- electric machine with differential and function for grounding the rotor and measuring angular position

Abstract

Disclosed is an electromotive unit (UU) comprising an electric machine having a rotor (9) and a rotor shaft (1) with a tubular body, the electromotive unit comprising: a differential mechanism (DF) housed inside the rotor shaft, with a planet carrier element rotated by the rotor shaft; a differential cover (7) inserted from the outside onto the first axial end of the rotor shaft, the differential cover having an axial opening (72) leaving a passage for a first drive shaft; a rotation sensor (92) mounted on the casing element; a rotating sensor target (8) arranged on the differential cover, with target patterns positioned facing the rotation sensor (92); an electrical friction track (70) on the differential cover or on the sensor target (8), which is designed to receive a friction of hairs or brushes linked to a stationary element that is electrically coupled to the electrical ground of the electromotive unit.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: Electric machine with differential and rotor electrical grounding function and angular position measurement

[0003]

[0001] The present invention relates to an electrical machine integrating a differential and a function for electrically grounding the rotor and for measuring angular position.

[0004]

[0002] The rotor of an electrical machine can accumulate electrical charges as it rotates. This is true for both permanent magnet rotors and wound rotors.

[0005]

[0003] The electrical charges induced by the rotation of the rotor can be discharged via the bearings but the small electrical arcs caused by the discharge of these electrical charges through the bearings damage the balls and / or the raceways of these bearings (the so-called 'pitting' phenomenon).

[0006]

[0004] It is therefore preferable to be able to dissipate the electrical charges induced by the rotation of the rotor by a path other than that of the rotor bearings.

[0007]

[0005] Among the known solutions, there is a brush ring fixed in rotation to the rotor with brushes that rub against a stationary part, or conversely a stationary brush ring whose brush ends rub against a rotating part such as the rotor shaft.

[0008]

[0006] Such a known solution occupies a non-negligible amount of space in the environment of the rotor shaft.

[0009]

[0007] Furthermore, in order to avoid using permanent magnets that consume natural rare earth resources, there is a trend towards using wound rotors, which must be excited from the stationary zone through excitation friction rings.

[0010]

[0008] Finally, in the present context, it is relevant to arrange a differential device in the immediate vicinity of the electric machine or even partially housed in the axial area of ​​the rotor, which increases the possibilities of integrating an electromotive unit or an electromotive group.

[0011]

[0009] There therefore remains a need to propose a more relevant solution from an economic and ecological point of view, combining this with good compactness.

[0012]

[0010] To this end, an electromotive unit is proposed here comprising an electric machine including a rotor, at least one housing element and a rotor shaft having a tubular body, extending from a first axial end to a second axial end along a main axis, the electromotive unit comprising:

[0013] - a differential mechanism housed inside the rotor shaft, with a planet carrier element driven in rotation by the rotor shaft,

[0014] - a differential cover inserted externally onto the first axial end of the rotor shaft, the differential cover comprising an axial opening configured to allow passage of a first drive shaft,

[0015] - a rotation sensor mounted on the housing element,

[0016] - a rotating sensor target (usually annular) arranged on the differential cover or on the sensor target, with target patterns positioned opposite a sensitive part of the rotation sensor,

[0017] - an electrical friction track arranged / linked to the hood or target and suitable for receiving friction from the eyelets or brushes linked to a stationary element in electrical coupling with the electrical mass of the electromotive unit.

[0018]

[0011] Thanks to these arrangements, excellent compactness is obtained in the arrangement of the position sensor function and the grounding function.

[0019]

[0012] The electrical excitation system of the wound rotor occupies one end and the other end is occupied by the position / speed sensor as well as the rotor grounding device, with free axial passage at both ends of the tubular rotor shaft to allow passage of the transmission shafts to the wheels,

[0020]

[0013] Grounding helps to avoid the "pitting" phenomenon of bearings caused by electrical / electrostatic discharges.

[0021]

[0014] The position speed information allows for fine control by the control system of the electric machine.

