Page 328 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

3
310 Automobile mechanical and electrical systems

frequency of which increases as the car comes nearer to the obstruction,
becoming almost continuous as impact is imminent. Some cars have ‘all-round’
obstacle avoidance and also use the car speakers in a way such that the sound
comes from the direction of the obstacle.
The units fi tted in the rear bumper as shown in Fig. 3.108 transmit a radio signal
and also receive the reply if the signal bounces off a nearby object. The time it
takes to receive the signal tells the system the distance.

3.4.4 Cruise control

Cruise control is the ideal example of a closed loop control system. The purpose
of cruise control is to allow the driver to set the vehicle speed and let the
system maintain it automatically. The system reacts to the measured speed of
the vehicle and adjusts the throttle accordingly. The reaction time is important
so that the vehicle’s speed does not feel to be surging up and down. Other
Defi nition facilities are included such as allowing the speed to be gradually increased or
decreased at the touch of a button ( Fig. 3.109 ). Most systems also remember
Closed loop control system
A system in which the output of the the last set speed. They will resume this speed at the touch of a button. The
system has a direct effect on the main switch switches on the cruise control and this, in turn, is ignition controlled.
input because of a feedback loop. Most systems do not retain the speed setting in memory when the main switch
has been turned off. Operating the ‘set’ switch programs the memory, but this
normally will only work if conditions similar to the following are met:

Vehicle speed is greater than 40 km/h.
●
Vehicle speed is less than 120 km/h.
●
Change of speed is less than 8 km/h/s.
●
Automatics must be in ‘drive’.
●
Brakes or clutch are not being operated.
●
Engine speed is stable.
●
Once the system is set, the speed is maintained to within 1–2 mph until it is

deactivated by pressing the brake or clutch pedal, pressing the resume switch
or turning off the main control switch. The last set speed is retained in memory
except when the main switch is turned off. If the cruise control system is required
again, then either the set button will hold the vehicle at its current speed or
the resume button will accelerate the vehicle to the previous set speed. When

Figure 3.109 Cruise control switch