JP2008114787A - Electric power steering device - Google Patents

Abstract

An electric power steering apparatus is provided that can integrate a worm and a motor output shaft to suppress deterioration of cogging torque characteristics while being small and light.
An electric motor for generating a steering assist force for a steering system, a worm 13c meshing with a worm wheel 13b mounted on the steering system formed integrally with an output shaft 62 of the electric motor 14, An electric motor having a bearing device 13d having a mechanism for supporting an axial reaction force of the worm 13c and allowing a deviation angle of the output shaft of the electric motor, and a preload mechanism 21 for pressing the worm 13c against the worm wheel 13b with a constant pressure. In the power steering apparatus, the electric motor 14 is configured by a brushless motor having a slot combination that is diagonally in phase.
[Selection] Figure 2

Description

  The present invention relates to an electric motor that generates a steering assist force for a steering system, a worm that meshes with a worm wheel that is integrally formed with an output shaft of the electric motor, and that is meshed with the worm wheel, and an axial reaction of the worm. The present invention relates to an electric power steering apparatus having a bearing device that has a mechanism that supports force and allows a deviation angle of an output shaft of the electric motor, and a preload mechanism that presses the worm against the worm wheel with a constant pressure.

In recent years, since it is desired to increase the output of the electric power steering apparatus, the electric motor and the worm speed reducer are increased in size, and the allowable size and the allowable weight for mounting on the vehicle body are reached. Therefore, there is an increasing demand for reduction in size and weight of the electric power steering device.
As a conventional electric power steering apparatus, for example, a motor output shaft and a worm are separated from each other, and both are connected by a spline or the like (see, for example, Patent Document 1). When this structure is adopted, four bearings are required to support the worm and the motor output shaft, the electric power steering device becomes longer toward the motor in the axial direction of the worm, and the worm gear housing and the motor frame are separated. There is a problem that the number of parts also increases.

In order to solve this problem, the worm and the motor output shaft are integrated to be compact, and the number of parts is reduced (see Patent Document 1).
Japanese Patent Laying-Open No. 2004-306898 (first page, FIGS. 2 and 20)

  However, in the conventional example described in Patent Document 1, when the worm and the motor output shaft are integrated, the integrated shaft causes the worm to lift in the direction perpendicular to the axis when the electric power steering apparatus is operated. As a result, there is an unsolved problem that the influence is up to the motor output shaft, the cogging torque characteristics are deteriorated, and the steering feeling during operation of the electric power steering apparatus is deteriorated.

  Accordingly, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and the deterioration of cogging torque characteristics can be suppressed while integrating the worm and the motor output shaft while being small and light. An object is to provide an electric power steering device.

  In order to achieve the above object, an electric power steering apparatus according to claim 1 is mounted on an electric motor that generates a steering assist force for a steering system, and the steering system that is integrally formed on an output shaft of the electric motor. A worm that meshes with the worm wheel, a bearing device that supports an axial reaction force of the worm and allows a deviation angle of the output shaft of the electric motor, and a preload that presses the worm against the worm wheel at a constant pressure An electric power steering apparatus having a mechanism, wherein the electric motor is configured by a brushless motor having a slot combination that is diagonally in phase.

An electric power steering apparatus according to a second aspect is the invention according to the first aspect, wherein the brushless motor is configured by 8 poles and 12 slots.
Furthermore, the electric power steering apparatus according to claim 3 is the invention according to claim 1 or 2, wherein the brushless motor includes a cylindrical stator around which a coil is wound, a magnetic pole and an output shaft facing the stator. A rotor provided with the rotor, an angle detector that detects a rotation angle of the rotor, a frame that houses the stator and the angle detector, and a bearing device that rotatably supports the rotor with respect to the frame, The frame is characterized in that it is integrated with at least a gear housing that houses the worm.

Furthermore, the electric power steering apparatus according to a fourth aspect is the invention according to the third aspect, wherein the frame is formed of a material having a high thermal conductivity.
Still further, an electric power steering apparatus according to a fifth aspect is the invention according to the fourth aspect, wherein the frame is formed of any one of aluminum, an aluminum alloy, magnesium and a magnesium alloy.

