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12PFL - 0362
Modeling Torque Converter Characteristics in Automatic Drivelines:
Lock-up Clutch and Engine Braking Simulation
Hadi Adibi Asl Ph.D. Candidate, Mechanical and Mechatronics Engineering, University of Waterloo
Nasser Lashgarian Azad Assistant Professor, Systems Design Engineering, University of Waterloo
John McPhee Professor, Systems Design Engineering, University of Waterloo
Copyright © 2012 SAE International
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.
The approach of powertrain modeling with physically 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 track
the effects of the parameters on the system's operation. For instance, the 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 from the left to the right of the diagram. For instance, the most complex approach is using computational fluid dynamics
(CFD) analysis which accurately simulates the interactions between the torque converter fluid and mechanical elements.
The level of complexity must be defined based on the application 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
vehicle longitudinal dynamics to evaluate the torque converter characteristics in the automatic driveline. Since our focus is towards design and control applications, the model must be able to capture both transient and...