Adaptive Cruise Control Report

Adaptive Cruise Control

TABLE OF CONTENTS

1) INTRODUCTION 3

2) CRUISE CONTROL 4

i. PRI NCIPLE 4

ii. WORKING 6

3) ADAPTIVE CRUISE CONTROL 7

i. OVERVIEW 7

ii. WHY ADAPTIVE CRUISE CONTROL 8

iii. COMPONENTS OF ADAPTIVE CRUISE CONTROL 9

iv. WORKING 10

v. TYPES 12

vi. APPLICATIONS 14

vii. FEATURES OF ADAPTIVE CRUISE CONTROL 16

viii. COLLISION REPAIRS 16

ix. CAUTION 17

x. ADVANTAGES 18

xi. LIMITATIONS 18

4) CONCLUSION 19

5) REFERENCE 20

1Department of Mechanical Engineering | VVCE, Mysore


LIST OF FIGURES

FIGURE 1 - CRUISE CONTROL LEVER 4

FIGURE 2 - CRUISE CONTROL WORKING SYSTEM 6

FIGURE 3 - WITHOUT ACC 7

FIGURE 4 - ACC BUTTONS ON STEERING WHEEL 7

FIGURE 5 - COMPONENTS OF ACC 9

FIGURE 6 - CONCEPT OF ACC 10

FIGURE 7 - WITH ACC 12

FIGURE 8 - LASER BASED SENSOR 12

FIGURE 9 - RADAR BASED SENSOR 13

FIGURE 10 - DISPLAY OF DISTRONIC SYSTEM 15

FIGURE 11 - DISPLAY OF DISTRONIC SYSTEM 15



INTRODUCTION

Mentally, driving is a highly demanding activity - a driver must maintain a high level

of concentration for long periods and be ready to react within a split second to

changing situations. In particular, drivers must constantly assess the distance and

relative speed of vehicles in front and adjust their own speed accordingly.

Those tasks can now be performed by Adaptive Cruise Control (ACC) system, which

is an extension of the conventional cruise control system.

Like a conventional cruise control system, ACC keeps the vehicle at a set constant

speed. The significant difference, however, is that if a car with ACC is confronted

with a slower moving vehicle ahead, it is automatically slowed down and then follows

the slower vehicle at a set distance. Once the road ahead is clear again, the ACC

accelerates the car back to the previous set cruising speed. In that way, ACC

integrates a vehicle harmoniously into the traffic flow.



CRUISE CONTROL

Cruise Control is a system which is capable of maintaining the speed of a car at a

desired level. The conventional the basic systems are capable of taking over the

throttle once the driver activates Cruise Control and sets the desired speed.

In most of the cars, the cruise control buttons are mounted on the steering wheel, just

like the audio control buttons, whereas in older car models a separate lever is

provided similar to the ones used for windscreen wipers and headlights. The basic

ones are often equipped with four buttons: on, off, resume and coast whereas the

newer current systems are offered with one or two controls only but are way too

convenient. Once enabled the new ones only ask the driver to set the maximum and

minimum cruising speeds after which it takes over the controls and the same gets

disabled as soon as the driver presses the throttle, brake or clutch pedal.

This feature is very useful for long drives where the roads are fairly good and high

speed cruising is possible. The driver can set the car’s cruise control system close to

the speed limit of the road and just relax with his foot off from the accelerator and

brakes, the car will maintain the speed set on the cruise control system using the

arrangements (car’s computers, activators etc.) which are provided in the car.

PRINCIPLE

Figure 1: Cruise control lever



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. 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 speeds less than

25 mph (40 kph).

The system pictured below has five buttons: On, Off, Set/Accel, Resume and Coast. It

also has a sixth control - the brake pedal, and if your car has a manual transmission

the clutch pedal is also hooked up to the cruise control.

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 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.



WORKING

Figure 2: Cruise control working system

The modern systems constitute of a computer control system, several inputs signals,

vacuum actuator and throttle position sensor. The main computers takes the input

from the starring wheel controls, vehicle speed signals etc. and sends these to a

vacuum actuator through a vacuum valve. The actuator in turn is connected to the

throttle valve by a cable and the throttle valve has a position sensor mounted on it.

The sensor directs the signals back to the main computer, so it forms a loop.

Signals are sent from the computer to the actuator which further positions the throttle

through a cable. The position of the throttle is sensed and the signals are sent back to

the computer thereby ensuring that the correct position for the set speed has been

reached and if it is not there, the computer again positions the throttle.



ADAPTIVE CRUISE CONTROL

OVERVIEW

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 systems, manual inputs from the driver, both to the

accelerator and brake, take priority over the ACC system.

