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Camshaft and assembling method thereofRelated Patent Categories: Metal Working, Method Of Mechanical Manufacture, I.c. (internal Combustion) Engine Making, Camshaft MakingCamshaft and assembling method thereof description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060064872, Camshaft and assembling method thereof. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a camshaft used in an internal combustion engine of an automobile or the like. BACKGROUND ART [0002] A camshaft used in an engine of an automobile is generally an integral-type camshaft formed by casting. However, recently, use of an assembling type of camshaft has been increased, in which one or more cam pieces are press-fitted to a shaft. [0003] Every automobile part is required to weigh less. In the assembling type of camshaft, a hollow pipe may be used for the shaft, so that weight reduction and cost saving may be easily achieved. In addition, when the cam pieces need to have a predetermined hardness, only the cam pieces may be thermally processed, so that the cam pieces may be easily made harder than the shaft. Thus, the assembling type of camshaft can be manufactured at lower cost, compared with a case wherein the whole unitary camshaft undergoes a thermal process. [0004] An example of the assembling type of camshaft is shown in FIG. 10. In the assembling type of camshaft 101 shown in FIG. 10, the inside diameter of a cam piece 106 is formed a little smaller than the outside diameter of a shaft 102. Then, the cam piece 106 is fixed to the shaft 102 by means of the difference (interference). [0005] Herein, an assembling method of the camshaft 101 as shown in FIG. 10 is explained. The cam piece 106 is press-fitted to a predetermined position on the shaft 102 while a phase of the cam piece 106 is adjusted, from a one-side end of the shaft 102 that is hollow. Subsequently, the other cam pieces 106 are press-fitted in turn. Thus, the cam shaft 101 is assembled. [0006] Herein, since the inside diameter of the cam piece 106 is a little smaller than the outside diameter of the shaft 102, the outside surface of the camshaft 102 and the inside surface of the cam piece 106 may be damaged while the cam piece 106 moves to LABEL the predetermined position on the shaft 102. If their surfaces are damaged, the press-fitting strength between the cam piece 106 and the shaft 102 may be deteriorated. [0007] In addition, in order to enhance the press-fitting strength in a rotation direction, the interference has to be increased. However, if the interference is increased too much, residual stress of the cam piece 106 may be increased too much, and fatigue strength thereof may be deteriorated, that is, durability of the camshaft 101 may be deteriorated. [0008] Furthermore, the cam piece 106 has to be press-fitted to the shaft 102 under a state wherein the phase of the cam piece 106 has been adjusted in advance. However, the phase of the cam piece 106 may be undesirably changed during the press-fitting step. [0009] In another assembling type of camshaft 201 as shown in FIG. 11, spline engaging grooves 208 are formed in a cam piece 206, and spline engaging teeth 204 are formed in a shaft 202. The spline engaging grooves 208 and the spline engaging teeth 204 are engaged in a spline manner with each other. In the camshaft 201, since the spline engaging grooves 208 of the cam piece 206 are press-fitted to the spline engaging teeth 204 of the shaft 202, rotation of the cam piece 206 may be inhibited. In addition, phase relation between the cam piece 206 and the shaft 202 may be adjusted at the same time. [0010] However, in the camshaft 201 as shown in FIG. 11 as well, since the spline engaging grooves 208 of the cam piece 206 are smaller than the spline engaging teeth 204 of the shaft 202, the spline engaging teeth 204 of the shaft 202 and the spline engaging grooves 208 of the cam piece 206 may be damaged while the cam piece 206 moves to a predetermined press-fitting position on the shaft 202. DISCLOSURE OF THE INVENTION [0011] As described above, the problem of the conventional assembling type of camshaft wherein the shaft is press-fitted into a shaft hole of the cam piece by using an interference is that an outside surface of the shaft and an inside surface of the cam piece may be damaged while the cam piece moves to a predetermined press-fitting position on the shaft, so that press-fitting strength of the shaft and the cam piece may be deteriorated. [0012] Accordingly, it is an object of the present invention to solve the aforesaid problems and to provide a camshaft and an assembling method thereof wherein press-fitting surfaces suffer no damage during the assembling step so that press-fitting strength is not deteriorated. [0013] The present invention is an assembling type of camshaft comprising: a cam piece having a shaft hole; and a shaft to be press-fitted into the shaft hole of the cam piece; wherein a press-fitting groove and a penetration groove are respectively formed to extend in an axial direction in an inside circumferential surface of the shaft hole of the cam piece; a press-fitting tooth is formed to extend in the