Adaptive
Cruise Control for Modern Automobile
Abstract:
Adaptive cruise control is
basically used for avoiding of danger of accident due lapsing of concentration
or sleepy feeling. In ACC first the hazardous object in the trajectory of
vehicle is detected and then proper action is taken accordingly. ACC system may be employed on front; rear and
side of vehicle. ACC systems are of two types namely active and passive.
Passive system can only give an audio or visual warning to the driver about the
potential hazard present but it cannot take any corrective action itself. On
the other hand, active system can take a corrective action to avoid possible
collision. Active system may take corrective action in the form of putting
brakes or steering the vehicle away from path. For ACC to work properly
reliable detection of hazardous object is of great importance. There is various
method of object detection .Most of the method used principle of RADAR.
Depending upon the time interval between transmission and reception of wave the
distance between the host vehicle and hazardous object is detected and proper
action is taken. For more reliable detection of object camera based system are
also employed. ACC is used in collision avoidance system. If employed properly
and used properly it can acts as a life saving system in certain condition.
1) INTRODUCTION:
The basic aim of any cruise control is to warn or to
alert the driver of a vehicle of a potential hazard and assist him in taking
action to avoid that hazard. Although object detection & collision
avoidance systems may still be regarded as being in their infancy, there perceived
value in enhancing safety and reducing accident is very high. These system
promise special benefits for older drivers.
Development engineers are proceeding very
cautiously with active collision avoidance work. Any system that takes control
of brakes (and in future steering)from the potential sources of litigation,
particularly in north America Standard & Federal regulation s will emerge
during the next few years , which will cover such system. For Ex. In United
States, the national highway traffic safety administration (NHTSA) is
establishing functional requirements for collision avoidance system. These will
cover parameter such as sensor range & sensitivity, system reliability,
driver warning information & data architecture standards. Similarly, in
Japan the Ministry of Transport is conducting an advance safety program (ASP).
Like all other automotive safety systems, to
be truly effective & influence safety statistic, these system will need to
be widely adopted, and that in turn will require a low production cost.
Technology impact is
significant as an improvement in sensing capability on the vehicle is
necessary, & increased computing throughout is required. The challenge now
facing the suppliers is to find a viable balance between perceived value by the
driving public, &the cost of producing such system.
It should be noted that the
cost of such system might largely be hidden within an existing vehicle cost, as
there will be much reuse of existing electronic controllers. It is now common
place for vehicle to have engine controllers, antilock breaking system,
electronic steering controllers, and audio systems. The collision warning and
avoidance systems will use these existing system control units for additional
functions.
Once more challenge faced by
major suppliers is type of required traffic. Today advance version of “Cruise
Control”(adaptive , on which our discussion is centered) have the capability to
maintain the vehicle at a desired speed set by the driver .So in the regions
where traffic situations commonly permit steady speeds (such as in United
States)this function has been widely accepted. That’s why Cruise Control is
fitted in more than 90% of U.S. vehicles. In regions characterized by irregular
traffic situation with frequent speed changes, rise control is seldom found. In
Europe this feature is fitted in less than 10% of vehicles.
2) Adaptive Cruise Control:
Adaptive
cruise control (ACC) introduces a function in automobiles, which relieves the
driver of significant amount of task of driving, in comfortable manner. The
historical development of ACC can be seen as further development of cruise
control, which maintains constant speed for the driver.
The majority of speed
changes can be taking place in traffic can be attributed to standard situations,
which are measurable, by technical equipment. By measuring the host vehicle’s
distance from &relative speed to preceding vehicles, and by employing
suitable actuator systems for speed control, vehicle speed can be controlled in
manner , which automatically makes most necessary speed adjustments.
ACC takes a desired speed
from the driver &keeps the vehicle at the set speed as long as there is no
danger in the range of sensor used. The moment ACC identifies a potential
hazard ahead in the trajectory of host vehicle, it warns the driver of the
vehicle about hazard. Till now, proper control on steering is not developed, so
mainly the brakes are applied .The brakes intensity increases as the distance
between host &preceding vehicle decreases. As long as the relative velocity
between the two vehicles becomes ‘0, the brake system disengages. When the
track ahead is clear, ACC accelerates the vehicle to set speed & maintains
that speed.
Despite of many developments
going on in this field, the basic structure of ACC remains the same. It
consists of basic 5 blocks.
1) Sensor:-
It comprises of the sensor used in the
vehicle to detect the hazard. Depending on the situation encountered, one or
more of the different types of available sensors like scanning laser, FMCW etc.
are used.
2) Computing Unit:-
It is the heart of cruise
control. It is here that all computation work, like calculating the distance
between host and preceding vehicle, relative velocity, brake intensity etc. is
done.
