DRIVING MECHANISM FOR ELECTRIC REAR-VIEW MIRROR

Abstract: A mirror housing (14) is supported rotatably on a shaft (20) fixed to a mirror base (16) which is secured to a vehicle body in such a manner that it can be turned between a normal position and a retracted position by a driving mechanism including a motor (30). The driving mechanism consists of a motor, a reduction gear (32) composed of a plurality of plane­ tary gear units (U1-U4) including a sun gear (90) connected to an output shaft of the motor, and a group of transmission gears including a spur gear (36) mounted fixedly on the shaft (20) and another spur gear (34) connected to an output shaft of the reduction gear and meshed with the spur gear (36). The reduction gear (32) consists of a first casing (70) housing therein some (U1-U3) of the planetary gear units on the same shaft and provided on the inner circumferential surface thereof with a ring gear (72) which is common to these planetary gear units, a second casing (76) which houses therein the remaining planetary gear unit (U4) on the same shaft as the planetary gear units in the first casing so that these planetary gear units are meshed with each other, and which is provided on the inner circumferential surface thereof with a ring gear (74) corresponding to the gear unit (U4), and a bolt (80) by which the first and second casings are combined unitarily with each other. Accordingly, a plurality of planetary gear units can be assembled very easily, and the degree of freedom of de­ signing the driving mechanism with respect to the strength thereof can be greatly increased.

Description: The present invention relates to a drive mechanism for use in an automotive rear-view mirror assembly of a motor-driven folding type, and more particularly to a drive mechanism destined for use in such mirror assembly to pivot in relation to the mirror base which is to be fixed to a car body the mirror housing supporting the mirror in such a manner that the latter can be turned vertically and horizontally, thereby folding the mirror to the folded position or returning to the normal position. The drive mechanism for an automotive rear-view mirror assembly of a motor-driven folding type comprises an electric motor fixed in a mirror housing, a speed reducer including reduction gears to reduce the revolution of the motor, and a device to convert the revolution output of the speed reducer into a revolution of the mirror housing itself. Normally, remote-controlled mirror assemblies have disposed in the mirror housing thereof a drive unit to turn the mirror itself vertically and horizontally. Thus, the drive unit comprising a drive motor, speed reducer and converter is to be disposed in a limited space in the mirror housing. Such a drive mechanism is known from JP-A-62-77 256. The speed reducer forming a part of the drive unit used in such automotive rear-view mirror of a motor-driven folding type is a relatively compact, lightweight one which uses planet gears in order to a high reduction ratio. However, a single-stage speed reduction by a single planet gear cannot provide a desired reduction ratio. Normally, a multi-stage planet gear unit is used in the form of plural planet gear units housed in an elongated cylindrical casing having common ring gears formed on the inner wall thereof. More particularly, the required sizes of the ring gears, sun gears, planet gears and planet carriers in the multi-stage planet gear unit disposed in the limited space in the mirror housing are extremely small. Therefore, the manual assembling the planet gear units one by one into the elongated casing is very complicated and needs still at present a great skill, much time and labor. The present invention has an object to provide a drive mechanism for a rear-view mirror of a motor-driven folding type using planet gears which can be easily assembled without any great skill. DISCLOSURE OF THE INVENTION The above object is attained by providing a drive mechanism for a rear-view mirror of a motor-driven folding type, comprising an electric motor to pivot between the normal position and the folded position a mirror housing pivotably supported on a shaft fixed to a mirror base which is to be fixed to a car body, a speed reducer comprising plural planet gear units including a sun gear coupled to an output shaft of the motor, and a transmission gear group including at least a spur gear fixed on the shaft and another spur gear coupled to the output shaft of the speed reducer and which is in mesh with the first spur gear. According