Rotor equipment of an electric machine comprising an auxiliary wheel with friction track for an electric contact pad

Abstract

Rotor equipment for an electrical machine, comprising a rotor (ROT) which comprises a first electrical circuit (2) intended to be coupled via at least one friction contact to a static portion, the rotor comprising at least a first circular track (3) forming part of the first electrical circuit, in which an auxiliary wheel (1) is provided comprising a first roller (11) in permanent engagement with the first circular track and having a first diameter D1, and a contact pad (5) forming an electrical coupling between a conductor belonging to the static portion and a friction track (4) belonging to the auxiliary wheel. Abstract figure: Fig. 3

Description

Title of the invention: Rotor equipment of an electric machine comprising an auxiliary wheel with friction track for an electric contact pad

[0001] The present invention relates generally to electrical machines and more precisely to rotor equipment for an electrical machine, in a configuration where the rotor comprises at least one electrical circuit electrically connected to a non-rotating portion of the machine.

[0002] We are particularly interested here in electrical machines used in motor vehicles.

[0003] An electrical machine generally comprises a rotor forming a rotating part around a machine axis, and a stator forming a complementary non-rotating part, all housed in a casing also called a frame.

[0004] In some machines, the rotor is equipped with permanent magnets and does not need to be electrically connected to the static part of the machine.

[0005] The subject of the present disclosure is concerned, on the contrary, with the case where the rotor comprises at least one electrical circuit intended to be electrically coupled to a static portion by means of a rubbing contact. It is noted that the electrical coupling in question is not of the contactless (electromagnetic) type that can sometimes be found in the art. On the contrary, a material electrical continuity is established here between the electrical circuit arranged in the rotor and an electrical circuit in the static portion.

[0006] To establish such an electrical contact between the rotating part and the non-rotating part, an electrical track is used in the long-known art on the rotor in the form of a cylindrical ring of revolution with an outer surface intended to be contacted by a rubbing pad. The terms "slip ring" and "brush" are also used in the art respectively for the ring and the rubbing pad. The pad does not rotate with the rotor, but it can have a small relative movement because it is biased by a spring in the direction of the ring to be contacted.

[0007] At the point of contact between the ring and the friction pad, there is a relative movement whose speed is proportional on the one hand to the rotation speed of the rotor and on the other hand to the distance of radius R which separates the outer surface of the ring and the axis of rotation. For the relative movement, the magnitude of the tangential speed is used, which can be written 2 ir RQ or ir DQ, where D is the diameter and Q is expressed in revolutions per second.

[0008] The contact body of the friction pad is made of carbon or graphite which is a material with a reasonable cost. Other materials are possible but they are much more expensive, such as silver, nickel or platinum.

[0009] Furthermore, the higher the speed of the relative movement, the greater the wear of the friction pad. It is therefore generally sought to have a ring diameter (D=2R) as small as possible, in order to guarantee a long service life of the friction pad, in practice beyond a prescribed durability threshold.

[0010] But some electrical machine configurations induce geometric constraints on the shaft and associated parts, which leads to large, even very large, ring diameters. For example, in some cases the rotor shaft is hollow to allow another mechanical part such as another rotating shaft to pass through. In some other cases, it may be necessary to arrange fluid lines that run inside the shaft, which increases the shaft diameter. As a result, the friction rings may have diameters of several centimeters, and are larger than the friction rings known in the standard art.

[0011] In said configurations, the tangential speed 2 ir RQ is important for the usual high rotation speeds Q of the machines, say at least up to 100 revolutions per second, or even beyond.

[0012] In these configurations, the use of a carbon or graphite friction pad gives a service life which proves to be too short due to rapid wear.

[0013] There therefore remains a need to propose a solution for using inexpensive carbon or graphite friction pads, in cooperation with large diameter friction rings on the rotor of the electric machine.

