Patent Application
20100060061
This application is based on and claims priority under 35 U.S.C. ยง119 to Japanese Patent Application 2008-232828 filed on Sep. 11, 2008, the entire contents of which is incorporated herein by reference.
The present invention relates to a power seat driving apparatus for a vehicle having a decelerating mechanism for decelerating a driving force of a power supply and transmitting the decelerated driving force to a moving unit of a seat.
A seat apparatus for a vehicle is known, in which a motor, serving as a power supply, and a decelerating mechanism for decelerating a driving force of the motor and transmitting the decelerated driving force to a moving unit of a seat, are combined and operated in order to adjust an inclination of a front portion of a seat cushion of a seat for a vehicle in an upper-lower direction of the seat and in order to slidably adjust an entire seat in a front-rear direction of the vehicle, for example. The decelerating mechanism includes gear deceleration portions, which engage with each other at a predetermined deceleration ratio. A large torque may be obtained according to the deceleration ratio. In a seat apparatus for adjusting an inclination of a seat, a plurality of deceleration portions is combined because a large torque may be required in order to raise the seat. In such configured power seat driving apparatus for vehicle, it is important to reduce a backlash at an inside of the decelerating mechanism in order to improve stability of an operation of the decelerating mechanism. Further, when the backlash is reduced, it is expected to reduce gear noise in order to improve comfortableness.
A rotation transmission mechanism disclosed in JP2005-344757A includes a decelerating mechanism that is adaptable to a power seat driving apparatus for vehicle. The rotation transmission mechanism according to JP2005-344757A includes a planetary gear mechanism having a first central gear, a second central gear, a first planetary gear and a second planetary gear. Not only the planetary gear mechanism, according to JP2005-344757A, but also a general planetary gear mechanism may be configured with a relatively small backlash.
When the decelerating mechanism is configured with a general gear set without using the planetary gear mechanism, a dimensional clearance is generally provided at the inside of the decelerating mechanism because a tolerance at the time of production and operational restriction are considered. On the other hand, when a rotational speed is reduced, a gear may idly rotate for an amount corresponding to a backlash because of inertia, and tooth surfaces of gears may clash with each other, thereby causing generation of stress. Furthermore, when the rotation stops, clashing damage may be generated. Therefore, sufficient mechanical strength is necessary to be secured for the stress and the damage as well as normally transmitted torque. As a result, supporting portions of a case for rotatably supporting the gears are generally made of metal. Extensive stress and damage may occur specifically in a mechanism in which a deceleration rate is large. Therefore, the supporting portion may be required to be made of iron, and the like,
According to the planetary gear mechanism disclosed in JP2005-344757A, although the backlash may be reduced, other drawbacks may exist, such that the number of components is increased, a size of the mechanism is enlarged, and a cost is increased. On the other hand, when a general gear set is used for deceleration, it may be difficult to reduce the backlash and to improve the stability because torque outputted from the gear set becomes large. Further, the supporting portion may be required to be made of metal. Therefore, weight may not be reduced.
A need thus exists for a power seat driving apparatus for a vehicle, which is not susceptible to the drawback mentioned above.
According to an aspect of the present invention, a power seat driving apparatus for a vehicle includes a moving unit adapted to be arranged between a seat and a vehicle floor so as to move the seat relative to the vehicle floor and a decelerating mechanism connected to the moving unit so as to decelerate a driving force outputted by a power supply and transmit the decelerated driving force to the moving unit. The deceleration mechanism includes a driving gear, a driven gear engaging with the driving gear and driven to rotate while decelerating a rotational speed of the driving gear, a supplemental gear coaxially connected to the driven gear in an interlocking manner, made of a resin material having elasticity and lower rigidity than the driven gear, having a larger tooth thickness than a tooth thickness of the driven gear by an amount corresponding to a backlash, and engaging the driving gear together with the driven gear; and a housing accommodating and rotatably supporting the driving gear, the driven gear and the supplemental gear.