Cruise control systems may also be known as speed control systems.

Figure 3: Without ACC

An ACC system uses a distance sensor that projects a beam forward to detect a

vehicle ahead.



Figure 4: ACC buttons on BMW steering wheel

WHY ADAPTIVE CRUISE CONTROL

Comfortable distance to the car ahead increases driving safety and ensures a more

relaxed driving experience. Adaptive Cruise Control ensures that there is enough

distance to the car ahead, even if it unexpectedly lowers the speed.

With Adaptive Cruise Control we have enhanced the conventional systems for speed

control to a driver assistant with an added value. The system makes it possible to

adapt the distance to the car ahead without the driver’s intervention, effectively

relieving the driver. Highway and rural road drives are more relaxed and traffic flows

better altogether, since acceleration and braking maneuvers are automatically

adjusted.

Two companies are developing a more advanced cruise control that can automatically

adjust a car's speed to maintain a safe following distance. This new technology, called

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 proper distance between

vehicles in the same lane. This is achieved through a radar headway sensor, digital

signal processor and longitudinal controller. 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.

The 77-GHz Autocruise radar system made by TRW has a forward-looking range of

up to 492 feet (150 meters), and operates at vehicle speeds ranging from 18.6 miles

per hour (30 kph) to 111 mph (180 kph). Delphi's 76-GHz system can also detect

objects as far away as 492 feet, and operates at speeds as low as 20 mph (32 kph).

Adaptive cruise control is just a preview of the technology being developed by both

companies. These systems are being enhanced to include collision warning



capabilities that will warn drivers through visual and/or audio signals that a collision

is imminent and that braking or evasive steering is needed.

Adaptive Cruise Control (ACC) technology improves upon the function of standard

cruise control by automatically adjusting 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.

COMPONENTS OF ADAPTIVE CRUISE CONTROL

Figure 5: Components of ACC

The basic components of adaptive cruise control (ACC) are

Distance sensor

Wheel speed sensors



Engine control module

ABS module

ACC control module

ACC function controls

WORKING

Figure 6: THE CONCEPT OF ACC

The radar headway sensor sends information to a digital signal processor, which in

turn translates the speed and distance information for a longitudinal controller. The

result? 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.

The adaptive cruise control (ACC) system depends on two infrared sensors to detect

cars up ahead. Each sensor has an emitter, which sends out a beam of infrared light

energy, and a receiver, which captures light reflected back from the vehicle ahead.

The first sensor, called the sweep long-range sensor, uses a narrow infrared beam to

detect objects six to 50 yards away. At its widest point, the beam covers no more than



the width of one highway lane, so this sensor detects only vehicles directly ahead and

doesn't detect cars in other lanes. Even so, it has to deal with some tricky situations,

like keeping track of the right target when the car goes around a curve. To deal with

that problem, the system has a solid-state gyro that instantaneously transmits curve-

radius information to the sweep sensor, which steers its beam accordingly.

Another challenge arises when a car suddenly cuts in front of an ACC-equipped car.

Because the sweep sensor's beam is so narrow, it doesn't "see" the other car until it's

smack in the middle of the lane. That's where the other sensor, called the cut-in

sensor, comes in. It has two wide beams that "look" into adjacent lanes, up to a

distance of 30 yards ahead. And because it ignores anything that isn't moving at least

30 percent as fast as the car in which it is mounted, highway signs and parked cars on

the side of the road don't confuse it.

Information from the sensors goes to the Vehicle Application Controller (VAC), the

system's computing and communication center. The VAC reads the settings the driver

has selected and figures out such things as how fast the car should go to maintain the

proper distance from cars ahead and when the car should release the throttle or

downshift to slow down. Then it communicates that information to devices that

control the engine and the transmission.

There are several inputs:

System on/off: If on, denotes that the cruise-control system should maintain the car

speed.

Engine on/off: If on, denotes that the car engine is turned on; the cruise-control

system is only active if the engine is on.

Pulses from wheel: A pulse is sent for every revolution of the wheel.

Accelerator: Indication of how far the accelerator has been pressed.

Brake: On when the brake is pressed; the cruise-control system temporarily reverts to

manual control if the brake is pressed.

Increase/Decrease Speed: Increase or decrease the maintained speed; only applicable

if the cruise-control system is on.

Resume: Resume the last maintained speed; only applicable if the cruise-control

system is on.



Clock: Timing pulse every millisecond.

There is one output from the system:

Throttle: Digital value for the engineer throttle setting.