[0014] For this purpose, rotor equipment for an electrical machine is proposed, comprising a rotor which includes a first electrical circuit intended to be coupled via at least one friction contact to a static portion, the rotor comprising at least a first circular track forming part of the first electrical circuit, characterized in that an auxiliary wheel is provided comprising a first roller in permanent engagement with the first circular track and having a first diameter D1, and a contact pad forming an electrical coupling between a conductor belonging to the static portion and a friction track belonging to the auxiliary wheel.

[0015] Cleverly, the auxiliary wheel is interposed, functionally and physically, between the first circular track and the contact pad. The contact pad presses on a friction track distinct from the first track; at the location of the frictional contact, there is a lower tangential speed than the tangential speed prevailing on the first circular track. The phenomenon of wear of the friction pad is consequently reduced.

[0016] Advantageously, the tangential speed at the interface between the contact pad and the friction track can be at least 2 times lower than the tangential speed which prevails at the location of the first circular track.

[0017] It will be seen that the friction track can take for example a flat shape or a cylindrical shape. In this document, the term 'contact pad' is equivalent to the term 'brush'.

[0018] It is noted that the trick proposed above makes it possible to establish an electrical path between the rotor and the non-rotating part. But it should be noted that, by adapting elements and / or duplicating certain elements, two electrical paths can be established between the rotor and the non-rotating part, for example to generate excitation of windings in the rotor. Continuing, it is not excluded to be able to establish more than 2 electrical paths between the rotor and the non-rotating part, each of the paths passing through a large diameter ring.

[0019] It should also be noted that, advantageously, the fact of offsetting the rubbing contact at a greater distance from the machine axis, due to the interposition of the auxiliary wheel, makes it possible to facilitate on the one hand the evacuation of the calories generated by the friction of the pad and on the other hand the management of the coal dust. The location of the rubbing contact being further from the axis, it is easier to install a thermal conduction device and / or a device for recovering or evacuating the coal dust, without direct interference with the axis or the axis bearing.

[0020] The term "static portion" refers to an entity that does not rotate with the rotor, whether the stator itself or another static part.

[0021] The first circular track is typically formed by a conductive ring, for example a metal ring crimped and insulated from the rotor shaft.

[0022] According to one embodiment, the friction track is formed as a cylindrical friction track belonging to the auxiliary wheel.

[0023] The cylindrical friction track rotates at the same speed as the auxiliary wheel. The cylindrical friction track has a smaller diameter than the diameter of the first roller, which creates a coefficient of proportionality reducing the tangential speed at the contact pad.

[0024] According to one embodiment, the friction track is formed as a discoid friction track belonging to the auxiliary wheel and arranged at the end of the axle of the auxiliary wheel.

[0025] According to one embodiment, the discoid friction track is flat and its surface is perpendicular to the axis of rotation of the rotor.

[0026] According to one embodiment, the contact pad is centered on the axis B of the auxiliary wheel.

[0027] Under these conditions, the relative movement at the level of the rubbing contact pad is a rotation around the axis, the speed of the relative movement being less than ir E5 Ql, where E5 is the transverse dimension of the rubbing body of the pad.

[0028] Thanks to the trick of the frictional contact pressing in the axial direction at the end of the axle of the auxiliary wheel, the relative friction speed of the friction pad is considerably reduced.

[0029] According to one embodiment, a second roller is provided integral with the first roller, the second roller having a second diameter D2, smaller than the first diameter D1, and the friction track is formed like the outer surface of the second roller.

[0030] As a result, the auxiliary wheel is an easy part to manufacture. The outer surface of the rollers is electrically conductive, although the body of the wheel can be made of a non-conductive material provided that conductive metal rings are crimped around the circumference.

[0031] According to one embodiment, the second roller is adjacent to the second roller, and the two rollers are formed as a single piece.

[0032] According to one embodiment, the ratio (D2 / D1) of the second diameter divided by the first diameter is less than 0.4 and preferably less than 0.3.

