JP5800233B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that uses a rotational output of an electric motor as an auxiliary steering force.

  The electric power steering device decelerates and torques the rotation output of an electric motor by a reduction mechanism and transmits it to a steering mechanism to assist the driver in steering the steering wheel. In this case, the steering force input from the steering wheel to the speed reduction mechanism via the steering shaft is detected by the torque sensor and input to the CPU. Then, the CPU supplies electric power according to the detected operation force and vehicle speed to the electric motor to generate an appropriate auxiliary steering force.

  As a speed reduction mechanism provided in such an electric power steering apparatus, a mechanism having a worm gear and a worm wheel that mesh with each other is used. That is, the worm gear is provided on the worm shaft connected to the motor shaft of the electric motor, the worm wheel is provided on the steering shaft side orthogonal to the worm shaft, and the rotation of the electric motor is decelerated by the worm gear and the worm wheel. The direction is converted to a right angle while being transmitted to the steering mechanism.

  By the way, the worm shaft and the motor shaft are connected by spline fitting, and both ends in the axial direction of the worm shaft are rotatably supported by bearings, but the spline fitting portion between the worm shaft and the motor shaft has a diameter. Since there is play in the direction and the bearing has play due to an internal gap, there is a possibility that the worm shaft and the motor shaft vibrate when the vehicle travels on a rough road or the like, and noise is generated. In addition, since there is a backlash in the spline fitting part between the worm shaft and the motor shaft, there is a problem that abnormal noise occurs due to contact between metals at the moment when the electric motor is started or when the rotation direction of the electric motor is changed. There is.

  Therefore, in Patent Document 1, a circumferential groove is formed on the outer periphery of a worm shaft that is spline-fitted inside a cylindrical motor shaft, and an elastic ring (O-ring) is fitted into the circumferential groove, and the wire diameter of the elastic ring is determined. The elastic ring is crushed in the radial direction by forming the circumferential groove eccentrically or by forming the circumferential groove eccentrically, and the elastic reaction force caused by the crushing of the elastic ring causes the worm shaft to move radially outward. A configuration has been proposed in which the noise is prevented from occurring by pressing the worm shaft and the motor shaft.

  In Patent Document 2, a motor shaft and a worm shaft are spline-fitted by a sleeve, and a compression coil spring is mounted between each end surface of the motor shaft and the worm shaft inside the sleeve. Thus, a configuration has been proposed in which the worm shaft is urged in the axial direction to eliminate the backlash of the bearing that supports the worm shaft, thereby preventing the generation of abnormal noise.

JP 2003-034256 A JP 2003-072563 A

  However, the configuration proposed in Patent Document 1 eliminates the backlash of the fitting portion between the worm shaft and the motor shaft, and the configuration proposed in Patent Document 2 eliminates the backlash of the bearing that supports the worm shaft. Each of them does not eliminate the play of the spline fitting part and the play of the bearing at the same time. If both configurations are adopted, the play of the spline fitting portion and the play of the bearing can be eliminated at the same time, but there is a problem that the structure becomes complicated.

  Further, in the configurations proposed in Patent Documents 1 and 2, both the amount of play of the spline fitting portion between the motor shaft and the worm shaft is the same at the moment when the electric motor is started or the rotation direction of the electric motor is changed. However, since no means for suppressing the relative rotation or means for reducing the impact caused by metal contact are provided, it is difficult to reliably prevent the generation of abnormal noise.

  The present invention has been made in view of the above problems, and the object of the present invention is to prevent the generation of noise caused by the spline fitting portion between the motor shaft and the worm shaft and the play of the bearing with a simple configuration. An object of the present invention is to provide an electric power steering device that can be used.

