Ev unit

Abstract

This EV unit comprises: a housing that is provided with a motor stator and that is electrically grounded; a shaft that is provided with a motor rotor and a gear of a speed reducer unit; a pair of motor bearings that pivotally support the shaft at positions on both axial-direction sides of the motor rotor; and a pair of speed reducer bearings that pivotally support the shaft at positions on both axial-direction sides of the gear. The shaft is electrically connected to the housing at a position on the reverse side from the motor rotor when viewed from the motor bearings. Each of the pair of motor bearings is an insulating bearing which is electrically insulating. Each of the pair of speed reducer bearings is a conductive bearing which is conductive.

Description

EV unit

[0001] The present disclosure relates to an EV unit.

[0002] Conventionally, various methods have been known to prevent electrolytic corrosion in machine bearings, such as insulating the bearing from the bracket with an electrically insulating housing, or sealing a conductive lubricant inside the bearing to prevent discharge within the bearing (see, for example, Patent Document 1 below).

[0003] Japanese Patent Application Laid-Open No. 2016-208579

[0004] However, in machines such as EV units, the effectiveness of electrolytic corrosion countermeasures may not be fully achieved unless the above-mentioned countermeasure elements are placed in appropriate locations, taking into consideration the overall condition of the machine. Furthermore, providing countermeasure elements in locations where they are not actually required increases the manufacturing cost of the machine, so it is desirable to minimize countermeasures. The present disclosure aims to provide an EV unit that efficiently suppresses electrolytic corrosion of bearings using the minimum necessary countermeasures.

[0005] The present disclosure includes at least the following [1] to [9].

[0006] [1] An EV unit comprising a motor section and a reducer section that reduces the speed of the motor section, the EV unit comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a gear of the reducer section are provided; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a reducer bearing that is interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the gear and support the shaft, wherein the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the gear side, and both of the pair of motor bearings are electrically insulating bearings, and the reducer bearing is an electrically conductive bearing.

[0007] [2] The EV unit according to [1], further comprising another reducer bearing interposed between the housing and the shaft at a position between the gear and the first motor bearing and supporting the shaft, the another reducer bearing being an electrically conductive bearing.

[0008] [3] An EV unit comprising a motor section and a reducer section that reduces the speed of the motor section, the EV unit comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a gear of the reducer section are provided; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a reducer bearing that is interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the gear and supports the shaft; the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the gear side; a second motor bearing that is the other of the pair of motor bearings and is an insulating bearing that is electrically insulating; and the first motor bearing and the reducer bearing are conductive bearings.

[0009] [4] The EV unit according to [3], further comprising another reducer bearing interposed between the housing and the shaft at a position between the gear and the first motor bearing and supporting the shaft, the another reducer bearing being an electrically conductive bearing.

[0010] [5] An EV unit comprising a motor section and a reducer section that reduces the speed of rotation of the motor section, the EV unit comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a reduction mechanism of the reduction mechanism section are provided; a pair of motor bearings interposed between the housing and the shaft at positions on both axial sides of the motor rotor and supporting the shaft; and a reduction gear bearing interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the reduction gear mechanism and supporting the shaft, wherein the reduction gear mechanism is a coaxial reduction mechanism that reduces the rotation of an input shaft on the motor rotor side and transmits it to an output shaft coaxial with the input shaft, the shaft having the input shaft and the output shaft connected to the reduction gear mechanism, and the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings and located on the reduction gear mechanism side,

[0011] [6] An EV unit including a motor section and a speed reducer section that reduces the rotation speed of the motor section, the EV unit including: a housing in which a motor stator of the motor section is provided and which is electrically grounded; a shaft in which a motor rotor of the motor section and a speed reduction mechanism of the speed reducer section are provided; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a speed reducer bearing that is interposed between the housing and the shaft at a position on the opposite side of the motor rotor from the speed reduction mechanism and support the shaft, an EV unit having a coaxial reduction mechanism that reduces the rotation of an input shaft on a motor side and transmits the reduced rotation to an output shaft coaxial with the input shaft, the shafts having the input shaft and the output shaft connected to the reduction mechanism, the shafts being electrically connected to the housing at a position on the opposite side of the motor rotor from a first motor bearing that is one of the pair of motor bearings located on the reduction mechanism side, the second motor bearing that is the other of the pair of motor bearings being an insulating bearing that is electrically insulating, and the first motor bearing and the reducer bearing are conductive bearings that are electrically conductive.

