JP2008044425A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact electric power steering device with sufficient mountability to a vehicle. <P>SOLUTION: An intermediate shaft of a parallel axis gear mechanism 7 for decelerating rotation of an electric motor is integrally rotatably provided with a first intermediate gear 23 driven by a drive gear provided on an input shaft; and a second intermediate gear 24 for transmitting rotation to a driven gear provided on an output shaft. A tooth 231 of the first intermediate gear 23 and a tooth 241 of the second intermediate gear 24 are a shape twisted counterclockwise. An axial component F1 of reaction force F received from the drive gear by the first intermediate gear 23 and an axial component G1 of reaction force G received from the driven gear by the second intermediate gear 24 are directed in a direction opposite to each other. Since both components F1, G1 are offset, mutual resultant force H1 (H1=F1-G1) becomes small. <P>COPYRIGHT: (C)2008,JPO&amp;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).
JP 2005-319971 A

However, 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 is not easily mounted on a vehicle. Become.
The present invention has been made in view of the above problems, and an object thereof is to provide an electric power steering device that is small in size and has good mountability on a vehicle.

  In order to achieve the above object, the present invention includes a parallel shaft gear mechanism (7) for decelerating the output rotation of the electric motor (6) for assisting steering, and the parallel shaft gear mechanism is a rotation of the electric motor. An input shaft (19) disposed coaxially with the shaft (6a), an intermediate shaft (20) and an output shaft (3b) disposed in parallel with the input shaft, and a drive gear (21 provided on the input shaft) ), First and second intermediate gears (23, 24) which are provided so as to be integrally rotatable with the intermediate shaft and are spaced apart in the axial direction of the intermediate shaft, and driven gears (22) provided on the output shaft. The intermediate shaft is rotatably supported by bearings (27, 28; 27A, 28A) held by the housing (8), the first intermediate gear is driven by the drive gear, and the second intermediate gear is used. The driven gear is driven and the first intermediate gear (231; 232) and the teeth (241; 242) of the second intermediate gear are twisted in the same direction. As a result, the reaction force (F) that the first intermediate gear receives from the drive gear (F) The axial component (F1; FA1) of FA) and the axial component (G1; GA1) of the reaction force (G; GA) received by the second intermediate gear from the driven gear are directed in opposite directions. It is characterized by being.

  In the present invention, since some of the axial components of the driving reaction force received by the first and second intermediate gears can be canceled out, the load on the bearing supporting the intermediate shaft can be reduced. . As a result, the bearing life can be improved. Further, it is possible to use a bearing having a small load capacity. As a result, it is possible to realize an electric power steering device that is small in size and easy to mount on a vehicle.

  In the present invention, as the bearing, there are provided first and second bearings that rotatably support corresponding end portions in the axial direction of the intermediate shaft, and the first bearing is provided in the first intermediate gear. The second bearing is disposed relatively close to the second intermediate gear, and the axial component (F1) of the reaction force (F) received by the first intermediate gear from the drive gear is relatively close. ) Is directed to the first bearing (27) side, and the axial component (G1) of the reaction force (G) received by the second intermediate gear from the driven gear is the second bearing (28) side. In some cases, the first bearing regulates the axial movement of the intermediate shaft, and the second bearing allows the axial movement of the intermediate shaft.

  In this case, most of the axial component of the reaction force received by the first intermediate gear and the axial component of the reaction force received by the second intermediate gear cancel each other, and the intermediate shaft is directed toward the first bearing. A slight axial force acts as a resultant force. Therefore, the first bearing only needs to receive the slight axial force, and the second bearing which is free in the axial direction does not receive the axial load. Therefore, the load on both bearings can be reduced and the bearing can be downsized.

  In the present invention, as the bearing, there are provided first and second bearings that rotatably support corresponding end portions in the axial direction of the intermediate shaft, and the first bearing is provided in the first intermediate gear. The second bearing is disposed relatively close to the second intermediate gear, and the axial component (FA1) of the reaction force (FA) received by the first intermediate gear from the drive gear is relatively close. ) Is directed to the second intermediate gear side, and the axial component (GA1) of the reaction force (GA) received by the second intermediate gear from the driven gear is directed to the first intermediate gear side. The first bearing (27A) allows axial movement of the intermediate shaft, and the second bearing (28A) regulates axial movement of the intermediate shaft (claim 3). .

  In this case, the axial component of the reaction force received by the first intermediate gear and the axial component of the reaction force received by the second intermediate gear face each other, and most of each cancels out. A slight axial force acts on the intermediate shaft toward the second bearing. Therefore, the second bearing only needs to receive the slight axial force, and the first bearing which is free in the axial direction does not receive the axial load. Therefore, the load on both bearings can be reduced and the bearing can be downsized.

