JP2006044382A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce backlash as much as possible while reducing friction, and eliminate an increase in the number of parts and upsizing of the device with regard to a worm shaft and a worm wheel of an electric power steering device. <P>SOLUTION: A plurality of tooth grooves 47 are respectively partitioned and formed among adjacent teeth 41 in a peripheral direction C of the worm wheel 28. Width centers B of the plurality of tooth grooves 47 are arranged in the peripheral direction C at equal pitches. The plurality of tooth grooves 47 include a first and second tooth grooves 48, 49 alternately arranged in the peripheral direction C, and width W1 of the first tooth groove 48 is larger than the width W2 of the second tooth groove 49 (W1>W2). One tooth 34 of the worm shaft 27 is engaged with a corresponding tooth 41 of the worm wheel 28 at the time of linear traveling, and three teeth 34 of the worm shaft 27 are respectively engaged with corresponding teeth 41 of the worm wheel 28 upon steering. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device that transmits output rotation of an electric motor for assisting steering to a steering mechanism via a worm shaft and a worm wheel meshing with the worm shaft.

Usually, in this type of device, the meshing between the worm shaft and the worm wheel requires an appropriate backlash in order to reduce the friction (friction resistance). However, for example, when driving on a rough road and receiving a reaction force (reverse input) from the tire, a rattling sound (rattle sound) may be generated due to the backlash.
Therefore, in order to minimize the generation of friction and rattling noise, it is necessary to strictly adjust the backlash amount within the range of processing accuracy. In other words, when assembling the worm shaft and worm wheel, each part was selected according to the degree of variation in dimensional accuracy, and the components with the appropriate combination accuracy were combined (so-called matching operation). It took a lot of work and the manufacturing cost was high.

Further, the worm wheel is usually formed of a synthetic resin, but in this case, the backlash amount fluctuates due to expansion and contraction associated with wear of the worm wheel, temperature change, moisture absorption, and the like.
Therefore, while supporting one end of the worm shaft to the worm wheel side so as to be able to be biased, and providing an urging means for elastically urging one end of the worm shaft to the worm wheel side, it eliminates backlash while suppressing friction. Has been proposed (see, for example, Patent Document 1). Specifically, a hole is provided in the housing that accommodates the worm shaft, and the pressing member and the spring are accommodated in the hole. The spring biases one end of the worm shaft toward the worm wheel via the pressing member.
JP 2000-43739 A.

  However, providing the urging means increases the number of parts and increases the size of the apparatus. The present invention has been made under such a background, and it is possible to reduce the backlash as much as possible while suppressing the friction. Further, the electric power that does not increase the number of parts and increase the size of the apparatus. An object is to provide a steering device.

  In order to achieve the above object, the present invention provides an electric power steering apparatus for assisting steering by transmitting an output of an electric motor to a steering mechanism, a worm shaft coupled to an output shaft of the electric motor, and a steering mechanism meshing with the worm shaft. The worm wheel includes a plurality of teeth, and a plurality of tooth spaces defined between adjacent teeth, and the center of the width of the plurality of tooth spaces is the width of the worm wheel. The plurality of tooth spaces are arranged at an equal pitch in the circumferential direction, and the plurality of tooth spaces include first and second tooth spaces alternately arranged in the circumferential direction of the worm wheel, and the width of the first tooth space is the second tooth It is characterized by being wider than the width of the groove.

  Usually, three teeth of the worm shaft are arranged in the meshing region between the worm shaft and the worm wheel. In the present invention, by providing the wide first tooth gap and the narrow second tooth groove alternately in the circumferential direction of the worm wheel, the number of teeth of the worm shaft meshed with the worm wheel during straight running can be reduced. For example, it can be reduced to one. Therefore, even if the backlash is set small, an increase in friction can be suppressed. The backlash can be set as small as possible, and the generation of noise due to the rattling noise can be suppressed.

