JP2008162531A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of abnormal noise caused by a clearance in a rotational direction between a worm shaft in a speed reduction mechanism and a joint member connecting the worm shaft to a rotary shaft of a motor. <P>SOLUTION: This electric power steering device P has the electric motor 14 for steering aid and the speed reduction mechanism 20 reducing the speed of the rotation of the rotary shaft 21 of the electric motor 14, and the reduction mechanism 20 includes the worm shaft 21 driven by the rotary shaft 21 of the motor 14, and a worm wheel 23 driven by the worm shaft 22. Furthermore, the device has a joint section 28 connecting the rotary shaft 21 and the worm shaft 22 so that drive can be transmitted, and an energizing means 32 arranged in the joint section 28 and energizing the worm shaft 22 in the axial and rotational direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

  In an electric power steering device for an automobile, when a steering member such as a steering wheel is rotated by the driver in order to reduce the driver's labor at the time of steering, the steering power applied to the steering member is Thus, the output rotation of the electric motor for assisting the steering force is controlled. The rotational force of the electric motor is transmitted to the steering mechanism via the speed reduction mechanism, and the operation of the steering mechanism is assisted in accordance with the rotation operation of the steering member.

As the speed reduction mechanism, there is known a mechanism including a worm shaft coupled to a rotating shaft of an electric motor so as to be integrally rotatable, and a worm wheel meshing with a worm of the worm shaft, and the worm shaft is rotated by a bearing device. It is supported freely.
However, since there is a thrust gap between the inner ring and the outer ring fitted via a plurality of rolling elements in the bearing device, the worm rattles in the axial direction due to the thrust gap. Noise may occur during operation.

  Therefore, in order to prevent the occurrence of such abnormal noise, it has been proposed to bias the worm shaft toward the non-motor side by a coil spring (see, for example, Patent Document 1). The electric power steering device described in Patent Document 1 is configured such that the worm shaft is biased toward the opposite side of the motor by a coil spring disposed so as to contact the end surface of the worm shaft on the motor side. Is applied with a preload, thereby preventing the generation of abnormal noise due to the thrust gap of the bearing device.

JP 2003-72563 A

  By the way, the rotating shaft and the worm shaft of the electric motor are normally connected to each other by a sleeve-like joint member so as to be integrally rotatable. In this case, power transmission between the joint member and the worm shaft is often performed via serration portions formed on the inner peripheral surface of the joint member and the outer peripheral surface of the worm shaft. However, there is a small gap (play) between the two serration portions, and this gap cannot be eliminated by applying the preload in the worm axis direction described above. Therefore, the rotational force of the electric motor is transmitted through the joint member. When transmitted to the worm shaft, abnormal noise may occur in the serration portion.

  The present invention has been made in view of such circumstances, and an abnormal noise caused by a gap in a rotational direction between a worm shaft in a speed reduction mechanism and a joint member connecting the worm shaft to a rotation shaft of a motor. An object of the present invention is to provide an electric power steering device that can prevent the occurrence of the above.

The electric power steering apparatus of the present invention includes an electric motor for assisting steering and a speed reduction mechanism for reducing the rotation of the rotation shaft of the electric motor, and the speed reduction mechanism is driven by the rotation shaft of the electric motor. An electric power steering device including a worm shaft and a worm wheel driven by the worm shaft,
A joint for connecting the rotating shaft and the worm shaft so as to be able to transmit drive;
An urging means provided in the joint portion for urging the worm shaft in an axial direction and a rotation direction;
It is characterized by having.

  In the electric power steering apparatus of the present invention, the worm shaft is biased in the axial direction and the rotational direction to the joint portion for connecting the worm shaft in the speed reduction mechanism and the rotating shaft of the electric motor so as to be capable of driving transmission. Therefore, the preload can be applied to the worm shaft in the axial direction and the rotational direction. Therefore, it is possible to prevent not only abnormal noise caused by play in the axial direction of the worm shaft but also abnormal noise caused by play in the rotational direction.

  Preferably, the joint portion includes a sleeve connected to the rotating shaft and the worm shaft so as to be integrally rotatable, and the urging means is provided on an outer periphery of the sleeve. In this case, the biasing means provided on the outer periphery of the sleeve can apply preload to the worm shaft in the axial direction and the rotational direction, and space is saved compared to the case where preloading in both directions is performed by separate means. Can be saved.

  The biasing means comprises a coil spring, one end of the coil spring engages with an engagement portion provided on one of the worm shaft or the rotation shaft, and the other end is an end portion of the sleeve. And it is preferable that it engages with the engaging part provided in the edge part of the other side of the said worm shaft or a rotating shaft. According to this configuration, since the preload in the axial direction and the rotational direction is applied to the worm shaft by using the coil spring disposed on the outer periphery of the sleeve, the rotational shaft of the electric motor using the rubber spring or the rubber coupling is used. As compared with the case where power is transmitted between the worm shaft and the worm shaft, the radial dimension can be reduced.

  According to the electric power steering apparatus of the present invention, it is possible to prevent the generation of noise due to the rotational clearance between the worm shaft in the speed reduction mechanism and the joint member connecting the worm shaft to the rotation shaft of the motor. Can do.

