JPWO2007088919A1 - Electric power steering device - Google Patents

Abstract

The rack assist type electric power steering apparatus 10 uses a motor 1 as a drive source. The stator 11 of the motor 1 has a stator core 13 that includes a ring-shaped yoke portion 16 and teeth 17 that are formed to protrude inward from the yoke portion 16. The stator core 13 is formed such that a ratio Wy: Wt between the radial width Wy of the yoke portion 16 and the circumferential width Wt of the teeth 17 is 1: 1.4 to 1.8. By setting the yoke portion 16 and the teeth 17 of the stator core 13 to this value, the stator core 13 can be set to be least susceptible to torque sag in a limited space.

Description

  The present invention relates to an electric power steering apparatus using an electric motor as a drive source, and more particularly to a rack assist type electric power steering apparatus in which a rack shaft of a vehicle is inserted in a motor central portion.

  In recent years, many vehicles have been equipped with so-called power steering devices for assisting steering force of automobiles and the like. As such power steering devices, in recent years, vehicles equipped with electric power steering devices (so-called electric power steering devices) are increasing from the viewpoint of reducing engine load and weight. This electric power steering device (hereinafter abbreviated as EPS as appropriate) is generally applied to a rack and pinion type steering device, and is roughly classified into three types depending on the location of the motor. In other words, from the side closer to the driver, the motor is arranged on the steering shaft, the column assist type with a motor, the pinion assist type with a motor arranged at the connection between the steering shaft and the rack shaft, and the motor arranged coaxially with the rack shaft. Three types of rack assist type are known.

  The EPS of Patent Document 1 is a rack assist type device. The rack assist type EPS is given a steering assist force by a motor coaxially provided on the rack shaft. FIG. 6 is a cross-sectional view showing a configuration of a rack assist type EPS as in Patent Document 1. In FIG. In the EPS 51 of FIG. 6, a motor 53 is provided coaxially with the rack shaft 52. The steering assist force generated by the motor 53 is transmitted to the rack shaft 52 via the ball screw mechanism 54. Steering wheels are connected to both ends of the rack shaft 52 via tie rods, knuckle arms, or the like (not shown). The rack shaft 52 is coupled to the steering shaft 55 in a rack-and-pinion manner, and operates in the axial direction (left-right direction in the figure) by a driver's turning operation. The motor 53 has a configuration in which a magnet 57, a cylindrical rotor shaft 58, and a rotor core 59 are coaxially inserted into a cylindrical yoke 56. A rack shaft 52 is inserted into the rotor shaft 58.

In the EPS 51, when the steering shaft 55 is rotated by operating the handle, the rack shaft 52 is moved in a direction corresponding to the rotation, and a steering operation is performed. By this operation, a steering torque sensor (not shown) is activated, and electric power is appropriately supplied to the motor 53 based on this detected torque. When the motor 53 is activated, the rotation is transmitted to the rack shaft 52 via the ball screw mechanism 54. That is, the ball screw mechanism 54 converts the rotation of the motor 53 into an axial movement of the rack shaft 52, and a steering assist force is applied to the rack shaft 52. The steering wheel is steered by the steering assist force and the manual steering force, thereby reducing the driver's handle operation burden.
Japanese Patent Laid-Open No. 10-152058 JP 2000-78780 A JP 2001-218439 A Japanese Patent Laid-Open No. 2003-158856

  On the other hand, the rack assist type EPS as shown in FIG. 6 is likely to interfere with the engine layout, and thus severe restrictions are often imposed on its physique (particularly the outer dimensions). For example, in the case of EPS for small passenger cars, generally those having an outer diameter of more than 100 mm have poor merchantability. For this reason, it is necessary for the rack assist EPS motor to have a motor having an outer diameter of 100 mm or less and to establish an optimum specification that satisfies the required performance. On the other hand, the rack shaft passing through the inside of the motor itself has an outer diameter of about 20 to 30 mm. Accordingly, the inner diameter of the rotor shaft through which the rack shaft is inserted is required to be about 20 to 40 mm. That is, in the rack assist type EPS motor, the outer diameter must be suppressed to 100 mm or less in a configuration in which the rack shaft passes through the center, and a desired output must be obtained with the physique. In addition, the EPS motor is required to have low friction (rotational resistance when no power is supplied), low torque ripple, and low cost.

