Application of Floating Pedal Regenerative Braking for a Rear-Wheel-Drive Parallel-Series Plug-In Hybrid Electric Vehicle with an Automatic Transmission

As the world continues to move further away from our reliance on fossil fuels, hybrid vehicles are becoming ever more popular. Braking is a system on both hybrid and normal vehicles that involves a significant amount of power and energy. A hybrid can recapture some of that energy using regenerative braking. In this thesis, a method is devised to blend hydraulic and regenerative braking in the most effective manner. A MATLAB Simulink model was built to simulate a parallel-series plug-in hybrid electric vehicle. The model allows for the implementation of a regenerative brake controller that utilizes floating pedal regen, custom shift logic, and brake pedal blended regen. The floating pedal controller activates regenerative braking when the driver releases the accelerator pedal. This is done by remapping the pedal based on vehicle speed, gear position, and wheel torques. The custom shift logic utilizes the motor rpm and efficiencies curves to determine when to shift the transmission. The brake pedal regen is added to the hydraulic braking based on brake pedal position. This regenerative brake controller can recharge the battery by 2% SOC during one deceleration event from 130 kph to 20 kph, while maintaining a comfortable deceleration rate less than 3m/sec^2

Predictive Approaches to Rear Axle Regenerative Braking Control in Hybrid Vehicles

We consider the problem of controlling the regenerative braking at rear axle in hybrid vehicles. In particular, thefocus of this work is the maximization of regenerative braking in cornering maneuvers on low friction surfaces. In such cases, excessive braking at the rear axle might induce instability.We present and compare two predictive control approaches,where the objective is maximizing the regenerative braking and distributing the friction braking at the four wheels, while (i) delivering the braking force requested by the driver, (ii) preserving vehicle stability and (iii) fulfilling system constraints (e.g., bounds on regenerative braking set by the hybrid powertrain).We present simulation results in combined braking andcornering scenarios, showing that the proposed approaches are able to distribute the requested braking at the four wheels in order to counteract undesired effects, on vehicle stability, introduced by regenerative braking

Mild Hybrid Electric Vehicles: Powertrain Optimization for Energy Consumption, Driveability and Vehicle Dynamics Enhancements

This thesis deals with the modeling, the design and the control of mild hybrid electric vehicles. The main goal is to develop accurate design tools and methodologies for preliminary system and component level analysis. Particular attention is devoted to the configuration in which an electric machine is mounted on the rear axle of a passenger car. The use of such a machine in parallel with the internal combustion engine allows one to exploit different functionalities that are able to reduce the overall fuel consumption of the vehicle. In addition, the indirect coupling between the thermal and the electric machine, realized through the road and not by means of mechanical couplers, together with the position of the latter in the overall vehicle chassis system, enables such an architecture to be efficient both from the energy recovery and the full electric driving point of view. Chapter 1 introduces the problem of fuel consumption and emissions reduction in the overall world context and presents the main hybrid architectures available. Chapter 2 is devoted to the study of the influence of the electric machine position in the powertrain regarding the regenerative braking potentialities concerned. The model considered for the analysis will be described on each of its subcomponents. The braking performance of the vehicle in electric mode is presented considering no losses in the electric powertrain (electric motor, battery, inverter). Chapter 3 is dedicated to the design of an electric machine for a rear axle powertrain. The specifications of such machine are optimized considering both the vehicle and the application under analysis. The design takes into account analytical techniques for the computation of electrical parameters (such as phase and DC currents) and the torque - speed map, as well as numerical ones for its thermal behavior. In Chapter 4 the electrical and thermal characteristics of the designed electric motor are implemented in the model presented in Chapter 2. The overall vehicle model is therefore used both to assess a simple torque split strategy between thermal and electric machine and to perform an optimal sizing of the battery considering all the limitations imposed by the electric powertrain (e. g. maximum currents, maximum temperatures). Chapter 5 makes a step forward and analyzes the different implications that the use of the rear axle electric motor to brake the vehicle has on the vehicle dynamics. Open loop analysis will present a degradation of the vehicle handling comfort caused by the introduction of an oversteering moment to the vehicle. Through the use of a simplified vehicle model, the introduced oversteering yaw moment is evaluated, while a control strategy based on a new stability detector will show how to find a trade off between handling comfort and regenerable energy. At last, Chapter 6 deals with the problem of longitudinal driving comfort. Drivelines and chassis are lightly damped systems and the application of an impulsive torque imposed by the driver can cause the vehicle longitudinal acceleration (directly perceived by the driver) to be oscillating and non smooth. A sensitivity analysis on a conventional powertrain is presented demonstrating which of the different components are more influential in the different modes of vibration, and possible solutions to improve the driveability are proposed. One of these relates to the use of the rear axle electric machine in order to give more responsiveness to the vehicle. Finally, concluding remarks are given in Chapter 7