Embodiments of an electric power steering apparatus (hereinafter also simply referred to as “power steering apparatus”) according to the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a power steering device P according to an embodiment of the present invention. This power steering device P is a type of power steering device in which the steering member 1 and the wheel 2 are mechanically connected. However, in the present invention, the mechanical connection between the steering member 1 and the wheel 2 is released. The present invention is also applicable to a power steering device configured as a so-called steer-by-wire.

  The steering member 1 is coupled to the steering shaft 3 so as to be integrally rotatable, and a pinion gear 4 is provided at the tip of the steering shaft 3. The pinion gear 4 meshes with a rack gear 6 formed on a rack shaft 5 extending in the left-right direction of the vehicle. Tie rods 7 are coupled to both ends of the rack shaft 5, and each tie rod 7 is connected to the wheel 2 via a corresponding knuckle arm (not shown).

  When the steering member 1 is rotated and the steering shaft 3 is rotated, this rotation is converted by the pinion gear 4 and the rack gear 6 into a linear motion of the rack gear 6 along the left-right direction of the vehicle. Thereby, the wheel 2 is steered in a desired direction.

  The steering shaft 3 includes a cylindrical first steering shaft 8 connected to the steering member 1 and a second steering shaft 9 connected to the pinion gear 4, and these first and second steering shafts. 8 and 9 are connected to each other on the same axis via a torsion bar 10. A torque sensor 11 for detecting a steering torque by a relative rotational displacement between the first steering shaft 8 and the second steering shaft 9 via the torsion bar 10 is disposed in the vicinity of the torsion bar 10, and this torque sensor 11 torque detection results are transmitted to the controller 12. The control unit 12 controls the voltage applied to the steering assisting electric motor 14 via the driver 13 based on the transmitted torque detection result. The rotation of the rotating shaft 21 (see FIG. 2) of the electric motor 14 is transmitted to the second steering shaft 9 via a speed reduction mechanism 20 described later, and the driver's steering is assisted.

  The speed reduction mechanism 20 decelerates the rotation of the rotating shaft 21 of the electric motor 14 and transmits it to the second steering shaft 9, and is driven by the rotating shaft 21 of the electric motor 14 as shown in FIG. A worm shaft 22 and a worm wheel 23 driven by the worm shaft 22. The rotating shaft 21 and the worm shaft 22 are disposed so as to be integrally rotatable on the same axis. The worm wheel 23 is disposed so as to mesh with a worm 24 formed in the vicinity of the intermediate portion of the worm shaft 22 in the axial direction, and is engaged with the second steering shaft 9 so as to be integrally rotatable.

  The vicinity of the motor side end portion and the non-motor side end portion of the worm shaft 22 are rotatably supported by bearing devices 25a and 25b, respectively. The bearing devices 25a and 25b are both ball bearings, and are rotatably arranged between the outer rings 26a and 26b, the inner rings 27a and 27b disposed inside the outer rings 26a and 26b, and the two rings. A plurality of balls 40 provided, and a cage (not shown) that holds the balls 40 at predetermined intervals in the circumferential direction are provided.

  As shown in FIG. 3, the rotary shaft 21 and the worm shaft 22 are connected to the outer periphery of the tip end portion 21a of the rotary shaft 21 and the outer periphery of the motor side end portion 22a of the worm shaft 22 so as to be able to transmit driving. A joint portion 28 is provided. In the present embodiment, the joint portion 28 includes a sleeve 29 that is connected to the rotary shaft 21 and the worm shaft 22 so as to be integrally rotatable. The sleeve 29 is produced by, for example, punching serration after forging. can do.

  A serration portion 30 is formed on the inner peripheral surface of the sleeve 29 on the side opposite to the motor, and the serration portion 30 is formed on the outer periphery of the motor-side end portion 22a of the worm shaft 22. Serrations fit with the part 31. On the other hand, the tip 21 a of the rotating shaft 21 is press-fitted into the inner peripheral surface of the sleeve 29 on the motor side. As a result, the rotation of the rotating shaft 21 of the electric motor 14 is transmitted to the worm shaft 22 via the sleeve 29.

  A coil spring 32 as an urging means is disposed on the outer periphery of the sleeve 29, and one end (motor side end) of the coil spring 32 is an end of the sleeve 29 and is on the rotating shaft 21 side. Is engaged with an engaging portion 33 provided at the end of the. On the other hand, the other end of the coil spring 32 is engaged with an engaging portion 34 provided on the motor side with respect to the bearing device 25 a on the outer periphery of the worm shaft 22. More specifically, one end of the coil spring 29 is engaged with an engagement portion 33 formed of a flange portion integrally formed on the outer periphery of the end portion of the sleeve 29 on the motor side, and the other end of the coil spring 29 is at the center. Is engaged with an engaging portion 34 formed of a disc body having an opening. The engagement portion 34 is restricted from moving toward the non-motor side by a ring-shaped convex portion 35 formed on the outer peripheral surface of the worm shaft 22. FIG. 4 is an explanatory front view of the engaging portion 34 as viewed from the motor side. As shown in FIG. 4, the ring-shaped convex portion 35 has a protrusion 35a protruding toward the motor side. Two portions are formed at equal intervals in the direction. On the other hand, a notch 34 a that can engage with the protrusion 35 a is formed on the periphery of the opening of the engaging portion 34. Further, by disposing the engaging portion 34 so that the protrusion 35a engages with the notch 34a, the engaging portion 34 can be prevented from rotating on the outer peripheral surface of the worm shaft 22. The serration portion 31 formed on the outer periphery of the motor-side end portion 22a of the worm shaft 22 is formed up to the convex portion 35, while the serration portion is formed on the periphery of the opening of the engagement portion 34 to form the serration portion. By engaging the serration with 31, the engagement portion 34 can be prevented from rotating.

