Patent Application
20180172134
The present invention relates to an improvement of a worm reducer to be assembled, for example, in an electric power steering device.
As shown in
In the above-described steering device, there has been known an electric power steering device including an electric assist device for reducing a force required to operate the steering wheel 1 while using an electric motor 10 as an auxiliary power source. A reducer is assembled in such an electric power steering device. As such reducer, there has been widely known a worm reducer having a large lead angle and reversibility with respect to a transmission direction of the power as described in Patent Document 1 or the like.
The housing 12 is supported and fixed to the electric motor 10 (see
In view of reduction in size, the conventional worm reducer as described above has room for improvement. That is, an outer ring 19 configuring the rolling bearing 18a that is supported and fixed on a base end side portion of the worm 14 (the right side in
The present invention has been made in consideration of the above-mentioned circumstances for realizing a worm reducer configuration by which reduction in size is easily achieved.
A worm reducer of the present invention includes a housing, a worm wheel and a worm.
The worm wheel is supported on a driven shaft rotatably supported by the housing to be concentric with the driven shaft and rotates together with the driven shaft.
In a state where an axial one end portion (base end portion) is joined with a drive shaft provided at a skew position with respect to the driven shaft, and worm teeth provided on an axial intermediate portion are engaged with the worm wheel, an axial one side portion with respect to a portion where the worm teeth are provided is rotatably supported by a bearing with respect to the housing.
Particularly, in the worm reducer of the present invention, the bearing is a rolling bearing which includes: an outer ring having an outer ring raceway on an inner circumferential surface; an inner ring having an inner ring raceway on an outer circumferential surface; and a plurality of rolling elements rotatably arranged between the outer ring raceway and the inner ring raceway. Furthermore, an outer circumferential surface of an axial one end portion of the outer ring is provided with a flange portion which protrudes radially outward. The housing is formed with a holding portion to be internally fitted with the outer ring. In a state where an axial another side portion of the outer ring is internally fitted in an axial another side portion of the holding portion and an axial another side face of the flange portion is abutted against an axial one side face of the housing, an axial another side face of a retaining plate supported to the housing is abutted against an axial one side face of the flange portion. In other words, the flange portion is sandwiched in the axial direction between the axial one side face of the housing and the axial another side face of the retaining plate.
In implementing the worm reducer of the present invention described above, the worm reducer may be preferably configured such that the axial another side face of the outer ring is not abutted against any portion of the housing.
In implementing the worm reducer of the present invention described above, the flange portion is preferably arranged at an entire circumference or at intervals in the circumferential direction on the outer circumferential surface of the axial one end portion of the outer ring.
Furthermore, in implementing the worm reducer of the present invention described above, an axial one end portion of the holding portion is provided with a large diameter stepped part, an inner diameter of which is larger than that of an axial another side portion (portion except for the axial one end portion), at an entire circumference or at intervals in the circumferential direction. A stepped surface at an axial another end portion of the large diameter stepped part defines the axial one side face of the housing. In a state where the axial another side of the outer ring is internally fitted in the axial another side portion of the holding portion and the axial another side face of the flange portion is abutted against the stepped surface, an axial another side face of the retaining plate supported by the housing is abutted against the axial one side face of the flange portion.
Furthermore, in implementing the worm reducer of the present invention described above, preferably, the retaining plate has a stepped shape including an outer diameter side portion supported by the housing and an inner diameter side face abutted against the axial another side face of the flange portion.
In implementing the worm reducer of the present invention described above, for example, the large diameter stepped part is configured by a pair of recess portions arranged on two radially opposite positions deviated by 90 degrees respectively from an engagement portion between the worm wheel and the worm teeth in the circumferential direction. Further, the flange portion is configured by a pair of flange pieces arranged on two radially opposite positions deviated by 90 degrees respectively from the engagement portion between the worm wheel and the worm teeth in the circumferential direction. Urging means is provided between the worm and the housing and radially urges the worm (the worm teeth is elastically urged against the worm wheel) to suppress a backlash at the engagement portion between the worm wheel and the worm teeth.
Further, the electric assist device of the present invention includes an electric motor and a worm reducer.
The worm reducer includes a housing, a worm wheel, and a worm.
