A model-based design approach for an optimal electro-hydraulic system within automatic transmissions

Fast and precise actuation plays a key role to reach challenging drivability targets of an automatic transmission. Electro-hydraulic actuation systems are mainly used to fulfill the demanding requirements in state-of-the-art applications. Additionally to control tasks, the electro-hydraulic system is responsible for the cooling and lubrication of gears, clutches and other parts of the transmission. The focus of this article is to optimize a hydraulic layout design, satisfying various demands from lubrication, cooling, transmission efficiency as well as production costs. The presented approach analyses the different requirements in detail and derives corresponding rules for possible hydraulic layouts. A standard automotive test cycle is used to illustrate and quantify the design considerations of the different topologies. Additionally, worst-cases scenarios are considered to take into account cases that are not covered explicitly in the provided test cycle. The system costs and the average power consumption of the hydraulic layout are shown to be the two essential optimization criteria finally left for the design decision. With respect to essential optimal criteria a corresponding multi-objective optimization is performed and the optimal solutions are discussed.