Constant velocity joints

The cardan joint, described in the specialized article of this treatise, is used either as a unit if the break angle is low, or much more commonly as a pair, i.e. in a two-joint transmission with a symmetrical configuration in terms of both break angle and wedge angle, so that the driven shaft has, as far as possible, an angular speed constantly equal to that of the driving shaft.

These two arrangements have been used, in particular, to link the gearbox to the rear axle of rear-wheel drive vehicles. For heavy-duty vehicles, the only solution currently available is a transmission with two joints, one of which is sliding, possibly combined with one or two half transmissions.

When the so-called "front-wheel drive" passenger car became established, it was necessary to structure the link between the transaxle and the suspended, driven and steered wheels. When the front wheels are "unsteered", the wheel axle and the axle output shaft are almost parallel, and it would be possible to envisage a universal joint at each end of the drive shaft. However, as soon as the wheels are turned, the angle of the joint on the axle side hardly varies, whereas the angle of the joint on the wheel side increases. The result is a cyclic angular offset between the axle output shaft and the wheel shaft, resulting in cyclic acceleration and deceleration of the wheel at a frequency of twice per revolution; the existence of the differential in the front axle only complicates the situation. As a result, the vehicle shakes and mechanical components are subjected to unacceptable stress.

In addition, it is necessary to ensure, without any appreciable axial reaction, that the – transmission length variations due to suspension travels are largely eliminated – - something that splines on cardan joint transmissions do not do very well.

New solutions were therefore needed: the – fixed and – sliding constant velocity joints are designed to meet these different requirements, and their development has been closely linked to that of front-wheel drive; in addition to the agricultural sector, which uses this type of joint, other industries could also be users. After the historic Hooke joint (1664), we find closer to home the Clemens joint (1876), followed by the Delaunay-Belleville (1914), Retel (1922), Weiss (1924), Parvillée (1926), Fenaille (1926), Rzeppa (1927), Causan (1930), Glaenzer-Spicer (1934) and Orain (1962) patents.

Currently, with 45 million cars –, generally front-wheel drive – produced per year, the automotive market alone requires the manufacture of some 180 million constant velocity joints; other markets appear to be negligible. Under these conditions, specialized and reputed parts manufacturers such as GKN, with locations...