JP2005333711A - Electric power steering device and method of manufacturing electric motor for electric power steering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering motor which improves steering feeling and increases steering torque assisting capacity by suppressing the loss torque ripple caused by the slot opening of an electric motor and increasing the output of the motor. <P>SOLUTION: A brushless motor as the electric motor of the electric power steering device is equipped with a stator. The core 34A of this stator is equipped with a roughly tubular back yoke part BY, two or more teeth TS which are made separately from this back yoke part and are projected from the back yoke part in question toward the diametrical center of the back yoke part in question at assembly, and coils which are wound on these two or more teeth. The intervals of the slot openings among the two or more teeth in the circumferential direction of the back yoke part are set to values smaller than the diameter of the coil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle electric power steering (EPS) device that assists (assisted) a manual steering force operated by a driver with an electric motor, and a method for manufacturing an electric motor for an electric power steering. The present invention relates to an electric power steering device with improved steering force assisting capability and a method for manufacturing an electric motor for electric power steering.

  Many recent vehicles are equipped with an electric power steering (ESP) device. In general, the electric power steering apparatus includes a torque sensor that detects a steering torque applied to the steered wheels and an electric motor for assisting operation, and drives the electric motor according to the steering torque detected by the torque sensor. . The rotation output of the electric motor becomes auxiliary steering torque, and this rotation output is decelerated by the gear mechanism and transmitted to the output shaft of the steering mechanism. Thus, the vehicle is steered while assisting the steering force applied to the steering wheel.

  As an electric motor used for this electric power steering apparatus, a motor with a brush has been mainstream, but in recent years, a brushless motor is being shifted in order to improve output and further improve efficiency.

  However, this brushless motor has fewer brushless stator slots than brushed rotor slots compared to brushed motors, and is generated by stator slot opening and rotor magnet attraction / repulsion. There is a problem that the loss torque fluctuation is large.

  The loss torque is a friction loss based on the structure of the motor and a loss based on electromagnetic factors in the output torque of the electric motor. An unintended force is applied to the direction, or a force in the opposite direction is added, which deteriorates the steering feeling.

  In particular, when this loss torque fluctuation is large, there arises a problem that this fluctuation becomes physical vibration and is transmitted to the steering wheel. Since this loss torque fluctuation gives the driver discomfort and discomfort, the electric motor used in the electric power steering apparatus is required to have a small loss torque fluctuation.

  As means for reducing the loss torque fluctuation, as described in Patent Document 1 and Patent Document 2, a technique is known in which the loss torque fluctuation is reduced by a combination of the number of stator salient poles and the number of rotor magnet magnetic poles. Further, as described in Patent Document 3, an electric power steering apparatus including an electric motor in which loss torque fluctuation is reduced by such a technique is also known.

  However, there is a current situation that sufficient countermeasures have not yet been taken for the loss torque fluctuation caused by the slot opening of the stator. About this, for example, as shown in Patent Document 4, the wider the slot opening (that is, the greater the ratio of the circumferential length of the slot opening to the circumferential pitch of the teeth core), To the extent that it is known that the loss torque fluctuation is large.

On the other hand, in order to assemble a stator in the manufacture of a brushless motor, coils (wires) are attached to slots provided in a large number of cores. As this coil mounting method, a method in which a coil is directly wound around a tooth of a stator (see Patent Document 5) and a method called an insert method are known. In the insert method, a coil wound in a predetermined shape is set in a coil guide, and the set coil is pushed into the slot via a slot opening of the core with a pushing jig using hydraulic pressure or the like. This is an insertion method.
JP-A-62-110468 JP 2001-275325 A JP 2003-250254 A JP-A-6-54468 JP 2001-186703 A

  As described above, when the brushless motor is used as the electric motor of the electric power steering apparatus, the countermeasure against the loss torque fluctuation caused by the slot opening is insufficient, and a sufficiently smooth steering feeling is not yet obtained.

  Furthermore, in the conventional coil mounting method, there is a limit to securing the coil space factor (ratio of the cross-sectional area of the coil wire to the cross-sectional area of the slot), and it can meet the demand to further increase the motor output. Not. In addition, if the slot opening is wide, there is a disadvantage that the magnetic resistance increases, the total magnetic flux decreases, and the output decreases.