to the present invention, the speed reducer comprising a first cylindrical casing housing coaxially some of the plural planet gear units and which has formed on the inner circumferential wall thereof a ring gear common to the above-mentioned some planet gear units, a second cylindrical casing housing coaxially the remaining planet gear units among the plural planet gear units so as to be in mesh with the above-mentioned some planet gear units and has formed on the inner circumferential face thereof a ring gear common to the remaining planet gear units, and a means for coupling together the first and second casings. Since the casing assembly housing the plural planet gear units composing the speed reducer is of a longitudinally split structure, namely, it is composed of the first and second casings, and some of the plural planet gear units can be housed in the first casing while the remaining planet gear units be housed in the second casing, so the drive mechanism according to the present invention can be very easily assembled without any great skill. Also, because of the split structure of the casing assembly, a material and module can be freely selected for each of the planet gear units housed in the first and second casings, and thus the gear rigidity can be designed more freely. More particularly, for planet gear units at the side of a motor of a low load torque, a material and module can be selected without the necessary of taking in consideration the large torque of the planet gear units at the output side. Therefore, since the module of the ring gear for the motor-side planet gear units can be designed small, a higher reduction ratio can be provided and the casing housing the motor-side planet gear units can be made from a synthetic resin. Furthermore, the first and second casings can be connected to each other by a faucet joint. So during assembling of the drive mechanism into the mirror assembly, the first and second casings can be held concentrically with each other with the planet gear units housed therein, respectively, and the gears can be put into mesh with each other with the casings being turned with respect to each other. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 thru 4 show an embodiment of the drive mechanism according to the present invention, of which Fig. 1 is a front view of a motor-driven folding type rear-view mirror assembly in which the drive mechanism according to the present invent is adopted, showing the internal structure with the mirror surface partially fragmented, Fig. 2 is a partially sectional front view of the planet gear speed reducer forming a part of the drive mechanism shown in Fig. 1, Fig. 3 is a schematic perspective exploded view, enlarged in scale, of the planet gear speed reducer, and Fig. 4 is a schematic, partially fragmental, exploded view of the planet gear speed reducer; and Fig. 5 is a schematic exploded view of an variant of the planet gear speed reducer, explaining the faucet joint of the two casings. The present invention will be better understood from the ensuing description made, by way of example, of the drive unit for a motor-driven folding type rear view mirror assembly according to the present invention with respect to the drawings. Figs. 1 thru 4 show an embodiment of the drive unit according to the present invention. In Fig. 1, the entire motor-driven folding type rear-view mirror is indicated with the reference numeral 10 and has a mirror 12 covering the opening of a mirror housing 14 and which is supported pivotably in relation to the mirror housing 14. The mirror housing 14 has disposed therein a bracket 15 having fixed thereto a mirror drive unit (not shown) comprising a drive motor to turn the mirror 12 vertically and horizontally as remote-controlled. The mirror housing 14 is pivotably mounted on a shaft 20 fixed with a screw 18 to a mirror base 16 which is to be fixed to a car body. Namely, the bracket 15 inside the mirror housing 14 has formed thereon coaxially with the shaft 20 a cylindrical portion 22 of which the inner diameter is slightly larger than the outer diameter of the shaft 20 and in which the shaft 20 is fitted. The shaft 20 has fitted thereon and disposed at the base portion thereof a ring 24 which is also positioned in contact with the lower opening edge of the cylindrical portion 22 to form a thrust bearing. Also, the cylindrical portion 22 has formed in the lower inner circumferential wall thereof an circular recess being somewhat larger than the inner diameter of the cylindrical portion 22 