The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein:
A first embodiment of a power seat driving apparatus 1 for a vehicle will be provided hereinafter with reference
A rear portion of the cushion frame 22 is supported by the side bracket 21 by means of a first support pin 212 arranged at an intermediate portion of the side bracket 21. The front pivot-link mechanism 23 includes a pivot link 24, a front link 25 and a frame pivot link 26. A support hole 241 is formed at an intermediate portion of the pivot link 24, and the pivot link 24 is supported by the side bracket 21 by means of a second support pin 211 arranged at a front end of the side bracket 21. A rear end of the pivot link 24 is pivotably connected to an upper rail 99 by the front link 25 pivotably connected to the pivot link 24 at a first joint portion 243. A second joint portion 242 provided at a front end of the pivot link 24 is pivotably connected to a front portion of the cushion frame 22 by the frame pivot link 26 by means of a third support pin 221. Further, a sector gear 244 is integrally formed at one of the left and right pivot links 24. The sector gear 244 is formed into a substantially sectorial shape expanding toward a rear direction centering the support hole 241, and teeth are formed at a rear end of the sector gear 244 along an arc surface of the sectorial shape. The left and right pivot links 24 are connected to each other by means of a transmission rod, which is coaxially provided with the second support pin 211, so as to pivot integrally. A rear portion of the rear pivot link 27 is supported by the side bracket 21 by means of a fourth support pin 213, arranged at a lower-rear end of the side bracket 21. A front portion of the rear pivot link 27 is pivotably supported at the upper rail 99. A moving unit of a seat being capable of moving the seat relative to a vehicle floor, is configured by the side bracket 21 and the cushion frame 22.
The front driving device 28 includes a motor (a power supply) 281, outputting a driving force, and a decelerating portion 3, having an output gear 282 engaging with the sector gear 244. When the output gear 282 is driven to rotate in a counter-clockwise direction in
In the front and rear driving devices, only the decelerating portion 3 applied to the front driving device 28 will be described hereinafter as an example, with reference
The housing 6 includes a housing main body 61 and a housing cover 65, each of which is made of resin. The housing main body 61 and the housing cover 65 face each other to accommodate the first and second deceleration portions 4 and 5 at an inside portion of the housing 6 surrounded by the housing main body 61 and the housing cover 65. Protruding portions 611 are provided at four portions of a rim of the housing main body 61. Hook portions 651 are provided at the housing cover 65 so as to face the corresponding protruding portions 611. The protruding portions 611 engage with the corresponding hook portions 651, and thereby the housing main body 61 and the housing cover 65 are connected to each other to configure the housing 6. First attachment holes 612 are formed at three portions of the rim of the housing main body 61. Second attachment holes 652 are formed at three portions of a rim of the housing cover 65, corresponding to the first attachment hole 612. The housing main body 61 and the housing cover 65 are integrally attached to the side bracket 21 shown in
A driving-portion bearing hole is formed at a back-left portion of an inside of the housing main body 61 in
The first deceleration portion 4 includes a worm 41, which is a driving portion of the first deceleration portion 4, and a helical gear 42, which is a driven portion of the first deceleration portion 4. The worm 41 and the helical gear 42 engage with each other. The first deceleration portion 4 decelerates the driving force and changes a rotational axis of the driving force substantially 90 degrees from the first axis C1, which extends substantially horizontally, to the second axis C2, which extends substantially vertically. The worm 41 is axially rotatably supported by the driving-portion bearing hole formed at the housing main body 61. The worm 41 is connected to an output shaft of the motor 281 so as to integrally rotate therewith, using a joint member, whose ends in a longitudinal direction thereof are formed into a quadrangular shape when seen in a cross-sectional view. The helical gear 42, which engages with the worm 41, includes a shaft portion 421, which protrudes downwardly in
The second deceleration portion 5 includes a pinion gear 51 (a driving gear), a spur gear 52 (a driven gear) and an elastic gear 53 (a supplemental gear). The second deceleration portion 5 further decelerates the driving force, which has been decelerated by the first deceleration portion 4. The pinion gear 51, which is a driving portion of a second deceleration portion 5, includes a first gear portion 511, a first lower shaft portion 512 and a first upper shaft portion 513. The first gear portion 511 includes a spur gear formed along an outer circumferential surface of a cylindrical portion of the pinion gear 51. The first lower and upper shaft portions 512 and 513 are coaxially formed at lower and upper ends of the first gear portion 511, respectively, so that a radius of each of the first lower and upper portions 512 and 513 is smaller than that of the first gear portion 511. The first lower shaft portion 512 engages with the first shaft hole 422 of the helical gear 42, while a lower portion of the first gear portion 511 engages with the first inner teeth portion 423 of the helical gear 42 so as not to rotate relative to each other, and therefore, the pinion gear 51 and the helical gear 42 rotate integrally with each other. An outer circumferential surface of the upper shaft portion 512 is axially rotatably supported by the first cover bearing hole 67 of the housing cover 65.
