, and
- a variable speed electric motor arranged in the low pressure volume, the electric motor comprising a rotor and a stator, the rotor including permanent magnets, the stator including a stator core provided with a plurality of radially extending tooth portions and with a plurality of slots formed between the radially extending tooth portions, and stator windings wound on the radially extending tooth portions.

In such a scroll-type compressor, the stator windings almost completely fill out the slots provided in the stator core. Therefore, in operation, the low temperature low pressure refrigerant entering the low pressure volume flows essentially through a small annular gap delimited between the rotor core and the stator core.
As a result, the cooling of the stator windings and of the permanent magnets provided in the rotor core could be insufficient. This could lead to a demagnetization of the permanent magnets due to excessive heating of the permanent magnets by the hot stator windings. This issue is more critical at low rotational speed when the refrigerant flow is low.
Further, due to the flow of refrigerant through the small annular gap delimited between the rotor core and the stator core, the pressure drop for the refrigerant is high, which reduces the compressor efficiency especially at high rotational speed when the refrigerant flow is high.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved variable speed scroll compressor which can overcome the drawbacks encountered in conventional scroll compressors.
Another object of the present invention is to provide a variable speed scroll compressor which is reliable and has an enhanced efficiency.
According to the invention such a variable speed scroll compressor comprises:

- a closed casing comprising a low pressure volume and a high pressure volume,
- a compression unit adapted for compressing refrigerant,
- an electric motor arranged in the low pressure volume and comprising a rotor and a stator, the rotor including permanent magnets, the stator including a stator core provided with a plurality of radially extending tooth portions and with a plurality of slots formed between the radially extending tooth portions, and stator windings wound on the radially extending tooth portions, each stator winding being wound around a respective tooth portion,
- a drive shaft adapted for driving the compression unit, the drive shaft being rotatably coupled to the rotor, and
- 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 sliding movements between the rotor and the drive shaft,

wherein at least one slot formed between a first and a second adjacent radially extending tooth portions includes a first slot portion in which extends a winding portion of a first stator winding wound around the first radially extending tooth portion, a second slot portion in which extends a winding portion of a second stator winding wound around the second radially extending tooth portion, and a third slot portion arranged between the first and second slot portions and defining a refrigerant flow passage.
Such a winding of the stator windings on the tooth portions of the stator core allows maintaining a large free flow section within the stator slots for the flow of the refrigerant through said stator slots. This leads on the one hand to reduce pressure drop for the refrigerant, which enhances compressor efficiency, and on the other hand to improve the cooling of the stator windings even at low rotational speed of the motor.
Consequently, the stator and rotor cores, and especially the permanent magnets are effectively protected against any degradation whatever the operating conditions of the compressor according to the invention.
According to an embodiment of the invention, each slot formed between a first and a second adjacent radially extending tooth portions includes a first slot portion in which extends a winding portion of a first stator winding wound around the first radially extending tooth portion, a second slot portion in which extends a winding portion of a second stator winding wound around the second radially extending tooth portion, and a third slot portion arranged between the first and second slot portions and defining a refrigerant flow passage.
According to an embodiment of the invention, the variable speed scroll compressor further comprises a refrigerant suction inlet opening into the low pressure volume.
According to an embodiment of the invention, the variable speed scroll compressor is configured to force at least a part of the refrigerant entering the refrigerant suction inlet to pass through the refrigerant flow passages of the slots in order to cool the stator windings and the permanent magnets.
According to an embodiment of the invention, the ratio of the sum of the refrigerant flow passages cross-sectional areas to the stator cross-sectional area is between 3 and 14%, preferably between 5 and 10%, and for example between 6 and 8%. The stator cross-sectional area does not comprise the central opening for accommodating the rotor.
According to an embodiment of the invention, the electric motor is a variable-speed electric motor.
The variable speed scroll compressor may further comprise an intermediate jacket surrounding the stator, the intermediate jacket delimiting an annular outer volume with the closed casing and at least a first inner chamber which contains a first winding head of the stator directed towards the high pressure volume.
According to an embodiment of the invention, the variable speed scroll compressor may further comprise a securing member for securing the stator core to the closed casing, the intermediate jacket being formed by a cap covering an end portion of the stator core directed towards the high pressure volume.
The variable speed scroll compressor may further comprise conveying means for conveying at least some of the refrigerant entering the refrigerant suction inlet into the inner chamber. According to an embodiment of the invention, the conveying means include an intake orifice provided in the cap and facing the refrigerant suction inlet.
According to an embodiment of the invention, the electric motor is entirely arranged in the intermediate jacket, the intermediate jacket being mounted on a support frame separating the low and high pressure volumes.
According to an embodiment of the invention, the variable speed scroll compressor further comprises a centering member secured to the closed casing and on which is secured an end portion of the intermediate jacket opposite to the high pressure volume, the centering member and the intermediate jacket delimiting a second inner chamber which contains a second winding head of the stator opposite to the first winding head, the centering member being further provided with at least one refrigerant passage aperture opening into the second inner chamber.
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 play (or clearance).
According to an embodiment of the invention, the centering member is provided with a guide bearing arranged to guide an end portion of the drive shaft opposite to the compression unit.
According to an embodiment of the invention, the variable speed scroll compressor further comprises 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.
For example, 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. The locking element may be adapted to allow limited relative angular sliding movements between the rotor and the drive shaft.
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 and/or angular sliding movements between the rotor and the drive shaft.
According to an embodiment of the invention, the variable speed scroll compressor further comprises a positioning element secured on the drive shaft, the positioning element having an axial stop surface arranged to slidably co-operate with an end portion of the rotor opposite to the compression unit. The positioning element may be 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, in use, the drive shaft extends substantially vertically.
According to an embodiment of the invention, a lower end portion of the rotor rests on the axial stop surface of the positioning element.
These and other advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, two embodiments of the variable speed scroll compressor according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of embodiments 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 embodiments disclosed.

