Title of Invention

"A WASHING MACHINE"

Abstract

OBJECT: To provide a reduction gear mechanism which couples an inner gear of a planetary gear mechanism to a brake drum in a corotatable manner. Engagement portions of the inner gear and the brake drum are liable to cause a noise when an excess load is exerted thereon. CONSTRUCTION: In a bearing portion (16) as the reduction gear mechanism for the washing machine, an inner gear (38) is coupled to a cylindrical brake drum with the outer circumferential surface of the inner gear being in involute serration engagement with the inner circumferential surface of the brake drum. Regular-pitch serrations are formed on the entire circumferential engagement surfaces of the inner gear and the brake drum, so that a load exerted thereon can be distributed over the brake drum. Therefore, the profile of the brake drum can be maintained at a high precision for prevention of a gear noise due to meshing of gear teeth and for prevention of a brake noise due to contact of a brake shoe (49) with the brake drum. EFFECT: The brake drum can be produced at a lower cost. SELECTED DRAWING: Fig. 5

Full Text

FIELD OF THE INVENTION The present invention relates to a washing machine and more particularly to a driving mechanism for a washing machine. DESCRIPTION OF RELATED ART Automatic washing machines adapted to perform washing and dehydration operations in a single tub space generally have an outer tub for retaining water, an inner tub provided within the outer tub for retaining laundry, and a pulsator provided in the inner tub. During the washing and rinsing operations, the inner tub is not rotated but only the pulsator is rotated at a low speed. During the dehydration operation, the inner tub and the pulsator are corotated at a high speed. A driving mechanism for driving the inner tub and the pulsator includes a planetary gear mechanism for reducing the rotation force of the motor and transmitting the rotation force to the pulsator, and an outer shaft fitted around the planetary gear mechanism for transmitting the rotation force of the motor to the inner tub. The transmission of the rotation force applied from the motor to the outer shaft is permitted or interrupted by a clutch. When the clutch is disengaged, the outer shaft is braked for prevention of the rotation of the outer shaft and the inner tub. The planetary gear mechanism is provided within the outer shaft as described above. An inner gear of the planetary gear mechanism is fixed on an inner circumferential surface of the outer shaft. Exemplary gear fixing methods are to fix the inner gear within the outer shaft by engaging an axially extending key with keyways formed in the opposed circumferential surfaces of the outer shaft and the inner gear and to fix the inner gear within the outer shaft in convexo-concave engagement by forming projections and recesses extending radially of the outer shaft on the opposed surfaces of the outer shaft and the inner gear. Where the inner gear is fixed within the outer shaft by either of the aforesaid gear fixing methods, a play is formed between the outer shaft and the inner gear, or the inner gear is torsionally deformed during a prolonged use. This results in a gear noise. SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a driving mechanism for a washing machine, which is free from a gear noise and the like even if used for a long time. It is another object of the present invention to provide a driving mechanism for a washing machine, wherein an inner gear of a planetary gear mechanism is fixed to an outer shaft in an improved manner. Accordingly, there is provided a washing machine which comprises an outer tub for retaining water therein, an inner tub provided within the outer tub for retaining laundry therein, and a pulsator provided in the inner tub and is adapted to perform washing and rinsing operations by rotating only the pulsator but not rotating the inner tub and to perform a dehydration operation by corotating the inner tub and the pulsator at a high speed, the driving mechanism comprising: an inner shaft attached to the pulsator and downwardly extending therefrom; an outer shaft attached to the inner tub, downwardly extending therefrom and enclosing the inner shaft; a drive shaft provided coaxially with the inner shaft below the inner shaft; a sun gear fixed to an upper end of the drive shaft; an inner gear provided coaxially with the sun gear as defining an outer circumference of the sun gear; a plurality of planetary gears each disposed between the sun gear and the inner gear in engagement with the sun gear and the inner gear; and a gear retainer fixed to a lower end of the inner shaft and interconnecting shafts of the planetary gears; wherein the outer shaft has a large diameter portion projecting radially outwardly of a center axis thereof, and an outer circumferential