Bearing assembly and method of manufacturing the same

Abstract: The bearing assembly comprises a stepped-diameter shaft (1) having a large-diameter portion (1a) formed with an inner raceway groove (2a). Balls (4) are located between the inner groove (2a) and an outer raceway groove (2b) in an outer race ring (3). A conventional ball bearing unit (5) is mounted on a small-diameter portion (1b) of the shaft, with a spacer sleeve (7) located between the outer race ring (5b) of the unit (5) and the outer race ring (3). Reduced-diameter portions (7a, 7b) at opposite ends of the sleeve (7) position the sleeve accurately relative to the outer race rings. The components are pre-assembled into the bearing assembly by a bearing manufacturer, to enable a user to be free from the task of assembling rotatable portions, or a cylindrical rotary shaft and associated bearing means, of a computer and/or its peripheral device. In use, the bearing assembly is coaxially mounted in the cylindrical rotary shaft or the like by the user, to rotatably support the cylindrical rotary shaft or the like in the computer or its peripheral device.

Description: The present invention relates to a bearing assembly and a method of manufacturing the same. The bearing assembly may be used in the rotating portions of a computer and/or its peripheral devices. In a conventional bearing assembly, in which a pair of ball bearing units A, B are mounted on a rotary shaft D of rotating portions of a computer or its peripheral devices, as shown in Figs. 2(a) and (b), it is necessary to produce the components of the assembly separately. Consequently, a sleeve-like spacer C and the pair of ball bearing units A, B are produced separately from each other. These components A, B, C of the conventional bearing assembly are then delivered to a user. After receipt of the components, the user mounts the components A, B, C on the rotary shaft D to complete the conventional bearing assembly, as shown in Fig. 2(b). As described above, in the conventional bearing assembly, it is necessary for the user or customer, such as the manufacturer or assembler of the computers or peripheral devices, to mount the pair of ball bearings units A, B and the spacer C on the rotary shaft D with the ball bearing units A, B spaced apart from each other by the spacer C. Consequently, the conventional bearing assembly suffers from the following problems: (a) While it needs to possess sufficient rigidity, the rotary shaft D is also required to have an outer diameter which is small enough to cooperate with the inner race rings of the ball bearing units A, B; (b) Since the spacer C is a separate component independent of the pair of ball bearing units A and B, it is necessary for the opposite end surfaces of the spacer C to be machined or otherwise worked to improve their mutual parallelism and also their flatness, in relation to the dimensions of the ball bearing units A, B being assembled together with the spacer C; and (c) Since the spacer C is merely sandwiched between the outer race rings of the two ball bearing units A and B, it is necessary for the user to coaxially mount the spacer C on the rotary shaft D with a high degree of accuracy. A further prior art bearing assembly for use in office automation equipment (on which the preamble of claim 1 is based) is described in patent EP-A-0591587. The bearing includes a one-piece sleeve in which first and second outer ball bearing raceways are formed. A first row of balls runs between the first outer raceway and an inner raceway formed directly in an outer surface of a larger-diameter portion of a shaft journalled for rotation within the sleeve. A second row of balls runs between the second outer raceway and an inner raceway formed in an inner ring mounted on a smaller diameter portion of the shaft. The outer sleeve of this bearing assembly, with two raceways formed in its inner surface, is difficult to manufacture with sufficient accuracy and leads to complications in the assembly of the bearing components. It is an object of the present invention to alleviate or effectively solve the above problems by providing a bearing assembly and a method of manufacturing the same, the bearing assembly being capable of being easily mounted in rotating portions of a computer and/or its peripheral devices at the user's end or production line. According to one aspect of the present invention, there is provided a bearing assembly comprising: a stepped-diameter shaft provided with a portion having a larger diameter than another portion of the shaft, and an annular inner raceway groove formed directly in the outer peripheral surface of the larger-diameter portion; a first outer race ring coaxially disposed around said larger-diameter portion of said stepped-diameter shaft and spaced apart therefrom to form an annular space therebetween, said first outer race ring having its inner peripheral surface formed with an outer raceway groove; a plurality of first balls rotatably mounted