[0022]

[0015] Regarding the terminology related to the differential device, it should be noted that "planetary gears" can be simply called "planetary" and "satellite gears" can be simply called "satellites".

[0023]

[0016] According to an advantageous embodiment, in the case of a wound rotor, at least two annular excitation tracks are provided on the side of the second axial end of the rotor shaft, configured to allow excitation of the rotor winding, the second axial end of the rotor shaft being open on the axis at the second end.

[0024]

[0017] Accordingly, the rotor shaft carries the following combination of functions: the excitation tracks for the wound rotor, the rotating target for the position and speed sensor, the friction track for grounding the rotor, and at least partially the housing for the differential device. Thanks to the friction track discussed above, it is not necessary to provide a third track in addition to the two excitation tracks for the wound rotor.

[0025]

[0018] According to one embodiment, the two excitation tracks are of smaller diameter than the electric friction track.

[0026]

[0019] Advantageously, given the high rotational speeds of the rotor, the linear speed at the point of friction of the electrical excitation brushes remains within the expected range. The friction track for grounding has a larger diameter and results in higher friction speeds with the grounding brushes, but this is not problematic since the electrical charge is a rather slow phenomenon and only an occasional discharge is required for the grounding function to be properly performed; brush wear remains low.

[0027]

[0020] According to one embodiment, the sensor target comprises a tubular portion for tight mounting and a discoidal portion bearing the patterns. In this case, the reading is taken in the axial direction. In other words, the target patterns are in a flat ring perpendicular to the main axis.

[0028]

[0021] Alternatively, the patterns could also be installed on a tubular section of the same diameter or, preferably, a larger diameter. In this case, the reading would be taken in the radial direction.

[0022] According to one embodiment, the sensor target has magnetic patterns or mechanical teeth. In practice, these can be either physical teeth or magnetic teeth.

[0029]

[0023] According to one embodiment, the sensor target is shrink-fitted onto the differential cover. Such an assembly is simple and robust.

[0030]

[0024] According to one embodiment, the speed sensor function and the grounding function together occupy an axial thickness, and said axial thickness is less than 25 mm.

[0031]

[0025] We thus have a remarkable compactness in the direction of the axis to perform the two functions: velocity capture and grounding.

[0032]

[0026] According to one embodiment, the stationary element is formed like an eyelash or brush ring, and is mounted from the outside once the housing element is assembled.

[0033]

[0027] The assembly method is simple. The stationary element may include a support ring with an L-shaped profile.

[0034]

[0028] According to one embodiment, the eye or brush ring is positioned on the inner side relative to the rotation sensor, and on the outer side relative to the rotor rotation mounting bearing B1. The assembly process is simple, and the configuration is particularly compact.

[0035]

[0029] According to one embodiment, the outer diameter of the rotor shaft, denoted D1, is less than 62 mm. It is advantageous to house the differential substantially within such a diameter in the configuration where the differential is driven directly by the rotor at its rotational speed.

[0036]

[0030] According to one embodiment, the outer diameter of the sensor target, denoted D8, can be between 75 mm and 90 mm. Despite this remarkable compactness, very satisfactory accuracy can be obtained in position and velocity detection.

[0037]

[0031] According to one embodiment, a bearing is provided outside the rotor shaft, arranged to surround the second planetary gear, in the same axial position, for guiding the transmission device in rotation.

[0038]

[0032] The present invention also relates to a motor vehicle, comprising at least one electromotive unit as described above.

[0039]

[0033] The vehicle in question may be an electric or hybrid vehicle.

[0040]

[0034] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which:

[0041] - [Fig.1] illustrates a front view of an example of a motorized axle of a motor vehicle, with an electromotive unit in which the present invention is implemented;

[0042] - [Fig.2] schematically represents in cross-section an example of an electromotive unit according to the present invention;

[0043] - [Fig.3] illustrates a cross-sectional view of an electric machine rotor shaft receiving the elements of the differential mechanism end-to-end;

[0044] - [Fig.4] illustrates in cross-section the two ends of a machine rotor shaft with electrical, with on the right the electrical excitation system of the wound rotor and on the left the differential device with the position / speed sensor as well as the rotor grounding device;

[0045] - [Fig.5] schematically represents in cross-section and in more detail the area of ​​the first end, on the left in the illustrated representation; - [Fig.6] represents an exploded view, allowing to illustrate the elements involved in the proposed differential device and which also illustrates the assembly process of the device and the sensor target;

[0046] - [Fig.7] schematically represents in cross-section a variant of the area of ​​the first end;

[0047] - [Fig.8] illustrates an example of a brush ring for grounding.

