Double skate device for electric machine

Abstract

Double skate device (3) for an electrical machine comprising a rotor (8), the device comprising a first contact element (1) and a second contact element (2), the contact elements being housed in a case (4), having a case bottom (40), each of the contact elements being mounted movably inside the case along a bearing axis (X), with a front face intended to rub against a rotating portion of the rotor, a first compression spring (61) and a second compression spring (62), interposed between the case bottom and respectively a rear face of the first element and second contact element, the first contact element comprising an internal housing (12) in which the second contact element is housed, the first contact element is made of a first material (M1), and the second contact element is made of a second material. Abstract figure: Fig. 1

Description

Title of the invention: Double skate device for an electric machine

[0001] The present invention relates generally to electrical machines and more specifically to a double skate device 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, in particular electric traction machines having a power of several tens of kilowatts.

[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] To avoid this phenomenon, it has already been proposed to have a friction pad, called 'axial', which comes into contact by pressing axially on an end track arranged on the rotor shaft in a position substantially on the axis, ie using a shaft end contact configuration.

[0009] Although the speed of the relative movement is low at this location, the space available and the surface area available for this axial contact at the end of the shaft is however limited.

[0010] Furthermore, for a wound rotor of a vehicle traction machine, the currents to be passed through the rubbing contacts are greater than 20 amps, often close to 25 amps, which is difficult to pass through a rubbing contact with a small surface area, while at the same time ensuring a very long service life.

[0011] In this context, a need has arisen to improve the reliability and durability of an axial contact pad.

[0012] For this purpose, a double skate device for an electrical machine is proposed, comprising a rotor, the device comprising a first contact element and a second contact element, the first and second contact elements being housed in a case, having a case bottom and a mouth, each of the first and second contact elements being slidably mounted inside the case along a support axis, each of the first and second contact elements having a front face intended to rub against a rotating portion of the rotor, a first compression spring interposed between the bottom of the case and a rear face of the first contact element, a second compression spring interposed between the bottom of the case and a rear face of the second contact element, characterized in that: the first contact element comprises an internal housing in which the second contact element is housed, the first contact element is made of a first material, and the second contact element is made of a second material.

[0013] Thanks to these arrangements, two concentric contact pads are available, i.e. one nested within the other, to establish reliable and durable electrical contact between the end of the rotor and a static portion.

[0014] Advantageously, the double redundancy, i.e. redundancy of parts and redundancy of materials, makes it possible to respond to a wide variety of usage profiles, with very diverse loads and rotation speed profiles.

[0015] In this document, the term 'contact pad' is equivalent to the term 'brush'.

[0016] According to one embodiment, the first material is graphite-based and the second material is silver-based.

[0017] Silver wears out less quickly than graphite, and therefore even if the material of the first contact element is exhausted, the second contact element continues to ensure the electrical connection and the electrical machine can continue to be used, possibly with a power limitation.

[0018] Advantageously, functional redundancy is thus obtained which increases the reliability of the electrical machine.

[0019] According to one embodiment, the case has a square cross-section and, for a case section close to the mouth, the first contact element (1) and the second contact element together occupy substantially the entire internal section of the case, leaving a functional clearance of less than 0.2 mm, without any element interposed between the first contact element and the second contact element.

[0020] This maximizes the use of available space while providing the desired redundancy.

[0021] The first friction track at the end of the rotor shaft exerts a torque on the contact elements. The shape of the case, which is not of revolution, makes it possible to prevent the rotation of the contact elements relative to the static portions of the machine.

[0022] According to an alternative embodiment, the cross-section may be polygonal. It is noted that any polygonal shape can work. For example, an octagonal shape can be chosen.

[0023] According to one embodiment, a current section of the first contact element (1) has a first area SI, and a current section of the second contact element (2) has a second area S2, and it is provided that SI > 2 x S2, preferably SI is between 2.5 x S2 and 10 x S2, and even more preferably SI is between 3 x S2 and 8 x S2.

[0024] The tangential friction speeds at the locations where the second contact element presses on the first friction track are higher than the tangential friction speeds at the locations where the first contact element presses on the first friction track. It follows that the wear per unit area is greater on the second contact element, but cleverly the surface area available for the second element being greater, the general wear of the two contact elements can be of the same magnitude according to the usual mission profiles of the engine.

[0025] According to one embodiment, the double skate device further comprises a braid for connecting the second contact element to a stationary electrical terminal.

