Compound ball bearing

Abstract: A compound ball-bearing includes a spindle (1) surrounded by a sleeve (2) in an inner surface of which two outer races (4,8) are formed. A first row of balls (5) run between one of the outer races (4) and a first inner race (3) formed in a first part (1a) of the spindle (1) and a second row of balls (9) run between the other outer race (8) and a second inner race (7) formed in an inner ring (6) mounted on a second part (1b) of the spindle (1). The inner ring (6) is integrally formed in one piece with a base (15) of a motor. The spindle (1) may be stepped and the first part (1a) may have a larger diameter than the second part (1b).

Description: This invention relates to ball-bearings mainly used for office automation (OA) apparatus motors and components thereof eg in computers. A usual spindle motor used for OA apparatuses, as shown in Figure 2 comprises a spindle 30, a rotor hub 31 and a base flange 32. The spindle is supported by a ball-bearing 33 which comprises an inner and an outer ring provided in a sleeve 34. The motor further comprises a yoke 37 supported on the base flange 32 by means of a yoke holder 35 and supporting a coil means 38. A permanent magnet 36 is connected for rotation with the hub 31. These components are individually formed as separate members. A further prior art bearing assembly for OA apparatus is described in Patent US 4,713,704 (on which the precharacterising part of claim 1 is based). The bearing assembly includes a motor flange connected to a sleeve in which two inner races are formed. A first row of balls runs between one of the inner races and a race formed in an outer surface of a larger diameter portion of a central shaft and a second row of balls runs between the other inner race and a race formed in an outer surface of a ring fitted on a smaller diameter portion of the shaft. Another prior art bearing assembly for OA apparatus is described in Patent US 5,045,738. In the various embodiments described, a motor hub is supported by two parallel rows of balls which run around spaced races formed in an outer surface of a spindle. In some embodiments the spindle is press-fitted into a fitting member which is to be fitted to a frame of the motor. Since the prior art motor components are thus independent parts, the motor has a large number of components. Besides, it is necessary to assemble these components, leading to a large number of steps involved in the motor's manufacture and thus to a high cost of manufacture. Further, in the prior art ball-bearing structure, it is not easy to obtain the vibration accuracy of the spindle, and it is difficult to expect substantial improvement of vibration accuracy. Accordingly avoidance of vibration in prior art, spindle motors is difficult to achieve. An object of the invention is to reduce the number of components and number of steps of assembling apparatus such as that described above, thus permitting reduction of the cost of manufacture. Another object of the invention is to provide a compound ball-bearing, in which the inner or outer ring can be secured in a proper position by facilitating pre-loading or a press fitting technique, thus obtaining improved spindle vibration accuracy, and reducing spindle motor vibration. In the compound ball-bearing according to the invention, a motor flange is moulded as a one-piece moulding with the inner ring, as a component of the bearing body. More specifically, according to the invention there is provided a compound ball bearing comprising a bearing assembly including a spindle which is a stepped spindle having a larger diameter portion and a smaller diameter portion, a sleeve surrounding said spindle having first and second inner races formed therein, a first row of balls between said first inner race and an outer race in the larger diameter portion of the spindle and a second row of balls between said second inner race and an outer race formed in an inner ring fitted on the smaller diameter portion of said spindle characterised in that said inner ring is integrally formed in one piece with a flange of a motor. The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a sectional view showing an embodiment of the invention; and Figure 2 is a view, partly in section, showing a typical prior art spindle motor. Figure 1 shows an embodiment of the compound ball-bearing according to the invention. Referring to Figure 1 there is shown a double-row ball bearing, in which a spindle 1 and a sleeve 2 corresponding thereto as an outer ring form a bearing body for retaining bearing balls 5 and 9 provided in two rows. The spindle 1 is stepped and has a larger and a smaller diameter portion 1a and 1b respectively. The larger diameter portion 1a has an outer race 3 for a first row of balls 5, while the sleeve 2 has an inner race 4 corresponding to the outer race 3 of the spindle. Balls 5 in the first row are provided between the two races 3 and 4. On the smaller diameter portion 1b of the spindle, an inner ring 6 is fitted. A second row of balls 9 is provided between an outer race 7 formed in the inner ring and a corresponding inner race 8 formed in the sleeve 2. A motor flange 15 is moulded as a one-piece moulding with the inner ring 6. The inner ring 6 which has been loosely fitted on the spindle, is pre-loaded and secured with an adhesive to the spindle. Each ball is suitably made of a high carbon chromium bearing steel. According to the invention, the motor flange is moulded as a one-piece moulding with the inner ring. Thus, unlike the prior art bearing structure, in which all of the hub, the flange, the yoke holder or the like are separate from the bearing body, it is possible to readily assemble parts when manufacturing a motor. Efficient assembling is obtainable by using machines thus reducing the cost of motor manufacture. These merits are highly beneficial in industrial production. Furthermore when a part such as a motor flange is moulded as a one-piece moulding with the inner ring, the motor manufacture of motor component assembling can be carried out without the need of centring of the spindle with respect to any of the components noted above. Thus it is possible to provide a motor or the like, which is free from shaft vibration and has high accuracy of rotation. Further, the inner ring can be readily pre-loaded, for installation on the appropriate part, by applying a pressure to it in the axial direction. The inner ring thus can be secured in a proper position to obtain a highly accurate ball-bearing.

Claims: A compound ball bearing comprising a bearing assembly including a spindle (1) which is a stepped spindle having a larger diameter portion (1a) and a smaller diameter portion (1b), a sleeve (2) surrounding said spindle (1) having first and second inner races (4, 8) formed therein, a first row of balls (5) between said first inner race (4) and an outer race (3) in the larger diameter portion (la) of the spindle and a second row of balls (9) between said second inner race (8) and an outer race (7) formed in an inner ring (6) fitted on the smaller diameter portion (1b) of said spindle (1) characterised in that said inner ring (6) is integrally formed in one piece with a flange (15) of a motor.

Inventors: OBARA RIKURO, TATSUNO KATASHI, OBARA, RIKURO, TATSUNO, KATASHI, Obara, Rikuro, Minebea K.K., Tatsuno, Katashi, Minebea K.K.
Applicants: MINEBEA KK, MINEBEA KABUSHIKI-KAISHA
Application year: 1993
Main classification: H02K7
IPC codes: F16C33, F16C35, F16C19, H02K5, G11B19, F16C25