[0048]

[0035] In the various figures, the same reference numerals designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale.

[0049]

[0036] Figure 1 shows an axle of a motor vehicle, in this case a motorized axle in which an electromotor unit GEM drives right and left wheels referenced 47 according to a first embodiment.

[0050]

[0037] In the illustrated example, this refers to an electric motor in a hybrid or pure electric vehicle.

[0051]

[0038] As will be seen in detail later, the rotor shaft drives a differential device DF, each of whose outputs in turn drives a speed reducer (R1, R2). Each of the reducers R1, R2 includes an output pinion which drives the respective wheel 47 by means of a homokinetic transmission T1, T2 as known per se.

[0052]

[0039] The reference numeral MEL designates the electric machine with a stator and a rotor, denoted 9. The electric machine operates as a motor or a generator depending on the operating conditions. The reference numeral UU designates an electromotive unit comprising the machine and the differential device DF.

[0053]

[0040] Reference GEM designates the electromotor group which includes the electric machine MEL, the differential device DF, the left reducer R1 and the right reducer R2.

[0054]

[0041] Figure 2 shows the electromotive unit in cross-section, which includes the electric machine MEL and the differential device DF. The electric machine includes a housing CM, composed here of three parts: a main housing C0 in the shape of a sleeve, a first end housing C1 and a second end housing C2.

[0055]

[0042] The electric machine comprises a stator ST and a rotor 9. The illustrated electric machine is radial flux, but the invention can also be applied to an axial flux electric machine.

[0056]

[0043] The rotor comprises a rotor shaft 1, of tubular shape.

[0057]

[0044] The rotor shaft 1 is connected to the housing by a rotating assembly around Y1 by means of two bearings B1 and B2.

[0058]

[0045] Bearing B1 is mounted in an internal bearing surface of the first end housing C1. Bearing B2 is mounted in an internal bearing surface of the second end housing C2.

[0059]

[0046] Figure 2 illustrates, according to one embodiment, the position of the differential device DF in the electromotive unit UU relative to the electric machine. The differential device drives intermediate drive shafts, more precisely the short intermediate shaft A1 on the left and the long intermediate shaft A2 on the right.

[0060]

[0047] On the left in Figure 2, the output pinion 31 forms one of the outputs of the electromotive unit UU. The output pinion 31 is driven by the short intermediate shaft A1. On the right in the figure, the output pinion 32 forms the other output of the electromotive unit UU. The output pinion 32 is driven by the long intermediate shaft A2.

[0048] When the vehicle travels along a curved track, one of the drive shafts rotates faster than the other, as is known, which causes each planetary pinion to rotate on its own axis, a phenomenon known as differential slippage.

[0061]

[0049] The short drive shaft A1, once assembled, drives the first reducer R1 via the output pinion 31. The long drive shaft A2, once assembled, drives the second reducer R2 via the output pinion 32. The output pinion 31 is guided in rotation by a bearing B3. The output pinion 32 is guided in rotation by a bearing B4.

[0062]

[0050] The rotor shaft noted 1 is hollow and is configured to house the long drive shaft A2. The rotor shaft 1 is integral with the rotor 9 of the machine.

[0063]

[0051] The rotational locking of the rotor and the drive shaft can be achieved by a shrink-fitting process. In the illustrated example, grooves 14 are provided in the rotor shaft which receive internal projections of the rotor's ferromagnetic plates. The grooves and projections cooperate by complementary shapes.

