Conducting unit, bearing electric corrosion preventing structure, and electric motor

Abstract

To provide a conducting unit that electrically connects a shaft and a housing to simplify the configuration thereof.SOLUTION: A conducting unit is provided with a conductive brush 2 that extends in a direction surrounding a shaft 12. The conductive brash 2 comprises: conductive fibers 5 that contact at least the shaft 12; conductive fibers 5 that contact at least a housing 11; and a plurality of conductive wire portions 4b, 4b that are entangled to hold the conductive fibers 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric current-carrying unit that electrically connects a shaft to a housing surrounding the shaft, and to a bearing electric corrosion structure and an electric motor that use the same. [Background technology]

[0002] For example, the shaft of the rotor of the electric motor is rotatably supported by rolling bearings such as ball bearings. In recent years, electric motors have been driven by inverter control to operate efficiently. In particular, in the case of electric motors mounted on e-axle units in which the electric motor, inverter, and reducer are integrated, it is necessary to use as small an electric motor as possible efficiently over a wide range due to the ease of mounting, and more precise control is performed.

[0003] Conventionally, shaft voltages and currents are generated on the shaft, which can cause radio noise and electric discharges between the rolling elements and raceways of the rolling bearings that support the shaft, resulting in electrolytic corrosion of the rolling elements. As a measure to prevent these problems, the shaft is earthed via a current path that does not pass through the rolling bearings that support the shaft. To achieve this earthing, the housing is electrically connected to the earth, and an electric current unit is installed between the housing and the shaft.

[0004] The current-carrying unit disclosed in Patent Document 1 has a pair of conductive annular members facing each other in the axial direction, a cup or the like that holds the outer periphery of the conductive annular members, and a number of conductive fibers fixed between the conductive annular members. Each conductive fiber has a base end sandwiched between the conductive annular members and a tip end that protrudes radially inward from between the conductive annular members and extends into the hollow. The many conductive fibers are distributed all around the circumference along the circumferential direction. As a specific means for fixing the base end of each conductive fiber to each conductive annular member, a conductive adhesive and an adhesive tape have been proposed. When the cup of the current-carrying unit is fitted into the inner circumference of the housing of the electric motor and the tip ends of the many conductive fibers are brought into contact with the shaft, the housing and the shaft can be electrically connected by the current-carrying unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 8,199,453 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when an adhesive or adhesive tape is used as a means for fixing the base end of each conductive fiber between a pair of conductive annular members as in the current-carrying unit of Patent Document 1, it becomes important to prevent separation of the pair of conductive annular members in order to prevent peeling of the conductive annular members. If a structure is used in which the outer periphery of the pair of conductive annular members is restrained by crimping a cup, it is possible to prevent separation of the pair of conductive annular members, but there is a problem in that the structure becomes complicated in that parts for restraining and a crimping process are required.

[0007] In view of the above background, an object of the present invention is to simplify the configuration of an energizing unit that electrically connects a shaft and a housing. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention adopts configuration 1, which is an electric current-carrying unit that electrically connects a shaft and a housing surrounding the shaft, comprising a conductive brush extending in a direction surrounding the shaft, the conductive brush having conductive fibers in contact with at least the shaft, conductive fibers in contact with at least the housing, and a plurality of conductive wire portions entangled in a state that holds the conductive fibers.

[0009] According to the above-mentioned configuration 1, since the conductive fibers are held by intertwining the multiple conductive wires, it is possible to eliminate the need for adhesion or restraint of other members to prevent separation of the conductive wires and the conductive fibers. Furthermore, since at least the conductive fibers in contact with the shaft, the conductive fibers in contact with at least the housing, and the multiple conductive wires that hold them form a continuous conductive path, the shaft and the housing can be electrically connected via the conductive brush. In this way, the configuration of the current-carrying unit that electrically connects the shaft and the housing can be simplified.

[0010] In the above configuration 1, configuration 2 can be adopted in which the conductive fibers are arranged so as to surround a range exceeding half the circumference of the shaft.

[0011] According to the above configuration 2, the conductive brush can be easily arranged around the shaft.

[0012] In the above configuration 1 or 2, a configuration 3 can be adopted in which the two conductive wire portions are twisted together so as to form alternating intersecting and non-intersecting portions in a direction surrounding the axis, and two or more conductive fibers are bundled together at each non-intersecting portion.

[0013] According to the above configuration 3, the conductive fibers are bundled and held between each non-intersecting portion of the two twisted conductive wires, so that the conductive brush is arranged over a range of more than half the circumference of the shaft while extending in various radial directions from the center of the twisted conductive wires. This makes it possible to increase the number of conductive fibers that come into contact with the shaft or housing, while eliminating the need for strict dimensional control, as is required with press-fitting, to position the conductive brush relative to the shaft or housing.