[0012] [7] An EV unit comprising a motor section and a reducer section that reduces the speed of the motor section, the EV unit comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a gear of the reducer section are provided; a pair of motor bearings that are interposed between the housing and the shaft on both axial sides of the motor rotor and support the shaft; and a pair of reducer bearings that are interposed between the housing and the shaft on both axial sides of the gear and support the shaft, wherein the shaft is electrically connected to the housing at a position opposite to the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the gear side; and both of the pair of motor bearings are electrically insulating bearings, and both of the pair of reducer bearings are electrically conductive bearings.

[0013] [8] An EV unit comprising a motor section and a reducer section that reduces the speed of the motor section, the EV unit comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a gear of the reducer section are provided; a pair of motor bearings interposed between the housing and the shaft on both axial sides of the motor rotor and supporting the shaft; and a pair of reducer bearings interposed between the housing and the shaft on both axial sides of the gear and supporting the shaft, wherein the shaft is electrically connected to the housing at a position opposite to the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the gear side; a second motor bearing that is the other of the pair of motor bearings is an insulating bearing that is electrically insulating; and the first motor bearing and the pair of reducer bearings are all conductive bearings that are electrically conductive.

[0014] [9] The EV unit according to any one of [1] to [8], wherein the insulating bearing has an inner ring fitted on the shaft, an outer ring fitted in the housing, and rolling elements that roll between the inner ring and the outer ring, and at least one of the inner ring, the outer ring, and the rolling elements is electrically insulating.

[0015] According to the present disclosure, it is possible to provide an EV unit that effectively suppresses electrolytic corrosion of bearings by taking the minimum necessary measures.

[0016] 1A and 1B are cross-sectional views showing an EV unit according to a first embodiment. (a) and (b) are cross-sectional views showing examples of insulating bearings. (a) is a cross-sectional view showing a circulating current that can be generated in the EV unit due to a first cause of electrolytic corrosion, and (b) is a cross-sectional view showing a common mode current that can be generated in the EV unit due to a second cause of electrolytic corrosion. (a) and (b) are cross-sectional views showing current that can be generated in the EV unit. (a) is a cross-sectional view showing an EV unit in which a conductor is provided at the left end of the shaft, and (b) is a cross-sectional view showing the right end of the shaft. (a) is a cross-sectional view showing an EV unit according to a second embodiment. (b) is a cross-sectional view showing an EV unit according to a third embodiment. (c) is a cross-sectional view showing an EV unit according to a fourth embodiment. (d) is a cross-sectional view showing an EV unit according to a fifth embodiment. (e) is a cross-sectional view showing an EV unit according to a sixth embodiment.

[0017] First Embodiment A first embodiment of an EV unit according to the present disclosure will now be described in detail with reference to the drawings. As shown in Fig. 1 , an EV unit 1 according to this embodiment includes a motor unit 3 that serves as a power source for an EV (electric vehicle) and a speed reducer unit 5 that reduces the rotation speed of the motor unit 3, and is also referred to as an "E-axle." The EV unit 1 includes a housing 7 and a shaft 9 rotatably supported relative to the housing 7.

[0018] The housing 7 includes a motor housing 37 that is the housing of the motor unit 3, and a reducer housing 57 that is the housing of the reducer unit 5. The motor housing 37 and the reducer housing 57 are joined in the axial direction of the shaft 9. The motor housing 37 and the reducer housing 57 are both made of steel and are conductive, and are electrically connected to each other. The housing 7 is electrically grounded. In other words, the housing 7 is electrically connected to the earth 13. The motor stator 31 of the motor unit 3 is provided in the motor housing 37.

