JP2008260379A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device with less noise. <P>SOLUTION: The electric power steering device has a gear row in which parallel axis gear mechanisms as speed-reducer for speed-reducing output rotation of an electric motor are engaged in a plurality of stages. Tooth thickness t1, t2 of teeth 211, 231 of a drive gear 21 and a first intermediate gear 23 engaged with each other of the gear row are gradually increased regarding reversely directed directions X1, X2 in a tooth trace direction. An elastic member gives urging force along one direction A1 in an axial direction of the intermediate shaft relative to an intermediate shaft unit U1 including the first intermediate gear 23. With a tooth groove 212 of one gear, the tooth 231 of the other gear is engaged in a wedge-like shape regarding the tooth trace direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that obtains a steering assist force by an electric motor.

  In this type of electric power steering device, the rotation of the rotating shaft of the electric motor is decelerated via a decelerating mechanism and transmitted to a steering mechanism such as a rack and pinion mechanism. In general, since an electric motor is a low-torque, high-rotation type, a high reduction ratio is required as a reduction mechanism. Conventionally, the rotating shaft of the electric motor is arranged in parallel with the steering shaft, and as a speed reduction mechanism, the driving gear arranged coaxially with the rotating shaft of the electric motor and the output shaft of the steering shaft are integrated coaxially. There has been proposed an electric power steering device using a parallel shaft gear mechanism having a configuration in which a driven gear arranged rotatably is meshed (see, for example, Patent Document 1).

In the electric power steering device of Patent Document 1, the parallel shaft gear mechanism as the speed reduction mechanism is not a multi-stage configuration, so that the driven gear has a large diameter, and as a result, the entire device becomes large and mountability on the vehicle is deteriorated.
On the other hand, as a speed reduction mechanism, an electric power steering device that employs a helical gear reducer with helical teeth has been proposed (see, for example, Patent Document 2).
JP 2005-319971 A JP-A-62-214055

By the way, in the parallel shaft gear mechanism, a predetermined amount of backlash is required to smoothly rotate the gear.
However, when the steering wheel is turned back and the steering direction is switched, or when the vehicle travels straight on a rough road and receives a reverse input from the road surface, a rattling noise is generated due to backlash and causes noise.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering device with less noise due to rattling noise caused by backlash.

  In order to achieve the above object, the present invention comprises a parallel shaft gear mechanism (7) for decelerating the output rotation of an electric motor (6) for steering assistance, and the parallel shaft gear mechanism has one or more stages. The at least one pair of gears (21, 23; 22, 24) that mesh with each other in the gear train is supported so that one gear (23; 24) is movable in the axial direction. The one gear is meshed with the other gear (21; 22) while being urged by its own weight or one of the axial directions (Z1) by the elastic member (55). To do.

  In this case, backlash can be eliminated by applying a preload between gears meshing with each other. As a result, it is possible to prevent the occurrence of rattling noise due to backlash when the steering wheel is turned back or when the vehicle travels straight on a rough road. Although it is preferable to obtain an urging force by both the own weight and the elastic member in terms of reducing the load on the elastic member and reducing the size, the elastic member may be eliminated and only the own weight may be used.

  In addition, at least a pair of gears that mesh with each other in the gear train has a tooth thickness (t1, t2; t3, t4) that gradually increases with respect to directions (X1, X2; Y1, Y2) opposite to each other in the tooth trace direction. (Claim 2). In this case, in the relationship between the pair of gears meshing with each other, the tooth groove (212; 222) of one gear meshes with the tooth (231; 241) of the other gear in a wedge shape with respect to the tooth line direction. As a result, backlash can be reliably eliminated and noise can be reliably prevented.

