Patent Application
20120174882
The invention relates to a camshaft apparatus that is driven for rotation in synchronization with the rotation of an engine.
An existing camshaft apparatus used in an engine for an automobile rotatably supports a camshaft having a plurality of cams for actuating intake and exhaust valves via a plurality of bearings (for example, see Patent Document 1). As shown in
The existing camshaft apparatus that uses the plain bearings for all the bearings has a large friction resistance because the plain bearings are used, so there is a problem that the running torque of the camshaft increases and the fuel economy performance of the engine decreases. In order to solve the above problem, there is proposed that rolling bearings are used for all the bearings (for example, see Patent Document 2),
Patent Document 1: Japanese Patent Application Publication No. 8-218817
Patent Document 2: Japanese Patent Application Publication No. 2006-226183
In the camshaft apparatus in which all the bearings that support the camshaft are rolling bearings, when coaxiality is low at the time of assembling the rolling bearings to an engine-side cylinder head, or the like, the camshaft cannot smoothly rotate, so it is necessary to set the coaxiality among the rolling bearings so as to be high. Therefore, it is necessary to increase the machining accuracy of assembled portions of the cylinder head, or the like, so there is a problem that it is difficult to manufacture the assembled portions. One of objects of the invention is contemplated in light of the above situation, and is to provide a camshaft apparatus that is able to reduce the running torque of the camshaft and that is able to easily manufacture the assembled portions to which the bearings that support the camshaft are assembled.
A camshaft apparatus according to one aspect of the invention includes: a camshaft having a plurality of cams in an axial direction and one end to which a pulley is connected; and a plurality of bearings that rotatably support the camshaft on a housing, wherein, among the plurality of bearings, the bearing closest to the pulley is formed of a rolling bearing, and the other bearing is formed of a plain bearing, the rolling bearing includes: a roller bearing portion that has a first outer ring raceway surface and a plurality of rollers that roll on the first outer ring raceway surface; and a ball bearing portion that is arranged next to the roller bearing portion in the axial direction and that has a second outer ring raceway surface and a plurality of balls that roll on the second outer ring raceway surface, and the first outer ring raceway surface and the second outer ring raceway surface are formed on an inner periphery of a single outer ring.
Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings.
The camshaft 1 has a linear shaft body 11, a shaft member 12 connected to one end (right side in
The cams 2 are arranged in units of pair at predetermined intervals along the axial direction of the shaft body 11. A through hole 2a for press-fitting the cam 2 to the outer peripheral surface 11a of the shaft body 11 is formed in each cam 2.
Each plain bearing 3 is arranged between a corresponding one of pairs of the cams 2, and rotatably supports the shaft body 11. Each plain bearing 3 is formed in a cylindrical shape, and its outer peripheral surface 3a is fixedly fitted to an accommodating chamber inner surface of a housing H. In addition, the outer peripheral surface 11a of the shaft body 11 is in sliding contact with the inner peripheral surface 3b of each plain bearing 3 via an oil film.
The rolling bearing 4 is a bearing closest to the pulley P, and rotatably supports the shaft member 12 of the camshaft 1.
The roller bearing portion 5 includes a first outer ring raceway surface 51 formed on the outer ring 7, a first inner ring raceway surface 52 formed on the shaft member 12, a plurality of cylindrical rollers 53 rollably arranged between the first outer ring raceway surface 51 and the first inner ring raceway surface 52 and a first cage 54 that retains the cylindrical rollers 53 at predetermined intervals along the circumferential direction to thereby form a cylindrical roller bearing.
The first outer ring raceway surface 51 is integrally formed with a step 7c formed at one end side (left side in
The ball bearing portion 6 is arranged next to the roller bearing portion 5 on the side adjacent to the shaft body 11 in the axial direction. In addition, the ball bearing portion 6 includes a second outer ring raceway surface 61 formed on the outer ring 7, a second inner ring raceway surface 62 formed on the shaft member 12, a plurality of balls 63 rollably arranged between the second outer ring raceway surface 61 and the second inner ring raceway surface 62 and a second cage 64 that retains the balls 63 at predetermined intervals along the circumferential direction to thereby form a deep groove ball bearing.
The second outer ring raceway surface 61 is formed in a circular arc shape in cross section at the other end (right side in
Incidentally, particularly, a portion adjacent to the pulley P to which power is transmitted within the camshaft 1 receives a large load applied because of belt tension. The applied loading occupies about 70% of the entire applied loading that acts on the whole of the camshaft 1. Therefore, in the rolling bearing 4, the roller bearing portion 5 that has a loading capacity of about three times as large as that of the ball bearing portion 6 is arranged close to the pulley P. By so doing, a portion having a large applied loading within the camshaft 1 may be stably supported by the roller bearing portion 5 having a large loading capacity. In addition, displacement of the camshaft 1 toward both sides in the axial direction is restricted by the ball bearing portion 6.