  However, such a small, high-performance and low-cost EPS motor requires very delicate and complicated adjustments when determining the specifications. That is, when designing the structure of the motor, there are various parameters such as the configuration of the stator and rotor, magnets, and windings. In addition, these parameters are often in a trade-off relationship. For this reason, it is often difficult for a skilled designer to set each specification so as to satisfy the above-described elements. For example, when focusing on the magnetic circuit portion composed of the stator and the rotor among these elements, there is a trade-off relationship in terms of physique (stator dimensions) and securing torque from the viewpoint of magnetic flux saturation.

  That is, since the stator is used as a magnetic path in the motor, if its size is small, the magnetic resistance increases and magnetic flux saturation is likely to occur. For this reason, in a motor with a small stator core, magnetic flux saturation occurs in the core, and the output torque decreases at high loads (torque is large). FIG. 7 is an explanatory diagram showing the relationship between the stator core shape and the motor torque. As shown in FIG. 7, when the stator core is small, a phenomenon occurs in which the torque sag (the torque increase rate decreases) at the time of a high load such as stationary due to the influence of magnetic flux saturation in the stator core. Therefore, if the design has a dimensional allowance in order to secure torque, the product will be uncompetitive due to an increase in size and a decrease in winding space. For this reason, in the EPS motor, it is difficult to achieve both torque securing and downsizing, which has been a big problem in reducing the size and performance of the EPS.

  An object of the present invention is to achieve both the securing of torque and the miniaturization of the EPS motor, and to miniaturize the electric power steering apparatus optimally without deteriorating the performance and the assemblability.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus including a rotor including a permanent magnet and a stator disposed on an outer peripheral side of the rotor, and the stator includes a ring-shaped yoke. And a stator core provided with a tooth portion that protrudes inward from the yoke portion, and the stator core has a ratio of magnetoresistance values of the yoke portion and the teeth portion of 1: 1.4 to 1 It is formed in .8.

  In the present invention, the stator core of the EPS motor can be most used in a limited space by setting the magnetoresistance ratio of the yoke portion and the teeth portion of the stator core to 1: 1.4 to 1.8. It can be set so that torque sagging (decrease in torque increase rate) hardly occurs. As a result, a small and high-performance EPS motor with excellent layout and high torque linearity can be configured, and the small size and high performance of the EPS can be achieved. In addition, since the stator core is set to an optimum shape and unnecessary portions can be eliminated, the cost and weight of the EPS motor can be reduced, and the commercial value of the EPS can be improved. Furthermore, when designing the motor, the design of the EPS can be reduced because the ratio of the magnetoresistance values of the yoke part and the tooth part can be designed in a predetermined form.

  Another electric power steering apparatus according to the present invention is an electric power steering apparatus including a rotor having a permanent magnet and a stator disposed on an outer peripheral side of the rotor, wherein the stator has a ring shape. A stator core having a yoke portion and a teeth portion protruding inward from the yoke portion, the stator core having a radial width Wy of the yoke portion and a circumferential width of the teeth portion; The ratio Wy: Wt of the dimension Wt is formed to be 1: 1.4 to 1.8.

  In the present invention, by setting the ratio of Wy, Wt to 1: 1.4 to 1.8, the stator core of the EPS motor is set to be least susceptible to torque sag in a limited space. Can do. As a result, a small and high-performance EPS motor with excellent layout and high torque linearity can be configured, and the small size and high performance of the EPS can be achieved. In addition, since the stator core is set to an optimum shape and unnecessary portions can be eliminated, the cost and weight of the EPS motor can be reduced, and the commercial value of the EPS can be improved. Furthermore, when designing the motor, the design can be performed in a form in which the ratio of Wy and Wt is determined to some extent in advance.

  In the electric power steering apparatus, the motor may be arranged coaxially around a rack shaft connected to a steering wheel, and a steering assist force may be supplied to the rack shaft by the motor.

  According to the electric power steering device of the present invention, in the electric power steering device including the rotor including the permanent magnet and the stator disposed on the outer peripheral side of the rotor, the ring-shaped yoke portion is provided on the stator. And a stator core provided with a tooth portion protruding inward from the yoke portion, and the ratio of the magnetoresistive value of the stator core yoke portion to the tooth portion is set to 1: 1.4 to 1.8. In the EPS motor with a strict demand for the physique, the stator core can be set to be the least susceptible to torque sagging under the severe restrictions. Therefore, according to the present invention, it is possible to provide an EPS that uses a small and high-performance motor that has excellent layout characteristics and high torque linearity, and it is possible to reduce the size and performance of the EPS.