  In order to achieve the above object, the invention according to claim 1 is to spline-fit a motor shaft of an electric motor and a worm shaft, and to rotatably support an axial end portion of the worm shaft by a rolling bearing, In the electric power steering apparatus that transmits the rotation output of the electric motor as an auxiliary steering force to the steering mechanism from the motor shaft through the worm shaft, a worm gear provided on the worm shaft, and a worm wheel meshing with the worm gear, the motor An engaging groove is formed on each of the opposing end surfaces of the shaft and the worm shaft, and a pressurizing member for biasing the worm shaft in the axial direction is interposed between both end surfaces, and the pressurizing member is disposed on the motor shaft. And engaging with the engaging groove formed in the worm shaft.

  According to a second aspect of the present invention, in the first aspect of the present invention, the pressurizing member is constituted by a coil spring, and both ends of the coil spring are engaged with the engagement groove formed in the motor shaft and the worm shaft. It is characterized by being combined.

  According to a third aspect of the present invention, in the first aspect of the present invention, the pressurizing member is constituted by a wave washer, and the engaging protrusions protruding in opposite directions are provided at two opposite positions of the wave washer. It is engaged with the engaging groove formed in the motor shaft and the worm shaft.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the engagement groove formed in the motor shaft and the worm shaft is an arcuate concave groove, and the engagement protrusion of the wave washer is a circular shape. An arc-shaped protrusion is formed, and the arc-shaped protrusion is engaged with the arc-shaped groove.

  The invention according to claim 5 is the invention according to claim 4, wherein the radius of curvature of the arc-shaped protrusion is set larger than the radius of curvature of the arc-shaped concave groove.

  According to the present invention, since the worm shaft is urged in the axial direction by the pressurizing member interposed between the opposite end surfaces of the motor shaft and the worm shaft, the rolling bearing supporting the worm shaft is free from backlash. The generation of abnormal noise due to this play is reliably prevented. Here, a coil spring, a wave washer, etc. can be used as a pressurizing member.

  Also, at the moment when the electric motor is started or when the rotation direction of the electric motor is changed, the rotation torque of the motor shaft is first transmitted to the worm shaft by the pressurizing member, so that the spline fit between the motor shaft and the worm shaft is performed. The impact load applied to the joint portion is reduced, and the collision contact between metals in the spline fitting portion is suppressed. At the same time, the relative rotation between the motor shaft and the worm shaft is suppressed by the pressurizing member, and the rotational force of the motor shaft is gradually transmitted to the worm shaft through the pressurizing member, and the spline teeth in the spline fitting portion are Since the collision is alleviated and the impact at that time is absorbed by the pressurizing member, the generation of abnormal noise is effectively prevented.

  Thus, the above effect can be obtained by a simple configuration in which the pressurizing member is simply interposed between the opposed end surfaces of the motor shaft and the worm shaft, which may lead to a complicated structure and an increase in cost. Absent.

  By the way, a wave washer is used as the pressurizing member, an arc-shaped groove is formed in the motor shaft and the worm shaft, and an engaging protrusion of the wave washer that engages with the arc-shaped groove is formed as an arc-shaped protrusion. If the radius of curvature of the arc-shaped protrusion is set larger than the radius of curvature of the arc-shaped concave groove, the arc-shaped protrusion of the wave washer can be brought into contact at two points on both sides of the arc-shaped concave groove. In addition, the frictional resistance between the wave washer and each end face of the motor shaft and worm shaft is increased to suppress slippage between them, and the rigidity of the wave washer is increased to enhance its torque transmission function. Since the metal contact (collision of spline teeth) at the fitting portion is suppressed, the generation of abnormal noise is reliably prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a vehicle steering apparatus including an electric power steering apparatus according to Embodiment 1 of the present invention. It is the sectional view on the AA line of FIG. It is the B section enlarged detail drawing of FIG. It is sectional drawing of the electric power steering apparatus principal part which concerns on Embodiment 2 of this invention. It is a perspective view of the wave washer shown in FIG. It is sectional drawing of the electric power steering apparatus principal part which concerns on Embodiment 3 of this invention. It is the C section enlarged detail drawing of FIG.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
1 is a side view of a steering apparatus for a vehicle including an electric power steering apparatus according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. A steering device 10 shown in FIG. 1 includes a cylindrical steering column 11 that is inclined obliquely downward toward the front of the vehicle (leftward in FIG. 1). A steering shaft 12 is rotatably inserted. A steering wheel 13 is attached to the upper end of the steering shaft 12, and the lower end of the steering shaft 12 is connected to a steering gear box 16 constituting a steering mechanism via a universal joint 14 and an intermediate shaft 15. .