The rolling bearing 4 further includes seal members 8 and 9 for hermetically sealing the gaps between the outer ring 7 and the shaft member 12. The seal members 8 and 9 are mainly formed of an elastic body, such as synthetic rubber, and are respectively fitted to both axial ends of the inner peripheral surface 7b of the outer ring 7. Grease (not shown) is filled in the space S that is hermetically sealed by the seal members 8 and 9. By so doing, it is possible to reliably lubricate the roller bearing portion 5 and the ball bearing portion 6 by the grease filled in the space S while preventing foreign matter, such as carbon sludge and metal powder, contained in lubricating oil of an engine from entering the space S. In addition, it is possible to reduce noise generated from the roller bearing portion 5 and the ball bearing portion 6 by the grease filled in the space S.
With the thus configured camshaft apparatus C according to the present embodiment, the bearing closest to the pulley P is the rolling bearing 4 among the plurality of bearings that support the camshaft 1, so the maximum applied load that acts via the pulley P within the camshaft 1 may be supported by the rolling bearing 4 having a small friction resistance. Thus, it is possible to effectively reduce the running torque of the camshaft 1. In addition, the other bearings that support the camshaft 1 are the plain bearings 3, so, in comparison with the case where all are rolling bearings as in the case of the existing art, it is possible to set the coaxiality among the bearings so as to be low. This is because, when the plain bearings 3 are used as bearings that support the camshaft 1, a slight gap is formed between the outer peripheral surface 3a of each plain bearing 3 and the housing H, so, even when the coaxiality among the bearings is decreased, the camshaft 1 may be rotated without any trouble. As a result, it is not necessary to increase the machining accuracy of the assembled portions (housing H) to which the bearings that support the camshaft 1 are assembled, so it is possible to easily manufacture the assembled portions. In addition, the rolling bearing 4 is provided for the shaft member 12 at the end of the camshaft 1, so the rolling bearing 4 may be applied to a camshaft that is cast integrally from the cams 2 and the shaft body 11 other than the assembly-type camshaft 1 in which the cams 2 are externally fitted around the shaft body 11.
Furthermore, the rolling bearing 4 has the roller bearing portion 5 and the ball bearing portion 6, so the loading capacity may be increased by the roller bearing portion 5, and displacement of the camshaft 1 in the axial direction may be restricted by the ball bearing portion 6. Therefore, it is possible to suppress a decrease in the operating performance of the camshaft apparatus C due to the above applied load. In addition, the first outer ring raceway surface 51 of the roller bearing portion 5 and the second outer ring raceway surface 61 of the ball bearing portion 6 are formed of the inner peripheral surface 7b of the single outer ring 7, so the number of components may be reduced, and manufacturing cost may be reduced.
In addition, the first inner ring raceway surface 52 on which the cylindrical rollers 53 of the roller bearing portion 5 roll and the second inner ring raceway surface 62 on which the balls 63 of the ball bearing portion 6 roll are formed on the outer peripheral surface 12a of the shaft member 12 of the camshaft 1, so the camshaft 1 may be used as both the inner rings of the roller bearing portion 5 and ball bearing portion 6. Thus, the number of components may be reduced, and manufacturing cost may be further reduced. In addition, the first and second inner ring raceway surfaces 52 and 53 may be formed on the shaft member 12 before the shaft member 12 is connected to the shaft body 11, so machining the inner ring raceway surfaces 52 and 53 is easy.
The invention is not limited to the above described embodiment, but it may be modified in design where appropriate. For example, in the above embodiment, the camshaft 1 is formed such that the shaft body 11 is separately formed from the cams 2; instead, as described above, the camshaft 1 may be integrally formed by casting from the shaft body 11 and the cams 2. In addition, the roller bearing portion 5 may be formed as a needle bearing other than a cylindrical roller bearing. Furthermore, the ball bearing portion 6 may be formed as an angular contact ball bearing when mounting space may be ensured, other than a deep groove ball bearing. In addition, the inner ring raceway surface 52 of the roller bearing portion 5 and the inner ring raceway surface 62 of the ball bearing portion 6 are formed on the outer peripheral surface 12a of the shaft member 12; instead, the inner ring raceway surface 52 of the roller bearing portion 5 and the inner ring raceway surface 62 of the ball bearing portion 6 may be formed on the outer peripheral surface of an inner ring separately mounted on the shaft member 12.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-253123 | Nov 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/068350 | 10/19/2010 | WO | 00 | 3/16/2012 |
