The present invention relates to a compact electric centrifugal compressor which is more specifically but not exclusively adapted to be used in a Heat Ventilation Air Conditioning (HVAC) installation for vehicles.
The vehicles may include in particular terrestrial vehicles such as hybrid electric vehicles (HEV) or electric vehicles (EV) as well as aircrafts or other kinds of vehicles.
Conventional Electric compressors, such as HVAC compressors for vehicles are typically associated with an electric motor. An example of such electric motor driven compressor is given in patent document U.S. Pat. No. 6,183,215 B 1.
Such types of electric motor driven compressors have many drawbacks linked to lubrication, refrigerants, low operating speed, friction losses and loss of compactness.
Two main categories of HVAC electric compressors are used in HEV/EV vehicles: rotary like vane compressors and oscillating like scroll type compressors.
Both types of electric compressors which are associated with an electric motor have the following drawbacks:
Lubricants are needed for different mechanical parts,
It is necessary to check compatibility of lubricant oil with refrigerants (such as for example the haloalkane refrigerant R134a or the more recently used hydrofluoroolefin refrigerant HFO-1234yf),
Lubricants should be carefully chosen to protect the electric motor windings from the risk of insulation failure, An oil separator and leak detection devices are required to avoid contamination of the electric systems in EV/HEV vehicles,
The conventional electric compressors have a speed which is limited and cannot exceed 10,000 rpm. Friction losses are detrimental to the operation of the electric compressor.
Therefore, it is desired to provide an electric compressor which can solve most of these problems.
The invention is intended more especially, although not exclusively, to automotive air conditioning applications and therefore further aims at providing an electric compressor which takes into account the high level of vibrations generated in a vehicle and which is as compact as possible.
According to an embodiment of the present invention, there is provided a compact electric compressor comprising a motor portion and a centrifugal compressor portion driven by the motor portion through a shaft, wherein the motor portion comprises first and second radial bearingless motors spaced apart along the shaft and configured for rotating the shaft and maintaining it in a defined radial position in a contactless manner during functional operation of the electric compressor and axial electromagnetic means located between the first and second radial bearingless motors and configured for maintaining the shaft in a defined axial position during functional operation of the electric compressor and wherein auxiliary landing bearing are located at each end of the shaft in the vicinity of each of the first and second radial bearingless motors.
According to a first embodiment the axial electromagnetic means comprise an axial bearingless motor.
According to a second embodiment the axial electromagnetic means comprise an active axial magnetic bearing.
Separators may be provided between the radial bearingless motors and the axial electromagnetic means.
More specifically the radial bearingless motors each comprise a rotor portion having a plurality of pole pairs armatures and a stator portion comprising a core with slots for receiving windings configured to impress a motor torque and a radial bearing force.
Separate windings may be provided in the slots of the stator portion for impressing a motor torque and an axial bearing force.
Alternatively common windings may be provided in the slots of the stator portion for impressing a motor torque and an axial bearing force.
The radial bearingless motors comprise a rotor portion chosen among an induction rotor, a permanent magnet rotor, a hysteresis rotor and a reluctance rotor.
According to a specific embodiment the centrifugal compressor portion comprises a wheel at a first end of the shaft and control circuits associated with the radial bearingless motors and the axial electromagnetic means are located at a second end of the shaft and are connected to the radial bearingless motors and the axial electromagnetic means via a feedthrough.
The centrifugal compressor portion may comprise a variety of configurations and in particular may comprise a single wheel, double wheels, tandem wheels or double tandem wheels.
The axial bearingless motor may comprise a rotor portion having a plurality of pole pairs armatures and first and second stator portions each comprising a core with slots respectively for receiving windings configured to impress a motor torque and an axial bearing force, the first and second stator portions being located on each side of the rotor portion.
When the axial electromagnetic means are constituted by an active axial magnetic bearing or thrust bearing, the active axial magnetic bearing may comprise a disc armature integral with the shaft and first and second stator electromagnets facing the disc armature in a contactless manner on each side of the latter.
The present invention will be described in connection with preferred embodiments which are given by way of examples.
A rotor shaft 15 of a motor portion 20 is coupled to a centrifugal compressor wheel 11 of a compressor portion 10 to drive the centrifugal compressor wheel 11.
An electrical motor 30 comprises a rotor 31 which may be of any type chosen among induction rotor, permanent magnet rotor, hysteresis rotor and reluctance rotor. The electrical motor 30 further comprises a stator 32 with windings 32a.