According to a sixth aspect of the present invention, in the electric power steering apparatus according to any one of the third to fifth aspects, the frame is integrally formed by casting.
Further, according to a seventh aspect of the present invention, there is provided an electric power steering apparatus according to any one of the third to sixth aspects, wherein the stator includes a stator yoke extending in a circumferential direction that fits into a frame, and a circumference of the stator yoke. A plurality of split cores extending inward from the central portion in the direction and having a magnetic leg portion around which the motor coil is wound and having a T-shaped cross section perpendicular to the axial direction are arranged in the circumferential direction of the stator yoke. It is characterized in that both ends are connected to the circumferential end of the stator yoke of the adjacent split core and formed in an annular shape.

According to the present invention, the worm and the motor output shaft are integrated, and the electric motor is composed of a brushless motor having a slot combination that is diagonally in phase. The effect that the deterioration of the cogging torque due to the deviation can be reduced is obtained.
Here, by integrating the motor frame and at least the gear housing that accommodates the worm, the entire electric power steering apparatus can be made compact, the number of parts can be reduced, and the number of assembly steps can be reduced. Is obtained. In addition, it is possible to reduce the thermal resistance between the stator and the gear housing, increase the heat transfer from the motor coil wound around the stator to the gear housing, and increase the allowable copper loss, making it compact and lightweight. A brushless motor can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes an electric power steering apparatus. The electric power steering apparatus 1 includes a steering mechanism 2 that is steered by a driver. Yes.
The steering mechanism 2 includes a steering shaft 4 having an input shaft 4a and an output shaft 4b through which a steering force applied from a driver is transmitted to the steering wheel 3, and the steering shaft 4 is one end of the input shaft 4a. Is connected to the steering wheel 3, and the other end is connected to one end of the output shaft 4b via a steering torque sensor 5 as steering torque detecting means.

The steering force transmitted to the output shaft 4 b is transmitted to the lower shaft 7 via the universal joint 6 and further transmitted to the pinion shaft 9 via the universal joint 8. The steering force transmitted to the pinion shaft 9 is transmitted to the tie rod 11 via the steering gear 10 to steer a steered wheel (not shown).
Here, the steering gear 10 is configured in a rack and pinion type having a pinion 10a connected to the pinion shaft 9 and a rack 10b meshing with the pinion 10a, and the rotational motion transmitted to the pinion 10a is linearly moved by the rack 10b. It has been converted to movement.

A steering assist mechanism 12 that transmits a steering assist force to the output shaft 4b is connected to the output shaft 4b of the steering shaft 4. The steering assist mechanism 12 includes a worm speed reducer 13 connected to the output shaft 4 b and a brushless motor 14 as an electric motor that generates a steering assist force connected to the worm speed reducer 13.
The brushless motor 14 receives the steering torque applied to the steering wheel 3 detected by the steering torque sensor 5 and transmitted to the input shaft 4a, and the vehicle speed output from the vehicle speed sensor 15 that detects the vehicle speed. Drive control is performed by the control device 16 to which the detection value is inputted.

  The control device 16 refers to a control map that stores the relationship between the steering torque and the steering assist command value using the vehicle speed detection value as a parameter, calculates a steering assist command value, and calculates the calculated steering assist command value and the brushless motor. Based on the flowing motor current, feedback control is performed to calculate a motor current command value, and the calculated motor current command value is supplied to a motor drive circuit 17 constituted by an inverter circuit. By forming a three-phase motor drive current based on the command value and an angle detection signal from a resolver that detects the rotor rotation angle of the brushless motor 14 described later, and supplying this three-phase motor drive current to the brushless motor 14, The brushless motor 14 generates a steering assist force corresponding to the steering assist command value.

And the gear housing 13a of the worm reduction gear 13 and the frame half 23a, which will be described later, of the brushless motor 14 are integrated, and these have higher heat conductivity than the steel plate constituting the conventional frame, such as aluminum, aluminum alloy, magnesium and magnesium. Any one of the alloys is integrally formed by casting with a die casting machine.
As shown in FIG. 2, the worm speed reducer 13 is engaged with the worm wheel 13b and the worm wheel 13b that are connected to the output shaft 4b, and is integrated with the output shaft 14b of the brushless motor 14. The worm 13c is formed. Here, the opposite side of the worm 13c from the motor output shaft 14b is rotatably supported by a rolling bearing 13d fixed to the gear housing 13a via an elastic body 13e.