and which houses an O-ring 26 which is in contact with the outer circumferential surface of the shaft 20 and the inner circumferential wall of the cylindrical portion 22. There is disposed a slide bearing 28 above the O-ring 26 and between the shaft 20 and cylindrical portion 22. Such drive mechanism to turn about the shaft 20 the mirror housing 14 supported pivotably with respect to the shaft 20 comprises a motor 30 fixed to the bracket 15 inside the mirror housing 14, a reduction gears 32 coupled to the output shaft of the motor 30, a first spur gear 34 connected to the output shaft of the reduction gears 32, and a second spur gear 36 in mesh with the first spur gear 34 and mounted on the shaft 20 as checked against any rotation, and which is axially movable. In case the mirror housing 14 is to be rotated as the motor 30 runs, the revolution of the motor 30 is transmitted to the first spur gear 34 by means of the reduction gears 32. Since the second spur gear 36 in mesh with the first spur gear 34 is mounted on the shaft 20 as checked against any rotation, namely, the second spur gear 36 has formed in the center thereof an elongated hole of which the shape fits the circumference of the shaft 20 partially cut so as to have two opposite flat surfaces parallel to the axis of the shaft 20 above the top end of the cylindrical portion 22, so the first spur gear 34 moves around the second spur gear 36 as it rotates. There is provided a ring 38 between the second spur gear 36 and the top end of the cylindrical portion 22. The shaft 20 has a spring seat 42 fixed near the top end thereof, and there is interposed between the spring bearing 42 and the second spur gear 36 a compression coil spring 40 which forces the ring 38 to the top end of the cylindrical portion 22. The ring 38 forms a thrust bearing which lessens the friction between the top end of the cylindrical portion 22 and the mirror housing 14 when the latter rotates about the shaft 20. Thus, the ring 38 does not block the rotation of the mirror housing 14. The first spur gear 34 in mesh with the second spur gear 36 forms a clutch together with a holder 46. As will be described later, a portion of the output shaft 44 of the reduction gears 32 is shaped hexagonal. The holder 46 is fitted on the hexagonal portion and rotates along with the output shaft 44. The holder 46 is axially movable. The first spur gear 34 is fitted on the output shaft 44 of the reduction gears 32 and forced to the holder 46 by a compression coil spring 35 interposed between the first spur gear 34 and the casing of the reduction gears 32. The end of the hexagonal portion of the output shaft 44 on which the holder 46 is fitted is fixed to a seat member 48 loose-fitted in a small hole formed in the bracket 15. There is interposed between the bottom face of the holder 46 and the seat member 48 a push nut 50 positioned for the first spur gear 34 to be in mesh with the second spur gear 36. Thus, when the mirror housing 14 is turned as the motor 30 runs, the first spur gear 34 is forcibly pressed to the holder 46 by means of the compression coil spring 48, clutches the holder 46 and rotates along with the latter. When the mirror housing is turned by hand to the folded position, the first spur gear 34 is disengaged from the holder 46 and becomes freely rotatable about the output shaft 44. The reference numeral 60 indicates a circular recess formed in the flat base portion of the shaft 20 around the axis of the latter. The circular recess 60 is formed in a position corresponding to the folded and used positions of the mirror housing 14. The bracket 15 has formed therein a space housing a compression coil spring 64 and a ball 66. The ball 66 is forced to the flat base portion of the shaft 20 by means of the compression coil spring 64 and resiliently engaged in the recess 60 when the mirror housing 14 is placed in the folded position or normal position. The reduction gears 32 composing the drive unit for a rear-view mirror assembly of a motor-driven folding type is composed of four planet gear units U1, U2, U3 and U4 as shown in Figs. 2, 3 and 4. The planet gear units U1, U2 and U3 are housed in a casing 70 having formed in the inner cylindrical wall thereof a ring gear 72 common to these three planet gear units, while the planet gear unit U4 is housed in another casing 76 having another ring gear 74 formed in the inner wall thereof. The ring gears 72 and 74 are so formed as to have a same pitch circle diameter and they are jointed to each other with plural bolts 80 with the