Bearing device

Abstract: Bearing sleeves 1c and 6c of dynamic pressure bearings 1 and 6 are adjustably supported to mounting sleeves 1a and 6a by appropriately flexible connecting portions 1b and 6b, so that the center axes of the bearing sleeves 1c and 6c are fine adjusted so as to coincide with the center axis of the shaft 3. Thus the concentricity of the bearing sleeves 1c and 6c with respect to the shaft 3 can be enhanced without requiring any high-precision machining.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bearing devices such as dynamic pressure bearings and slide bearings. 2. Description of the Prior Art In bearing devices such as a dynamic pressure bearing and the like having a plurality of bearing portions, their bearing performance significantly depends on concentricity between inner and outer diameters of each bearing portion as well as on alignment of the plurality of bearing portions. If any misalignment takes place in setting up the bearing portions, the resulting performance would be quite a lower one. Accordingly, to attain a successful bearing performance, the machining of the bearing portions must be carried out at very high precision, which may cause a problem of increased prices of the bearing devices. This being the case, there has been provided a dynamic pressure bearing as shown in Fig. 5, intended to solve the foregoing problem. To provide this dynamic pressure bearing, a plurality of bearing portions 32 and 35 are integrally molded with a sleeve 31, so that the concentricity and alignment of the plurality of bearing portions 32, 35 can readily be ensured. The dynamic pressure bearing mentioned above, having a very small clearance between the bearing portions 32, 35 and a shaft (not shown) fitted thereto, is required to suppress the friction torque of grease between the sleeve 31 and the shaft. To do this, there is provided a concave portion 33 in the center of the inner periphery of the sleeve 31 other than the bearing portions 32,35, thereby giving a larger clearance between the concave portion 33 and the shaft. However, the process of forming the concave portion 33 in the center portions of the inner periphery of the sleeve 31 is difficult. Another difficulty arises in washing the concave portion 33. FR-A-1 407 153 discloses a bearing sleeve, which shows an example of the integration of the support member with the mounting plate, where the support member cooperates with a groove in the bearing sleeve. FR-A-1 546 285 discloses a bearing device according to the pre-characterizing portion of claim 1. In this device an additional annular groove is formed on the inner periphery of the mounting sleeve and an annular member engages both the annular groove formed on the inner periphery of the bearing sleeve and the annular groove formed on the inner periphery of the mounting sleeve. This makes the bearing sleeve according to this document complicated. SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a bearing device capable of ensuring the concentricity and alignment of its bearing portions successfully without requiring any high-precision machining, or any difficult processing or washing. In order to achieve the above mentioned object the present invention provides a bearing device according to claim 1. The further claims are related to different advantageous aspects of the present invention. With the above-described arrangement, the bearing sleeve for bearing the shaft is adjustably supported by the support member provided to the mounting sleeve disposed outside the bearing sleeve. As a result, the bearing sleeve can be ensured for a good concentricity and alignment with respect to the shaft by the adjusting support member without requiring any high-precision machining or difficult processing. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein figures 3(A), 3(B) and (4) show a bearing device in accordance with the invention and figures 1(A), 1(B), 2(A), 2(B), 2(C) and 3(C) show bearing devices having features which may be used in a bearing device according to the invention: Fig. 1 (A) is a sectional view of a bearing device showing some features of the present invention; Fig. 1 (B) is a sectional view of the aforementioned bearing device; Figs. 2 (A), (B), and (C) are plan views of this bearing device viewed from top; Fig. 3 (A) is a sectional view of a device according to an embodiment of the bearing device of the invention; Fig. 3 (B) is a transverse sectional view of the aforementioned bearing device; Fig. 3 (C) is a transverse sectional view of a variation of the aforementioned bearing device; Fig. 4 is a longitudinal sectional view of the aforementioned bearing device; and Fig. 5 is a sectional view of a conventional bearing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 (A) is a longitudinal sectional view of a device showing some features of the present invention in which dynamic pressure bearings 1 and 6, and a spacer 8 are press fitted into a cylindrical casing 7. The dynamic pressure bearings 1 and 6 are formed of a resin having appropriate elasticity such as polytetrafluoreoethylene (hereinafter referred to as PTFE), identical to each other in their construction. The dynamic pressure bearing 1 is provided with a bearing sleeve 1c having dynamic pressure grooves ld on its inner periphery. The dynamic pressure bearing 6 is equipped with a bearing sleeve 6c having dynamic pressure grooves 6d on its inner periphery. The bearing sleeves 1c and 6c are to support a shaft 3. Fig. 1 (B) is a longitudinal sectional view of the above-described dynamic pressure bearing 1. Fig. 2 (A) is a plan view of the dynamic pressure bearing 1 as viewed from top. On the outside of the bearing sleeve 1c of the dynamic pressure bearing 1 there is provided a mounting sleeve