3) Man Machine Interface:-
This interface between the
driver & the ACC of the vehicle. From the panel available in front, the
driver sets the ACC according to his /her requirement.
3) Engine and Brake
Control:-
This unit utilizes the
result of computing unit. It
practically realizes the ACC function
.According to the computed value, it applies brakes. Soon there will be
controls, which will govern the fuel inlet in the engine, there by helping in
more efficient control.
4) Warning System:-
This unit gives proper alarm
as soon as some potential hazard is spotted ahead. Generally it is blended with
–the MMI, which saves additional cost as well as contribute in making system
more compact.
3) Types of Cruise Control:-
According to types of action
the cruise control can be classified in two categories:
a) Passive Collision Warning
System:-
This system seeks the risk
of collision by warning the driver of an impending risk so that he/she can take
action to avoid the hazard.
There are many system s,
which provide warning to driver. The first warning system available on
production vehicle was typically “parking assist” type system, which provides
an audible tone when parallel parking and approaching a stationary object such
as another vehicle or wall. Today there are much sophisticated systems that
used radar and warn occupant of potential impending collision under normal
driving conditions.
In passive warning system a
visual and/or audible warning is signaled to the driver, but there is no active
intervention by system to avoid collision.
b) Active Collision
Avoidance System:-
Active system takes the
collision avoidance philosophy a stage further by interacting with the power
train, braking and even the steering systems. Every manufacturer appears to
have
A slightly different
approach, but the common goal is to sense objects that present a collision risk
with host vehicle, and then take preventing measure to avoid accident.
Advance active collision
systems use many clever techniques, over and object detection, to ensure that a
collision avoidance event is facilitated and efficiently. For example sensor on
the windshield can be used to detect the presence of rain and thus a
potentially slippery road surface.
4) Types of Vehicular
System:-
This section describes three
types of vehicular systems. The most popular today are front and rear, although
development in side warning system and lane sensing will be more important as
future highways become more automated.
4.1) Frontal Vehicle systems:-
There are two types of
frontal vehicular systems: active & passive. They both operate on the same
principle of object detection, although the active system will control the
throttle and possibly steering and braking system to avoid frontal collision.
Different type’s sensors with an algorithm are used to detect the hazardous
objects. This detection system is usually mounted at the front of the host
vehicle to detect objects in the vehicle’s forward path.
The forward rang of these
systems is usually about 100 to 200m,which gives about 3to 6 sec. Warning
hazard when the host vehicle is traveling at 100Km/h.
4.2) Rear Vehicular System:-
Rear warning system can use
shorter range, often non scanning sensor to provide closed range for parking
assist capability, or scanning radar for more advance sensing capability. This
will give the driver an indication of vehicle traveling dangerously close to
the host vehicle, or when backing up in a parking situation, would warn that
another object was nearby, perhaps a difficult to see bicycle, go-cart, or
such.
A near system would typically
use a lower frequency radar system than a frontal system.
4.3) Side Vehicular
Systems:-
Side warning systems use
radar sensor to detect objects in traditional blind spot that are often
responsible for causing accidents. The sensor used would be mounted in the rear
quarter area of the vehicle and detect object in adjacent lanes.
Radar mounted on the sides
are not just useful for blind spot warning, but may also aid in lane tracking,
in order to determine corridor trajectory.
5) System Interaction:-
The cruise control system
actually has a lot of functions other than controlling the speed of your car.
For instance this cruise control pictured below can accelerate or decelerate
the car by 1 mph with the tp 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 in fig.4 has five
buttons: On, off, Set or Accel, Resume and Coast. It also has a sixth control, the brake pedal:
and if the car has a manual transmission, the clutch pedal is also booked up to
the cruise control.
1) 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
drivers hits the set button.
2) The set/accel button tells the car to
maintain the speed you are currently driving. If you hits the set button at 45
mph, the car will maintain your speed 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. Taping it once will make the car go 1 mph
faster
3) 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.
4) Holding down the coast button will cause
the car to decelerate; just as if you took 1 your feet completely off the gas.
And on this car, tapping coast button once will cause the car to slow down by 1
mph.
5) 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 disengage the cruise control with a light tap on the brake
or clutch.
5.1 How it’s
connected:-
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 slave controls the power and
speed of the engine by limiting how much air the engine takes in. There are two cables connected to a pivot
that moves the actuator. When the cruise
control is engaged, the actuator moves the cable connected to the pivot, which
adjusts the throttle; but is also pulls on the cable that is connected to the
Accelerator pedal.
5.2 Controlling the “Cruise”
Control:-
The brain of a cruise control system is a
small computer that is normally found under the bonnet or behind the dashboard.
It connects to the throttle control seen in the previous section, as well as
several sensors. The diagram shown in fig 5 shows the inputs and outputs of a
typical cruise control system.