The worm wheel is supported on a rotational shaft rotatably supported by the housing to be concentric with the rotational shaft and rotates together with the rotational shaft.
In the worm, worm teeth are provided on an axial intermediate portion, and in a state where the worm teeth are engaged with the worm wheel, an axial one side portion with respect to a portion where the worm teeth are provided is rotatably supported by a bearing with respect to the housing.
An output shaft of the electric motor and the worm are connected to transmit torque.
The electric assist device is configured to increase the torque of the output shaft of the electric motor through the worm reducer and apply the torque to the rotational shaft, i.e. the rotational shaft rotated by the steering wheel supported and fixed on a rear end portion, or a portion movable with the rotation of the rotational shaft (a pinion shaft configuring the steering gear unit or a rotational shaft arranged at an axial portion of a rack configuring the steering gear unit and away from a pinion shaft).
In particular, in the electric assist device of the present invention, the worm reducer is the worm reducer of the present invention as described above. In this case, the output shaft of the electric motor corresponds to the drive shaft, and the rotational shaft corresponds to the driven shaft.
According to the worm reducer and the electric assist device of the present invention configured as described above, it is easier to achieve reduction in size.
That is, in the present invention, in a bearing, i.e. a rolling bearing, which supports the base end side (the axial one side) of the worm, a flange portion is provided on an outer circumferential surface of the axial one end portion of the outer ring, and the flange portion is sandwiched between the axial one side face of the housing and the axial another side face of the retaining plate supported by the housing. Thus, an axial component of the counter force applied from an engagement portion between the worm wheel and the worm teeth to the worm can be supported by the axial one side face of the housing and the retaining plate. Accordingly, in order to support the axial component of the counter force, there is no need to provide the housing with a stepped surface abutted against the axial another side face of the outer ring, and no need to provide the wheel-side support portion 24 for ensuring the strength of the stepped surface 21 against the axial component of the counter force as in the configuration illustrated in the
A first embodiment of the present invention is described with reference to
The worm wheel 13 is supported on a front end side portion of the steering shaft 5 serving as a driven shaft which is rotatably supported inside the wheel accommodation portion 15a to be concentric with the steering shaft 5 and rotates together with the steering shaft 5. Incidentally, a radial clearance 25 is provided between the outer circumferential surface of the worm wheel 13 and the outer circumferential surface of the wheel accommodation portion 15a to prevent the worm wheel 13 from contacting an inner surface of the wheel accommodation portion 15a during operation of the worm reducer 11a (during rotation of the worm wheel 13).
In a state where worm teeth 17 provided on an axial intermediate portion of the worm 14a is engaged with the worm wheel 13, the worm 14a is rotatably and swingably supported inside the worm accommodation portion 16a at two axial positions which interpose the worm teeth 17 by a pair of rolling bearings 18c, 18d. That is, an inner ring 28 configuring the rolling bearing 18c on the axial one side (the base end side, right side in
An outer circumferential surface of the axial one end portion of the outer ring 19a configuring the rolling bearing 18c on the axial one side is formed with a flange portion 30 protruding radially outward at an entire circumference. The inner circumferential surface of the axial one end portion of the worm accommodation portion 16a (opening) is formed with a cylindrical surface shaped holding portion 20a except for a portion, and the axial one end portion of the holding portion 20a is formed with a large diameter stepped part 31 having the inner diameter larger than the inner diameter of the axial another side portion (the remainder except for the axial one end portion, a cylindrical surface shaped portion) at an entire circumference. The axial another side portion of the outer ring 19a (a cylindrical portion except for the flange portion 30) is internally fitted to the axial another side portion of the holding portion 20a by a clearance fit, and the axial another side face of the flange portion 30 is abutted against a stepped surface 32 (the axial another side face of the housing 12a) provided at the axial another end portion of the large diameter stepped part 31. In this state, an inner diameter side portion of the axial another side face of a substantially ring shaped retaining plate 33, an outer diameter side portion of which is supported and fixed to the housing 12a (an opening side end face of the worm accommodation portion 16a) is abutted against the axial one side face of the flange portion 30. In other words, the flange portion 30 of the outer ring 19a is axially sandwiched between the stepped surface 32 and the retaining plate 33. Accordingly, the axial displacement of the outer ring 19a with respect to the worm accommodation portion 16a is restricted. In the present embodiment, the axial another end face of the outer ring 19a is not abutted against (supported by) any portion of the housing 12a.
