STIRLING-CYCLE COOLING DEVICE WITH EXTERNAL ROTOR MOTOR
A cooling device implementing a stirling-type thermodynamic cycle includes a compressor with a reciprocating piston driven by an electric motor rotating about an axis via a crankshaft. The electric motor comprises an internal stator and an external rotor and is connected to the crankshaft via a link with at least one degree of freedom in rotation about the axis of the electric motor.
This application claims priority to foreign French patent application No. FR 1874264, filed on Dec. 28, 2018, the disclosure of which is incorporated by reference in its entirety.
FIELD OF THE INVENTIONThe invention relates to a cooling device implementing a reverse Stirling-type thermodynamic cycle. Such a device is, for example, described in patent U.S. Pat. No. 4,365,982. Cooling is achieved by means of a coolant fluid circulating in a circuit comprising, principally, a compressor and a regenerator used as heat exchanger. The compressor comprises a piston that is movable in translation in a cylinder. The regenerator comprises a regeneration piston that is likewise movable in a second cylinder. The regenerator is sometimes called: “displacer”. The two pistons are each driven by a connecting rod/crank arm, both actuated by a crankshaft. The crankshaft is driven in rotation by a rotary motor.
BACKGROUNDIn a known manner, the reverse Stirling cycle comprises the following four phases:
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- an isothermal compression of a fluid at high temperature, obtained by the movement of a compression piston in a compression cylinder;
- an isochoric cooling of the fluid, from the high temperature to a low temperature, obtained by passage of the fluid through a regeneration piston, the piston moving in a regeneration cylinder and acting as a heat exchanger;
- an isothermal expansion of the fluid at the low temperature, obtained by return of the compression piston in the compression cylinder; and
- an isochoric heating of the fluid, from the low temperature to the high temperature, obtained by return of the regeneration piston in the regeneration cylinder.
Conventionally, the regeneration piston and the compression piston are driven by the crankshaft, via a connecting rod articulated, on the one hand, on a crankpin and, on the other, on the piston in question.
It is commonplace to use an internal rotor electric motor to drive the crankshaft. This type of motor is generally composed of an external stator and an internal rotor. More precisely, the stator has windings assembled in the form of a tube generating, inside the tube, a turning magnetic field. The rotor may have permanent magnets or windings. The rotor is arranged inside the stator and turns by engaging with the magnetic field generated by the stator.
During the compression and expansion phases, the reciprocal movement of the pistons in their respective cylinder generates reciprocal and potentially out-of-phase axial forces. Via the connecting rod/crank arm systems, the forces exerted by the pistons are translated into a variable resistive torque at the level of the drive. More precisely, this torque exhibits considerable amplitude variations between a value close to zero and a maximum value achieved twice per revolution.
Control of the electric motor makes it possible to adapt to these variations in torque but gives rise to electrical performance losses not only for the motor itself but also for the electronic device that controls it. Variations in toque give rise to variations in voltage and current in the electrical supply to the motor, potentially creating electromagnetic disturbances.
Moreover, the variations in torque give rise to oscillations of the angular speed of the motor and of the crankshaft. These speed oscillations generate vibrations that may degrade the acoustic signature of the cooling device and potentially give rise to accelerated mechanical fatigue of the various components of the device.
It is possible to limit the impact of these variations in resistive torque at the level of the drive with the aid of a flywheel added onto the drive shaft. However, the addition of this type of movable component gives rise to an increase in the volume, the mass and the cost of the cooling device.
SUMMARY OF THE INVENTIONThe invention aims to palliate all or some of the problems cited above by implementing an external rotor drive. The external rotor drive by construction exhibits a moment of inertia about its axis of rotation that is greater than in the case of an internal rotor configuration. In such a case it is thus possible to envisage being able to dispense with a flywheel.
Moreover, for a given volume and performance, an external rotor motor may generate a torque greater than that of an internal rotor motor. Similarly, for a given torque, the use of an external rotor motor thus makes it possible to facilitate the miniaturization of the cooling device.
Lastly, in a permanent magnet rotor motor, the magnets are arranged as close as possible to the stator. An internal rotor motor presents the risk of detachment of the magnets during rotation of the motor owing to the centrifugal force that tends to tear the magnets from their support. However, in an external rotor motor comprising magnets, the latter tend to be pressed against the bottom of their housing, thereby avoiding the implementation of specific means for holding the magnets, such as specific magnet holding rings. In an internal rotor motor, such holding means tend also to increase the gap between the rotor and the stator, which gives rise to a drop in the performance of the motor.
