Primer on Automobile Fuel Efficiency and Emissions - Pollution Probe

call parasitic loads on the crankshaft; they effectively steal power from the engine that would otherwise be delivered
to the drivetrain and the wheels. Thus, the engine must burn more fuel to maintain power sufficient to drive the
automobile. You may have noticed that when you turn on the A/C, your car appears to lose a bit of power, requiring
you to press further down on the accelerator pedal. Even when the A/C is off, it still draws some power from the
crankshaft, wasting fuel. Energy lost to parasitic loads can be minimized by disconnecting them from the crankshaft
and running them on electricity from a battery (although energy from the engine is still required to charge
the battery). This is because electrically powered accessories utilize energy more efficiently, they need less energy
to run, and they can be turned off when not in use. For example, some newer vehicles use electrical power steering
so that there is not a continual power draw from the engine, and instead draw electricity only as needed. Higher
voltage systems (42-volt and higher) can support even more loads (A/C, in particular) to run off electric power
than can conventional 12-volt systems.
Moving towards higher power electric architecture provides significant new opportunities for fuel saving systems.
For example, more electric power can support features such as Idle-Off and Launch Assist, in which the engine
shuts off when the vehicle brakes (thus conserving fuel). An electric motor then helps to get the vehicle quickly
moving again when the driver presses the accelerator. Without the extra electric power to run the motor, the driver
would need to wait until the engine restarted to get moving again. These features require additional electrical
power, which requires a battery capable of storing more electric energy (i.e., more electric charge). The battery can
discharge energy (i.e., supply electricity) to the vehicle’s systems as needed, but must also be recharged with available
energy wherever possible. This energy can be partly supplied by the engine, but additional power can also be
retrieved during braking using Regenerative Braking technology. In regenerative braking mode, a vehicle uses the
electric motor to help reduce speed. As the driver applies the brakes, the electric motor is engaged and turned
in reverse, acting as a generator that charges the battery. Resisting this motion, the motor applies a counter-force
to the wheels slowing the vehicle. This differs from conventional braking that slows the vehicle via friction pads,
converting the kinetic energy of the moving vehicle into heat, which is then lost to the surrounding air. Thus,
some of the energy normally lost during conventional braking is retrieved and stored in vehicles with regenerative
braking systems; this stored energy can then be used to power the vehicle.
55 Chapter 3 | Increasing Fuel Efficiency by Improving Automobile Technology