On the other hand, since the preload is applied to the meshing region by the power of the electric motor during steering, the three teeth of the worm shaft mesh with the teeth of the worm wheel, and there is no problem in durability. In addition, these effects can be achieved with a simple configuration by simply changing the width of the tooth space of the worm wheel, without increasing the number of parts and increasing the size of the apparatus.
The plurality of teeth of the worm wheel are preferably formed of a synthetic resin. In this case, the frictional resistance of the tooth surface of each tooth of the worm wheel can be sufficiently reduced, and the friction can be further reduced. Further, it can mesh with the teeth of the worm shaft elastically well, and the generation of rattling noise can be more reliably suppressed.

  The worm shaft preferably has a plurality of teeth. In this case, the number of worm shaft leads can be increased to sufficiently ensure the rotational speed of the worm wheel, and excellent responsiveness can be ensured.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6, and a rack shaft 10 that forms a rack 9 that meshes with a pinion 8 provided at the tip of the pinion shaft 7 and extends in the left-right direction of the vehicle. Have.

  Tie rods 11 are connected to both ends of the rack shaft 10, and each tie rod 11 is connected to a corresponding wheel 12 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is transmitted to the pinion 8 via the intermediate shaft 5 and the like, and the straight line of the rack shaft 10 along the left-right direction of the vehicle is driven by the pinion 8 and the rack 9. Converted into movement. Thereby, the steering of the wheel 12 is achieved.

The steering shaft 3 has a first steering shaft 13 as an input shaft connected to the steering member 2 and a second steering shaft 14 as an output shaft connected to the universal joint 4. The first and second steering shafts 13 and 14 are coaxially connected to each other via a torsion bar 15.
A torque sensor 16 that detects the amount of relative rotational displacement between the first steering shaft 13 and the second steering shaft 14 via the torsion bar 15 is provided. The detection signal of the torque sensor 16 is given to the control unit 17. The control unit 17 calculates the steering torque applied to the steering member 2 based on the detection signal from the torque sensor 16. Then, based on the calculated steering torque, a vehicle speed detection signal from the vehicle speed sensor 22, etc., the driving assist electric motor 19 is controlled via the driver 18. As a result, the electric motor 19 is driven, and its output rotation (power) is transmitted to the second steering shaft 14 via the worm gear mechanism 20. The power transmitted to the second steering shaft 14 is further transmitted to the steering mechanism 21 including the rack shaft 10, the tie rod 11, the knuckle arm and the like via the intermediate shaft 5 and the like to assist the driver's steering. .

FIG. 2 is a partial cross-sectional view of a main part of the electric power steering apparatus 1. With reference to FIG. 2, the electric power steering apparatus 1 is provided with a housing 23. The housing 23 attaches the electric motor 19 and houses the worm gear mechanism 20.
The electric motor 19 includes a motor housing 24 and an output shaft 25 protruding from the motor housing 24. The motor housing 24 is fixed to the annular flange portion 26 of the housing 23.

The worm gear mechanism 20 includes a worm shaft 27 and a worm wheel 28.
The worm shaft 27 is connected to the output shaft 25 of the electric motor 19 through a joint 29 such as a spline joint so as to be integrally rotatable. The worm shaft 27 includes a tooth portion 30, first and second supported portions 31 and 32 provided at each of the pair of end portions of the tooth portion 30, and one end portion 33 that is continuous with the first supported portion 31. It has.

The tooth part 30 is provided with teeth 34 composed of a plurality of teeth (for example, three). The first and second supported portions 31 and 32 are rotatably supported in corresponding support holes 37 and 38 of the housing 23 via corresponding bearings 35 and 36, respectively. The one end 33 is connected to the joint 29.
The worm wheel 28 is connected to the steering mechanism through the second steering shaft 14 and the like, and is made of a synthetic resin annular tooth body 39 and a metal disposed radially inward of the annular tooth body 39. And an annular holding body 40 made of metal.