On the other hand, the spur gear 52, which is a driven portion of the second deceleration portion 5, includes a second gear portion 521, a second shaft hole 522, a second inner teeth portion 523 and connecting holes 524. The second gear portion 521 includes a spur gear formed along an outer circumferential surface of a thin cylindrical portion of the spur gear 52. The second shaft hole 522 is formed at a center of the cylindrical portion. The second inner teeth portion 523 is formed at an inner circumferential surface of the second shaft hole 522. The connecting holes 524 are formed at four portions on a circumference centering the third axis C3. The second gear portion 521 of the spur gear 52 engages with an upper portion of the first gear portion 511 of the pinion gear 51. A deceleration ratio between the spur gear 52 and the pinion gear 51 is set to be the reciprocal of a ratio of teeth numbers therebetween.
The elastic gear 53 is made of resin material and is formed into a substantially annular shape. The elastic gear 53 includes elasticity and lower rigidity than the spur gear 52. The elastic gear 53 includes a third gear portion 531, a third shaft hole 532 and connection protruding portions 533. The third gear portion 531 includes a spur gear formed at an outer circumferential surface of the elastic gear 53. The third shaft hole 532 is formed at a central portion of the elastic gear 53. The connection protruding portions 533, protruding toward the spur gear 52 in an axial direction of the elastic gear 53, are formed at plural portions on the circumference centering the third axis C. The number of teeth formed at the third gear portion 531 of the elastic gear 53 is the same as that of the second gear portion 521 of the spur gear 52 while a tooth thickness of the third gear portion 531 of the elastic gear 53 is larger than that of the second gear portion 521 of the spur gear 52 by an amount slightly larger than a backlash (or by an amount corresponding to a backlash) at an engagement between the pinion gear 51 and the spur gear 52. The connection protruding portions 533 of the elastic gear 53 engage with the corresponding connecting holes 524 of the spur gear 52. Therefore, the spur gear 52 and the elastic gear 53 are coaxially connected to each other so as to engage with the pinion gear 51 in the same phase in an interlocking manner.
An output gear member 57 outputs the driving force, which is decelerated by the first and second deceleration portions 4 and 5. The output gear member 57 axially rotatably supports the spur gear 52 and the elastic gear 53 around the third axis C3. As illustrated in
Operations of the power seat driving apparatus 1, specifically operations of the decelerating portion 3 according to the first embodiment will be described hereinafter. When the motor 281 is actuated in order to transmit the driving force thereof, having a rotational speed, to the worm 41 of the first deceleration portion 4, the helical gear 42 is driven to rotate while decelerating the rotational speed, and thus a first deceleration is executed. Subsequently, when the decelerated rotation is transmitted to the pinion gear 51 of the second deceleration portion 5, which rotates integrally with the helical gear 42, the spur gear 52 and the elastic gear 53 are driven to rotate while further decelerating the rotational speed, and thus a second deceleration is executed. The driving force, which is converted into a low speed high torque by the first and second deceleration, is outputted from the output gear 282 so as to pivot the sector gear 244 shown in
In the second deceleration portion 5, the tooth thickness of the elastic gear 53 is larger than that of the spur gear 52 by the amount corresponding to the backlash. Therefore, the spur gear 52 and the pinion gear 51 engage with each other so as to include the backlash therebetween while the elastic gear 53 and the pinion gear 51 engage with each other so as not to include a backlash therebetween. Accordingly, when the rotational speed outputted from the motor 281 is decelerated and the rotational speed of the pinion gear 51 is decelerated, an idling rotation of the elastic gear 53, caused by inertia, for the amount corresponding to the backlash, is less likely to occur. Even though the elastic gear 53 may idly rotate, stress and impact sounds, which may occur when the spur gear 52 idly rotates and when a teeth surface of the spur gear 52 clashes with a teeth surface of the pinion gear 51, are extremely small. In other words, even when inertia may lead the spur gear 52 to rotate idly for the amount corresponding to the backlash, actually the backlash may not occur because the elastic gear 53, which is interlocked with the spur gear 52, restricts the idling rotation of the spur gear 52. Further, the elastic gear 53 is made of a resin material, which includes elasticity and a low rigidity. Therefore, the elastic gear 53 includes a large resistance relative to an instantaneous large deformation, so that the idling rotation of the spur gear 52 is restricted. On the other hand, the elastic gear 53 is elastically deformed relative to a normal transmission of rotation from the pinion gear 51 to the spur gear 52, so that the spur gear 52 is driven to rotate smoothly.