surface of the inner gear is fixed to an inner circumferential surface of the large diameter portion of the outer shaft in serration engagement therewith. In accordance with the present invention to attain the aforesaid object, there is provided a driving mechanism for a washing machine which comprises an outer tub for retaining water therein, an inner tub provided within the outer tub for retaining laundry therein, and a pulsator provided in the inner tub and is adapted to perform washing and rinsing operations by rotating only the pulsator but not rotating the inner tub and to perform a dehydration operation by corotating the inner tub and the pulsator at a high speed, the driving mechanism comprising: an inner shaft attached to the pulsator and downwardly extending therefrom; an outer shaft attached to the inner tub, downwardly extending therefrom and enclosing the inner shaft; a drive shaft provided coaxially with the inner shaft below the inner shaft; a sun gear fixed to an upper end of the drive shaft; an inner gear provided coaxially with the sun gear as defining an outer circumference of the sun gear; a plurality of planetary gears each disposed between the sun gear and the inner gear in engagement with the sun gear and the inner gear; and an gear retainer fixed to a lower end of the inner shaft and interconnecting shafts of the planetary gears; wherein the outer shaft has a large diameter portion projecting radially outwardly of a center axis thereof, and an outer circumferential surface of the inner gear is fixed to an inner circumferential surface of the large diameter portion of the outer shaft in serration engagement therewith. In the driving mechanism as described above, it is preferable that the serration engagement includes involute serration engagement. Additionally, if the outer shaft is of a metal, and the inner gear is of a resin, easy manufacturing will be achieved and the gear noise can be prevented. Further, in association with the outer diameter portion of the outer shaft, a brake mechanism may be further disposed for braking the outer shaft for prevention of the rotation thereof. EFFECTS OF THE INVENTION In accordance with the present invention, the load exerted on the inner gear can be distributed over the inner gear by the serration engagement. Therefore, the deformation of the inner gear can be prevented, so that the gear noise can be reduced when the inner gear is meshed with the outer shaft. In addition, the nonuniform deformation of the outer shaft in serration engagement with the inner gear can be prevented. Therefore, the wall thickness of the outer shaft can be reduced for reduction of the production cost thereof. Since the formation of the involute serrations is readily achieved through the high-precision machining and the outer shaft can be produced at a lower cost. Further, the inner gear made of the resin can further reduce the gear noise when the inner gear is meshed with the planetary gears. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side sectional view schematically illustrating the construction of an automatic washing machine according to one embodiment of the present invention. Fig. 2 is a sectional view illustrating the construction of a bearing portion in the automatic washing machine shown in Fig. 1. Fig. 3 is a diagram illustrating the bearing portion as viewed from the under side thereof in Fig. 2. Fig. 4 is an exploded perspective view illustrating major portions of the bearing portion of the automatic washing machine shown in Fig. 1. Fig. 5 is an enlarged sectional view of the major portions shown in Fig. 3. EMBODIMENT OF THE INVENTION One embodiment of the present invention will hereinafter be described in detail with reference to the attached drawings. Fig. 1 is a side sectional view schematically illustrating the construction of an automatic washing machine according to the embodiment of the present invention. The automatic washing machine has a box housing 1 having an opening on its top. The housing 1 defines the exterior of the automatic washing machine. Provided in the housing 1 are an outer tub 2 suspended from an upper portion of the housing 1 by spring-loaded suspension rods (not shown) and an inner tub 3 disposed within the outer tub 2. The inner tub 3 retains laundry put therein from the top opening of the housing 1. The inner tub 3 is formed with a multiplicity of perforations 3a, so that water supplied into the inner tub 3 is retained in the outer tub 2. A detergent retaining portion 4 in which a detergent to be used is temporarily retained is provided above the outer tub 2. One end of a water supply path 5 is exposed to the top face of the housing 1, and the other end thereof is connected to the detergent retaining portion 4. The one end of the water supply path 5 is connected to a water supply hose 6 extending, for example, from a faucet