[0064]

[0052] Turning to figures 2 to 7, the rotor shaft 1 has a tubular body and extends from a first axial end marked E1 to a second axial end marked E2 along a main axis marked Y1.

[0065]

[0053] The rotor shaft 1 includes housings 18 made in the tubular body at the first axial end E1. These housings 18 are intended to receive and drive a planet carrier element 2 forming part of the differential mechanism denoted DF.

[0066]

[0054] The differential mechanism DF comprises a planet carrier element 2 received in the housings 18 via bearings described later. The differential mechanism DF is of the bevel gear type here.

[0067]

[0055] Each housing 18 has an opening directed axially opposite to the second axial end E2 to allow end mounting on the side of the first axial end E1, in the direction of E2.

[0068]

[0056] The planet carrier element 2 is driven in rotation by the rotor shaft 1. The transmission device includes four planet gears (23, 24, 25, 26) mounted for rotation on the planet carrier 2.

[0069]

[0057] The satellite carrier element 2 is cross-shaped with four identical arms. Each arm end includes an end trunnion 27 around which a satellite mounted at that location can rotate.

[0070]

[0058] Each of the branches of the cross-shaped satellite carrier element extends along a local axis perpendicular to the main axis.

[0071]

[0059] The satellite carrier element 2 is made of steel, just like the satellites and planetary gears.

[0072]

[0060] The differential mechanism DF comprises a first planetary pinion 21 and a second planetary pinion 22.

[0073]

[0061] Each planetary gear meshes with the planetary gears. The planetary gears do not mesh with each other.

[0074]

[0062] The first planetary gear 21 is suitable for driving the short drive shaft AI. The second planetary gear 22 is suitable for driving the long drive shaft A2.

[0075]

[0063] The outside diameter D20 of the long drive shaft A2 (see Figure 4) is chosen to be around 25 mm, for example, within a range of values ​​between 22 and 26 mm. It should be noted that, depending on one option, the long drive shaft A2 has an axial lubrication passage along its entire length.

[0064] The number of planetary gears could be two. Thus, generally, the transmission device comprises at least two planetary gears (23, 24).

[0076]

[0065] A bearing 5 is provided interposed between each housing 18 and the satellite carrier 2. The bearing 5 allows the torque force produced by the rotor and allocated to the rotor shaft to be absorbed.

[0077]

[0066] The bearing 5 can be mushroom-shaped. For example, each bearing 5 comprises a head received in the respective opposite housing, and a bearing tube around which a satellite is mounted.

[0078]

[0067] Each of the bearing heads comprises two straight edges 55 parallel to the main axis Y1 orthogonal to the local axis of the bearing tube.

[0079]

[0068] Each of the bearings includes a front edge 56 which, once assembled, is flush with the free edge 1a of the shaft.

[0080]

[0069] The head is outwardly convex with an entry chamfer. The curvature follows the general profile of the outer wall of the rotor shaft once the bearing is in place. On the inner side, the head includes an annular flat on which a washer, discussed below, rests. The annular flat surrounds the base of the bearing tube.

[0081]

[0070] The bearing tube receives on its inner side a trunnion 27 of the planet carrier 2 which is received in an internal bearing. Furthermore, the bearing tube receives on its outer side, i.e. on its external cylindrical surface, the inner bore of the planet which can rotate at this point.

[0082]

[0071] The second planetary gear 22 bears against a front face of an annular-shaped planetary thrust bearing 6. The planetary thrust bearing 6 has a rear face which bears against a shoulder provided in the rotor shaft.

[0083]

[0072] Advantageously, pressure washers (4,4') are provided on the back of the satellites and planetary gears.

[0084]

[0073] Pressure washers are non-flat washers at rest. They exhibit a certain elasticity and can return to a flat shape under compressive stress. The pressure washers 4' on the back of the planetary gears contribute to compensating for axial play. The pressure washers 4 on the back of the satellite gears contribute to compensating for transverse play. The pressure washers also contribute to self-centering of the drive shafts during rotation. Furthermore, this eliminates hysteresis when torque direction changes.

