Test Vehicle for Regenerative Braking Emulation
Examensarbete för masterexamen
The recent increase in global environmental concern drives the development of fuel saving vehicle technologies. A way to save fuel is to recuperate kinetic energy into a usable form for propulsive purposes, which is known as regenerative (regen) braking. However, regen braking also influences the vehicle stability and the driver‟s perception of the brake system. The impact of the human factor imposes the use of a test vehicle during development of regen braking strategies. The production of a regen braking test vehicle was initiated by SAAB as part of their Hybrid Vehicles and eAWD project and conducted by this master thesis. The main use of the test vehicle is to analyze the limitations of additive regen braking, where additional electric motor brake torque is applied on top of the standard brake torque. Additive braking allows the original brake system to be retained, saving production costs while giving fuel consumption improvements. Also, it facilitates the transition process to hybrid vehicles. The perfect test vehicle for regen braking would possess one electric motor for each wheel and the necessary ancillaries. However, this vehicle project would have an intrinsic high level of packaging complexity, cost and engineering time. To overcome these negative aspects, another concept was conceived, in which a second hydraulic brake system is controlled to emulate electric motors. Electric motors are emulated in the sense that the friction brake wheel torque is equal to that produced by an electric motor. This concept consists of extra calipers clamping the original rotors, an Electro-Hydraulic Brake (EHB) unit delivering brake pressure and a dSpace onboard computer running the test program. Simulink models of a generic electric driveline were developed to emulate the behavior of regen braking. The models include the battery, electric motor, power converter, and motor controller. These models calculate the wheel torque to be applied, which needs to be converted to a pressure value for the EHB unit. A brake model was developed to calculate the pressure, taking into account the temperature which affects the friction coefficient between the pad and disc. A hardware-in-the-loop rig was used for calibration of the brake model. Additionally, torque measuring wheels were installed on the test vehicle to calibrate the software and to validate the performance of the vehicle. The result of this thesis is an easy-to-use test vehicle which can conduct experiments dealing with additive regen braking, as well as any brake based vehicle system. For engineers to get started quickly, an example case study and a user manual are provided. The result of the research utilizing the test vehicle will be seen in the next generation SAAB hybrid vehicles.
Transport , Farkostteknik , Transport , Vehicle Engineering