Vehicle drive device

Abstract

This vehicle drive device includes a housing which is electrically connected to a stator and which supports a first bearing ring of a bearing. The vehicle drive device includes a rotary shaft which is electrically connected to a rotor and which supports a second bearing ring of the bearing. The vehicle drive device includes a helical gear provided to the rotary shaft. The vehicle drive device includes a conductive plate provided between the first bearing ring and the housing and including: a ring body facing a first end surface of the first bearing ring; and a contact piece that extends in the radial direction from the ring body and that faces a second end surface of the second bearing ring.

Description

Vehicle drive unit

[0001] The present disclosure relates to a vehicle drive device.

[0002] Vehicles such as automobiles are equipped with a power unit equipped with an electric motor. The electric motor in the power unit has a stator assembled to a housing and a rotor housed in the center of the stator. In addition, a bearing that supports a rotating shaft connected to the rotor is attached to the housing of the power unit (see Patent Documents 1 to 3).

[0003] JP 2016-201900 A JP 2017-77148 A JP 2018-107853 A

[0004] Incidentally, when magnetic field fluctuations are generated in the stator coil, a shaft voltage may be generated on the rotating shaft connected to the rotor. In this case, if a shaft voltage is generated on the rotating shaft supported by the bearing, a potential difference will also be generated between the outer and inner rings of the bearing. Furthermore, depending on the magnitude of the potential difference between the outer and inner rings, there is a risk of electrolytic corrosion occurring due to discharge within the bearing. Since electrolytic corrosion can damage the raceway surfaces and rolling elements of the bearing, it is necessary to prevent electrolytic corrosion of the bearing.

[0005] According to the present disclosure, a vehicle drive device includes a housing electrically connected to a stator and holding a first bearing ring of a bearing. The vehicle drive device includes a rotating shaft electrically connected to a rotor and holding a second bearing ring of the bearing. The vehicle drive device includes a helical gear provided on the rotating shaft. The vehicle drive device includes a conductive plate provided between the first bearing ring and the housing, the conductive plate including a ring body facing a first end face of the first bearing ring and a contact piece extending radially from the ring body and facing a second end face of the second bearing ring. The conductive plate is deformable between a contact shape in which the contact piece is in contact with the second end face and a non-contact shape in which the contact piece is away from the second end face.

[0006] According to the present disclosure, it is possible to prevent electrolytic corrosion of bearings.

[0007] FIG. 1 is a diagram showing an example of a vehicle equipped with a power unit. FIG. 2 is a diagram showing an example of the internal structure of a power unit. FIG. 3 is a cross-sectional view showing a bearing and its vicinity. FIG. 4 is a cross-sectional view showing a bearing and its vicinity along line A-A in FIG. 3. FIG. 5 is a cross-sectional view showing a bearing and its vicinity. FIG. 6 is a cross-sectional view showing an enlarged view of the conductive plate and its vicinity in FIG. 3. FIG. 7 is a cross-sectional view showing a bearing and its vicinity. FIG. 8 is a cross-sectional view showing a bearing and its vicinity along line B-B in FIG. 7. FIG. 9 is a cross-sectional view showing a bearing and its vicinity. FIG. 10 is a cross-sectional view showing an enlarged view of the conductive plate and its vicinity in FIG. 7.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, identical or substantially identical configurations and elements will be designated by the same reference numerals and will not be described repeatedly.

[0009] <First Embodiment> <Power Unit> Fig. 1 is a diagram showing an example of a vehicle 12 including a power unit 11. The illustrated power unit 11 is provided with a vehicle drive system 10 according to one embodiment of the present disclosure. As shown in Fig. 1, the vehicle 12 has a power unit 11 including an engine 13 and motor generators MG1 and MG2. A rear wheel output shaft 14 of the power unit 11 is connected to rear wheels 17 via a propeller shaft 15 and a rear differential mechanism 16. The power unit 11 also includes a front differential mechanism 18, which is connected to front wheels 19. Note that the illustrated power unit 11 is an all-wheel drive power unit, but is not limited thereto and may be a front-wheel drive or rear-wheel drive power unit.

