Abstract
A simple and cost-effective approach to connect the sprocket wheels or belt pulleys of the engine´s auxiliaries drive system to the crank-shaft is fastening the parts using a central bolt. In this case, load transmission is carried out exclusively by the friction among the parts´ frontal contact surfaces. Consequently, such connections are typically dimensioned according to the torque load and the governing coefficient of friction. The auxiliaries´ increasing power demands involve much higher loads on such connections which may lead to severe failures, such as relative motions between the timing-sprocket and the crank-shaft. In order to understand and avoid those problems, the transmission behaviour of the contact surfaces has been investigated by means of analytical, experimental, and finite-element analyses. As shown in this contribution belt and chain forces lead to additional bending loads and shear forces in the frictional contacts that reduce the transferable torque dramatically. The "torque-only" dimensioning approach neglects these loads and, therefore, underestimates the required clamp load of the bolt. Theoretical considerations lead to a new analytical calculation model that allows the calculation of required axial pre-tension force bolt taking the additional bending and shear load components into account. As a result, the connections can now be dimensioned precisely avoiding both critical failures and unnecessarily high safety factors.
Keywords: Crankshaft, Auxiliary Drive, Bolted Joints, Torque Transmission, Transverse Shear Forces, Bolt Pre-Tension, Friction, Creeping