not shown. The water supply path 5 is provided with a water supply valve 7 such as comprised of an electromagnetic valve. When the water supply valve 7 is opened, water is supplied into the detergent retaining portion 4 from the faucet through the water supply hose 6 and the water supply path 5. The water supplied to the detergent retaining portion 4 flows into the inner tub 3 along with the detergent in the detergent retaining portion 4. A drainage hole 8 is formed in the bottom of the outer tub 2 for discharging the water retained in the outer tub 2 out of the washing machine. A drainage pipe 9 extending outside the housing 1 is connected to the drainage hole 8. The drainage pipe 9 is provided with a drainage valve 10 which is opened and closed by a torque motor not shown. When the drainage valve 10 is opened, the water retained in the outer tub 2 is discharged through the drainage pipe 9 out of the washing machine. The inner tub 3 serves as a dehydration tub, and has the multiplicity of dehydration perforations 3a formed in the circumference thereof as described above. A pulsator 11 for agitating the water in the inner tub to generate water current is provided on the bottom of the inner tub 3. The inner tub 3 and the pulsator 11 are rotatively driven by a drive mechanism 12 provided below the outer tub 2. The drive mechanism 12 includes a motor 13 for generating a rotative driving force, a small pulley 15 fixed to a rotation shaft 14 of the motor 13, a bearing portion 16 fixed to the bottom under face of the outer tub 2, a large pulley 18 fixed to the lower end of a drive shaft 17 held by the bearing portion 16, and an endless belt 19 stretched around the small pulley 15 and the large pulley 18. The driving force of the motor 13 is transmitted to the large pulley 18 via the small pulley 15 and the belt 19, and further transmitted to the bearing portion 16 via the drive shaft 17. A support shaft 20 for supporting the inner tub 3 is rotatively supported by the bearing portion 16 with the upper end thereof coupled to the bottom under face of the inner tub 3. A pulsator shaft 21 is rotatively fitted in the support shaft 20 with the upper end thereof coupled to the pulsator 11. The pulsator shaft 21 is always coupled to the drive shaft 17, so that the driving force of the drive shaft 17 is constantly transmitted to the pulsator 11. On the other hand, the support shaft 20 is coupled to the drive shaft 17 via a clutch mechanism 26 (which will be described later) provided in the bearing portion 16, so that the driving force of the drive shaft 17 is selectively transmitted to the support shaft 20 via the clutch mechanism 26. During the washing and rinsing operations, the transmission of the driving force to the support shaft 20 is interrupted by the clutch mechanism 26, so that the driving force of the drive shaft 17 is transmitted only to the pulsator shaft 21 to rotate the pulsator 11 back and forth. Thus, water current is generated in the inner tub 3 for washing or rinsing the laundry. During the dehydration operation, the clutch mechanism 26 is switched so that the driving force of the drive shaft 17 is also transmitted to the support shaft 20. Thus, the inner tub 3 and the pulsator 11 are corotated at a high speed, whereby the laundry within the inner tub 3 is centrifugally dehydrated. Fig. 2 is a half sectional view illustrating the construction of the bearing portion 16. Fig. 3 is a diagram illustrating the bearing portion 16 as viewed from the under side thereof in Fig, 2, but not illustrating the large pulley 18 for simplification. The bearing portion 16 has a mounting plate 60 attached onto the bottom under side of the outer tub 2 (see Fig. 1). The mounting plate 60 has a circular opening 60a formed in the center thereof. An upper bearing 22 for supporting the support shaft 20 coupled to the inner tub 3 is press-fitted in the opening 60a. The upper bearing 22 is a bearing having the one-way clutch function for transmitting a torque in one direction. One exemplary construction of the one-way clutch bearing is shown in Fig. 4. The upper bearing 22 has an outer ring 70, an inner ring 71 and a plurality of sprags 72 interposed between the outer ring 70 and the inner ring 71. The plurality of sprags 72 permit the inner ring 71 to rotate relative to the outer ring 70 in a clockwise direction O as seen in Fig. 4. When a force is exerted on the inner ring 71 in a counterclockwise direction X as seen in Fig. 4, the spacing between the outer ring 70 and the inner ring 71 is reduced so that the inner ring 71 is prevented from rotating relative to the outer ring 70. Thus, the support shaft 20 press-fitted in the inner ring 71 and supported by the upper bearing 22 is permitted to rotate only in the direction of the arrow A (dehydration rotation direction) in Fig. 2 and prevented from rotating in the direction opposite