A plurality of convex portions formed along the circumferential direction of the worm shaft 22 may be used instead of the ring-shaped convex portion 35. Further, the engaging portion 34 may be fixed to the outer periphery of the worm shaft 22 by adhesion or the like without using such a ring shape or a plurality of convex portions, and further, the engaging portion 34 abuts on the bearing device 25a. By doing so, the movement of the engaging portion 34 in the axial direction may be restricted.
Further, in the present embodiment, the engaging portion 33 is formed integrally with the sleeve 29, but a member configured as a separate member can be fixed to the sleeve 29.

  The coil spring 32 is disposed on the outer periphery of the sleeve 29 in a state in which the coil spring 32 is compressed and a torsion around an axis is applied. As a result, axial and rotational preloads can be applied to the worm shaft 22 via the engaging portion 34. The magnitude of this preload can be adjusted by changing the spring constant of the coil spring 32 and the degree of compression and torsion applied to the coil spring 32.

  By applying preload in the axial direction and the rotational direction to the worm shaft 22 in this way, not only abnormal noise due to axial play of the worm shaft 22 but also abnormal noise due to rotational play is generated. Can be prevented. Further, since the preload in the axial direction and the rotational direction is applied to the worm shaft 22 by the coil spring 32, which is a single member, disposed on the outer periphery of the sleeve 29, compared with the case where the preload is applied in both directions by separate means. Saving space. Further, by selecting a coil spring 32 having an inner diameter slightly larger than the outer diameter of the sleeve 29, a rubber spring or a rubber coupling is used between the rotating shaft 21 and the worm shaft 22 of the electric motor 14. As compared with the case where the power transmission is performed, the dimension in the radial direction can be reduced.

  In the above-described embodiment, the motor side end portion of the coil spring 32 is engaged with the engaging portion 33 formed of the flange portion formed on the outer periphery of the motor side end portion of the sleeve 29. The end of the coil spring 32 on the motor side can be engaged with an engaging portion provided on the rotary shaft 21 on the motor side of the sleeve 29. In this case, the end of the coil spring 32 on the side opposite to the motor is engaged with an engaging portion formed of a flange portion integrally formed on the outer periphery of the end on the side of the motor 29 opposite to the sleeve. The movement toward the non-motor side is restricted by the convex portion. Also in this embodiment, preloads in the axial direction and the rotational direction can be applied to the worm shaft 22, and not only abnormal noise caused by play in the axial direction of the worm shaft 22 but also due to play in the rotational direction. The generation of abnormal noise can be prevented.

It is a mimetic diagram showing a schematic structure of one embodiment of a power steering device of the present invention. FIG. 2 is a partial cross-sectional explanatory view showing a speed reduction mechanism in the power steering apparatus shown in FIG. 1. FIG. 3 is an enlarged explanatory view of a main part of FIG. 2. It is front explanatory drawing which looked at the engaging part from the motor side.

Explanation of symbols

14 Electric motor 20 Deceleration mechanism 21 Rotating shaft 22 Worm shaft 23 Worm wheel 24 Worm 25a Bearing device 25b Bearing device 26a Outer ring 26b Outer ring 27a Inner ring 27b Inner ring 28 Joint portion 29 Sleeve 30 Serration portion 31 Serration portion 32 Coil spring (biasing means)
33 engaging portion 34 engaging portion 40 ball P electric power steering device

Claims (3)

An electric motor for assisting steering, and a speed reduction mechanism that decelerates the rotation of the rotating shaft of the electric motor. The speed reducing mechanism is driven by the rotating shaft of the electric motor, and the worm shaft An electric power steering device including a driven worm wheel,
A joint for connecting the rotating shaft and the worm shaft so as to be able to transmit drive;
An urging means provided in the joint portion for urging the worm shaft in an axial direction and a rotation direction;
An electric power steering apparatus comprising:   The electric power steering apparatus according to claim 1, wherein the joint portion includes a sleeve coupled to the rotating shaft and the worm shaft so as to be integrally rotatable, and the urging means is provided on an outer periphery of the sleeve. .   The biasing means comprises a coil spring, one end of the coil spring engages with an engagement portion provided on one of the worm shaft or the rotation shaft, and the other end is an end portion of the sleeve. The electric power steering apparatus according to claim 2, wherein the electric power steering apparatus is engaged with an engaging portion provided at an end portion on the other side of the worm shaft or the rotating shaft.

Images