Geared motor

Abstract: In a geared motor (100) with reduction gears (101) having a pair of helical gears (105a, 101b) as reduction gear-coupling and a viscous grease (115) for lubricating the reduction gears (101) filled in a gear case (102), an integration of main oil seal (117) having a main lip (117a) and a dust lip and a sub oil seal (118) having a sub lip (118a) is used between a rotor shaft (105) and a housing (103, 107), for preventing the leakage of the grease (115) including metal powder resulted from wear of the gears (101), and a second grease (120) retained in a space formed between the sub lip (118a) and the main lip (117a); and an outer wheel (109a) of a ball bearing (109) for supporting the rotor shaft (105) is fixed on a bottom (103a) of the housing (103) in order not to move the rotor shaft (105) in its axial direction for firmly sealing the rotor shaft (105) by the oil seals (117,118).

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a motor with reduction gears to be used as a power source of a general industrial machine such as a conveying machine or a manufactual machine, and especially relates to improvement in sealing of grease for lubricating the gears. 2. DESCRIPTION OF THE RELATED ART In a geared motor, helical gears which are effective for noise reduction are used as initial reduction gears rotating in high speed. Furthermore, as a lubrication of the reduction gears of the motor, a grease-bath type lubrication is widely adopted for the noise reduction and for life extension of the gears, since it can be located free from the direction of the gears and its maintenance is easy. A conventional geared motor having the grease-bath type lubrication is described referring to FIG. 7. FIG. 7 is a cross-sectional view showing a constitution of the conventional geared motor, as published in a catalog "Panasonic With the application of Helical gear, low noise performance has been realized. *LOW NOISE *HIGH OUTPUT *LONG LIFE *VARIETY IN MODELS". In FIG.7, reduction gears 1 having an output shaft la are contained in a gear case 2. A frame 3 of the motor 50 has a hole 3a, to which a ball bearing 9 is fit, on the bottom thereof. A stator core 4 is fit to an inner face 3b of the frame 3 and fixed thereon. A helical gear 5a is formed on an end of a rotor shaft 5 and gear-coupled with another helical gear 1b of the initial gear of the reduction gears 1. A rotor 6 of the motor 50 is fixed on the rotor shaft 5. A bracket 7 of the motor 50 is fit to the inner surfaces 2a of the gear case 2 and 3b of the frame 3. An outer wheel 8a of a ball bearing 8 is fit in a hole 7a of the bracket 7 and an inner wheel 8b of the ball bearing 8 is press-fit to the rotor shaft 5. An outer wheel 9a of another ball bearing 9 is fit in the hole 3a of the frame 3 and an inner wheel 9b of the ball bearing 9 is press-fit on the rotor shaft 5. A spring washer 10 is provided between the ball bearing 9 and the bottom face of the hole 3a of the frame 3 for supplying a thrust pre-load to the ball bearing 9. A simplified brake mechanism 11 is provided in a side wall 3c of the hole 3a of the frame 3. The simplified brake mechanism 11 comprises: a brake shoe 11a and a spring 11b for supplying pressure to the brake shoe 11a which are provided in a hole 3d on the side wall 3c; a brake disc 11c fixed on the rotor shaft 5; and a spring cap lid. Braking force which is to be supplied to the motor 50 is made by friction between the brake disc 11c and the brake shoe 11a. The spring cap 11d is fixed on an outer face 3e of the frame 3 by a screw 12. In such a geared motor, the ball bearing 9 which is apart from the reduction gears 1 is generally smaller than the ball bearing 8 which is adjacent to the reduction gears 1, since the simplified brake mechanism 11 is provided in the side wall 3c of the hole 3a of the frame 3 to which the ball bearing 9 is to be fit. An oil seal 13 is provided between the output shaft 1a of the reduction gears 1 and the gear case 2 for preventing the leakage of the grease 15 which is filled in the gear case 2 to the outside of the gear case 2. And also, another oil seal 14 is provided between the rotor shaft 5 and the bracket 7 for preventing the leakage of the grease 15 to the inside of the motor 50 (or the inside of the frame 3). The oil seals 13 and 14 are made of rubber and each has a main lip 13a or 14a and a dust lip 13b or 14b. Generally, the dust lips 13b and 14b are positioned behind the main lips 13a and 14a against the object such as grease 15 to be sealed. In the