TECHNOLOGY CASE STUDY -

CRUISE CONTROL

CHRISTOPHER ALLISON

Mr Tait 5th Year Techy

Christopher Allison
 Introduction
Cruise control systems maintain the speed of a car at a level set by the driver,
without having to use the accelerator.

The main developer of cruise control was Ralph Teetor, who was a mechanical
engineer and had his first patent for the design of a speed cruise control device in
1945. Teetor was inspired to invent cruise control one day while riding with his
lawyer. The lawyer would slow down while talking and speed up while listening.
This rocking motion so annoyed Teetor that he was determined to invent a speed
control device. It took him a while to make it suitable for commercial use and was
first used in 1958 in a Chrysler.

Cruise Control is more common in American manufactured cars than European

cars as the roads are straighter and longer. There is less need to break in America
on the long journeys causing a cruise control system in a car to become more
effective. But luxury European cars like BMW, Mercedes-Benz and Audi are
developing adaptive cruise control which uses radar to follow the car in front
while maintaining a safe distance from the car. Safety precautions are necessary
to ensure the system fully works. Features like a manual override for the driver by
accelerating or breaking to avoid immediate danger need to be available.

This project focuses on the manual setting of cruise control not the adaptive CC;
this cruise control is a very good example of a feedback control system.

Analysis and Description

Throttle Position Sensor
Steering
Wheel
Controls Allison
Christopher

Vehicle
Speed Cruise Control Vacuum Throttle
Clutch
Pedal
Switch

Brake
Pedal
Switch

The cruise control system has a number of inputs, a control computer, and a
mechanical output connecting to the engine throttle. The block diagram above
shows the general arrangement of a cruise control system. Most updated cruise
control systems have a feedback loop from the throttle position. The feedback
signal is generated by the speed of the car and fed into the cruise control system
through the vehicles speed signal input.

Driver Interface & Inputs

The controls for cruise control have to be easy to use whilst driving and are
usually within range of the driver’s hands when steering.

The cruise control system actually has a lot of functions other than controlling the
speed of your car. For instance, the cruise control pictured below can accelerate
or decelerate the car by 1 mph with the tap of a button. Hit the button five times to
go 5 mph faster.
The system pictured below has five buttons: On, Off, Set/Accel, Resume and Coast.
Also the brake and clutch pedal are fitted with limit switches that detect pressure
and will automatically disable the cruise control.

Christopher Allison
 The on and off buttons don't actually do much. Hitting the on button does
not do anything except tell the car that you might be hitting another button soon.
The off button turns the cruise control off even if it is engaged. Some cruise
controls don't have these buttons; instead, they turn off when the driver hits the
brakes, and turn on when the driver hits the set button.
 The set/accel button tells the car to maintain the speed you are currently
driving. If you hit the set button at 45 mph, the car will maintain your speed at 45
mph. Holding down the set/accel button will make the car accelerate; and on this
car, tapping it once will make the car go 1 mph faster.
 If you have recently disengaged the cruise control by hitting the brake
pedal, hitting the resume button will command the car to accelerate back to the
most recent speed setting.
 Holding down the coast button will cause the car to decelerate, just as if you
took your foot completely off the gas. On this car, tapping the coast button once
will cause the car to slow down by 1 mph.
 The brake pedal and clutch pedal each have a switch that disengages the
cruise control as soon as the pedal is pressed, so you can shut off the cruise
control with a light tap on the brake or clutch.

Mechanical Arrangement

The cruise control system controls the speed of your car the same way a person
does - 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
Christopher Allison
the engine takes in. When the cruise control system is active and is controlling the
speed the accelerator pedal will move just like if the driver was pressing the
accelerator pedal down.

To Accelerator
Pedal

To Vacuum
Actuator

One of the cable is connected to the accelerator pedal, and the other two the
vacuum actuator. When the cruise control is engaged, the actuator moves the
cable connected to the pivot, which adjusts the throttle; but it also pulls on the
cable that is connected to the accelerator pedal - this is why the accelerator pedal
moves up and down when the cruise control system is engaged.

Christopher Allison
 The electronically-controlled vacuum actuator
that controls the throttle
Many cars use actuators powered by engine vacuum to open and close the throttle.
These systems use a small, electronically controlled valve to control the vacuum in
a diaphragm.

Cruise Control Software

The cruise control system is a small microcontroller computer that is normally

found under the hood or behind the dashboard of the car. It connects as scene in
the previous section to the throttle control as well as various other sensors. The
diagram below shows the inputs and outputs of a cruise control system.