[0010] FIG. 2 is a diagram showing an example of the internal structure of the power unit 11. As shown in FIG. 2, the power unit 11 has a main output shaft 20 that passes through the center of the motor generator MG2 to output engine power and motor power to the front and rear wheels 17, 19. The main output shaft 20 is connected to a front wheel output shaft 22 via a gear train 21 and to the rear wheel output shaft 14 via a transfer clutch 23. The main output shaft 20 is also connected to a power split mechanism 27 via a gear train 26 consisting of a pair of helical gears 24, 25. The power split mechanism 27 is connected to the motor generator MG1 and to the engine 13 via a gear train 28 and a damper mechanism 29. The main output shaft 20 is also connected to the motor generator MG2 via a planetary gear train 30. The front wheel output shaft 22 is connected to the front differential mechanism 18 described above.

[0011] Power split device 27 has a sun gear 32 connected to motor generator MG1 via a hollow shaft 31, a ring gear 34 connected to gear train 26 via a rotating shaft 33, and a carrier 36 connected to gear train 28 via a rotating shaft 35. Power split device 27 also has a pinion 37 that is rotatably supported by carrier 36 and meshes with sun gear 32 and ring gear 34. Bearings 41 and 42 are attached to a housing 40 of power unit 11, and rotating shaft 33 is rotatably supported by bearings 41 and 42. Bearings 43 and 44 are attached to housing 40, and rotating shaft 35 is rotatably supported by bearings 43 and 44.

[0012] Motor generator (electric motor) MG1 constituting vehicle drive device 10 has a stator 52 consisting of a stator core 50 and a stator coil 51, and a rotor 55 consisting of a rotor core 53 and a permanent magnet 54. Stator 52 is attached to housing 40 using fastening bolts or the like (not shown), and rotor 55 is connected to sun gear 32 of power split mechanism 27 via hollow shaft 31. Furthermore, because housing 40, power split mechanism 27, and the like constituting power unit 11 are formed using metal materials, stator 52 and housing 40 are electrically connected, and rotor 55 and rotating shaft 33 are electrically connected via power split mechanism 27. An inverter 56, which is a power conversion device, is connected to stator 52 of motor generator MG1.

[0013] <Support structure of rotating shaft> Hereinafter, a support structure of the rotating shaft 33 using the bearing 41 will be described, that is, a support structure of the rotating shaft 33 provided in the vehicle drive device 10. Fig. 3 is a cross-sectional view showing the bearing 41 and its vicinity, and Fig. 4 is a cross-sectional view showing the bearing 41 and its vicinity along line A-A in Fig. 3.

[0014] As shown in Figure 3, the rotating shaft 33 is provided with the helical gear 24 of the gear train 26, and an end 60 of the rotating shaft 33 is rotatably supported by a bearing 41. The housing 40 that holds the bearing 41 has an annular recess 63 formed with an inner circumferential surface 61 and a circular wall surface 62. The bearing 41 has an outer ring (first raceway) 64 attached to the inner circumferential surface 61 of the annular recess 63, an inner ring (second raceway) 65 attached to the end 60 of the rotating shaft 33, and a plurality of rolling elements 66 provided between the outer ring 64 and the inner ring 65. The outer ring 64, the inner ring 65, and the rolling elements 66 are made of a metallic material.

[0015] As shown in FIGS. 3 and 4 , a conductive plate 67 made of a metal material is provided between the bearing 41 and the wall surface 62 of the annular recess 63. A shim 68 made of a metal material is provided between the bearing 41 and the conductive plate 67, and a shim 69 made of a metal material is provided between the conductive plate 67 and the wall surface 62. The conductive plate 67 has a ring body 70 facing the end surface (first end surface) 64a of the outer ring 64 and a plurality of contact pieces 71 extending radially inward from the ring body 70 and facing the end surface (second end surface) 65a of the inner ring 65. The ring body 70 of the conductive plate 67 is formed with an annular protrusion 72 that protrudes toward the end surface 64a of the outer ring 64. The cross-sectional shape of the protrusion 72 in the radial direction of the ring body 70 is formed by bending a thin metal plate. The conductive plate 67 is a sheet metal part manufactured by sheet metal processing.