surroundings of the reduction gears 1, a large amount of the grease 15 for lubricating the gears is filled. Driving force of the motor 50 is transmitted to the reduction gears 1 via the rotation of the rotor shaft 5. The road of the rotor shaft 5 is born by the two bearings 8 and 9 since the inner wheels 8b and 9b are press-fit to and fixed on the rotor shaft 5. The outer wheels 8a and 9a are respectively fit in the holes 7a of the bracket 7 and 3a of the frame 3 with gaps of 10 to 20 µm. Gears of the reduction gears 1 are generally made of steel for the industrial use because of its strength. The steel gears, however, are easily worn and make large noise when they are geared each other without oil, so that they are necessary to be lubricated. In order to assure long life of the gears and for reducing the noise, the above-mentioned grease-bath type lubrication is widely adopted in the geared motor. In the above-mentioned grease-bath type lubrication, a large amount of the grease 15 having large viscosity and large inertia is used for lubricating the steel gears. The grease 15 always flows during the rotation of the gears, so that a plenty of grease 15 comes to the output shaft 1a which rotates to transmit the driving force of the motor 50 to the outside, and surges along the rotor shaft 5 which rotates to transmit the driving force to the reduction gears 1. Accordingly, the oil seals 13 and 14 are necessary to be provided for sealing the gaps around the shafts 1a and 5. In the above-mentioned conventional geared motor, the oil seals 13 and 14 are made of rubber, and hence there is a problem of short life of the seals 13 and 14 due to their crack, wear of the lips of the deals or hardening of the lips caused by friction heating. Furthermore, there are many problems for shortening the life of the seals 13 and 14 due to the following reasons. (1) The flow of the grease 15 changes responding to the rotation speed and/or rotation direction of the shafts 1a and and 5. Especially, the rotor shaft 5 rotates in high speed and thrust is generated by the helical gears 5a and 1b, so that the flow of the grease 15 impinges the lips 14a and 14b of the oil seal 14. When the rotation direction of the rotor shaft 5 alternately changes, the direction of the flow of the grease 15 also alternately changes. Thereby, a dynamic pressure due to the flow of the grease 15 is intermittently applied to the oil seal 14. The lips 14a and 14b of the oil seal 14 is, on one hand, strongly pressed on the rotor shaft 5 by such a dynamic pressure of the flow of the grease 15 and immoderate friction force is generated between the lips 14a and 14b and the rotor shaft 5. On the other hand, the lips 14a and 14b is moved in reciprocation in the axial direction by pressure inversion of the flow of the grease 15. Furthermore, when a thrust load due to the gear-coupling of the helical gears 5a and 1b is applied to the rotor shaft 5 in axial direction thereof, the rotor shaft 5 in reciprocative moves in the axial direction by the alternate inversionof the rotation direction, mince there is a gap between the ball bearing 9 and the bottom of the hole 3a of the frame 3 and the spring washer 10 is provided in the gap for supplying the pre-load to the bearing 9. When the rotor shaft 5 moves in reciprocation in the axial direction, the sealing between the rotor shaft 5 and the oil seal 14 is easily broken, since the sealing face of the oil seal 14 is designed short against the axial motion of the rotor shaft 5. Still more, when the rotor shaft 5 moves in reciprocation in the axial direction, the outer wheel 9a of the ball bearing 9 slides relatively on the spring washer 10 due to the creep of the outer wheel 9a, so that the spring washer 10 is often broken. (2) Furthermore, metal powder generated by the wear of the gears or bearings 1c, 1d, 1e and 1f of the reduction gears 1 is mixed in the grease 15. And when the metal powder reaches to the lips 13a, 13b, 14a and 14b of the oil seals 13 and 14 with the flow of the grease 15, the lips 13a, 13b, 14a and 14b are damaged and thereby the grease 15 leaks. (3) For sealing by the oil seals 13 and 14, it is necessary to form oil films on the slipping part between the shafts 1a and 5 and the oil seals 13 and 14 by the lubricant oil. For this purpose, another kind of grease 16 for lubricating the lips 13a, 13b, 14a and 14b of the oil seals 13 and 14, which is different from the grease 15 for lubricating the gears 1, is necessary to be filled in cavities 13c, 13d, 14c and 14d in the