Page 221 - Understanding Automotive Electronics

2735 | CH 6 Page 208 Tuesday, March 10, 1998 1:10 PM

6 SENSORS AND ACTUATORS

Figure 6.16
Coolant Temperature
Sensor

FPO

SENSORS FOR FEEDBACK CONTROL

The sensors that we have discussed to this point have been part of the
open-loop (i.e., feedforward) control. We consider next sensors that are
appropriate for feedback engine control. Recall from Chapter 5 that feedback
control for fuel delivery is based on maintaining the air/fuel ratio at
stoichiometry (i.e., 14.7:1). The primary sensor for fuel control is the exhaust
gas oxygen sensor.
Exhaust Gas Oxygen Sensor

Recall from Chapter 5 that the amount of oxygen in the exhaust gas is
used as an indirect measurement of the air/fuel ratio. As a result, one of the
most significant automotive sensors in use today is the exhaust gas oxygen
(EGO) sensor. This sensor is often called a lambda sensor from the Greek letter
lambda (λ), which is commonly used to denote the equivalence ratio:
( air/fuel)
λ = ------------------------------------------------------------
( air/fuel at stoichiometry)

Figure 6.17
Typical Coolant
Temperature Sensor
Circuit

FPO

208 UNDERSTANDING AUTOMOTIVE ELECTRONICS