  Further, a preload mechanism 21 that presses the worm 13c toward the worm wheel 13b with a constant pressure is disposed outside the rolling bearing 13. As shown in FIG. 3, the preload mechanism 21 includes a preload pad 23 disposed in a recess 22 formed in the gear housing 13a so as to be displaceable in the vertical direction, and a gear housing for guiding the preload pad 23 in the vertical direction. A pair of left and right guide pins 24 fixed to 13a and a torsion coil spring 25 for applying a preload downward to the preload pad 23 are provided. A small-diameter shaft portion 13d of the worm 13c is fitted to the central portion of the preload pad 23.

  Here, the preload pad 23 has a curvature substantially equal to the inner diameter of the upper torsion coil spring 25 by cutting the outer side symmetrically across the center at a horizontal chord position above the center of the disk. The selected umbrella-shaped plate portion 23a, and a protrusion that protrudes downward from the central portion of the lower surface of the umbrella-shaped plate portion 23a and is guided by the guide pin 24, and the lower surface is selected to have a radius smaller than the inner diameter of the torsion coil spring 25. A plate portion 23b is formed.

And the fitting hole 23c which fits the small diameter shaft part 13d of the worm 13c is formed in the center point of the circular arc of the umbrella-shaped board part 23a in the protrusion board part 23b, Furthermore, the lower surface of the umbrella-shaped board part 23a, the guide pin 24, and A gap is formed between the two.
A torsion coil spring 25 is wound around the preload pad 23 so as to contact the outer peripheral surface of the umbrella-shaped plate portion 23a and not to contact the arc surface of the lower surface of the protruding plate portion 23b. By locking the formed inwardly bent portion 25a on the side opposite to the umbrella-shaped plate portion 23a of the guide pin 24, the preload pad 23 is pressed downward by the torsion coil spring 25, whereby the worm 13c is Preloaded on the worm wheel 13b side.

  On the other hand, as shown in FIGS. 2, 4, and 5, the brushless motor 14 includes a frame 33 that houses a stator 31 and a resolver 32 as a rotation angle detector that detects a rotor rotation angle. Is a cylindrical frame half 33A that accommodates the stator 31 formed integrally with the gear housing 13a, and a frame half 33B that accommodates the resolver 32 joined to the right end of the frame half 33. It is divided into two and both are screwed at the joint surface.

  The frame half body 33A has a large diameter portion 37 that fits the stator 31 that extends in the axial direction from the end surface on the frame half body 33B side on the inner peripheral surface, and a small diameter portion 39 that houses the annular seal body 38 at the tip. Is formed. Further, the inner peripheral surface of the large-diameter portion 37 of the frame half body 33A has the same number of slots as the brushless motor extending from the end surface on the frame half body 33B side in the axial direction with a length substantially equal to the axial length of the stator 31. Concave portions 40 having a circular arc cross section are formed at equal intervals.

Further, as clearly shown in FIG. 2, the frame half body 33 </ b> B is formed with a large-diameter portion 41 that accommodates the resolver 32 on the inner peripheral surface opposite to the frame half-body 33 </ b> A, and is connected to the large-diameter portion 41. Thus, for example, a small-diameter portion 43 into which a rolling bearing 42 constituted by a deep groove ball bearing is fitted is formed.
Here, the frame half body 33B is formed by die-casting any one of aluminum, aluminum alloy, magnesium and magnesium alloy, similarly to the frame half body 33A.

As described above, both the frame halves 33A and 33B are manufactured by casting, but a portion requiring high accuracy such as an inlay portion is appropriately cut.
The stator 31 is fitted in the large diameter portion 37 of the frame half 33A. 4 and 5, the stator 31 has a configuration in which T-shaped split cores 51 in which 12 electromagnetic steel plates are stacked are connected in an annular shape.