A cruise control system will accelerate aggressively to the desired speed without
overshooting, and then maintains that speed with little deviation no matter how

Christopher Allison
 much weight is in the car, or big the gradient of the hill that it is
climbing/descending. 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. The simplest control system to keep the car’s speed at a
constant set level would be an on/off system. If the car’s speed was less than the
set speed, full throttle (off) would be applied until the actual speed was the same as
the set speed. At this point the throttle would be closed (off) and the car would
begin to decelerate. The cycle would constantly repeat with the speed fluctuating
above and below the desired speed.

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. As the speed increases towards the set speed the throttle will
start to gradually close. The effect of this is that there is less fluctuation in the
speed will be reduced.

PID control
Most cruise control systems use a control scheme called proportional-integral-
derivative control (PID control). This is the most technologically advanced system
as it takes in three main factors.
 The integral of speed, is when the speed is increased by a minimal amount
so to compensate with not accelerating it takes into account the distance the car
would have travelled if it was going at the desired speed in comparison with
distance it has done at the actual speed. It takes this distance into account and will
increase the speed to compensate for this lost distance when needed.
 The derivative of speed is the quickness the car responds to acceleration the
car will experience at hills, i.e. opening/closing the throttle earlier.
 The proportional control of the error described above.
A PID control system uses these three factors -- proportional, integral and
derivative, calculating each individually and adding them to get the throttle
position.
These factors all give PID control a huge advancement from the other cruise
control systems giving it the smoothest and finest control; this is why it is used in
all aspects of engineering, from industrial control through to aviation.

Christopher Allison
Adaptive Cruise Control

Adaptive cruise control uses forward-looking radar, installed behind the grill of a
vehicle, to detect the speed and distance of the vehicle ahead of it. Adaptive cruise
control is similar to conventional cruise control in that it maintains the vehicle's
pre-set speed. However, unlike conventional cruise control, this new system can
automatically adjust speed in order to maintain a safe distance between vehicles in
the same lane in front of it. If the lead vehicle slows down, or if another object is
detected, the system sends a signal to the engine or braking system to decelerate.
Then, when the road is clear, the system will re-accelerate the vehicle back to the
set speed.

Social, Economic and Environmental Effects

Social: +++With the introduction of cruise control the driving experience has
become more relaxed especially for long motorway drives where cruise control is
most effective. This is a positive factor as it means that drivers will become less
stressed and so can concentrate on other aspects of driving i.e. special awareness

Christopher Allison
of other cars around. So this will reduce car accidents. Also there will be less
cases of sore feet from pressing the throttle for long periods of time.

---But, drivers might take this relaxation as a negative and become less involved
with their driving as they are not concentrating on accelerating and braking. This
will increase the danger of drivers falling asleep and more accidents.

+++ When adaptive cruise control is introduces it will ensure that there is always
a safe following distance between you and the car in front. This is positive as it
will take into account reaction times when bad visibility and braking distance.

Economic: Jobs are being created for the research and development of adaptive
cruise control but nothing has changed within the instalment of the electronics as
it is all automated with robots. So no jobs have been lost due to the introduction of
cruise control. Car manufacturing is constantly changing from the old mechanical
engineering model to new electronically filled cars. This means that more of the
manufacturing of components is done overseas.

Environmental: As the car will be keeping at a more constant speed there will be
lower fuel consumption from constantly revving and burning fuel. So it will cost
the driver less. Therefore the impact on the environment will positive as less fuel
will be needed and used up, so less pollution given off. The electronics of cruise
control is made up of lots of circuit boards and components so will no doubt have
a small negative effect on the environment from the raw materials used up.

Conclusion
This report on cruise control is about the system and the main ideas about how it
works. Cruise control is fitted to many American cars and the luxury European
cars which makes the long motorway journeys more relaxable for the driver. The
electronics of cruise control is linked up to the cars main computer during the
main assembly line.

Cruise control is an example of a control system with Inputs, Outputs, Feedback

Loops and software processing. The inputs and transducers are quite simple but
the control software was very challenging to understand i.e. PID control.

Christopher Allison
Cruise Control is an example of the many new and innovative electronic ideas
which are being introduced for cars to increase the safety and relaxation of the
driving experience. Cruise control has a positive impact on driving with a benefit
to the environment.

BIBLIOGRAPHY

WEB PAGES

 www.howstuffworks.com
 http://www.motiontrends.com/ford/taurus_technology
 www.google.com/images
 http://www.cs.cmu.edu/~ModProb/CC.html
 http://www.antony-anderson.com/cruise/2-cc.htm
 www.visteon.com
 http://www.benefitcost.its.dot.gov

Christopher Allison