[0019] The shaft 9 extends from inside the motor housing 37 to inside the reducer housing 57. The shaft 9 includes a motor shaft 39, which is the shaft of the motor unit 3, and a reducer shaft 59, which is the shaft of the reducer unit 5. The motor shaft 39 and the reducer shaft 59 are integrally connected in the axial direction by a connection structure such as a spline connection. The motor shaft 39 and the reducer shaft 59 are both made of steel and are electrically conductive, and are electrically connected to each other.

[0020] The motor shaft 39 is provided with the motor rotor 33 of the motor section 3. The motor rotor 33 is housed in the motor housing 37 and is surrounded by the motor stator 31. The motor stator 31 and the motor rotor 33 together form the motor 35. The reducer shaft 59 is provided with a gear 53 of the reducer section 5. The gear 53 is housed in the reducer housing 57. The reducer housing 57 also houses the output shaft of the reducer section 5 and a driven gear provided on the output shaft, and the gear 53 meshes with the driven gear. The output shaft and driven gear are not shown in the figure.

[0021] In the motor 35, the motor stator 31 has a coil (not shown) that generates a magnetic field within the motor housing 37 by current supplied from the EV's power supply (not shown). The motor rotor 33 has a permanent magnet (not shown) that receives a circumferential force from the magnetic field. Cooperation between the motor stator 31 and the motor rotor 33 generates a driving force that rotates the motor shaft 39. The rotational drive of the motor 35 is controlled, for example, by an inverter (not shown) included in the power supply. When the motor shaft 39 rotates in this manner, the reducer shaft 59 and gear 53 also rotate, and the driving force is transmitted to the output shaft of the reducer unit 5 at a predetermined reduction ratio via the driven gear.

[0022] As described above, the motor unit 3 includes the motor housing 37 in which the motor stator 31 is provided, and the motor shaft 39 in which the motor rotor 33 is provided. The reducer unit 5 also includes the reducer housing 57 electrically connected to the motor housing 37, and the reducer shaft 59 connected to the motor shaft 39.

[0023] The motor section 3 has a pair of motor bearings BM, BM that support the motor shaft 39 on either axial side of the motor rotor 33. The motor bearing BM is a rolling bearing such as a ball bearing or a roller bearing. The motor bearing BM is interposed between the motor housing 37 and the motor shaft 39. That is, the motor bearing BM has an outer ring 43 fitted into the motor housing 37, an inner ring 42 fitted onto the motor shaft 39, and rolling elements 44 that roll between the outer ring 43 and the inner ring 42. In the following description, when distinguishing between the two motor bearings BM, BM, the one located on the gear 53 side will be referred to as the "motor bearing BM1" and the other as the "motor bearing BM2."

[0024] The reducer unit 5 has a pair of reducer bearings BD, BD that support the reducer shaft 59 on both axial sides of the gear 53. The configuration and installation structure of the reducer bearing BD are similar to those of the motor bearing BM. That is, the reducer bearing BD is interposed between the reducer housing 57 and the reducer shaft 59, and has an outer ring 43 fitted into the reducer housing 57, an inner ring 42 fitted into the reducer shaft 59, and rolling elements 44 that roll between the outer ring 43 and the inner ring 42. In the following description, when distinguishing between the two reducer bearings BD, BD, one located on the motor rotor 33 side will be referred to as the "reducer bearing BD2" and the other as the "reducer bearing BD1."

[0025] In an EV unit 1 configured as described above, measures to prevent electrolytic corrosion of the motor bearing BM and the reducer bearing BD are necessary. Measures to prevent electrolytic corrosion include using electrically insulating bearings for the motor bearing BM and the reducer bearing BD, or, for example, grounding the shaft 9. A possible structure for grounding the shaft 9 is to electrically connect the shaft 9 to the housing 7 via a conductor 11 (e.g., a carbon brush).

[0026] Hereinafter, the above-described electrically insulating bearing will be simply referred to as an "insulating bearing", and the insulating bearing will be designated with the reference number "21" in the drawings. In each drawing, the insulating bearing 21 is shaded. In contrast, a normal bearing has an inner ring 42, an outer ring 43, and rolling elements 44 made of steel, and is therefore electrically conductive. Hereinafter, such an electrically conductive normal bearing will be referred to as an "electrically conductive bearing", and the electrically conductive bearing will be designated with the reference number "22" in the drawings.

