Date of Award

2020

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Mahdi Shahbakhti

Advisor 2

Darrell Robinette

Committee Member 1

Jeremy Worm

Abstract

With the advancement in the automotive technologies, the customer scrutiny on the ride comfort of automobiles has come to light. Vehicle drivability is one of the important aspects that defines the ride comfort for a vehicle. Drivability of a vehicle is a qualitative measure and may differ from person to person, however, researches have come up to highlight a few parameters that can categorize the drivability performance of a vehicle into good or bad for a majority of the targeted audience. One of those parameters include shuffle, which is defined as the longitudinal oscillations that occurs in the drivetrain when a sudden demand for torque rise or drop is made. Another such parameter is the sluggishness in the delivery of torque at wheels against the requested torque by the driver. This can exist due to the shift in the dynamics during the drivetrain operation from locked torque converter clutch to slipping torque converter clutch.

This work addresses both the drivability related issues, namely, shuffle and torque lag mentioned in the preceding para. Initially, the shuffle oscillations generated in a vehicle are analyzed when subjected to a sudden positive to positive driver torque tip-in request. Further, a pre-compensator and feedback controller based control scheme is designed to damp those shuffle oscillations while keeping the torque delivery response fast. This control approach shapes the actuator torque (i.e., an engine or an e-motor) in such a way that the desired response is achieved. Next, the problem of sluggish torque response at wheels due to slipping of the torque converter clutch is addressed. Initially, a model-based feedforward and feedback controller is developed to control the actuator torque such that when the torque converter slips, an extra compensatory torque from the actuator is applied. This compensation torque ensures that the torque response at the turbine and succeeding driveline components up till the wheels is maintained as desired. However, the actuator has some physical limitations in terms of the maximum magnitude and rate of the torque delivery. So, at some instances, the torque request generated by the controller may not be feasible for the actuator to follow. This problem is addressed when another controller, based on model predictive control approach, is proposed. This controller is based on the approach that continuously updates the controller of the torque delivery of the actuator. The controller solves an optimisation problem over the defined constraints of the actuator and plant, and further finds the most feasible response for the actuator to follow within its defined operating range. Later, A comparison between the two controllers showed model predictive controller to be 15.3% better in terms of the propeller shaft torque response than the feedforward and feedback controller, for the problem under discussion.

Available for download on Monday, August 09, 2021

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