A Soft Piezo Mechanical Hydraulic Actuator with its Liquid Stiffness Identification and its Control*

The CO2 emissions of an internal combustion engine are directly proportional to the fuel consumption. The use of the fully variable valve control to reach the most efficient gas exchange of the engine is an option to reduce CO2 emissions. This paper deals with an alternative actuator solution based on an aggregate device consisting of a piezoelectric, mechanical and hydraulic actuation. The aggregate device realises a soft actuator. In mechanical systems hard actuators are more and more replaced by soft ones which present some advantages in terms of efficiency. Nevertheless, problems of control, because of a more complex dynamics of the actuator due to a higher order of the mathematical model of the actuator, arise. The softness of the actuator is realised by using two strategic mechanical springs and a hydraulic part which works as a displacement ratio. It is known that in piezo actuators, big forces but small displacement can be available. The hydraulic displacement ratio is used for a possible ”soft solution” to adapt force and displacement. The conception of the actuator and control simulation results are shown.