[0027] In the insulating bearing 21, at least one of the inner ring 42, outer ring 43, and rolling elements 44 is electrically insulating. Note that, to avoid increasing the manufacturing cost of the insulating bearing 21, only one of the inner ring 42, outer ring 43, and rolling elements 44 may be electrically insulating. As shown in FIG. 2( a), an example of an electrically insulating inner ring 42 has an inner ring body 42a made of ordinary steel and an electrically insulating layer 42b provided on the inner circumferential surface of the inner ring body 42a. As shown in FIG. 2( b), an example of an electrically insulating outer ring 43 has an outer ring body 43a made of ordinary steel and an electrically insulating layer 43b provided on the outer circumferential surface of the outer ring body 43a. The electrically insulating layers 42b, 43b are formed on the inner circumferential surface of the inner ring body 42a or the outer circumferential surface of the outer ring body 43a by, for example, ceramic spraying, resin molding, or sintered film formation. An example of the electrically insulating rolling elements 44 is a rolling element made of ceramic.

[0028] Here, simply replacing all bearings in the EV unit 1 with insulating bearings 21 or providing conductors 11 at various locations on the shaft 9 could result in excessive electrolytic corrosion countermeasures. Insulating bearings 21 that have been subjected to electrical insulation treatment are more expensive than conductive bearings 22 that do not require such treatment. In addition, installing the conductors 11 also incurs costs. Therefore, in order to reduce the manufacturing cost of the EV unit 1, it is desirable to keep the number of electrolytic corrosion countermeasure elements, such as insulating bearings 21 and conductors 11, to a minimum necessary. Therefore, in the EV unit 1 of this embodiment, the minimum necessary and efficient electrolytic corrosion countermeasures are implemented.

[0029] When examining countermeasures against electrolytic corrosion required for the EV unit 1, it is necessary to consider two causes of electrolytic corrosion (a first cause and a second cause) that can occur in the EV unit 1. In the following explanation, terms that express the concept of left and right, such as "right side / left side" and "right-facing / left-facing," are used to correspond to the left and right sides in Figure 1. Furthermore, the portion of the motor shaft 39 to the left of the motor rotor 33 (the side closest to the gear 53) is referred to as the motor shaft left portion 39a, and the portion to the right of the motor rotor 33 (the opposite side to the gear 53) is referred to as the motor shaft right portion 39b.

[0030] Of the two causes of electrolytic corrosion, the first is a potential difference inside the motor shaft 39 caused by magnetic imbalance in the motor 35. That is, magnetic imbalance in the motor 35 causes a potential difference between the left motor shaft portion 39a and the right motor shaft portion 39b. If no measures are taken to prevent electrolytic corrosion, this potential difference will cause a circulating current i1 to flow in the following order: motor shaft 39, motor bearing BM1, motor housing 37, motor bearing BM2, and motor shaft 39, as shown in FIG. 3(a), for example. In other words, in this case, a current will flow through the motor bearings BM1 and BM2, potentially causing electrolytic corrosion.

[0031] The second of the two causes of electrolytic corrosion is the common-mode voltage generated by inverter control of the motor 35. Parts of this common-mode voltage are applied in parallel to the motor shaft 39 at positions on both the left and right sides of the motor rotor 33. At this time, the left and right motor shaft portions 39a and 39b are at approximately the same potential. With this voltage, if no countermeasures against electrolytic corrosion are taken, a current i2 will flow from the motor shaft 39 through the motor bearings BM1 and BM2 and the reducer bearings BD1 and BD2 to the housing 7, as shown in FIG. 3( b), for example. In other words, a current will flow through the motor bearings BM1 and BM2 and the reducer bearings BD1 and BD2, potentially causing electrolytic corrosion.

[0032] Next, the minimum necessary countermeasures against electrolytic corrosion of the motor bearing BM and the reducer bearing BD, taking into consideration the first and second factors described above, will be described.