[0026] According to one embodiment, the first contact element is electrically connected to the case which itself is electrically connected to a stationary electrical terminal.

[0027] According to one embodiment, the first and second contact elements are electrically connected to each other, directly or indirectly, so that they are at the same electrical potential. This also provides electrical redundancy.

[0028] According to one embodiment, said double skate device supports, in continuous operation, a current of at least 20 Amps, preferably at least 23 Amps.

[0029] According to one embodiment, the external transverse dimension (L4) of the case is at most equal to 10 mm, preferably at most equal to 8 mm. The proposed solution is particularly compact, optimized and redundant to establish an electrical path between the end of the rotor shaft and the static / stationary portions of the machine.

[0030] The present invention also relates to an electrical machine comprising a stator and a wound rotor, the rotor comprising a first friction track (5) and a second friction track (7), the electrical machine comprising a double pad device, as described previously, rubbing on the first friction track and a plurality of second pads (6) rubbing on the second friction track.

[0031] According to one embodiment, the first and second friction tracks are coaxial and the second friction track has an axial position offset relative to the axial position of the first friction track.

[0032] According to one embodiment, the cumulative friction surface of the second pads is greater than the cumulative friction surface of the first and second contact elements of the double pad device.

[0033] 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 in axial section a double skate device according to the present invention; - [Fig.2] schematically illustrates in cross section the skate device double of [Fig.l]; - [Fig.3] schematically illustrates an axial section of an end zone of the rotor with electrical contact equipment including a double shoe device according to the present invention; - [Fig.4] schematically illustrates an end view of an end zone of the rotor and pad prints, according to line of sight IV visible in [Fig.3] - [Fig.5] schematically illustrates in cross-sectional view another example of a double skate device.

[0034] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not necessarily represented to scale.

[0035] 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. These may be so-called wound rotor electrical machines.

[0036] 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.

[0037] As already mentioned in the introductory part, and turning to [Fig. 3], an electrical machine generally comprises a rotor 8 forming a rotating part around a machine axis A, and a stator (not shown) forming a complementary non-rotating part. The rotor is arranged inside the stator.

[0038] 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.

[0039] 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.

[0040] The rotor 8 comprises, as known per se, a set of ferromagnetic plates and windings. In the configuration studied here, the rotor 8 comprises an electrical circuit comprising windings whose function is to generate a magnetic field. Two terminals are provided for connecting the windings, namely a positive terminal 36 and a negative terminal 37.

[0041] The electrical circuit is intended to be coupled via a pair of rubbing contacts to a static portion as will be seen in detail below.

[0042] We will examine more precisely the frictional contact solution proposed at the end of the rotor shaft.

[0043] Advantageously, according to the solution promoted, a double skate device is proposed, generally identified by the reference 3. Said double skate device comprises two contact elements housed in a case 4. Said case forms a parallelepiped or prismatic housing, it comprises a case bottom 40, longitudinal walls 42, here four in number, and a mouth 41. In the case bottom wall, a rear central orifice 48 is provided, the function of which will be seen later.

[0044] The case 4 is made for example of copper-plated steel. The case is intended to participate in electrical conduction, the internal wall is not coated with insulation, it forms an electrical coupling with the first contact element which will be presented later.

[0045] In the first example illustrated in figures 1 to 4, the case has a current section of square shape, the side of this section having an external dimension noted L4.

[0046] Said double skate device 3 comprises a first contact element 1 and a second contact element 2.

[0047] The first contact element 1 is hollow. It has a square section on the outside, with a side L1, and a square housing arranged in the middle, centered relative to the outer square. The section extends identically over the entire length L3 of the first contact element, along an axis X called the support axis.

[0048] The second contact element 2 is solid. It has a square section, with side L2, received with minimal play inside the housing 12 provided in the section of the first contact element

[0049] The section of the second element extends identically over the entire length L3 of the second contact element, along an axis X called the support axis. Here we note that the length L3 decreases progressively with the wear of the rubbing contacts. The reduction in length can be differentiated between the first contact element and the second contact element. In the example illustrated in [Fig.l], the first contact element has undergone slightly more wear than the second contact element which has retained a length slightly greater than that of the first contact element.

[0050] Each of the first and second contact elements (1, 2) is slidably mounted inside the case 4 along the support axis X.

[0051] Each of the first and second contact elements (1, 2) comprises a front face 15 intended to rub against a rotating portion of the rotor and a rear face 14 arranged opposite the case bottom 40.

