Motor and electric power steering apparatus

A motor includes a rotor, a stator surrounding an outer side of the rotor in a radial direction and including a coil, and a bus bar of a wire electrically connected to the coil and having conductivity, wherein the stator is provided with a hole extending in an axial direction, the bus bar includes stretched portions extending in the axial direction, and each of the stretched portions is disposed in the hole.

FIELD OF THE INVENTION

The present disclosure relates to a motor and an electric power steering apparatus.

BACKGROUND

Conventionally, a wire is used as a bus bar. For example, a conventional motor has a bus bar of a wire disposed in a groove of a stator.

In the above-described motor, there is a problem that a bus bar is easily detached from a groove. When the bus bar is detached from the groove, the bus bar may not be positioned on a stator.

SUMMARY

Example embodiments of the present disclosure provide motors and electric power steering apparatuses each capable of easily performing positioning of bus bars with respect to a stator.

One aspect of an example embodiment of the present disclosure is a motor including a rotor, a stator surrounding an outer side of the rotor in a radial direction and including a coil, and a bus bar of a wire electrically connected to the coil and having conductivity, wherein the stator is provided with a hole extending in an axial direction, the bus bar includes a stretched portion extending in the axial direction, and the stretched portion is disposed in the hole.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present disclosure will be described with reference to the drawings. Further, in the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

Further, in the following description, as shown inFIG. 1, when an axial direction in which a central axis A of a rotor30, that is, a shaft31extends is a vertical direction, an opening side of a housing10is referred to as an “upper side”, and a bottom portion12side of a housing is referred to as a “lower side”. However, the vertical direction in the present specification is used for specifying the positional relationship, and does not limit the actual direction. That is, a downward direction does not necessarily mean the direction of gravity.

Further, a direction orthogonal to the central axis A of the rotor is referred to as a “radial direction”, and the radial direction is centered on the central axis A. A circumference of the central axis A of the rotor is referred to as a “circumferential direction”.

Further, in the present specification, the term “extending in the axial direction” includes a state extending in the axial direction strictly and a state extending in a direction inclined in a range of less than 45 degrees with respect to the axial direction. Similarly, in the present specification, the term “extending in the radial direction” includes a state extending in the radial direction strictly and a state extending in a direction inclined in a range of less than 45 degrees with respect to the radial direction.

Motor

A motor, which is an example embodiment of the present disclosure, will be described with reference toFIGS. 1 to 4. As shown inFIG. 1, a motor1mainly includes a housing10, a bearing holder21, bearings22and23, a rotor30, a stator100, and a bus bar40.

Housing

The housing10has a cylindrical shape with a bottom. That is, the housing10includes a cylindrical portion11and a bottom portion12. An upper part of the housing10is open. The housing10accommodates the rotor30and the stator100therein.

Bearing Holder

The bearing holder21is disposed on an upper side of the stator100in an axial direction.

Bearing

The bearings22and23rotatably support a shaft31of the rotor30. The bearing22disposed on an upper side in the axial direction is held by the bearing holder21. The bearing23disposed on a lower side in the axial direction is held by the bottom portion12of the housing10.

Rotor

The rotor30includes the shaft31, a rotor core32, and a magnet33. The shaft31extends in the axial direction along a central axis A. The shaft31is supported by a pair of bearings22and23and rotates about the central axis A.

The rotor core32is a laminated steel plate in which a plurality of electromagnetic steel plates are laminated in the axial direction. The rotor core32is fixed to the shaft31passing through a center of the rotor core32and rotates together with the shaft31. The magnet33is fixed to an outer side surface of the rotor core32and rotates together with the rotor core32and the shaft31. Thus, the rotor30in the present example embodiment is a surface permanent magnet (SPM) type. Further, the rotor30may be an interior permanent magnet (IPM) type in which the magnet33is embedded in the rotor core32.

Configuration of Stator

The stator100surrounds an outer side of the rotor30in a radial direction. As shown inFIGS. 1 and 2, the stator100includes a stator core110, insulators120, and coils130.