vicinity of the main lips 13a and 14a and the dust lips 13b and 14b. It, however, is impossible in the conventional geared motor, to hold the lip-lubricating grease 16 in the cavities 13d and I4d facing to the reduction gears 1, since the gear-lubricating grease 15 containing the metal powder is easily mixed within the lip-lubricating grease 16. Furthermore, the gear-lubricating grease 15 is viscous for heavy load of the gear-coupling, and it is not suitable for lubricating in minute gaps between the oil seals 13 and 14 and the shafts 1a and 5, since necessary thin oil films are not formed therebetween by such viscous grease. Because the oil films of the lubricant is not formed between the oil seal 13 or 14 and the shaft 1a or 5, the oil seal 13 or 14 made of rubber directly slides on the shaft 1a or 5 made of metal. Therefore, the rubber becomes hard by friction heat and long time friction. As a result, the gear-lubricating grease 15 leaks out. By the above-mentioned reasons, it is known that the oil seals 13 and 14 in the conventional geared motor adopting the grease-bath type lubrication has a severe service condition. Namely, the conventional geared motor, which uses the oil seals 13 and 14 having only one main lips 13a and 14a for sealing the shaft 1a and 5, will raise the leakage of the grease 15 in relatively early stage. The grease 15, which is for lubricating the reduction gears 1 flowing in the interior of the motor, flows further to the inside of the ball bearings 8 and 9 and air gaps between the rotor 6 and the stator 4. The adhesion of the viscous grease 15 on the ball bearings 8 and 9 and so on raises loss of the output power of the motor 50 and also raises the failure in start or burning of the motor 50. For solving the above-mentioned problems, methods for increasing the interference of the main lips 13a and 14a of the oil seals 13 and 14 against the shafts 1a and 5 and for using two oil seals in series besides the above-mentioned type oil seal 13 or 14 have been proposed. Both methods, however, raise the increase of the mechanical loss due to the friction of the oil seals and the increase of the volume which is necessary for the provision of the sealing members. Therefore, the methods can not be adopted in a geared motor of small type, e.g. for outputting several watt to several tens watt. Generally, the frame 3, which has the hole 3a for being fit therein by the outer wheel 9a of the ball bearing 9, is made by aluminum, since aluminum has splendid workability. However, in case that a load which is to be driven by the geared motor is largely rippled, or in case that the load is intermittently and/or frequently driven, creeps in radial direction or in axial direction are generated on the surface of the outer wheel 9a by receiving the influences due to the vibrations of the machine and/or the motor itself. This is because: the coefficient of the thermal expansion of aluminum is larger than that of steel which is a material of the outer wheel 8a or 9a of the ball bearing 8 or 9; and hence a gap is made between the outer wheel 8a or 9a of the ball bearing 8 or 9 and the inner face of the hole 7a of the bracket 7 or 3a of the frame 3, which were closely fit to each other at the beginning of the driving, under a high temperature due to the driving of the motor. Especially, the ball bearing 9, which is not receive the load directly, easily creeps because the load, which is applied to the output shaft 1a of the reduction gears 1, is magnified by the principle of a lever wherein the ball bearing 8 serves as a fulcrum, and a force of magnified load is applied to the ball bearing 9. Furthermore, the ball bearing 9 is smaller than the ball bearing 8, and hence the ball bearing 9 is easily influenced by the creep. When the outer wheel 9a of the ball bearing 9 slips on the inside face of the hole 3a of the frame 3, abnormal noise may occur. Or, holding of the rotor shaft 5 by the ball bearing 9 may become unstable by abnormal friction between the outer wheel 9a of the bald bearing 9 and the inside face of the hole 3a. Furthermore, the life of the ball bearing 9 is shortened by abnormal heating thereof due to the abnormal friction heat or by the mixing of the metal powder in the the grease 15. As a result, the torque of the motor 50 is reduced or the motor 50 falls immovable state and finally burning occurs in the motor 50. The afore-mentioned two problems, that are the leakage of the grease 15 and the creep of the ball bearing 9, are the most weak point of the motor 50 with