Automotive Electricity: Electric Drive

Chapter 2

Basic Definitions ¹

2.1. Basic concepts

2.1.1. Basics of automotive energy

Most of the energy introduced into a vehicle is lost during transfers (friction, heat, pumping). Manufacturers continue to explore a number of possibilities for reducing these losses.

To talk about energetic concepts, we need to talk about efficiency.

Efficiency is the ratio of energy used with respect to the work involved in setting the vehicle in motion. It directly affects the consumption: the greater the efficiency, the lower the fuel consumption of the car.

– Let us examine how energy in a car is reduced.

When energy is introduced into an engine, only 30% remains when it comes to setting the wheels in motion. There are, throughout the process, losses which lower the efficiency. We estimate that 30% of energy is lost in the form of heat from the engine, approximately 30% leaves in the exhaust gas and 10% is dissipated by mechanical friction and driving the accessories (water pump, air-conditioning, etc.).

On arrival, the remaining 30% are reduced slightly further by the mechanical efficiency of the gear box and the transmissions.

Some of these losses are used to provide other services: the heat released by the cooling system is thus used for heating the cabin, the heat released through the exhaust supports the post-treatment mechanisms.

– Each transformation has its own efficiency.

The total efficiency of an engine (equal to 0.3 in the best cases) is the relationship between the energy supplied ...