Incidentally, the rolling bearing 18c on the axial one side is configured such that the internal clearance is negative (negative clearance) and a center axis of the inner ring 28 can be easily deviated from a center axis of the outer ring 19a. Accordingly, the worm 14a can displace swingingly using the rolling bearing 18c on the axial one side as a center. Here, an elastic member, such as rubber, may be sandwiched at least one of a portion between the inner circumferential surface of the inner ring 28 and the outer circumferential surface of the worm 14a and a portion between the outer circumferential surface of the axial another side portion of the outer ring 19a and the holding portion 20a, to allow the worm 14a supported by the housing 12a to displace swingingly.
The outer circumferential portion of the retaining plate 33 includes attachment plate portions 34, 34 which protrude radially outward, at a plurality of positions (three positions in the illustrated example) in the circumferential direction. The outer diameter side portion of the retaining plate 33 is supported and fixed to the worm accommodation portion 16a by screwing and fastening bolts 36, 36 which are inserted into through holes 35 formed on each of the attachment plate portions 34, 34 to the threaded hole 37 which opens to the opening side end face of the worm accommodation portion 16a. Incidentally, the retaining plate 33 may be supported and fixed to the worm accommodation portion 16a by screwing and fastening nuts on bolts inserted into each of the through holes 35 and into through holes formed to pass through the worm accommodation portion 16a in the axial direction. Alternatively, as the retaining plate to abut against the axial one side face of the flange portion 30, the locking ring as in the conventional configuration illustrated in
The inner ring configuring the rolling bearing 18d on the axial another side of the two rolling bearings 18c, 18d is pressed into the axial another side portion (a tip portion) of the worm 14a (externally fitted by an interference fit). The outer ring configuring the rolling bearing 18d on the axial another side is supported by a second holding portion 38 which has a bottomed cylindrical shape and is formed in an inner end portion (the axial another end) of the worm accommodation portion 16a. In the present embodiment, urging means (not shown) is arranged between the second holding portion 38 and the outer ring configuring the rolling bearing 18d on the axial another side and urges against the axial another side portion of the worm 14a in the radial direction (the worm teeth 17 are elastically urged towards the worm wheel 13 (downward in
Furthermore, in the present embodiment, an axial another end portion (the tip portion) of an output shaft 27 of the electric motor 10 is joined with an axial one end portion (the base end portion) of the worm 14a via a torque transmitting joint 39 so as to transmit torque. That is, the torque transmitting joint 39 is provided between a drive-side transmitting member 40 fixed to the axial another end portion of the output shaft 27 and a spline shaft 41 formed in the axial one end portion of the worm 14a. The torque transmitting joint 39 is configured by a drive-side elastic member 42 and a driven-side elastic member 43 which are made of elastomer material, such as rubber, and a coupling 44 made of material which is more difficult to deform (higher rigidity) compared to the elastomer material such as rubber. Accordingly, the transmitting characteristics of the torque between the output shaft 27 and the worm 14a can be divided into two stages based on the magnitude of the torque transmitted. Further, even if the worm 14a displaces swingingly, so that inconsistency occurs between the center axis of the output shaft 27 and the center axis of the worm 14a due to misalignment, the torque between the output shaft 27 and the worm 14a can be smoothly transmitted while the coupling 44 is inclined with respect to those axes. The details of the torque transmitting joint 39 will not be explained here as it is irrelevant to the subject of the present invention. The output shaft 27 may be directly joined with the worm 14a to transmit torque by spline engagement or the like.
According to the electric assist device 26 of the embodiment as described above, the longitudinal dimension of the worm reducer 11a may be suppressed in the axial direction of the worm 14a so as to achieve reduction in size.
