Cruise Control Devices
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29-12-2009, 01:48 PM



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ABSTRACT
The concept of assisting driver in the task of longitudinal vehicle control is known as cruise control. Starting from the cruise control devices of the seventies and eighties, now the technology has reached cooperative adaptive cruise control. This paper will address the basic concept of adaptive cruise control and the requirement to realize its improved versions including stop and go adaptive cruise control and cooperative adaptive cruise control. The conventional cruise control was capable only to maintain a set speed by accelerating or decelerating the vehicle. Adaptive cruise control devices are capable of assisting the driver to keep a safe distance from the preceding vehicle by controlling the engine throttle and brake according to the sensor data about the vehicle. Most of the systems use RADAR as the sensor .a few use LIDAR also. Controller includes the digital signal processing modules and microcontroller chips specially designed for actuating throttle and brake. The stop and go cruise control is for the slow and congested traffic of the cities where the traffic may be frequently stopped. Cooperative controllers are not yet released but postulations are already there. This paper includes a brief theory of pulse Doppler radar and FM-CW LIDAR used as sensors and the basic concept of the controller.

1. INTRODUCTION
Everyday the media brings us the horrible news on road accidents. Once a report said that the damaged property and other costs may equal 3 % of the worldâ„¢s gross domestic product. The concept of assisting driver in longitudinal vehicle control to avoid collisions has been a major focal point of research at many automobile companies and research organizations. The idea of driver assistance was started with the Ëœcruise control devicesâ„¢ first appeared in 1970â„¢s in USA. When switched on, this device takes up the task of the task of accelerating or braking to maintain a constant speed. But it could not consider the other vehicles on the road.
An ËœAdaptive Cruise Controlâ„¢ (ACC) system developed as the next generation assisted the driver to keep a safe distance from the vehicle in front. This system is now available only in some luxury cars like Mercedes S-class, Jaguar and Volvo trucks the U.S. Department of transportation and Japanâ„¢s ACAHSR have started developing ËœIntelligent Vehiclesâ„¢ that can communicate with each other with the help of a system called ËœCo operative Adaptive Cruise Controlâ„¢ .this paper addresses the concept of Adaptive Cruise Control and its improved versions.

2. ADAPTIVE CRUISE CONTROL (ACC)
2.1 PRINCIPLE OF ACC
ACC works by detecting the distance and speed of the vehicles ahead by using either a Lidar system or a Radar system [1, 2].The time taken by the transmission and reception is the key of the distance measurement while the shift in frequency of the reflected beam by Doppler Effect is measured to know the speed. According to this, the brake and throttle controls are done to keep the vehicle the vehicle in a safe position with respect to the other. These systems are characterized by a moderately low level of brake and throttle authority. These are predominantly designed for highway applications with rather homogenous traffic behavior. The second generation of ACC is the Stop and Go Cruise Control (SACC) [2] whose objective is to offer the customer longitudinal support on cruise control at lower speeds down to zero velocity [3]. The SACC can help a driver in situations where all lanes are occupied by vehicles or where it is not possible to set a constant speed or in a frequently stopped and congested traffic [2]. There is a clear distinction between ACC and SACC with respect to stationary targets. The ACC philosophy is that it will be operated in well structured roads with an orderly traffic flow with speed of vehicles around 40km/hour [3]. While SACC system should be able to deal with stationary targets because within its area of operation the system will encounter such objects very frequently.
2.2 CONSTITUENTS OF AN ACC SYSTEM:
1. A sensor (LIDAR or RADAR) usually kept behind the grill of the vehicle to obtain the information regarding the vehicle ahead. The relevant target data may be velocity, distance, angular position and lateral acceleration.
2. Longitudinal controller which receives the sensor data and process it to generate the commands to the actuators of brakes throttle or gear box using Control Area Network (CAN) of the vehicle.
3. SENSOR OPTIONS:
Currently four means of object detection are technically feasible and applicable in a vehicle environment [2]. They are
1. RADAR
2. LIDAR
3. VISION SENSORS
4. ULTRASONIC SENSOR
The first ACC system used LIDAR sensor.

3.1 LIDAR (Light Detection and Ranging)
The first acc system introduced by Toyota used this method. By measuring the beat frequency difference between a Frequency Modulated Continuous light Wave (FMCW) and its reflection [3].

