This invention is concerned with an assembled camshaft and, in particular but not exclusively, with an assembled camshaft suitable for use in operating the valves of an internal combustion engine.

Traditionally, camshafts have been cast in one piece but it is well-known to manufacture an assembled camshaft by forming an elongated shaft, forming a plurality of cam elements each having a hole therethrough in which the shaft can be received, and mounting said cam elements on said shaft at predetermined fixing points spaced along the shaft and at predetermined orientations relative to a longitudinal axis of the shaft. Various methods are known for securing the cam elements to the shaft and for ensuring driving connections between the shaft and the cam elements. For example, it is known to provide the shaft as a tube which is expanded by internal pressure into intimate engagement with the cam elements. Such methods require the application of high pressures to ensure a driving connection.

It is an object of the present invention to provide an improved method of manufacturing a camshaft which avoids the danger of splitting the cam elements without requiring close tolerances.

The invention provides a method of manufacturing a camshaft comprising forming an elongated shaft, forming a plurality of cam elements each having a hole therethrough in which the shaft can be received, and mounting said cam

elements on said shaft at predetermined fixing points spaced along the shaft and at predetermined orientations relative to a longitudinal axis of the shaft, characterised in that the shaft is formed so that, at least along a length thereof which includes said fixing points and an end of the shaft, it does not extend radially from the longitudinal axis of the shaft further than a first predetermined distance except that, at said fixing points, the shaft is formed with projections which extend radially to a second, greater, predetermined distance from said longitudinal axis, said projections at each fixing point being arranged in a plurality of circumferentially-spaced groups, and in that each cam element is formed so that the bounding surface of said hole is further radially from a longitudinal axis of said hole than said second predetermined distance except that the cam element is formed with projections which extend into said hole so that they reach a radial distance from the longitudinal axis of the hole which is less than said second predetermined distance but greater than said first predetermined distance, the projections of the cam element being arranged in a plurality of circumferentially-spaced groups which can pass through the gaps between the groups of projections of the shaft, and in that the method also comprises aligning the longitudinal axis of the hole in each cam element with the longitudinal axis of the shaft, orientating the cam element so that its projections are aligned with spaces between the groups of projections of the shaft, moving the cam element along the shaft until it is adjacent to its intended fixing point, turning the cam element to its predetermined orientation at which the projections of the shaft and the cam element are aligned with spaces between the projections of the cam element and the shaft, respectively, and moving the cam element on to its fixing point with intermeshing of at least some of the projections of the shaft and the cam element.

In a method in accordance with the invention, the cam elements, which may have one or more cam surfaces, can be easily mounted on the shaft and the projections ensure a driving connection.

Preferably, for ease of manufacture, the projections are in the form of longitudinally-extending splines.

The cam elements can be secured to the shaft (so that they do not move longitudinally) by any suitable means, eg adhesive, welding, crimping, or by heating said cam elements before they are mounted on said shaft so that they shrink into firm engagement with their fixing point. However, it is preferred that the projections of the shaft and each cam element are arranged to be an interference fit with one another. In order to reduce stress, said interference fit may be arranged to occur along flanks of the intermeshed projections.

The groups of projections on each fixing point of the shaft may be spaced at equal angles about the longitudinal axis of the shaft but, if desired, these spacings may be uneven.

Preferably, the number of groups of projections on each fixing point of the shaft is equal to the number of different orientations of the cam elements in the finished camshaft. Alternatively, different orientations may be achieved by intermeshing projections of each group only partially, ie some projections are not intermeshed. The groups on the shaft or on the cam elements may not have equal numbers of projections so that a large number of intermeshed orientations are possible.

There may be an equal number of groups of projections on each cam element as there are on each fixing point of

the shaft. Alternatively, however, one number of groups may be a multiple of the other, eg two and four.

Each group of projections of a cam element may contain one more projection than each group of projections on the shaft or vice versa. For example, each group on the shaft may have one projection ( the word "group" is used herein to mean one or more) and each group on the shaft may consist of two projections.

Where the cam elements are long, the projections thereon may be interrupted by a projection-free area which serves to relieve stress.

Other elements such as journals may be mounted on the shaft in the same manner as the cam elements.

The invention also provides a camshaft made by a method according to the invention.

There now follows a detailed description, to be read with reference to accompanying drawings, of a method of manufacturing a camshaft which is illustrative of the invention, and of an illustrative camshaft made by the illustrative method.

In the drawings:

Figure 1 is an end elevational view of a shaft of the illustrative camshaft;

Figure 2 is an end elevational view of a cam element of the illustrative camshaft;

Figures 3 and 4 illustrate successive stages of the illustrative method;

Figure 5 is a side elevational view, on a reduced scale compared to Figures 1 to 4, of a portion of the illustrative camshaft; and

Figure 6 is an enlarged view of projections of the shaft and cam element shown in Figures 1 and 2.