  Therefore, the present invention has been made in view of the problem inherent in the electric power steering apparatus in which the cogging of the brushless motor described above causes an uncomfortable feeling to the driver. It is an object of the present invention to provide an electric power steering device that can suppress and improve the steering feeling and can increase the auxiliary steering force by breaking the limit of the space factor of the brushless motor and increasing the motor output. To do.

  In order to achieve the above object, the electric power steering apparatus according to the present invention generates a steering assist torque in the electric motor in accordance with the steering torque applied to the steered wheels. The electric motor includes a stator and a rotor that are installed to face each other via a gap having a predetermined interval. The stator includes a substantially cylindrical back yoke portion and a plurality of teeth formed separately from the back yoke portion and projecting from the back yoke portion toward the radial center of the back yoke portion when assembled. And a coil wound around the plurality of teeth. The interval of the slot opening between the plurality of teeth in the circumferential direction of the back yoke portion is set to a value smaller than the diameter of the coil.

  Preferably, the electric motor is a brushless motor.

  Further, according to the method of manufacturing an electric motor for an electric power steering according to the present invention, a back yoke portion and a plurality of teeth forming a core of a stator of the electric motor are prepared separately, and each of the plurality of teeth is prepared. A coil is wound around and a plurality of teeth wound with the coil are attached to the back yoke portion.

  Preferably, a slot opening interval between the plurality of teeth is set to a value smaller than a diameter of the coil.

  According to the electric power steering apparatus and the electric motor for electric power steering according to the present invention, the stator core of the electric motor is formed in advance separately from the back yoke portion and the plurality of teeth, and each of the plurality of teeth. After the coil is wound, the teeth are attached to the back yoke portion. For this reason, the space factor of a coil rises and a motor output can be increased. In addition, this separate molding structure eliminates the need to put the coil into the slot via a slot opening during manufacturing. Therefore, the slot opening interval can be set to a value smaller than the diameter of the coil, and the loss torque fluctuation can be suppressed correspondingly, and the steering feeling can be improved.

  Hereinafter, an embodiment of an electric power steering apparatus according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, an electric power steering apparatus 1 according to this embodiment includes a handle shaft 3 coupled to a steering wheel 2, a worm gear 5 interposed between the handle shaft 3 and the column shaft 4, and The worm gear 5 is also engaged with an output shaft 6A of a brushless motor 6 as an electric motor. The column shaft 4 is coupled to the steered wheel SW via a gear 7 and a rack 8. The brushless motor 6 is rotationally driven in response to a command from the controller CNT and generates an auxiliary steering force.

  The steering force applied to the steering wheel 2 is transmitted to the worm gear 5 via the handle shaft 3. The worm gear 5 includes a speed reduction mechanism (not shown). Therefore, the worm gear 5 generates auxiliary torque while decelerating the output from the output shaft 6A of the brushless motor 6 while changing the rotation direction to the orthogonal direction. Since this auxiliary torque is added to the steering torque and transmitted to the column shaft 4, the steering force due to the brushless motor 6 is assisted by the steered wheels SW.

  The controller CNT receives a signal from a torque sensor (not shown) for detecting a steering force and information indicating the vehicle running state such as a steering angle and a vehicle speed, and calculates an auxiliary steering force based on the information. It calculates and commands the brushless motor 6 in the rotational direction and rotational speed commensurate with the auxiliary steering force.

  Thus, the driver's manual steering force applied to the steering wheel 2 is assisted (assisted) from the torque surface, and the assisted steering force is transmitted to the steered wheels SW, so that the electric power steering function is exhibited. .

  FIG. 2 shows a cross-sectional view along the axial direction of the brushless motor 6 described above. The brushless motor 6 includes a motor cover 11 that is formed in a substantially cylindrical shape as a whole, a motor unit 12 that is disposed inside the motor cover 11 and generates rotational torque, and a motor unit 12 that is disposed inside the motor cover 11. And a resolver 13 that detects the rotational position of the rotor of the motor unit 12 and a resolver support member 14 that supports the resolver 13 within the motor cover 11.

  As can be seen from FIG. 2, the motor cover 11 includes a motor yoke 21 having a predetermined diameter and a predetermined length, and a front flange 22 and a rear cover 23 positioned at both ends of the motor yoke 21 in the axial direction. That is, the motor cover 11 has a three-piece structure including the motor yoke 21, the front flange 22, and the rear cover. The axial direction of the motor cover 11 also forms the axial direction of the brushless motor 6, and is hereinafter simply referred to as “axial direction”.