[0085]

[0074] The invention cleverly proposes to use a differential cover noted 7 inserted externally on the first axial end E1 of the rotor shaft 1.

[0086]

[0075] The differential cover 7 is formed as a metal ferrule with a material thickness between 2 mm and 4 mm.

[0087]

[0076] The differential cover includes a covering skirt 70 delimited by a free circular border 74.

[0088]

[0077] As seen in the figures, the differential cover 7 includes an axial opening 72 configured to allow passage for the first drive shaft A1 which can be rotationally fixed to the first planetary pinion 21.

[0089]

[0078] Furthermore, the rotor shaft 1 is configured to house the second drive shaft A2 up to an axial through opening noted 19 at the second axial end E2 of the rotor shaft.

[0090]

[0079] The differential cover 7 is inserted onto the rotor shaft until the inner annular bearing contacts the free end 1a of the rotor shaft, as shown in Figure 3.

[0080] The differential cover 7 can be fixed by shrink fitting onto the rotor shaft 1. The overlap area of ​​the differential cover on the rotor shaft is substantial, which allows for a solid fixing of the differential cover to the shaft 1.

[0091]

[0081] Furthermore, for the speed-sensing function required for controlling the machine, the electromotive unit UU includes a rotation sensor 92 mounted on the housing element C1. The rotation sensor 92 includes a sensitive portion 92a. The rotation sensor 92 is connected to a control unit by wiring wires 93. The rotation sensor can be a Hall effect sensor or a sensor of another technology.

[0092]

[0082] The diameter of the differential cover 7 is noted D7. D7 exceeds D1 by 2 mm to 4 mm.

[0093]

[0083] A rotating sensor target 8 is provided on the rotor shaft 1. The sensor target is annular. The sensor target 8 is arranged on the differential cover 7. The sensor target 8 comprises target patterns positioned opposite a sensitive part 92a of the rotation sensor 92 (see Fig 7).

[0094]

[0084] An electrical friction track 70a is provided on the skirt of the differential cover 7.

[0095]

[0085] The sensor target 8 comprises a tubular portion 81 for tight mounting on the differential cover 7. The sensor target 8 comprises a discoidal portion 82 bearing the detection patterns. A frustoconical portion 85 is provided which connects the discoidal portion 82 to the tubular portion 81.

[0096]

[0086] The sensor target 8 has magnetic patterns or mechanical teeth. For example, as illustrated in Figure 6, the magnetic patterns may consist of a succession of North and South poles on a circumferential border.

[0097]

[0087] The diameter of the sensor target 8 is noted D8.

[0098]

[0088] Alternatively, as illustrated in Figure 7, the electrical friction track can be provided on the tubular skirt of the sensor target 8, illustrated in reference 84.

[0099]

[0089] The friction track 70a is suitable for receiving friction from the eyelets or brushes 96 linked to a stationary element in electrical coupling with the electrical mass of the electromotive unit.

[0100]

[0090] The stationary element is formed like an eyelash ring or broom.

[0101]

[0091] The wound rotor is electrically activated via excitation tracks P1, P2. The excitation tracks are arranged in an annular fashion at the second end E2 of the shaft opposite the position of the differential device.

[0102]

[0092] The two excitation tracks P1, P2 are by an insulating ring 48. Opposite is provided a system of rubbing pads generally marked 78, one or more pads rubbing on the excitation tracks.

[0103]

[0093] The two excitation tracks P1, P2 are of smaller diameter than the electric friction track 70a.

[0104]

[0094] As illustrated in figures 4, 7 and 8, the eyelet or brush ring 94 is mounted from the outside once the housing element C1 has been assembled.

[0105]

[0095] Relative to the center of the electric machine, the eye or brush ring 94 is positioned on the inner side relative to the rotation sensor, and on the outer side relative to the rotor rotation mounting bearing B1.

[0106]

[0096] The stationary element may include a support ring 94a with an L-shaped profile.

[0097] As illustrated in figure 8, the eyelashes 96 are arranged around the entire periphery of the ring with a balanced circumferential distribution.