in said annular space, between and engaging the inner raceway groove in the shaft and said annular outer raceway groove of said first outer race ring; and a sleeve-like spacer; a ball bearing unit which has a second outer race ring and an inner race ring mounted on the smaller-diameter portion of said shaft, said spacer being coaxially disposed around said shaft while spaced apart therefrom, and extending axially between said first outer race ring and said second outer race ring of said ball bearing unit which is provided with a plurality of second balls between said inner race ring and second outer race ring; whereby said first outer race ring, said spacer, said plurality of first balls, said ball bearing unit, and said shaft are assembled into a bearing assembly, characterised in that said spacer is provided with a pair of reduced-diameter portions at its opposite axial end portions, one of the reduced-diameter portions having an outer diameter equal to an inner diameter of said first outer race ring and being fitted in said first outer race ring and the other reduced-diameter end portion having an outer race ring of the ball bearing unit and being fitted in said second outer race ring and one end surface of said spacer is fitted closely to an axial end surface of said first outer race ring and an opposite end surface of said spacer is fitted closely to an axial end surface of said second outer race ring. .In one embodiment, the outer diameter of the inner race ring of the ball bearing unit is the same as that of the large-diameter portion of the stepped-diameter shaft, and the outer and inner diameters of the second outer race ring of the ball bearing unit are the same as those of the first outer race ring, respectively, whereby the first and the second balls are of the same diameter. The bearing assembly may also include a ball retainer coaxially and rotatably mounted in the annular space to rotatably retain the first balls therein. According to another aspect of the present invention, there is provided a method of manufacturing a bearing assembly, comprising the steps of: forming an annular inner raceway groove directly in the outer peripheral surface of a portion of a stepped-diameter shaft, which portion has a larger diameter than another portion of the shaft; mounting a plurality of first balls in an annular space defined between said annular inner raceway groove of said shaft and an annular outer raceway groove formed in the inner peripheral surface of a first outer race ring which is coaxially disposed around the larger-diameter portion of said shaft so as to be disposed opposite said annular inner raceway groove of said shaft; coaxially mounting a sleeve-like spacer around said shaft so as to be spaced apart therefrom, said spacer being provided with a pair of reduced-diameter portions at its axial end portions and having one of its reduced-diameter portions having an outer diameter equal to an inner diameter of said first outer race ring and coaxially fitted in said first outer race ring; slidably mounting the other of said reduced-diameter portions of said spacer having an outer diameter equal to an inner diameter of a second outer race ring of a ball bearing unit provided with a plurality of second balls and an inner ring in said second outer race ring said ball bearing unit having its inner race ring slidably mounted on the smaller-diameter portion of said shaft; closely fitting one end surface of said spacer to an axial end surface of said first outer race ring and closely fitting an opposite end surface of said spacer to an axial end surface of said second outer race ring; and bonding or otherwise fixing said inner race ring of said ball bearing unit to said smaller-diameter portion of said shaft by means of an adhesive or other connecting means in a condition in which a predetermined axially inward pre-load is applied to the outer end surface of said inner race ring or said second outer race ring of said ball bearing unit; whereby said first outer race ring, said spacer, said plurality of first balls, said ball bearing unit and said shaft are assembled into a bearing assembly. Reference will now be made to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view of an embodiment of a bearing assembly of the present invention; Fig. 2(a) is a longitudinal sectional view of the components of a conventional bearing assembly, i.e, a pair of ball bearing units and a spacer, from which the bearing assembly is assembled; and Fig. 2(b) is a longitudinal sectional view of the conventional bearing assembly after completion of assembly operation thereof, with the ball bearing units and the spacer properly mounted on a shaft. Fig. 1 shows an embodiment of a bearing assembly of the present invention. As shown in Fig. 1, a stepped-diameter shaft 1 is provided with a relatively large-diameter portion 1a and a relatively small-diameter portion 1b. An annular inner raceway groove 2a is formed directly in the outer peripheral surface