AXIAL FLOW ELECTRICAL MACHINE WITH STABILIZED AIR GAP

Abstract

The invention relates to an axial flux electric machine (10) comprising: - a housing (12, 12a, 12b), - a shaft (14), - at least one rotor disk (24) mounted to rotate about an axis X in said housing (12) to drive said shaft (14), - at least one stator (22a, 22b), mounted in said housing (12) axially opposite at least one rotor disk (24), at least one air gap (Ea, Eb) being defined between said at least one stator (22a, 22b) and said at least one rotor disk (24), in which said machine (10) is configured to axially immobilize said at least one disk (24) relative to said housing (12, 12a, 12b) at a radial distance from said shaft (14). Figure for the abstract: Figure 1.

Description

Title of the invention: AXIAL FLUID ELECTRICAL MACHINE WITH STABILIZED AIR GAP Technical field of the invention

[0001] The invention relates to an axial flux electric machine, in particular for motor vehicles. Technical background

[0002] Axial flux electric machines are electric machines in which the magnetic flux is oriented parallel to a principal axis of rotation of the machine. In such an axial flux machine, the magnetic flux therefore flows axially through the machine. This implies that the windings and magnets are arranged so that the flux flows along the principal axis. They can be alternating current (synchronous machines, for example) or direct current. They can also use permanent magnets to create the magnetic field.

[0003] These machines have the advantage of having a modular design, with rotors and stators that are flatter than a radial flux electric machine, which facilitates their manufacture and assembly and, due to their compactness, allows them to be used for applications where space is limited, particularly for automotive applications, especially for their motorization.

[0004] Among other advantages, axial flux electric machines offer superior performance to radial flux machines of equivalent size.

[0005] In the simplest axial flux electrical machines, two main architectures are distinguished.

[0006] According to a first architecture, a machine housing comprises two stators with a rotor disk interposed between them. According to a second architecture, a machine housing comprises a single stator with two rotor disks arranged on either side of it. In both cases, air gaps are defined between the stator(s) and the rotor disk(s). Maintaining these air gaps is crucial for satisfactory efficiency of the electric machine.

[0007] Conventionally, the electric machine comprises a rotor shaft which is mounted for rotation within the machine housing and which carries the rotor disc(s). This rotor shaft is either traversed by a drive shaft to which it is connected, or constitutes the drive shaft itself. It is mounted substantially at its ends on two bearings which are received within the housing.

[0008] The axial position of this rotor shaft relative to the housing determines the position of the disc(s) relative to the stator(s). Consequently, the axial position of the rotor shaft determines the air gap(s) of the electric machine.

[0009] The rough axial position of this shaft is determined by the location of its bearing housings and is generally refined using shims or spacers located at the rotor shaft, between the housing and the bearings, or possibly between the shaft and the bearings. A judicious choice of shim thickness allows for two substantially equal air gaps.

[0010] However, it was found that, while these shims made it possible to determine a satisfactory static positioning of the rotor shaft, this was not necessarily the case with regard to its dynamic positioning.

[0011] Indeed, due to manufacturing tolerances of the parts and clearances in the bearings, it has been observed that the rotor shaft can tilt slightly relative to the axial direction, for example around a radial axis lying in a plane perpendicular to the axis of rotation, when subjected to torque. This is particularly noticeable in situations such as torque recovery, rapid acceleration, or deceleration. The tilting of the shaft effectively alters the position of the disk(s) relative to the stator(s) and consequently the air gaps, resulting in a decrease in the efficiency of the electric machine.

[0012] There is therefore a real need for an electrical machine configuration that allows for limiting a variation in air gaps. Summary of the invention

[0013] The invention satisfies this need by proposing an electric machine equipped with a means of guiding the rotor disc(s) relative to the casing.

[0014] To this end, the invention proposes an axial flux electrical machine comprising:

[0015] - a housing,

[0016] - a tree,

[0017] - at least one rotor disc mounted to rotate about an X-axis in said housing for to train said tree,

[0018] - at least one stator, mounted in said housing axially opposite at least one rotor disc,

[0019] at least one air gap being defined between said at least one stator and said at least one rotor disk,

[0020] in which said machine is configured to axially immobilize said at least one disk relative to said housing at a radial distance from said shaft.

[0021] The axial immobilization provided by the invention between the housing and the disc makes it possible, by preventing the shaft from tilting, to limit the risks of variation of said at least an air gap. By placing this immobilizer at a distance from the shaft, this effect is further improved, including during dynamic operation.