[0016] <Deformation of the Conductive Plate> As shown in FIG. 2 , the rotating shaft 33 is provided with a helical gear 24 with helical tooth traces. Therefore, during drive, when torque is transmitted from the motor-generator MG1 to the gear train 26, an axial load is generated from the helical gear 24 toward the bearing 41. In other words, the twist direction of the tooth traces of the helical gear 24 is set to generate an axial load in the direction of arrow L1 during drive. As will be described later, during drive, the axial load is transmitted from the rotating shaft 33 to the bearing 41 and the shim 68 to the conductive plate 67. As shown in FIG. 3 , the outer ring 64 of the bearing 41 and the inner circumferential surface 61 of the annular recess 63 are fitted together loosely. Therefore, when an axial load L2 is input from the rotating shaft 33 to the bearing 41, the bearing 41 moves toward the conductive plate. The axial load is also called a thrust load.

[0017] Figure 5 is a cross-sectional view of bearing 41 and its vicinity. Figure 5 shows the same parts as Figure 3. Note that Figure 3 shows the non-contact shape of conductive plate 67 in which contact piece 71 is separated from inner ring 65, while Figure 5 shows the contact shape of conductive plate 67 in which contact piece 71 is in contact with inner ring 65.

[0018] 3, when the axial load L2 transmitted from the rotating shaft 33 to the bearing 41 is small or absent, the axial load L2 hardly presses the conductive plate 67, and the conductive plate 67 maintains a non-contact shape due to the repulsive force of the conductive plate 67. As shown in the enlarged portion of FIG. 3, when the conductive plate 67 has a non-contact shape, the contact piece 71 of the conductive plate 67 is separated from the end face 65a of the inner ring 65.

[0019] 5, when the axial load L2 transmitted from the rotating shaft 33 to the bearing 41 is large, the axial load L2 presses the conductive plate 67, and the axial load L2 deforms the conductive plate 67 from a non-contact shape to a contact shape. As shown in the enlarged portion of FIG. 5, when the conductive plate 67 is in a contact shape, the contact piece 71 of the conductive plate 67 is in contact with the end face 65a of the inner ring 65.

[0020] Here, Fig. 6 is an enlarged cross-sectional view of the conductive plate 67 and its vicinity in Fig. 3. As shown in Fig. 6, when an axial load L2 is input from the rotating shaft 33 to the outer ring 64 via the inner ring 65 and rolling elements 66, the outer ring 64 of the bearing 41 presses the shim 68 toward the convex portion 72 of the conductive plate 67. When the convex portion 72 of the conductive plate 67 is pressed by the outer ring 64 of the bearing 41 in this manner (arrow X1), the ring body 70 of the conductive plate 67 elastically deforms and expands (arrow X2), and the contact piece 71 extending from the ring body 70 is displaced toward the inner ring 65 of the bearing 41 (arrow X3).

[0021] That is, when the axial load L2 applied from the outer ring 64 to the ring body 70 exceeds the threshold value, the conductive plate 67 deforms into a contact shape against the repulsive force of the conductive plate 67. On the other hand, when the axial load L2 applied from the outer ring 64 to the ring body 70 is below the threshold value, the repulsive force of the conductive plate 67 deforms the conductive plate 67 into a non-contact shape. In this way, the conductive plate 67 can be deformed between a contact shape and a non-contact shape.

[0022] <Prevention of Galvanic Corrosion> A situation in which the axial load L2 increases means that the load on the bearing 41 increases, causing the lubricating oil film in the bearing 41 to become thinner, reducing the withstand voltage of the bearing 41 and making it more susceptible to galvanic corrosion. For this reason, when the axial load L2 applied to the conductive plate 67 increases, the conductive plate 67 is elastically deformed from a non-contact shape to a contact shape. As a result, even if a potential difference occurs between the outer ring 64 and the inner ring 65, current can flow through the conductive plate 67, thereby eliminating the potential difference between the outer ring 64 and the inner ring 65 and preventing galvanic corrosion. In this way, since galvanic corrosion of the bearing 41 can be prevented, the durability of the bearing 41 and the durability of the power unit 11 can be improved.