to the direction of the arrow A. An oil seal 23 is press-fitted in the opening 60a of the mounting plate 60 above the upper bearing 22. The oil seal 23 is fitted in an opening (not shown) formed in the bottom of the outer tub 2 when the bearing portion 16 is attached on the bottom under face of the outer tub 2. Thus, the water retained in the outer tub 2 is prevented from leaking out of the outer tub 2. Further, the pulsator shaft 21 for supporting the pulsator 11 is rotatively fitted within the support shaft 20 as described above. The bearing portion 16 further includes a gear case 24 fixed to the lower end of the support shaft 20, a reduction gear mechanism 25 for reducing the driving force of the drive shaft 17 for transmission thereof to the pulsator shaft 21, the clutch mechanism 26 for permitting or interrupting the transmission of the driving force of the drive shaft 17 to the support shaft 20, and a brake mechanism 27 for preventing the rotation of the inner tub 3. The gear case'24 includes an upper gear case 30 having a small diameter portion 28 fitted around the support shaft 20 and a large diameter portion 29 surrounding the reduction gear mechanism 25, and a lower gear case 33 having a cylindrical portion 31 fitted around the drive shaft 17 with a play and a flange 32 extending radially outwardly of the upper circumferential edge of the cylindrical portion 31. The small diameter portion 28 of the upper gear case 30 is fixed to the support shaft 20, and the flange 32 of the lower gear case 33 is connected to the lower circumferential edge of the large diameter portion 29 of the upper gear case 30. Thus, the support shaft 20 is corotated with the gear case 24. In this embodiment, the support shaft 20 and the gear case 24 constitute the dehydration shaft. The gear case 24 is surrounded by a bearing cover 35 fixed to the under surface of the mounting plate 60 by bolts 34. A lower bearing 36 is fixed within the bearing cover 35, and the lower gear case 33 is removably fitted in the lower bearing 36 so as to be rotatively supported by the lower bearing 36. Thus, the dehydration shaft constituted by the support shaft 20 and the gear case 24 is supported by the upper bearing 23 (first bearing) fixed to the mounting plate 60 and the lower bearing 36 (second bearing) fixed to the bearing cover 35. The reduction gear mechanism 25 provided in the gear case 24 has a sun gear 37 fixed at the upper end of the drive shaft 17, a stationary gear 38 formed on the inner circumferential surface of the large diameter portion 29 of the upper gear case 30, and planetary gears 39 rotatable around the sun .gear 37 in engagement with the sun gear 37 and the stationary gear 38. The planetary gears 39 are rotatively supported by a gear retainer 40 with one end thereof fixed to the lower end of the pulsator shaft 21. The clutch mechanism 26 includes a clutch sleeve 41 fixed to the outer circumference of the drive shaft 17 between the lower gear case 33 and the large pulley 18, a clutch spring 42 fitted around the clutch sleeve 41 and the cylindrical portion 31 of the lower gear case, a ratchet 43 fitted around the clutch spring 42 with a play, and a clutch piece 45 to be engaged with and disengaged from claws 44 formed on the outer circumferential surface of the ratchet 43. The clutch spring 42 is a coil spring which is fitted around the cylindrical portion 31 of the lower gear case 33 and the clutch sleeve 41 with the lower end thereof engaged with an engagement portion 46 formed within the ratchet 43. The clutch spring 42 connects the clutch sleeve 41 and the lower gear case 33 while gripping the clutch sleeve 41 and the lower gear case 33 by its resilient force exerted as shrinking itself in its winding direction. When the clutch spring 42 is twisted in such a direction as to relax itself (in a direction opposite to the winding direction of the clutch spring 42), a gap is formed between the clutch sleeve 41 and the clutch spring 42 with the lower portion of the clutch spring 42 loosened, so that the clutch sleeve 41 is disengaged from the lower gear case 33. The clutch piece 45 is centered on a pivot shaft 47 fixed to the bearing cover 35 so as to be shifted between an engaged state where the distal end of the clutch piece 45 is engaged with a claw 44 of the ratchet 43 (as shown by a solid line in Fig. 3) and a disengaged state where the distal end of the clutch piece 45 is disengaged from the claw 44 (as shown by a two-dot-and-dash line in Fig. 3). The clutch piece 45, when shifted from the disengaged state to the engaged state, rotates the ratchet 43 in the direction opposite to the direction of the arrow A. Thus, the clutch spring 42 is twisted in the relaxation direction, so that the clutch sleeve 41 is disengaged from the lower gear case 33. The brake mechanism 27 has a brake band 48 bent in a generally U-shape along the