Abstract:
A camshaft  10  has alignment formations at one axial end for enabling the camshaft  10  to be correctly aligned with another component during assembly. In the invention, the alignment formations comprise two bores  18  of the same diameter but different depth.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the alignment of a camshaft with another component during assembly. 
     BACKGROUND OF THE INVENTION 
     The phasing of a camshaft in relation to an engine crankshaft is of critical importance to engine operation and it is important to be able to position the camshaft in a predetermined orientation during its assembly with other components such as the gear that forms part of its drive train. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a camshaft having alignment formations by means of which the camshaft can be supported, which formations additionally serve to enable the camshaft to be correctly oriented in relation to another component during assembly. 
     Preferably, means are provided at one axial end of the camshaft for driving the camshaft and the alignment formations are located at the opposite axial end of the camshaft. The means for driving the camshaft may conveniently comprise a collar formed integrally with the camshaft and a gear secured to the collar and meshing with a gear fitted directly to one end, preferably the flywheel end, of the crankshaft. 
     The alignment formations may suitably comprise two bores of the same diameter but different depth which are preferably located diametrically opposite each other. When two bores of the same diameter are used as alignment formations, they can be drilled using the same tool thereby simplifying the manufacture of the camshaft while still enabling the camshaft to be located in a unique angular position by the use of a jig having two prongs of unequal length. 
     According to a second aspect of the present invention, there is provided a method of assembling an engine having a camshaft with alignment formations by means of which the camshaft can be supported, which formations additionally serve to enable the camshaft to be correctly oriented in relation to another component during assembly, which method comprises the steps of mounting the crankshaft in the engine block, positioning the crankshaft with a predetermined orientation in the engine block, inserting the camshaft into the engine block, positioning the camshaft with a predetermined orientation in relation to the engine block with the aid of a jig engaging said alignment formations, placing a drive gear on the camshaft to mesh with a gear on the crankshaft while the camshaft and the crankshaft are held in their respective predetermined positions and securing the drive gear to a collar on the camshaft for rotation therewith. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be described further, by way of example, with reference to the accompanying drawing, in which: 
     FIG  1  is a exploded view of a camshaft, a camshaft drive gear and a thrust plate to retain the camshaft in an engine block, 
     FIG. 2 is a schematic perspective view of the camshaft of FIG. 1 mounted in an engine with the block omitted in the interest of clarity, and 
     FIG. 3 is a section through one end of the crankshaft of the engine shown in FIG. 2, showing the crank gear and the collar in more detail. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a camshaft  10  having cams  12  and support bearings  14  of larger diameter than the lobes of the cams  12 . The camshaft is designed to be slid into an engine block from one end. In the engine illustrated in FIG. 2, the camshaft is inserted from the back end of the engine but this is not essential. 
     The support bearing  14  at one end of the camshaft has two diametrically opposed bores  18  of the same diameter but different depths. The bores  18  can be used to support the camshaft and act as alignment formations as will be described in more detail below. 
     A collar  20  is formed on the other end of the camshaft  10  and a gear  22  is fitted to the collar  20  by means of bolts  24 . The relative orientation of the camshaft  10  and the collar gear  22  is important because the latter drives the camshaft  10  and meshes directly, as described below, with a gear on the crankshaft. In the illustrated preferred embodiment of the invention, a dowel pin  26  is used to ensure the alignment of the cog  22  and the collar  20  but this is not essential. In principle, if the crankshaft and the camshaft are exactly positioned during factory assembly with a predetermined orientation by means of a very precise jig, a dowel pin would not be needed because on alignment of the single marking of the crankshaft gear  42  with the two markings on the cam gear  22 , the bores in the gear  22  and the collar  20  would match perfectly. However, the provision of a dowel pin assists dismantling and reassembling the engine in a workshop not equipped with an accurate alignment jig. 
     The camshaft  10  is retained in the engine block by means of a thrust plate  28  secured to the engine block by bolts  30  that can be tightened even after the gear  22  has been secured to the collar  20  by insertion of a socket spanner through cut-outs  32  formed in the gear  22 . 