  The parallel shaft gear mechanism includes an input shaft (19) disposed coaxially with the rotation shaft of the electric motor, an intermediate shaft (20) and an output shaft (3b) disposed in parallel with the input shaft, The drive gear (21) provided on the input shaft, the first and second intermediate gears (23, 24) provided to be rotatable integrally with the intermediate shaft and separated in the axial direction of the intermediate shaft, and provided on the output shaft The driven gear (22) and the gear train is constituted by the drive gear, the first and second intermediate gears, and the driven gear, and the intermediate shaft is rotatable by a bearing held by the housing. The intermediate shaft is supported so as to be displaceable in the axial direction, and the intermediate shaft is urged in one of the axial directions by the weight of the intermediate shaft and the first and second intermediate gears or by an elastic member. Is engaged with the drive gear and the second intermediate gear is engaged with the driven gear. (Claim 3).

  In this case, the first intermediate gear is engaged with the drive gear and the second intermediate gear is engaged with the driven gear by the own weight of the intermediate shaft or the like or the biasing force of the elastic member. That is, it is possible to eliminate the backlash by applying a preload between the meshing gears. As a result, it is possible to prevent the occurrence of rattling noise due to backlash when the steering wheel is turned back or when the vehicle travels straight on a rough road.

  The drive gear and the first intermediate gear gradually increase in tooth thickness with respect to the mutually opposite directions (X1, X2) of the tooth trace direction, and the driven gear and the second intermediate gear are opposite to each other in the tooth trace direction. The tooth thickness may increase gradually with respect to the direction (Y1, Y2). In this case, the teeth of the other gear mesh with one tooth groove of the pair of gears meshing with each other in a wedge shape with respect to the tooth trace direction. As a result, backlash can be reliably eliminated and noise can be reliably prevented.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

A preferred embodiment 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 according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering device (EPS) 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, and a steered wheel 4 as the steering shaft 3 rotates. Steering mechanism 5 composed of, for example, a rack and pinion mechanism for steering the vehicle, an electric motor 6 that generates a steering assist force, and a deceleration mechanism for decelerating and transmitting the output rotation of the electric motor 6 to the steering mechanism 5 And a parallel shaft gear mechanism 7.

In FIG. 1, the steering shaft 3 is schematically shown so as to extend in the vertical direction, but actually, the steering shaft 3 is mounted on the vehicle in an inclined state with respect to the vertical direction.
The steering shaft 3 is rotatably supported by a unit housing 8 constituting a part of the steering column via a plurality of bearings 9, 10, and 11. The unit housing 8 supports the parallel shaft gear mechanism 7 and the electric motor 6 as the speed reduction mechanism. The unit housing 8 is formed by combining the first and second housings 8a and 8b.

The steering mechanism 5 has a pinion shaft 12 connected to the steering shaft 3 via an intermediate shaft (not shown), and rack teeth 13a meshing with the pinion teeth 12a provided on the pinion shaft 12 in the lateral direction of the automobile. It has the rack bar 13 as a steered shaft that extends.
The rack bar 13 is supported in a housing 14 fixed to the vehicle body so as to be linearly reciprocable through a plurality of bearings (not shown). Both end portions of the rack bar 13 protrude to both sides of the housing 14, and tie rods 15 are coupled to the respective end portions. Each tie rod 15 is connected to a corresponding steering wheel 4 via a corresponding knuckle arm 16.

When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 13 along the left-right direction of the automobile by the pinion teeth 12a and the rack teeth 13a. Thereby, steering of the steering wheel 4 is achieved.
The steering shaft 3 has a first shaft 3a connected to the steering member 2 so as to be integrally rotatable, a second shaft 3b connected to the pinion shaft 12 so as to be integrally rotatable, and the first shaft 3a and the second shaft 3b being coaxial. And a torsion bar 3c that is connected to be relatively rotatable. The 2nd axis | shaft 3b comprises the output shaft of the parallel shaft gear mechanism 7 mentioned later.

Although the electric motor 6 is not shown in its mounting form, the motor housing 6a is integrally attached to the unit housing 8, and extends parallel to the steering shaft 3, and is rotatably supported by the motor housing 6a. And a rotating shaft 6b.
A parallel shaft gear mechanism 7 serving as a speed reduction mechanism includes an input shaft 19 that is coaxially connected to a rotation shaft 6 b of the electric motor 6 via a joint 18 and is integrally rotatable, and an intermediate shaft disposed in parallel with the input shaft 19. The shaft 20, the second shaft 3 b as an output shaft, which is also arranged in parallel with the input shaft 19, and a gear train 50 are provided.