  In addition, since the stator core can be set to an optimum shape, useless portions of the stator core can be eliminated, and the cost and weight of the EPS motor can be reduced. For this reason, the cost and weight of the EPS can be reduced, and the merchantability of the EPS can be improved. Furthermore, when designing the motor, the design of the magnetic resistance value ratio between the yoke part and the tooth part can be made in a predetermined form, so that it is possible to obtain an optimum motor design guideline for EPS, which is small, high output and low in power. An inexpensive EPS motor can be easily configured as compared to the conventional one, and the design man-hours for EPS can be reduced. Accordingly, the product development cost is also reduced accordingly, and the product cost can be reduced.

  According to another electric power steering apparatus of the present invention, in an electric power steering apparatus having a rotor having a permanent magnet and a stator disposed on the outer peripheral side of the rotor, a ring-shaped joint is connected to the stator. A stator core having an iron part and a tooth part projecting inwardly from the yoke part is provided, and the ratio Wy of the width dimension Wy in the radial direction of the yoke part of the stator core to the width dimension Wt in the circumferential direction of the tooth part: Since Wt is formed in the range of 1: 1.4 to 1.8, it is possible to set the stator core in such a way that torque sagging is hardly generated in the severely restricted EPS motor with a strict demand on the physique. Therefore, according to the present invention, it is possible to provide an EPS that uses a small and high-performance motor that has excellent layout characteristics and high torque linearity, and it is possible to reduce the size and performance of the EPS.

  In addition, since the stator core can be set to an optimum shape, useless portions of the stator core can be eliminated, and the cost and weight of the EPS motor can be reduced. For this reason, the cost and weight of the EPS can be reduced, and the merchantability of the EPS can be improved. Furthermore, when designing the motor, the design of the magnetic resistance value ratio between the yoke part and the tooth part can be made in a predetermined form, so that it is possible to obtain an optimum motor design guideline for EPS, which is small, high output and low in power. An inexpensive EPS motor can be easily configured as compared to the conventional one, and the design man-hours for EPS can be reduced. Accordingly, the product development cost is also reduced accordingly, and the product cost can be reduced.

It is sectional drawing which shows the structure of the electric power steering apparatus which is one Example of this invention. It is an expanded sectional view which shows the structure of the motor used for the electric power steering apparatus of FIG. It is explanatory drawing which shows the structure of the stator core in the motor of FIG. It is explanatory drawing which shows the flow of the magnetic flux in a stator core. It is explanatory drawing which shows the relationship between the effective magnetic flux and torque when changing a teeth width. It is sectional drawing which shows the structure of rack assist type EPS. It is explanatory drawing which shows the relationship between a stator core shape and a motor torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 2 Rack shaft 3 Ball screw mechanism 4 Steering shaft 10 Electric power steering apparatus 11 Stator 12 Housing 13 Stator core 14 Winding 15 Feeding wiring 16 Relay part 17 Teeth 18 Slot 21 Rotor 22 Rotor shaft 23 Rotor core 24 Magnet 25 Magnet cover 31 Housing 32 Bearing 33 Resolver 34 Resolver stator 35 Resolver rotor 36 Coil 41 Housing 42 Nut portion 43 Screw portion 44 Ball 45 Angular bearings 46a, 46b Bearing fixing ring 47 Step portion 48 Bearing fixing ring 49 Step portion 51 Electric power steering device 52 Rack shaft 53 Motor 54 Ball screw mechanism 55 Steering shaft 56 Yoke 57 Magnet 58 Rotor shaft 59 Rotorco A Wt Teeth width Wy

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of an electric power steering apparatus according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view showing a configuration of an EPS motor used in the electric power steering apparatus of FIG. is there. The electric power steering apparatus (EPS) 10 of FIG. 1 has a rack assist type configuration similar to that of FIG. 6, and uses the motor 1 as a power source. However, in the EPS 10, a brushless motor is used as the motor 1 in order to reduce the size and performance of the EPS.

  Inside the motor 1, the rack shaft 2 penetrates coaxially with the motor 1. The rotation of the motor 1 is transmitted to the rack shaft 2 via the ball screw mechanism 3 and becomes a steering assist force. Steering wheels are connected to both ends of the rack shaft 2 via tie rods, knuckle arms, or the like (not shown). The rack shaft 2 is also rack-and-pinion-coupled with the steering shaft 4 and operates in the axial direction (left-right direction in the figure) by the driver's turning operation.