Stator Core

As shown inFIG. 2, in the stator core110, a plurality of electromagnetic steel plates are laminated in the axial direction. The plurality of electromagnetic steel plates are fixed by caulking or the like. Further, the stator core110may be constituted by one member.

Further, as shown inFIGS. 2 and 3, the stator core110of the present example embodiment is constituted by split cores split in a circumferential direction. The split core is one piece in which the stator core110is circumferentially split. When the split cores are used, the cores may be assembled after winding the coil wire around the split core. The configuration of the stator core is not limited to the split core and may be a straight core, a round core, or the like.

The stator core110includes core backs111and teeth112. One split core includes one core back111and one tooth112.

A plurality of core backs111have an annular shape concentric with the central axis A. The core back111includes a core back groove111athat is recessed inward in the radial direction on an outer surface in the radial direction. Each core back groove111ais located on an outer side of each tooth112in the radial direction.

The tooth112extends inward in the radial direction from an inner side surface of the core back111. The teeth112are arranged at equal intervals in the circumferential direction on the inner side surface of the core back111in the radial direction. The tooth112includes an umbrella113extending in the circumferential direction on an inner side end in the radial direction.

Insulator

The insulator120covers at least a part of the stator core110. The insulator120is attached to each tooth112. The insulator120according to the present example embodiment is constituted by a split body provided on each split core of the stator core110.

The insulator120has insulation properties and is formed of, for example, an insulating material such as an insulating resin.

As shown inFIG. 3, the insulator120includes a body portion121and a flange portion122. Each of the plurality of split bodies includes one body portion121and one flange portion122.

The body portion121covers the tooth112. The flange portion122protrudes outward in the radial direction from the body portion121. The flange portion122is located on an inner end of the core back111in the radial direction. The flange portion122extends in the axial direction and the circumferential direction.

The flange portion122is provided with a hole123extending in the axial direction. The hole123is configured such that the bus bar40may be inserted from the axial direction. When the hole123is formed in the insulator120, since the insulator120has an insulation property, the process for securing the insulation may be omitted.

In addition, since the hole123is formed in the flange portion122, the hole123is located on an outer side of the teeth112in the radial direction. Thus, the stator100having a high space factor of the coil130may be realized. Further, the hole123may be formed on an inner side of the teeth112in the radial direction.

A plurality of holes123are formed. The plurality of holes123include a hole in which the bus bar40to be described below is disposed and a hole in which the bus bar40is not disposed. The plurality of holes123have the same shape. Further, the shape of the hole123is not particularly limited, and the hole123may pass through in the axial direction or may be a recessed portion recessed in the axial direction. InFIG. 3, the hole123has a circular cross-section, but may have the same outer shape as axially stretched portions41and47.

InFIG. 2, the plurality of holes123are formed along the circumferential direction. Thus, the holes123may be positioned in the circumferential direction of the bus bar40.

In the present example embodiment, the holes123are formed in each of the split bodies. The number of holes123formed in the split body is not particularly limited, but may be two. In this case, since the processing of the holes123may be minimized, the cost may be reduced. Two holes123in the split body have the same distance from a circumferential edge of the flange portion122of the split body.

As shown inFIG. 2, the coil130is configured by winding a coil wire around the tooth112through the insulator120. The coil130is configured of a coil corresponding to any one of a U-phase, a V-phase, and a W-phase, and is disposed side by side in the circumferential direction in the order of the U-phase, the V-phase, and the W-phase. The number of coils130is twelve, which is the same as the number of teeth112. Thus, in the present example embodiment, there are four coil sets, each of which includes a U-phase coil, a V-phase coil, and a W-phase coil. Further, the connection method of the coils130is a so-called delta connection method.

Two lead wires of a first lead wire131and a second lead wire132are drawn out upward in the axial direction from each coil130. Accordingly, the total of the first lead wire131and the second lead wire132drawn out from each coil130is twenty-four.