specified planet gear units housed therein, respectively, to form the reduction gears or speed reducer 32. Further, the casing 70 has the motor 30 jointed thereto with a bolt 82, and the speed reducer 32 and motor 30 are fixed together by the holder to the bracket 15 inside the mirror housing 46 (which is not shown). The planet gear unit U1 comprises, as shown in Fig. 3, a sun gear 90 fixed to the output shaft of the motor 30, three planet pinions 92 in mesh with the sun gear 90 as well as with the ring gear 72, and a planet carrier 94 having three protrusions 96 loose-fitted in the respective planet pinions 92 and thus supporting the planet pinions 92. This planet gear unit U1 decelerates one step and converts the revolution of the motor 30 to a slower rotation of the planet carrier 94. The planet gear unit U2 similarly comprises a sun gear 190 fixed on the shaft of the planet carrier 94 of the planet gear unit U1, three planet pinions 192 in mesh with the sun gear 190 as well as with the ring gear 72, and a planet carrier 194 having three protrusions 196 loose-fitted in the respective planet pinions 192 and thus supporting the planet pinions 192. This planet gear unit U2 converts the rotation of the planet carrier 94 to a slower rotation of the planet carrier 194. Similarly to the above planet gear units, the planet gear units U3 (U4) comprises a sun gear 290 (390), three planet pinions 292 (392) in mesh with the sun gear 290 (390) as well as with the ring gear 72, and a planet carrier 294 (394) having three protrusions 296 (396) loose-fitted in the respective planet pinions 292 (392) and thus supporting the planet pinions 292. These planet gear units U3 and U4 convert the revolution of the motor 30 to a predetermined slow rotation of the last-stage planet carrier 394. There is disposed as checked against any rotation on the shaft of the planet carrier 394 composing the planet gear unit U4 one end of the output shaft 44 which is to be coupled to the previously-mentioned clutch holder 46. The end of the output shaft 44 is shaped in the form of a hexagon as having been described. The output shaft 44 is introduced through a hexagonal through-hole (not shown) formed in the clutch holder 46 and the hexagonal end is secured to the seat member 48 and the first spur gear 34 is pressed by the compression coil spring 44 toward the clutch holder 46 as loose-fitted on the body of the output shaft 44. Each of the ring gear 72, planet gears 90, 190 and 290, and planet pinions 92, 192 and 292 composing the U1 thru U3 among the four planet gear units having been described in the foregoing has the module selected to be 0.4. The casing 70 having the ring gear 72 formed on the inner circumferential wall thereof is made of nylon 66 containing glass in 30 percent by weight, the planet pinion 92 in mesh with the sun gear 90 fixed to the output shaft of the motor 30 is made of a synthetic resin such as polyacetal or the like, and the remainder of the component elements are made of a sintered alloy. The module of each of the ring gear 74, sun gear 390 and planet pinion 392 composing the planet gear unit U4 is selected to be 0.5. The casing 76 having the ring gear 74 formed on the inner circumferential wall thereof is made of a zinc die casting and the rest of the component elements is made of a sintered alloy. In this embodiment, the modules of the ring gears 72 and 74 are selected to be 0.4 and 0.5, respectively. This is because the module of the ring gear 72 can be set small since the load torque of the ring gear 72 at the side of the motor 30 is smaller than that of the ring gear 74 at the output side. Therefore, the number of teeth of the ring gear 72 can be increased provided that the pitch circle diameters of the ring gears 72 and 74 are equal to each other. In the conventional reduction gears, a plurality of planet gear units is disposed in a single die casting-made casing having formed therein a ring gear common to the planet gear units. The module of the ring gear is determined depending upon the load torque at the output side, and so it is not possible to freely design the reduction ratio. However, the planet gear mechanism forming the drive mechanism according to the present invention adopts such a structure of the casing in which a ring gear is formed as is split into two parts along a plane perpendicular to the axis of the casing. The sub-casing at the motor side has disposed therein three planet gear units, while the sub-casing at the output side has one planet gear unit disposed therein. The modules