[0033] In order to avoid the circulating current caused by the first factor above (see FIG. 3(a)), it is possible to consider using the insulating bearing 21 for at least one of the motor bearing BM1 (first motor bearing) and the motor bearing BM2 (second motor bearing). Here, if only the motor bearing BM1 were used as the insulating bearing 21 as shown in FIG. 4(a), a circulating current i3 would be generated that would flow, for example, through the shaft 9, reducer bearing BD2, housing 7, motor bearing BM2, and shaft 9 in that order. In order to avoid this circulating current i3, it is necessary to use at least the motor bearing BM2 as the insulating bearing 21.

[0034] Furthermore, in order to avoid current flowing through the motor bearings BM1 and BM2 due to the second factor described above, it is necessary to use the motor bearing BM1 as an insulating bearing 21 as well. That is, as shown in FIG. 4( b ), it is necessary to use both motor bearings BM1 and BM2 as insulating bearings 21. Furthermore, even if both motor bearings BM1 and BM2 are insulating bearings 21, the potential of the motor shaft 39 due to the second factor will cause a current i4 to flow from the shaft 9 through the reducer bearings BD1 and BD2 to the housing 7. That is, there is a possibility that a current will flow through the reducer bearings BD1 and BD2, causing electrolytic corrosion in the reducer bearings BD1 and BD2.

[0035] Therefore, to prevent current from flowing through the reducer bearings BD1 and BD2, it is necessary to provide a conductor 11 that electrically connects the shaft 9 and the housing 7, as shown in FIG. 5( a). The conductor 11 electrically connects the shaft 9 and the housing 7 via a route other than the route passing through the motor bearing BM or the reducer bearing BD. If the conductor 11 were provided, for example, at the right end of the shaft 9 as shown in FIG. 5( b), a circulating current i5 would be generated due to the first factor, flowing in the following order: shaft 9, reducer bearing BD2, housing 7, conductor 11, and shaft 9. Therefore, to prevent this circulating current i5, the conductor 11 is positioned at least to the left of the motor bearing BM1. As a specific example, as shown in FIG. 5( a), the conductor 11 is positioned at the left end of the shaft 9, further to the left of the reducer bearing BD1, and electrically connects the shaft 9 and the housing 7 at this position.

[0036] To summarize the above, as shown in Fig. 1, the EV unit 1 of this embodiment has the following configurations (1A) and (2A) as countermeasures against electrolytic corrosion. Furthermore, since the configurations (1A) and (2A) are sufficient as countermeasures against electrolytic corrosion, there is no need to employ any further insulating bearings 21. Therefore, in order to avoid an increase in manufacturing costs, the EV unit 1 of this embodiment further has the following configuration (3A).

[0037] (1A) At a position to the left of motor bearing BM1, shaft 9 is electrically connected to housing 7 by conductor 11. (2A) Motor bearings BM1 and BM2 are both insulating bearings 21. (3A) Reducer bearings BD1 and BD2 are both ordinary conductive bearings 22.

[0038] Furthermore, there is no need to provide any further electrical connection points between the shaft 9 and the housing 7. Therefore, in the EV unit 1 of this embodiment, the only electrical connection point between the shaft 9 and the housing 7 via the conductor 11 is provided at the above-mentioned single point (1A). With this EV unit 1, electrolytic corrosion of the motor bearing BM and the reducer bearing BD can be efficiently suppressed with the minimum necessary measures.

[0039] Second Embodiment Next, a second embodiment of an EV unit according to the present disclosure will be described in detail. Differences from the first embodiment will be mainly described below. Components that are the same as or equivalent to those in the first embodiment are designated by the same reference numerals in the drawings, and redundant description will be omitted. The EV unit 201 of this embodiment shown in FIG. 6 is particularly specialized for suppressing electrolytic corrosion caused by the first factor described above. The EV unit 201 is used under conditions where, for example, the first factor of electrolytic corrosion is significantly greater than the second factor, and the second factor can be ignored.