To that end, a subject of the invention is a Stirling-cycle cooling device comprising a compressor with a reciprocal piston driven by an electric motor rotating about an axis via a crankshaft, wherein the electric motor comprises an internal stator and an external rotor and wherein the internal stator is connected to the crankshaft via a link with at least one degree of freedom in rotation about the axis of the electric motor.
Advantageously, the internal stator has a solid cylindrical form extending along the axis of the electric motor.
Advantageously, the stator has a cylindrical form comprising an axial opening and extending along the axis and wherein a drive shaft integral with the external rotor can turn.
The axial opening partially or completely may traverse the stator.
The external rotor is advantageously integral with a drive shaft carried by the link with at least one degree of freedom in rotation and the link with at least one degree of freedom in rotation is produced in two parts each arranged on one side of the motor along the axis.
Each of the parts is, for example, formed by a bearing.
A housing of the device advantageously comprises a tubular bearing surface extending along the axis, partially or completely traversing the stator, which is fixed on the exterior of the tubular bearing surface. The drive shaft extends inside the tubular bearing surface and the link with at least one degree of freedom in rotation connects the interior of the tubular bearing surface and the drive shaft.
The device advantageously comprises a monoblock body integral with the stator. The link with at least one degree of freedom in rotation along the axis connects the monoblock body and a drive shaft integral with the rotor and the piston of the compressor moves in a cylinder formed in the monoblock body.
The body advantageously comprises the tubular bearing surface.
Advantageously, only the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft. Furthermore, the link with at least one degree of freedom of rotation along the axis connects the body and the drive shaft directly.
The rotor is integral with a drive shaft advantageously comprising a bearing surface extending along the axis and integral with the crankshaft, a tube segment inside which is fixed the rotor and a web connecting the tube segment and the bearing surface.
The motor is advantageously arranged between the body and the web.
The kinematic link with at least one degree of freedom in rotation along the axis comprises a link or a link assembly amongst:
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- a pivot link;
- a sliding pivot link;
- an annular linear link and a ball link associated in parallel;
- two ball links associated in parallel;
- a ball link and a rectilinear linear link (36) associated in parallel;
- a sliding pivot link and a punctiform link (40) associated in parallel;
- an annular linear link and a planar bearing link associated in parallel.
The invention will be better understood and further advantages will become apparent upon reading the detailed description of embodiments given by way of example, which description is illustrated by the attached drawing, in which:
For the sake of clarity, the same elements will bear the same references in the different figures.
DETAILED DESCRIPTIONAn external rotor motor 10 is shown in
The motor 10 comprises a rotor 20 produced in the form of an axisymmetrical tube about the axis 14. The rotor 20 is arranged radially about the stator 12. The rotor 20 may comprise windings or permanent magnets designed to engage with the magnetic field generated by the stator windings. The use of permanent magnets makes it possible to dispense with the implementation of turning contacts, such as brushes or carbon brushes, for powering the rotor windings.
In
It can perfectly well be envisaged to implement the invention with other link configurations that have not been shown previously in
The stator 12 is assembled on the housing 16 and, more precisely, on the cover 62 in the example of
The drive shaft 70 is integral with the rotor 20. More precisely, the drive shaft 70 comprises a tube 72 inside which the rotor 20 is fixed. The drive shaft 70 also comprises a bearing surface 74 extending along the axis 14, integral with the crankshaft (not shown) and a web 76 connecting the bearing surface 74 and the tube 72. The web 76 has the form of a disc centred on the axis 14. The drive shaft 70 makes it possible to increase the moment of inertia of the turning part of the device. More precisely, the inertia of the drive shaft 70 is principally due to the presence of the tube 72. Indeed, the inertia of the turning part of the motor 10 is all the greater when it comprises mass at a distance from the axis 14. Thus, the tube 72 performs two functions: the mechanical holding of the rotor 20 and a significant share of the inertia of the turning part of the motor 10. A further significant share of the inertia is provided by the rotor 20. The inertia of such an assembly is much greater than that of an internal rotor motor, in which the essential part of the mass of the turning part of the motor is concentrated in the immediate vicinity of its axis of rotation.