  Also in the EPS 10, as in the EPS 51 of FIG. 6, when the steering shaft is rotated by operating the handle, the rack shaft 2 moves in a direction corresponding to the rotation. When a steering torque sensor (not shown) is activated by the operation of the steering shaft 4, electric power is appropriately supplied to the motor 1 based on this detected torque. When the motor 1 is operated, the rotation is transmitted to the rack shaft 2 through the ball screw mechanism 3. Thereby, the rotation of the motor 1 is converted into the movement of the rack shaft 2 in the axial direction, and a steering assist force is applied to the rack shaft 2. The steering wheel is steered by the steering assist force and the manual steering force.

  The motor 1 is an inner rotor type brushless motor having a stator 11 on the outside and a rotor 21 on the inside. The stator 11 includes a housing 12, a stator core 13 fixed to the inner peripheral side of the housing 12, and a winding 14 wound around the stator core 13. The housing 12 is formed of iron or the like, and the outer periphery thereof is suppressed within 100 mm. The stator core 13 has a structure in which many steel plates are laminated. A plurality of teeth project from the inner peripheral side of the stator core 13.

  FIG. 3 is an explanatory diagram showing the configuration of the stator core 13. The stator core 13 is formed of a ring-shaped yoke portion 16 and teeth 17 that are formed so as to protrude inward from the yoke portion 16. In the motor 1, nine teeth 17 are provided. Slots 18 (9) are formed between the teeth 17 and the motor 1 has a 9-slot configuration. A winding 14 is wound around each tooth 17 by concentrated winding. The winding 14 is accommodated in each slot 18. Winding 14 is connected to a battery (not shown) via power supply wiring 15.

  The rotor 21 is disposed inside the stator 11. The rotor 21 has a configuration in which a cylindrical rotor shaft 22, a rotor core 23, a magnet 24, and a magnet cover 25 are arranged coaxially. The rack shaft 2 is inserted inside the rotor shaft 22. A cylindrical rotor core 23 is externally provided on the outer periphery of the rotor shaft 22. A magnet 24 having a 6-pole configuration is fixed to the outer periphery of the rotor core 23, and the motor 1 has a 6-pole 9-slot configuration.

  The magnet 24 is a rare earth magnet such as a neodymium iron magnet that is small and has a high magnetic flux density. Thus, by using a rare earth magnet for the magnet 24, the motor can be miniaturized, the inertia of the rotor 21 is reduced, and the steering feeling is improved. The magnet 24 has a ring shape, and a plurality of magnetic poles are alternately arranged N and S in the circumferential direction. A plurality of segment magnets may be used as the magnet 24. A magnet cover 25 is externally provided on the outside of the magnet 24. The magnet cover 25 prevents the motor 1 from being locked by a broken piece even if the magnet 24 is broken.

  An aluminum die-cast housing 31 is attached to the right end side of the housing 12 in the figure. The housing 31 accommodates a bearing 32 that supports the right end side of the rotor 21 and a resolver 33 that detects the rotation of the rotor 21. The resolver 33 includes a resolver stator 34 fixed to the housing 31 side and a resolver rotor 35 fixed to the rotor 21 side. A coil 36 is wound around the resolver stator 34, and an excitation coil and a detection coil are provided. A resolver rotor 35 fixed to the rotor shaft 22 is disposed inside the resolver stator 34. The resolver rotor 35 has a configuration in which metal plates are laminated, and has convex portions in three directions.

  When the rotor shaft 22 rotates, the resolver rotor 35 also rotates in the resolver stator 34. A high frequency signal is given to the exciting coil of the resolver stator 34, and the phase of the signal output from the detection coil changes due to the proximity of the convex portion. The rotational position of the rotor 21 is detected by comparing the detection signal with the reference signal. Then, based on the rotational position of the rotor 21, the current to the winding 14 is appropriately switched, and the rotor 21 is rotationally driven.

  A housing 41 made of aluminum die casting is attached to the left end side of the housing 12 in the drawing. A ball screw mechanism 3 is incorporated in the housing 41. The ball screw mechanism 3 includes a nut portion 42, a screw portion 43 formed on the outer periphery of the rack shaft 2, and a large number of balls 44 interposed between the nut portion 42 and the screw portion 43. . The rack shaft 2 is rotatably supported by the nut portion 42 in a state where it can reciprocate in the left-right direction, and moves in the left-right direction as the nut portion 42 rotates.