Fig 1.Range estimation using FMCW-LIDAR
A company named Vorad Technologies has developed a system which measured up to one hundred meters. A low powered, high frequency modulated laser diode was used to generate the light signal.
Most of the current acc systems are based on 77GHz RADAR sensors. The RADAR systems have the great advantage that the relative velocity can be measured directly, and the performance is not affected by heavy rain and fog. LIDAR system is of low cost and provides good angular resolution although these weather conditions restrict its use within a 30 to 40 meters range.
3.2 RADAR (Radio Detection and Ranging):
RADAR is an electromagnetic system for the detection and location of reflecting objects like air crafts, ships, space crafts or vehicles. It is operated by radiating energy into space and detecting the echo signal reflected from an object (target) the reflected energy is not only indicative of the presence but on comparison with the transmitted signal, other information of the target can be obtained. The currently used ËœPulse Doppler RADARâ„¢ uses the principle of ËœDoppler effectâ„¢ in determining the velocity of the target [5].
3.2.1 PULSE DOPPLER RADAR:
The block diagram of pulse Doppler radar is as shown in figure.2.
The continuous wave oscillator produces the signal to be transmitted and it is pulse modulated and power amplified. The Ëœduplexerâ„¢ is a switching device which is fast-acting to switch the single antenna from transmitter to receiver and back. The duplexer is a gas-discharge device called TR-switch. The high power pulse from transmitter causes the device to breakdown and to protect the receiver. On reception, duplexer directs the echo signal to the receiver. The detector demodulates the received signal and the Doppler filter removes the noise and outputs the frequency shift Ëœfdâ„¢.

Fig2. Block diagram of pulse Doppler radar

3.2.2 EFFECT OF DOPPLER SHIFT:
The transmitter generates a continuous sinusoidal oscillation at frequency Ëœftâ„¢which is then radiated by the antenna. On reflection by a moving object, the transmitted signal is shifted by the Doppler Effect by Ëœfdâ„¢.
If the range to the target is ˜R™, total number of wavelength is ˜™ in the two way- path is given by,
n = 2R/
The phase change corresponding to each =2p
So total phase change, p=2n
=2(2R/ ) p
So, if target moves, ËœRâ„¢ changes and hence Ëœfâ„¢ also changes.
Now, the rate of change of phase, or the Ëœangular frequencyâ„¢ is
W=df/dt =4 p (df/dt)/
Let Vr be the linear velocity, called as Ëœradial velocityâ„¢
Wd = 4 pVr/ =2pfd.
Fd=2Vr /
But = ft, the transmitted velocity.
Fd= (2c Vr)/ ft
So by measuring the shift, Vr is found. The Ëœplusâ„¢ sign indicates that the target and the transmitter are closing in. i.e. if the target is near, the echoed signal will have larger frequency.
3.2.3 RADAR ANTENNA SCHEMES:
Radar systems employ a variety of sensing and processing methods to determine the position and speed of vehicles ahead. Two such important schemes are:
1. mechanically steered antenna
2. electronically steered antenna
1. Mechanically steered antenna:

A parabolic reflector is used as mechanically steered antenna. The parabolic surface is illuminated by the source of energy placed at the focus of the parabola. Rotating about its axis, a circular parabola is formed. A symmetrical beam can be thus obtained. The rays originating from focus are reflected parallel to the axis of parabola. [fig (3).]

Fig 3.Parabolic reflector antenna
2. Electronically steered phased array radar antenna
A phased array is a directive antenna made up of a number of individual antennas, or radiating elements. The radiation pattern is determined by the amplitude and phase of current at each of its elements. It has the advantage of being able to have its beam electronically steered in angles by changing phase of current at each element. The beam of a large fixed phased array antenna is therefore can be rapidly steered from one direction to another without mechanical positioning [1, 5].
Consider the following figure with ˜N elements placed (equally separated) with a distance˜d™ apart. Suppose they have uniform response to signals from all directions. Element ˜1™ is taken as reference with zero phase.


Fig 4. Phased array elements (example: reception of the beams)
From simple geometry, we can get difference between path lengths of beam1 and that of beam2 is x = d sin, where ˜™ is the angle of incidence of the beams. This gives phase difference between adjacent elements as F= 2p (d sin)/ , where ˜™ is the wave length of the signal. But if the current through a ferro electric element is changed, the dielectric constant ˜e™ is changed since electron density is changed, and for an electromagnetic radiation, F = 2px /
=2pxf/v,
here the velocity v = f = 1/ (vµ e)
Hence F=2pxf (vµ e).