  A drive gear 21 is provided on the input shaft 19 so as to be integrally rotatable, and a driven gear 22 is provided on the second shaft 3b as an output shaft so as to be integrally rotatable. On the other hand, the intermediate shaft 20 is provided with a first intermediate gear 23 that meshes with the drive gear 21 so as to be integrally rotatable, and a second intermediate gear 24 that meshes with the driven gear 22 is provided so as to be integrally rotatable. ing. The first intermediate gear 23 and the second intermediate gear 24 are separated in the axial direction of the intermediate shaft 20. Each of the drive gear 21, the first intermediate gear 23, the second intermediate gear 24, and the driven gear 22 is constituted by, for example, a spur gear or a helical gear.

The drive gear 21, the first intermediate gear 23, the second intermediate gear 24, and the driven gear 22 constitute a gear train 50 that meshes with a plurality of stages.
The input shaft 19 is rotatably supported by a pair of bearings 25 and 26 held by the unit housing 8. The intermediate shaft 20 is supported rotatably and axially movable by first and second bearings 27 and 28 held by the unit housing 8. The second shaft 3b as the output shaft is rotatably supported by the bearing 10 and the bearing 11 held by the unit housing 8.

Further, the unit housing 8 accommodates a torque sensor 29 for detecting a steering torque according to the relative rotation of the first shaft 3a and the second shaft 3b via the torsion bar 3c.
Referring to FIG. 2, input shaft 19 has first and second end portions 19a and 19b and an intermediate portion 19c between first end portion 19a and second end portion 19b. The drive gear 21 is integrally formed of a single material on the intermediate portion 19 c of the input shaft 19. Note that the drive gear 21 may be a gear that is formed separately from the input shaft 19 and is attached to the input shaft 19 so as to be rotatable integrally with the input shaft 19 but not relatively movable in the axial direction.

The first end 19 a of the input shaft 19 is rotatably supported via the bearing 25 held by the unit housing 8, and the second end 19 b of the input shaft 19 is held by the unit housing 8. Further, it is rotatably supported via the bearing 26 described above.
The inner ring 30 of the bearing 25 is attached to the input shaft 19 in a state where axial movement with respect to the input shaft 19 is restricted. Specifically, the inner ring 30 of the bearing 25 is interposed between a positioning step portion 31 provided on the input shaft 19 and a nut 32 screwed into a screw portion at the tip of the first end portion 19 a of the input shaft 19. It is pinched. Further, the axial movement of the outer ring 33 of the bearing 25 is restricted by the unit housing 8. Specifically, the outer ring 33 of the bearing 25 is sandwiched between the positioning step 34 formed in the unit housing 8 and the retaining ring 35 fitted in the annular groove of the unit housing 8. Thereby, the axial movement of the input shaft 19 and the drive gear 21 is restricted.

The intermediate shaft 20 includes first and second end portions 20a and 20b, and an intermediate portion 20c between the first end portion 20a and the second end portion 20b. The first and second intermediate gears 23 and 24 are disposed in the intermediate portion 20c of the intermediate shaft 20 so as to be separated in the axial direction.
The first intermediate gear 23 is coupled to the intermediate portion 20c of the intermediate shaft 20 in a state where the first intermediate gear 23 can rotate integrally and the relative movement in the axial direction is restricted. The second intermediate gear 24 is provided adjacent to the first intermediate gear 23 and is formed integrally with the intermediate shaft 20 from a single material. Note that the second intermediate gear 24 may be a gear that is formed separately from the intermediate shaft 20 and is attached to the intermediate shaft 20 so as to be capable of rotating integrally with the intermediate shaft 20 and not being relatively movable in the axial direction.