[0033] This results in a very significant gain in the tangential speed seen by the contact pad. Expressed differently, we can propose a solution with a rotor ring 4 times larger than the standard, while continuing to use the same rubbing contact pad.

[0034] According to one embodiment, the first circular track has a base diameter D0, and D1 / D0 is between 0.8 and 1.2.

[0035] Since the diameters are similar, the risk of slipping at the contact between the first circular track and the first roller is thus minimized.

[0036] Considering that there is no sliding at the contact between the first circular track and the first roller, we can write the relation ir D0 Q = ir Dl Ql, therefore Ql / Q = D0 / DL

[0037] Q is the rotational speed of the rotor and Ql is the rotational speed of the auxiliary wheel.

[0038] According to one embodiment, the first roller is hollowed out and the cylindrical friction track is arranged radially inside the first roller, at the same axial position.

[0039] Expressed differently, the cylindrical friction track and the outer surface of the first roller are concentric.

[0040] This optimizes the axial compactness, the size of the contact pad and the pressure arm is small, it can be of the order of 130% of the axial thickness of the first roller.

[0041] According to one embodiment, the auxiliary wheel is rotatably mounted on a pressurizing support arm. For example, the pressurizing support arm may be mounted in rotation on a C axis. By means of this, the first roller exerts contact pressure against the first circular track in order to avoid any risk of slippage at the interface between the first roller and the first circular track. Certain small out-of-round effects can also be compensated thanks to this pivoting support arm.

[0042] It is noted that the pivoting support arm performs two functions: on the one hand it allows the auxiliary wheel to be urged in the direction of the first circular track and on the other hand it forms a support to hold the friction contact pad in the desired position.

[0043] According to one embodiment, an elastic element, for example a spring 8, is provided to push the support arm, so that the auxiliary wheel and in particular the first roller is in pressed contact on the first circular track.

[0044] According to one embodiment, the contact pad is urged towards the friction track by an elastic element. As a result, the contact force is sufficient and the contact resistance is low. Furthermore, the progressive wear of the pad can be compensated.

[0045] The present invention also relates to an electrical machine comprising a stator and rotor equipment as described previously, the electrical machine being intended to move a motor vehicle.

[0046] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates an end portion of the automatic equipment proposed according to a first exemplary embodiment of the present invention, the part of IA showing an axial section and the right part IB showing a section transverse to the axis; - [Fig.2] schematically illustrates an end portion of the equipment at automation proposed according to a second exemplary embodiment of the present invention, the part of 2A showing an axial section and the right part 2B showing a section transverse to the axis; - [Fig.3] schematically illustrates an end portion of the equipment at automation proposed according to a third exemplary embodiment of the present invention, in an axial section; - [Fig.4] illustrates an example of the embodiment of the friction contact pad in its accommodation ; - [Fig.5] illustrates in more detail the auxiliary wheel proposed in the second embodiment.

[0047] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not nec- necessarily represented to scale.

[0048] The present document concerns electrical machines used in motor vehicles. These may be machines of fairly substantial power belonging to an electromotive group capable of moving the vehicle. They may be smaller electrical machines meeting specific requirements.

[0049] It should be noted, however, that the principle and technical solution put forward in this document can be applied to electrical machines outside of use in a motor vehicle.

[0050] As already mentioned in the introductory part, an electric machine generally comprises a rotor ROT forming a rotating part around a machine axis A, and a stator forming a complementary non-rotating part. The rotor is arranged inside the stator.

[0051] At a first axial end of the machine is the mechanical interface of the electrical machine with the external environment, in the form of a splined shaft or an output pinion. At the other axial end are the electrical connections, for example for powering the stator windings, but also specifically of particular interest here are the electrical connections which make it possible to power one or more electrical functions embedded in the rotor.

[0052] Figures 1 to 3 show the casing 10 or 'carcass' in part. The stator, not shown in the figures, is mounted in the casing 10.

[0053] The rotor is rotatably mounted relative to the casing by means of bearings as known per se. More specifically, the rotor comprises a rotor shaft 32 supported by the inner rings of the bearings.