As described above, the power seat driving apparatus 1 according to the first embodiment includes the elastic gear 53, which is coaxially interlocked with the spur gear 52, and whose tooth thickness is larger than the tooth thickness of the spur gear 52 by the amount corresponding to the backlash. Therefore, the backlash is restricted. Accordingly, operational stability of the decelerating portion 3 is improved. Further, damage, such as clash corresponding to the backlash, is reduced. Therefore, the housing main body 61 and the housing cover 65 may be made of resin. Accordingly, a weight and a cost are reduced. Furthermore, gear noise, which may occur in accordance with the backlash, is reduced.
A second embodiment of the power seat driving apparatus 1 will be described hereinafter with reference to
The elastic gear 54 according to the second embodiment is made of resin material and is formed into a substantially annular shape. The elastic gear 53 includes elasticity and lower rigidity than the spur gear 52. The elastic gear 54 includes a third gear portion 541, a third shaft hole 542 and connection protruding portions 543. The third gear portion 531 includes a spur gear formed at an outer circumferential surface thereof. The third shaft hole 542 is formed at a central portion of the elastic gear 54. The connection protruding portions 543, protruding toward the spur gear 52 in an axial direction of the elastic gear 54, are formed at plural portions on the circumference centering the third axis C. The number of teeth formed at the third gear portion 541 of the elastic gear 54 is the same as that of the second gear portion 521 of the spur gear 52 while a tooth thickness of the third gear portion 541 of the elastic gear 54 is larger than that of the second gear portion 521 of the spur gear 52 by the amount corresponding to the backlash. The connection protruding portions 543 of the elastic gear 54 engage with the corresponding connecting holes 524 of the spur gear 52. Therefore, the spur gear 52 and the elastic gear 54 are coaxially connected to each other so as to engage with the pinion gear 51 in the same phase in an interlocking manner.
Further, protruding portions 544, which slidably contact an inner wall surface 64 of the housing main body 61, are formed at a surface of the elastic gear 54 opposite from a surface thereof facing the spur gear 52. In other words, as illustrated in
In a decelerating portion 30 according to the second embodiment, when the spur gear 52 and the elastic gear 54 of the second deceleration portion 50 are driven to rotate in an interlocking manner, the protruding portions 544 of the elastic gear 54 slidably contact the inner wall surface 64 of the housing main body 61 from an axial direction of the elastic gear 54 while the second lower shaft portion 571 of the output gear member 57 is fitted into the inner circumferential surface 547 of the supplemental shaft portion 545 of the elastic gear 54, and outer circumferential surface 547 of the supplemental shaft portion 545 slidably contacts the supplemental bearing hole 69 of the housing main body 61. Accordingly, a backlash between the elastic gear 54 and the housing main body 61 in axial and radial directions of the elastic gear 54 is reduced. As a result, a backlash between the spur gear 52 and the housing 6 is reduced.
As described above, the decelerating portion 3 according to the first embodiment is modified in the second embodiment. According to the second embodiment, the protruding portions 544 and the supplemental shaft portion 545 are formed at the elastic gear 54 in order to reduce the backlash between the second deceleration portion 50 and the housing 6 in the axial and radial directions. Therefore, displacement of each of the spur gear 52 and the elastic gear 54 relative to the housing 6 in axial and radial directions is restricted. Accordingly, stability of operation of the decelerating portion 30 is improved.
A third embodiment of the power seat driving apparatus 1 will be described hereinafter with reference to
A second deceleration portion 7 (a deceleration mechanism) according to the third embodiment includes a pinion gear (a driving gear) 71, a spur gear (a driven gear) 72, and an elastic gear (a supplemental gear) 73. The second deceleration portion 7 further includes a stopper pin 74 and a stopper plate 75. The pinion gear 71, which is a driving portion of the second declaration portion 7, is coaxially integrally formed at an upper end of the helical gear 42 of the first deceleration portion 4. The pinion gear 71 and the helical gear 42 include a shaft hole at a central portion thereof. A first inner teeth portion 712 is formed at an inner circumferential surface of the shaft hole.