Figure 7: Using laser/ radar sensors behind the front grille of your vehicle, adaptive cruise control not

only maintains speed like traditional cruise control, but measures the speed travelled by and distance

from the vehicle in front of you. It then adjusts your speed to maintain a safe distance(WITH ACC)

TYPES

Adaptive cruise control is generally classified into two

Laser based Adaptive cruise control system

Radar based Adaptive cruise control system



Figure 8: Here is a laser based distance sensor on a 2004 Toyota Sienna

Figure 9: Here is a radar based distance sensor on a 2004 BMW

Laser-based systems and radar-based systems compete in quality and price. Laser-

based ACC systems do not detect and track vehicles in adverse weather conditions

nor do they reliably track extremely dirty (non-reflective) vehicles. Laser-based

sensors must be exposed, the sensor (a fairly large black box) is typically found in the

lower grille offset to one side of the vehicle.

Radar-based sensors can be hidden behind plastic fascias; however, the fascias may

look different from a vehicle without the feature. For example, Mercedes packages the

radar behind the upper grille in the center, and behind a solid plastic panel that has

painted slats to simulate the look of the rest of the grille.



Single radar systems are the most common. Systems involving multiple sensors use

either two similar hardware sensors like the 2010 Audi A8 or the 2010 Volkswagen

Touareg, or one central long range radar coupled with two short radar sensors placed

on the corners of the vehicle like the BMW 5 and 6 series.

Assisting systems

Radar-based ACC often feature a Pre-crash system, which warns the driver and/or

provides brake support if there is a high risk of a collision. Also in certain cars it is

incorporated with a lane aintaining system which provides power steering assist to

reduce steering input burden in corners when the cruise control system is activated.

Multi-sensor systems

GPS-aided ACC: the GPS navigation system provides guidance input to the ACC. On

the motorway, the car in the front is slowing down, but with turn signal on and it is

actually heading for a highway off-ramp. A conventional ACC would sense the car in

front was decelerating and it would simply apply brakes accordingly. But with GPS-

guided ACC takes into account the approaching highway exit and it simultaneously

receives images from a camera attached e.g. behind the front pane to the rearview

mirror. The camera may detect the turn signal from the car ahead. So instead of

braking, this new system continues uninterrupted, because it knows that the car in

front will exit the lane.

Cooperative systems

The next generation will include information served from a vehicle ahead in the same

lane. Such dependant approach however requires standardization across

manufacturers and model generations. There is no vision when such agreement could

come into practice. All designs without such cooperative support will operate with

comparably lower dynamic, but promise better reliability and independent operation.

The cooperative approach is the better advances concept to improve road capacity.

Therefore reach of detection must exceed the capabilities of on-board laser or radar. A



wireless communication between vehicles in a queue may not serve for braking, but

surely for adjusting speed to avoid longitudinal oscillations.

APPLICATIONS

Current vehicle makers that are offering adaptive cruise control systems as options on

some of their vehicles include, but may not be limited to, Audi (2004 A8), BMW

(2003–2004 7 Series and 2004 5 Series), General Motors (2003–2004 Cadillac XLR),

Infiniti (2003–2004 Q45 and FX), Jaguar (2003–2004 XKR), Lexus (2001–2004

S430) and Mercedes-Benz (2000–2004 S-Class and CL-Class, 2003–2004 E-Class

and SL- Class)

The Mercedes-Benz adaptive cruise control system is called Distronic. When the

Distronic system is set, the instrument panel display shows a digital reading of the set

speed. The following distance that is set is shown with an arrow on a graduated scale

in front of a vehicle icon (see Figure 10).

When another vehicle is in the same lane in front, it is shown as a second vehicle

icon, with the distance that it is ahead graphed on the same graduated scale (see

Figure 11).

Figure 10: This is the display just after setting the speed and following distance on the Distronic system on a 2001 Mercedes-Benz CL600.



Figure 11: This is the display on the Mercedes-Benz Distronic system when another vehicle is ahead in the same lane at a distance of about 91 m (300 ft).

BMW calls their system active cruise control (ACC). With ACC, the driver sets a

time interval rather than a distance between vehicles. There are four time intervals

that can be set from 1.5–2.8 seconds. The system control module then sets the

following distance based on the speed of the vehicle. The faster the vehicle is

traveling, the greater the following distance will be for a given time interval.

FEATURES OF ADAPTIVE CRUISE CONTROL

Maintains a safe, comfortable distance between vehicles without driver

interventions

Maintains a consistent performance in poor visibility conditions.

Maintains a continuous performance during road turns and elevation changes

Alerts drivers by way of automatic braking.

COLLISION REPAIRS



When a radar unit is damaged and requires replacement, alignment of the unit

on the vehicle is critical to proper system operation.