So if Ëœeâ„¢ is changed ËœFâ„¢ also changes and inserting ËœNâ„¢ phase shifting elements to steer the beam, we can obtain an electronically steered beam.
Regardless of the scanning mechanism the radars typically operate in the millimeter wave region at 76-77 GHz.
The system should be mounted inside the front grille of the car as shown in figure (5). So its size is to be small. A typical radar produced by Delphi-Delco Electronic systems is having the size of two stacked paper back books(14x7x10 cm)[1].
3.3 FUSION SENSOR
The new sensor system introduced by Fujitsu Ten Ltd. and Honda through their PATH program includes millimeter wave radar linked to a 640x480 pixel stereo camera with a 40 degree viewing angle. These two parts work together to track the car from the non-moving objects. While RADAR target is the carâ„¢s rear bumper, the stereo camera is constantly captures all objects in its field of view.

Fig5. A prototype of a car with fusion sensor arrangement

Fig 6.Block diagram of sensing and controlling process
The image processor measures the distances to the objects through triangulation method. This method includes an algorithm based on the detection of the vertical edges and distance. Incorporating both the 16-degree field of view of radar and 40-degree field of view of camera enhances the performance in tight curves [4].
4. SPACE OF MANEUVERABILITY AND STOPPING DISTANCE
The space of maneuverability is the space required by the driver to maneuver a vehicle. An average driver uses larger sideways acceleration while vehicle speed is low. If the curve radius of a possible trajectory is Ëœrâ„¢ for a given velocity Ëœvâ„¢ and sideways acceleration Ëœayâ„¢ ,then r= / ay [2].so to get the required Ëœrâ„¢ ,when Ëœvâ„¢ is low, Ëœayâ„¢ is also to be low correspondingly. The stopping distance is given by, Ds = .5 u /ax + td u, where Ëœuâ„¢ is the initial speed Ëœtdâ„¢ is the time taken by the system to receive and process the sensor data and Ëœaxâ„¢ is the acceleration of the vehicle .the figure shows the detection of edges of the preceding vehicles.

Fig 7.Detection of vehicle edges by the fusion sensor
5. CONTROLLER
The controller translates the situation into appropriate actions through brake and pedal and throttle control actions.
Depending on the present traffic situation, two types of controls are possible.
1. Speed control
2. Headway control
If there is no vehicle presently in front, then the speed is controlled about a set point just as in conventional cruise control. But in order to keep a safe distance between the vehicle s, the headway control is required.
5.1ARTIFICIAL COGNITION
The conversion of raw information from sensors to control actions by the two steps:-
1. Analyzing the traffic conditions
2. Deciding on a particular situation
The controller translates the desired situation into appropriate control action through brake and throttle actuation.[2]. The controller concept is simplified in the flow-diagram:

Fig 8.Flow diagram of controlling process
5.2. EXAMPLE OF ADAPTIVE CRUISE CONTROLLER (MOTOROLA ACC)

The Motorola ACC constitutes a DSP module having MGT5200 which provides a multiply-accumulator. The sensor data such as Radar information, that from camera and an IR sensor are processed in it, to generate the input data for the controller modules like HC12 and MPC565.[6].

Fig9. Motorola ACC
5.2.1 MPC565
It is a throttle controller or an engine speed controller. It consists of the following features
1. SRAM (1MB to10 MB)
2. FLASH 1MB
3. EEPROM (4KB to 32 KB)
4. Real time clock
5. 4 x UART interfaces
6. 3 X CAN interfaces
7. 64-bit floating point unit.
The MPC 565 can be programmed to generate the control signals according to the sensor data. ËœThe Phycore-MPC 565 developersâ„¢ are available to program and develop the desired controller.
The throttle valve is actuated and the air intake is controlled so the requirement of fuel for the right proportion with the air also increases. So more fuel is injected and engine speed is changed.
5.2.2 HC12
The HC12 is a breaking controller which receives data from the wheel speed sensors and from the DSP module. It generates the braking control signal.
5.2.3 CAN (Control Area Network) BUS
CAN BUS is the network established between microcontrollers. It is a2-wire, half-duplex, high speed network for high speed high speed applications with short messages. It can theoretically link up to 2032 devices on a network. But today the practical limit is 110 devices. It offers high speed communication rate up to 1Mbits per second and allows real time control. [7].
Each module in the ACC connected to the CAN is called Ëœa nodeâ„¢. All are acting as transceivers. The CAN bus carries data to and from all nodes and provides quicker control transfer to each module.
The actuator used for throttle control is a solenoid actuator. The signal through the coil can push or pull the plunger.
6. CO OPERATIVE ADAPTIVE CRUISE CONTROL [CACC]
Though conventional ACC and SACC are still expensive novelties, the next generation called Cooperative ACC is already being tested. While ACC can respond to the difference between its own behavior and that of the preceding vehicle, the CACC system allows the vehicles to communicate and to work together to avoid collision.[2,4].
Partners of Advanced Transit Highways (PATH) “a program of California Department of Transportation and University of California with companies like Honda conducted an experiment in which three test vehicles used a communication protocol in which the lead car can broadcast information about its speed, acceleration ,breaking capacity to the rest of the groups in every 20ms.
PATH is dedicated to develop systems that allow cars to set up platoons of vehicles in which the cars communicate with each other by exchanging signals using protocols like Bluetooth.
6.1. MAIN POSTULATIONS ABOUT CACC:

1. In CACC mode, the preceding vehicles can communicate actively with the following vehicles so that their speed can be coordinated with each other.
2. Because communication is quicker, more reliable and responsive compared to autonomous sensing as in ACC.
3. Because braking rates, breaking capacity and other important information about the vehicles can be exchanged, safer and closer vehicle traffic is possible.
Fig 10.Under CACC, both the leading and following vehicles are electronically tied to a virtual reference vehicle, as well as to each other.
7. ADVANTAGES
1. The driver is relieved from the task of careful acceleration, deceleration and braking in congested traffics.
2. A highly responsive traffic system that adjusts itself to avoid accidents can be developed.
3. Since the breaking and acceleration are done in a systematic way, the fuel efficiency of the vehicle is increased.
DISADVANTAGES
1. A cheap version is not yet realized.
2. A high market penetration is required if a society of intelligent vehicles is to be formed.
3. Encourages the driver to become careless. It can lead to severe accidents if the system is malfunctioning.
4. The ACC systems yet evolved enable vehicles to cooperate with the other vehicles and hence do not respond directly to the traffic signals.
8. CONCLUSION
The accidents caused by automobiles are injuring lakhs of people every year. The safety measures starting from air bags and seat belts have now reached to ACC, SACC and CACC systems. The researchers of Intelligent Vehicles Initiative in USA and the Ertico program of Europe are working on technologies that may ultimately lead to vehicles that are wrapped in a cocoon of sensors with a 360 “degree view of their surroundings. It will probably take decades, but car accidents may eventually become as rare as plane accidents are now, even though the road laws will have to be changed, upto an extent since the non-human part of the vehicle controlling will become predominant.
9. REFERENCES
1. Willie D. Jones, Keeping cars from crashing. , IEEE Spectrum September 2001.
2. P.Venhovens, K. Naab and B. Adiprasto, Stop And Go Cruise Control, International Journal of Automotive Technology, Vol.1, No.2, 2000.
3. Martin D. Adams, Co axial range Measurement-Current trends for Mobile robotic Applications, IEEE Sensors journal, Vol.2, no.1 Feb.2002.
4. path.Berkeley.edu
5. Merril I.Skolnik, Introduction To RADAR Systems.Tata Mc Grawhill edition 2001.
6. motorola /semiconductor.com
7. computer-solutions.co.uk


CONTENTS
1. INTRODUCTION
2. PRINCIPLE OF ACC
2.1 PRINCIPLE OF ACC
2.2 CONSTITUENTS OF AN ACC SYSTEM
3. SENSOR OPTIONS
3.1 LIDAR
3.2 RADAR
3.2.1 PULSE DOPPLER RADAR
3.2.2 EFFECT OF DOPPLER SHIFT
3.2.3 RADAR ANTENNA SCHEMES
3.3 FUSION SENSOR
4. SPACE OF MANEUVERABILITY AND STOPPING DISTANCE:
5. CONTROLLER
5.1ARTIFICIAL COGNITION
5.2. EXAMPLE OF ADAPTIVE CRUISE CONTROLLER
6. CO OPERATIVE ADAPTIVE CRUISE CONTROL [CACC]
6.1. MAIN POSTULATIONS ABOUT CACC
7. ADVANTAGES AND DISADVANTAGES
8. CONCLUSION
9. REFERENCES

ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof. P.Sukumaran Head of Department for giving us his invaluable knowledge and wonderful technical guidance
I express my thanks to Mr. Muhammed Kutty our group tutor and also to our staff advisor Ms. Biji Paul and Mr. Noushad V.M for their kind
co-operation and guidance for preparing and presenting this seminar and presentation.
I also thank all the other faculty members of AEI department and my friends for their help and support.
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please use this link to download
topicideashow-to-cruise-control-devices--5439
seminar and presentationproject and implimentationsattachment.php?aid=3116 the Adaptive cruise Control (ACC) technical report
Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
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Cruise Control Devices
ABSTRACT

The concept of assisting driver in the task of longitudinal vehicle control is known as cruise control. Starting from the cruise control devices of the seventies and eighties, now the technology has reached cooperative adaptive cruise control. This paper will address the basic concept of adaptive cruise control and the requirement to realize its improved versions including stop and go adaptive cruise control and cooperative adaptive cruise control. The conventional cruise control was capable only to maintain a set speed by accelerating or decelerating the vehicle. Adaptive cruise control devices are capable of assisting the driver to keep a safe distance from the preceding vehicle by controlling the engine throttle and brake according to the sensor data about the vehicle. Most of the systems use RADAR as the sensor .a few use LIDAR also. Controller includes the digital signal processing modules and microcontroller chips specially designed for actuating throttle and brake. The stop and go cruise control is for the slow and congested traffic of the cities where the traffic may be frequently stopped. Cooperative controllers are not yet released but postulations are already there. This paper includes a brief theory of pulse Doppler radar and FM-CW LIDAR used as sensors and the basic concept of the controller.

Reference: topicideashow-to-cruise-control-devices--5439#ixzz11CgWEgjL
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Cruise Control Devices


INTRODUCTION

Everyday the media brings us the horrible news on road accidents. Once a report said that the damaged property and other costs may equal 3 % of the world’s gross domestic product. The concept of assisting driver in longitudinal vehicle control to avoid collisions has been a major focal point of research at many automobile companies and research organizations. The idea of driver assistance was started with the ‘cruise control devices’ first appeared in 1970’s in USA. When switched on, this device takes up the task of the task of accelerating or braking to maintain a constant speed. But it could not consider the other vehicles on road.

An ‘Adaptive Cruise Control’ (ACC) system developed as the next generation assisted the driver to keep a safe distance from the vehicle in front. This system is now available only in some luxury cars like Mercedes S-class, Jaguar and Volvo trucks the U.S. Department of transportation and Japan’s ACAHSR have started developing ‘Intelligent Vehicles’ that can communicate with each other with the help of a system called ‘Co operative Adaptive Cruise Control’ .this paper addresses the concept of Adaptive Cruise Control and its improved versions.
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Cruise Control Device

INTRODUCTION

Everyday the media brings us the horrible news on road accidents. Once a report said that the damaged property and other costs may equal 3 % of the world’s gross domestic product. The concept of assisting driver in longitudinal vehicle control to avoid collisions has been a major focal point of research at many automobile companies and research organizations. The idea of driver assistance was started with the ‘cruise control devices’ first appeared in 1970’s in USA. When switched on, this device takes up the task of the task of accelerating or braking to maintain a constant speed. But it could not consider the other vehicles on the road.

An ‘Adaptive Cruise Control’ (ACC) system developed as the next generation assisted the driver to keep a safe distance from the vehicle in front. This system is now available only in some luxury cars like Mercedes S-class, Jaguar and Volvo trucks the U.S. Department of transportation and Japan’s ACAHSR have started developing ‘Intelligent Vehicles’ that can communicate with each other with the help of a system called ‘Co operative Adaptive Cruise Control’ .this paper addresses the concept of Adaptive Cruise Control and its improved versions.
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DONE BY:

K.Raghunath


CRUISE CONTROL

Abstract— The cruise control system in a vehicle is studied in details. First, control concepts in cruise control system are investigated. Second, simplified cruise control models are developed and simulated. Third, an introduction to adaptive cruise control system is presented. Fourth, modeling of adaptive cruise control system in a traffic simulation is carried. Finally, the future development of the advanced adaptive cruise control system is presented.

INTRODUCTION
Cruise control system has become a common feature in automobiles nowadays. Instead of having the driver frequently checking the speedometer and adjusting pressure on the gas pedal or the brake, cruise control system control the speed of the car by maintaining the constant speed set by the driver. Therefore, cruise control system can help reduce driver’s fatigue in driving a long road trip. This paper presents the control system behind the cruise control.