The illustrative method is a method of manufacturing the illustrative camshaft 10 which has cam elements 11 projecting at four predetermined orientations spaced at 90° intervals. The method comprises forming an elongated shaft 12 which may be solid as shown in Figure 1 or tubular. The shaft 12 is preferably formed from steel. The shaft 12 is formed so that, at least along a length thereof which includes longitudinally-spaced fixing points 14 (which have a slightly greater radius than the rest of the shaft and an end 16 of the shaft) it does not, except for projections 22 at the fixing points 14, extend radially from a longitudinal axis 18 of the shaft 12 further than a first predetermined distance 20 equal to the radius of the fixing points 14.

At the fixing points 14, the shaft 12 is formed with projections 22 in the form of longitudinally-extending splines. These projections 22 extend radially to a second predetermined distance 24 from the axis 18. The distance 24 is greater than the first predetermined distance 20. The distance 24 is the same for all the projections 22 so that the crests of the projections 22 lie on a cylindrical surface with a radius equal to the distance 24. Each fixing point 14 has identical projections 22 but the projections do not extend into the gaps between the fixing points 14.

At each fixing point 14, there are twenty projections 22 which are arranged in four circumferentially-spaced groups 26 with five projections 22 in each group 26. The

groups 26 are spaced at equal angles about the axis 18 so that the centre projections 22 of the groups 26 are spaced at 90° intervals. It should be noted that the number of groups 26 and their angular spacings are equal to the number of different orientations of the cam elements 11 in the finished camshaft 10 and their angular spacings.

The illustrative method also comprises forming a plurality of the cam elements 11. These can be formed by chill-casting, by a powder metallurgy process or by any other suitable method. Each cam element 11 has a hole 30 therethrough in which the shaft 12 can be received.

Each cam element 11 is formed so that the bounding surface of the hole 30 is further radially from a longitudinal axis 31 of the hole 30 than said second predetermined distance 24 except that the cam element is formed with projections 32 which extend into said hole 30. The hole 30 is cylindrical about the axis 31 except for the projections 32 with a radius greater than the distance 24. Thus, at points where there are no projections 32, the projections 22 of the shaft 12 will fit into the hole 30.

The projections 32 of the cam element 11 extend into the hole 30 so that they reach a radial distance 34 from the axis 31 which is less than said second predetermined distance 24 but greater than said first predetermined distance 20. Thus, when the axes 18 and 31 are coincident, the projections 22 and 32 overlap one another between the radial distances 20 and 24 from these axes.

The projections 32 are in the form of longitudinally- extending splines. There are twenty-four projections 32 which are arranged in four circumferentially-spaced groups 36 which each contain six projections 32. The groups 36 are spaced at equal angles about the axis 31 so that the central spaces between the projections 32 of the groups 36

are spaced at 90° intervals. The groups 36 are spaced so that the groups 26 of projections 22 of the shaft 12 can pass through the gaps between the groups 36. Also, the groups 36 can themselves pass through the gaps between the groups 26.

The illustrative method also comprises mounting the cam elements 11 on the shaft 12 at the fixing points 14 and at predetermined orientations relative to the axis 18. To do this, each cam element 11 is first moved to the end 16 of the shaft 12 and its axis 31 is aligned with the axis 18. The cam element 11 is orientated so that its projections 32 are aligned with the spaces between the groups 26 of projections 22 on the shaft 12 (the condition is shown in Figure 3) . The cam element 11 is now moved on to and along the shaft 12 which is possible as the projections 22 and 32 do not foul one another.

The cam element 11 is moved along the shaft 12 until it is adjacent to its intended fixing point 14 (the first element 11 goes to the point 14 most remote from the end 16 and so on) . Then, with the projections 32 over a portion of the shaft 12 away from the fixing point 14, the cam element 11 is turned to its predetermined orientation at which the projections 22 are aligned with spaces between the projections 32, and the projections 32 are aligned with spaces between the projections 22 (this condition is shown in Figure 4) . The cam element 11 is then moved on to its fixing point 14 with intermeshing of the projections 22 and 32.

Once in position on its fixing point 14, a cam element 11 can be driven by rotation of the shaft 12 with the projections 22 and 32 transmitting the drive.

In order to secure the cam element 11 against moving off its fixing point in a longitudinal direction, the cam

element is secured to the shaft 12 by arranging that the projections 22 and 32 are an interference fit with one another. This means that the cam element has to be forced on to its fixing point 14 and, to assist this, the leading edge of each fixing point tapers inwardly as shown at 39. The interference fit is illustrated in Figure 6 where it can be seen that the projections 32 have flat tops 38 and the projections 22 have flat tops 40. The "valleys" between the projections 22 and 32 have concavely-curved bottoms. The projections 32 fit tightly in the spaces between the projections 22 and vice versa with tight engagement on the flanks of the projections. However, the flat tops 38 and 40 prevent engagement near the bottoms of said valleys so that the stress created does not become excessive.

The illustrative method depends on the fact that the projections (22 and 32) are arranged in groups (26 and 36) so that an element can pass a fixing point (14) in certain orientations and then be turned to bring its projections (32) into intermeshing engagement with the projections (32) of its own fixing point (14) .