BMW states that horizontal misalignment of as little as 1° will cause system

performance degradation and amounts greater than 1° may cause system

malfunction. Alignment of the BMW radar is only possible using a vehicle-

specific BMW scan tool and special ACC adjustment tools.

The radar alignment specification on the 2004 Cadillac XLR is listed as 0° +/-

2°. A diagnostic trouble code (DTC) sets when the radar unit is misaligned by

3.9° or more.

If there is misalignment between 2.1° and 3.8°, performance will be affected

but the unit will still operate. If the unit misalignment is not severe, the system

is capable of automatic alignment.

To perform the automatic alignment, a scan tool is required to place the

system into the alignment mode. The vehicle must then be driven on a road

with stationary objects such as mailboxes, road signs, trees, and poles. The

vehicle must be driven until the scan tool displays the alignment procedure as

complete.

The more stationary objects there are on the road, the quicker the internal

automatic alignment is achieved. If the radar unit is too far out of alignment,

automatic alignment is not possible, and the out-of-alignment DTC sets.

The radar unit then requires manual alignment. To perform the manual

alignment or radar aiming procedure, the J-45442 Distance Sensing Cruise

Control aiming tool is required.

This tool is equipped with a laser and is installed to the front of the radar and

control unit. The vehicle needs to be on a level, unobstructed area, 12.8 m (42

ft) by 3.6 m (12 ft) with a vertical wall at one end.



Tape or painted lines are used to mark the floor and wall to position the

vehicle. A 51 mm (2”) circle painted on the wall in the correct location is

used as a target for the laser.

The horizontal and vertical aiming screws on the back of the radar unit are

adjusted until the laser beam is in the center of the target.

Cautions

ACC is intended for use on main roads and motorways.

The field of view of the radar sensor is limited. In some situations (for

example a motorcycle, or a vehicle driving far off centre) other traffic can be

detected later than expected or not be detected at all.

ACC is a supporting system that will contribute to more relaxed and safer

driving. However, ACC is not an autopilot. The driver himself will at all times

remain fully responsible for his vehicle.

ADVANTAGES

Some of those advantages include:

Its usefulness for long drives across sparsely populated roads. This usually

results in better fuel efficiency.

Some drivers use it to avoid unconsciously violating speed limits. A driver

who otherwise tends to unconsciously increase speed over the course of a

highway journey may avoid a speeding ticket. Such drivers should note,

however, that a cruise control may go over its setting on a downhill which

is steep enough to accelerate with an idling engine.



Reduction in accident rate for vehicles fitted with collision avoidance type

systems

Reduction in driver fatigue

Interconnection to more advanced future systems.

LIMITATIONS

One of the biggest challenges in designing ACC systems today are the costs

associated with the robust system. Though current costs are substantial, they are

slowly decreasing.

Auto manufacturers stress that advanced cruise control does not drive the car for you,

and it's not meant to be used in heavy traffic. But, for long trips, it's a convenience

that allows you to focus more on your driving.

CONCLUSION

Despite the introduction of the system to the market place, these are still early days.

The current system can measure up to 150m ahead of the car and reduce the car's

speed if an obstruction appears. What it can't do, at the moment, is bring the car to a

halt.

Whatever happens, the ACC market looks set to explode. The projected figures make

startling reading. In 2002 there are no more than 100,000 vehicles fitted with ACC,

but that figure is set to reach eight million in four years' time, with Europe, South-East



Asia and the US accounting for about a third each. Around 17% of all European-built

cars are likely to have ACC fitted as standard by then.

Expansion is bound to slow down thereafter, but by 2010 the global market will be

11.5 million units, representing an industry value of around $2.4 billion - and

enormously more than that saved in repair bills, hospital bills and, indeed, funeral

bills.

REFERENCES

1. University of Michigan (July 12, 2004). U-M physicist: Smart cruise control

eliminates traffic jams. Press release.

2. L. C. Davis (2004). "Effect of adaptive cruise control systems on traffic flow".

Physical Review Letters E 69 (6): 066110 (article ID; no page reference).

3. CY Liang, H Peng (1999). "Optimal Adaptive Cruise Control with Guaranteed

String Stability". Vehicle System Dynamics 32 (4-5): 313-330.



4. P Venhovens, K Naab, B Adiprasito (2000). "Stop and Go Cruise Control".

Proc. FISITA World Automotive Congress, Seoul, Korea.

5. L. C. Davis, “Effect of adaptive cruise control systems on traffic flow”

Physics Department, University of Michigan, Ann Arbor, Michigan 48109,

USA The American Physical Society (Received 27 October 2003; revised 22

January 2004; published 4 June 2004)

6. MBD Associates. Presentation on Adaptive cruise control.


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