  The steering column 11 is fixed to the steering support member 19 by attaching a bracket 17 attached thereto to a steering support member 19 on the vehicle body side with a bolt 18.

  Thus, the steering device 10 according to the present embodiment is provided with the electric power steering device 1 using the rotation output of the electric motor 2 as an auxiliary steering force. Here, details of the configuration of the electric power steering apparatus 1 will be described below with reference to FIGS. 2 and 3.

  As shown in FIG. 2, the electric motor 2 that is a driving source is arranged such that a motor shaft 3 that is an output shaft thereof is orthogonal to the steering shaft 12, and the motor shaft 3 rotates in a housing 4. It is connected to the worm shaft 5 accommodated by spline fitting. Here, the motor shaft 3 is formed in a cylindrical shape, and a female spline portion 3a is formed on the inner periphery thereof. The worm shaft 5 is disposed coaxially with the motor shaft 3, and both axial ends thereof are rotatably supported by the housing 4 by rolling bearings (ball bearings) 6. A male spline portion 5 a is formed on the outer periphery of one end small diameter portion 5 A connected to the motor shaft 3 of the worm shaft 5, and the one end small diameter portion 5 A of the worm shaft 5 extends axially inside the motor shaft 3. The worm shaft 5 is movable in the axial direction with respect to the motor shaft 3 by fitting the male spline portion 5a formed on the outer periphery thereof to the female spline portion 3a formed on the inner periphery of the motor shaft 3. In the circumferential direction, the motor shaft 3 and the motor shaft 3 are connected so as to be rotatable.

  Incidentally, a torsion bar (not shown) is provided in the middle of the steering shaft 12, and the worm wheel 7 is bound to the steering shaft 12. The worm wheel 7 meshes with a worm gear 5b formed at the intermediate portion of the worm shaft 5 in the axial direction. Although not shown, the electric power steering apparatus 1 includes a torque sensor for detecting a steering force (steering torque) input from the steering wheel 13 to the steering shaft 12 based on the torsion amount of the torsion bar, and the torque. A CPU is provided as a control means for supplying the electric motor 2 with electric power corresponding to the steering force and vehicle speed detected by the sensor to generate an appropriate auxiliary steering force.

  Thus, in the present embodiment, as shown in detail in FIG. 3, engagement holes 3b and 5c are formed in opposite end surfaces of the motor shaft 3 and the worm shaft 5, respectively. The coil spring 8 which is a pressurizing member is interposed. The coil spring 8 biases the worm shaft 5 in the axial direction (on the side opposite to the motor shaft 3 and in the left direction in FIG. 2), and both ends thereof are opposed to each other between the motor shaft 3 and the worm shaft 5. Are inserted into and engaged with the engagement holes 3b and 5c formed in the axial direction on the end surfaces.

  As described above, in the electric power steering apparatus 1 configured as described above, when the driver rotates the steering wheel 13 shown in FIG. 1 while the vehicle is traveling, the operating force is transmitted from the steering shaft 12 to the universal joint 14 and the intermediate shaft 15. The left and right front wheels (not shown), which are steered wheels, are steered by being transmitted to the steering gear box 16.

  At the same time, the operating force of the driver input to the steering shaft 12 is detected by the torque sensor as described above, and the detection signal is transmitted to the CPU. Then, the CPU supplies electric power according to the detected operation force and vehicle speed to the electric motor 2 to start the electric motor 2, and causes the electric motor 2 to generate appropriate auxiliary power.