[0023] On the other hand, a situation in which the axial load L2 is small means that the load on the bearing 41 decreases, the lubricating oil film inside the bearing 41 becomes thicker, the withstand voltage of the bearing 41 increases, and electrolytic corrosion is less likely to occur. For this reason, when the axial load L2 applied to the conductive plate 67 is small, the conductive plate 67 is elastically deformed from a contact shape to a non-contact shape. As a result, in a situation in which electrolytic corrosion of the bearing 41 is less likely to occur, the contact piece 71 is moved away from the rotating inner ring 65, thereby reducing the rotational resistance of the inner ring 65, i.e., the rotating shaft 33, and improving the power transmission efficiency of the power unit 11.

[0024] Incidentally, the potential difference between outer ring 64 and inner ring 65, which is the cause of electrolytic corrosion, is thought to be generated by inverter driving of motor generator MG1. In other words, when magnetic field fluctuations are generated in stator coil 51 by inverter driving, a shank voltage is generated in rotating shaft 33 connected to rotor 55. When the shank voltage of rotating shaft 33 exceeds the dielectric breakdown voltage of the lubricating oil film, discharge occurs within bearing 41, which is thought to damage the raceway surfaces and rolling element surfaces of bearing 41. Note that, although stator coil 51 of motor generator MG1 has a concentrated winding structure, this is not limiting and stator coil 51 may have a distributed winding structure.

[0025] <Second embodiment> <Support structure for rotating shaft> In the above description, the outer ring 64 of the bearing 41 is attached to the housing 40, while the inner ring 65 of the bearing 41 is attached to the rotating shaft 33. However, this is not limited to this, and the outer ring 64 of the bearing 41 may be attached to the rotating shaft 33, while the inner ring 65 of the bearing 41 may be attached to the housing 40.

[0026] Below, a support structure for a rotating shaft 82 using bearing 81, that is, a support structure for a rotating shaft 82 provided in a vehicle drive device 80 of another embodiment, will be described. Fig. 7 is a cross-sectional view showing bearing 81 and its vicinity, and Fig. 8 is a cross-sectional view showing bearing 81 and its vicinity along line B-B in Fig. 7. In the following description, bearing 81 is a bearing provided in the same position as bearing 41 described above, rotating shaft 82 is a rotating shaft provided in the same position as rotating shaft 33 described above, and housing 83 is a housing provided in the same position as housing 40 described above.

[0027] As shown in FIG. 7 , a rotating shaft 82 is provided with a helical gear 24 of the gear train 26, and an end 84 of the rotating shaft 82 is rotatably supported by a bearing 81. An annular recess 86 with an annular inner peripheral surface 85 is formed in the end 84 of the rotating shaft 82. The bearing 81 also has an outer ring (second raceway) 87 attached to the inner peripheral surface 85 of the annular recess 86, an inner ring (first raceway) 88 attached to a support shaft portion 90 of the housing 83, and a plurality of rolling elements 89 provided between the outer ring 87 and the inner ring 88. The inner ring 88 of the bearing 81 is fitted loosely with the outer peripheral surface 90 a of the support shaft portion 90. The outer ring 87, the inner ring 88, and the rolling elements 89 are made of metal.

[0028] As shown in FIGS. 7 and 8 , a conductive plate 92 made of a metal material is provided between the bearing 81 and a wall surface 91 around the support shaft portion 90. A shim 93 made of a metal material is provided between the bearing 81 and the conductive plate 92, and a shim 94 made of a metal material is provided between the conductive plate 92 and the wall surface 91. The conductive plate 92 has a ring body 95 facing the end face (first end face) 88 a of the inner ring 88 and a plurality of contact pieces 96 extending radially outward from the ring body 95 and facing the end face (second end face) 87 a of the outer ring 87. The ring body 95 of the conductive plate 92 is formed with an annular protrusion 97 that protrudes toward the end face 88 a of the inner ring 88. The cross-sectional shape of the protrusion 97 in the radial direction of the ring body 95 is formed by bending a thin metal plate. The conductive plate 92 is a sheet metal part manufactured by sheet metal processing.