[0054] In practice, a bearing, not shown, is provided on the side of the first axial end and a bearing illustrated in the figures by the reference 9 on the side of the second axial end.

[0055] In the examples illustrated in the figures, the bearing is located completely outside relative to the electrical contact equipment. However, the bearing 9 could just as easily be located further inside, namely interposed between the main body of the rotor and the electrical contact equipment.

[0056] The ROT rotor comprises, as known per se, a set of ferromagnetic plates. In the configuration studied here, the ROT rotor comprises a first electrical circuit 2 intended to be coupled via at least one rubbing contact to a static portion as will be seen in detail below.

[0057] In the case of a single electrical path physically connected between the rotor and the stator, the use may be coupling to a temperature sensor element embedded in the rotor.

[0058] Another function that may be present in the rotor relates to electrical excitation electromagnetism of all or part of the rotor. In this perspective, it may be necessary to establish two physically connected electrical paths between the rotor and the stator. Depending on other functional needs, it may be necessary to establish three or four physically connected electrical paths between the rotor and the stator.

[0059] The rotor comprises at least a first circular track 3 forming part of the first electrical circuit 2. The first circular track 3 is cylindrical of revolution and has a diameter, called the base diameter, noted DO. To give an idea, DO can range from 20 mm to 50 mm.

[0060] Cleverly according to the proposed solution, an auxiliary wheel 1 is provided pivotally mounted relative to a second axis B. The second axis B is parallel to the first axis A. The second axis B is spaced relative to the first axis A by a distance (D0+Dl) / 2.

[0061] The auxiliary wheel 1 comprises a first roller 11 in permanent engagement with the first circular track 3. The first roller 11 is cylindrical in revolution, it has a first diameter D1.

[0062] With specific reference to the first embodiment illustrated in [Fig.l], a second roller 12 is provided, secured to the first roller. The second roller 12 is cylindrical in revolution and has a second diameter D2, smaller than the first diameter D1 of the first roller 11.

[0063] A contact pad 5 is provided, which rubs against the outer surface of the second roller 12. The contact pad 5 forms an electrical coupling between a conductor 52 belonging to the static portion and the outer surface of the second roller 12. The conductor 52 is in the example illustrated a braid.

[0064] The ratio D2 / D1 of the second diameter D2 divided by the first diameter is D1 less than 0.4 and preferably less than 0.3.

[0065] The first circular track 3 is electrically coupled to a conductor 22 or to a track internal to the rotor. It should be noted that the electrical path of interest is isolated from the rotor body and from the shaft 32 of the rotor. The axial length / dimension of the first circular track is denoted E3. The axial length / dimension of the auxiliary wheel 1 is denoted El. The values ​​El and E3 are close or even identical, El and E3 can take values ​​between, for example, 8 mm and 16 mm.

[0066] According to an optional feature, a support arm 7 is provided which has the function of supporting and holding the auxiliary wheel 1 and supporting and guiding the contact pad 5.

[0067] The support arm 7 is mounted to rotate around an axis C which is parallel to the axes A and B but is located at a distance from the axis B.

[0068] A needle bearing 19 is interposed between the auxiliary wheel and the auxiliary shaft 15 around which the auxiliary wheel rotates. It is noted that, according to the first mode of realization, the auxiliary shaft 15 does not rotate with the auxiliary wheel, it is part of the static elements.

[0069] The auxiliary wheel 1 is rotatably mounted on the auxiliary shaft 15. The auxiliary shaft 15 only supports low forces and can thus have a diameter D4 much smaller than the diameter D3 of the shaft 32 of the rotor.

[0070] The support arm 7 comprises bearings in which the auxiliary shaft 15 is received.

[0071] A housing 55 is provided in the support arm 7 for receiving the contact pad 5 and its biasing spring 6.

[0072] Generically, the contact pad 5 is urged towards the friction track 4 by any elastic element.