That is, in the present embodiment, the flange portion 30 is formed on the outer circumferential surface of the axial one end portion of the outer ring 19a configuring the rolling bearing 18c on the axial one side among the pair of rolling bearings 18c, 18d which rotatably support the worm 14a in the worm accommodation portion 16a. The flange portion 30 is sandwiched between the stepped surface 32 formed in the worm accommodation portion 16a and the axial another side face of the retaining plate 33 supported and fixed to the worm accommodation portion 16a. Thus, an axial component of the counter force applied from the engagement portion between the worm wheel 13 and the worm teeth 17 to the worm 14a can be supported by the stepped surface 32 and the retaining plate 33. Accordingly, in order to support the axial component of the counter force, there is no need to provide the housing 12a with the stepped surface abutted against the axial another side face of the outer ring 19a, and no need to provide the wheel-side support portion 24 for ensuring the strength of the stepped surface 21 against the axial component of the counter force as in the configuration illustrated in the
Accordingly, in the present embodiment, compared to the conventional configuration, since the position where the rolling bearing 18c supports the worm 14a can be moved toward the tip side of the worm 14a by the length corresponding to the omission of the wheel-side support portion 24, the axial dimension of the worm 14a can be reduced, so that the length of the worm reducer 11a in the axial direction of the worm 14a can be reduced. The worm reducer 11a and the electric assist device 26 may be reduced in size and weight. As a result, the layout of the electric power steering device assembled with the electric assist device 26 is improved.
In the embodiment described above, when the worm 14a is in a trend of swing based on the counter force applied to the worm 14a from the engagement portion between the worm wheel 13 and the worm teeth 17, the rolling bearing 18e on the axial one side swings around the two flange pieces 46. Furthermore, in the present embodiment, since the flange portion 30 is configured by the two flange pieces 46, compared with the case where the flange portion 30 is provided at an entire circumference on the outer circumferential surface of the axial one end portion of the outer ring 19 as in the first embodiment, a clearance between the outer circumferential surface of the outer ring 19b and the holding portion 20b is increased. Therefore, the rolling bearing 18e on the axial side is allowed to swing easily, and swing displacement of the worm 14a can be performed smoothly.
Configurations and functions of other portions are same as those of the first embodiment described above.
A step portion 34a is formed on a radially inner side of the attachment plate portion 34 of the retaining plate 33, and an auxiliary attachment plate portion 34b is formed continuously. The axial length of a step between the attachment plate portion 34a and the auxiliary attachment plate portion 34b is shorter than the axial length of the flange portion 30. Therefore, in a state where the retaining plate 33 is fixed to the housing 12a, the axial one side face of the flange portion 30 of the bearing is elastically abutted against the axial another side face of the auxiliary attachment plate portion 34b. Therefore, the axial component of the counter force applied by the engagement portion between the worm wheel 13 and the worm teeth 17 to the worm 14a is supported by the opening side end face 20c of the holding portion 20a and the axial another side face of the auxiliary attachment plate portion 34b.
Configurations and functions of other portions are same as those of the first embodiment described above.
In the meantime, the present invention is not limited to the above embodiments, and may be changed or improved as appropriate.
In the present embodiment, the inner ring 28 configuring the rolling bearing 18c is externally fitted to the axial one end side portion of the worm 14a by an interference fit, and the axial another side portion of the outer ring 19a is internally fitted in the axial another side portion of the holding portion 20a by a clearance fit, but the inner ring 28 may be externally fitted in the axial one end side portion of the worm 14a by a clearance fit, and the axial another side portion of the outer ring 19a is internally fitted to the axial another side portion of the holding portion 20a by an interference fit.
The case of applying the worm reducer to an electric power steering device of column assist type are described in the above embodiments, but the present invention is no limited to the application to the electric power steering device of column assist type and is applicable to other types of electric power steering device. That is, when the worm reducer is assembled in an electric power steering device of pinion assist type, the worm wheel of the worm reducer is supported and fixed on an input shaft (pinion shaft) of a steering gear unit. On the other hand, when the worm reducer is assembled in an electric power steering device of rack assist type, the worm wheel is supported and fixed on a rotational shaft arranged at an axial portion of a rack configuring the steering gear unit and away from a pinion shaft.
The present invention is based on Japanese Patent Application No. 2014-251020 filed Dec. 11, 2014 and Japanese Patent Application No. 2015-229838 filed Nov. 25, 2015, contents of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-251020 | Dec 2014 | JP | national |
| 2015-229838 | Nov 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/084437 | 12/8/2015 | WO | 00 |