FIG. 1 is a longitudinal section view of a scroll-type refrigeration compressor according to a first embodiment of 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. 6 is a cross sectional view of the scroll-type refrigeration compressor according to FIG. 1.

FIG. 7 is a top view of a stator core and a rotor core of the scroll-type refrigeration compressor according to FIG. 1.

FIG. 8 is a longitudinal section view of a scroll-type refrigeration compressor according to a second embodiment of the invention.

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 a 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.
The refrigeration compressor 2 further comprises a scroll compression unit 8 disposed above the support frame 7. 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 end plate 12 of the fixed scroll member 9 includes, in its central part, a discharge aperture 17 opening into the central compression chamber 16 and leading to a high pressure discharge chamber 18.
The refrigeration compressor 2 also includes a refrigerant suction inlet 19 opening into the low pressure volume to achieve the supply of refrigerant to the compressor, and a discharge outlet 20 which opens into the discharge chamber 18.
The refrigeration compressor 2 further comprises an electric variable-speed motor disposed below the support frame 7, i.e. in the low pressure volume. The electric motor has a rotor 21 and a stator 22 disposed around the rotor 21.
As shown in FIG. 7, the rotor 21 includes a rotor stack or rotor core 23 provided with an axial through passage 24, and permanent magnets 25 inserted into longitudinal slots provided in the rotor core 23. The permanent magnets 25 are for example regularly arranged around the axial through passage 24.
As shown in FIGS. 6 and 7, the stator 22 includes a stator stack or stator core 26, and stator windings 27 wound on the stator core 26, The stator core 26 is provided on its inner periphery with a plurality of radially extending tooth portions 28, and with a plurality of longitudinal slots 29 formed between the radially extending tooth portions 28. According to the invention, each stator winding 27 is wound directly around a respective tooth portion 28 and extends in the longitudinal slots 29 formed on each side of said respective tooth portion 28. Each slot 29 includes a first slot portion in which extends a winding portion of a first adjacent stator winding 27, a second slot portion in which extends a portion of a second adjacent stator winding 27, and a third slot portion arranged between the first and second slot portions and defining a refrigerant flow passage 30.
The stator core 26 may for example includes six tooth portions 28 and six longitudinal slots 29, and the stator 22 may therefore includes six stator windings 27.
Furthermore the refrigeration compressor 2 comprises a drive shaft 31 adapted for driving the orbiting scroll member 11 in an orbital movement. The drive shaft 31 extends into the axial through passage 24 of the rotor 21 and is rotatably coupled to the rotor 21 so that the drive shaft 31 is driven to rotate by the rotor 21 about a rotational axis.
The drive shaft 31 comprises, at its top end, an eccentric pin 32 which is off-centered from the center of the drive shaft 31, and which is inserted in a connecting sleeve part 33 of the orbiting scroll member 11 so as to cause the orbiting scroll member 11 to be driven in an orbital movement relative to a fixed scroll member 9 when the electric motor is operated.
The bottom end of the drive shaft 31 drives an oil pump 34 which supplies oil from a sump defined by the closed casing 3 to a lubrication passage 35 formed inside the central part of the drive shaft 31.
The refrigeration compressor 2 further includes a positioning ring 36 secured to the drive shaft 31. For example, the positioning ring 36 is heat shrink fitted to the drive shaft 31. The positioning ring 36 may be made of non-magnetic material.
The positioning ring 36 has an axial stop surface 37 on which rests a lower end portion of the rotor 21, and more precisely a radial abutment surface 38 provided on the lower end portion of the rotor 21. Thus the positioning ring 36 is arranged to axially position the rotor 21.
As shown in FIGS. 2 and 3, the refrigeration compressor 2 includes a first annular axial abutment surface 39 provided on the rotor 21 and a second annular axial abutment surface 41 provided on the drive shaft 31. As particularly shown in FIG. 3, a predetermined axial gap may be provided between the first and second axial abutment surfaces 39, 41 in order to allow limited relative axial sliding movements between the rotor 21 and the drive shaft 31. For example, the predetermined axial gap is between a few micrometers 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 28 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 comprises a locking pin 42 adapted to rotatably couple the drive shaft 31 to the rotor 21. For example the locking pin 42 is made of non-magnetic material.
The locking pin 42 extends respectively into a first longitudinal recess 43 provided on the outer surface of the drive shaft 31 and into a second longitudinal recess 44 provided on the inner surface of the rotor core 23, the first and second longitudinal recesses 43, 44 being circumferentially aligned. The section dimensions of the locking pin 42 and of the first and second longitudinal recesses 43, 44 are adapted to allow limited relative axial and angular sliding movements between the rotor 21 and the drive shaft 31. The locking pin 42 may be slightly larger than the first longitudinal recesses 43 so that the locking pin 42 is press fitted into the first longitudinal recess 43, and the locking pin 42 may be slide-fitted into the second longitudinal recess 44. However, alternately the locking pin 42 may be slide-fitted into the first and second longitudinal recesses 43, 44.