[0014] In any one of the above configurations 1 to 3, a configuration 4 can be adopted in which the conductive fiber is made of carbon fiber or conductive nylon.

[0015] In any one of the above configurations 1 to 4, a configuration 5 can be adopted in which the conductive line portion is made of a metal wire.

[0016] By adopting configuration 6, which is a bearing electrolytic corrosion prevention structure comprising an electrolytic unit according to any one of configurations 1 to 5 above and a rolling bearing supporting the shaft relative to the housing, wherein the impedance of the conductive brush is lower than the impedance of the rolling bearing, it is possible to electrically connect the shaft and the housing with a simple electrolytic unit and prevent electrolytic corrosion of the rolling bearing, etc.

[0017] Configuration 7 can be adopted, which is an electric motor provided with the bearing electrolytic corrosion prevention structure according to configuration 6 above. Effect of the Invention

[0018] As described above, by employing the above configuration 1, the present invention can simplify the configuration of the current-carrying unit that electrically connects the shaft and the housing. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a vertical cross-sectional view showing an electric motor equipped with a current-carrying unit and a bearing electrolytic corrosion prevention structure according to an embodiment of the present invention; [Diagram 2] Partial cross-sectional view of the motor in FIG. [Diagram 3] FIG. 2 is a partial perspective view showing a conductive brush of the current-carrying unit shown in FIG. [Figure 4] Schematic diagram showing the manufacturing process of the conductive brush of FIG. [Diagram 5] FIG. 13 is a partial cross-sectional view showing a modified example of the conductive brush according to the embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A motor including a current-carrying unit and a bearing electrolytic corrosion prevention structure according to a first embodiment of the present invention will be described with reference to the accompanying drawings, in which: FIG.

[0021] The current-carrying unit 1 shown in FIG. 1 is configured to be attached to a housing 11 of an electric motor 10 so as to electrically connect a shaft 12 of the electric motor 10 and the housing 11. As shown in FIG.

[0022] The electric motor 10 includes a stator 13 accommodated in a housing 11, a rotor 14 attached to a shaft 12, and rolling bearings 15, 16 that support the shaft 12 relative to the housing 11, and is driven and controlled by an inverter (not shown, same applies below). The electric motor 10 is, for example, an in-vehicle electric motor that serves as a vehicle drive source for an e-axle unit or the like.

[0023] Hereinafter, the direction along the central axis of shaft 12 (not shown, same below) will be referred to as the "axial direction", the direction perpendicular to that central axis will be referred to as the "radial direction", and the circumferential direction going around the central axis will be referred to as the "circumferential direction".

[0024] The shaft 12 serves as the central axis of rotation of the rotor 14, and rotates together with the rotor 14 due to torque generated by the electromagnetic action of the stator 13 and the rotor 14 working together.

[0025] The housing 11 is a cover that radially surrounds the shaft 12. Since the housing 11 is the motor case of this electric motor, it is configured to radially surround and cover the shaft 12, the rolling bearings 15 and 16 for supporting the shaft, the stator 13, and the rotor 14, and to radially support the rolling bearings 15 and 16 for supporting the shaft.

[0026] The shaft 12 and the housing 11 are each electrically conductive and generally made of one or more metal members.

[0027] The housing 11 is a part that serves as a reference potential with respect to the potential at the shaft 12. The housing 11 is generally electrically connected to the body of the machine, the ground, or the like, to which the charge is to be released. The housing 11 may further accommodate mechanical elements that are driven by the shaft 12, in addition to the rolling bearings 15, 16, the rotor 14, and the stator 13. For example, in the case of an e-axle, the housing may be configured to also accommodate a reducer that is connected to the shaft, and this may be electrically connected to the vehicle body (body earth circuit).

[0028] Each of the rolling bearings 15, 16 includes an inner ring fitted onto the shaft 12, an outer ring fitted onto the inner periphery of the housing 11, a plurality of rolling elements arranged between the raceway surfaces of the inner and outer rings, and a cage for holding the rolling elements. Generally, ball bearings are used as each of the rolling bearings 15, 16.

[0029] The current-carrying unit 1 is composed of a conductive brush 2 extending in a direction surrounding a shaft 12 , and a case 3 for positioning the conductive brush 2 with respect to a housing 11 and the shaft 12 .

[0030] The conductive brush 2 is composed of a conductive core 4 that runs around a shaft 12 and a large number of conductive fibers 5 held by the conductive core 4, as shown in FIGS.