la, and it is arranged that a thin flexible ring-shaped connecting portion 1b as a support member, which integrally couples the entire circumference of the outer-peripheral, axially approximately center portion of the bearing sleeve 1c with the entire circumference of the inner-peripheral, axially approximately center portion of the mounting sleeve 1a, supports the bearing sleeve 1c to the mounting sleeve 1a, adjustably. On the outside of the bearing sleeve 6c of the dynamic pressure bearing 6, as shown in Fig. 1 (A), there is disposed a mounting sleeve 6a, and it is arranged that a thin flexible ring-shaped connecting portion 6b, which integrally couples the entire circumference of the outer-peripheral, axially approximately center portion of the bearing sleeve 6c with the entire circumference of the inner-peripheral, axially approximately center portion of the mounting sleeve 6a, supports the bearing sleeve 6c to the mounting sleeve 6a, adjustably. Since the bearing sleeves 1c and 6c of the dynamic pressure bearings 1 and 6 are adjustably supported by the flexible connecting portions 1b and 6b, the center axes of the bearing sleeves 1c and 6c are fine adjusted so as to coincide with the center axis of the shaft 3. As a result, the concentricity of the bearing sleeves 1c and 6c with respect to the shaft 3 as well as the alignment of the bearing sleeves 1c and 6c can be ensured successfully. Also since the dynamic pressure bearings 1 and 6 are provided discretely from the casing 7 and the inner periphery of the casing 7 is not a bearing surface for directly supporting the shaft 3. It is allowable to roughly process the inner periphery of the casing 7, and thus the inner periphery of the casing 7 is easy to machine. Because the dynamic pressure bearings 1,6 and the spacer 8 are detachably fitted in the cylindrical casing 7, it is easy to wash them. Further, because the spacer 8 is provided discretely from the dynamic pressure bearings 1,6 and the cylindrical casing 7 accommodates the dynamic pressure bearings 1,6 and the spacer 8, it is easy to machine and arrange the dynamic pressure bearings 1,6, the spacer 7 and the inner periphery of the casing 7 so that the clearance between the spacer 8 and the shaft 3 resulting when the spacer 8 is press fitted to the center portion of the inner periphery of the casing 7, which will generate no dynamic pressure, becomes large as compared with an extremely narrow clearance between the dynamic pressure sleeves ld, 6d, which will generate dynamic pressure, and the shaft 3. This allows the friction torque between the casing 7 and the shaft 3 to be easily reduced without requiring any difficult machining. In the dynamic pressure bearing 1, between the bearing sleeve 1c and the mounting sleeve 1a there was provided a connecting portion 1b continuing in the circumferential direction, as shown in Fig. 2 (A). However, the connecting portion of the dynamic pressure bearing 1 may be provided in the form of flexible spokes radially extending at four or three circumferential points between the mounting sleeve la and the bearing sleeve 1c, such as connecting portions 1e or 1f shown in Fig. 2 (B) or (C). The spoke-shaped connecting portion may also be provided at two points in the circumferential direction. Further, although the bearing device was a dynamic pressure bearing, yet the features disclosed above can be applied to slide bearings. As apparent from the above description, the bearing device according to Fig 1 and 2 is so arranged that the connecting portion for integrally connecting the bearing sleeve and the mounting sleeve outside thereof supports the bearing sleeve, which supports the shaft, to the mounting sleeve, adjustably. As a result, the bearing sleeve can be aligned so that its center axis will coincide with the center axis of the shaft, thus giving a successful concentricity and alignment with respect to the shaft without the need of subjecting the bearing sleeve to any high-precision machining. Further, when a dynamic pressure generating groove is provided to the inner periphery of the bearing sleeve, high-precision machining of the dynamic pressure bearing as has conventionally been needed for attaining an accurate concentricity and alignment can be eliminated, thus allowing the good concentricity and alignment of the dynamic pressure bearing with respect to the shaft to be simply attained. (Present Invention) Fig. 3 (A) is a longitudinal sectional view of a bearing device according to an embodiment of the present invention, wherein dynamic pressure bearings U and D are press fitted into a casing 207. The dynamic pressure bearings U and D are of the absolutely same construction. The dynamic pressure bearings U and D are equipped with a bearing sleeve 202 having dynamic pressure grooves 202a on its inner periphery and a bearing sleeve 206 having dynamic pressure grooves 206a on its inner periphery, so that the dynamic pressure bearings support a shaft 203. A resin material good in wear resistance and low in friction, such as fluororesin, for example, is used as the material for the bearing sleeves 202 and 206, thereby offering a long service life of the bearing sleeves 202 and 206. Fig. 3 (B) shows a transverse section of the dynamic pressure bearing U. Fig. 4 shows a longitudinal section of the dynamic pressure bearing U. Outside the bearing sleeve 202 of the dynamic pressure bearing U there is disposed a mounting sleeve 201 made up of two semi-cylindrical components 201a and 201b. To the inner periphery of the mounting sleeve 201 there are formed adjusting flanges 210a and 210b as support members which are fitted to grooves 202b formed on the outer periphery of the bearing sleeve 202 to adjustably support the bearing sleeve 202. Also, outside the bearing sleeve 