of the two ring gears 72 and 74 can be determined depending upon the load torque at the motor side and that at the output side, respectively. Thus, the reduction ratio can be designed to be large. The planet gear units can be assembled into the respective casings very easily and the rigidity of the gears can be designed more freely. Fig. 5 shows a variant of the planet gear mechanism. The casings 70 and 76 are jointed to each other by a faucet joint. Namely, the edge of the end face, to be jointed to the casing 76, of the casing 70 in which the ring gear 72 is formed is extended axially of the casing 70. The extension rim 400 thus made and the joining end face of the casing 70 define together a space receiving the end of the casing 76. The inner end of the casing 76 is so formed as to receive the extension rim 400 of the casing 70. When the casings 60 and 76 are coupled together, the outer circumferential receiving edge of the casing 76 fits the inner circumferential wall of the extension rim 400 of the casing 70. After the planet gear units U1 to U3 are housed in the casing 70 while the planet gear unit U4 is placed into the casing 76, the casings 70 and 76 can be easily coupled with their axes aligned to each other owing to the above-mentioned faucet joint system. Namely, the faucet joint permits easy and accurate positioning of the casings 70 and 76. In the embodiments having been described in the foregoing, the planet gear units U1, U2 and U3 are housed in the casing 70 at the side of the motor 30, while the planet gear unit U4 is housed in the casing 76 at the output side. However, the present invention is not limited to this configuration, but the planet gear units U1 and U2 may be housed in the casing 70 while the planet gear units U3 and U4 be housed in the casing 76. Also, the casings 70 and 76 having ring gears formed therein, respectively, are made of different materials in the aforementioned embodiments, but they may be made of a zinc die casting or a synthetic resin.

Claims: A drive mechanism for a rear-view mirror (10) of a motor-driven folding type, comprising: an electric motor (30) to pivot between the normal position and the folded position a mirror housing (14) pivotably supported on a shaft (20) fixed to a mirror base (16) which is to be fixed to a car body; a speed reducer (32) comprising plural planet gear units (U1-U4) including a sun gear (90,190,290,390) coupled to an output shaft of said motor (30), and; a transmission gear group including at least a spur gear (36) fixed on said shaft and another spur gear (34) coupled to said output shaft of said speed reducer (32) and which is in mesh with said first spur gear (36), characterized in that , said speed reducer (32) comprising a first cylindrical casing (70) housing coaxially some of said plural planet gear units (U1-U3) and which has formed on the inner circumferential wall thereof a ring gear (72) common to said some planet gear units (U1-U3), a second cylindrical casing (76) housing coaxially the remaining planet gear units (44) among said plural planet gear units (U1-U4) so as to be in mesh with said some planet gear units (U1-U3) and has formed on the inner circumferential face thereof a ring gear (74) common to said remaining planet gear units (44), and a means for coupling together said first and second casings (70,76). A drive mechanism as claimed in claim 1, wherein the ring gear (72) formed in said first casing (70) and the one (74) formed in said second casing (76) are formed with different modules. A drive mechanism as claimed in claim 1 or 2, wherein said first casing (70) houses at least the planet gear unit (41) including said sun gear (90) coupled to the output shaft of said motor (30) and the ring gear (72) formed in said first casing (70) is formed with a smaller module than that of the ring gear (74) formed in said second casing (76). A drive mechanism as claimed in at least one of the preceding claims 1 to 3, wherein said first casing (70) is made of a synthetic resin while said second casing (76) is made of a die casting. A drive mechanism as claimed in at least one of the preceding claims 1 to 4, wherein the opening ends of said first and second casings (70,76) have faucet joints formed thereon, respectively.

Inventors: ENOMOTO MASAO, NAGAYAMA YOSHIRO, YAMAMOTO MASAMI, YAMAUCHI YOSHINORI, ENOMOTO, MASAO, NAGAYAMA, YOSHIRO, YAMAMOTO, MASAMI, YAMAUCHI, YOSHINORI
Applicants: ICHIKO INDUSTRIES LTD, ICHIKOH INDUSTRIES LIMITED
Application year: 1988
Main classification: B60R1
IPC codes: F16H1, B60R1