Modeling Torque Converter Characteristics in Automatic Drivelines: Lock-up Clutch and Engine Braking Simulation

A torque converter, which is a hydrodynamic clutch in automatic transmissions, transmits power from the engine shaft to the transmission shaft either by dynamically multiplying the engine torque or by rigidly coupling the engine and transmission shafts. The torque converter is a critical element in the automatic driveline, and it affects the vehicle’s fuel consumption and longitudinal dynamics. This paper presents a math-based torque converter model that is able to capture both transient and steady-state characteristics. The torque converter is connected to a mean-value engine model, transmission model, and longitudinal dynamics model in the MapleSim environment, which uses the advantages of an acausal modeling approach. A lock-up clutch is added to the torque converter model to improve the efficiency of the powertrain in higher gear ratios, and its effect on the vehicle longitudinal dynamics (forward velocity and acceleration) is studied. We show that the proposed model can capture the transition from the forward flow to the reverse flow operations during engine braking or coasting. The simulation results also show that the engine braking phenomenon (due to the flow reversal) can effectively assist the braking system to slow down the vehicle.