1. Field of the Invention
The invention relates to a roller lifter that contacts through a roller a cam reciprocating a member for pumping a liquid in a liquid pump such as a high-pressure fuel pump configuring a fuel supply system of an automobile engine, a method of producing the roller lifter and a liquid pump.
2. Description of the Related Art
Roller lifters (roller tappets) that contact a member for pumping a liquid with a reciprocating cam through a roller have conventionally been used as lifters (also referred to as tappets) provided in liquid pumps such as high-pressure fuel pumps composing fuel supply systems of automobile engines, for example. More specifically, this type of liquid pump as described above is provided with a member for pumping a liquid in the form of a plunger and a cam that causes the plunger to reciprocate by rotating. The plunger is urged in the direction of reciprocation that faces the cam by an elastic member such as a coil spring. Namely, liquid pumps provided with a roller lifter are composed in the form of plunger drive pumps that pump a liquid by causing a plunger, which is urged toward a cam that rotates centering about a prescribed axis of rotation, to reciprocate by rotation of the cam. In this configuration, the roller lifter is interposed between the plunger and the cam.
In addition to supporting one end of the plunger, the roller lifter contacts the cam while urged toward the cam by an elastic member for urging the plunger. In other words, the plunger is urged in the direction facing the cam mediated by the roller lifter together with receiving rotation of the cam. Thus, the roller lifter reciprocates together with the plunger accompanying rotation of the cam. The roller lifter is mediated by a rotating body in the form of a roller during contact with the cam.
The roller in the roller lifter is in a state in which the mutual outer peripheral surface thereof contacts the cam while being supported so that the direction of the axis of rotation is the same as that of (parallel to) the cam. While in this state, the roller moves in the direction of reciprocating motion of the plunger mediated by the roller lifter, namely in the direction opposing the urging force applied by an elastic member of the plunger, and in the opposite direction thereof (direction in which urged by the elastic member). Here, the roller in contact with the cam rotates by frictional force and so forth in response to rotation of the cam.
This type of roller lifter has a portion that holds the roller that contacts the cam, and a portion that forms guide surfaces that guide reciprocating motion of the roller lifter by contacting a prescribed sliding surface formed by a member, for example, that houses the plunger. According to this type of roller lifter, frictional force accompanying cam rotation at contacting portions of the roller lifter and the cam is absorbed by rotation of the roller, thereby reducing wear of the contacting portions.
An example of a technology relating to a roller lifter is disclosed in Japanese Patent Application Publication No. 9-125915 (JP-A-9-125915). JP-A-9-125915 discloses a configuration containing a hollow body made of a pressed sheet metal material, and a block housed in the body having a cylindrical bearing surface that houses a roller. In this configuration, the body configures a portion that forms guide surfaces, and the block configures a portion that holds the roller.
In JP-A-9-125915, the portion that forms the guide surfaces and the portion that holds the roller in the roller lifter are composed by different members. In other words, the roller lifter of JP-A-9-125915 has a structure in which a plurality of members containing the body and the block are assembled. Consequently, the number of constituent parts and the number of production steps increase, thereby resulting in increased costs.
In addition, some typical conventional roller lifters are produced by cold forging. More specifically, after forming a rod-shaped (cylindrical) material by cold forging, the material is formed into a prescribed shape by machining. In other words, portions having a prescribed shape in the roller lifter, such as the portion that holds the roller, the portion that forms the guide surfaces, and the portion that supports the plunger, are formed by machining a material formed by cold forging.
In this manner, according to a roller lifter produced by cold forging, although the number of constituent parts is less than the previously described configuration of JP-A-9-125915, numerous machining steps are required after cold forging. Namely, since there are limitations on the shapes that can be formed by cold forging, it is difficult to form portions having a prescribed shape such as the portion that holds the roller by cold forging alone. Thus, since cold forging only enables parts to be formed to a shape that is far removed from a final target shape (finished product shape), cold forging requires numerous machining steps. Consequently, the number of production steps increases resulting in increased costs.
In addition, it is difficult to realize both lightweight and reduced costs in the case of a roller lifter produced by cold forging. Namely, since there are limitations on the shapes that can be formed by cold forging as previously described, a relatively large surplus portion (surplus material) remains in the material after forming, and that surplus material serves to impair weight reduction of the finished product. Although this surplus material can be removed by increasing the number of machining steps, an increase in the number of machining steps results an increased costs.
On the other hand, there are cases in which a rotation stopper in the form of a portion having a shape for preventing rotation of the roller lifter is provided in the roller lifter for preventing rotation of a roller lifter in which the direction of reciprocating motion of the roller lifter is the direction of the axis of rotation. In other words, the rotation stopper is a portion having a shape for preventing relative rotation of the roller lifter with respect to a member in which a reciprocating roller lifter is enclosed. The rotation stopper is provided from the viewpoint of maintaining urging of the roller to contact the cam and preventing uneven wear at contacting portions of the roller and cam.
It is difficult to form such a rotation stopper by cold forging since there are limitations on the shapes that can be formed by cold forging as previously described. Therefore, there are cases in which it is necessary to provide a separate member from the material formed by cold forging in order to provide a rotation stopper in the roller lifter. In such cases, both production steps and costs increase due to the need for machining steps for fabricating the separate member and forming a portion having a shape corresponding to the separate member (such as a hole) in the material after forming.