axial direction partially in an outside circumferential surface of the shaft; and the press-fitting tooth is adapted to be press-fitted into the press-fitting groove in the axial direction and to pass through the penetration groove in the axial direction. [0014] According to the above feature, since the press-fitting groove of the cam piece and the press-fitting tooth of the shaft are press-fitted to each other, press-fitting strength in a rotation direction may be enhanced. Thus, it is unnecessary to increase the interference. In addition, residual stress can flee to the penetration groove. Thus, deterioration of fatigue strength may be inhibited. [0015] Preferably, a plurality of press-fitting teeth is formed at regular or odd intervals in a circumferential direction of the outside circumferential surface of the shaft, a plurality of press-fitting grooves and a plurality of penetration grooves are respectively formed at regular or odd intervals in a circumferential direction of the inside circumferential surface of the shaft hole of the cam piece, correspondingly to an arrangement of the plurality of press-fitting teeth, and the plurality of press-fitting teeth is adapted to be press-fitted into the plurality of press-fitting grooves in the axial direction together and to pass through the plurality of penetration grooves in the axial direction together. In the case, the press-fitting strength in a rotation direction may be enhanced more. In addition, the residual stress can flee to the penetration groove more effectively. [0016] For example, the press-fitting manner between the plurality of press-fitting teeth and the plurality of press-fitting grooves may be an involute spline manner wherein the press-fitted area (contact line) follows an involute curve. In the case, the contact surface of the cam piece and the shaft is stable. Thus, generation of looseness (backlash) may be remarkably inhibited. [0017] Alternatively, the press-fitting manner between the plurality of press-fitting teeth and the plurality of press-fitting grooves may be a serration manner wherein the press-fitted area (contact area) forms a serration plane. In the case too, the contact surface of the cam piece and the shaft is stable. Thus, generation of looseness (backlash) may be remarkably inhibited. [0018] Preferably, the number of press-fitting grooves is a multiple of twelve, the press-fitting grooves are formed at regular intervals in the circumferential direction of the inside circumferential surface of the shaft hole of the cam piece, the number of penetration grooves is also a multiple of twelve, the penetration grooves are also formed at regular intervals in the circumferential direction of the inside circumferential surface of the shaft hole of the cam piece. Such a cam piece may be widely used for respective engine shafts of a three-cylinder engine, a four-cylinder engine, a six-cylinder engine and an eight-cylinder engine. [0019] In addition, the present invention is an assembling type of camshaft comprising: a plurality of cam pieces each of which has a shaft hole; and a shaft to be press-fitted into the shaft holes of the plurality of cam pieces; wherein a press-fitting groove and a penetration groove are respectively formed to extend in an axial direction in an inside circumferential surface of the shaft hole of each cam piece; a plurality of press-fitting-tooth parts is formed at regular or odd intervals in the axial direction in an outside circumferential surface of the shaft, each of the plurality of press-fitting-tooth parts having a press-fitting tooth extending partially in the axial direction; and the press-fitting tooth is adapted to be press-fitted into the press-fitting groove in the axial direction and to pass through the penetration groove in the axial direction. [0020] According to the above feature, since the press-fitting groove of each cam piece and the press-fitting tooth of the shaft are press-fitted to each other, press-fitting strength in a rotation direction may be enhanced. Thus, it is unnecessary to increase the interference. In addition, residual stress can flee to the penetration groove. Thus, deterioration of fatigue strength may be inhibited. [0021] Preferably, each of the plurality of press-fitting-tooth parts has a plurality of press-fitting teeth formed at regular or odd intervals in a circumferential direction of the outside circumferential surface of the shaft, a plurality of press-fitting grooves and a plurality of penetration grooves are respectively formed at regular or odd intervals in a circumferential direction of the inside circumferential surface of the shaft hole of each cam piece, correspondingly to an arrangement of the plurality of press-fitting teeth, and the plurality of press-fitting teeth is adapted to be press-fitted into the plurality of press-fitting grooves in the axial direction together and to pass through the plurality of penetration grooves in the axial direction together. In the case, the press-fitting strength in a rotation direction may be enhanced more. In addition, the residual stress can flee to the penetration groove more effectively. 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