  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 system (EPS) 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, and a steered wheel as the steering shaft 3 rotates. As a steering mechanism 5 including, for example, a rack and pinion mechanism for steering 4, an electric motor 6 that generates a steering assist force, and a speed reduction mechanism for decelerating and transmitting the output rotation of the electric motor 6 to the steering mechanism 5 The parallel shaft gear mechanism 7 is provided.

  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 and the second shaft 3b as an output shaft disposed in parallel with the input shaft 19 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 meshing with the drive gear 21 so as to be integrally rotatable, and a second intermediate gear 24 meshing 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 from each other 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 a helical gear.

  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 rotatably supported by first and second bearings 27 and 28 held by the unit housing 8. The second shaft 3 b as an 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, an outer ring 33 of the bearing 25 is sandwiched between a positioning step 34 formed in the unit housing 9 and a retaining ring 35 fitted in an annular groove of the unit housing 9. 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 arranged 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 connected to the intermediate portion 20c of the intermediate shaft 20 in a state where the first intermediate gear 23 can rotate integrally and the 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 rotatable integrally with the intermediate shaft 20 but not 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 input 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 threaded 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 27, thereby the axial direction of the first intermediate gear 23 relative to the intermediate shaft 20. Movement is restricted.

  The axial movement of the outer ring 39 of the first bearing 27 is restricted by the unit housing 8. Specifically, an outer ring 39 of the first bearing 27 is sandwiched between a positioning step portion 40 formed in the unit housing 8 and a retaining ring 41 fitted in an annular groove of the unit housing 9. As a result, the axial movement of the intermediate shaft 20 and the first and second intermediate gears 23 and 24 is restricted.

  On the other hand, the inner ring 42 of the second bearing 24 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. Thereby, the 2nd bearing 24 is supporting the intermediate shaft 20 so that an axial direction movement is possible. The outer ring 43 of the second bearing 24 is fixed to the corresponding bearing holding portion of the unit housing 8 by press fitting.

  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 able to rotate integrally and not to move in the axial direction.
With reference to FIG. 3 which is a schematic view of the support structure of the intermediate shaft 20, the feature of the present embodiment is that the teeth 231 of the first intermediate gear 23 and the teeth 241 of the second intermediate gear 24 are The first intermediate gear 23 is twisted in the same direction, and as a result, the axial component F1 of the reaction force F received by the first intermediate gear 23 from the drive gear 21 and the reaction received by the second intermediate gear 24 from the driven gear 22 are obtained. The axial component G1 of the force G is directed in the opposite directions.

  Specifically, in the present embodiment, the teeth 231 of the first intermediate gear 23 and the teeth 241 of the second intermediate gear 24 are twisted counterclockwise (counterclockwise direction). For this reason, the axial component F1 of the reaction force F received by the first intermediate gear 23 from the drive gear 21 is directed to the first bearing 27 side relatively close to the first intermediate gear 23, and the second The axial component G1 of the reaction force G received by the intermediate gear 24 from the driven gear 22 is directed to the second bearing 28 side that is relatively close to the second intermediate gear 24.

  As described above, the axial component F1 and the axial component G1 are opposite to each other, but the magnitude of the axial component F1 of the reaction force F received by the first intermediate gear 23 is the second intermediate gear 24. Becomes larger than the axial component G1 of the reaction force G received (F1> G1). This is because the first intermediate gear 23 constitutes a driven gear for the drive gear 21, and the second intermediate gear 24 constitutes a drive gear for the driven gear 22. This is because the intermediate gear 23 has a larger diameter than the second intermediate gear 24.

That is, the axial component F1 and the axial component G1 cancel each other, and the resultant force H1 between the axial component F1 and the axial component G1 is the difference between the two components (that is, H1 = F1-G1). Orient to the side.
In the present embodiment, since the axial movement of the intermediate shaft 20 is restricted by the first bearing 27, the resultant force H1 is received only by the first bearing 27, but the resultant force H1 is Since it is small, the load applied to the first bearing 27 is small. Further, since the second bearing 28 allows the intermediate shaft 20 to move in the axial direction, the second bearing 28 does not receive a load related to the axial direction of the intermediate shaft 20. Thus, the load concerning both the bearings 27 and 28 can be reduced. As a result, the bearing life can be improved. Further, it is possible to use a bearing having a small load capacity. As a result, it is possible to realize an electric power steering device that is small in size and easy to mount on a vehicle.