  The nut portion 42 is fixed to the left end portion of the rotor shaft 22 and is rotatably held by an angular bearing 45 fixed to the housing 41. The angular bearing 45 is fixed in a state where axial movement is restricted between the bearing fixing rings 46 a and 46 b screwed into the opening of the housing 41 and the stepped portion 47 formed inside the housing 41. Has been. Further, the axial movement of the angular bearing 45 is regulated by a bearing fixing ring 48 screwed into the left end of the nut portion 42 and a step portion 49 formed on the outer periphery of the nut portion 42.

  In the EPS 10, when the steering handle is operated and the steering shaft 4 is rotated, the rack shaft 2 is moved in a direction corresponding to the rotation, and a steering operation is performed. By this operation, a steering torque sensor (not shown) is activated, and electric power is supplied from the battery to the winding 14 via the power supply wiring 15 according to the detected torque. When electric power is supplied to the winding 14, the motor 1 operates and the rotor shaft 22 rotates. When the rotor shaft 22 rotates, the nut portion 42 coupled therewith rotates, and the steering assist force in the axial direction is transmitted to the rack shaft 2 by the action of the ball screw mechanism 3. Thereby, the movement of the rack shaft 2 is promoted, and the steering force is assisted.

  By the way, in the EPS motor, as described above, it is difficult to ensure both torque securing and motor miniaturization. In this regard, as a result of repeated experiments by the inventors, there is a certain relationship between the magnetoresistance ratio of the yoke portion 16 and the teeth 17 of the stator core 13 and the output torque. It was found that the output torque can be maximized by setting within the predetermined range. As a result, the stator core 13 capable of maximizing the output torque can be obtained within the physique limitation, and both the securing of torque and the miniaturization of the motor can be maximized. In addition, a magnetic resistance is proportional to the width | variety, when the yoke 16 and the teeth 17 have the same magnetic resistance value. Therefore, in this embodiment, taking the case where both have the same magnetoresistance value as an example, the dimension ratio of the width of the yoke portion 16 and the tooth 17 will be described below instead of the magnetoresistance ratio.

  Here, the flow of magnetic flux in the stator core 13 is considered. FIG. 4 is an explanatory view showing the flow of such magnetic flux, and shows an enlarged part of the stator core 13. As shown in FIG. 4, the magnetic flux that has entered the teeth 17 stops at the yoke portion 16, and divides into the left and right and flows into the yoke portion 16. If this magnetic flux flow is obstructed, the output of the motor 1 naturally decreases. That is, when magnetic flux saturation occurs in both the teeth 17 and the yoke portion 16, torque sagging occurs at high load as shown in FIG. 7. For this reason, in order to ensure the maximum output torque, it is necessary to prevent magnetic saturation from occurring in either the yoke portion 16 or the teeth 17. Accordingly, it is necessary to design the width Wy of the yoke portion 16 and the width Wt of the teeth 17 to optimum values in a limited space (outer diameter) in order to ensure the minimum width necessary for passing the magnetic flux without waste. There is.

  FIG. 5 is an explanatory diagram showing the relationship between the effective magnetic flux and the torque, and shows the difference in motor torque when Wy is 10 mm and Wt is appropriately changed under the conditions. In addition, the effective magnetic flux said here means the magnetic flux effective in order to generate motor torque. In FIG. 5, the effective magnetic flux is arranged on the horizontal axis. However, the torque depends not only on the winding current but also on the magnetic flux of the rotor magnet. Since the characteristics are different, the horizontal axis is the effective magnetic flux for accuracy.

  As shown in FIG. 5, in the experiment by the inventors, when the ratio of the widths Wy and Wt of the yoke portion 16 and the teeth 17 is set to 1: 1.4 to 1.8, it is difficult for torque sagging to occur. On the other hand, when the ratio between the two was 1: 1.11 (Wt = 11 mm) or 1: 2.0 (Wt = 20 mm), the effective magnetic flux leveled or decreased from around 0.0045 Wb. This is presumably because when Wt = 11 mm, the yoke portion 16 has a margin, but magnetic saturation occurred in the teeth 17 and torque sagging occurred. In addition, when Wt = 20 mm, the teeth 17 have a margin, but it seems that magnetic saturation occurred in the yoke portion 16 and torque sagging occurred. As for torque sagging, Wt = 18 mm is the best, but the winding area in the slot 18 is reduced by the larger width of the teeth 17. Therefore, in terms of total balance, Wt = 15 mm (Wy: Wt = 1: 1.5), which is not much different from the case of Wt = 18 mm, is optimal.