  When the electric motor 2 is started as described above, the rotational power is converted to a right angle while being decelerated from the motor shaft 3 through the worm shaft 5, the worm gear 5 b formed on the worm shaft 5, and the worm wheel 7. Since this is transmitted as an auxiliary steering force to the steering shaft 12, the driver's operating force is reduced by this auxiliary steering force, and the physical burden on the driver is reduced.

  Thus, in the electric power steering apparatus 1 according to the present embodiment, the worm shaft 5 is axially moved by the coil spring 8 interposed between the opposed end surfaces of the motor shaft 3 and the worm shaft 5 (FIG. 2). (I.e., the coil spring 8 is biased in the direction of separating the motor shaft 3 and the worm shaft 5), so that the rolling bearing 6 that supports the worm shaft 5 is free from rattling. Thus, the generation of abnormal noise due to this rattling is reliably prevented.

  Further, at the moment when the electric motor 2 is started or the rotation direction of the electric motor 2 is changed, the rotational torque of the motor shaft 3 is first caused by friction of the coil spring 8 or engagement holes 3b at both ends of the coil spring 8. Since it is transmitted to the worm shaft 5 by the engagement with 5c, the impact load applied to the spline fitting portion between the motor shaft 3 and the worm shaft 5 is reduced, and the collision contact between metals in the spline fitting portion is suppressed. At the same time, the relative rotation between the motor shaft 3 and the worm shaft 5 is suppressed by the coil spring 8, and the rotational force of the motor shaft is gradually transmitted to the worm shaft via the coil spring 8 to spline the spline at the spline fitting portion. Since the collision of the teeth is alleviated and the impact at that time is absorbed by the coil spring 8, the generation of abnormal noise is effectively prevented.

  The above effects can be obtained by a simple configuration in which the coil spring 8 is simply interposed between the opposed end surfaces of the motor shaft 3 and the worm shaft 5, which may lead to a complicated structure and an increase in cost. Absent.

<Embodiment 2>
Next, a second embodiment of the present invention will be described below with reference to FIGS.

  4 is a cross-sectional view of a main part of the electric power steering apparatus according to Embodiment 2 of the present invention, and FIG. 5 is a perspective view of the wave washer shown in FIG. Since the basic configuration is the same as that of the first embodiment, only the characteristic part of the present embodiment will be described below.

  This embodiment is characterized in that a wave washer 9 is used as the pressurizing member in place of the coil spring 8 in the first embodiment. Here, as shown in FIG. 5, engaging projections 9a are formed in two opposite positions of the wave washer 9 so as to project in opposite directions (vertical direction in FIG. 5). As shown in FIG. 4, the mating protrusion 9 a is engaged with engaging grooves 3 b and 5 c formed on the opposite end surfaces of the motor shaft 3 and the worm shaft 5.

  Thus, also in this embodiment, the wave washer 9 as a pressurizing member abuts against the opposite end surfaces of the motor shaft 3 and the worm shaft 5 and urges the motor shaft 3 and the worm shaft 5 in the direction of separating them. doing. In other words, since the worm shaft 5 is urged in the axial direction (leftward in FIG. 4) by the wave washer 9, there is no backlash of the rolling bearing 6 that supports the worm shaft 5, and abnormal noise caused by this backlash is generated. Is reliably prevented.

  Further, at the moment when the electric motor 2 is activated or when the rotation direction of the electric motor 2 is changed, the rotational torque of the motor shaft 3 is first caused by the friction of the wave washer 9 or the engagement protrusion 9a of the wave washer 9 and the engagement groove. 3b, 5c is transmitted to the worm shaft 5 by engagement with the worm shaft 5, so that the impact load applied to the spline fitting portion between the motor shaft 3 and the worm shaft 5 is reduced, and the collision contact between metals in the spline fitting portion is suppressed. It is done. At the same time, the relative rotation between the motor shaft 3 and the worm shaft 5 is suppressed by the wave washer 9, and the rotational force of the motor shaft is gradually transmitted to the worm shaft through the wave washer 9, so that the spline in the spline fitting portion. Since the collision of the teeth is alleviated and the impact at that time is absorbed by the wave washer 9, the generation of abnormal noise is effectively prevented.