The stopper pin 74 includes a first outer teeth portion 741, a stopper cam 742 and a first upper shaft portion 744. The first outer teeth portion 741 includes outer teeth formed along an outer circumferential surface of a cylindrical portion of the stopper pin 74. The stopper cam 742 is integrally formed at an upper end of the first outer teeth portion 741 in
On the other hand, the spur gear 72, which is a driven portion of the second deceleration portion 7, includes a first gear portion 721, a first shaft hole 722, a second inner teeth portion 723 and connecting holes 724. The first gear portion 721 includes a spur gear formed along an outer circumferential surface of a cylindrical portion of the spur gear 72. The first shaft hole 722 is formed at a center of the spur gear 72. The second inner teeth portion 723 is formed at an inner circumferential surface of the first shaft hole 722. The connecting holes 724 are formed at four portions on a circumference centering the third axis C3. The first gear portion 721 of the spur gear 72 engages with the pinion gear 71. A deceleration ratio between the spur gear 72 and the pinion gear 71 is set to be the reciprocal of a ratio of teeth numbers therebetween.
The elastic gear 73 is made of resin material and is formed into a substantially annular shape. The elastic gear 73 includes elasticity and lower rigidity than the spur gear 72. The elastic gear 53 includes a second gear portion 731, a second shaft hole 732 and connection protruding portions 733. The second gear portion 731 includes a spur gear formed at an outer circumferential surface of the elastic gear 73. The second shaft hole 732 is formed at a central portion of the elastic gear 73. The connection protruding portions 733, protruding toward the spur gear 72 in an axial direction of the elastic gear 73, are formed at plural portions on the circumference centering the third axis C. The number of teeth formed at the second gear portion 731 of the elastic gear 73 is the same as that of the first gear portion 721 of the spur gear 72 while a tooth thickness of the second gear portion 731 of the elastic gear 73 is larger than that of the first gear portion 721 of the spur gear 72 by the amount corresponding to the backlash. The connection protruding portions 733 of the elastic gear 73 engage with the corresponding connecting holes 724 of the spur gear 72. Therefore, the spur gear 72 and the elastic gear 73 are coaxially connected to each other so as to engage with the pinion gear 71 in the same phase in an interlocking manner.
The stopper plate 75 includes a plurality of engagement portions 751, a third shaft hole 752 and a third inner teeth portion 753. The plurality of engagement portions 751 is formed at an outer rim of the plate-shaped stopper plate 75. The third shaft hole 752 is formed at a central portion of the stopper plate 75. The third inner teeth portion 753 is formed at an inner circumferential surface of the third shaft hole 752. The stopper plate 75 is arranged at the same height as the stopper cam 742 of the stopper pin 74 so as to face the stopper cam 742.
An output gear member 77 outputs the driving force, which is decelerated by the first and second deceleration portions 4 and 7. The output gear member 77 axially rotatably supports the spur gear 72, the elastic gear 73 and the stopper plate 75 around the third axis C3. As illustrated in
Operations of the decelerating portion 300 according to the third embodiment will be described hereinafter. When the driving force, whose rotational speed is decelerated by the first deceleration portion 4, is transmitted to the pinion gear 71 of the second deceleration portion 7 via the helical gear 42, the spur gear 72 and the elastic gear 73 are driven to rotate while further decelerating the rotational speed. When the spur gear 72 and the elastic gear 73 rotate, as in the first embodiment, the backlash may not occur because of the operation of the elastic gear 73.
Further, according to the third embodiment, when the pinion gear 71 and the stopper pin 74 integrally rotate, the stopper plate 75 and the spur gear 72 integrally rotate. When the stopper pin 74 rotates for a predetermined number of times, the engagement protruding portion 743 of the stopper cam 742 contacts and engages with a first engagement portion 751 of the stopper plate 75 so as to restrict a rotation of the stopper plate 75. Further, when the stopper pin 74 rotates for a predetermined number of times in an opposite direction, the engagement protruding portion 743 of the stopper cam 742 contacts and engages with a second engagement portion 751 of the stopper plate 75 so as to restrict a rotation of the stopper plate 75. Thus, a rotation angle range of the stopper plate 75 is restricted, and consequently, a rotation angle range of the output gear 282 is restricted. The rotation angle range may be set freely in a manner where shapes of the stopper cam 742 and the stopper plate 75 are modified.
As described above, according to the third embodiment, the first embodiment is modified so that the stopper pin 74 and the stopper plate 75 are provided in order to restrict the rotation angle range of the output gear 282. Therefore, upward and downward movement range of the moving unit 21 to 27 of the seat is appropriately restricted, and a necessity of arranging a restricting means after the output gear 282 is reduced.
