Page 1 of 11 12PFL - 0362 Modeling Torque Converter Characteristics in Automatic Driveline s: Lock -up Clutch and Engine Braking Simulation Hadi Adibi Asl Ph.D. Candidate , Mechanical and Mechatronics Engineering, University of Waterloo Nasser Lashgarian Azad Assistant Profes sor, System s Design Engineering, University of Waterloo John McPhee Professor, System s Design Engineering, University of Waterloo Copyright © 201 2 SAE International ABSTRACT A torque converter, which is a hydrodynamic clutch in automatic transmissions, tra nsmits 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 affect s the vehicle’s fuel consumption and longitudinal dynamics. This paper presents a math -based torque converter model that is able to ca pture both transient and steady -state characteristics. The torque converter is connected to a mean -value engine model, tr ansmission 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 rat ios, 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. INTRODUCTION The approach of powertrain modeling with physical ly meaningful parameters and equations, which is called physics -based modeling , gives a detailed view of powertrain components and operations. The most important benefit of using physics -based models is to tr ack the effects of the parameters on the system’s operation. For instance, t he schematic diagram in Figure 1 shows different approaches to the modeling of a torque converter . As indicated in Figure 1, the torque converter model includes more physical parameters by approaching fro m the left to the right of the diagram. For instance, the most complex approach is using computationa l fluid dynamics (CFD) analysis which accurately simulates the interactions between the torque converter fluid and mechanical elements. The level of comp lexity must be defined based on the applica tion of the model, and there is a tradeoff between the model accuracy and the simulation time . In this study, the math -based torque converter model is used along with a mean -value engine model, gearbox, and vehicl e longitudinal dynamics to evaluate the torque converter characteristics in t he automatic driveline. Since our focus is towards design and control applications , the model must be able to capture both transient and steady -state characteristics while having fairly fast simulation response. Page 2 of 11 Figure 1: Level of complexity in torque converter modeling The torque converter i ncludes three rotating elements: the pump (impeller), the turbine, and the stator ( Figure 2). The pump is attached to the engine shaft, which is called the prime mover, and the turbine is connected to the transmission shaft. The st ator, which is placed between the pump and the turbine, redirects the returning fluid from the turbine to t he pump. The one -way clutch is used along with the stator to either lock or unlock the stator depending on the fluid direction