The first end portion 20 a of the intermediate shaft 20 is rotatably supported via the first bearing 27 held by the unit housing 8, and the second end portion 20 b of the intermediate shaft 20 is supported by the unit housing 8. Is supported rotatably via the second bearing 28 described above.
A nut 36 screwed into a screw portion formed at the tip of the first end portion 20a of the intermediate shaft 20 and a positioning step portion 37 (second intermediate gear 24) formed in the intermediate portion 20c of the intermediate shaft 20 Between the inner ring 38 of the first bearing 27 and the first intermediate gear 23, thereby the axial direction of the first intermediate gear 23 relative to the intermediate shaft 20. Movement is restricted.

Further, the outer ring 39 of the first bearing 27 is held in a bearing holding hole 51 formed in the first housing 8a of the unit housing 8 by a clearance fit. That is, the rotation of the outer ring 39 is restricted by the inner peripheral surface of the bearing holding hole 51, but the axial movement of the outer ring 39 is allowed.
Further, the inner ring 42 of the second bearing 28 is opposed to the other end surface of the second intermediate gear 24 with a gap S1, and the inner ring 42 is fitted to the second end 20b of the intermediate shaft 20. Is a clearance fit. Thus, the second bearing 28 supports the intermediate shaft 20 so as to be movable in the axial direction and rotatable.

The outer ring 43 of the second bearing 28 is fixed to the bearing holding hole 52 of the second housing 8b of the unit housing 8 by press fitting (interference fitting).
As described above, the axial relative movement between the outer ring 39 of the first bearing 27 and the corresponding bearing holding hole 51 is allowed, and the equivalent movement in the axial direction between the inner ring 42 of the second bearing 28 and the intermediate shaft 20 is allowed. Since it is permitted, the axial movement of the intermediate shaft unit U1 including the intermediate shaft 20 and the first and second intermediate gears 23 and 24 is permitted.

  On the other hand, a nut 54 made of, for example, a cap nut is screwed into a predetermined position into a screw hole 53 concentrically connected to the first bearing holding hole 51, and an end surface 54a of the nut 54 and the first bearing 27 opposed to the end surface 54a. An elastic member 55 made of, for example, a disc spring is interposed between the end face of the outer ring 39. The elastic member 55 elastically urges the intermediate shaft unit U1 toward the second bearing 28 side, which is one Z1 in the axial direction of the intermediate shaft 20, via the outer ring 39 of the first bearing 27. Yes. In the present embodiment, since the vehicle is mounted on the vehicle in the state shown in FIG. 1, the weight of the intermediate shaft unit U1 is the same as that of the intermediate shaft unit U1 in the axial direction of the intermediate shaft 20 on the second bearing 28 side. Work to urge towards.

By adjusting the screwing position of the nut 54, the amount of bending of the elastic member 55 is changed, thereby adjusting the urging force (pre-pressure). As the elastic member 55, a compression coil spring may be used instead of the above-described disc spring.
The inner ring 44 of the bearing 11 that supports the second shaft 3b as the output shaft is between a positioning step portion 45 formed on the second shaft 3b and a nut 46 that is screwed to the screw portion of the second shaft 3b. As a result, the axial movement of the inner ring 44 relative to the second shaft 3b is restricted. Further, the outer ring 47 of the bearing 11 is sandwiched between a positioning step portion 48 formed in the unit housing 8 and a retaining ring 49 fitted in an annular groove formed in the unit housing 8. Thereby, the axial movement of the second shaft 3b is restricted.

The driven gear 22 is connected to the second shaft 3b between the bearing 10 and the bearing 11 by, for example, press-fitting so as to be integrally rotatable and not axially movable.
As described above, the axial movement of the intermediate shaft unit U1 including the intermediate shaft 20 and the first and second intermediate gears 23 and 24 is allowed, and the intermediate shaft unit U1 is moved to one axial direction Z1 of the intermediate shaft 20. In addition to the point being biased toward, the features of the present embodiment are as follows.