[0052] The first contact element 1 is elastically biased towards the surface of the rotor to be contacted by a first compression spring 61 interposed between the bottom of the case and the rear face of the first contact element.

[0053] The second contact element 2 is elastically biased towards the surface of the rotor to be contacted by a second compression spring 62 interposed between the bottom of the case and the rear face of the second contact element.

[0054] The first and second compression springs are helical springs, they are manufactured by forming from steel wires in a conventional manner.

[0055] As seen in [Fig.2], the first compression spring 61 has a outer diameter slightly smaller than the side dimension Ll and an outer diameter slightly smaller than the diagonal of the housing 12.

[0056] The second compression spring 62 has an outside diameter slightly smaller than the side dimension L2 of the second contact element 2.

[0057] Compliance with these dimensional constraints makes it possible to have total independence of sliding between the first contact element with its biasing spring and the second contact element with its second biasing spring. Each of the contact elements can slide independently of the other.

[0058] The centering of the first compression spring is obtained naturally by insertion into the case housing which circumscribes it. For the centering of the second compression spring 62, a bead 43 is provided projecting from the bottom of the case 40 inwards and extending generally circularly in the bottom of the case.

[0059] The second contact element 2 is provided with a connecting braid denoted 52 which passes through the rear central orifice 48 of the case, to ensure an electrical connection of the second contact element with a terminal located in the static portion of the machine.

[0060] On the rear face of the second contact element, a handle 66 or a small ear is provided for connecting the braid 52, the handle 66 is circumscribed by the final turn of the second spring in contact with the second contact element 2.

[0061] For its part, the first contact element 1 is electrically connected to the case by means of direct physical contact, facilitated by the torque exerted on the contact element when the rotor rotates. As seen in [Fig.l], the case 4 is electrically connected to an electrical terminal of the static portions of the machine by a braid marked 51.

[0062] It is noted that the first and second contact elements (1, 2) are electrically connected to each other, directly or indirectly, they are at the same electrical potential. The two contact elements are therefore arranged in a parallel electrical configuration. They both contribute to the passage of current between the rotating part, namely here the first friction track 5, and a static portion of the machine.

[0063] The first contact element 1 is made of a first material Ml. The first material Ml is based on graphite or carbon, hence the practical name 'carbon'.

[0064] The second contact element is made of a second material M2.

[0065] Generally speaking, the second material M2 can be chosen from various materials including silver. It is noted that the material M2 of the second contact element is more expensive than the material M1 of the first contact element, graphite, which is very common, and which makes it possible to make hollow contact element shapes, as proposed, at very affordable cost prices.

[0066] The current section of the first contact element 1 has a first area denoted SI, and a current section of the second contact element (2) has a second area denoted S2.

[0067] Advantageously, it is provided that SI is at least double S2. For example, it is possible to choose preferably SI is between 2.5 x S2 and 10 x S2.

[0068] We can choose SI is between 3 x S2 and 10 x S2. We can choose SI is between 3 x S2 and 8 x S2.

[0069] According to a particular example, the section S2 is between L22 = 3x3 mm (9 mm2) and L22 = 4x4 mm on each side (16mm2) for a total size of L42 = 10 x 10 mm (100 mm2).

[0070] Turning to Figures 3 and 4, the rotor has been shown without any structural detail but of course it can be formed with a shaft and a body mounted around the shaft as known per se.

[0071] The rotor comprises two notches for housing conductors between the friction tracks and the terminals 36, 37 for connecting the windings / windings.

[0072] The rotor comprises a cylindrical end portion with a transverse face 80 and a cylindrical wall 81 of diameter D1. The diameter DI can take values ​​of the order of 10 mm to 20 mm, 12 mm to 16 mm according to typical examples.

[0073] Moving away from the end of the rotor, a shoulder 82 is provided, which delimits a second cylindrical portion of larger size (diameter D2) of which the cylindrical wall 83.

[0074] Moving away from the axial end of the rotor, we have another shoulder 84 which delimits another cylindrical portion 85 of diameter D3. There is still another shoulder 86 provided which delimits yet another cylindrical portion 87 of diameter D4.

[0075] The rotor comprises a first friction track 5, central, and a second friction track 7.

[0076] The double skate device 3 presented above is mounted to come into contact with the first central friction track.

[0077] The second friction track 7 is annular and flat. The second friction track 7 is coaxial with the first friction track but its position is offset along the axis, i.e. further back relative to the first friction track which is located at the very end of the rotor.