outer circumference of the large diameter portion 29, a brake shoe 49 bonded to a portion of the brake band 48 in contact with the large diameter portion 29, and a brake lever 50 rotatively supported by the pivot shaft 47 and interlocked with the clutch piece 45. One end of the brake band 48 is fixed to the bearing cover 35 by a bolt 51, while the other end thereof is engaged with the brake lever 50. A brake spring 52 is fitted around the pivot shaft 47 which supports the brake lever 50 and the clutch piece 45. Thus, the brake lever 50 is biased in such a direction as to pull the brake band 48 by a resilient force of the brake spring 52. Therefore, where the brake lever 50 receives a force only from the brake spring 52, the brake band 48 is pulled in the direction of the arrow A, so that the brake shoe 49 is brought into intimate contact with the outer circumference of the large diameter portion 29 to prevent the rotation of the upper gear case 30. The large diameter portion 29 has a greater outer diameter than the small diameter portion 28 and, therefore, the inner tub 3 can efficiently be braked by bringing the brake shoe 49 into intimate contact with the large diameter portion. Further, the clutch piece 45 is shifted to the engagement state with the resilient force of the brake spring 52 shown by the solid line in Fig. 3, so that the rotation of the ratchet 43 is also prevented. As shown in Fig. 3, a torque motor 54 is connected to the distal end of the brake lever 50 via a wire 53. The torque motor 54 is driven during the dehydration operation, and the wire 53 is pulled toward the torque motor 54, so that the brake lever 50 is shifted from the state shown by the solid line to the state shown by the two-dot-and-dash line. Thus, the brake band 48 connected to the brake lever 50 is slacked, thereby bringing the upper gear case 30 out of a braked state. The clutch piece 45 is shifted from the engaged state shown by the solid line to the disengaged state shown by the two-dot-and-dash line, so that the ratchet 43 is brought into a freely rotatable state. When the ratchet 43 is in the freely rotatable state, the clutch spring 42 is tightly wound around the clutch sleeve 41 to couple the clutch sleeve 41 to the lower gear case 33. During the dehydration operation, the torque motor 54 is on, so that the clutch sleeve 41 is coupled to the lower gear case 33 by the clutch spring 42. When the motor 13 is driven in this state to rotate the drive shaft 17 and the clutch sleeve 41 in the direction of the arrow A, the rotation of the clutch spring 41 is transmitted to the lower gear case 33 via the clutch spring 42. Then, the rotation of the lower gear case 33 is transmitted to the support shaft 20 via the upper gear case 30, so that the inner tub 3 coupled to the support shaft 20 is rotated in the direction of the arrow A at a high speed. Since the drive shaft 17 and the upper gear case 30 are rotated at the same speed, the planetary gears 39 revolve around the sun gear 37 at the same speed as the drive shaft 17. As a result, the pulsator shaft 21 is rotated at the same high speed as the upper gear case 30, so that the pulsator 11 fixed to the pulsator shaft 21 is rotated at a high speed. More specifically, the inner tub 3 and the pulsator 11 are corotated at the high speed during the dehydration operation, whereby the laundry within the inner tub 3 is centrifugally dehydrated. After a lapse of a predetermined time from the turn-off of the motor 13 upon the completion of the dehydration operation, the torque motor 54 is turned off. Upon the turn-off of the torque motor 54, the upper gear case 30 is braked by the brake band 48 with the brake lever 50 being shifted by the resilient force of the brake spring 52, and the ratchet 43 is braked with the clutch piece 45 being shifted to the engaged state. At this time, the ratchet 43 is rotated in the direction opposite to the direction of the arrow A by the clutch piece 45, whereby the clutch spring 42 is relaxed to disengage the clutch sleeve 41 from the lower gear case 33. During the washing and rinsing operations, the motor 13 is rotatively driven with the clutch sleeve 41 being disengaged from the lower gear case 33. Therefore, the driving force of the motor 13 is inputted to the drive shaft 17 to rotate the drive shaft 17 and the clutch sleeve 41. At this time, the clutch sleeve 41 and the clutch spring 42 run at idle, so that the rotation of the clutch sleeve 41 (drive shaft 17) is not transmitted to the lower gear case 33. Accordingly, the inner tub 3 fixed to the support shaft 20 is not positively rotated. The rotation of the drive shaft 17 is transmitted to the planetary gears 39 via the sun gear 37 fixed to the drive shaft 17- Since the upper gear case 30 formed with the . stationary gear 38 is braked by the brake band 48 at this time, the planetary gears 39 revolve