The annular tooth body 39 has a plurality of teeth 41 on the outer periphery. These teeth 41 are formed over the entire circumference of the annular tooth body 39 and mesh with the teeth 34 of the worm shaft 27 in the meshing area A. Each tooth 41 is formed in, for example, a shell.
The annular holding body 40 is inserted when the annular tooth body 39 is molded, and is formed integrally with the annular tooth body 39. An insertion hole 42 is formed in the annular holding body 40, and is connected to the second steering shaft 14 inserted through the insertion hole 42 through a key 43 so as to be integrally rotatable. Specifically, concave grooves 44 and 45 are provided on the outer peripheral surface of the second steering shaft 14 and the inner peripheral surface of the insertion hole 42 of the annular holding body 40, respectively. The concave grooves 44 and 45 extend in the axial direction of the second steering shaft 14 (a direction perpendicular to the paper surface in FIG. 2) and in the radial direction R (hereinafter simply referred to as “radial direction R”) of the worm wheel 28. Opposite.

The key 43 is interposed between the concave grooves 44 and 45 and is fitted and held in the concave groove 44 of the second steering shaft 14. A gap is provided in the circumferential direction C (hereinafter simply referred to as “circumferential direction C”) and the radial direction R of the worm wheel 28 between the concave groove 45 of the annular holder 40 and the key 43.
Further, a gap is provided between the outer peripheral surface of the second steering shaft 14 and the inner peripheral surface of the annular holding body 40, and an elastic member 46 is interposed in this gap. The elastic member 46 is, for example, a ring-shaped end member formed of rubber or the like, and sandwiches the key 43 from both sides in the circumferential direction C. The outer peripheral surface and the inner peripheral surface of the elastic member 46 are vulcanized and bonded to the corresponding inner peripheral surface of the annular holding body 40 and the outer peripheral surface of the second steering shaft 14, respectively. Thus, the worm wheel 28 is supported on the second steering shaft 14 via the elastic member 46. As a result, the worm wheel 28 is elastically slightly movable relative to the second steering shaft 14 and the worm shaft 27 in the circumferential direction C and the radial direction R. Therefore, the worm wheel 28 can move in a direction away from the worm shaft 27. As a result, for example, even if the inter-shaft distance between the second steering shaft 14 and the worm shaft 27 becomes too close due to an assembly error, the worm wheel 28 moves and the worm shaft 27 and the worm wheel 28 are moved. The backlash between the two can be prevented from being clogged excessively, and an increase in friction can be suppressed.

  Further, when the worm gear mechanism 20 is assembled, the concave groove 44 of the second steering shaft 14 and the concave groove 45 of the annular holding body 40 are arranged to face each other in the meshing direction V, so that the mesh region A and the worm gear A key 43 is interposed between the center of the wheel 28 (second steering shaft 14). The meshing direction V is a direction in which the distance X between the axis L1 of the worm shaft 27 and the axis L2 of the worm wheel 28 (extending in the direction perpendicular to the paper surface) changes.

FIG. 3 is a partially enlarged view of the worm wheel 28 of FIG. Referring to FIG. 3, a plurality of tooth grooves 47 are defined in the space between the teeth 41 adjacent to each other in the circumferential direction C of the worm wheel 28. That is, the plurality of tooth spaces 47 are defined by a pair of tooth surfaces facing each other in the circumferential direction C of the corresponding pair of teeth 34 and a tooth bottom surface between the pair of tooth surfaces.
The plurality of tooth grooves 47 are arranged at an equal pitch along the circumferential direction C. That is, the width centers B of the plurality of tooth grooves 47 are arranged in the circumferential direction C at an equal pitch. The width center B refers to the position of the center of each of the plurality of tooth spaces 47 in the circumferential direction C. The distance between adjacent width centers B is set to a predetermined value E.

  4 is a cross-sectional view taken along line II-II in FIG. 2 and shows a state viewed along the circumferential direction C. FIG. Referring to FIG. 4, in the meshing area A, each of the teeth 34 of the worm shaft 27 passes through a corresponding tooth groove 47 of the worm wheel 28. That is, in the meshing area A, the teeth 41 of the worm wheel 28 can mesh with the three teeth 34 of the worm shaft 27.