The kinematic link between the housing 16 and the rotor 20 is provided by two bearings 80 and 82. The bearing 80 is arranged between the bearing surface 74 of the drive shaft 70 and the body 60. The bearing 82 is arranged between the tube 72 and the tubular part 66 of the cover 62. The bearings 80 and 82 may, for example, be ball bearings. Certain types of bearing, when the rings are immobilized, may be likened to a ball link since, complementing rotation about the axis 14, they have a rotational mobility about two axes perpendicular to the axis 14. This assembly with two ball bearings may thus fulfill the function of the link shown in
The bearing 80 lies between the bearing surface 92 and the body 60. In
In
In
The compressor 100 of the refrigeration device is shown in
In this embodiment, the function of the cover 62 is only to form a shell of the motor 50 and it no longer supports the stator 52. The stator 52 is fixed to the exterior of the tubular bearing surface 106. The arrangement of the bearings 80 and 94 between the body and the drive shaft simplifies the dimensional chain passing via the body, the drive shaft, the crankshaft 110, the connecting rod 120, and the piston 102, thereafter returning towards the bodies 60. This dimensional chain does not pass via the cover as in the embodiments shown in
In this embodiment, the drive shaft 108 comprises a solid bearing surface 112 extending along the axis 14, and on which the bearings 80 and 94 are mounted. The crankshaft 110 is formed by the end of the bearing surface 112 and a crankpin 113 integral with the bearing surface 112 and extending in the extension thereof. The piston 102 is driven by the drive shaft 108 via the crankpin 113 and a connecting rod 120. The drive shaft 108 further comprises a tube segment 114 similar to the tube segment 72 and carrying the external rotor 20 and also a web 116 connecting the bearing surface 112 and the tube segment 114. The web 116 has the form of a disc centred on the axis 14. In the embodiments of
In
Claims
1. A stirling-cycle cooling device comprising a compressor with a reciprocal piston driven by an electric motor rotating about an axis via a crankshaft, wherein the electric motor comprises an internal stator and an external rotor and in that the internal stator is connected to the crankshaft via a link with at least one degree of freedom in rotation about the axis of the electric motor.
2. The device according to claim 1, wherein the internal stator has a solid cylindrical form extending along the axis of the electric motor.
3. The device according to claim 1, wherein the stator has a cylindrical form comprising an axial opening and extending along the axis and wherein a drive shaft integral with the external rotor can turn.
4. The device according to claim 3, wherein the axial opening partially or completely traverses the stator.
5. The device according to claim 4, wherein the external rotor is integral with a drive shaft carried by the link with at least one degree of freedom in rotation and in that the link with at least one degree of freedom in rotation is produced in two parts each arranged on one side of the motor along the axis.
6. The device according to claim 5, wherein each of the parts is formed by a bearing.
7. The device according to claim 1, wherein a housing of the device comprises a tubular bearing surface extending along the axis, partially or completely traversing the stator, in that the stator is fixed on the exterior of the tubular bearing surface, in that the drive shaft extends inside the tubular bearing surface and in that the link with at least one degree of freedom in rotation connects the interior of the tubular bearing surface and the drive shaft.
8. The device according to claim 1, wherein it comprises a monoblock body integral with the stator, in that the link with at least one degree of freedom in rotation along the axis connects the body and a drive shaft integral with the rotor and in that the piston of the compressor moves in a cylinder formed in the body.
9. The device according to claim 7, wherein the monoblock body comprises the tubular bearing surface.
10. The device according to claim 9, wherein only the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft and in that the link with at least one degree of freedom in rotation along the axis connects the body and the drive shaft directly.
11. The device according to claim 1, wherein the rotor is integral with a drive shaft comprising a bearing surface extending along the axis and integral with the crankshaft, a tube segment inside which is fixed the rotor and a web connecting the tube segment and the bearing surface.
12. The device according to claim 11, wherein the motor is arranged between the body and the web.
13. The device according to claim 1, wherein the kinematic link with at least one degree of freedom in rotation along the axis comprises a link or a link assembly amongst:
- a pivot link;
- a sliding pivot link;
- an annular linear link and a ball link associated in parallel;
- two ball links associated in parallel;
- a ball link and a rectilinear linear link associated in parallel;
- a sliding pivot link and a punctiform link associated in parallel;
- an annular linear link and a planar bearing link associated in parallel.
Type: Application
Filed: Dec 27, 2019
Publication Date: Jul 2, 2020
Inventors: Mikel SACAU (BLAGNAC), Jean-Yves MARTIN (BLAGNAC), Julien LE BORDAYS (BLAGNAC)
Application Number: 16/728,740