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This article presents the latest developments of a research project aimed at studying the evolution of the transmissibility curve of dry clutches for automobile uses during the life of the component. In particular, the instruments developed for the experimental measurement of this characteristic are illustrated, separating the effects of thinning of the disc by wear from fatigue of the clutch pushplate mechanism. The instruments developed were used to collect a large quantity of experimental data which are presented and discussed.

The paper presents an experimental study to investigate the relationships among diaphragm spring clutch transmitted torque, thermal phenomena during clutch engagement and clutch wear. The work describes the development of a test bench presented by the Authors in a former paper. The original techniques were developed to measure the desired magnitudes and to develop the experimental methodology to investigate the relationships. The main results were obtained considering different operating conditions, dynamics of thermal phenomena and clutch wear.

The paper discusses a fuzzy supervisor for ensuring co-operation between clutch and engine control reference values during standing starts and gear shifts in a vehicle equipped with a servoactuated transmission. A mathematical model of the powertrain was developed to identify the optimal control strategy for different clutch friction characteristics and operating conditions. The powertrain is modeled as a six d.o.f. dynamic system, consisting of the engine and flywheel assembly, clutch disk, mainshaft and countershaft, transmission shaft with differential and hub, front wheels, tires and car body with rear wheels. The engine is described by its experimental mechanical characteristic. The model considers lumped parameters, and springiness of the shafts is neglected. A large number of simulations was carried out in order to identify control strategies which minimize dissipated power and judder and prevent engine stalling during standing starts.

A crucial problem in designing a servoactuated manual transmission is posed by the clutch torque variations which depend on operating conditions with equal clutch pedal position and clutch slip. An experimental study of the phenomena that determine torque variations can be particularly useful in coping with this problem. To this end, the authors developed a powertrain test bench. The bench makes it possible to measure the main magnitudes (disc temperature, clutch slip, clamp load and clutch disc displacement) which can influence transmitted torque. Test bench layout is described. Some experimental results are presented and discussed, with particular attention to the problems connected with clutch controller design.