  The plurality of tooth spaces 47 include first and second tooth spaces 48 and 49. The first and second tooth spaces 48 and 49 are alternately arranged in the circumferential direction C. The width W1 of the first tooth groove 48 is wider than the width W2 of the second tooth groove 49 (W1> W2). The width W1 of the first tooth groove 48 refers to the width in the circumferential direction C of the first tooth groove 48, and the width W2 of the second tooth groove 49 refers to the circumferential direction of the second tooth groove 49. The width of C.

The width W1 of the first tooth groove 48 is set wider than the tooth thickness W3 in the circumferential direction C of the teeth 34 of the worm shaft 27 (W1> W3). Thus, a backlash F is provided between the teeth 34 of the worm shaft 27 passing through the first tooth gap 48 and the teeth 41 on both sides in the circumferential direction C of the teeth 34.
The width W2 of the second tooth groove 49 is substantially equal to the tooth thickness W3 of the worm shaft 27 (W2≈W3). Thereby, the teeth 34 of the worm shaft 27 passing through the second tooth gap 49 and the teeth 41 on both sides in the circumferential direction C of the teeth 34 mesh with each other without a gap.

  The first and second tooth spaces 48 and 49 can be manufactured by changing the cutter width of the hob cutter for forming the teeth 41. For example, as shown in FIG. 5A, first, a manufacturing intermediate 50 having a tooth gap composed of the second tooth groove 49 is formed, and then the teeth 100 on both sides of the second tooth groove 49A are formed. By cutting the tooth surfaces facing each other by the same amount, the first tooth groove 48 can be formed as shown in FIG. 5B (the tooth surface before cutting is shown by a two-dot chain line). .

The above is the schematic configuration of the electric power steering apparatus 1. Next, the main operation of this apparatus will be described.
Referring to FIG. 4, when the vehicle travels straight (when the steering member 2 is in the steering neutral position), in the meshing area A, the worm shaft 27 has one tooth 34 entering the second tooth groove 49. The worm wheel 28 meshes with a corresponding pair of teeth 41 without backlash. Further, the remaining two teeth 34 are respectively in the corresponding first tooth spaces 48, but are not engaged with the teeth 41 of the worm wheel 28 because of the backlash F.

  When the vehicle is steered, the worm shaft 27 is rotationally driven by the output of the electric motor 19 in a direction corresponding to the rotational direction of the steering member 2, and power is transmitted from the worm shaft 27 to the worm wheel 28. Thereby, as shown in FIG. 6, the one tooth 34 of the worm shaft 27 presses the corresponding tooth 41 of the worm wheel 28 to one side in the circumferential direction C (for example, the right side in FIG. 6) to be elastic. As a result, the three teeth 34 in the meshing area A mesh with the corresponding teeth 41 of the worm wheel 28, respectively.

In addition, at the initial stage of steering (at the time of minute steering), the steering torque from the steering member 2 is below a predetermined threshold value, and torque assist by the electric motor may not be performed. Since only one tooth 34 meshes with the corresponding tooth 41 of the worm wheel 28, the friction is low and a light steering feeling can be realized.
In addition, as shown in FIG. 2, the second steering shaft 14 and the worm wheel 28 are elastically rotatable relative to each other with an elastic member 46 interposed therebetween. In this case, even if the second steering shaft 14 rotates as the steering member 2 is operated, the worm wheel 28, the worm shaft 27, and the output shaft 25 of the electric motor 19 can be prevented from being rotated. As a result, it is possible to prevent the steering feeling from becoming heavy and to realize a lighter steering feeling.

  As described above, according to the present embodiment, the first gear groove 48 and the second tooth groove 49 having a narrow width are alternately provided in the circumferential direction C. The number of teeth 34 of the worm shaft 27 meshing with the wheel 28 can be reduced to one. Therefore, even if the backlash between the worm shaft 27 and the worm wheel 28 is set to be small, an increase in friction can be suppressed. The backlash can be set as small as possible, and the generation of noise due to the rattling noise can be suppressed.