[0022] According to various additional features of the invention, which may be taken together or separately and which constitute so many embodiments of the invention: - Said machine includes at least one stop, interposed, in particular axially, between said casing and at least one rotor disc, - When the machine has a single stop, it is a double-acting stop. - When the machine has at least two stops, these are single-point stops effect or double effect, - There are two of these stops, - Said stops are interposed between said housing and two opposite faces or faces turned towards each other of at least one rotor disc, - Each stop comprises at least one track received in a groove of said housing and / or of said at least one disc, - Each stop is arranged in contact with one face of a peripheral ring of at least one rotor disc, - Said casing or at least one disc has one or more bearing surfaces intended to cooperate with said thrust bearing(s), - When the track is received in the groove of at least one disc, said groove is formed in the face of the peripheral rim of said disc, - The stops are of the same diameter, - The stops are arranged radially beyond the air gaps, - The said stops are arranged according to a larger diameter due to at least one rotor disc, - Thrusters are rotating thrust bearings, notably those with sliding rings, balls, needles, or rollers. - Said machine comprises said disk and two said stators, arranged on either side of said disk, - Said stops are axially arranged on either side of said rotor disc, - The casing comprises two adjoining half-casings arranged on either side of a median plane of said disc, - When the track of each stop is received in the groove of the housing, this groove is formed in one face of one of the housing halves facing said disc, - The shaft includes a rotor shaft and / or a drive shaft, - The disc is fixed to the rotor shaft, which is mounted to rotate within the housing. - The rotor shaft is traversed by the drive shaft, - The rotor shaft is coupled to the drive shaft, notably by grooves, - The rotor shaft has a protruding flange to which the disc is attached, - One side of the collar is fixed to one side of the disc, - At least one screw passes through the disc and the flange, - The rotor shaft is mounted to rotate within the housing at each of its ends by an end bearing, - Each end bearing is a ball bearing. Brief description of the figures

[0023] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent in the course of the detailed explanatory description which follows, of at least one embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawing in which:

[0024] Fig. 1 is a schematic half-view in cross-section of an electrical machine according to the invention. Detailed description of the invention

[0025] In the description that follows, identical reference numerals designate identical parts or parts having similar functions.

[0026] Figure 1 shows an axial flux electrical machine 10 made according to the invention. The electrical machine 10 and its components will be described with reference to the directions of the trihedron "X, Y, Z" where "X" designates an axial direction, "Y" designates a first transverse direction substantially perpendicular to the axial direction "X", and "Z" designates a second transverse direction substantially vertical perpendicular to the axial direction "X" and to the first transverse direction "Z".

[0027] The electric machine 10 generally comprises a casing 12, and a shaft 14 with axis X. The shaft 14 is here a rotor shaft which is substantially tubular and is traversed by a drive shaft 16 to which it is coupled, in particular by a set of splines 18. The drive shaft 16 is for example intended to be coupled to a transmission (not shown) of a motor vehicle.

[0028] The rotor shaft 14 is mounted to rotate in the housing 12 at each of its ends 14a, 14b by means of two end bearings 20a, 20b. Each of these end bearings is, in a non-limiting manner of the invention, a ball bearing.

[0029] By way of non-limiting description of the invention, the electrical machine comprises two stators 22a, 22b, through which the shaft 14 passes, and a rotor disc 24, carried by the shaft 14, which is received between the two stators 22a, 22b. The disc 24 is fixed to the rotor shaft 14. The stators 22a, 22b and disc 24 extend in the Y, Z plane. They are annular.

[0030] This configuration is not limiting of the invention, and alternatively, according to another configuration, the electric machine 10 could comprise a single stator through which the shaft 14 passes, this shaft 14 carrying two rotor discs arranged on either side of the stator.

[0031] In the configuration shown here, the rotor shaft 14 has a protruding flange 26 in the Y, Z plane to which the disc 24 is attached. A face 28 of the flange 26 is attached to a face 30 of the disc 24. The disc 24 is held on the flange 26 by means of one or more screws 32 which pass through the disc 24 and are received in the flange 26 by passing through it.

[0032] This configuration is not limiting to the invention, and the shaft 14 could directly be a drive shaft. In this case, the disk 24 would be directly coupled to the drive shaft.

