Page 162 - Understanding Automotive Electronics

2735 | CH 5 Page 149 Tuesday, March 10, 1998 11:10 AM

THE BASICS OF ELECTRONIC ENGINE CONTROL 5

Figure 5.1
Chassis
Dynamometer

FPO

Government test proce- A chassis dynamometer is a test stand that holds a vehicle such as a car or
dures use a chassis dyna- truck. It is equipped with instruments capable of measuring the power that is
mometer to simulate delivered at the drive wheels of the vehicle under various conditions. The
actual driving conditions vehicle is held on the dynamometer so that it cannot move when power is
in a controlled environ- applied to the drive wheels. The drive wheels are in contact with two large
ment. rollers. One roller is mechanically coupled to an electric generator that can
vary the load on its electrical output. The other roller has instruments to
measure and record the vehicle speed. The generator absorbs all mechanical
power that is delivered at the drive wheels, and the horsepower is calculated
from the electrical output. (746 watts of electrical output equals 1
horsepower.) The controls of the dynamometer can be set to simulate the

UNDERSTANDING AUTOMOTIVE ELECTRONICS 149