[0040] In the EV unit 201, the motor bearing BM2 is an insulating bearing 21. This prevents the circulating current caused by the first factor as shown in FIG. 3A. In addition, a conductor 11 is provided to the left of the motor bearing BM1, electrically connecting the shaft 9 and the housing 7. This reduces the potential difference in the shaft 9 caused by the first factor, preventing current from flowing through the motor bearing BM1 and the reducer bearings BD1 and BD2. As a specific example, the conductor 11 is disposed at the left end of the shaft 9, further to the left of the reducer bearing BD1, and electrically connects the shaft 9 and the housing 7 at this position.

[0041] To summarize the above, the EV unit 201 of this embodiment has the following configurations (1B) and (2B) as countermeasures against electrolytic corrosion. Furthermore, since the configurations (1B) and (2B) are sufficient as countermeasures against electrolytic corrosion against the first cause, there is no need to employ any further insulating bearings 21. Therefore, in order to avoid an increase in manufacturing costs, the EV unit 201 of this embodiment further has the following configuration (3B).

[0042] (1B) At a position to the left of motor bearing BM1, shaft 9 is electrically connected to housing 7 by conductor 11. (2B) Motor bearing BM2 is an insulating bearing 21. (3B) Motor bearing BM1 and reducer bearings BD1 and BD2 are all ordinary conductive bearings 22.

[0043] Furthermore, there is no need to provide any further electrical connection points between the shaft 9 and the housing 7. Therefore, in the EV unit 201 of this embodiment, the electrical connection point between the shaft 9 and the housing 7 via the conductor 11 is provided at only one point (1B) above. With this EV unit 201, electrolytic corrosion of the motor bearing BM and the reducer bearing BD due to the first cause can be efficiently suppressed with the minimum necessary measures.

[0044] Third Embodiment Next, a third embodiment of an EV unit according to the present disclosure will be described in detail. Differences from the first embodiment will be mainly described below. Components that are the same as or equivalent to those in the first embodiment are designated by the same reference numerals in the drawings, and redundant description will be omitted. As shown in FIG. 7 , an EV unit 301 of this embodiment is the EV unit 1 ( FIG. 1 ) of the first embodiment from which the reducer bearing BD2 has been omitted.

[0045] The EV unit 301 of this embodiment has the following configurations (1C), (2C), and (3C). (1C) The shaft 9 is electrically connected to the housing 7 by a conductor 11 at a position to the left of the motor bearing BM1. (2C) Both the motor bearings BM1 and BM2 are insulating bearings 21. (3C) The reducer bearing BD1 is a normal conductive bearing 22.

[0046] With this type of EV unit 301, electrolytic corrosion of the motor bearing BM and the reducer bearing BD can be efficiently suppressed using the minimum necessary measures, based on the same principle as with the EV unit 1 of the first embodiment.

[0047] Fourth Embodiment Next, a fourth embodiment of an EV unit according to the present disclosure will be described in detail. Differences from the second embodiment will be mainly described below. Components that are the same as or equivalent to those in the second embodiment are designated by the same reference numerals in the drawings, and redundant description will be omitted. As shown in FIG. 8 , the EV unit 401 of this embodiment is the EV unit 201 of the second embodiment ( FIG. 6 ) from which the reducer bearing BD2 has been omitted. Like the EV unit 201 of the second embodiment, the EV unit 401 of this embodiment is particularly specialized for suppressing electrolytic corrosion due to the first factor described above.

[0048] The EV unit 401 of this embodiment has the following configurations (1D), (2D), and (3D). (1D) The shaft 9 is electrically connected to the housing 7 by a conductor 11 at a position to the left of the motor bearing BM1. (2D) The motor bearing BM2 is an insulating bearing 21. (3D) The motor bearing BM1 and the reducer bearing BD1 are ordinary conductive bearings 22.

[0049] With this type of EV unit 401, the electrolytic corrosion of the motor bearing BM and the reducer bearing BD caused by the first factor can be efficiently suppressed by taking the minimum necessary measures, using the same principle as the EV unit 201 of the second embodiment.