[0031] The conductive core 4 is composed of a conductive folded line portion 4a formed by folding a single metal wire in two, two conductive line portions 4b, 4b extending from the conductive folded line portion 4a and twisted together, and two conductive connection portions 4c, 4c continuing from the conductive line portion 4b to the conductive folded line portion 4a.

[0032] The two conductive line portions 4b, 4b are twisted together so as to form intersecting and non-intersecting portions alternately in the circumferential direction.

[0033] The two conductive connection parts 4c, 4c are connected to the conductive folded line part 4a, so that the conductive brush 2 is maintained in a ring shape going around the shaft 12. The connection between each of the conductive connection parts 4c, 4c and the conductive folded line part 4a can be easily realized by forming each of the conductive connection parts 4c, 4c into a hook shape that hooks onto the conductive folded line part 4a in the circumferential direction.

[0034] The two conductive wire portions 4b, 4b extend in a direction surrounding the shaft 12. This direction is set in the circumferential direction, and the two conductive wire portions 4b, 4b extend over an angular range greater than 180° in the circumferential direction. As a result, the conductive core portion 4 extends in an arc shape along the circumferential direction and goes substantially around the shaft 12.

[0035] The intermediate portion of the conductive fiber 5 is located between the non-intersecting portions of the two conductive line portions 4b, 4b. Each non-intersecting portion of the two conductive line portions 4b, 4b bundles a large number of conductive fibers 5. Both ends of the conductive fiber 5 extend in the radial direction from the conductive core portion 4 consisting of the two conductive line portions 4b, 4b at the center, and are arranged so as to surround the axis 12 over approximately the same circumferential range as the two conductive line portions 4b, 4b.

[0036] As the two conductive wire portions 4b, 4b are twisted at a predetermined pitch in the circumferential direction, the general protruding direction in which the bundles of conductive fibers 5 protrude from the conductive core portion 4 changes at a predetermined pitch with respect to the bundles of conductive fibers 5 adjacent in the circumferential direction. As a result, the conductive brush 2 is an annular body having a large number of bundles of conductive fibers 5 protruding at least on one axial side and the opposite other side with respect to the two conductive wire portions 4b, 4b, and a large number of bundles of conductive fibers 5 protruding at least radially inward and outward with respect to the two conductive wire portions 4b, 4b.

[0037] The conductive core 4 and the conductive fibers 5 may be made of any material having electrical conductivity. For example, the metal wire forming the conductive line portion 4b etc. may be wire made of metal such as iron or copper. Also, the conductive fibers 5 may be carbon fiber or conductive nylon. The term "conductive" refers to a material having a volume resistivity of 106 The volume resistivity is measured in accordance with the average cross-sectional area method specified in JIS H 0505.

[0038] The conductive brush 2 as described above can be easily manufactured, for example, by the following process: That is, as shown in Fig. 4, a metal wire is folded in two, and the two folded pieces are twisted together once near the folded ends to prepare a workpiece having a loop (a portion to be the conductive folded line portion 4a, and for convenience of explanation, designated by reference number 4a in the figure), a parallel folded middle portion (a portion to be the two conductive line portions 4b, and for convenience of explanation, designated by reference number 4b in the figure), and two folded tip portions (a portion to be the two conductive connection portions 4c, and for convenience of explanation, designated by reference number 4c in the figure), and the loop portion 4a is hung on the hook R of a rotating body, and the folded tip portions 4c, 4c are clamped by a fixed chuck C, and linear conductive fibers 5 are filled between the folded middle portions 4b, 4b in a densely aligned state. As a result, each conductive fiber 5 is set in a state where it is sandwiched between the folded intermediate portions 4b, 4b at the center of its fiber length. In this set state, the hook R of the rotating body is rotated in one direction to twist the folded intermediate portions 4b, 4b together. As a result, the folded intermediate portions 4b, 4b form twisted intersections P1, P2 at a constant pitch, and non-intersections are formed between adjacent intersections P1, P2, and the conductive fibers 5 are partitioned between adjacent intersections P1, P2 and bound into a bundle. When the hook R is rotated a predetermined number of times, a linear conductive brush is obtained, which has the conductive bent line portion 4a and two conductive line portions 4b, 4b twisted and entangled in a state of holding the bundle of conductive fibers 5. Then, although not shown in the figure, the folded tip portions 4c, 4c are bent into a hook shape to create two conductive connection portions 4c, 4c, the straight conductive brush is rolled into a ring shape, and the two conductive connection portions 4c, 4c are joined to the conductive folded line portion 4a, completing the conductive brush 2 shown in Figures 1 to 3.