around the sun gear 37 in engagement with the stationary gear 38. The revolutions of the planetary gears 39 are transmitted to the pulsator shaft 21 via the gear retainer 40 thereby to rotate the pulsator shaft 21 at a low speed. Therefore, by driving the motor 13 for alternate back and forth rotation, the pulsator 11 fixed to the pulsator shaft 21 is rotated alternately in the direction of the arrow A and in the direction opposite thereto. Thus, water current is generated in the inner tub 3, and the laundry is washed and rinsed by the water current. As described above, the inner tub 3 is braked for prevention of the rotation thereof by bringing the brake band 48 (brake shoe 49) into intimate contact with the large diameter portion 29 of the upper gear case 30 during the washing and rinsing operations, but the braking force is'small because the frictional force generated between the brake shoe 49 and the large diameter portion 29 is exerted in such a direction as to slack the brake band 48 when the inner tub 3 is rotated in the direction opposite to the direction of the arrow A. In this embodiment, however, the upper bearing 22 supporting the support shaft 20 coupled to the inner tub 3 has the one-way clutch function, which prevents the support shaft 20 from being rotated in the direction opposite to the direction of the arrow A shown in Fig. 2. Further, the upper gear case 30 is braked with the brake shoe 49 being in intimate contact with the outer circumference of the upper gear case 30 by pulling the brake band 48 in the direction of the arrow A. Therefore, when a force is exerted on the inner tub 3 in the direction of the arrow A, the frictional force generated between the brake shoe 49 and the upper gear case 30 is exerted in such a direction as to tense the brake band 48, so that the upper gear case 30 is effectively braked by the brake shoe 49 for prevention of the rotation thereof. Thus, the inner tub 3 is prevented from being rotated in the direction of the arrow A during the washing and rinsing operations. The inner gear 38 is coupled to the brake drum by the following coupling mechanism. Fig. 4 is an exploded perspective view illustrating major portions of the bearing portion. Fig. 5 is an enlarged sectional view illustrating major portions of the coupling mechanism. The coupling mechanism includes a pair of serrations which are engaged with each other, more specifically, a pair of involute serrations which are in convexo-concave engagement. That is, the inner circumferential surface of the large diameter portion 29 is engaged with the outer circumferential surface of the inner gear 38. The inner gear 38 has a regular-pitch fine serration 38a formed on the outer circumferential surface thereof, while the large diameter portion 29 has a regular-pitch fine serration 29a formed on the inner circumferential surface thereof. The serration 29a is engaged with the serration 38a over the entire outer circumference of the inner gear 38. Therefore, the inner gear 38 is firmly fixed to the large diameter portion 29 in coaxial relation. More specifically, the pair of serrations 38a and 29a each have a multiplicity of serration teeth each having an involute profile. The serrations 38a and 29a have the same number of serration teeth each having the same module and pressure angle (e.g., 45 degrees). These serration teeth can readily be formed in the same manner as ordinary gear teeth through precision machining. The large diameter portion 29 is formed of a metal material, which has a high wear resistance. As previously described, the multiplicity of involute serration teeth 29a are formed on the inner circumferential surface of the large diameter portion 29. These teeth 29a are continuously and regularly pitched over the entire inner circumference of the large diameter portion 29, and each extend along an axis thereof. Where the large diameter portion 29 has an outer diameter of 90 mm and an inner diameter of 80.55 mm, for example, the serration teeth 29a each have a height of 1.5 mm and the number of the teeth 29a is 108. As described above, the brake shoe 49 is brought into contact with the outer circumferential surface portion of the large diameter portion 29. Therefore, the contact surface portion and the serration 29a are respectively located on the outer and inner circumferential surfaces of the large diameter portion 29 in axially substantially the same position. The inner gear 38 is formed of a resin as having a cylindrical shape. The inner gear 38 has a plurality of inner gear teeth 38b formed on the inner circumferential surface thereof, and the multiplicity of involute serration teeth 38a formed on the outer circumferential surface thereof. The serration teeth 38a are continuously and regularly pitched over the entire outer circumference of the inner gear 38, and each extend along an axis thereof. With