Bus Bar

As shown inFIG. 2, the bus bar40is electrically connected to the coil130. The bus bar40shown inFIGS. 2 to 4is a neutral point bus bar. The motor1includes a plurality of neutral point bus bars, and the motor1includes four neutral point bus bars in the present example embodiment. As shown inFIGS. 2 and 3, a plurality of bus bars40are arranged side by side in the circumferential direction.

The bus bar40is a wire having conductivity. The material of the bus bar40is not particularly limited as long as it is conductive, and is, for example, a metal. The bus bar40of the present example embodiment is a coil wire (bare wire). Also, the shape of the bus bar40is not particularly limited as long as it is a wire, and may be a round wire having a circular cross-section shown inFIG. 4or a rectangular wire having a rectangular cross-section.

As shown inFIG. 4, the bus bar40includes the axially stretched portions41and47, coil connection portions42,44, and46, and circumferentially stretched portions43and45. From one end toward the other end in the circumferential direction, a first axially stretched portion41, a first coil connection portion42, a first circumferentially stretched portion43, a second coil connection portion44, a second circumferentially stretched portion45, a third coil connection portion46, and a second axially stretched portion47are located in this order. The bus bar40, which is composed of the first axially stretched portion41, the first coil connection portion42, the first circumferentially stretched portion43, the second coil connection portion44, the second circumferentially stretched portion45, the third coil connection portion46, and the second axially stretched portion47, is formed by bending one rod-shaped member.

Specifically, the first axially stretched portion41extends downward in the axial direction. The first coil connection portion42is connected to an upper end portion of the first axially stretched portion41in the axial direction and extended toward the other end in the circumferential direction. The first circumferentially stretched portion43is connected to the other end portion of the first coil connection portion42in the circumferential direction and extended toward the other end in the circumferential direction. The second coil connection portion44is connected to the other end portion of the first circumferentially stretched portion43in the circumferential direction and extended toward the other end in the circumferential direction. The second circumferentially stretched portion45is connected to the other end portion of the second coil connection portion44in the circumferential direction and extended toward the other end in the circumferential direction. The third coil connection portion46is connected to the other end portion of the second circumferentially stretched portion45in the circumferential direction and extended toward the other end in the circumferential direction. The second axially stretched portion47is connected to the third coil connection portion46and extended downward in the axial direction.

As shown inFIGS. 2 and 3, the axially stretched portions41and47are disposed in the holes123of the insulator120, respectively. That is, the axially stretched portions41and47of the bus bar40are disposed in the holes123extending in the axial direction of the insulator120, respectively. Thus, since the axially stretched portions41and47of the bus bar40may be suppressed from being detached from the holes123of the insulator120, the bus bar40may be positioned. Accordingly, the bus bar40may be easily positioned with respect to the stator100.

Thus, when the bus bar40is easily positioned with respect to the stator100, the positional accuracy may be enhanced at the time of connecting the coil connection portions42,44, and46of the bus bar40to be described below and the first lead wire131of the coil130. That is, by maintaining the position of the bus bar40in the hole123, connection with the coil130is easy.

Gaps may not be formed between the holes123and the axially stretched portions41and47, but it is preferable that the gaps are provided. That is, the axially stretched portions41and47may be press-fitted into the holes123, but are preferably inserted into the holes123. Thus, the holes123are greater than the axially stretched portions41and47. By forming the gaps, the axially stretched portions41and47may be passed through the holes123by insertion instead of press-fitting. As described above, the axially stretched portions41and47may be insertion portions capable of being inserted into the holes123from the axial direction.

The gaps between the holes123and the axially stretched portions41and47may be small. In this case, since the axially stretched portions41and47are held at the positions of the holes123, the positioning accuracy of the bus bar40is high.

Each of the axially stretched portions41and47is disposed in its respective hole123. Further, two axially stretched portions41and47may be disposed in one hole123.

One bus bar40includes a plurality of coil connection portions42,44, and46. The coil connection portions42,44, and46are connected to the coils130. The number of coil connection portions42,44, and46is the same as the number of first lead wires131. InFIG. 2, three coil connection portions42,44, and46are electrically connected to ends of three first lead wires131drawn out from one coil set, that is, the first lead wires131of the U-phase, the V-phase, and the W-phase. Thus, the neutral point bus bar40connects one coil set to each other to form an electrical neutral point.

