1. Field of the Invention
The present invention relates to a rolling bearing or a rolling bearing apparatus suitably used to rotatably support a cam shaft in a cylinder head of an engine. More specifically, the present invention relates to a two-split outer ring that is split in two parts in the circumferential direction and to a rolling bearing having the same.
2. Related Art
A large end part of a connecting rod, which is a bar for connecting a piston and a crankshaft in an engine, is coupled to the crankshaft with a rolling bearing disposed therebetween. As the rolling bearing, a split bearing ring (outer ring) that is split in two parts, for example, is used because of the features of the crankshaft.
A technology related to the rolling bearing apparatus is described in JP-A-2005-180459, for example.
As shown in FIG. 20, a rolling bearing 110 of Patent Document 1 is a shell bearing that is configured to be attached to a journal portion 101 of a cam shaft 100 from outside in the radial direction.
The rolling bearing 110 includes a plurality of rolling elements 111, a two-split cage 112 that retains the rolling elements 111, and a two-split shell-type outer ring 113 having a raceway surface of the rolling elements 111. The two-split cage 112 is attached to the journal portion 101 of the cam shaft 100 from outside in the radial direction. The two-split shell-type outer ring 113 is attached to the outer side of the cage 112. The cam shaft 100 is attached to a cylinder head 200 of an engine. At this time, the rolling bearing 110 is fitted to a semicircular concave portion 201h of the cylinder head 200. In such a state, the rolling bearing 110 is pressed by a semi-ring shaped cap 205, and both ends of the cap 205 are fixed with bolts to both sides of the semicircular concave portion 201h of the cylinder head 200. With this, the shell-type outer ring 113 of the rolling bearing 110 is fastened by the cap 205 and the semicircular concave portion 201h of the cylinder head 200. Thus, the rolling bearing 110 can have a favorable degree of roundness.
However, in recent years, the cylinder head 200 is mostly formed of aluminum alloy and the shell-type outer ring 113 of the rolling bearing 110 is usually formed of steel sheet. For this reason, as the engine temperature rises by the differing thermal expansion coefficient between the aluminum alloy and the steel sheet, a gap is generated between the shell-type outer ring 113 and the semicircular concave portion 201h and cap 205 of the cylinder head 200. With this, the degree of roundness of the shell-type outer ring 113 of the rolling bearing 110 is lowered. Moreover, the gap in the radial direction within the rolling bearing 110 increases and thereby to generate noise.
On the other hand, when the split bearing ring is split such that the splitting surfaces are linear, the splitting surfaces are likely to be misaligned with each other at the time of attachment and thus the handling properties are poor. For this reason, it is desired to form the splitting surfaces in a curved or inflected shape such as an S character with respect to the axial direction. According to a technology regarding a splitting method disclosed in JP-A-S54-163247, notches for inducing the splitting are formed in the outer peripheral surface of the bearing ring, and the bearing ring is pressurized by a pressure jig with the pressure focusing on the notches, thereby splitting the bearing ring along the notches into two parts. According to a technology regarding a splitting method disclosed in JP-A-2005-337352, a strip-shaped metal plate of which the end portions have a concave-and-convex shape is bent to form semicircular split parts.
With the advance of the technology, it has become possible to form the splitting surfaces to be greatly bent or inflected with respect to the axial direction when splitting the bearing ring. Thus, misalignment in the axial direction is efficiently prevented. However, a new attachment problem attributable to such a splitting method is generated.
For example, since the splitting surfaces of the split parts are connected with each other in the circumferential direction, they form a circular arc of which the central angle is larger than 180 degrees as viewed in side view. Specifically, as shown in FIG. 21A, a split part 150 has a semicircular arc (central angle: 180 degrees) on the right side of a straight line Y perpendicular to an axial line Z. A splitting surface 151 portion extends to the left side of the straight line Y. At this time, as shown in FIG. 21B, an opening width d between front end portions 151a of the splitting surface 151 is smaller than the inner diameter D of the inner peripheral surface 150a of the split part 150. Therefore, as shown in FIG. 22, for example, when the split part 150 (outer ring) received in a connecting rod (not shown) is fitted to a roller-attached cage CR wound around a crankshaft, the front end portions 151a serve as an obstacle, thereby deteriorating the attachment properties. This is because the outer diameter of the roller-attached cage CR is the same as the inner diameter D of the inner peripheral surface 150a of the split part 150, in which the inner peripheral surface 150a is used as a raceway surface of the roller, and because the opening width d is smaller than the outer diameter D as viewed in the X direction (see FIG. 21A).
As described forgoing, the splitting process is not stable and it is difficult to form the same splitting surfaces in a controlled manner. For example, when only one of the splitting surfaces is defective, it cannot be substituted by another one, thereby increasing the cost. Meanwhile, by cutting an end portion into a strip-shaped metal plate, the splitting surface can be formed in a shape in which the misalignment in the axial direction is not likely to occur. However, curving the metal plate in a semicircular shape is troublesome.
In JP-A-2005-337352, an end portion is cut into a strip-shaped metal plate and the metal plate is bent into a semicircular shape. Straight portions are provided at both ends of the metal plate, and the metal plate is fitted to a housing by elastically deforming the straight portions toward an inner side. However, such process steps are troublesome.
A method can be conceived in which the split bearing ring is formed by a cutting process rather than the splitting process. However, as shown in FIG. 23A, for example, when a circular bearing ring 160 is cut along a straight line U by a wire-cut discharge process, the bearing ring 160 is split into two split parts 161 and 161 (see FIG. 23B). At that time, a cut portion 161a is also removed by a wire. Therefore, as shown in FIG. 23C, when the two split parts 161 and 161 are assembled with each other, the assembled bearing ring 160 cannot form a perfect circle but forming an elliptical shape deformed from the original shape before the splitting since the cut portion 161a is removed. Since the two split parts 161 and 161 cannot be maintained in the assembled state, it is difficult to polish the outer peripheral surface into a circular shape. Therefore, in such a state, it cannot be used as the outer ring of a rolling bearing.