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 that it can tell what the
desired speed is and when to disengage.
The most important input is the speed signal: the cruise control system
does a lot with this signal.
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.
PID Control:
Most cruise control systems use a control
called proportional-integral-derivative (PID) control. APID system uses basic math’s calculus in
that the integral of speed is distance, and the derivative of speed is
acceleration.
A PID control system uses
these three factors
-Proportional
-Integral
-Derivative
Calculating each
individually and adding them to get the throttle position.
The integral factor is based
on the time integral the vehicle speed error.
Translation: the difference
between the distance your car actually traveled and the distance it would have
traveled if it were going at the desired speed, calculated over a period of
time. This factor helps the car deal with hills, and also helps it settle into
the correct speed and stay there. So if car starts to go up hill and slow down.
After a little while, the integral control will start to increase the throttle,
opening it more and more, because the longer the car maintains a speed slower
than the desired speed, the larger the distance error gets.
Now add in the final factor,
the derivative. Remember that the derivative of speed is acceleration. This
factor helps the cruise control respond quickly to changes, such as hills.
6) Object Detection System:-
Object detection system is the most
important part of an adaptive cruise control system. For proper working go ACC,
object detection reliably is important
Objects may be classified as:
1) Stationary and Moving
2) Hazardous and Non
hazardous
Hazardous objects are those
objects, which are in the trajectory or corridor of vehicle. Trajectory of
corridor of vehicle is defined as:
Corridor: It is an intended
path of a vehicle.
Some of the examples of the
stationary, moving, hazardous and non-hazardous objects are:
Stationary: tree, signboard.
Moving: Any vehicle.
Hazardous: Any vehicle in corridor.
Non hazardous: Trees along roadside.
6.1 Radar Based Systems
There
are two types:
1. Scanning pulse laser radar
2. Frequency modulate
continuous wave radar
6.2 Camera Based System:-
Poor
night visibility particularly in bad whether is a dangerous. Troublesome and al
too familiar for drivers. The visibility problems include:
Ø The short range of sight
with low beams, which is generally underestimated.
Ø The blinding by headlights
of oncoming vehicle and by their reflection from wet roads.
Ø The reduced range of vision
under conditions of rain, fog or snow flurries.
The system consist of near
infrared laser headlight, a close coupled device(CCD) camera to generate a
video image, and a liquid crystal display(LCD) to present the image to the
driver. These headlights are installed in addition to the standard visible
units and will be mounted along with the vehicle’s flashers in the existing
housing. The laser headlights illuminate the top of the bus and optical filters
are mounted in front of the camera objective of the LCD display at a distance
of 0.85 meters from the driver, avoiding frequent accommodation of the eyes
from the traffic séance to the display.
Under dry
weather conditions, fig illustrates the driver’s view through the windshield of
a car and the position of the image. On the road is another car with low beam
headlights at a 40-m distance and a pedestrian at 50 m. the driver could not
see the pedestrian who could be seen clearly on the video image. The course of
road was visible for 150-200 m in the video image.
7. High End Collision Avoidance System:-
a fully
equipped system, which includes all of the subsystems, is as shown in fig.7
this level of technology would be considered high end and would support an
advance system such as automated highways. The collision avoidance electronic
control unit is shown at the center of the fig. the frontal vehicular system
features two sensors: a 77GHz FMCW and a camera system. Data from both these
sources is fused to map out a reliable picture of potential hazard. As well as
determining the best information about environment by correlating data from two
sources, having two objects detection system is excellent as back up. Many
vehicular systems have inherent redundancy for safety, and this especially
needs to be addressed in a system such as collision avoidance, where the
vehicle is maneuvered automatically. Providing several sources of information
is good strategy if it can be achieved economically. Low frequency radar is
used for rear object detection, side radar system also integrated in to the
total system.
Steering
angle is an important input to the system. Although sensor such as yaw, pitch
and roll will be used to provide information on actual dynamics of vehicle,
steering angle is an indication of intended direction of driver. The vehicle
speed input could be determined independently or may be supplied by ABS ECU.
The ABS system calculates individual wheel speed from sensor inputs. The
vehicle speed is then estimated using an algorithm. Alternatively, speed over
ground can be determined more accurately using radar. The viper status input is
also used as audio alert for the system. This system would switch radio an
automatically and provide the driver the darning of an impending risk.
Conclusion:-
-ACC must be regarded as beginning of the
development leading to more powerful driver assistance system.
-
While most of the development going on, the next generation ACC’s is
being worked on in parallel.
- In
the end, financial success will depend on the acceptance of system, in which so
far hundred million dollars have been invested worldwide.
Reference:
- Handbook of automotive engineering- Jordan
-Automotive mechanics-Crouse and Anglin
-Automotive engineering magazine-July1999.
-WWW.isa.com.
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