According to the first to third embodiments, a seat tilt apparatus, in which the front portion of the cushion frame 22 pivots in order to move a front portion of the seat cushion upwardly and downwardly, serves as a power seat driving apparatus. However, not limited to the first to third embodiments, a seat slide apparatus for moving a seat cushion in a front-rear direction of a vehicle, or a seat lifter apparatus for moving an entire seat cushion upwardly and downwardly, may be applied, for example. In other words, a power seat driving apparatus, in which a driving force of a power supply is decelerated and transmitted so as to move a moving unit, may be applied.
Further, the power seat driving apparatus 1 according to the first to third embodiments may be applied to an apparatus having a motor and a decelerating mechanism, such as a power window apparatus for a vehicle, and the like, so as to reduce size and weight and so as to improve credibility.
According to the first to third embodiments, the spur gear 52, 72 and the elastic gear 53, 54, 73 are connected to each other and each of the spur gear 52, 72 and the elastic gear 53, 54, 73 engages with the pinion gear 51, 71 to be driven to rotate in an interlocking manner. In the second deceleration portion 5, 50, 7, the tooth thickness of the elastic gear 53, 54, 73 is larger than that of the spur gear 52, 72 by the amount corresponding to the backlash. Therefore, the spur gear 52, 72 and the pinion gear 51, 71 engage with each other so as to include the backlash therebetween while the elastic gear 53, 54, 73 and the pinion gear 51, 71 engage with each other so as not to include a backlash therebetween. Accordingly, when the rotational speed of the pinion gear 51, 71 is reduced, the idling rotation of the elastic gear 53, 54, 73 for the amount corresponding to the backlash is less likely to occur. Even though the elastic gear 53, 54, 73 may idly rotate, a degree of the idling rotation may be extremely small. In other words, even when inertia leads the spur gear 52, 72 to rotate idly for the amount corresponding to the backlash, the idling rotation of the spur gear 52, 72 corresponding to the backlash does not actually occur because the elastic gear 53, 54, 73, which is interlocked with the spur gear 52, 72 restricts the idling rotation of the spur gear 52, 72. Accordingly, stress and damage applied to the gears and housing 6 are reduced. Further, the elastic gear 53, 54, 73 is made of a resin material, which includes elasticity and a low rigidity. Therefore, the elastic gear 53, 54, 73 includes a large resistance relative to an instantaneous large deformation so that the idling rotation of the spur gear 52, 72 is restricted. On the other hand, the elastic gear 53, 54, 73 is elastically deformed relative to a normal transmission of rotation from the pinion gear 51, 71 to the spur gear 52, 72 so that the spur gear 52, 72 is driven to rotate smoothly. As a result, operational stability of the decelerating mechanism 3, 30, 300 is improved. Further, gear noise, which may occur in accordance with the backlash, is reduced.
According to the first to third embodiments, the spur gear 52, 72 and the elastic gear 53, 54, 73 are a spur gear having the same number of teeth and the same phase.
Accordingly, configuration for engaging both of the spur gear 52, 72 and the elastic gear 53, 54, 73 with the pinion gear 51, 71 may be achieved by a small number of components. As a result, a cost is reduced.
According to the second embodiment, the protruding portion 544 slidably contacting the inner wall surface 64 of the housing 6 is formed on the surface of the elastic gear 54 opposite from a surface thereof facing the spur gear 52.
Accordingly, the backlash between the spur gear 52 and the inner wall surface 64 of the housing 6 in the axial direction of the spur gear 52 is reduced. Therefore, displacement of each of the spur gear 52 and the elastic gear 54 relative to the housing 6 not only in a rotational direction but also in the axial direction of the gears is restricted. Accordingly, stability of operation of the decelerating portion 30 is improved.
According to the second embodiment, the driven gear 52 integrally or separately includes the second lower shaft portion 571 extending in an axial direction of the spur gear 52 and rotatably supported by the second main-body bearing hole 63 formed at an inner circumferential surface of the housing 6, at an outer circumferential surface thereof. The elastic gear 54 includes the supplemental shaft portion 545 arranged between the second lower shaft portion 571 of the spur gear 52 and the supplemental bearing hole 69 formed at the housing 6 coaxially with the second main-body bearing hole 63, the supplemental shaft portion 545 fitted with the second lower shaft portion 571 while slidably contacting the supplemental bearing hole 69.
Accordingly, the backlash among the spur gear 52, the elastic gear 54 and the housing 6 in the radial direction of the gears is reduced. Therefore, displacement of each of the spur gear 52 and the elastic gear 54 relative to the housing 6 is restricted not only in the rotational direction but also in the radial direction. Accordingly, stability of operation of the decelerating portion 30 is improved.
The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-232828 | Sep 2008 | JP | national |