[0029] <Deformation of the Conductive Plate> Fig. 9 is a cross-sectional view showing the bearing 81 and its vicinity. Fig. 9 shows the same parts as Fig. 7. Note that Fig. 7 shows a non-contact shape of the conductive plate 92 in which the contact piece 96 is separated from the outer ring 87, while Fig. 9 shows a contact shape of the conductive plate 92 in which the contact piece 96 is in contact with the outer ring 87.

[0030] 7, when the axial load L2 transmitted from the rotating shaft 82 to the bearing 81 is small or absent, the axial load L2 hardly presses the conductive plate 92, and the conductive plate 92 maintains its non-contact shape due to the repulsive force of the conductive plate 92. As shown in the enlarged portion of FIG. 7, when the conductive plate 92 has a non-contact shape, the contact piece 96 of the conductive plate 92 is separated from the end face 87a of the outer ring 87.

[0031] 9, when the axial load L2 transmitted from the rotating shaft 82 to the bearing 81 is large, the axial load L2 presses the conductive plate 92, and the axial load L2 deforms the conductive plate 92 from a non-contact shape to a contact shape. As shown in the enlarged portion of FIG. 9, when the conductive plate 92 is in a contact shape, the contact piece 96 of the conductive plate 92 is in contact with the end face 87a of the outer ring 87.

[0032] Here, Figure 10 is an enlarged cross-sectional view of the conductive plate 92 and its vicinity in Figure 7. As shown in Figure 10, when an axial load L2 is input from the rotating shaft 82 to the inner ring 88 via the outer ring 87 and rolling elements 89, the inner ring 88 of the bearing 81 presses the shim 93 toward the convex portion 97 of the conductive plate 92. When the convex portion 97 of the conductive plate 92 is pressed by the inner ring 88 of the bearing 81 in this way (arrow X1), the ring body 95 of the conductive plate 92 elastically deforms and expands (arrow X2), and the contact piece 96 extending from the ring body 95 is displaced toward the outer ring 87 of the bearing 81 (arrow X3).

[0033] That is, when the axial load L2 applied from the outer ring 87 to the ring body 95 exceeds the threshold value, the conductive plate 92 deforms into a contact shape against the repulsive force of the conductive plate 92. On the other hand, when the axial load L2 applied from the outer ring 87 to the ring body 95 is below the threshold value, the repulsive force of the conductive plate 92 deforms the conductive plate 92 into a non-contact shape.

[0034] <Prevention of Galvanic Corrosion> A situation in which the axial load L2 increases means that the load on the bearing 81 increases, causing the lubricating oil film in the bearing 81 to become thinner, reducing the withstand voltage of the bearing 81 and making it more susceptible to galvanic corrosion. For this reason, when the axial load L2 applied to the conductive plate 92 increases, the conductive plate 92 is elastically deformed from a non-contact shape to a contact shape. As a result, even if a potential difference occurs between the outer ring 87 and the inner ring 88, current can be passed through the conductive plate 92, eliminating the potential difference between the outer ring 87 and the inner ring 88 and preventing galvanic corrosion. In this way, since galvanic corrosion of the bearing 81 can be prevented, the durability of the bearing 81 and the durability of the power unit 11 can be improved.

[0035] On the other hand, a situation in which the axial load L2 is small means that the load on the bearing 81 decreases, the lubricating oil film inside the bearing 81 becomes thicker, the withstand voltage of the bearing 81 increases, and electrolytic corrosion is less likely to occur. For this reason, when the axial load L2 applied to the conductive plate 92 is small, the conductive plate 92 is elastically deformed from a contact shape to a non-contact shape. As a result, in a situation in which electrolytic corrosion of the bearing 81 is less likely to occur, the contact piece 96 is moved away from the rotating outer ring 87, thereby reducing the rotational resistance of the outer ring 87, i.e., the rotating shaft 82, and improving the power transmission efficiency of the power unit 11.