  As shown in FIG. 4, each of the split cores 51 has a cross section orthogonal to the axial direction. The stator yoke 52 has an arcuate outer peripheral surface and extends in the circumferential direction, and a circle on the inner peripheral surface of the stator yoke 52. A magnetic leg portion 53 that extends inward toward the central axis at the center in the circumferential direction is formed of a T-shaped iron core, and a hat portion 53 a is formed at the tip of the magnetic leg portion 53. A motor coil 54 is wound around the magnetic leg 53 by concentrated winding. The hat portion 53a has a shape in which a slight slot opening width is formed in a state where 12 T-shaped split cores 51 are combined into an annular shape, and the slot opening width is a magnet wire used for the motor coil 44. Is set below the diameter. The surface of the stator yoke 52 fitted to the frame half 33A has substantially the same curvature as that of the frame, but the portion of the magnetic leg 53 that is directly behind the neck is flattened. It becomes the shape which carries out line contact at two points at the time of fitting.

On the other hand, the slot side of the stator yoke 52 has a linear shape orthogonal to the neck center line of the magnetic leg portion 53. The portion where the adjacent split core 51 abuts is a linear shape of ± 15 ° intersecting at the center of rotation with respect to the center line of the magnetic leg portion 53 to which the motor coil 54 is applied, and is in a shape in surface contact with each other. .
Also, convex half portions 55 each having a quarter of a cross section engaging with the concave portion 40 of the frame half body 33A are formed over the entire axial direction at both ends in the circumferential direction on the outer peripheral surface of the outer peripheral side base portion 52. Yes. Therefore, when the split cores 51 are connected to each other, as shown in an enlarged view in FIG. 4, both the convex halves 55 are identical to the concave portions 40 that engage with the concave portions 40 formed in the frame half body 33 </ b> A having a semicircular cross section. A convex portion 56 having a shape in which the central point is slightly shifted to the stator central axis side with respect to the central point of the concave portion 40 of the frame half body 33A is formed. Then, in a state where the divided cores 51 are connected in an annular shape, the convex portion 56 is welded by laser welding or the like, whereby the annular stator 31 is configured, and the stator 31 has a large diameter of the frame half body 33A. The convex portion 56 is engaged with the concave portion 40 and is fitted to the portion 37. At this time, the yoke 53 of the stator 31 is positioned in contact with a stator yoke abutting portion 57 formed on the frame half 33A.

The terminal of the motor coil 54 of each phase is connected to the motor drive circuit 17 through a four-layered annular ring (not shown) insulated for each Y connection midpoint, U phase, V phase, and W phase.
Thus, by using the split core system for the stator 31, a space for passing a winding nozzle necessary for winding in the integral core system, and a space for guiding the winding in dropping into the slot. For example, a useless slot space that is generated only for the winding configuration is not required, so that high-density winding is possible.

  Further, in the split core 51, by setting the slot opening width formed by the hat portion 53a to be equal to or less than the diameter of the magnet wire used for the motor coil 54, even if the motor coil 54 is loosened or disconnected, it becomes an air gap. Since it is not bitten, the steering wheel lock due to the motor lock, which is a failure that should not occur in the electric power steering apparatus, can be prevented.

Further, in the split core 51, the surface of the stator yoke 52 that is fitted to the frame half body 33A has a shape that makes line contact at two points when the frame is fitted, so that a reaction force is applied to the magnetic leg portion 56 when torque is generated. Even if it is applied, the T-shaped split core 41 is unlikely to fall down, so noise and vibration can be reduced.
Further, in the T-shaped split core 41, the slot side of the stator yoke 52 is formed in a linear shape perpendicular to the center line of the neck of the magnetic leg portion 53, so that the stator yoke 52 does not interfere during winding, so that high-density winding is possible. A line is possible.