First and second active radial magnetic bearings 40, 50 are located on each side of the electrical motor 30 to support the shaft 15 in levitation during functional operation of the electric compressor. Each active radial magnetic bearing 40, 50 comprises a rotor 41, 51 fast with the shaft 15 and a stator 42, 52 with windings 42a, 52a.
An active axial magnetic bearing 60 (thrust bearing) comprises on the one hand a disc 61 which is mounted perpendicular to the axis of the shaft 15 and constitutes a rotor armature and on the other hand first and second stators 62, 63 each having at least one annular coil or winding 62a, 63a located in a stator 62, 63 which may have a C-shaped core, as shown in
The radial bearing rotors 41, 51 are equipped with ferromagnetic laminations which are held in position by the magnetic fields created by the electromagnets of the stators 42, 52.
The shaft 15 is levitated in a contactless manner due to the radial magnetic bearings. The shaft's position is monitored by sensors (not shown), e.g. of the variable inductive type, which detect any deviation from nominal position and emit signals which are used in a control system (not shown in
Auxiliary landing bearings 8 are used for supporting the shaft 15 essentially during a starting or stopping operation of the motor portion 20, but also during brief intermittent periods in case of shock-loads due to the usually high level of vibrations present in a vehicle.
Generally speaking where a rotary shaft is suspended by means of an active magnetic suspension servo-controlled on the basis of sensors for detecting the position of the rotary shaft, auxiliary bearings, also known as emergency bearings, are provided in order to support the shaft while the machine is being stopped or in the event of a total or partial failure of the magnetic suspension, thereby preventing direct contact between the magnetic circuits of the rotors and the stators of the magnetic bearings or bearingless motors when the windings of the stator electromagnets are not properly powered, thus avoiding damage to the laminations thereof. In normal operation, auxiliary bearings leave clearance about the rotary shaft and do not themselves, rotate. The clearance provided for the auxiliary bearings is generally about one half the width of the air gap of the magnetic bearings or bearingless motors.
The auxiliary landing/touch down bearings 8 may have a variety of designs and may be for example rolling bearings, needle bearings, plain bearings, bushings, etc. . . .
Separators 9 may be located between the stator windings of the magnetic bearings 40, 50, 60 and of the electrical motor 30.
The casing or flanges and cooling systems with a refrigerant are conventional and are not represented in the drawings.
In
As shown in
Thus as shown in
Preferred embodiments of the invention will now be described in connection with
The embodiment of
The radial bearingless motors 140, 150 each comprise a disc-like central armature 141, 151 integral with the shaft 15 and a stator 142, 152 with windings 142a, 152a.
An example of radial bearingless motor 180 is represented in
Basically the stator windings 185 achieve both functions of torque windings and suspension force windings. As an example if two magnetic fields, which may be created by two winding sets with a difference in the pole pair number of one, are superposed, a torque and a radial force will be produced. It is thus possible for example to combine a 4-pole motor winding of a reluctance motor with a 2-pole bearing winding, but many other embodiments are possible.
U.S. Pat. No. 6,727,618 B1 discloses an example of bearingless switched reluctance motor.
In the stator portions 142, 152, 182 of the radial bearingless motors 140, 150, 180 separated coils may be used to impress the bearing force and the motor torque.
Alternatively the needed bearing force and motor torque may be generated in each coil by combined windings. In such a case a single coil will carry jointly the required motor and bearing ampere-turns.
In
As mentioned earlier reference numeral may also designate an axial bearingless motor. In such a case the embodiment of
In the stator portions 132, 133 of the axial bearingless motor separated coils may be used to impress the bearing force and the motor torque.
Alternatively the needed bearing force and motor torque may be generated in each coil by combined windings. In such a case a single coil will carry jointly the required motor and bearing ampere-turns.
A plurality of pole pairs armatures 138 are shown in
As a non-limiting example, the stator 132 and the rotor 131 with permanent magnets 138 may constitute a permanent magnet motor, where the permanent magnets 138 on the rotor surface produce an axial force in a first direction (upward direction in the configuration of
Active radial magnetic bearings 140 and 150 similar to previously described active radial magnetic bearings 40 and 50 and comprising a rotor armature 141, 151 and a stator 142, 152 with windings 142a, 152a may be located on each side of an axial bearingless motor 130.
However as mentioned above first and second radial bearingless motors 140, 150 are preferably used in combination with an axial bearingless motor 130 or a thrust magnetic bearing.
Although preferred embodiments have been shown and described, it should be understood that any changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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12305730 | Jun 2012 | EP | regional |