Cardan shafts and cardan shaft lines - Homokinematic mechanisms
|Publication Date:||1 August 2003|
|ICS Code (Shafts):||21.120.10|
Basic principles and terms
This guideline will be concerned solely with Cardan shafts and Cardan shaft lines which contain universal joints. Cardan shafts consist of a drive shaft, a universal joint 1), an intermediate shaft, another universal joint and an output shaft. Cardan shaft lines have more than two universal joints. When installed in machines and vehicles Cardan shafts and Cardan shaft lines are supported in bearings. Such arrangements represent multiple universal-joint mechanisms. When one universal-joint mechanism is concerned and its input and output shafts run in bearings, this is referred to as a single universal-joint mechanism.
The transmission ratio in the single universal-joint mechanism is not constant. This means that an incoming, temporally constant rotary movement results in an uneven rotary movement of the output shaft. In order to ensure a constant transmission ratio (homokinematic) between the driving and driven shafts several universal joints must be linked together to form multiple universal-joint mechanisms, and here special geometric assembly conditions (homokinematic conditions) must be satisfied. If the homokinematic conditions are not met, a constant input motion results in uneven, periodic rotary movements, which can interfere with a downstream work process. In addition, not only excited torsional and flexural vibrations but also wear on force closed components of a drive train will arise.
However, even when Cardan shafts or Cardan shaft lines do comply with the homokinematic conditions, vibrations may still occur, such as those, for example, resulting from the uneven rotational movement of intermediate shafts.
The aim of this guideline is to outline from the kinematic point of view the possibilities for connecting universal-joint mechanisms in series and to describe the conditions for a homokinematic transmission of movement between the driving and driven shafts of Cardan shafts and Cardan shaft lines.