2. The cruise control system has a lot of functions other than controlling
the speed of your car. The cruise control pictured below can accelerate
or decelerate the car by 1 Mph/Kmph with the tap of a button. Hit the
button five times to go 5 mph faster. There are also several important
safety features -- the cruise control will disengage as soon as you hit
the brake pedal, and it won't engage at less speeds.
CONVENTIONAL CRUISE CONTROL
OPERATION
3. Cruise Control Acceleration and Deceleration
• The cruise control system controls the speed of
your car the same way you do -- by adjusting the
throttle position. But cruise control actuates the
throttle valve by a cable connected to an
actuator, instead of by pressing a pedal. The
throttle valve controls the power and speed of
the engine by limiting how much air the engine
takes in.
• Many cars use actuators powered by engine
vacuum to open and close the throttle. These
systems use a small, electronically-controlled
valve to regulate the vacuum in a diaphragm. This
works in a similar way to the brake booster, which
provides power to your brake system.
4. Controlling the Cruise Control
• The brain of a cruise control system is a small computer that is normally
found under the hood or behind the dashboard. It connects to the throttle
control seen in the previous section, as well as several sensors. The
diagram below shows the inputs and outputs of a typical cruise control
system.
• A good cruise control system accelerates aggressively to the desired speed
without overshooting, and then maintains that speed with little deviation
no matter how much weight is in the car, or how steep the hill you drive
up. Controlling the speed of a car is a classic application of control system
theory. The cruise control system controls the speed of the car by adjusting
the throttle position, so it needs sensors to tell it the speed and throttle
position. It also needs to monitor the controls so it can tell what the
desired speed is and when to disengage.
5. • The most important input is the speed signal; the cruise control system does a lot
with this signal. First, let's start with one of the most basic control systems you
could have -- a proportional control.
• In a proportional control system, the cruise control adjusts the throttle
proportional to the error, the error being the difference between the desired
speed and the actual speed. So, if the cruise control is set at 60 mph and the car
is going 50 mph, the throttle position will be open quite far. When the car is going
55 mph, the throttle position opening will be only half of what it was before. The
result is that the closer the car gets to the desired speed, the slower it
accelerates. Also, if you were on a steep enough hill, the car might not accelerate
at all.
• Most cruise control systems use a control scheme called proportional-integral-
derivative control.
• The integral of speed is distance.
• The derivative of speed is acceleration.
6.
7. Adaptive Cruise Control (ACC)
• Adaptive Cruise Control (ACC) technology automatically adjust the vehicle
speed and distance to that of a target vehicle.
• ACC uses a long range radar sensor to detect a target vehicle up to 200
meters in front and automatically adjusts the ACC vehicle speed and gap
accordingly.
• ACC automatically decelerates or accelerates the vehicle according to the
desired speed and distance settings established by the driver.
• As per standard cruise control the driver can override the system at any
time.
• This is achieved through a radar headway sensor, digital signal processor and
longitudinal controller.
8. Two types of ACC
• Radar-Based System :
Three overlapping radar-beams (76-77kHz)
Detects moving object up to 120 m
work in poor weather conditions
• Laser-Based System (lidar) :
less expensive and easier to package
light beams are narrower than water droplet and snowflakes
9. • ACC is an extension of conventional cruise control systems. An ACC system is a driver convenience
feature designed to maintain a set following distance from the vehicle ahead. ACC is not a collision
warning or avoidance system.
• An ACC system is designed to assist the driver and is not a fully independent driving system.
• As with conventional cruise control system manual inputs from the driver, both to accelerator and
brake, take priority over the ACC system.