BACKGROUND
Before getting into to the control system concepts of cruise control, the components and the basic mechanism of the cruise control system in a vehicle are summarized.
A. Components of Cruise Control
Cruise control system can be divided in to three main parts, which are the input, the processor, and the output. The input of the system includes the setting buttons on the steering wheel, gas pedal, brake, clutch and the feedback signal of the cruise control. The processor of the system is to control the speed of the car by utilizing the control system theory. The output is the throttle position, which is corresponding to the actual speed of the car.
1) Input of Cruise Control
There are usually three to five setting buttons on the steering wheels for the input to the cruise control system. The buttons are on/off, set/accel, resume, and coast. The on button turns on the cruise control function. The off button turns off the cruise control function. The set/accel button is to set the speed of the car to the current speed that the car is driving at. Also, by tapping the set/accel button once can increase the speed of the car by 1mph and so forth. The resume button is to set the speed of the car back to the last maintained speed, which is he speed right before the cruise control is disengaged. The coast button is to decrease the speed of the car.
The brake and the clutch are the other inputs to the cruise control system. When the pedal is pressed, the cruise control system is disengaged, so the speed control of the car is taken over by the driver in adjusting the gas pedal and the brake.
Furthermore, the speed for the cruise control can be set by pressing the gas pedal to accelerate the car to the desired speed, and then hitting the set button. Also, when the cruise control is engaged, the gas pedal overrides the set speed from the cruise control, so the car accelerates as long as the gas pedal is pressed.
Finally, the feedback signal from the measured speed of the car is taken into account of the input of the curse control system. This input is closely related to the control system of the cruise control. The detailed of the feedback input is presented under the control system of cruise control later.
2) Processor of Cruise Control
The processor of a cruise control is a control system designed to obtain the speed set by the driver. It plays an important role in the cruise control system. The processor is integrated with electronic components to a system transfer function, which is discussed under the control system of cruise control in detail.
3) Output of Cruise Control
The output of the cruise control is the throttle position. The actual speed of the car varies corresponding to different throttle position, as the throttle valve limiting how much air the engines takes in. A different air-to-fuel ratio in the combustion process affects the power and the speed of the engine, and this eventually leads to the change of the car speed.
B. Mechanism of Cruise Control
An overview of the relationship between different components of cruise control system is shown in Fig. 1. The processor of the cruise control system is shown as the Cruise Control Computer in the figure.
The process of the cruise control system in a vehicle is: First, the driver sets the desired speed of the car by turning on the cruise control at the desired speed that the car is traveling at and hit the set button. An alternate way to set the desired speed of the car is by tapping the set/accel button to increase the speed of the car or by tapping the coast button to decrease the speed of the car. Second, the processor of the system gets the input signal, and then sends the output signal to the actuator. Third, the actuator adjusts the throttle position. Finally, the changes in the throttle position would leads to the changes in the speed of the car traveling. Also, the actual speed of the car is measured by a sensor and sent to the processor. The process of sending the current speed of the car continues for the processor to maintain the desired speed, as long as the cruise control is engaged [1]. This process is explained in details in terms of control system concepts later.



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hi ,
seminar and presentation report and ppt on adaptive cruise control available in several pages see some of them
topicideashow-to-adaptive-cruise-control-full-report
topicideashow-to-adaptive-cruise-control-full-report?page=2
topicideashow-to-seminar and presentation-report-on-cruise-control-devices
topicideashow-to-cruise-control-devices--5439
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1. INTRODUCTION

Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicle's cruise control system to adapt the vehicle's speed to the traffic environment. A radar system attached to the front of the vehicle is used to detect whether slower moving vehicles are in the ACC vehicle's path. If a slower moving vehicle is detected, the ACC system will slow the vehicle down and control the clearance, or time gap, between the ACC vehicle and the forward vehicle. If the system detects that the forward vehicle is no longer in the ACC vehicle's path, the ACC system will accelerate the vehicle back to its set cruise control speed. This operation allows the ACC vehicle to autonomously slow down and speed up with traffic without intervention from the driver. The method by which the ACC vehicle's speed is controlled is via engine throttle control and limited brake operation.




2. Definitions and Physical Overview





2.1 DEFINITIONS

ADAPTIVE CRUISE CONTROL (ACC) – An enhancement to a conventional cruise control system which allows the ACC vehicle to follow a forward vehicle at an appropriate distance.