reduction gears 1, and the life of such an electric motor 50 is determined inconsistent with the merit of the grease-bath type lubrication directed for elongating the life of the gears. As an example, in a small and typical geared motor which outputs several watt to several tens watt and has a square section of 60 mm to 90 mm of a side of the case of the reduction gears, the life time of conventionally lubricated spur gears on which a few of grease is spread is about 5,000 hours. On the other hand, according to theoretical view point, the life of the geared motor adopting the grease-bath type lubrication and the helical gears can be elongated two times as long as that of the above-mentioned conventional ideal case. It, however, is actually limited in a range of 3,000 to 5,000 hours by the above-mentioned problems of the leakage of the grease and the creep of the bearing. SUMMARY OF THE INVENTION Purpose of the present invention is to solve the above-mentioned problems and to provide an improved geared motor of the grease-bath type lubrication and the helical gears, and achieve a having long life service. A geared motor in accordance with the present invention is defined by the features of claim 1, the precharacterizing portion of which refers to the prior art as discussed with reference to FIG. 7. In the above-mentioned constitution, the sub lip is positioned nearer to the grease for lubricating the reduction gears than the main lip. Therefore, the arrival to the main lip of the grease contaminated by mixing of worn metal powder of the gears can be prevented by the sub lip. And further, the sub lip absorbs fluctuation of pressure of the flow of the grease, thereby reducing the effect of the pressure change of the grease to the main lip. Furthermore, the main oil seal and the sub oil seal are integral configurated into one body, so that a sufficient amount of lip-lubricating grease, which hitherto can not be filled, can be sealed in a space formed between the main oil seal and the sub oil seal. As a result, the main lip can be maintained in a good lubrication state by the clean lip-lubricating grease substantially permanently. Still more, the outer wheel of the ball bearing which is apart from the reduction gears is fixed on the frame by the bearing fixing means, and the inner wheel of the bearing is press fit to the rotor shaft of the motor. Therefore, the rotor shaft does not move in reciprocation in the axial direction, and thereby the sealing of the oil seals are not broken. While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a cross-sectional side view showing a constitution of a preferred embodiment of a geared motor in accordance with the present invention, wherein the section plane is vent against an axis of the motor. FIG.2 is a perspective view showing the details of a cup shaped part 1030 of a frame 103 of the motor 100 shown in FIG.1 formed on a bottom of the frame 103. FIG.3 is a perspective view showing the details of a bearing fixing plate 116. FIG.4 is a cross-sectional side view showing a manufacturing process of the geared motor in accordance with the present invention. FIG.5 is a plan view showing the fitting of the bearing fitting plate 116 in a groove of the cup shaped part 103. FIG.6 is a cross-sectional side view showing the details of oil seals 117, 118 used on the rotor shaft 105 of the motor. FIG.7 is the cross-sectional side view showing the constitution of the conventional geared motor, wherein the section plane is vent against the axis of the motor. DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a geared motor in accordance with the present invention is described referring to FIGs. 1, 2, 3, 4, 5 and 6. FIG.1 is a cross-sectional side view showing a constitution of an embodiment of the geared motor in accordance with the present invention. In FIG.1, reduction gears 101 having an output shaft 101a are contained in a gear case 102. A frame 103 of the motor 100 has a cup shaped part 1030 on a bottom of the frame 103. A ball bearing 109 is fit in a center hole 103a of the cup shaped part 1030. A stator core 104 of the motor 100 is fit to an inner face 1031 of the frame 103 and fixed thereon. A helical gear 105a is formed on an end of a rotor shaft 105 of the motor 100 and the helical gear 105a is gear-coupled with another helical gear 101b of the initial gear of the reduction gears 101. A rotor 106 of the motor 100 is fixed on the rotor shaft 105. A bracket 107 of the motor 100 is fit to the inner surfaces 102a of the gear case 102 and 1031 