  That is, the drive gear 21 and the first intermediate gear 23 as a pair of gears meshing with each other in the gear train 50 of the parallel shaft gear mechanism 7 are connected to each other in the tooth trace direction as schematically shown in FIG. The tooth thicknesses t1 and t2 of the respective teeth 211 and 231 are gradually increased with respect to the opposite directions X1 and X2, and the intermediate shaft unit U1 is biased along one axial direction Z1 of the intermediate shaft 20. As a result, the teeth 211 and 231 of the drive gear 21 and the first intermediate gear 23 mesh with each other in a wedge shape, and the backlash is removed. When the drive gear 21 and the first intermediate gear 23 are spur gears, one axial direction Z1 of the intermediate shaft 20 that is the urging direction is parallel to the directions X1 and X2 that are the tooth trace directions. On the other hand, when the drive gear 21 and the first intermediate gear 23 are helical gears, one of the axial directions Z1 of the intermediate shaft 20 that is the urging direction is the direction X1 and X2 that are the tooth trace directions. It becomes the direction which crosses diagonally.

  Further, in the gear train 50, the driven gear 22 and the second intermediate gear 24 as a pair of gears meshed with each other are formed in directions Y1 and Y1, which are opposite to each other in the tooth line direction, as schematically shown in FIG. Regarding Y2, the tooth thicknesses t3 and t4 of the respective teeth 221 and 241 are gradually increased, and the intermediate shaft unit U1 is urged along one axial direction Z1 of the intermediate shaft 20, whereby the driven gear 22 is provided. Further, the teeth 221 and 241 of the second intermediate gear 24 mesh with each other in a wedge shape so that the backlash is removed. When the driven gear 22 and the second intermediate gear 24 are spur gears, one axial direction Z1 of the intermediate shaft 20 that is the urging direction is parallel to the directions Y1 and Y2 that are the tooth trace directions. On the other hand, when the driven gear 22 and the second intermediate gear 24 are helical gears, the direction Y1, Y2 in which one of the axial directions Z1 of the intermediate shaft 20 that is the urging direction is the tooth direction It becomes the direction which crosses diagonally.

And one Z1 in the axial direction of the intermediate shaft 20, which is the direction in which the intermediate shaft unit U1 is biased, meshes the teeth 211, 231 of the drive gear 21 and the first intermediate gear 23 with each other in a wedge shape, The directions are such that the teeth 221 and 241 of the driven gear 22 and the second intermediate gear 24 can be engaged with each other in a wedge shape.
When machining the teeth of the drive gear 21, the first intermediate gear 23, the driven gear 22, and the second intermediate gear 24, the cutting amount of the hob for gear cutting is continuously changed by changing the gear cutting machining program. Instead, it is only necessary to continuously displace the tooth surfaces, and these gears 21 to 24 can be easily formed.

  According to the present embodiment, the first intermediate gear 23 is meshed with the drive gear 21 in a preload state by the own weight of the intermediate shaft 20 and the like and the biasing force of the elastic member 55, and the second intermediate gear 24 is driven. It meshes with the gear 22 in a preload state. That is, it is possible to eliminate the backlash by applying a preload between the gears 21, 23; As a result, it is possible to prevent the occurrence of rattling noise due to backlash when the steering wheel is turned back or when the vehicle travels straight on a rough road.

  In particular, the drive gear 21 and the first intermediate gear 23 are driven by the urging force of the elastic member 55 and the like because the tooth thicknesses t1 and t2 are gradually increased with respect to the directions X1 and X2 opposite to each other in the tooth trace direction. The teeth 231 of the first intermediate gear 23 mesh with the tooth grooves 212 of the gear 21 in a wedge shape. Similarly, in the driven gear 22 and the second intermediate gear 24, the tooth thicknesses t3 and t4 are gradually increased with respect to the directions Y1 and Y2 opposite to each other in the tooth line direction. The teeth 241 of the second intermediate gear 24 mesh with the tooth grooves 222 of the driven gear 22 in a wedge shape. As a result, backlash can be reliably eliminated and noise can be reliably prevented.