ACC VEHICLE – the subject vehicle equipped with the ACC system.

ACTIVE BRAKE CONTROL – a function which causes application of the brakes without driver application of the brake pedal.

CLEARANCE – distance from the forward vehicle's trailing surface to the ACC vehicle's leading surface.

FORWARD VEHICLE – any one of the vehicles in front of and moving in the same direction and traveling on the same roadway as the ACC vehicle.

SET SPEED – the desired cruise control travel speed set by the driver and is the maximum desired speed of the vehicle while under ACC control.







SYSTEM STATES


ACC OFF STATE – direct access to the 'ACC active' state is disabled.

ACC STANDBY STATE – system is ready for activation by the driver.

ACC ACTIVE STATE – the ACC system is in active control of the vehicle's speed.

ACC SPEED CONTROL STATE – a substate of 'ACC active' state in which no forward vehicles are present such that the ACC system is controlling vehicle speed to the 'set speed' as is typical with conventional cruise control systems.

ACC TIME GAP CONTROL STATE – a substate of 'ACC active' state in which time gap, or headway, between the ACC vehicle and the target vehicle is being controlled.










TARGET VEHICLE – one of the forward vehicles in the path of the ACC vehicle that is closest to the ACC vehicle.

TIME GAP – The time interval between the ACC vehicle and the target vehicle. The 'time gap' is related to the 'clearance' and vehicle speed by:
Time Gap = Clearance / Acc Vehicle Speed







2.2 Physical Layout


As shown in Figure 3, the ACC system consists of a series of interconnecting components and systems. The method of communication between the different modules is via a serial communication network known as the Controller Area Network (CAN).


ACC MODULE – The primary function of the ACC module is to process the radar information and determine if a forward vehicle is present. When the ACC system is in 'time gap control', it sends information to the Engine Control and Brake Control modules to control the clearance between the ACC Vehicle and the Target Vehicle.

ENGINE CONTROL MODULE – The primary function of the Engine Control Module is to receive information from the ACC module and Instrument Cluster and control the vehicle's speed based on this information. The Engine Control Module controls vehicle speed by controlling the engine's throttle.

BRAKE CONTROL MODULE – The primary function of the Brake Control Module is to determine vehicle speed via each wheel and to decelerate the vehicle by applying the brakes when requested by the ACC Module. The braking system is hydraulic with electronic enhancement, such as an ABS brake system, and is not full authority brake by wire.


INSTRUMENT CLUSTER – The primary function of the Instrument Cluster is to process the Cruise Switches and send their information to the ACC and Engine Control Modules. The Instrument
Cluster also displays text messages and telltales for the driver so that the driver has information regarding the state of the ACC system.

CAN – The Controller Area Network (CAN) is an automotive standard network that utilizes a 2 wire bus to transmit and receive data. Each node on the network has the capability to transmit 0 to 8 bytes of data in a message frame. A message frame consists of a message header,
followed by 0 to 8 data bytes, and then a checksum. The message header is a unique identifier that determines the message priority. Any node on the network can transmit data if the bus is free. If multiple nodes attempt to transmit at the same time, an arbitration scheme is used to determine which node will control the bus. The message with the highest priority, as defined in its header, will win the arbitration and its message will be transmitted. The losing message will retry to send its message as soon as it detects a bus free state.

CRUISE SWITCHES – The Cruise Switches are mounted on the steering wheel and have several buttons which allow the driver to command operation of the ACC system. The switches include:
'On': place system in the 'ACC standby' state
'Off'': cancel ACC operation and place system in the 'ACC off' state
'Set +': activate ACC and establish set speed or accelerate
'Coast': decelerate
'Resume': resume to set speed
'Time Gap +': increase gap
'Time gap –': decrease gap


BRAKE SWITCHES –
There are two brake switches, Brake Switch 1 (BS1) and Brake Switch 2 (BS2). When either brake switch is activated, Cruise Control operation is deactivated and the system enters 'ACC standby' state.

BRAKE LIGHTS –
When the Brake Control Module applies the brakes in response to an ACC request, it will illuminate the brake lights to warn vehicles behind the ACC vehicle that it is decelerating.

