Transcript
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
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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
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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.
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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
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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.
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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.
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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.
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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
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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
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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
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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.
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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
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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.
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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
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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.
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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
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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.
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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.
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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
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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.
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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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