[0073] In the illustrated example, a return means is provided, in the form of a spring 8, to push the pivoting support arm 7, so that the auxiliary wheel 1 is pressed against the first circular track 3, and consequently slippage between the auxiliary wheel (its first roller 11) and the first circular track is avoided.

[0074] The friction track is formed as the outer surface of the second roller 12. The auxiliary wheel is an easy-to-manufacture part, either in conductive monomaterial, or with a body on which conductive rings are fixed.

[0075] The outer surface of the rollers is electrically conductive, although the body of the wheel can be made of a non-conductive material provided that conductive metal rings are crimped around the perimeter.

[0076] The tangential speed at the non-sliding interface between the first circular track 3 and the first roller 11 is denoted VI. The speed tangential to the interface between the second roller and the friction contact pad is denoted V2.

[0077] We have VI = ir D0 Q = ir DI QL

[0078] V2 = irD2Ql

[0079] We note that the direction of rotation of the auxiliary wheel and of the first roller is the opposite of the direction of rotation of the rotor and of the first circular track 3 but we reason in absolute speed value here.

[0080] Q2 / Ql = DI / D2. This ratio represents the gain in speed reduction at the location of the pad friction.

[0081] Concerning the elements embedded in the rotor, a track or a conductive wire 22 is provided to implement the rotating electrical function.

[0082] In the second embodiment illustrated in [Fig.2], the auxiliary wheel 1 is such that the first roller is hollowed out and the cylindrical friction track is arranged radially inside the first roller, at the same axial position.

[0083] More specifically, [Fig.5] is a more detailed view centered on the hollowed-out auxiliary wheel.

[0084] The axial length of the wheel is denoted El. The auxiliary wheel comprises a hub 14 and a rim 13. The outer surface of the rim 13 is cylindrical and rolls on the first circular track of the rotor shaft. The hub 14 is pivotally mounted on the auxiliary shaft 15.

[0085] A needle bearing 19 is provided interposed between the auxiliary shaft 15 and the hub 14, thus supporting the auxiliary wheel in rotation around the axis B.

[0086] The axial length of the support arm 7 is denoted E4. E4 can be between 120% of El and 130% of El.

[0087] In the example of the pivotally mounted arm, the support arm 7 comprises, at one of its ends, a bearing 76 for rotational mounting relative to the axis C. At the other of its ends, two lugs 71, 72 are provided which frame the auxiliary wheel and form the bearings for the auxiliary shaft, rotating or not rotating, of the auxiliary wheel.

[0088] Concerning the mounting and guiding of the friction contact pad, the support arm comprises walls 73, 74, which guide the contact pad 5 in translation perpendicular to the axis B.

[0089] Furthermore, [Fig.2] partially illustrates elements provided for establishing a second electrical path between the rotor and the stator. In the case of a wound rotor, it is usually necessary to establish a positive path and a reference path between the stator and the rotor.

[0090] For the second electrical track, a second circular track 103, a second wire 24 embedded in the rotor, a second auxiliary wheel 111 are provided.

[0091] Turning to the right part 2B of [Fig.2], it is noted that the second auxiliary wheel 111 can be angularly offset relative to the first here by approximately 90°, which makes it possible to place the components of a second support arm on a distinct angular range and therefore to optimize the axial compactness of the electrical equipment to establish the two necessary paths.

[0092] A needle bearing 19 is provided interposed between the shaft 15 supporting the auxiliary wheel and the auxiliary wheel itself.

[0093] In the third embodiment illustrated in [Fig.3], the friction track 4 is formed as a discoid friction track belonging to the auxiliary wheel 1 and arranged at the end of the axle of the auxiliary wheel.

[0094] The friction zone 4 is here a disc centered on the axis B.

[0095] It is noted that the auxiliary wheel integrates its shaft 15' which rotates with said auxiliary wheel.

