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Turbocharging is significantly changing design and control strategies for Diesel and gasoline engines. This paper will review new advances in the turbocharger speed measurement. Until recently, the highly accurate and fast turbocharger speed data, based on the physical speed sensor signal, has been mainly used to safely decrease conservative safety margins for turbocharger speed and surge limits. In addition to significantly increasing power and low end torque, new generation sensor technology is providing new opportunities to utilize turbocharger speed data.

On downsized turbocharged engines, turbo speed is correlated with maximum engine airflow and therefore with maximum engine power. To ensure safe operation in the field, auto makers introduce significant engineering margins to the turbocharger maximum speed limit. Physical turbo speed sensors provide one way to reduce this engineering margin, but are not appropriate for some applications. An accurate mathematical estimation of turbocharger speed using virtual sensor can help reduce these margins, therefore increasing available power. This paper examines the best turbo speed estimation accuracy that can be achieved using a given set of production engine sensors. “Best” is defined in a minimax sense as the smallest turbo speed error interval achievable assuming the worst case combination of sensor and actuator errors and plant parameter mismatch.