On-line estimation of clutch pressures in hydraulically powered stepped automatic transmissions can be useful for on-line diagnostics or development of closed-loop transmission control to improve shift quality. This paper presents the development and implementation of a model-based sliding mode observer to provide on-line estimates of clutch pressures for the clutches involved in gear shifts. The estimation of transmission input torque (torque converter turbine torque), which is needed by the

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... server for accurate clutch pressure estimation but is not available, is also addressed here and implemented using an adaptive sliding mode observer. The resulting observers are validated via off-line simulation tests, as well as on-line tests at different sampling frequencies on a test vehicle, in order to demonstrate observer performance and establish the feasibility of the approach.