[0050] Fifth Embodiment Next, a fifth embodiment of an EV unit according to the present disclosure will be described in detail. Differences from the third embodiment will be mainly described below. Components that are the same or equivalent to those in the third embodiment are designated by the same reference numerals in the drawings, and redundant description will be omitted. As shown in FIG. 9 , an EV unit 501 of this embodiment includes a planetary gear mechanism 54 instead of the gear 53 of the EV unit 301 ( FIG. 7 ) of the third embodiment. Furthermore, a reduction gear shaft 59 of the shafts 9 includes an input shaft 59 b and an output shaft 59 a that are coaxially arranged with the planetary gear mechanism 54 interposed therebetween in the axial direction. The input shaft 59 b and the output shaft 59 a are electrically connected via the planetary gear mechanism 54. That is, the reduction gear shaft 59 of this embodiment includes the input shaft 59 b and the output shaft 59 a that are electrically connected to each other.

[0051] The planetary gear mechanism 54 is a coaxial reduction mechanism that reduces the rotation of the input shaft 59b on the motor rotor 33 side and transmits the reduced rotation to the coaxial output shaft 59a. The planetary gear mechanism 54 is a known mechanism that includes a sun gear 54a, planet gears 54b, a ring gear 54c, and a carrier 54d. The sun gear 54a is attached to the input shaft 59b, and the carrier 54d is attached to the output shaft 59a. The ring gear 54c is fixed to a reducer housing 57. A predetermined electrical insulation measure is taken between the ring gear 54c and the reducer housing 57. For example, specifically, the ring gear 54c is attached to the reducer housing 57 via a predetermined electrical insulating member. This electrically insulates the ring gear 54c from the reducer housing 57. In other words, the planetary gear mechanism 54 is electrically insulated from the reducer housing 57.

[0052] The EV unit 501 of this embodiment has the following configurations (1E), (2E), and (3E). (1E) The shaft 9 is electrically connected to the housing 7 by a conductor 11 at a position to the left of the motor bearing BM1. (2E) Both the motor bearings BM1 and BM2 are insulating bearings 21. (3E) The reducer bearing BD1 is a normal conductive bearing 22.

[0053] With this type of EV unit 501, electrolytic corrosion of the motor bearing BM and the reducer bearing BD can be efficiently suppressed by taking the minimum necessary measures, based on the same principle as with the EV unit 301 of the third embodiment.

[0054] Note that a reducer bearing BD may be added to EV unit 501, which is interposed between reducer housing 57 and input shaft 59 b and supports input shaft 59 b. That is, a reducer bearing BD may be provided on each side of planetary gear mechanism 54 in the axial direction.

[0055] Sixth Embodiment Next, a sixth embodiment of an EV unit according to the present disclosure will be described in detail. Differences from the fourth embodiment will be mainly described below. Components that are the same or equivalent to those in the fourth embodiment are designated by the same reference numerals in the drawings, and redundant description will be omitted. As shown in FIG. 10 , the EV unit 601 of this embodiment includes the planetary gear mechanism 54 described in the fifth embodiment, instead of the gear 53 of the EV unit 401 ( FIG. 8 ) of the fourth embodiment. Like the EV unit 401 of the fourth embodiment, the EV unit 601 of this embodiment is specifically designed to suppress electrolytic corrosion caused by the first factor described above.

[0056] The EV unit 601 of this embodiment has the following configurations (1F), (2F), and (3F). (1F) The shaft 9 is electrically connected to the housing 7 by a conductor 11 at a position to the left of the motor bearing BM1. (2F) The motor bearing BM2 is an insulating bearing 21. (3F) The motor bearing BM1 and the reducer bearing BD1 are ordinary conductive bearings 22.

[0057] With this type of EV unit 601, the electrolytic corrosion of the motor bearing BM and the reducer bearing BD caused by the first factor can be efficiently suppressed by taking the minimum necessary measures, based on the same principle as the EV unit 401 of the fourth embodiment.

[0058] Note that a reducer bearing BD may be added to the EV unit 601, which is interposed between the reducer housing 57 and the input shaft 59 b and supports the input shaft 59 b. That is, a reducer bearing BD may be provided on each side of the planetary gear mechanism 54 in the axial direction.

