Serpentine belt pulley drives are often used in front end accessory drive of automotive engine. The accessories resistant torques are getting higher within new technological innovations asstater-alternator, and belt transmissions are always asked for higher capacity. Two kindof tensioners are used to maintain minimum tension that insure power transmission and minimize slip: dry friction or hydraulic tensioners. An experimental device and a specifictransmission error measurement method have been used to evaluate the performancesof a generic transmission by determining the pulleyCbelt slip for these two kinds of tensioner.
        Transmission error between pulleys, pulley/belt slip are deduced from pulley rotationangle measurements. Results obtained show that: the use of tensioner limits belt slipon pulleys, pulleyCbelt slip is reachable from transmission error measurement, belt nonuniform characteristics are responsible of low frequency modulations of transmissionerror.

        Multi ribbed (serpentine) belt transmission are often used in the industry machinery to transmit power. Another field ofapplication concerns the Front End Accessory Drive of automotive engine, it recently asks for better performances in order toallow the development of new technological innovations as starterCalternator integration in the transmission. Resistant torquesof the driven accessories are getting higher and design solutions have to be found in order to prevent pulleyCbelt slipand belt fatigue. Because of, serpentine belt constitution based on cords and rubber, long belt spans and operating conditions (engine acyclism, fluctuating torques), the following phenomena occur during FEAD operation: longitudinal and transversebelt span vibrations, pulleyCbelt slip. In these transmissions, two kinds of tensioners can be used in order to reduce vibrationand insure sufficient belt tension to transmit power and to avoid slipping. They differ in the way damping is generated: oneis called dry friction tensioner, the other uses a hydraulic damper . Both are equipped with a spring (compression ortorsion). Many works have conducted numerical analysis on the dynamics of serpentine belt drives, they aimed atdetermining belt tension fluctuations, pulley rotations, belt longitudinal and transverse vibrations. PulleyCbelt slip has beeninvestigated both numerically and experimentally by Gerbert [9] on v-belt in steady state operating conditions. Transmissionerror has been studied for synchronous agriculture belt drives [11,12] and for gear transmissions as in [6]. The work presented here is anexperimental analysis that aims at determining pulleyCbelt slip from the transmission error measurement in the case of a multi ribbed belt generic transmission. A test bench has been designed where belt pulley rotation angles are determined fromoptical encoder signals using a specific data acquisition system and process.