     As seen from FIG. 2, when the camshaft  10  is inserted in the engine block, the gear  22  meshes with a gear  42  that is directly mounted on the crankshaft  44 . The gear  22  also meshes with other cogs  48  and  50  that drive ancillary equipment of the engine, such as a fuel pump. 
     The crankshaft gear  42 , as better shown in the section of FIG. 3, is located behind a collar  46  that is mounted on the crankshaft at the rear end of the engine to receive a flywheel. The flywheel damps oscillations of the crankshaft and positioning the cam drive gear  22  at the rear of the engine in this way serves to reduce noise and wear. However, because the collar  46  has a larger diameter than the camshaft gear  42 , the gear  22  can only be mounted on the camshaft collar  20  when the camshaft is in situ. 
     The collar  46  needs to have a relatively large diameter to be able to receive the bolts for fixing the flywheel to it. The diameter of the camshaft gear  42  could be increased so that it would become equal to or even larger than the diameter of the collar  46 . However, then the centres of the crankshaft  44  and camshaft  10  would then either need to be moved further apart from each other, necessitating a totally different engine block casting, or one or more idler gears would be needed between the crankshaft gear  42  and the camshaft gear  22 , adding to the complexity of the engine. 
     In order to set the timing correctly, the crankshaft gear  42  has a single marking on the radial side of one of its teeth. If the crankshaft gear  42  and the collar  46  were to abut each other, then it would be impossible to see this marking. For this reason, as shown in FIG. 3, a space is left between the gear  42  and the collar  46 . Moreover, the collar  46  is formed with a chamfered edge on its side facing the gear  42  to improve visibility further. 
     The bores  18  in the camshaft  10  allow it to be picked up and correctly oriented by a jig having two prongs that engage in the bores. If the prongs are of different depth and they penetrate fully into the bores, then it is ensured that the camshaft can only be held in the jig in a unique orientation. 
     Lastly, one hole is used to feed back to the engine block any oil that has squeezed out of the tail end of the bushing oil feed, which improves bushing life. 
     The crank gear  42  is attached to the crankshaft  44  in the following manner. The gear  42  is first heated, pressed onto the crankshaft  44  and then cooled. As already mentioned, there is a single marking on the gear  42 , but none on the crankshaft  44 . To achieve correct orientation of the gear  42  on the crankshaft  44 , the crankshaft is positioned in a jig with a predetermined orientation, and then the gear is presented to the shaft again with a predetermined orientation by using a suitable tool. The crank gear  42  and the collar  46  are heated and pressed onto the crankshaft  44  separately because the force needed to push on the collar  46  is higher than that required to push on the gear  42  and the larger force could damage the gear  42 . 
     The thrust plate  28  could in principle be mounted on the engine block before the gear  22  is fitted to the camshaft  10 . This would obviate the need for the cut-outs  32  in the gear  22 . However, to be able to rotate and axially shift the camshaft  10  more easily during assembly, the bolts  30  are fastened only after the gear  22  has been attached to the camshaft  10 . 
     The sequence in which the elements are mounted in the engine block is therefore as follows. After the crank gear  42  and the collar  46  have been fitted to the crankshaft  44 , the crankshaft  44  is mounted onto the engine block. The camshaft  10  is slid into the engine block from the rear end of the engine, i.e. from the side of the flywheel. By using the bores  18  with different depths, the crankshaft is positioned with a predetermined orientation in the engine block. The gear  22  is then attached to the camshaft  10  with the line passing through the centres of the bores  18  pointing in a predetermined direction e.g. to the right. With such orientation, it is possible to insert the bolts  24  for attaching the gear  22  as the bores in the gear  22  and the collar  20  will overly each other. While sliding the cam gear  22  in place, it is assured that the single alignment marking on the crankshaft gear  42  is located between the two markings of the cam gear  22  in order to obtain the correct valve timing.