of the frame 103. An outer wheel 108a of a ball bearing 108 is fit in a hole 107a of the bracket 107 shown in FIG.6, and an inner wheel 108b of the ball bearing 108 is press-fit to the rotor shaft 105. An outer wheel 109a of the ball bearing 109 is fit in the center hole 103a of the cup shaped part 1030 of the frame 103, and an inner wheel 109b of the ball bearing 109 is press-fit to the rotor shaft 105. A spring washer 110 is provided between the ball bearing 108 which is positioned adjacent to the reduction gears 101 and an offset part 107b of the bracket 107. A brake assembly 111 is provided in a side wall 103b of the cup shaped part 1030 of the frame 103. The brake assembly 111 comprises: a brake disc 111c fixed on the rotor shaft 105; plurality of brake shoes 111a (for simplification of illustration, only one of plural brake shoes is shown in FIG.1) which are put in holes 103e (shown in FIG.2) and contact the brake disc 111c; the same number of springs 111b for supplying pressure to respective brake shoes 111a provided in the holes 103e; and a spring cap 111d. Braking force which is to be supplied to the motor 100 is generated by friction between the brake disc 111c and the brake shoes 111a. FIG.2 is a perspective view showing the details of the cup shaped part 1030 of the frame 103 of the motor 100 and FIG.3 is a perspective view showing the details of the bearing fixing plate 116. In FIG. 2, the cup shaped part 1030 of the frame 103 has plurality of the holes 103e in its side wall 103b to which the brake shoes 111a are put and a pair of guide grooves 103c and 103c which are symmetrically positioned with respect to the axis of the center hole 103a. On respective guide grooves 103c and 103c, screw holes 103d and 103d are provided. In FIG.3, the bearing fixing plate 116 comprises a ring part 116d and protruded parts 116a and 116a provided symmetrically with respect to the center of a center hole 116c of the ring part 116d. On respective protruded parts 116a and 116a, female screw parts Il6b and 116b, to which male screws 112 are screw-coupled from outside of the frame 103 as shown in FIG.1, are formed. Outer periphery of the ring part 116d is to be fit in the center hole 103a of the cup shaped part 1030 with a predetermined gap therebetween, and also the protruded parts 116a and 116a are to be fit in the guide grooves 103c and 103c of the cup shaped part 1030 with predetermined gaps therebetween. The center hole 116c of the ring part 116d is to be press-fit lightly to the offset part 105b of the rotor shaft 105 as shown in FIG.4. FIG.6 is an enlarged cross-sectional side view showing the details of the oil seals 117 and 118. In FIG.6, the main oil seal 117 has a main lips 117a and a dust lip 117b and the sub oil seal 118 has a sub lip 118a. The main oil seal 117 and the sub oil seal 118 are coupled integral into one body and positioned in a manner that: an outer periphery 117c of the main oil seal 117 is fit to an inner surface of the hole 107a of the bracket 107; an outer periphery 118b of the sub oil seal 118 is fit to an inner periphery 117d of the main oil seal 117; the sub lip 118a of the sub oil seal 118 faces to the reduction gears 101 as shown in FIG.1; the dust lip 117b of the main oil seal 117 faces to the ball bearing 108 as shown in FIG.1; and the main lip 117a is positioned between the sub lip 118a and the dust lip 117b. Lip-lubricating grease 120 for lubricating the lips 117a, 117b and 118a is filled in a space 117e formed between the main lip 117a and the dust lip 117b and in a space 118c formed between the main lip 117a and the sub lip 118a. Assembling of the ball bearing 109 which is apart from the reduction gears 101 is described referring to FIGs. 4 and 5. At first, the center hole 116c of the bearing fixing plate 116 is lightly press-fit to the offset part 105b of the rotor shaft 105. And the inner wheel 109b of the assembled ball bearing 109 is press-fit on the rotor shaft 105. After that, the ball bearing 109 is put in the center hole 103a of the cup-shaped part 1030 of the frame 103. The protruded parts 116a and 116a are put on the upper face of the side wall 103b of the cup shaped part 1030, for example, shown by broken lines in FIG.5. And then, when the rotor shaft 105 is rotated in a clockwise direction shown by arrow in FIG.5, the bearing fixing plate 116 which is lightly press-fit to the offset part 105b of the, rotor shaft 105 also rotates at the same time. The rotation of the rotor shaft 105 is stopped to make the protruded parts 116a and 116a