  Furthermore, in the T-shaped split core 51, a simple annular stator yoke portion is formed by providing a half-cracked convex half 55 on the outer peripheral side of the portion where the stator yoke 52 of the adjacent split core 51 abuts. The abutting area is larger than that of the divided core method, and the T-shaped split core 51 is unlikely to fall even if a reaction force is applied to the magnetic leg portion 53 when torque is generated. Furthermore, since the convex half portion 55 protruding to the outer peripheral side is welded, the magnetic flux passing through the welded portion is small and the hysteresis loss can be reduced. These effects can reduce noise, vibration, and iron loss.

Further, since the convex portion 56 protrudes to the outer peripheral side, it is possible to prevent magnetic path narrowing due to the fact that the slot side of the stator yoke 52 has a linear shape perpendicular to the neck centerline of the magnetic leg portion 53. it can.
Moreover, since the convex part 56 has a large gap in the radial direction with respect to the concave part provided in the frame half body 33A, but has almost no gap in the rotational direction, when the divided cores 51 are welded together. It is possible to shrink the frame half body 33A without removing the generated beads and bulges. Further, only the ambient temperature of the brushless motor 14 rapidly increases and only the frame half 33A becomes high temperature, or the frame half 33A is cracked by an unexpected external force, etc. Since the stator 31 does not run idle even if the tightening allowance is lost, it is possible to reliably prevent torque reduction, torque ripple, torque difference due to the rotation direction, and self-steer, which is a failure that should not occur in the electric power steering device. Can be prevented.

Further, as described above, the recess 40 of the frame half 33A extends in the same shape from the side where the frame half 33B is attached to the stator fitting portion to a position slightly deeper than the stator yoke butting portion. There is no need to change the shape of the electromagnetic steel sheet depending on the direction of the accumulated pressure, and the stator 31 can be composed of the same shape of T-shaped electromagnetic steel sheet.
These features are obtained by connecting the same number of T-shaped split cores 51 as the number of slots 12, and the same effect can be obtained even when applied to a developed core type stator that becomes an annular stator 31 by bending the connecting portion. can get.

Further, a resolver stator 31 s constituting the resolver 32 is fitted into the large diameter portion 41 of the frame half body 33B.
On the other hand, the rotor 61 is rotatably supported by the gear housing 13a and the frame half 33B by the rolling bearings 13 and 32 held by them. The rotor 61 includes an output shaft 62 rotatably supported by the rolling bearings 13 and 42, a magnetic pole portion 63 fixed at a position facing the stator 31 of the output shaft 62, and a resolver stator of the output shaft 62. It is comprised with the resolver rotor 32r which comprises the resolver 32 fixed to the position facing 32s. Thus, the rotor 61 is assembled in the order of the magnetic pole portion 63, the rolling bearing 42, the resolver rotor 32r, and the lock nut 64 as viewed from the worm 13c side of the frame half 33A.

  Here, as clearly shown in FIG. 5, the magnetic pole portion 63 is composed of a cylindrical rotor yoke 65 that is inserted through the output shaft 62 and eight sheets that are bonded to the outer peripheral surface of the rotor yoke 65 at equal intervals in the circumferential direction. The permanent magnet 66 includes a cap 67 made of austenitic nonmagnetic stainless steel that covers the outer peripheral surface of the permanent magnet 66. The permanent magnet 66 serving as the magnetic pole is a segment magnet divided for each pole, and the shape of the permanent magnet 66 is formed in a saddle shape in which the arc center on the outer peripheral side is intentionally shifted from the rotation center.

  The outer peripheral part of the permanent magnet 66 constituting the magnetic pole part 63 is covered with a cap 67. The cap 67 is a clearance fit, but is fixed to the permanent magnet 66 by using an adhesive together. It is fixed more firmly by caulking the end face of it with rivets. Furthermore, the rolling bearing 42 prevents the displacement of the output shaft 62 from the inner ring due to the axial load applied to the output shaft 62 by press-fitting the inner ring into the output shaft 62 and then tightening the inner ring with the lock nut 64 via the resolver rotor 32r. .

