1. Field of the Invention
The present invention relates to a method of manufacturing a connecting rod. More particularly, the present invention relates to a method of manufacturing a connecting rod, which achieves a reduction in manufacturing costs, an improvement in positioning accuracy for a bearing metal, and the like.
2. Description of Background Art
In the background art, a bearing metal is inserted into a bearing hole in a big end part of a split type connecting rod (which includes a rod side upper half, on which a piston is provided, and a cap side lower half, which is fastened onto the rod side upper half) of an internal combustion engine (engine) used for a vehicle and the like. Specifically, the bearing metal is formed of a pair of bearing metal halves, each of which has a semi-arc-shaped cross section and is made of soft metal such as aluminum and brass. Moreover, lubricating oil circulating inside the engine forms an oil film between the bearing metal and a crank pin. Thus, lubrication between the connecting rod and the crank pin is achieved when the engine is operating.
In general, the pair of bearing metal halves as described above are positioned so as not to move in a circumferential direction and in an axial direction and are attached to the rod side upper half and the cap side lower half, respectively, on the big end part of the split type connecting rod.
In Japanese Examined Patent Publication No. Hei 2 1990-19328 and Japanese Patent Laid-Open No. 2000-17953, a projection that projects radially outward is formed on an end on either side in a circumferential direction of each bearing metal half having a semi-arc-shaped cross section. Moreover, a locking groove is formed on a mating surface side of an inner circumferential surface of each of upper and lower halves of a big end part of a split type connecting rod. Accordingly, positioning of the bearing metal halves inserted into a bearing hole of the big end part is performed by engagement between the projection and the locking groove on the connecting rod side.
A method of manufacturing a split type connecting rod is classified roughly into a separate-split type connecting rod and a fracture-split type connecting rod. Specifically, the separate-split type connecting rod is used by separately forming a rod side upper half and a cap side lower half of a big end part of a connecting rod and bonding both halves together. The fracture-split type connecting rod is used by integrally die-forming a whole connecting rod including a rod side upper half and a cap side lower half, fracturing the connecting rod into two parts including a rod side half including an upper half of a big end part and a cap side half that is the same as a lower half of the big end part after the die-forming, and assembling both halves so as to attach fracture surfaces to each other.
Among those described above, as to the separate-split type connecting rod, locking grooves formed on an inner circumferential surface of each of upper and lower halves of the big end part of the connecting rod are formed by cutting each of the halves. Thus, costs for manufacturing the separate-type connecting rod are generally increased. In the case of manufacturing by fracture-splitting, it is required to perform cutting to form a bearing hole so as to allow bottoms of the locking grooves and bottoms of the V-shaped grooves to be on the same plane, in order to form one continuous fracture surface after fracture. Moreover, if it is tried to perform cutting finish for the locking grooves in a state where an integrally formed material of the split type connecting rod is fractured into two halves at a position of the V-shaped groove and, thereafter, the two halves are attached to each other and assembled on the fracture surface, it is impossible to perform cutting to form the locking grooves so as to be located at different positions with each other in an axial direction of a bearing hole across the fracture surface. Thus, only a pair of locking grooves that face each other across the fracture surface and communicate with each other can be formed by cutting.
Consequently, without adopting a method of performing cutting to form the locking grooves located at axially different positions across the fracture surface, a method of integrally forming locking grooves by die-pressing while applying a compressive load in the axial direction of the big end part of the connecting rod may be adopted. However, when the connecting rod is formed by applying the compressive load in the axial direction of the big end part, only a locking groove opened in an end face in the axial direction of the big end part can be formed. Thus, in order to axially position the bearing metal inserted into the bearing hole of the big end part, it is required to provide locking grooves at two spots (on one end face in the axial direction of the big end part and the other end face thereof). Thus, it is required to similarly form projections of the respective bearing metal halves, which are engaged with the locking grooves, at two spots. Accordingly, costs for processing the bearing metal are increased.