The second longitudinal recess 44 provided on the rotor 21 can extend along the entire length of the rotor core 23. Advantageously, the first longitudinal recess 43 extends only along a partial length of the drive shaft 31 and delimits an axial stop surface 45 for the upper end of the locking pin 42. Furthermore the axial stop surface 37 provided on the positioning ring 36 forms also an axial stop for the lower end of the locking pin 42.
The refrigeration compressor 2 also includes an annular fixing member 46 for fixing the stator 22 to the closed casing, and a centering member 47 secured to the closed casing 3 and provided with a guide bearing 40 arranged to guide the lower end portion of the drive shaft 31.
The refrigeration compressor 2 further comprises an intermediate jacket 48 surrounding the stator 22 and covering the upper end of the electric motor. The intermediate jacket 48 and the closed casing 3 delimit an annular outer volume 49 into which opens the refrigerant suction inlet 19. The intermediate jacket 48 delimits, with the electric motor, an inner chamber 50 containing the winding head 27 a of the stator 22 oriented towards the scroll compression unit 8. The winding head 27 a is formed by the portions of the stator windings 27 extending towards outside from the end face 26 a of the stator core 26 oriented towards the scroll compression unit 8.
The intermediate jacket 48 is provided with an intake orifice 51 opening into the proximal chamber 50 and facing the refrigerant suction inlet 19 in order to allow admission of refrigerant into the proximal chamber 49. Further, the support frame 7 comprises one or several refrigerant passage apertures 52 opening into the low pressure volume and into the scroll compression unit 8.
In operation, a first part of the refrigerant entering through the refrigerant suction inlet 19 flows into the annular outer volume 49, and then flows upwardly directly towards the scroll compression unit 8 via the refrigerant passage apertures 52.
Further, a second part of the refrigerant entering the refrigerant suction inlet 19 flows into the inner chamber 50 through the intake orifice 51 of the intermediate jacket 48, and then flows downwardly towards the centering member 47 by passing through the refrigerant flow passages 30 (shown in FIG. 6) delimited by the stator core 26 and the stator windings 27. It should be noted that a part of the refrigerant that has entered into the inner chamber 50 may also flow downwardly towards the centering member 47 through gaps 54 delimited between the stator core 26 and the rotor core 23. The refrigerant passing through the refrigerant flow passages 30 cools down the stator windings 27, while the refrigerant passing through the gaps 54 cools down the stator core 26 and the rotor core 23, which protects the stator core, the rotor core and the permanent magnets of the latter against damage.
Next, the refrigerant travels upwards through the low pressure volume towards the scroll compression unit 8 and enters the compression chambers 16 via the refrigerant passage apertures 52.
Then, the refrigerant entering the scroll compression unit 8 is compressed in the compression chambers 16 and escapes from the centre of the fixed and orbiting scroll members 9, 11 through the discharge aperture 17 leading to the discharge chamber 18, from which the compressed refrigerant is discharged by the discharge outlet 20.
FIG. 8 shows a scroll-type refrigeration compressor 2 according to a second embodiment of the invention which differs from the one disclosed in FIGS. 1 to 7 essentially in that the electric motor is entirely arranged in the intermediate jacket 48, and in that the intermediate jacket 48 and the electric motor define a proximal chamber 55 a containing the winding head 27 a of the stator 22 oriented towards the scroll compression unit 8 and a distal chamber 55 b containing the winding head 27 b of the stator 22 opposite to the first winding head 27 a, the winding heads 27 b being formed by the portions of the stator windings 27 extending towards outside from the end face 26 b of the stator core 26 opposite to the end face 26 a.
According to the second embodiment, the upper end of the intermediate jacket 48 is secured to the support frame 7 and the lower end of the intermediate jacket 48 is secured to the centering member 47, so that the intermediate jacket 48 serves to fix the stator core 26. It should be noted that an annular connection element 56 may be arranged between the intermediate jacket 48 and the stator 22.
Further, according to the second embodiment, the centering member 47 is further provided with at least one refrigerant passage aperture 57 opening into the distal chamber 54 b.
In operation, the refrigerant entering through the refrigerant suction inlet 19 flows downwardly in the annular outer volume 49 towards the centering member 47. Then, the refrigerant flows through the refrigerant passage aperture 57 provided in the centering member 47, and enters the distal chamber 55 b. The refrigerant that has entered into the distal chamber 55 b flows upwardly towards the scroll compression unit 8 via the refrigerant flow passages 30 delimited by the stator core 26 and the stator windings 27, the proximal chamber 55 a and refrigerant passage apertures (non shown in FIG. 8) provided in the support frame 7. It should be noted that a part of the refrigerant that has entered into the distal chamber 55 b may flow upwardly towards the scroll compression unit 8 through gaps (not shown in FIG. 8) delimited by the intermediate jacket 48 and the outer periphery of the stator 22.
Next, the refrigerant entering the scroll compression unit 8 is compressed in the compression chambers 16 and escapes from the centre of the fixed and orbiting scroll members 9, 11 through the discharge aperture 17 leading to the discharge chamber 18, from which the compressed refrigerant is discharged by the discharge outlet 20.
Of course, the invention is not restricted to the embodiments described above by way of non-limiting examples, but on the contrary it encompasses all embodiments thereof.