this coupling mechanism, the inner gear 38 is coupled to the upper gear case 30 for corotation therewith. Where only the pulsator 11 is to be driven, the inner gear 38 is braked by the brake mechanism 27, so that a rotational counterforce from the planetary gears 39 is exerted on the inner gear 38. The counterforce is received by the brake shoe 49 via the coupling mechanism and the large diameter portion 29. At this time, a pressing force from the brake shoe 49 and the counterforce from the inner gear 38 are exerted on the large diameter portion 29. The load exerted on the large diameter portion 29 is distributed throughout the large diameter portion 29 for prevention of the nonuniform deformation of the large diameter portion 29, as will be described later. As a result, the profile or roundness of the outer circumference of the large diameter portion 29 can be maintained at a high precision for prevention of the distortion of the circular sectional configuration of the large diameter portion 29. Therefore, the brake shoe 49 wound around the large diameter portion 29 can be prevented from nonuniformly contacting the outer circumferential surface of the large diameter portion 29. Thus, uniform contact of the brake shoe with the outer circumferential surface of the large diameter portion 29 can be ensured for prevention of the brake noise. At this time, the deformation of the inner gear 38 due to the load applied thereto from the planetary gears 39 can be suppressed, as will be described later. Therefore, the inner gear 38 can properly be meshed with the planetary gears 39, whereby the gear noise can be prevented. The serration engagement allows the inner gear 38 to be firmly coupled to the large diameter portion 29 with the circumferential serration teeth 29a engaged with the circumferential serration teeth 38a. Even if the inner gear is over-loaded, the load is distributed over the entire circumference thereof, so that the inner gear is less liable to rattle. As a result, the gear noise due to the rattle can be prevented. Further, the serration engagement allows the inner gear 38 to be coupled to the large diameter portion 29 in coaxial relation therewith with a high precision. Therefore, the gear mechanism 25 can be assembled with a high precision for reduction of the gear noise of the inner gear 38. Since the regular-pitch serration is formed on the entire inner circumferential surface of the large diameter portion 29, the nonuniform deformation of the large diameter portion 29 can be prevented which may otherwise occur due to the load exerted thereon or a force applied thereto during the machining thereof. As a result, the profile of the large diameter portion 29 can be maintained at a high precision. Thus, the brake noise can be prevented. It is noted that, if four keyways were equidistantly formed in the inner circumferential surface of the large diameter portion 29 as in a conventional case, the sectional configuration of the large diameter portion 29 would be liable to be nonuniformly distorted, for example, into a square shape, resulting in a brake noise. The large diameter portion 29 is in full circumferential serration engagement with the inner gear 38, so that the load exerted on the large diameter portion 29 from the inner gear 38 is distributed over the entire circumference of the large diameter portion 29. As a result, the profile of the large diameter portion 29 can be maintained at a high precision. Thus, the brake noise can assuredly be prevented. Since the serration 29a and the surface portion to be brought into contact with the brake shoe 49 are respectively located on the inner and outer circumferential surfaces of the large diameter portion 29 in axially substantially the same position, the inner gear 38 fixed within the large diameter portion 29 bears the force applied from the brake shoe 49 during the braking operation. The deformation of the large diameter portion 29 can readily be suppressed, so that the brake noise can assuredly be prevented. Since the inner gear 38 is in full circumferential serration engagement with the large diameter portion 29, the load exerted on the inner gear 38 can uniformly be distributed over the entire circumference of the inner gear 38. As a result, the deformation of the inner gear 38 can be prevented. Therefore, the inner gear 38 can properly be meshed with the planetary gears 39 for prevention of the gear noise. Particularly, the inner gear 38 is coupled to the large diameter portion 29 with the outer circumferential surface thereof being in contact with the large diameter portion, and the serration 38a and the gear teeth 38b are respectively-located on the outer and inner circumferential surfaces of the inner gear 38 in axially substantially the same position.. Therefore, the torsional deformation of the inner gear 38 during the transmission of the driving