206, as shown in Fig. 3 (A), there is disposed a mounting sleeve 205 made up of two semi-cylindrical components 205a and 205b. To the inner periphery of the mounting sleeve 205 there is formed adjusting flanges 250a and 250b which are fitted to a groove 206b formed on the outer periphery of the bearing sleeve 206 to adjustably support the bearing sleeve 206. An appropriately hard resin material such as PTFE is used as the material for the mounting sleeves 201 and 205, so that an optimum alignment can be attained. The mounting sleeves 201 and 205 are fixed inside the casing 7. Since the bearing sleeves 202 and 206 of the dynamic pressure bearings U and D are alignably supported by the mounting sleeves 201 and 205 having adjusting flanges 210a, 210b and 205a, 250b, thus the center axes of the bearing sleeves 202 and 206 can be fine adjusted so that they coincide with the center axis of the shaft 203. As a result, the concentricity of the bearing sleeves 202 and 206 with respect to the shaft 203 as well as the alignment of the bearing sleeves 202 and 206 can be ensured successfully without requiring any high-precision machining. Also, since the mounting sleeves 201 and 205 and the bearing sleeves 202 and 206 are provided separately from the casing 207 and the inner periphery of the casing 207 does not directly support the shaft 203, the inner periphery of the casing 207 is unnecessary to subject a fine machining, thus being easy to machine. Also, it is easy to machine the dynamic pressure bearings 201, 206 and the casing 207 so that the clearance between the inner-peripheral center portion of the casing 207, which will generate no dynamic pressure, and the shaft 3, becomes large as compared with an extremely narrow clearance between the bearing sleeves 202 and 206, which will generate dynamic pressure, and the shaft 3, because they are formed separately. This allows the friction torque between the casing 207 and the shaft 203 to be easily reduced without requiring any difficult machining. In the dynamic pressure bearings U and D of the present embodiment, the mounting sleeves 201 and 205 were each made up of two semi-cylindrical components. In Fig. 3(C) the mounting sleeve is provided by a singly cylindrical component 100 and three adjusting protrusions 100a as support members are provided on the inner periphery of the component 100 at regular intervals in the circumferential direction. Also, although not shown, a spacer may be disposed between the mounting sleeves 201 and 205. Further, although in the present embodiment the bearing device was a dynamic pressure bearing, yet the present invention can be applied to slide bearings. As apparent from the above description, the bearing device according to this embodiment of the invention is so arranged that the support members provided to the mounting sleeves disposed outside the bearing sleeves adjustably support the bearing sleeves, which support the shaft. As a result, the bearing sleeves are aligned so that their axes coincide with the center axis of the shaft, thus allowing a good concentricity and alignment with respect to the shaft to be attained successfully without subjecting the bearing sleeves to any high precision machining. Furthermore, when a dynamic pressure generating groove is provided on the inner periphery of the bearing sleeves, high-precision machining of the dynamic pressure bearings as has conventionally been needed especially for obtaining a highly accurate concentricity and alignment because of an extremely small clearance can be eliminated, thus allowing the concentricity and alignment of the dynamic pressure bearings with respect to the shaft to be easily obtained at high accuracy. The invention being thus described, it will be obvious that the same may be varied in many ways within the scope of the following claims.

Claims: A bearing device, comprising: a bearing sleeve (202, 206) for bearing a shaft; a mounting sleeve (201a, 201b, 205a, 205b) disposed outside said bearing sleeve (202, 206); a support member (210a, 210b, 250a, 250b) for adjustable supporting said bearing sleeve (202, 206) on said mounting sleeve (201a, 201b, 205a, 205b), and an annular groove (202b, 206b) formed on the outer periphery of said bearing sleeve (202, 206); wherein said bearing sleeve (202, 206) and said mounting sleeve (201a, 201b, 205a, 205b) are discrete from each other, said bearing device being characterized in that said support member (210a, 210b, 250a, 250b) is formed integrally with said mounting sleeve (201a, 201b, 205a, 205b) which comprises two semicylindrical components, said support member comprises an adjusting flange (210a, 210b, 250a, 250b) on the inner periphery of each said semi-cylindrical component thereof, and said adjusting flange (210a, 210b, 250a, 250b) is fitted into said annular groove (202b, 206b). The bearing device of claim 1, wherein said support member comprises a plurality of protrusions formed on the inner periphery of said mounting sleeve, at regular intervals in the circumferential direction. The bearing device of claim 1, wherein said bearing sleeve (202, 206) is composed of a first material good in wear resistance and small in frictional force and said mounting sleeve (201a, 201b, 205a, 205b) is composed of a second material, said second material being polytetrafluoroethylene. The bearing device of claim 3, wherein said first material (202, 206) is fluororesin. The bearing device of claim 1, wherein a dynamic pressure generating groove (202a, 206a) is provided on the inner periphery of said bearing sleeve.

Inventors: ONISHI MASAYOSHI, TAKAHASHI TAKESHI, ONISHI, MASAYOSHI, TAKAHASHI, TAKESHI
Applicants: KOYO SEIKO CO, KOYO SEIKO CO., LTD.
Application year: 1992
Main classification: F16C23
IPC codes: F16C33, F16C23, F16C35