The resolver rotor 32r has a small diameter of a resolver shaft 73 fitted on an output shaft 62 having a large diameter portion 71 that abuts the inner ring of the rolling bearing 42 in the axial direction and a small diameter portion 72 connected to the large diameter portion 71. It is fitted on the part 72 and its axial position is fixed by a lock nut 64.
Thus, since the brushless motor 14 is formed in 8 poles and 12 slots, it has a diagonal in-phase structure in which the permanent magnets 66 that are opposite to each other across the central axis of the rotor 61 are magnetized in the same phase. Thus, since the brushless motor 14 is configured in a diagonal in-phase structure, it is possible to suppress the deterioration of the cogging torque characteristics due to the axial misalignment.

Next, the operation of the first embodiment will be described.
Assuming that the vehicle is now stopped, in this state, when the steering wheel 3 is turned to the right (or left), the steering torque applied to the steering wheel 3 is the steering torque. The detected steering torque detected by the sensor 5 is input to the control device 16, and the zero vehicle speed detection value detected by the vehicle speed sensor 15 is input to the control device 16.

  For this reason, the control device 16 refers to the control map based on the steering torque and the detected vehicle speed value, calculates a relatively large steering assist command value, and feeds back the deviation between the steering assist command value and the detected motor current value. A motor current command value is calculated by performing control, and this motor current command value is output to the motor drive circuit 17, so that the motor drive circuit 17 performs three-phase based on the rotor rotation angle detected by the resolver 22. A motor current is output to the brushless motor 14.

  Therefore, the brushless motor 14 is rotationally driven to generate a relatively large steering assist force, and this steering assist force is transmitted to the worm 13c of the worm speed reducer 13 integrally connected to the output shaft 62, and is transmitted to the worm gear 13c. By rotating the meshing worm wheel 13b, a large steering assist torque can be applied to the output shaft 4b of the steering shaft 4 in the same direction as the rotation direction of the steering wheel 3, and the steering wheel 3 can be lightly steered.

When the vehicle is driven from this state, the calculated steering assist command value becomes a small value even if the steering torque is the same as the vehicle speed detection value increases, and the brushless motor 14 is driven to rotate accordingly. The steering assist force generated by the brushless motor 14 is smaller than that at the time of stationary, and the optimum steering assist force corresponding to the vehicle speed can be generated.
At this time, the output shaft 62 of the brushless motor 14 is integrally formed with the worm 13c constituting the worm speed reducer 13, and the output shaft 62 is held by the rolling bearing 13d held by the gear housing 13a and the frame half body 33B. Since it is rotatably held by the rolling bearing 42, the overall length of the output shaft 62 can be shortened to shorten the axial length of the worm 13c and the brushless motor 14, and the protruding length of the brushless motor 14 can be shortened. Thus, the size can be reduced, and the number of parts can be reduced to reduce the number of assembling steps.

  In addition, since the magnetic pole portion 63 of the rotor 61 and the stator 31 have a slot combination of 8 poles and 12 slots, the configuration is four times that of the most basic 2 pole 3 slot type. Thus, by making the configuration of the magnetic pole portion 63 and the stator 31 diagonally in phase, which is 2n times the basic configuration (n is an integer), the magnetic attraction force in the radial direction is offset, so that the rotor vibration during rotation can be reduced. There is an advantage. For this reason, by integrating the worm 13 c and the output shaft 62 of the brushless motor 14, the lift force in the vertical direction generated at the meshing portion of the worm 13 c and the worm wheel 13 b is transmitted through the output shaft 62 to the rotor of the brushless motor 14. However, it is possible to suppress the influence of the lift force and suppress the deterioration of the cogging torque characteristics.

Incidentally, as shown in FIG. 6, when the magnetic pole part 63 of the rotor 61 and the stator 31 are in a slot combination of 10 poles and 12 slots, the magnetic pole part 63 is diagonally out of phase. It cannot cancel out, rotor vibration during rotation increases, and cogging torque characteristics deteriorate.
Cogging torque when the magnetic gap, outer diameter, and stator shape of the 8-pole 12-slot motor are shifted by 0.1 mm, 0.2 mm, and 0.3 mm with the same dimensions. The ratio of the magnitude of cogging torque was calculated using the finite element method, and the analysis results shown in FIG. 7 are summarized. As can be seen from FIG. 7, by adopting a configuration having diagonal in-phase, the rate of increase in cogging torque characteristics deterioration due to motor shaft misalignment could be reduced.