[0059] The present disclosure can be implemented in various forms, including the above-described embodiments, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, it is also possible to configure modified examples by utilizing the technical matters described in the above-described embodiments. The configurations of the respective embodiments may be used in appropriate combination.

[0060] 1,201...EV unit, 3...motor section, 5...reduction gear section, 7...housing, 9...shaft, 11...conductor, 21...insulating bearing, 22...conductive bearing, 31...motor stator, 33...motor rotor, 43...outer ring, 42...inner ring, 44...rolling element, 53...gear, BM, BM1, BM2...motor bearing, BD, BD2, BD1...reduction gear bearing.

Claims

1. An EV unit comprising a motor section and a reducer section that reduces the rotation of the motor section, comprising: an electrically grounded housing in which a motor stator of the motor section is mounted; a shaft on which a motor rotor of the motor section and a gear of the reducer section are mounted; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a reducer bearing that is interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the gear and supports the shaft, wherein the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the gear side, and both of the pair of motor bearings are electrically insulating bearings, and the reducer bearing is an electrically conductive bearing.

2. The EV unit according to claim 1, further comprising another reducer bearing interposed between the housing and the shaft at a position between the gear and the first motor bearing and supporting the shaft, wherein the another reducer bearing is an electrically conductive bearing.

3. An EV unit comprising a motor section and a reducer section that reduces the rotation of the motor section, comprising: a housing in which a motor stator of the motor section is provided and which is electrically grounded; a shaft on which a motor rotor of the motor section and a gear of the reducer section are provided; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a reducer bearing that is interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the gear and supports the shaft; wherein the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings and located on the gear side; a second motor bearing that is the other of the pair of motor bearings is an insulating bearing that is electrically insulating; and the first motor bearing and the reducer bearing are conductive bearings.

4. The EV unit according to claim 3, further comprising another reducer bearing interposed between the housing and the shaft at a position between the gear and the first motor bearing and supporting the shaft, wherein the another reducer bearing is an electrically conductive bearing.

5. An EV unit comprising a motor section and a reducer section that reduces the rotation of the motor section, comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a reduction mechanism of the reduction mechanism section are provided; a pair of motor bearings interposed between the housing and the shaft at positions on both axial sides of the motor rotor and supporting the shaft; and a reducer bearing interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the reduction mechanism and supporting the shaft, wherein the reduction mechanism is a coaxial reduction mechanism that reduces the rotation of an input shaft on the motor rotor side and transmits it to an output shaft coaxial with the input shaft, the shaft having the input shaft and the output shaft connected to the reduction mechanism, and the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing, which is one of the pair of motor bearings located on the reduction mechanism side, both of the pair of motor bearings being electrically insulating insulating bearings, and the reducer bearing being an electrically conductive bearing.

6. An EV unit comprising a motor section and a reducer section that reduces the rotation of the motor section, comprising: an electrically grounded housing in which a motor stator of the motor section is provided; a shaft in which a motor rotor of the motor section and a reduction mechanism of the reduction mechanism section are provided; a pair of motor bearings that are interposed between the housing and the shaft at positions on both axial sides of the motor rotor and support the shaft; and a reduction gear bearing that is interposed between the housing and the shaft at a position opposite the motor rotor as viewed from the reduction mechanism and supports the shaft; the reduction mechanism is a coaxial reduction mechanism that reduces the rotation of an input shaft on the motor rotor side and transmits it to an output shaft that is coaxial with the input shaft, the shaft having the input shaft and the output shaft connected to the reduction mechanism; the shaft is electrically connected to the housing at a position opposite the motor rotor as viewed from a first motor bearing that is one of the pair of motor bearings located on the reduction mechanism side; and the other of the pair of motor bearings, a second motor bearing, is an electrically insulating bearing. The EV unit, wherein the first motor bearing and the reducer bearing are electrically conductive bearings.

7. An EV unit according to any one of claims 1 to 6, wherein the insulating bearing has an inner ring fitted on the shaft, an outer ring fitted in the housing, and rolling elements that roll between the inner ring and the outer ring, and at least one of the inner ring, the outer ring, and the rolling elements is electrically insulating.

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