  As described above, when the ratio of Wy and Wt is set to 1: 1.4 to 1.8, the stator core 13 can be set to be least susceptible to torque sag in a limited space. Therefore, according to the present invention, it is possible to provide an EPS that uses a small, high-performance motor that has excellent layout characteristics and high torque linearity. Further, in the EPS according to the present invention, the stator core 13 of the motor 1 is set to an optimum shape, and wasteful meat can be dropped (a wasteful part is eliminated), so that the cost and weight of the motor 1 can be reduced. Therefore, the cost and weight of the EPS 10 can be reduced, and the merchantability of the EPS can be improved. Finally, it can contribute to fuel saving.

  Furthermore, when designing a brushless motor, the shape of the stator core is one of the items that should be paid most attention since it has a great influence on the motor performance. In that respect, since the motor 1 can be designed with the ratio of Wy and Wt determined in advance to some extent, the specifications of each part of the motor may be determined in accordance with the above ratio when designing the structure. That is, according to the present invention, an optimum motor design guideline for EPS can be obtained, and a small, high-output and low-cost EPS motor can be easily configured as compared with the related art. Accordingly, it is possible to optimally design the EPS motor, and the design man-hour for the EPS motor can be reduced. For this reason, product development costs can be reduced, and EPS product costs can also be reduced.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.
For example, in the above-described embodiment, an example in which the present invention is applied to a rack assist type EPS is shown, but the present invention can also be applied to a column assist type EPS. Moreover, in the above-mentioned embodiment, taking the case where the yoke 16 and the teeth 17 have the same magnetic resistance value as an example, the ratio of the widths of the two is the above value (Wy: Wt = 1: 1.4 to 1.8). However, basically, the optimum design is possible by setting the ratio of the magnetic resistance of the yoke portion 16 and the tooth 17 to the above value. Therefore, when the yoke portion 16 and the teeth 17 of the stator core 13 have a magnetic resistance value, the width dimension is set so that the magnetoresistance ratio becomes the above value according to the magnetic resistance value of each portion.

  Furthermore, even in the case of the same material, for example, when the silicon (Si) content in the silicon steel plate is changed depending on the part, or when a directional electromagnetic steel plate is used, the magnetoresistance value of the yoke portion 16 and the teeth 17 is used. There are different cases. In the case of a silicon steel sheet, if the amount of silicon is large, the magnetoresistance value increases, and in the grain-oriented electrical steel sheet, the magnetoresistance value in the rolling direction decreases. Therefore, in such a case, the width dimension is determined in consideration of the magnetic resistance value of each part. In general, a non-oriented electrical steel sheet is often used for the stator core of the motor, and in this case, the magnetic resistance values of the yoke portion 16 and the teeth 17 are equal as in the above example. The ratio of the widths of both may be set to the above value.

  On the other hand, in the above-described embodiment, the motor 1 has a 6-pole 9-slot configuration, but the configuration of the number of poles and the number of slots is not limited to this, and in the configuration of an integral multiple of 2 poles and 3 slots, the yoke portion 16 By setting the magnetic resistance value of the teeth 17 to the above value, it is possible to perform an optimum design with reduced torque sagging. The present invention is applicable not only to a motor having a power supply voltage of 12V but also to an EPS using a motor of 42V.

Claims (3)

An electric power steering apparatus including a motor including a rotor including a permanent magnet and a stator disposed on an outer peripheral side of the rotor,
The stator has a stator core that includes a ring-shaped yoke portion and a teeth portion that protrudes inward from the yoke portion.
The electric power steering apparatus according to claim 1, wherein the stator core is formed such that a ratio of a magnetic resistance value between the yoke portion and the tooth portion is in a range of 1: 1.4 to 1.8. An electric power steering apparatus including a motor including a rotor including a permanent magnet and a stator disposed on an outer peripheral side of the rotor,
The stator has a stator core that includes a ring-shaped yoke portion and a teeth portion that protrudes inward from the yoke portion.
The stator core is formed such that a ratio Wy: Wt between a radial width dimension Wy of the yoke portion and a circumferential width dimension Wt of the teeth portion is 1: 1.4 to 1.8. Electric power steering device.   3. The electric power steering apparatus according to claim 1, wherein the motor is coaxially disposed around a rack shaft connected to the steering wheel and supplies a steering assist force to the rack shaft. Electric power steering device.

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