of the large-diameter portion la. An outer race ring 3 is disposed opposite the inner raceway groove 2a, and is provided with an annular outer raceway groove 2b in its inner peripheral surface. A plurality of balls 4 are rotatably mounted between the inner raceway groove 2a of the shaft 1 and the outer raceway groove 2b of the outer race ring 3. A ball bearing unit 5 comprising an inner race ring 5a, an outer race ring 5b and a plurality of balls 6 rotatably mounted between the race rings 5a and 5b, has its inner race ring 5a fixedly mounted on the small-diameter portion 1b of the shaft 1 in an insertion manner. A sleeve-like spacer 7 is arranged coaxially with the shaft 1 so as to cover the shaft 1, and is provided with a pair of reduced-or small-diameter portions 7a, 7b, for example annular steps, in or at its axially opposite end portions. The outer diameter of each of the small-diameter portions 7a, 7b is dimensioned to permit it to accurately fit into its associated outer race ring 3 or 5b, respectively. The outer diameter of the inner race ring 5a of the ball bearing unit 5 is equal to the outer diameter of the large-diameter portion 1a of the stepped-diameter shaft 1. Further, there is no difference between the outer and inner diameters of the outer race rings 5b and 3, so that the balls 4 and 6 are of the same diameter. The balls 4, 6 are rotatably supported in ball cages or retainers 9, and travel in the annular inner and outer raceway grooves 2a, 2b, 8a and 8b of the bearing assembly. In this embodiment, the inner race ring 5a of the ball bearing unit 5 is slidably mounted on the small-diameter portion 1b of the stepped-diameter shaft 1 in an insertion manner, and its outer end surface (i.e., right-hand side as viewed in Fig. 1) is subjected to a predetermined axially inward pre-load. Under such circumstances, the inner race ring 5a of the ball bearing unit 5 is bonded or anchored to the small-diameter portion 1b of the stepped-diameter shaft 1 by means of suitable adhesive or like connecting means, and/or is a press-or interference-fit thereon. Thus the components, such as the spacer 7, the outer race ring 3, and the ball bearing unit 5 are successively mounted on the shaft 1 to complete the bearing assembly. Although the balls 4, 6 are of the same diameter in the above embodiment of the present invention, it is also possible to use any other balls which are different in diameter from the balls 4, 6. In other words, the balls used in the small-diameter portion 1b of the shaft 1 may be different in diameter from those associated with the large-diameter portion 1a of the shaft 1. The bearing assembly embodying the present invention constructed as described above has the following actions and effects: (1) Since the outer race ring 3, balls 4, spacer 7, ball bearing unit 5 and the stepped diameter shaft 1 are pre-assembled, for example by the bearing manufacturer, into the bearing assembly or unit, the user, for example the manufacturer of the computers and/or peripheral devices, is relieved of the cumbersome work of assembling the bearing assembly. The assembly may be easily mounted inside a sleeve-like rotating element by the user, by inserting the assembly into the rotating element and fixing the assembly therein; (2) Since the bearing assembly uses a stepped-diameter shaft 1 provided with a large-diameter portion 1a having its outer peripheral surface directly formed with the annular inner raceway groove 2a, instead of a conventional type of inner race ring which would require the diameter of the shaft to be reduced, the rigidity of the shaft is improved; (3) Since the stepped-diameter shaft 1 is provided with the large-diameter portion 1a and therefore possesses increased rigidity, it is possible to increase the resonance point of a spindle or drive motor which is associated with the bearing assembly and used in office automation instruments and like systems, so that the spindle motor may be prevented from resonating to, or inducing resonance in, the remaining components of the instruments, whereby these instruments are improved in reliability; (4) The spacer 7 may be fabricated by a bearing maker so as to align with the ball bearing unit 5 and the outer race ring 3 with a high degree of accuracy. Further, the spacer 7 has its small-diameter annular portions 7a and 7b fitted in the outer race rings 3 and 5b, respectively. In other words, these components 7, 4, 5b are firmly united. As a result, the spacer 7 may be arranged coaxially with the stepped-diameter shaft 1 with a high degree of accuracy, which enables the vibration and noise of the bearing assembly to be considerably reduced; and (5) The number of conventional ball bearing units used in the bearing assembly is reduced to one, i.e. the ball bearing unit 5. Consequently, the bearing assembly embodying the present invention uses only one inner race ring 5a, and the number of its components is therefore reduced in comparison with conventional bearing assemblies.

