Sharon Liu

Optimal and robust control and estimation of linear paths to transition

Optimal and robust control theories are used to determine effective, estimator-based feedback control rules for laminar plane channel flows that effectively stabilize linearly unstable flow perturbations at Re = 10000 and linearly stable flow perturbations, characterized by mechanisms for very large disturbance amplification, at Re = 5000. Wall transpiration (unsteady blowing/suction) with zero net mass flux is used as the control, and the flow measurement is derived from the wall skin friction. The control objective, beyond simply stabilizing any unstable eigenvalues (which is relatively easy to accomplish), is to minimize the energy of the flow perturbations created by external disturbance forcing. This is important because, when mechanisms for large disturbance amplification are present, small-amplitude external disturbance forcing may excite flow perturbations with sufficiently large amplitude to induce nonlinear flow instability. The control algorithms used in the present work account for system disturbances and measurement noise in a rigorous fashion by application of modern linear control techniques to the discretized linear stability problem

A survey of today's CVT controls

For over one hundred years, the principle of continuously and infinitely variable transmissions (C/IVT) has eluded practical automotive utility. With the advent of durable materials, sophisticated electronic controls, and improved lubricants, a viable assortment of C/IVT powertrain systems with innovative ratio shift control strategies is now feasible. A few of these progressive system designs are described in this survey. Pertinent fundamental relationships of C/IVT powertrains are also discussed.

Adjoint-based system identification and feedforward control optimization in automotive powertrain subsystems

Tuning the response of automotive powertrain subsystems can both improve the performance and ease overall system integration in both conventional powertrains and innovative new powertrain designs. Existing control strategies for both the powertrain and its subsystems usually incorporate extensive feedforward maps because the systems of interest are nonlinear and difficult to model, operating ranges of interest are large, and maps are relatively inexpensive to implement. Augmenting or replacing such maps with dynamic feedforward control strategies based on predictive dynamic models can possibly provide significant performance improvements. The present work develops adjoint-based optimization approaches to: 1) identify the several unknown parameters of a nonlinear model of a powertrain torque converter and transmission using empirical data; and 2) based on this identified model, optimize the feedforward controls for a powertrain gear shift to achieve the desired shift characteristics. It is shown that the adjoint-based system identification procedure yields an accurate system model and that the adjoint-based control optimization procedure improves the anticipated system performance.

A phase and frequency locking loop for engine air-fuel ratio control

In the spirit of the recent articles in [5], featuring classical controls revisited, a phase-lock loop concept is applied to an automotive air-fuel ratio closed-loop control system. This classical solution is analyzed, simulated, and experimentally implemented in a vehicle. The results demonstrate that the automobile engine air-fuel ratio system can be controlled to robustly meet emissions and driving performance requirements by using a simple classical control methodology with feedback from the common switching oxygen sensor.