[0036] <Modifications> The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present disclosure. In the illustrated example, the vehicle drive device 10 (80) is provided for the power unit 11 having multiple power sources, but this is not limited to this. For example, the vehicle drive device 10 (80) may be provided for a power unit having one motor generator as a power source, or the vehicle drive device 10 (80) may be provided for an electric axle having a motor generator.

[0037] In the illustrated example, the conductive plate 67 (92) is configured with a ring body 70 (95) and three contact pieces 71 (96), but this is not limited thereto and the conductive plate may be configured with a ring body 70 (95) and one contact piece 71 (96). The conductive plate may also be configured with a ring body 70 (95) and two contact pieces 71 (96), or with a ring body 70 (95) and four or more contact pieces 71 (96). In the illustrated example, the conductive plate 67 (92) is attached to the bearing 41 (81) that supports the rotating shaft 33 (82), but this is not limited thereto and the conductive plate 67 (92) may also be attached to other bearings 42, 43, 44, etc.

[0038] In the illustrated example, two shims 68, 69 (93, 94) are provided to sandwich the conductive plate 67 (92), but this is not limiting. For example, the shim 68 (93) may be provided only between the bearing 41 (81) and the conductive plate 67 (92), or the shim 69 (94) may be provided only between the conductive plate 67 (92) and the wall surface 62 (91). Furthermore, by removing the shims 68, 69 (93, 94) from between the bearing 41 (81) and the wall surface 62 (91), the conductive plate 67 (92) may be in direct contact with the bearing 41 (81), or the conductive plate 67 (92) may be in direct contact with the housing 40 (83).

[0039] In the above description, the conductive plate 67 (92) is deformed into a contact shape when the axial load generated during driving increases, but this is not limited to this, and the conductive plate 67 (92) may also be deformed into a contact shape when the axial load generated during braking increases. In other words, the twist direction of the tooth trace of the helical gear 24 may be set so that an axial load is generated in the direction of arrow L1 during braking to cause the motor generator MG1 to generate regenerative power, that is, during braking to transmit torque from the main output shaft 20 to the rotating shaft 33.

[0040] 10...vehicle drive device, 24...helical gear, 33...rotating shaft, 40...housing, 41...bearing, 52...stator, 55...rotor, 64...outer ring (first bearing ring), 64a...end face (first end face), 65...inner ring (second bearing ring), 65a...end face (second end face), 67...conductive plate, 68, 69...shim, 70...ring body, 71...contact piece, 72...protrusion, 80...vehicle drive device, 81...bearing, 82...rotating shaft, 83...housing, 87...outer ring (second bearing ring), 87a...end face (second end face), 88...inner ring (first bearing ring), 88a...end face (first end face), 92...conductive plate, 93, 94...shim, 95...ring body, 96...contact piece, 97...protrusion, MG1...motor generator (electric motor)

Claims

1. A vehicle drive device equipped with a stator and rotor of an electric motor, comprising: a housing electrically connected to the stator and holding a first raceway of a bearing; a rotating shaft electrically connected to the rotor and holding a second raceway of the bearing; a helical gear provided on the rotating shaft; and a conductive plate provided between the first raceway and the housing, the conductive plate comprising: a ring body facing a first end face of the first raceway; and a contact piece extending radially from the ring body facing a second end face of the second raceway, wherein the conductive plate is deformable between a contact shape in which the contact piece is in contact with the second end face and a non-contact shape in which the contact piece is away from the second end face.

2. A vehicle drive device according to claim 1, wherein the conductive plate deforms into the contact shape when the axial load applied to the ring body from the first end face exceeds a threshold value, and deforms into the non-contact shape when the axial load applied to the ring body from the first end face falls below the threshold value.

3. A vehicle drive device according to claim 1, wherein the ring body has a protrusion that protrudes toward the first end face.

4. A vehicle drive device according to claim 1, wherein the first bearing ring is an outer ring, and the second bearing ring is an inner ring.

5. A vehicle drive device according to claim 4, wherein the contact piece extends radially inward from the ring body.

6. A vehicle drive device according to claim 1, wherein a shim is provided between the first bearing ring and the conductive plate, or between the conductive plate and the housing.

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