Road to All-Electric Vehicle Concept
The electrification process aims at replacing other sources of energy with electrical energy. The goal is justified with better energy savings, smaller and simpler systems, better controllability, including herein safety, and convenience functions impossible to imagine before.
Conventionally, only 2-8% of a vehicle’s total power output has gone toward powering accessories through other energy sources. Advanced accessories require more energy that may not be possible to be driven out of the engine w'ith current means. There is a justified need for high voltage batteries with more storage capacity. Such batteries are also charged from an alternator, and can level off load peaks so that better utilization of the power distribution system occurs.
The second trend required by electrification is the increase in the dc bus voltage. Since the load power is evidently increased with more and more loads, the current through wires and associated loss can be kept at bay with an increase of the dc bus voltage. Until a full conversion is implemented, modern automotive systems employ dual systems, w'ith both 12 V and 48 V distribution dc buses. For instance, 2018 Audi A8, Audi SQ7 TDI, Porsche Panamera, and Bentley Bentayga, employ both 12-V and 48-V systems inter-connected with a dc/dc converter.
Due to the increase of the dc bus voltage, motors used within the chassis applications are rated at higher power levels than the body systems (previously grouped as mechatronics). Higher installed power means more possible loss, and it is justified to have advanced control through microcontrollers and PWM converters. A good control means understanding the dynamics of the overall system and applying principles of modern digital control, maybe with state-space based equations. Hence, this chapter also includes some examples of the dynamic modeling of electromechanical systems used in chassis applications.
FIGURE 6.1 Drum brakes.
6.2 BRAKE SYSTEMS 6.2.1 Drum Brakes
From the beginning, motor vehicles were equipped with brakes. Traditionally, a brake is a mechanical device that inhibits motion by absorbing energy from the motor vehicle. It is used for slowing or stopping a moving vehicle, most often accomplished with friction, converting the vehicle’s kinetic energy into heat energy. There are two major types of brakes, drum brakes and disk brakes. Improvements are possible w'ith the assistance of electric power systems, and their operation is studied herein.
Old cars w'ith drum brakes do not need an electric power assist. A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating cylinder-shaped part called a brake drum. Drum brakes are still often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Figure 6.1 illustrates a drum brake system.