  One end of the motor yoke 21 in the axial direction (end located on the speed reducer side) has a flange 11A integrally formed by bending outward in a direction orthogonal to the axial direction. A front flange 22 is fixed to the flange 11A with a bolt BT. As a result, one opening in the axial direction of the motor yoke 21 is closed by the front flange 22. The front flange 22 is fixed to a gear housing, which is an element of the electric power steering apparatus, by fixing means such as a bolt (not shown). In the center portion of the front flange 22 in the radial direction, a housing portion for the rolling bearing is formed.

  The opening of the other end (rear end) of the motor yoke 21 in the axial direction is closed by a resolver support member 14 that supports the resolver 13 as shown in the figure. A rear cover 23 is attached to the resolver support member 14 so as to cover the rear side surface of the resolver support member 14. In the center portion of the resolver support member 14, a housing portion for the rolling bearing is formed.

  The motor unit 12 includes a motor rotor 33 having a rotatable motor output shaft 6A and a cylindrical rotor core 32, and a motor stator 34. The rotor core 32 is fixed around the motor output shaft 6A so as to penetrate the motor output shaft 6A along the axial direction, and rotates integrally with the motor output shaft 6A. The motor stator 34 is fixed to the inner peripheral surface of the motor yoke 21 and is disposed so as to face the rotor core 32 through a certain gap. The motor output shaft 6A is pivotally supported by rolling bearings 35 and 36 fixed to the central accommodating portions of the front flange 22 and the resolver support member 14 described above. Thereby, the motor output shaft 6 </ b> A, that is, the motor rotor 33 is rotatably supported with respect to the motor stator 34.

  A permanent magnet (motor magnet) 37 for rotational driving is mounted on the outer circumferential surface of the rotor core 32 in the radial direction.

  As shown in FIGS. 3 and 4, the motor stator 34 includes a stator core 34 </ b> A. The stator core 34A has a substantially cylindrical back yoke part BY and a plurality of teeth TS projecting from the back yoke part BY toward the radial center of the back yoke part BY. A slot SL for winding is formed between TS. A coil (motor coil) 38 is wound using this slot SL (see FIG. 2), and is formed on the motor stator 34.

  In the present embodiment, the cylindrical back yoke part BY and the plurality of substantially rail-shaped teeth TS constituting the stator core 34A are formed as separate bodies, as shown in FIGS. The back yoke portion BY and the plurality of teeth TS have a structure in which thin electromagnetic steel plates are stacked along the axial direction in the attached state in order to reduce eddy current loss.

  On the inner cylinder side surface of the back yoke part BY, as shown in FIG. 5, a plurality of substantially reverse wedge-shaped attachment grooves BY1 extending in the axial direction are formed at a plurality of circumferential tooth attachment positions. .

  On the other hand, as shown in FIG. 6, one end portion of each tooth TS, which is located on the outer peripheral side in a state of being attached to the back yoke portion BY, matches the cross-sectional shape of the above-described substantially inverted wedge-shaped attachment groove BY1. A substantially reverse wedge-shaped attachment portion TS1 is formed. A flange TS2 is formed at the other end of each tooth TS, that is, at the end located on the inner peripheral side.

  For this reason, at the time of manufacture, each tooth TS formed as a separate body is wound with a coil 38, and then each of the teeth TS wound with a coil is attached to its attachment portion TS1 to each attachment groove of the back yoke portion BY. The stator core 34A is completed by fitting to BY1.

  At the time of completion, the gap between the flange portions TS2 of the plurality of teeth TS, that is, the interval of the slot opening SO (see FIG. 7) is set to a predetermined allowable value narrower than the diameter of the coil 38.

  Returning to FIG. 2, the resolver support member 14 is a disk-shaped member made of a nonmagnetic material. The resolver support member 14 is positioned at the axial rear opening of the motor yoke 21 and is attached so as to close the opening. The above-described rolling bearing 36 is fixed to a bearing housing portion formed in the radial center portion of the resolver support member 14. For this reason, one end portion of the motor output shaft 6 </ b> A of the rotor 33 in the axial direction is pivotally supported by the bearing 36.

  The resolver 13 includes a resolver rotor 41 fixed to the circumferential surface of the motor output shaft 6A, and a resolver stator 42 disposed to face the resolver rotor 41 with a predetermined gap.