Further, since the winding coefficient of this slot combination is “0.866” and concentrated winding, there is an advantage that a large torque can be obtained against copper loss.
However, since the amount of change in the interlinkage magnetic flux due to each magnetic pole appears as it is as cogging torque and torque ripple, in order to apply it to the electric power steering apparatus 1, cogging torque and torque ripple that give unpleasant vibration and noise to the driver are used. Further reduction is necessary. In the present embodiment, the permanent magnet 66 serving as a magnetic pole is a segment magnet divided for each pole, and the shape thereof is formed in a saddle shape in which the arc center on the outer peripheral side is intentionally shifted from the rotation center. With such a magnetic pole, the amount of change in the interlinkage magnetic flux can be converted into a sine wave, and the cogging torque and the torque ripple when the sine wave is energized can be reduced.

  Further, by supplying a relatively large motor current to the motor coil 54 of the stator 31 in the brushless motor 14, a rotating magnetic field is generated to rotationally drive the rotor 61. The motor driving current is a large current. As a result, the motor coil 54 generates heat. This heat generation is conducted to the frame half body 33A through the split core 51 of the stator 31, and this frame half body 33A is formed integrally with the gear housing 13a, and has a higher thermal conductivity than that of a normal steel frame. In addition, since any one of aluminum alloy, magnesium and magnesium alloy is die-cast and integrally molded, there is no joint between the frame half 33A and the gear housing 13a, and the worm speed reducer from the stator 31 Since the heat resistance between the gear housing 13 and the gear housing 13a is reduced, the heat generated in the motor coil 54 is effectively transferred to the gear housing 13a of the worm speed reducer 13 so that the motor coil 54 can tolerate copper loss. Can be larger than the example. Further, since the stator 31 is disposed on the gear housing 13a side, the distance between the stator 31 and the gear housing 13a of the worm speed reducer 13 can be minimized so that the thermal resistance can be reduced, and a greater heat transfer effect can be achieved. Can be demonstrated.

  Further, in the above-described embodiment, at least the gear housing 13a of the worm reduction gear 13 and the frame half 33A of the brushless motor 14 are die-cast using any one of aluminum, aluminum alloy, magnesium, and magnesium alloy. Therefore, there is no restriction on the thickness as in the case of narrowing the thin steel plate as in the conventional example, and the specific gravity is about 1/3 of that of the thin steel plate. In contrast, the wall thickness can be about three times. In addition, the aluminum alloy is a material having a thermal conductivity three times that of iron, and further provided with a stator tip abutting portion 58 and filled with a heat transfer body 59 between the coil ends, thereby causing a copper loss. The heat of the coil end can be transferred to the frame half 33 </ b> A via the stator tip abutting portion 58 and the heat transfer body 59. Due to these effects, the heat loss of 10 times or more can be transferred to the gear housing 13a of the worm speed reducer 13 while the gear housing and frame have the same weight as the conventional example. Can be significantly larger than the example.

  Further, since the resolver 22 is disposed at the nearest position of the rolling bearing 42, the axial displacement between the resolver stator 32s and the resolver rotor 32r is prevented by the difference in linear expansion coefficient between the frame material and the shaft material when the motor temperature changes. Can do. In particular, in the case of a combination having a large difference in linear expansion coefficient between the shaft material and the frame material as in this embodiment, the effect is remarkable.

In addition, by mechanically positioning the magnetic pole part 63 and the resolver rotor 32r, there is no torque drop or torque ripple that occurs when the phase of both of them deviates, a torque difference due to the rotation direction, or even an electric power steering device. It is possible to surely prevent a phenomenon such as self-steering.
Further, by covering the permanent magnet 66 constituting the magnetic pole portion 63 with the cap 67, even if the permanent magnet 66 is chipped or cracked, or the permanent magnet 66 is peeled off from the rotor yoke 65, the permanent magnet 66 is in the air. Since it does not bite into the gap, it is possible to reliably prevent the wheel steering lock due to the motor lock, which is a failure that should not occur in the electric power steering apparatus.