face to the guide grooves 103c and 103c as shown by solid lines in FIG.5. At this time, plurality of the holes 103e are not closed by the bearing fixing plate 116, so that the brake shoes 111a and the springs 111b can be put in the holes 103e. As mentioned above, the female screw parts 116b and 116b are exactly positioned for facing to the screw holes 103d and 103d (in FIG.2) on the guide grooves 103c and 103c of the cup shaped part 1030. And the male screws 112 are screwed in the screw holes 103d and 103d from outside of the frame 103 and screw-coupled with the female screw parts 116b and 116b as shown in FIG.4. By turning the male screw 112, the bearing fixing plate 116 is pulled to the ball bearing 109. Thereby, the bearing fixing plate 116, which was at first fit to the rotor shaft 105, is disconnected from the offset part 105b of the rotor shaft 105. And finally the bearing fixing plate 116 is fixed contacting to an end of the outer wheel 109a of the ball bearing 109 on the cup shaped part 1030 of the frame 103. Namely, the outer wheel 109a of the ball bearing 109 is firmly fixed on the center hole 103a of the cup shaped part 1030 of the frame 103. In this state, the center hole 116c of the bearing fixing plate 116 is positioned on the same plane of another offset part 105a of the rotor shaft 105 which has a smaller diameter than that of the offset part 105b as shown in FIGs.1 and 4. Therefore, the rotor shaft 105 can be rotated without touching the bearing fixing plate 116. By turning of the male screws 112, the spring cap 111d is fixed on an outer face 1032 of the frame 103, and thereby the assembly of the brake assembly 111 is completed. Operation of the above-mentioned geared motor in accordance with the present invention is described. When the motor 100 is driven, rotation force is transmitted to the reduction gears 101 via the rotation of the rotor shaft 105. The grease 115, which is for lubricating the gears and filled in the gear case 102 flows in the gear case 102 by the rotation of the gears. At this time, worn metal powder generated by gear-coupling of the gears is mixed in the grease 115. The flow of the grease 115 reaches to the oil seals 117 and 118 positioned in the vicinity of the initial gear-coupling of the reduction gears 101 for sealing the rotor shaft 105 of the motor. Since the sub oil seal 118 has the sub lip 118a which is positioned ahead against the grease 115, the flow of the grease 115 reaches the sub lip 118a at first. In this embodiment, the sub lip 118a has a thickness of about 1mm and a length 2--3mm from the root to the top and designed to contact substantially parallel to the rotor shaft 105. By means of its lip-like shape, the sub lip 118a can be deformed flexibly responding to a force applied thereto. Accordingly, when a pressure shown by arrow P in FIG.6 is applied to the sub lip 118a by the flow of the grease 115, the sub lip 118 is distorted by the pressure as shown by dotted line in FIG.6, to be pressed to contact more on the rotor shaft 105, and thereby the rotor shaft 105 is certainly sealed. Due to the above-mentioned function made by the sub lip 118a during the flow of the grease 115, the interference of the sub lip 118a and the rotor shaft 105 can be minimized or zero. In this embodiment, the interference of the sub lip 118a and the rotor shaft 105 is selected to be in a range of 0 to 0.4mm. Mechanical loss of the output power of the motor 100 in this case of using the sub lip 118a is smaller than that in the conventional apparatus of using two-staged oil seals 17 shown in FIG.7. Therefore, this embodiment can be adopted in a small electric motor for outputting several tens watt or below. Furthermore, a considerable amount of the lip-lubricating grease 120 is stably filled in the space 118c formed between the main lip 117a and the sub lip 118a as shown in FIG.6, and hence the good lubrication of the main lip 117a can be maintained for long time; and thereby the life of the oil seal 117 can be elongated. In the above-mentioned embodiment of the geared motor in accordance with the present invention, the main oil seal 117 having the main lip 117a and the sub oil seal 118 having the sub lip 118a are integrally configurated and used for sealing the rotor shaft 105 of the motor 100. The grease 115, which is for lubricating the reduction gears 101 and filled in the gear case 102, and is contaminated by the worn metal powder from the gears, is certainly sealed by the sub lip 118a, which receives the dynamic pressure of the flow of the