Moreover, since the loss torque of each bearing 27 and 28 can be reduced, there also exists an advantage that the steering feeling at the time of operating the steering member 2 can be improved.
FIG. 4 shows another embodiment of the present invention. Referring to FIG. 4, this embodiment is mainly different from the embodiment of FIG. 3 in that teeth 232 of first intermediate gear 23A and teeth 242 of second intermediate gear 24A are clockwise ( The first bearing 27A allows the intermediate shaft 20 to move in the axial direction, and the second bearing 28A allows the first bearing 27 to move toward the intermediate shaft 20. That is, the movement in the axial direction is restricted.

  In the present embodiment, the axial component FA1 of the reaction force FA received by the first intermediate gear 23A from the drive gear 21 is directed to the second intermediate gear 24A side, and the second intermediate gear 24A is moved from the driven gear 22. The axial component GA1 of the reaction force GA received is directed to the first intermediate gear 23 side. That is, the axial direction component FA1 and the axial direction component GA1 are directed in the direction in which they face each other, and the resultant force HA1 of both axial direction components FA1 and GA1 is directed to the second bearing 28A side.

Also in the present embodiment, since the resultant force HA1 can be reduced, the bearing load can be reduced, the bearing life can be improved, and the steering feeling can be improved.
3 and 4, when the electric motor 6 is reversely rotated according to the steering direction and the intermediate shaft 20 is reversely rotated accordingly, the components F1, G1, The directions of the forces of FA1 and GA1 are all reversed, and the same effect can be achieved.

  The present invention is not limited to the above-described embodiments, and 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 a schematic diagram of the support structure of an intermediate shaft for demonstrating the component of the force which acts on an intermediate shaft. It is a schematic diagram of the support structure of the intermediate shaft of another embodiment of this invention, and is a figure for demonstrating the component of the force which acts on an intermediate shaft.

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, 22 ... driven gear, 23, 23A ... first intermediate gear, 231, 232 ... first intermediate gear teeth, 24, 24A ... second intermediate gear, 241, 242 ... Second intermediate gear teeth, 27, 27A ... first bearing, 28, 28A ... second bearing, F, FA ... reaction force received by the first intermediate gear from the drive gear, F1, FA1 ... first Axial direction component of reaction force received by intermediate gear from drive gear, G, GA ... Reaction force received by second intermediate gear from driven gear, F1, FA1 ... Axial direction of reaction force received by second intermediate gear from driven gear Ingredients, H1, HA1,.

Claims (3)

A parallel shaft gear mechanism for decelerating the output rotation of the steering assist electric motor;
The parallel shaft gear mechanism includes an input shaft disposed coaxially with the rotating shaft of the electric motor, an intermediate shaft and an output shaft disposed in parallel with the input shaft, a drive gear provided on the input shaft, A first and a second intermediate gear that are provided so as to be integrally rotatable on the shaft and are spaced apart in the axial direction of the intermediate shaft; and a driven gear that is provided on the output shaft;
The intermediate shaft is rotatably supported by a bearing held by the housing,
The first intermediate gear is driven by the drive gear, and the driven gear is driven by the second intermediate gear,
The teeth of the first intermediate gear and the teeth of the second intermediate gear are twisted in the same direction, and as a result, the axial component of the reaction force that the first intermediate gear receives from the drive gear An electric power steering apparatus characterized in that an axial component of a reaction force received by a second intermediate gear from a driven gear is directed in opposite directions. In Claim 1, the said bearing is provided with the 1st and 2nd bearing which respectively supports the axially corresponding edge part of the said intermediate shaft rotatably,
The first bearing is disposed relatively close to the first intermediate gear and the second bearing is disposed relatively close to the second intermediate gear;
The axial component of the reaction force received by the first intermediate gear from the drive gear is directed to the first bearing side, and the axial component of the reaction force received by the second intermediate gear from the driven gear is second. Oriented to the bearing side of
An electric power steering device characterized in that the first bearing restricts the axial movement of the intermediate shaft and the second bearing allows the axial movement of the intermediate shaft. In Claim 1, the said bearing is provided with the 1st and 2nd bearing which respectively supports the axially corresponding edge part of the said intermediate shaft rotatably,
The first bearing is disposed relatively close to the first intermediate gear and the second bearing is disposed relatively close to the second intermediate gear;
The axial component of the reaction force received by the first intermediate gear from the drive gear is directed to the second intermediate gear, and the axial component of the reaction force received by the second intermediate gear from the driven gear. Is directed to the first intermediate gear side,
An electric power steering device characterized in that the first bearing allows the axial movement of the intermediate shaft and the second bearing regulates the axial movement of the intermediate shaft.

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