  The rear cover 23 is a circular disk member, and a bent portion 23 </ b> A is formed on a circumferential portion thereof. The bent portion 23 </ b> A is attached to the outer peripheral surface of the flange portion 14 </ b> B of the resolver attachment member 14 so as to have the same diameter as the motor yoke 21.

  The electric power steering apparatus 1 according to the present embodiment is configured as described above and can assist the steering torque with respect to the manual steering force. In particular, as shown in FIG. 3, the stator core 34 </ b> A of the stator 34 is divided into a back yoke portion BY and a plurality of teeth TS, and each is formed as a separate body. Is coupled to the back yoke BY. For this reason, there is no need to insert a coil from the slot opening SO into the slot SL as in the prior art, and accordingly, the coil winding operation is facilitated, and the volume of the slot SL can be used effectively. That is, the coil space factor can be increased. Accordingly, the output of the brushless motor 6 can be increased correspondingly, the assisting power for the steering of the electric power steering apparatus 1 is increased, and the power steering function can be improved.

  Further, as described above, since it is not necessary to use the slot opening SO when the coil 38 is wound around each tooth TS, the diameter can be narrower than the diameter of the coil 38 of the slot opening SO. By this narrowing, the loss torque fluctuation of the brushless motor 6 can be reduced, and the steering feeling can be improved.

  A modification of the above-described stator core 34A is shown in FIG. The stator core 34A has substantially the same manufacturing method as that described above, but has a different structure in which a plurality of teeth TS are laminated. That is, when laminating each tooth TS with an electromagnetic steel plate, at least one electromagnetic steel plate PT positioned at each of both ends in the laminating direction, that is, the axial direction of the brushless motor 6, is a single sheet of the plurality of teeth TS. It is made of sheet material. This sheet material has a structure in which the circumferential end portion of the flange portion TS2 positioned on the radially inner peripheral side when each tooth TS is assembled is connected by a bridging portion BG having a small cross-sectional area between adjacent teeth. doing. The bridging portion BG has an effect of integrating a plurality of teeth TS during assembly, facilitating the assembly work of the teeth TS to the back yoke BY, and preventing the teeth TS from being damaged or peeled off. Other functions and effects are the same as those of the above-described embodiment.

It is a figure explaining schematic structure of the electric power steering device concerning one embodiment of the present invention. It is an axial sectional view showing the structure of a brushless motor as an electric motor mounted on the electric power steering apparatus according to the embodiment. The perspective view which shows the stator core of a brushless motor. The side view which shows a stator core. The side view which shows the back yoke part of a stator core. The perspective view which shows the teeth of a stator core. The figure explaining the slot opening of a stator core. The figure explaining the one part steel plate which connects between the teeth of a stator core.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 6 Brushless motor 6A as an electric motor Motor output shaft 33 Motor rotor 34 Motor stator 34A Stator core 38 Coil BY Back yoke part TS Teeth SL Slot SO Slot opening BG Bridge part

Claims (5)

In the electric power steering device that generates the steering assist torque in the electric motor in accordance with the steering torque applied to the steered wheels,
The electric motor includes a stator and a rotor that are installed to face each other through a gap of a predetermined interval,
The stator is formed of a substantially cylindrical back yoke portion and a plurality of teeth formed separately from the back yoke portion and projecting from the back yoke portion toward the radial center of the back yoke portion when assembled. And a coil wound around the plurality of teeth,
An electric power steering apparatus using an electric motor, wherein a slot opening interval between the plurality of teeth in a circumferential direction of the back yoke portion is set to a value smaller than a diameter of the coil.   Each of the plurality of teeth is formed by laminating a plurality of lamina sheets, and at least one lamina sheet at each of both end portions in the laminating direction is a radial direction of the lamina sheets. The electric power steering apparatus according to claim 1, wherein a bridging portion that integrally connects adjacent teeth is provided at an end portion.   The electric power steering apparatus according to claim 1, wherein the electric motor is a brushless motor. In a method of manufacturing an electric motor for an electric power steering that is used in an electric power steering device and generates a steering assist torque according to a steering torque applied to a steered wheel,
A back yoke portion and a plurality of teeth forming a stator core of the electric motor are prepared separately,
A coil is wound around each of the plurality of teeth,
A method of manufacturing an electric motor for an electric power steering, wherein a plurality of teeth around which the coil is wound are attached to the back yoke portion. The manufacturing method of an electric motor for an electric power steering, wherein a slot opening interval between the plurality of teeth is set to a value smaller than a diameter of the coil.

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