Page 288 - Understanding Automotive Electronics

2735 | CH 8 Page 275 Tuesday, March 10, 1998 1:19 PM

VEHICLE MOTION CONTROL 8

cylinder chamber is nearly at manifold vacuum level. Consequently, the piston
will move against the restoring spring and cause the throttle opening to
increase. As a result the engine will produce more power and will accelerate the
vehicle until its speed matches the command speed.
It should be emphasized that, regardless of the actuator type used, a
microprocessor-based cruise control system will:
1. Read the command speed.
2. Measure actual vehicle speed.
3. Compute an error (error = command – actual).
4. Compute a control signal using P, PI, or PID control law.
5. Send the control signal to the driver electronics.
6. Cause driver electronics to send a signal to the throttle actuator such that
the error will be reduced.
An example of electronics for a cruise control system that is basically
analog is shown in Figure 8.10. Notice that the system uses four operational
amplifiers (op amps) as described in Chapter 3 and that each op amp is used for

Figure 8.10
Cruise Control
Electronics
(Analog)

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 275