Claims

1. A variable speed scroll compressor comprising:

a closed casing comprising a low pressure volume and a high pressure volume,

a compression unit adapted for compressing refrigerant,

an electric motor arranged in the low pressure volume and comprising a rotor and a stator. the rotor including permanent magnets, the stator including a stator core provided with a plurality of radially extending tooth portions and with a plurality of slots formed between the radially extending tooth portions, and stator windings wound on the radially extending tooth portions, each stator winding being wound around a respective tooth portion,

a drive shaft adapted for driving the compression unit, the drive shaft being rotatably coupled to the rotor, and

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 sliding movements between the rotor and the drive shaft,

wherein at least one slot formed between a first and a second adjacent radially extending tooth portions includes a first slot portion in which extends a winding portion of a first stator winding wound around the first radially extending tooth portion, a second slot portion in which extends a winding portion of a second stator winding wound around the second radially extending tooth portion, and a third slot portion arranged between the first and second slot portions and defining a refrigerant flow passage.

2. The variable speed scroll compressor according to claim 1, wherein the ratio of the sum of the refrigerant flow passages cross-sectional areas to the stator cross-sectional area is between 3 and 14%.

3. The variable speed scroll compressor according to claim 1, wherein the variable speed scroll compressor is configured to force at least a part of the refrigerant entering the refrigerant suction inlet to pass through the refrigerant flow passages of the slots.

4. The variable speed scroll compressor according to claim 1, further comprising an intermediate jacket surrounding the stator, the intermediate jacket delimiting an annular outer volume with the closed casing and at least an inner chamber, which contains a first winding head of the stator directed towards the high pressure volume.

5. The variable speed scroll compressor according to claim 1, further comprising a locking element adapted to rotatably couple the drive shaft to the rotor.

6. The variable speed scroll compressor according to claim 5, 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.

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

8. The variable speed scroll compressor according to claim 1, further comprising a positioning element secured on the drive shaft the positioning element having an axial stop surface arranged to slidably co-operate with an end portion of the rotor opposite to the compression unit.

9. The variable speed scroll compressor according to claim 8, wherein the positioning element is a positioning ring secured to the drive shaft.