In the above embodiment, the case where the stator 31 is a split core method has been described. However, the present invention is not limited to this, and a developed core method in which a stator integrated with laminated steel plates is formed may be used.
In the above embodiment, the case where the resolver 32 is applied as a rotation angle detector for detecting the rotation angle of the rotor has been described. However, the present invention is not limited to this, and a magnetic detection element such as a Hall element or a rotary encoder Any rotation angle detector such as can be applied.

Further, in the above embodiment, the case where at least the gear housing 13a and the frame half body 23A are die cast molded has been described. However, the present invention is not limited to this, and in the case of lost wax, sand mold, magnesium and magnesium alloy, injection molding, etc. , Other casting methods may be applied.
Furthermore, the preload mechanism 21 that presses the worm 13c toward the worm wheel 13b is not limited to the above configuration, and any preload mechanism that can preload the worm 13c toward the worm wheel 13b is applied. can do.

It is a schematic structure figure showing one embodiment of the present invention. It is the front view which made the principal part which the electric power steering device of the present invention shows the section. It is sectional drawing on the AA line of FIG. It is sectional drawing on the BB line of FIG. It is a disassembled perspective view of the brushless motor which can be applied to this invention. It is sectional drawing similar to FIG. 4 which shows the comparative example with respect to this invention. It is a characteristic diagram which shows the ratio with respect to the amount of axial deviation which shows the analysis result of this invention and a comparative example, and no axial deviation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering mechanism, 3 ... Steering wheel, 4 ... Steering shaft, 4a ... Input shaft, 4b ... Output shaft, 10 ... Steering gear, 12 ... Steering assist mechanism, 13 ... Worm speed reducer, 13a DESCRIPTION OF SYMBOLS ... Gear housing, 13b ... Worm wheel, 13c ... Worm, 13d ... Rolling bearing, 13e ... Elastic body, 14 ... Brushless motor, 16 ... Controller, 17 ... Motor drive circuit, 21 ... Preload mechanism, 31 ... Stator, 32 ... Resolver 33 ... Frame, 33A, 33B ... Frame half, 42 ... Rolling bearing, 51 ... Split core, 52 ... Stator yoke, 53 ... Magnetic legs, 54 ... Motor coil, 61 ... Rotor, 62 ... Output shaft, 63 ... magnetic pole part, 64 ... rotor yoke, 66 ... permanent magnet, 67 ... cap

Claims (7)

An electric motor for generating a steering assist force for the steering system, a worm meshed with a worm wheel mounted on the steering system formed integrally with an output shaft of the electric motor, and supporting an axial reaction force of the worm; An electric power steering device having a bearing device having a mechanism that allows a deviation angle of an output shaft of the electric motor, and a preload mechanism that presses the worm against the worm wheel at a constant pressure,
The electric power steering apparatus, wherein the electric motor is configured by a brushless motor having a slot combination that is diagonally in phase.   The electric power steering apparatus according to claim 1, wherein the brushless motor is configured with 8 poles and 12 slots.   The brushless motor includes a cylindrical stator around which a coil is wound, a rotor having a magnetic pole and an output shaft facing the stator, an angle detector that detects a rotation angle of the rotor, the stator, and the angle detection And a bearing device that rotatably supports the rotor with respect to the frame, wherein the frame is integrated with at least a gear housing that houses the worm. Item 3. The electric power steering device according to Item 1 or 2.   The electric power steering apparatus according to claim 3, wherein the frame is made of a material having high thermal conductivity.   The electric power steering apparatus according to claim 4, wherein the frame is formed of any one of aluminum, an aluminum alloy, magnesium, and a magnesium alloy.   6. The electric power steering apparatus according to claim 3, wherein the frame is integrally formed by casting.   The stator is perpendicular to the axial direction by a circumferentially extending stator yoke that fits into the frame and a magnetic leg portion around which the motor coil is wound, extending inward from the circumferential central portion of the stator yoke. A plurality of split cores having a T-shaped cross section are formed in an annular shape by connecting both circumferential ends of the stator yoke to the circumferential ends of the stator yokes of the adjacent split cores. The brushless motor according to any one of claims 3 to 6, wherein:

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