  On the other hand, since the preload is applied to the meshing area A by the power of the electric motor 19 at the time of steering, the three teeth 34 of the worm shaft 27 mesh with the teeth 41 of the worm wheel 28, and there is no problem in durability. In addition, these effects can be achieved with a simple configuration by simply changing the width of the tooth groove 47 of the worm wheel 28, without increasing the number of parts and increasing the size of the apparatus.

Further, by forming each tooth 41 of the worm wheel 28 from a synthetic resin, the frictional resistance of the tooth surface of each tooth 41 of the worm wheel 28 can be sufficiently lowered, and the friction with the worm shaft 27 is further reduced. be able to. Further, it can mesh with the teeth 34 of the worm shaft 27 elastically and satisfactorily, and the generation of rattling noise can be more reliably suppressed.
Further, since the teeth 34 of the worm shaft 27 are formed in a plurality of teeth, the number of leads of the worm shaft 27 can be increased to sufficiently ensure the rotational speed of the worm wheel 28 and to ensure excellent responsiveness. .

The present invention is not limited to the above embodiment. For example, each of the plurality of teeth 41 of the worm wheel 28 may be formed of a material (for example, metal) other than the synthetic resin. Further, the teeth 34 of the worm shaft 27 may be one, two or four or more.
Further, the elastic member 46 may be fitted into the gap between the second steering shaft 14 and the worm wheel 28 without being vulcanized and bonded. In this case, the apparatus can be manufactured as follows, for example. That is, first, the second steering shaft 14 and the manufacturing intermediate 50 are prepared. Then, a spacer having the same shape as the elastic member 46 is attached between the second steering shaft 14 and the manufacturing intermediate body 50, and the second steering shaft 14 and the manufacturing intermediate body 50 are temporarily assembled. Then, in the temporarily assembled state, the manufacturing intermediate 50 is subjected to gear cutting to form the worm wheel 28, and then the spacer is removed and the elastic member 46 is attached. In this case, it is possible to prevent an unnecessary load from acting on the elastic member 46 when the apparatus is manufactured.

  Further, the key 43 and the elastic member 46 may be eliminated, and the second steering shaft 14 and the worm wheel 28 may be press-fitted and fitted.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is a partial cross section figure of the principal part of an electric power steering device. FIG. 3 is a partially enlarged view of the worm wheel of FIG. 2. It is sectional drawing which follows the II-II line of FIG. It is a figure for demonstrating manufacture of a worm wheel, (A) is a partial cross section side view of the manufacture intermediate body of a worm wheel, (B) is a partial cross section side view of a worm wheel. It is a partial cross section figure of the principal part for demonstrating operation | movement of an electric power steering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 19 Electric motor 21 Steering mechanism 25 Output shaft 27 Worm shaft 28 Worm wheel 34 (Warm shaft) tooth 41 (Worm wheel) tooth 47 Tooth groove 48 First tooth groove 49 Second tooth groove B Width center C circumferential direction W1 (first tooth gap) width W2 (second tooth gap) width

Claims (3)

In the electric power steering device for assisting steering by transmitting the output of the electric motor to the steering mechanism,
A worm shaft coupled to the output shaft of the electric motor;
With a worm wheel meshing with the worm shaft and continuing to the steering mechanism,
The worm wheel includes a plurality of teeth and a plurality of tooth spaces each defined between adjacent teeth,
The width centers of the plurality of tooth spaces are arranged at an equal pitch in the circumferential direction of the worm wheel,
The plurality of tooth gaps include first and second tooth grooves alternately arranged in the circumferential direction of the worm wheel, and the width of the first tooth groove is wider than the width of the second tooth groove. Electric power steering device.   2. The electric power steering apparatus according to claim 1, wherein the plurality of teeth of the worm wheel are each formed of a synthetic resin. 3. The electric power steering apparatus according to claim 1, wherein the worm shaft has a plurality of teeth.

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