grease 115 and deformed to contact to the rotor shaft 105 tightly On the other hand, the main lip 117a is lubricated by the lip-lubricating grease 120, and hence, the wear, cracking and/or hardening of the main lip 117a are/is prevented. And thereby, the lives of the oil seals 117 and 118 are elongated by means of releasing the change of the dynamic pressure of the flow of the grease 115. Furthermore, the sub oil seal 118 make substantially no mechanical loss of the output of the motor 100. The sub oil seal 118 in accordance with the present invention does not require particular large space for providing the oil seals, since it is made integral with the main oil seal 117. Since the bearing fixing plate 116 is previously lightly press-fit to the offset part 105b of the rotor shaft 105, it can be easily positioned in a manner to make the protruded parts 116a and 116a face to the guide grooves 103c and 103c by rotating the rotor shaft 105. Furthermore, the male screws 112 for fixing the bearing fixing plate 116 are put in the screw holes 103d and can be screwed from the outside of the frame 103, so that the outer wheel 109a of the ball bearing 109 is easily and firmly fixed on the bottom of the center hole 103a of the cup shaped part 1030 of the frame 103. The bearing fixing plate 116 has the ring part 116d to be put in the center hole 103a of the cup shaped part 1030 and has rather simple configuration having the protruded parts 116a and 116a, which are outwardly protruded from the ring part 116d and is for positioning of the bearing fixing plate 116 on the cup shaped part 1030 of the frame 103 and the female screw parts 116b and 116b formed on the protruded parts 116a and 116a. That is, the bearing fixing plate 116 has a simple shape which is easily manufactured, and is very much effective to improve assembly of the bottom part of the electric motor. Since the ball bearing 109 is fixed on the frame 103 by the bearing fixing plate 116, the ball bearing 109 or the rotor shaft 105 does not move in axial direction of the rotor shaft 105. Therefore, the sealing of the rotor shaft 105 by the main lip 117a of the main oil seal 117 is not broken and the creep of the ball bearing 109 may not occur. As a result, the abnormal noise due to the creep of the ball bearing 109 and/or the locking or burning of the motor 100 are prevented.

Claims: A geared motor comprising: a housing (103, 107); a motor (100) having a stator (104) fixed to inside face of said housing and a rotor (106) which is held rotatable with respect to said stator; a plurality of reduction gears (101) which is provided in a case (102) which is fixed to said housing (103, 107) of said motor (100) and is for reducing rotation speed of said motor and lubricated by a grease (115); sealing means (117, 118) which is provided between a rotor shaft (105) and said housing (107), positioned adjacent to said reduction gears (101); at least two ball bearings (108, 109) for rotatably supporting said rotor shaft (105); a cup-shaped part (1030) on an end face of said housing (103) to which one of said ball bearing (109) is fit; characterized in that said sealing means integrally has a main oil seal member (117) with main lip (117a) and a sub oil seal member (118) with sub lip (118a), said sub lip (118a) being positioned nearer to said grease (115) to be sealed than said main lip; and that bearing fixing means (116) are fixed on a side wall (103b) of said cup-shaped part (1030) of said housing (103) by screws (112) from outside of said housing (103), thereby fixing an outer wheel (109a) of said one of ball bearing (109) in said cup-shaped part (1030) of said housing (103). A geared motor in accordance with claim 1, wherein a helical gear (105a) of a pair of helical gears (101b, 105a) is formed on an end of said rotor shaft (105) and in engagement with the other helical gear (101b) being an initial gear of said reduction gears (101). A geared motor in accordance with claim 1, wherein another grease (120) for lubricating said main lip (117a) of said main oil seal member (117) is filled in a space (118c) formed between said main lip (117a) of said main oil seal member (117) and said sub lip (118a) of said sub oil seal member (118). A geared motor in accordance with claim 3, wherein said another grease (120) has lower viscosity than that of said grease (115).

Inventors: KITAMURA HIROSHI, KOMINE MIZUO, KITAMURA, HIROSHI, KOMINE, MIZUO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: F16J15
IPC codes: H02K5, E02B7, H02K7, E02B8, F16J15