COMPOSITE CAMSHAFT FOR INTERNAL COMBUSTION ENGINES AND A METHOD FOR ITS MANUFACTURE

Abstract: Composite camshaft (1) for internal combustion engines, comprising a support shaft (2) carrying a series of sintered cam members (3) in which through-holes (3c) are formed in their lobe parts (3b) defining the cam profiles. The shaft (2) is tubular and the cam members (3) are coupled to the shaft by hot driving.

Description: The present invention relates in general to camshafts for internal combustion engines. More particularly, the invention concerns a composite camshaft of the type comprising a support shaft carrying a series of sintered cam members, each having an annular part for shrinking them onto the shaft, from said annular part projects a lobe part defining the cam profile. In camshafts of the above-mentioned type, disclosed for instance in EP-A-159.811, the uneven radial thickness of the cams around the support shaft due to their lobed configuration, may result in a concentration of radial stresses in their interference fit on the shaft, with risks of breakage thereof. In order to avoid the above inconvenience, the camshaft according to the invention is characterised by the features set forth in claim 1. By virtue of this characteristic, each cam member has an almost uniform radial thickness around the support shaft, which allows it to be an interference fit on the shaft without the danger that the cam member might break as a result of concentrations of radial stresses. Secondary features of the camshaft according to the invention are defined in sub-claims 2-4, and the process for the manufacture thereof is recited in claim 5. The camshaft according to the invention can be manufactured in a relatively simple and cheap manner and, since the correct surface finishing and the required tolerance values for the cam members are obtained as a result of the coining, no supplementary finishing is needed after assembly of the cam members. The invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, axial-sectional view of a composite camshaft according to the invention, and Figure 2 is a side elevational view taken on the arrow II of Figure 1, and Figures 3 and 4 are two cross-sectional views taken on the lines III-III and IV-IV of Figure 1. In the drawings, a composite camshaft for internal combustion engines for motor vehicles is generally indicated 1. The camshaft 1 is constituted by a support shaft 2 formed from a ground steel tube, and a series of cam members 3 coupled torsionally to the shaft 1 in axially spaced positions. A toothed drive pulley 4 is also keyed to one end of the support shaft 2. The cam members 3 are formed by hot sintering of metal powders and are subsequently subjected to a coining treatment so as to give the correct surface finish and ensure that the dimensions fall within the designed tolerances. Each cam member 3 has a conventional shape defined by an annular part 3a for coupling to the shaft 2 and a lobe part 3b projecting radially and defining the cam profile. According to the invention, a through-hole 3c is formed in the lobe part 3b of each cam member 3 and, in the example illustrated, has a profile geometrically similar to that of the lobe part 3. The hole 3c is disposed at a distance from the support shaft 2 corresponding substantially to the outer radius R of the annular part 3a and has a radially inner edge 3d with a shape having a radius of curvature substantially corresponding to the radius R. Thus, each cam member 3 is formed with an almost uniform thickness around the support shaft 2, which avoids dangerous concentrations of radial stresses arising in these members 3 upon coupling to the support shaft 2. In effect, the cam members 3 are formed so as to achieve a certain interference (normally between 4 and 7 hundredths) between the annular part 3a and the support shaft 2, and their coupling to the shaft 2 is achieved by hot driving. The assembly of the camshaft 1 is thus relatively simple and cheap and does not require further grinding or surface finishing. The drive pulley 4 is also made by sintering and is keyed onto the shaft 2 by hot driving with the use of respective angular references, not illustrated in the drawings. This allows keying errors due to assembly clearances caused by the presence of mechanical coupling members, such as bolts, pins, keys, etc., to be avoided. Naturally, the details of realisation and forms of embodiment of the invention may be varied widely with respect to that described and illustrated, without thereby departing from the scope of the present invention.

Claims: Composite camshaft for internal combustion engines, comprising a support shaft (2) carrying a series of sintered cam members (3) each having an annular part (3a) for shrinking them onto the shaft, from said annular part projects a lobe part (3b) defining the cam profile, characterised in that a single through-hole (3c) is formed in the lobe part (3b) of each cam member (3) and is disposed at a distance from the support shaft (2) corresponding substantially to the outer radius (R) of the annular coupling part (3a) of the cam member (3), so that each cam member has an almost uniform radial thickness around the support shaft, and in that the said through-hole (3c) has a radially inner curved edge (3d) with a radius of curvature centered on the shaft axis and corresponding substantially to the outer radius (R) of the annular coupling part (3a). Shaft according to Claim 1, characterised in that the through-hole (3c) has a profile geometrically similar to that of the lobe part (3b). Shaft according to any one of the preceding claims, characterised in that the support shaft (2) is tubular and the cam members (3) are coupled to the support shaft (2) by hot driving. Shaft according to any one of the preceding claims, characterised in that the cam members (3) are subjected to a coining treatment after sintering. Method for the manufacture of a composite camshaft for internal combustion engines, constituted by a support shaft (2) carrying a series of sintered cam members (3) each having an annular part (3a) for shrinking them onto the shaft, from said annular part extends a lobe part (3b) defining the cam profile, characterised in that the cam members (3) are subjected to a coining treatment after sintering, in that a single through-hole (3c) is formed in the lobe part (3b) of the cam members (3) at a distance from the axis of the annular coupling part (3a) corresponding substantially to the outer radius (R) of the annular part (3a) so that each cam member has an almost uniform radial thickness around the support shaft, the said through-hole (3c) being formed with a radially inner curved edge (3d) having a radius of curvature centered on the shaft axis and corresponding substantially to the outer radius of the annular coupling part (3a), and in that the cam members (3) are coupled to the support shaft (2) by a hot shrinkage fit.

Inventors: BURGIO DI ARAGONA, ANTONIO
Applicants: FIAT AUTO S.P.A.
Application year: 1987
Main classification: F16H53
IPC codes: F16H53, F01L1