[0039] 1, the conductive brush 2 can be fitted around the shaft 12 at its inner periphery, with the ends of the numerous conductive fibers 5 protruding radially inward being brought into contact with the shaft 12, and the ends of the numerous conductive fibers 5 protruding on one axial side being brought into contact with the outer side surface of the housing 11. At this time, the conductive wire portion 4b surrounds more than half the circumference of the shaft 12, so that when fitted around the shaft 12, it can be arranged with a predetermined coaxiality with the shaft 12, and can be easily arranged around the shaft 12. Note that, although the conductive brush 2 is made into a substantially circular ring shape in the illustrated example, it is also possible to change the conductive brush to a ring shape that is divided at one point in the circumferential direction.

[0040] When the hollow cup-shaped case 3, which is inserted into the shaft 12, is coupled to the end face of the housing 11 with the conductive brush 2 fitted onto the shaft 12, the case 3 and the housing 11 are electrically connected, and the conductive brush 2 is sandwiched between the case 3 and the housing 11 in a state where it is axially pressurized, and is also sandwiched between the shaft 12 and the case 3 in a state where it is radially pressurized. As a result, the ends of the many conductive fibers 5 protruding radially outward are pushed radially inward by the inner circumference of the case 3, ensuring a state where the ends of the many conductive fibers 5 protruding radially inward are pressed against the shaft 12, and the ends of the many conductive fibers 5 protruding on the other axial side are pushed toward one axial side by the inner side surface of the case 3, ensuring a state where the ends of the many conductive fibers 5 protruding on one axial side are pressed against the end face of the housing 11. As a result, the conductive fibers 5 in contact with at least the shaft 12, the conductive fibers 5 in contact with at least the housing 11, and the two conductive line portions 4b, 4b that hold them form a continuous conductive path, so that the shaft 12 and the housing 11 can be reliably electrically connected via the conductive brush 2. This provides the electric motor 10 equipped with a bearing electrolytic corrosion prevention structure that can prevent electrolytic corrosion of the rolling bearings 15, 16.

[0041] The distance between the bearing 15 and the current-carrying unit 1 is preferably within 50 mm, and more preferably within 30 mm.

[0042] In the above-mentioned bearing electrolytic corrosion prevention structure provided in the electric motor 10, the impedance of the conductive brush 2 is lower than the impedance of each of the rolling bearings 15, 16. Therefore, the shaft current generated in the shaft 12 during operation of the electric motor 10 flows more easily to the conductive brush 2 than to the rolling bearings 15, 16, and electrolytic corrosion of the rolling bearings 15, 16 can be effectively prevented. The impedance is measured by the automatic balancing bridge method using an LCR meter or an impedance analyzer. The impedance of the conductive brush 2 is measured using the conductive fiber 5 in contact with the shaft 12 and the conductive fiber 5 in contact with the housing 11 as electrodes, and the impedance of the rolling bearings 15, 16 is measured in the state of the rolling bearing alone, using the inner ring and the outer ring, which are components, as electrode terminals.

[0043] In order to increase the number of conductive paths that run from shaft 12 through conductive brush 2 to housing 11 without passing through rolling bearings 15 and 16, it is preferable that case 3 is also made of a conductive material.

[0044] As described above, the current-carrying unit 1 according to the first embodiment electrically connects the shaft 12 and the housing 11 surrounding the shaft 12, and in particular includes the conductive brush 2 extending in a direction surrounding the shaft 12. The conductive brush 2 has at least the conductive fiber 5 in contact with the shaft 12, the conductive fiber 5 in contact with the housing 11, and a plurality of conductive wires 4b, 4b entangled in a state in which the conductive fibers 5 are held, thereby realizing simplification that does not require adhesion or restraint of other members to prevent separation of the conductive wires 4b, 4b and the conductive fiber 5, and further, the conductive fiber 5 in contact with at least the shaft 12, the conductive fiber 5 in contact with the housing 11, and the plurality of conductive wires 4b, 4b holding them form a series of conductive paths, so that the shaft 12 and the housing 11 can be electrically connected via the conductive brush 2. In this way, the current-carrying unit 1 can simplify the configuration of the current-carrying unit that electrically connects the shaft 12 and the housing 11. Although it may in principle be possible to hold the conductive fiber in contact with the shaft and the housing using a single conductive wire portion, this is thought to make assembly difficult.

[0045] Furthermore, since the conductive fibers 5 of the current-carrying unit 1 are arranged so as to surround an area exceeding half the circumference of the shaft 12, the conductive brush 2 can be easily arranged around the shaft 12.

