Assembled Shaft and Process for Production Thereof

The invention relates to an assembled shaft comprising a tubular member and driving or coupling elements attached to it, especially a camshaft or driveshaft, as well as a process for producing such a shaft. Camshafts and driveshafts are only given by way of example, other applications also being possible.

Camshafts produced in accordance with the above mentioned process have already been described (P 36 33 435.9). Like conventional single-part shafts, camshafts of this type are guided in friction bearings whose size is determined by the diameter of the shaft member whose cross section is determined by existing strength requirements. It goes without saying that with the same boundary conditions, i.e. especially with a pre-determined torque load, the outer diameters of shafts with a hollow tube member are usually larger than those of solid shafts. Apart from the strength of the tube itself, it is especially the seat surface required for a friction-locking fit of the driving or coupling elements on the tubular member which is decisive. A further aspect in determining the size of the tubular member is the required inner diameter which must be free for inserting a probe for connecting the tubular member and the driving elements.

A disadvantage of the above mentioned shafts is that, because of the size of their bearings, they have an undesirably high friction loss. Furthermore, the problem of bearing lubrication is not solved satisfactorily because for supplying the lubricating oil special measures have to be taken inside the shaft which increase production costs.

It is therefore the object of the present invention to provide an improved type of an assembled shaft and a process for producing assembled shafts which permits the cost-effective production of shafts which have a reduced friction loss and which, at the same time, have been freed from the above-mentioned disadvantages regarding lubrication. The object is achieved in that, in bearing regions, roller bearings with at least undivided outer bearing races with initially loosely slid-on driving or coupling elements are finish--assembled and that subsequently by hydraulically expanding the inside of the tubular member in portions, the driving or coupling elements are fixed exclusively outside the axial regions taken up by the roller bearings. The type of shaft in accordance with the invention makes it possible to produce camshafts supported in roller bearings and the like with reduced friction losses and without there occurring any lubrication problems while keeping costs at an acceptable level, which costs are largely determined by the simple production method of using roller bearings with undivided outer races. In a particularly advantageous embodiment, the tubular member itself is designed as the inner bearing race, and even prior to sliding on the driving elements and the bearings in an alternating sequence, the bearing race regions may be machined, hardened and polished.

The fact alone that these process steps may be carried out on a smooth tubular member saves considerable costs. Because of the small radial size of the bearings, for example in the form of needle bearings, conventional friction bearings may quite easily be replaced in the case of shafts produced in accordance with the present invention. The inventive method of excluding the region of the inner bearing race from being subjected to pressure for joining purposes is particularly important in this case where finish--machining takes place prior to assembly.

The tubular member does not, of course, have to be in one part, but it may also be provided in an assembled design consisting of individual tubular pieces and sleeves, as corresponding to the current state of the art.

FIG. 1 illustrates a preferred embodiment of an assembled shaft pursuant to the invention.

FIGS. 2-6 illustrate alternative embodiments of an assembled shaft pursuant to the invention.

FIG. 1 shows an inner tubular member 1 with individual thickened wall portions 2,3 onto which stepped sleeves 4,5 are slid which, with collar regions 6,7 with reduced diameters, engage underneath two driving elements 8,9 in the form of cams offset relative to each other by 90.degree.. An outer tubular member 10 has been slid onto the inner tubular member 1 between the sleeves 4,5 and is connected to it in a force-locking way by radially expanding the inner tubular member in the regions pre-determined by sealing rings as indicated. At the outer tubular member 10, there has been turned in a bearing track 11 which at the same time serves to axially secure needle bearings 12,13 arranged in two rows. These are held by an outer bearing race 14 whose inner diameter is smaller than the diameter of the driving elements 8,9 in their largest size. Underneath the raised cam portions the driving elements 8,9 comprise the apertures 15,16 for weight saving purposes.

While the invention has been illustrated and described as embodied in an assembled shaft and process for production thereof, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspect of this invention.