Abstract
The main enabler for chassis controls development in HIL and SIL environment are CAE models that predict accurate dynamic behavior and run in real time (for SIL, real time requirement is not there, but it is still desirable for the models to run fast and with fixed time step solvers). Automatic transmission models with clutch to clutch shifting capabilities that can run in real time, are then a requirement for chassis controls development in HIL environment. Existing automatic transmission models are either too simplified and do not incorporate clutch to clutch shifting capabilities or are too detailed and do not run in realtime. The present work shows the development of automatic transmission models that incorporate clutch to clutch shifting capabilities and run in real time.The transmission plant model was developed using a modified Lagrangian approach that extracts the independent degrees of freedom and solves for them. The traditional Lagrangian method for automatic transmissions, involves taking the inverse of an (n+p) x (n+p) matrix, where n is the number of states and p is the number of constraints, and integration of n states. In the modified Lagrangian method, only an (n-p) x (n-p) matrix needs to be inverted and integration of n-p independent states needs to be carried out. The clutches were modeled as simple friction elements. A simplified model of the torque converter was incorporated. The transmission controller implements clutch to clutch controls using separate torque and inertia phases and includes torque converter clutch slip controls which replicate the behavior of real transmission controllers. All upshifts and downshifts, except power off downshifts were modeled. The plant and controller were integrated in Simulink and runs with the ode14x solver with a fixed time step of 1 millisecond. The behavior of the integrated model was compared to a simplified transmission model, developed using an internal tool of GM. The behavior compares well with the simplified transmission model, with the added benefit that the clutch torques can now be obtained during the shift events - something which was not possible with the simplified transmission model.