[0046] In addition, the current-carrying unit 1 has two conductive wire portions 4b, 4b twisted together in a direction surrounding the shaft 12 to alternately form intersection portions P1, P2 and non-intersection portions, and two or more conductive fibers 5 are bundled together at each non-intersection portion, thereby forming a conductive brush 2 in which the conductive fibers 5 extend in various radial directions from the twisted conductive wire portions 4b, 4b at the center and are arranged over a range of more than half a circumference of the shaft 12.This allows the number of conductive fibers 5 in contact with the shaft 12 and the housing 11 to be increased, while eliminating the need for strict dimensional control, as is required for press-fitting, in order to position the conductive brush 2 relative to the shaft 12 and the housing 11.

[0047] In addition, a bearing electrolytic corrosion prevention structure is provided that includes an electrolytic unit 1 and rolling bearings 15, 16 that support the shaft 12 relative to the housing 11, and in which the impedance of the conductive brush 2 is lower than the impedance of the rolling bearings 15, 16. An electric motor 10 equipped with this bearing electrolytic corrosion prevention structure electrically connects the shaft 12 and the housing 11 with the simple electrolytic unit 1, and can prevent electrolytic corrosion and radio noise in the rolling bearings 15, 16.

[0048] In the illustrated example, the conductive brush 2 is positioned in the axial direction by sandwiching it between the case 3 and the housing 11, but there is no particular limitation on the structure for axial positioning of the conductive brush 2. For example, the conductive bent wire portion 4a of the conductive brush 2 may be fastened in the axial direction to the housing 11 with a male screw member by utilizing a hole formed by the conductive bent wire portion 4a, in which case it becomes unnecessary to sandwich the conductive brush in the axial direction between the case and the housing.

[0049] It is also possible to omit the case for positioning the conductive brush. For example, it is also possible to fit the outer periphery of the conductive brush 2 inside the housing of the motor to ensure radial contact between the shaft and the housing and the conductive fibers 5, and to screw the conductive bent line portion 4a of the conductive brush 2 to the inner end face of the housing so that the conductive brush 2 is arranged in a state of non-contact with the rolling bearings 15, 16, or to provide a restricting wall portion in the housing to prevent the conductive brush 2 from moving toward the rolling bearings 15, 16, so that the conductive brush 2 is arranged in a state of non-contact with the rolling bearings 15, 16.

[0050] In the illustrated example, the conductive brush 2 is annular, but it may be changed to a conductive brush having a linearly extending portion. For example, the cross-sectional shape of the inner circumference of a case or housing that receives the conductive brush in the radial direction may not be annular, and the conductive brush may be received in the radial direction at a portion having linear sides. In this case, as shown in FIG. 5, the conductive core 4 may be changed to a substantially rectangular ring shape having four linear sides and four corners, and the conductive fibers 5 and the shaft 12 may be brought into contact with each other at a portion of each linear side.

[0051] In addition, in the illustrated example, an example of twisting two conductive wire portions 4b, 4b together is shown as a method of intertwining the multiple conductive wire portions 4b, 4b, but the method of intertwining is not limited to this. For example, it is possible to change to a conductive brush in which three conductive wire portions are braided and each braid holds one or more conductive fibers. However, since this would make the intertwining method more complicated, it is preferable to twist two conductive fibers together.

[0052] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0053] 1 Power supply unit 2 Conductive brush 4b Conductive wire part 5. Conductive Fiber 10 Electric motor 11. Housing 12 Axis 15, 16 Rolling bearings

Claims

1. A current-carrying unit electrically connecting a shaft and a housing surrounding the shaft, A conductive brush extending in a direction surrounding the shaft is provided. An energizing unit characterized in that the conductive brush has conductive fibers that contact at least the shaft, conductive fibers that contact at least the housing, and a plurality of conductive wire portions entangled in a state that holds these conductive fibers.

2. The current-carrying unit according to claim 1 , wherein the conductive fibers are arranged so as to surround a range exceeding half the circumference of the shaft.

3. The conductive unit according to claim 1 or 2, wherein the two conductive line portions are twisted together to form alternating intersecting and non-intersecting portions in a direction surrounding the axis, and each non-intersecting portion bundles two or more conductive fibers together.

4. 3. The current-carrying unit according to claim 1, wherein the conductive fibers are made of carbon fibers or conductive nylon.

5. The current-carrying unit according to claim 1 or 2, wherein the conductive wire portion is made of a metal wire.

6. A current-carrying unit according to any one of claims 1 to 5, and a rolling bearing that supports the shaft relative to the housing, A structure for preventing electrical corrosion of a bearing, in which the impedance of the conductive brush is lower than the impedance of the rolling bearing.

7. An electric motor comprising the bearing electrolytic corrosion prevention structure according to claim 6.

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