[0107]

[0098] The eyelash ring has an outer diameter denoted D6 and an inner diameter excluding eyelashes denoted D5. The free end of the eyelashes is located at a diameter D4 which corresponds substantially to the diameter of the friction track 70a (or alternatively 84).

[0108]

[0099] It is noted that the DF transmission device is devoid of bearings inside the rotor shaft, which increases the compactness of the differential mechanism.

[0109]

[0100] The bearing B1 is arranged to surround the second planetary gear 22, in the same axial position, for guiding the rotation of the transmission device

[0110]

[0101] Regarding the relative dimensions, it is noted that in the first embodiment, we have D1 / L9 < 0.5 where L9 is the axial length of the rotor. We also have D1 / D9 < 0.4 where D9 is the diameter of the rotor. The diameter D1 is therefore small, even though the rotor shaft houses the differential mechanism.

[0111]

[0102] Furthermore, we can have D1 / DM < 0.25 where DM is the diameter of the electrical machine MEL (see figures 2 and 3).

[0112]

[0103] The electromotive unit UU therefore integrates the differential function in a form factor which differs very little from a form factor of an electric machine alone for the same power characteristics.

[0113]

[0104] According to a particular application example on a motor vehicle drive axle, D1 < 62 mm for a motor torque to be passed up to the order of 800 Nm.

[0114]

[0105] The combination described above allows the differential device to be sized as precisely as possible and to be housed inside a rotor shaft of an electric machine, here on one end of this shaft opposite the electrical excitation tracks when the rotor is wound.

Claims

DEMANDS 1. Electromotive unit (EMU) comprising an electric machine (EM) including a rotor (9), at least one housing element (C1) and a rotor shaft (1) having a tubular body, extending from a first axial end (E1) to a second axial end (E2) along a main axis (Y1), the electromotive unit comprising: - a differential mechanism (DF) housed inside the rotor shaft, with a planet carrier element driven in rotation by the rotor shaft, - a differential cover (7) inserted externally on the first axial end of the rotor shaft, the differential cover comprising an axial opening (72) configured to allow passage of a first drive shaft (A1), - a rotation sensor (92) mounted on the housing element, - a rotating sensor target (8) arranged on the differential cover (7), with target patterns positioned opposite a sensitive part (92a) of the rotation sensor (92), - an electrical friction track (70) arranged on the differential cover (7) or on the sensor target (8), the electrical friction track being suitable for receiving friction from the eyelets or brushes linked to a stationary element in electrical coupling with the electrical mass of the electromotive unit.

2. Electromotive unit according to claim 1, wherein at least two annular excitation tracks (P1, P2) are provided on the side of the second axial end of the rotor shaft, configured to permit excitation of the rotor winding, the second axial end of the rotor shaft being open on the axis at the second end (E2).

3. Electromotive unit according to claim 2, wherein the two excitation tracks (P1, P2) are of smaller diameter (D9) than the electric friction track.

4. Electromotive unit according to any one of claims 1 to 3, wherein the sensor target (8) comprises a tubular portion (81) for tight mounting and a discoidal portion (82) bearing the patterns.

5. Electromotive unit according to any one of claims 1 to 4, wherein the sensor target (8) has magnetic patterns or mechanical teeth.

6. Electromotive unit according to any one of claims 1 to 5, wherein the sensor target (8) is clamped onto the differential cover (7).

7. Electromotive unit according to any one of claims 1 to 6, wherein the speed sensor function and the grounding function together occupy an axial thickness (W1), and said axial thickness is less than 25 mm.

8. Electromotive unit according to any one of claims 1 to 7, wherein the stationary element is formed as a lash or brush ring (94), mounted externally once the housing element (C1) is assembled.

9. Electromotive unit according to any one of claims 1 to 8, wherein the eye or brush ring (94) is positioned on the inner side with respect to the rotation sensor, and on the outer side with respect to the rotor rotation mounting bearing (B1).

10. Motor vehicle, preferably electric or hybrid, comprising an electromotive unit according to any one of claims 1 to 9.

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