[0033] In the configuration shown here, the housing 12 is subdivided into two adjoining half-housings 12a, 12b which are joined by opposite faces (not shown). The junction of the half-housings is outside the plane of section of the single figure and has therefore not been shown. These two half-housings 12a, 12b are arranged on either side of a median plane P of the disk 24. Half-housing 12a therefore receives the bearing 20a and half-housing 12b therefore receives the bearing 20b.

[0034] The rotor disc 24 is therefore mounted to rotate along the X axis in said housing 12 to drive the shaft 14, at least in motor mode of the operation of said electric machine.

[0035] Each of the stators 22a, 22b is mounted axially in the housing 12 opposite along the X axis of the rotor disk 24. As a result, an air gap Ea, Eb is defined between each of the stators 22a, 22b and one of the faces 30a, 30b of the disk 24, as shown in [Fig.1].

[0036] In the absence of any other particular configuration, the value of the air gaps Ea, Eb is defined by the axial position of the shaft 14. This axial position is usually adjusted using shims (not shown) which are interposed between each of the half-casings 12a, 12b and the shaft 14, for example, between each of the half-casings 12a, 12b and the corresponding bearing 20a, 20b. This configuration makes it possible to maintain substantially equal air gaps Ea, Eb between the disk 24 and each of the stators 22a, 22b as long as the rotor 24 is stationary.

[0037] On the other hand, in a dynamic configuration, that is to say for example when the rotor 24 is subjected to accelerations, decelerations, or torque surges, the internal play of the bearings 20a, 20b, can, depending on the direction of rotation, cause the shaft 14 to tilt inward relative to the X-axis by a slight inclination. This tilting has the effect of modifying the values ​​of the air gaps Ea, Eb in undesirable proportions which reduce the efficiency of the electrical machine 10.

[0038] The invention proposes a solution to this problem by means of an electric machine 10 which is configured to axially immobilize said at least one disc 24 with respect to said housing 12 at a radial distance from the shaft 14.

[0039] The axial immobilization provided by the invention between the housing 12 and the disc 24 makes it possible to limit the risk of variation of each of the air gaps Ea, Eb by preventing the tilting of the shaft 14, including in dynamic conditions.

[0040] Preferably, to immobilize the disc 24 at a radial distance from the shaft 14, the machine 10 includes at least one stop interposed between the housing 12 and the rotor disc 24. This at least one stop is preferably a rotating stop, such as a sliding ring thrust bearing, ball thrust bearing, needle thrust bearing, or roller thrust bearing. It could be a single stop, in which case it would be a double-acting stop, allowing the disc to be axially immobilized in two opposite directions along the X-axis.

[0041] However, in the configuration shown here, the electric machine 10 includes two stops 32a, 32b, each interposed between one of the half-casings 12a, 12b, and the corresponding facing 30a, 30b of the disk 24. As mentioned above, these stops 32a, 32b are, in the simplest terms, single-acting stops, each of these stops 32a, 32b being designed to oppose the movement of the disk 24 in one of two directions along the X-axis. Of course, without limiting the invention, these two stops 32a, 32b could be double-acting stops.

[0042] In the single rotor disc 24 configuration shown in the figure, the two stops 32a, 32b are naturally interposed between the two half-cases 12a, 12b of the case 12 and the two opposite faces 30a, 30b of the rotor disc 24. They are therefore arranged on either side of the rotor disc 24.

[0043] It will be understood that in the case of an alternative (not shown) where the machine 10 would comprise a stator and two discs arranged on either side of this stator, the stops would be axially arranged on either side of this stator and would be interposed between the housing and two opposite faces of the two discs, or between the housing and two faces turned towards each other of the two discs.

[0044] Rotary thrust bearings, like ball thrust bearings, conventionally comprise at least one track and balls trapped in a cage and rolling on this track. They may also comprise two tracks, the balls still being trapped in a cage and rolling between the two tracks. In the context of the invention, each thrust bearing 32a, 32b comprises at least one track 34a, 34b which is received in a groove 36a, 36b of the associated half-housing 12a, 12b and / or of said at least one disc 24. In the embodiment example which has been represented here, each of these grooves 36a, 36b is formed in a face 37a, 37b of one of the half-casings 12a, 12b which is turned towards the disc 24.

[0045] It will be understood that the track 34a, 34b could alternatively be received in a groove of the disc 24, or that each stop 32a, 32b could have two tracks, one of which is received in a groove 36a, 36b of the associated half-case 12a, 12b and the other of which would be received in a groove (not shown) of the disc 24.