<Embodiment 3>
Next, a third embodiment of the present invention will be described below with reference to FIGS.

  4 is a cross-sectional view of the main part of the electric power steering apparatus according to Embodiment 3 of the present invention, and FIG. 7 is an enlarged detail view of part C of FIG. 6, showing the basics of the electric power steering apparatus according to the present embodiment. Since the configuration is the same as that of the first embodiment, only the characteristic part of the present embodiment will be described below.

  Also in the present embodiment, the wave washer 9 is used as the pressurizing member as in the second embodiment. However, in the present embodiment, the opposite end surfaces of the motor shaft 3 and the worm shaft 5 are formed in an arc shape. The concave grooves 3b and 5c are respectively formed, and the engaging projections of the wave washer 9 engaging with the circular arc-shaped concave grooves 3b and 5c are arc-shaped protrusions 9a. As shown in detail in FIG. The radius of curvature R is set larger than the radius of curvature r of the arcuate grooves 3b and 5c (only the arcuate groove 3b on the motor shaft 3 side is shown in FIG. 7) (R> r).

  Thus, in the present embodiment, the same effect as in the first and second embodiments can be obtained, but in this embodiment, the radius of curvature R of the arc-shaped protrusion 9a of the wave washer 9 is set to the motor shaft 3. Since the radius of curvature r of the arcuate grooves 3b and 5c formed on the worm shaft 5 is set larger, the arcuate protrusion 9a of the wave washer 9 can be brought into contact at two points on both ends of the arcuate grooves 3b and 5c. The torque transmission by the wave washer 9 is effectively performed, and the collision of the spline teeth at the spline fitting portion between the motor shaft 3 and the worm shaft 5 is mitigated, thereby preventing the generation of abnormal noise. An effect is obtained.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Electric motor 3 Motor shaft 3a Motor shaft female spline part 3b Motor shaft engagement groove 5 Worm shaft 5a Worm shaft male spline part 5b Worm gear 5c Worm shaft engagement groove 6 Rolling bearing 7 Warm Wheel 8 Coil spring (pressurizing member)
9 Wave washer (pressurizing member)
9a Engaging projection of wave washer 10 Steering device 12 Steering shaft 13 Steering wheel R Radius of curvature of arcuate engaging projection of wave washer r Radius of curvature of arcuate engaging recess of motor shaft and worm shaft

Claims (5)

The motor shaft of the electric motor and the worm shaft are spline-fitted, the axial end of the worm shaft is rotatably supported by a rolling bearing, and the rotation output of the electric motor is transmitted from the motor shaft to the worm shaft, In an electric power steering device that transmits an auxiliary steering force to a steering mechanism via a worm gear provided on a worm shaft and a worm wheel meshing with the worm gear,
The motor shaft and the worm shaft are respectively formed with engaging grooves on opposite end faces, and a pressurizing member for biasing the worm shaft in the axial direction is interposed between both end faces, and the pressurizing member is An electric power steering device, wherein the motor shaft and the worm shaft are engaged with the engagement grooves.   2. The electric power according to claim 1, wherein the pressurizing member is constituted by a coil spring, and both ends of the coil spring are engaged with the engagement grooves formed in the motor shaft and the worm shaft. Steering device.   The pressurizing member is constituted by a wave washer, and engaging protrusions protruding in opposite directions at two opposite positions of the wave washer are engaged with the engaging grooves formed in the motor shaft and the worm shaft. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is combined.   The engaging groove formed in the motor shaft and the worm shaft is an arcuate groove, the engaging protrusion of the wave washer is an arcuate protrusion, and the arcuate protrusion is engaged with the arcuate groove. 4. The electric power steering apparatus according to claim 3, wherein the electric power steering apparatus is combined. 5. The electric power steering apparatus according to claim 4, wherein a radius of curvature of the arcuate protrusion is set larger than a radius of curvature of the arcuate groove.

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