Neither under- nor over-running
when in an angled state |
The constant velocity joint transfers the torque from the axle-drive (sprung mass) to the drive wheel (unsprung mass) uniformly. Unlike universal joints,
during rotation there is neither under- nor over-run when compared with the drive components. Because of the uniform transmission, even when the constant velocity joints are angled, they are also called homo-
kinetic joints. Moreover, length compensation is also possible. These joints are found on the final drive side in axle drive shafts, and with rear-wheel drive also on the wheel drive shafts.
| Low friction-loss, high torque transmission |
The constant velocity joint is also called a tripod joint because the external casing has three large, long gaps evenly distributed around the perimetre, in which three needle-bearing rollers can move axially. In the
above figure1, it can be seen how the left shaft ends in the joint with three short spindle stubs on which the rollers are arranged. In figure 2, the left shaft is cut open so that the needle bearings in the rollers can be
seen. These joints are also similarly found in ball joints, only that the ball-trajectories here also run lengthwise.
High mechanical stress, task
sharing between the joints |
In figure 3, one can see the complete front axle drive shaft with internal tripod joint and wheel-side ball-joint, in the enlargement even the serrated ring of the ABS sensor can be
seen. The maximum diffraction angle amounts to about 20 ° and the length compensation, above all necessary because of the vehicle suspension springing, to approx. 30 mm. Because of the high load demands,
the surfaces gliding on each other are hardened. Constant velocity joints are permanently lubricated with grease. Their protective rubber collars (figure 4) should be regularly checked for damages to avoid the escape
of grease and the penetration of dirt which will cause unnecessarily fast wear and tear. 09/08