[0078] The first friction track 5 is electrically connected to the on-board positive terminal 36 by means of the conductive line 71. The conductive line 71 is housed in a notch 34 and surrounded by an insulating element.

[0079] The second friction track 7 is electrically connected to the on-board negative terminal 37 by means of the conductive line 72. The conductive line 72 is housed in another notch 33 and surrounded by an insulating element.

[0080] The cylindrical wall 83 is interrupted by the two diametrically opposite notches 33, 34. The remainder of the wall is cylindrical and forms the interface where the inner ring of the bearing 9 meets.

[0081] For example, the conductors 71, 72 are each overmolded in an insulating sheath.

[0082] As can be seen in particular in [Fig.4], a plurality of second pads is provided. 6 rubbing on the second friction track, here five in number. The number of second pads can be between 2 and 6, one can preferentially choose between 3 and 4 pads.

[0083] Each of the second pads 6 is connected to a braid 56 electrically connected to a stationary terminal, here the negative terminal.

[0084] In [Fig. 3], the machine casing is very partially shown at reference 10 for the portion in which the bearing 9 is received.

[0085] Furthermore, a seal 16 is provided which makes it possible to separate the inner zone of the machine which can be lubricated by a lubricating oil and an outer zone where the coal dust can be accumulated.

[0086] The double skate device 3 and the plurality of second skates 6 are mounted in an end plate referenced 11 and shown in phantom in [Fig.3].

[0087] [Fig.5] illustrates a shape variant for the case and the two contact elements. Here all take the hexagonal shape which presents a better optimization of the available surface. Compared to a disc-shaped area of ​​diameter D1, the space occupied by the hexagonal shapes of the two contact elements is greater than that shown in [Fig.2].

Claims

Claims

1. Double skate device (3) for an electrical machine comprising a rotor (8), the device comprising a first contact element (1) and a second contact element (2), the first and second contact elements (1, 2) being housed in a case (4), having a case bottom (40) and a mouth (41), each of the first and second contact elements (1, 2) being slidably mounted inside the case along a support axis (X), each of the first and second contact elements (1, 2) having a front face intended to rub against a rotating portion of the rotor (8), a first compression spring (61) interposed between the case bottom (40) and a rear face of the first contact element (1), a second compression spring (62) interposed between the case bottom (40) and a rear face of the second contact element (2),characterized in that: the first contact element (1) comprises an internal housing (12) in which the second contact element (2) is housed, the first contact element (1) is made of a first material (M1), and the second contact element (2) is made of a second material (M2).,

2. A dual skate device according to claim 1, wherein the first material M1 is graphite-based and the second material M2 is silver-based.

3. Double skate device (3) according to any one of claims 1 to 2, wherein the case (4) has a square cross-section and, for a case section close to the mouth (41), the first contact element (1) and the second contact element (2) together occupy substantially the entire internal section of the case (4), leaving a functional clearance of less than 0.2 mm, without any element interposed between the first contact element (1) and the second contact element (2).

4. A double skate device according to any one of claims 1 to 3, wherein a running section of the first contact element (1) has a first area SI, and a running section of the second contact element (2) has a second area S2, and it is provided that SI > 2 x S2, preferably SI is between 2.5 x S2 and 10 x S2, and even more preferably SI is between 3 x S2 and 8 x S2.

5. Double skate device (3) according to any one of the claims 1 to 4, further comprising a braid (52) for connecting the second contact element (2) to an electrical terminal.

6. Double skate device (3) according to any one of claims 1 to 5, wherein the first and second contact elements (1,2) are electrically connected to each other, directly or indirectly, so that they are at the same electrical potential.

7. Double skate device (3) according to any one of claims 1 to 6, characterized in that said double skate device (3) supports, in continuous operation, a current of at least 20 Amps, preferably at least 23 Amps.

8. Double skate device (3) according to claim 7, wherein the external transverse dimension (L4) of the case is at most equal to 10 mm, preferably at most equal to 8 mm.

9. An electrical machine comprising a stator and a wound rotor, the rotor comprising a first friction track (5) and a second friction track (7), the electrical machine comprising a double pad device (3) according to any one of claims 1 to 8, rubbing on the first friction track and a plurality of second pads (6) rubbing on the second friction track (7).

10. An electrical machine according to claim 9, wherein the cumulative friction surface area of ​​the second pads (6) is greater than the cumulative friction surface area of ​​the first and second contact elements (1, 2) of the double pad device (3).

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