[0096] In the example illustrated, two needle bearings 19 are provided, arranged axially on either side of the first roller 11. In this configuration, there is no second roller; it is the transverse discoidal track at the end of the integrated shaft 15' which forms the friction zone.

[0097] Thus, generically, on all embodiments, the skate of contact 5 forms an electrical coupling between a conductor belonging to the static portion and a friction track 4 belonging to the auxiliary wheel, whatever the shape of the friction track as seen in the examples illustrated above.

[0098] It is noted in the light of [Fig.3], that the support arm can be mounted in a translational movement to push the auxiliary wheel towards the first circular track. The outer bearings of the bearings can be guided in an oblong slot slide system.

[0099] For example, a base supporting the auxiliary wheel axle bearings can be mounted in a slide with a return by means of two compression springs 8' which push the base and the auxiliary wheel bearings towards the first circular track 3.

[0100] In the example of [Fig.3], a seal 16, for example a lip seal, is provided, which comes into contact with the auxiliary shaft portion 15'. This seal makes it possible to form a separation between a compartment on the right where the friction contact and its waste in the form of carbon dust are located, and a main compartment on the left which houses the rotor and the oil cooling system. It is easier to form such a separation at the location of the auxiliary wheel than directly on the rotor shaft.

[0101] It is noted that in the third embodiment, with axial thrust of the pad, the pad and its holding case can be mounted securely relative to the casing of the machine, independently of the sliding base of the pivoting arm guiding the auxiliary wheel as mentioned above.

[0102] With reference to [Fig.4], generally speaking, the friction pad may have a square section and be received in a square case. 4 side walls 60 are provided forming a square housing, a bottom wall 62 in which a central orifice 64 is provided through which the braid 52 passes.

[0103] A circlip 47 is provided which holds the wheel axially in its position relative to the axis 15.

[0104] It should be noted that the invention is not limited to the examples which have just been described and various adjustments can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different variant embodiments of the invention envisaged in this application can be combined to achieve the invention, to the extent that these variants are not incompatible with each other.

Claims

Claims

1. Rotor equipment for an electrical machine, comprising a rotor (ROT) which comprises a first electrical circuit (2) intended to be coupled via at least one friction contact to a static portion, the rotor comprising at least a first circular track (3) forming part of the first electrical circuit, characterized in that an auxiliary wheel (1) is provided comprising a first roller (11) in permanent engagement with the first circular track and having a first diameter D1, and a contact pad (5) forming an electrical coupling between a conductor belonging to the static portion and a friction track (4) belonging to the auxiliary wheel (1).

2. Rotor equipment according to claim 1, wherein the friction track (4) is formed as a cylindrical friction track belonging to the auxiliary wheel (1).

3. Rotor equipment according to claim 1, wherein the friction track (4) is formed as a discoid friction track belonging to the auxiliary wheel (1) and arranged at the end of the axis of the auxiliary wheel.

4. Rotor equipment according to claim 2, characterized in that a second roller (12) is provided integral with the first roller, the second roller (12) having a second diameter D2 smaller than the first diameter D1, and in that the friction track is formed as the outer surface (12a) of the second roller.

5. Rotor equipment according to claim 4, in which the ratio (D2 / D1) of the second diameter divided by the first diameter is less than 0.4 and preferably less than 0.

3.

6. Rotor equipment according to any one of claims 1 to 5, in which the first circular track has a base diameter DO, and D1 / D0 is between 0.8 and 1.

2.

7. Rotor equipment according to claim 2 or 4, wherein the first roller is hollowed out and the cylindrical friction track is arranged radially inside the first roller, at the same axial position.

8. Rotor equipment according to any one of claims 1 to 7, wherein the auxiliary wheel is rotatably mounted on a pressurizing arm (7).

9. Rotor equipment according to any one of claims 1 to 8, in which the contact pad (5) is biased towards the friction track (4) by an elastic element (6).

10. An electrical machine comprising a stator and rotor equipment according to any one of claims 1 to 9, the electrical machine being intended to move a motor vehicle.

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