The first to third coil connection portions42,44, and have a U-shape recessed outward or inward in the radial direction. Thus, the coil connection portions42,44, and46may sandwich the first lead wires131therein. The neutral point bus bar40and the first lead wire131are electrically connected by laser welding or the like in a state in which the first lead wire131is sandwiched in the coil connection portions42,44, and46, and preferably, in a caulked state.

Further, a direction in which the bus bar40is inserted into the stator100by the hole123is the axial direction, and a direction in which the bus bar40is brought into contact with the first lead wire131by the coil connection portions42,44, and46is the radial direction. The bus bar40is held in the axial direction by the holes123and the axially stretched portions41and47in an outer side in the radial direction, and the bus bar40is held in the radial direction by the first lead wires131and the coil connection portions42,44, and46in an inner side in the radial direction. Since the directions are different, the welding is easy, and the bonding strength between the bus bar40and the coil130is high.

The coil connection portions42,44, and46may have a recessed shape recessed outward in the radial direction, but the first to third coil connection portions42,44, and46inFIGS. 2 to 4are recessed inward in the radial direction. In other words, the first to third coil connection portions42,44, and46have a U-shape recessed toward a center of the coil130. Further, in other words, the first to third coil connection portions42,44, and46have a U-shaped opening directed outward in the radial direction. The size in the radial direction may be suppressed. In addition, when the axially stretched portions41and47are positioned on an outer side in the radial direction with respect to the teeth112, the coil connection portions42,44, and46may be more easily connected to the coils130, and thus it is particularly preferable. In this case, the bus bar40is connected to the coil130in the inner side in the radial direction in a state of being positioned in the outer side in the radial direction with respect to the stator by the hole123.

Further, the coil connection portions42,44, and46may have a flat plate shape. In this case, the coil connection portions42,44, and46have a rectangular cross-sectional shape, and portions other than the coil connection portions42,44, and46have a circular cross-sectional shape.

The bus bar is manufactured by various machining processes such as, for example, press processing and forging.

Other Configurations

The motor1may further include a phase bus bar and a bus bar holder. The bus bar holder is disposed above the insulator120. Specifically, the bus bar holder is disposed above the neutral point bus bar40. The bus bar holder holds the phase bus bar. The phase bus bar is electrically connected to the end of the withdrawn second lead wire132.

Modified Example

In the above-described example embodiment, the bus bar having the axially stretched portions41and47extending downward in the axial direction has been described as an example, but a stretched portion of the present disclosure may extend upward in an axial direction.

In the present example embodiment, the structure in which the neutral point bus bar is positioned on the insulator has been described as an example, but a neutral point bus bar of the present disclosure may be positioned on another member of a stator. When a hole in which the stretched portion is disposed is formed in a conductive member of the stator, an insulation treatment process is performed. However, the bus bar holder is not included in the stator.

Further, in the present disclosure, a phase bus bar may be disposed in the hole of the stator instead of or in addition to the neutral point bus bar.

Electric Power Steering Apparatus

An example in which the above-described motor1is mounted on an electric power steering apparatus500will be described with reference toFIG. 5.

Vehicles such as automobiles are generally provided with an electric power steering apparatus. The electric power steering apparatus generates auxiliary torque for assisting steering torque of a steering system generated when a driver operates a steering wheel. The auxiliary torque is generated by an auxiliary torque mechanism and may reduce the burden of the driver's operation. For example, the auxiliary torque mechanism includes a steering torque sensor, an electronic control unit (ECU), a motor, a reduction mechanism, and the like. The steering torque sensor detects the steering torque in the steering system. The ECU generates a driving signal on the basis of a detected signal of the steering torque sensor. The motor generates auxiliary torque corresponding to the steering torque on the basis of the driving signal and transmits the auxiliary torque to the steering system through the reduction mechanism.

The electric power steering apparatus500includes a steering system520and an auxiliary torque mechanism540.