force can be suppressed, so that the gear noise can assuredly be prevented. Since the inner gear 38 is made of the resin, the gear noise can be further reduced when the inner gear 38 is meshed with the planetary gears 39. The formation of the involute serrations can readily be achieved by precision machining, thereby realizing high-precision coupling between the large diameter portion 29 and the inner gear 38. Therefore, the load applied to the inner gear 38 and the large diameter portion 29 can uniformly be distributed over the entire circumferences thereof, so that the magnitude of the load per unit area can be reduced. In addition, the nonuniform deformation of the inner gear 38 and the large diameter portion 29 can assuredly be prevented, thereby preventing the gear noise and the brake noise. Since the large diameter portion 29 having the serration over the entire inner circumference thereof is free from nonuniform deformation, the wall thickness of the large diameter portion 29 can be reduced. As a result, the large diameter portion 29 can be produced at a lower cost. Particularly where the large diameter portion 29 has the involute serration, the load exerted on the large diameter portion 29 can be distributed over the entire circumference of the large diameter portion 29, so that the magnitude of the load per unit area on the large diameter portion 29 can be reduced. Therefore, the wall thickness of the large diameter portion 29 can be reduced for reduction of the production cost thereof. For example, the large diameter portion 29 may be formed from a metal plate. In addition, the formation of the involute serration is easy. The engagement mechanism according the embodiment described above employs the involute serrations, but not limited thereto. For example, the engagement mechanism may employ triangular serrations. What is important is that the large diameter portion and the inner gear are coupled to each other via a pair of serrations respectively formed on engagement surfaces thereof. Although the serration is formed on the inner circumferential surface of the large diameter portion 29 in the embodiment described above, the serration may be formed on any other portion of the outer shaft. It should be understood that various modifications may be made within the spirit and scope of the invention as defined by the appended claims - WE CLAIM: A washing machine which comprises an outer tub for retaining water therein, an inner tub provided within the outer tub for retaining laundry therein, and a pulsator provided in the inner tub and is adapted to perform washing and rinsing operations by rotating only the pulsator but not rotating the inner tub and to perform a dehydration operation by corotating the inner tub and the pulsator at a high speed, the driving mechanism comprising: an inner shaft attached to the pulsator and downwardly extending therefrom; an outer shaft attached to the inner tub, downwardly extending therefrom and enclosing the inner shaft; a drive shaft provided coaxially with the inner shaft below the inner shaft; a sun gear fixed to an upper end of the drive shaft; an inner gear provided coaxially with the sun gear as defining an outer circumference of the sun gear; a plurality of planetary gears each disposed between the sun gear and the inner gear in engagement with the sun gear and the inner gear; and a gear retainer fixed to a lower end of the inner shaft and interconnecting shafts of the planetary gears; wherein the outer shaft has a large diameter portion projecting radially outwardly of a center axis thereof, and an outer circumferential surface of the inner gear is fixed to an inner circumferential surface of the large diameter portion of the outer shaft in serration engagement therewith. A washing machine as claimed in claim 1, wherein the serration engagemient includes involute serration engagement. A washing machine as claimed in claim 1 or 2, wherein the outer shaft is of a metal, and the inner gear is of a resin. A washing machine as claimed in any one of claims 1 to 3, comprising a brake mechanism disposed in association with the outer diameter portion of the outer shaft for braking the outer shaft for prevention of the rotation thereof. A washing machine substantially as herein described with reference to the accompanying drawings.

Documents:

2534-del-1998-abstract.pdf

2534-del-1998-claims-(cancelled).pdf

2534-del-1998-claims.pdf

2534-del-1998-complete specification(granted).pdf

2534-del-1998-correspondence-others.pdf

2534-del-1998-correspondence-po.pdf

2534-del-1998-description (complete).pdf

2534-del-1998-drawings.pdf

2534-del-1998-form-1.pdf

2534-del-1998-form-13.pdf

2534-del-1998-form-19.pdf

2534-del-1998-form-2.pdf

2534-del-1998-form-3.pdf

2534-del-1998-form-6.pdf

2534-del-1998-gpa.pdf

2534-del-1998-petition-137.pdf

2534-del-1998-petition-138.pdf