Analytical Models for Spring One-Way Clutch and Torsional Vibration Dampening Systems with Experimental Correlation

Among the alternatives for solving NVH (Noise, Vibration and Harshness) problems in automobiles, the alternator pulley has become one of the most promising alternatives in the Frond-End Accessory Drive (FEAD) of modern engines. The rigid pulley has evolved from a simple device whose only function is torque transmission to a system with much more complex functions. At this higher level of complexity, many innovative designs have been created, such as pulleys with overrunning function and pulleys with both One-Way Clutch (OWC) and vibration dampening functions, which are devices that require a high level of study in order to guarantee an adequate design of the system for each new application. This paper presents the steps taken in dimensioning two distinct types of springs: a clutch spring and a torsion spring, to be applied in alternator pulleys with OWC and vibration dampening systems. The method begins with preliminary dimensioning of the springs using analytic formulae, and then comparing these results to FE simulation and experimental tests of prototype pulleys. Known analytic equations for torsion spring dimensioning showed good coherence with experimental and Finite Element modeling results. However, existing analytic expressions for clutch springs were not representative of the FEA or test bench results, requiring new empirical formulation in order to obtain the desired correlation to the prototype and FEA results. An overall correlation of approximately 95% is obtained for the torque transmission capacity of the clutch spring. As for the torsion spring, the correlation was of 80% for its torsional stiffness, and of 90% for its angular deflection when limited by a given diameter.