[0046] In the embodiment shown here, each stop 32a, 32b has only one track 34a, 34b, rollers 38a, 38b of these stops rolling directly on bearing surfaces 40a, 40b of the disc 24. Of course, according to a simple mechanical reversal, the bearing surfaces could be arranged on the half-cases 12a, 12b.

[0047] To ensure the stability of the disk 24, it is sufficient that the thrust bearings 32a, 32b be arranged at a radial distance from the shaft 14, in particular at a distance from its end bearings 20a, 20b. The greater this radial distance in the Y, Z plane, the more the disk 24 will be stabilized by the thrust bearings. Therefore, preferably the thrust bearings 32a, 32b are arranged radially beyond the air gaps Ea, Eb. Furthermore, to ensure the equilibrium of the disk 24 in terms of forces, the thrust bearings 32a, 32b are of the same diameter.

[0048] The best configuration is obtained when the stops 32a, 32b are arranged along a larger diameter than at least one rotor disc, because they are then arranged at maximum radial distance from the shaft 14.

[0049] In the context of a radial flux electric machine, the disk 24 receives permanent magnets 42 in a known manner, which are held in the disk by a peripheral ring 44. This peripheral ring 44 is necessarily arranged with a larger diameter than the disk 24. Therefore, preferably, the faces 30a, 30b against which the stops 32a, 32b bear are faces of this peripheral ring 44. In such an embodiment, the peripheral ring 44 thus includes the bearing surfaces 40a, 40b of the disk 24.

[0050] It will be understood that in the case where the tracks of the stops 32a, 32b were instead received in grooves (not shown) of the disk 30, these grooves would be formed in the peripheral rim 44 of the disk 24.

[0051] The invention makes it possible to stabilize the air gap Ea, Eb of an axial flux electrical machine 10 in a simple and efficient manner.

Claims

Demands

1. An axial flux electric machine (10) comprising: - a housing (12, 12a, 12b), - a shaft (14), - at least one rotor disk (24) mounted to rotate about an axis X in said housing (12) to drive said shaft (14), - at least one stator (22a, 22b), mounted in said housing (12) axially opposite at least one rotor disk (24), at least one air gap (Ea, Eb) being defined between said at least one stator (22a, 22b) and said at least one rotor disk (24), in which said machine (10) is configured to axially immobilize said at least one disk (24) relative to said housing (12, 12a, 12b) at a radial distance from said shaft (14).

2. Electric machine (10) according to the preceding claim, comprising at least one stop (32a, 32b), interposed between said housing (12, 12a, 12b) and at least one rotor disc (24).

3. Electric machine (10) according to the preceding claim, comprising two stops (32a, 32b) interposed between said housing (12, 12a, 12b) and two faces (30a, 30b) opposite or turned towards each other of at least one rotor disc (24).

4. Electric machine (10) according to any one of claims 2 or 3, wherein each stop (32a, 32b) comprises at least one track (34a, 34b) received in a groove (36a, 36b) of said housing (12, 12a, 12b) and / or of said at least one disc (24).

5. Electric machine (10) according to any one of claims 2 to 4, wherein the stops (32a, 32b) are arranged radially beyond the air gaps (Ea, Eb), in particular along a larger diameter of at least one rotor disk (24).

6. Electric machine (10) according to any one of claims 2 to 5, wherein each stop (32a, 32b) is arranged in contact with a face (30a, 30b) of a peripheral ring (44) of at least one rotor disc (24).

7. Electric machine (10) according to any one of claims 2 to 6, wherein said casing (12, 12a, 12b) or said at least one disc (24) has one or more rolling surfaces (40a, 40b) intended to cooperate with said stop(s) (32a, 32b).

8. Electric machine (10) according to any one of claims 2 to 7, wherein the stops (32a, 32b) are rotating stops, in particular sliding ring, ball, needle, or roller stops.

9. Electric machine (10) according to any one of claims 2 to 8, wherein said machine (10) comprises said disc (24) and two said stators (22a, 22b), arranged on either side of said disc (24), said stops (32a, 32b) being axially arranged on either side of said rotor disc (24).

10. Electric machine (10) according to the preceding claim, in which the housing (12) comprises two joined half-housings (12a, 12b) arranged on either side of a median plane (P) of said disc (24).