Since the backlash can be removed as described above, it is called the conventional sorting and assembly of parts (assembling by assembling by combining parts of the group so that each part can be sized and grouped to achieve proper backlash). Troublesome work can be abolished.
In the present embodiment, the weight of the intermediate shaft unit U1 and the urging force of the elastic member 55 are used in combination, which is preferable in that the load on the elastic member 55 can be reduced and the size can be reduced. However, as shown in FIG. 5, the elastic member 55 may be abolished and only its own weight may be used. In this case, the structure can be further simplified.

In the above-described embodiment, a tight fit is provided between the inner ring 42 of the second bearing 28 and the intermediate shaft 20, and a clear fit is provided between the outer ring 43 of the second bearing 28 and the bearing holding portion 52. Good.
In the above-described embodiment, the description has been given based on the example in which the gear train 50 of the parallel shaft gear mechanism 7 meshes in two stages. However, the present invention is not limited to this, and the present invention is not limited to this. The present invention can also be applied to an electric power steering apparatus including a gear train that meshes with the above.

  In addition, various modifications can be made within the scope of the claims of the present invention.

1 is a schematic cross-sectional view of an electric power steering device according to an embodiment of the present invention. It is an enlarged view of the principal part of FIG. It is typical sectional drawing which shows the tooth | gear of the drive gear and 1st intermediate | middle gear which mesh | engage mutually. It is typical sectional drawing which shows the tooth | gear of the driven gear and 2nd intermediate | middle gear which mesh | engage mutually. It is typical sectional drawing of the electric power steering device of another embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, Steering shaft ... 3, 3b ... 2nd axis | shaft (output shaft of a parallel shaft gear mechanism), 6 ... Electric motor, 6b ... Rotating shaft, 7 ... Parallel shaft gear mechanism, 19 ... Input shaft, 20 ... intermediate shaft, 21 ... drive gear, 211 ... tooth of drive gear, 22 ... driven gear, 221 ... tooth of driven gear, 23 ... first intermediate gear, 231 ... tooth of first intermediate gear, 24 ... second Intermediate gear, 241 ... second intermediate gear teeth, 27 ... first bearing, 28 ... second bearing, 50 ... gear train, 55 ... elastic member, U1 ... intermediate shaft unit, X1, X2 ... tooth trace Directions opposite to each other, Y1, Y2 ... directions opposite to each other in the tooth trace direction, Z1 ... one of the axial directions of the intermediate shaft, t1 to t4 ... tooth thickness

Claims (4)

A parallel shaft gear mechanism for decelerating the output rotation of the steering assist electric motor;
The parallel shaft gear mechanism includes a gear train that meshes with one or more stages,
With respect to at least a pair of gears meshing with each other in the gear train, one gear is supported so as to be movable in the axial direction,
An electric power steering apparatus, wherein the one gear is meshed with the other gear while being urged in the axial direction by its own weight or an elastic member.   2. The electric power steering apparatus according to claim 1, wherein at least a pair of gears meshing with each other in the gear train has a tooth thickness gradually increasing in directions opposite to each other in a tooth line direction. 2. The parallel shaft gear mechanism according to claim 1, wherein the parallel shaft gear mechanism is provided on an input shaft disposed coaxially with a rotation shaft of the electric motor, an intermediate shaft and an output shaft disposed in parallel with the input shaft, and the input shaft. A drive gear, a first and a second intermediate gear provided so as to be integrally rotatable with the intermediate shaft and spaced apart in the axial direction of the intermediate shaft, and a driven gear provided on the output shaft;
The gear train is constituted by the drive gear, the first and second intermediate gears, and the driven gear,
The intermediate shaft is supported rotatably and axially displaceable by a bearing held by the housing,
The intermediate shaft is engaged with the drive gear while the first intermediate gear is urged in one of the axial directions by the weight of the intermediate shaft and the first and second intermediate gears, or by an elastic member. An electric power steering device, wherein two intermediate gears are meshed with a driven gear.   The drive gear and the first intermediate gear have a tooth thickness that gradually increases in directions opposite to each other in the tooth line direction, and the driven gear and the second intermediate gear are opposite to each other in the tooth line direction. An electric power steering apparatus characterized in that the tooth thickness gradually increases in the direction of orientation.

Images