Claims: A bearing assembly comprising: a stepped-diameter shaft (1) provided with a portion (1a) having a larger diameter than another portion (1b) of the shaft, and an annular inner raceway groove (2a) formed directly in the outer peripheral surface of the larger-diameter portion (1a) ; a first outer race ring (3) coaxially disposed around said larger-diameter portion (1a) of said stepped-diameter shaft and spaced apart therefrom to form an annular space therebetween, said first outer race ring (3) having its inner peripheral surface formed with an outer raceway groove (2b) ; a plurality of first balls (4) rotatably mounted in said annular space, between and engaging the inner raceway groove (2b) in the shaft (1) and said annular outer raceway groove (2b) of said first outer race ring (3); and a sleeve-like spacer (7) ; a ball bearing unit (5) which has a second outer race ring (5b) and an inner race ring (5a) mounted on the smaller-diameter portion (1b) of said shaft (1), said spacer (7) being coaxially disposed around said shaft (1) while spaced apart therefrom, and extending axially between said first outer race ring (3) and said second outer race ring (5b) of said ball bearing unit (5) which is provided with a plurality of second balls (6) between said inner race ring (5a) and second outer race ring (5b) ; whereby said first outer race ring (3), said spacer (7), said plurality of first balls (4), said ball bearing unit (5), and said shaft (1) are assembled into a bearing assembly, characterised in that said spacer (7) is provided with a pair of reduced-diameter portions (7a, 7b) at its opposite axial end portions, one of the reduced-diameter portions (7a) having an outer diameter equal to an inner diameter of said first outer race ring (3) and being fitted in said first outer race ring (3) and the other reduced-diameter end portion (7b) having an outer diameter equal to an inner diameter of the second outer race ring (5b) of the ball bearing unit (5) and being fitted in said second outer race ring (5b) and one end surface of said spacer (7) is fitted closely to an axial end surface of said first outer race ring (3) and an opposite end surface of said spacer (7) is fitted closely to an axial end surface of said second outer race ring (5b). The bearing assembly claimed in claim 1, wherein: the outer diameter of said inner race ring (5a) of said ball bearing unit (5) is the same as that of said larger-diameter portion (1a) of said shaft (1); and the outer and inner diameters of said second outer race ring (5b) of said ball bearing unit (5) are the same as those of said first outer race ring (3), respectively; whereby said first and second balls (4, 6) are of the same diameter. The bearing assembly claimed in claim 1 or 2, further comprising a ball retainer (9) coaxially and rotatably mounted in said annular space to rotatably retain said first balls (4) therein. A bearing assembly as claimed in any preceding claim incorporated in a rotating portion of a computer or a peripheral device therefor. A method of manufacturing a bearing assembly, comprising the steps of: forming an annular inner raceway groove (2a) directly in the outer peripheral surface of a portion (1a) of a stepped-diameter shaft (1), which portion (1a) has a larger diameter than another portion (1b) of the shaft; mounting a plurality of first balls (4) in an annular space defined between said annular inner raceway groove (2a) of said shaft (1) and an annular outer raceway groove (2b) formed in the inner peripheral surface of a first outer race ring (3) which is coaxially disposed around the larger-diameter portion (1a) of said shaft so as to be disposed opposite said annular inner raceway groove (2a) of said shaft; coaxially mounting a sleeve-like spacer (7) around said shaft (1) so as to be spaced apart therefrom, said spacer (7) being provided with a pair of reduced-diameter portions (7a, 7b) at its axial end portions and having one of its reduced-diameter portions (7a) having an outer diameter equal to an inner diameter of said first outer race ring (3) and coaxially fitted in said first outer race ring (3) ; slidably mounting the other of said reduced-diameter portions (7b) of said spacer having an outer diameter equal to an inner diameter of a second outer race ring (5b) of a ball bearing unit (5) provided with a plurality of second balls (6) and an inner ring (5a) in said second outer race ring (5b) said ball bearing unit (5) having its inner race ring (5a) slidably mounted on the smaller-diameter portion (1b) of said shaft (1); closely fitting one end surface of said spacer (7) to an axial end surface of said first outer race ring (3) and closely fitting an opposite end surface of said spacer (7) to an axial end surface of said second outer race ring (5b); and bonding or otherwise fixing said inner race ring (5a) of said ball bearing unit (5) to said smaller-diameter portion (1b) of said shaft by means of an adhesive or other connecting means in a condition in which a predetermined axially inward pre-load is applied to the outer end surface of said inner race ring (5a) or said second outer race ring (5b) of said ball bearing unit; whereby said first outer race ring (3), said spacer (7), said plurality of first balls (4), said ball bearing unit (5) and said shaft (1) are assembled into a bearing assembly.

Inventors: OBARA RIKURO, OBARA, RIKURO, OBARA, RIKURO. C/O MINEBEA K.-K.
Applicants: MINEBEA KK, MINEBEA KABUSHIKI-KAISHA
Application year: 1996
Main classification: F16C35
IPC codes: F16C25, F16C19, F16C35