The steering system520includes, for example, a steering wheel521, a steering shaft522(also referred to as a “steering column”), universal joint couplings523A and523B, a rotating shaft524(also referred to as a “pinion shaft” or “input shaft”), a rack and pinion mechanism525, a rack shaft526, left and right ball joints552A and552B, tie rods527A and527B, knuckles528A and528B, and right and left steered wheels (for example, right and left front wheels)529A and529B. The steering wheel521is connected to the rotating shaft524through the steering shaft522and the universal joint couplings523A and523B. The rack shaft526is connected to the rotating shaft524through the rack and pinion mechanism525. The rack and pinion mechanism525includes a pinion531provided on the rotating shaft524and a rack532provided on the rack shaft526. The right steered wheel529A is connected to a right end of the rack shaft526through the ball joint552A, the tie rod527A, and the knuckle528A in this order. Similar to the right side, the left steered wheel529B is connected to a left end of the rack shaft526through the ball joint552B, the tie rod527B, and the knuckle528B in this order. Here, the right side and the left side correspond to a right side and a left side viewed from a driver sitting in a seat, respectively.

According to the steering system520, steering torque is generated when the driver operates the steering wheel521, and is transmitted to the right and left steered wheels529A and529B through the rack and pinion mechanism525. Thus, the driver may operate the right and left steered wheels529A and529B.

The auxiliary torque mechanism540includes, for example, a steering torque sensor541, an ECU542, a motor543, a reduction mechanism544, and a power conversion device545. The motor543corresponds to the above-described motor1.

The auxiliary torque mechanism540provides auxiliary torque to the steering system520including from the steering wheel521to the right and left steered wheels529A and529B. The auxiliary torque may be referred to as “additional torque”.

The steering torque sensor541detects steering torque of the steering system520provided by the steering wheel521. The ECU542generates a driving signal for driving the motor543on the basis of the detected signal (hereinafter referred to as a “torque signal”) from the steering torque sensor541. The motor543generates auxiliary torque corresponding to the steering torque on the basis of the driving signal. The auxiliary torque is transmitted to the rotating shaft524of the steering system520through the reduction mechanism544. The reduction mechanism544is, for example, a worm gear mechanism. Further, the auxiliary torque is transmitted from the rotating shaft524to the rack and pinion mechanism525.

The electric power steering apparatus500may be classified into a pinion assist type, a rack assist type, a column assist type, and the like according to the location in which the auxiliary torque is provided to the steering system520. The pinion assist type electric power steering apparatus500is illustrated inFIG. 5. However, the electric power steering apparatus500may be a rack assist type, a column assist type, or the like.

For example, not only a torque signal but also a vehicle speed signal may be input to the ECU542. An external device560is, for example, a vehicle speed sensor. Alternatively, the external device560may be another ECU capable of communicating in an in-vehicle network, for example, such as a controller area network (CAN) or the like. A microcontroller of the ECU542may perform vector control or pulse width modulation (PWM) control on the motor543on the basis of the torque signal, the vehicle speed signal, or the like.

The ECU542sets a target current value on the basis of at least the torque signal. The ECU542may set the target current value in consideration of the vehicle speed signal detected by the vehicle speed sensor, or a rotation signal of a rotor detected by an angle sensor. The ECU542may control the driving signal of the motor543, that is, a driving current, such that the actual current value detected by a current sensor coincides with the target current value.

According to the electric power steering apparatus500, the right and left steered wheels529A and529B may be operated by the rack shaft526using the combined torque obtained by adding the auxiliary torque of the motor543to steering torque of the driver. In particular, since the electric power steering apparatus500includes the above-described motor1, the bus bar40may be easily positioned with respect to the stator100.

Further, although the electric power steering apparatus500is described here as an example of a using method of the motor1, the using method of the motor1is not limited. The motor of the present disclosure may be widely used in a variety of devices including various motors, such as a cleaner, a dryer, a ceiling fan, a washing machine, a refrigerator, and an electric power steering apparatus.

Features of the above-described preferred example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.