Effect of pump selection on fuel economy in a dual clutch transmission vehicle

Positive displacement pumps are used in automotive transmissions to provide pressurized fluid to various hydraulic components in the transmission and also lubricate the mechanical components. The output flow of these pumps increases with speed, almost linearly, but the flow requirements often saturate at higher speeds resulting in the excess flow draining back to the sump. This represents a parasitic loss in the transmission leading to a loss in fuel economy. To overcome this issue, variable displacement pumps have been used in the transmission, where the output flow is reduced by controlling the displacement of the pump. The use of these pumps in automatic transmissions, has resulted in better fuel economy as compared to some types of fixed displacement pumps. However, the literature does not fully explore the benefits of variable displacement pumps to a specific type of transmission namely, dual-clutch transmission, that has different pressure & flow requirements than an epicyclic gear-train. This paper presents an analysis on the effect of pump selection on fuel economy in a five speed dual clutch transmission of a commercial vehicle. Models of the engine, transmission & vehicle are developed along with the models of two different types of pumps: a fixed displacement gerotor pump and a variable displacement vane pump. The models are then parameterized using experimental data and the fuel economy of the vehicle is simulated on a standard driving cycle. The results suggest that the fuel economy benefit obtained by the use of the variable displacement pump in dual clutch transmissions is comparable to that of automatic transmissions.