3. Operational Overview


The driver interface for the ACC system is very similar to a conventional cruise control system. The driver operates the system via a set of switches on the steering wheel. The switches are the same as for a conventional cruise control system except for the addition of two switches to control the time gap between the ACC vehicle and the target vehicle. In addition there are a series of text messages that can be displayed on the instrument cluster to inform the driver of the state of the ACC system and to provide any necessary warnings. The driver engages the ACC system by first pressing the ON switch which places the system into the 'ACC standby' state. The driver then presses the Set switch to enter the 'ACC active' state at which point the ACC system attempts to control the vehicle to the driver's set speed dependent upon the traffic environment.





3.1 Control System Interfaces

Figure 4 shows the information and signal flows between the different systems for ACC operation.




3.2 Initialization

When the ignition key is in the off position, no power is applied to any of the systems. When the key is cycled to the on position, the ACC system initializes to the 'ACC off' state.

3.3 Engaging Cruise Control

ENTERING 'ACC STANDBY' -
Before active cruise control can be engaged the driver must first enter 'ACC standby'. This is performed by the driver pressing the ACC 'On' button. If no system faults are present, the ACC system will transition to the 'ACC standby' state.

ENTERING 'ACC ACTIVE' –
The driver enters the 'ACC active' state by pressing the 'Set' or 'Resume' button. If a prior set speed is present in memory, the system uses this prior value as the target speed when Resume is pressed, else, the current speed of when the Set button was pressed will become the target speed. The following conditions must be true for the system to enter 'ACC active' in response to the cruise switches:

Brake Switch 1 = brake not applied
Brake Switch 2 = brake not applied
Vehicle Speed >= 25 mph



When entering active ACC control, the vehicle speed is controlled either to maintain a set speed or to maintain a time gap to a forward vehicle, whichever speed is lower.

3.4 Operation During Speed Control Mode (ACC Speed Control)

Operation during this mode is equivalent to that of conventional speed control. If no forward vehicle is present within the Time Gap or clearance of the system, the vehicle's speed is maintained at the target speed. The engine control system controls the engine output via throttle control to maintain the vehicle speed at the target speed.


3.5 Operation During Follow Mode (ACC Time Gap Control)

The ACC system enters follow mode or 'ACC time gap control' if the radar detects a forward vehicle at or within the clearance distance. During this mode of operation, the ACC system sends a target speed to the Engine Control Module and deceleration commands to the Brake
Control module to maintain the set time gap between the vehicles.



DECELERATION CONTROL –
The ACC system decelerates the vehicle by lowering the target speed sent to the Engine Control Module and sending a brake deceleration command to the Brake Control Module. The maximum allowed braking effort of the system is 0.2 [g]. During brake deceleration events, the Brake Control Module activates the brake lights.

ACCELERATION CONTROL –
The ACC system accelerates the vehicle by increasing the target speed sent to the Engine Control Module. The Engine Control Module tries to maintain the target speed and can accelerate the vehicle at a rate of up to 0.2 [g] of acceleration.

ADJUSTING THE TIME GAP –
The driver can adjust the time gap via the 'Time Gap +' and 'Time Gap –' switches. Pressing the 'Time Gap +' switch causes the time gap value to increase and therefore the clearance between the two vehicles to increase. Pressing the 'Time Gap' switch causes the time gap value to decrease and therefore the clearance between the two vehicles to decrease.

REACTION TO A SLOW MOVING OR STOPPED VEHICLE –
Situations may occur such that the ACC system is not able to maintain the time gap within the deceleration authority of the system, 0.2 [g]. The clearance between the ACC vehicle and the forward vehicle may be rapidly decreasing or the minimum vehicle speed of 25 [mph] may be reached. Under these situations the ACC system enters 'ACC standby' and alerts the driver by displaying a "Driver Intervention Required" text message on the instrument cluster and by turning on an audible chime. If the brakes were being applied by the ACC system, they will be slowly released. At this point the driver must take control of the vehicle.


3.6 Transitioning Between Speed Control and Follow Modes


The ACC system automatically transitions between Speed Control and Time Gap (Follow) Modes. The mode of operation is determined by the lower of the set speed for Speed Control Mode and the target speed to maintain the gap between the ACC vehicle and a forward vehicle. Basically, if no vehicle is present within the clearance distance, the system will operate in Speed Control mode, else, it will operate in Time Gap mode.


3.7 Canceling Cruise Control Operation

Cruise Control operation may be canceled by the operator or automatically via the ACC system. Either of the following conditions will deactivate ACC:

Brake pedal is pressed
'Off' button is pressed
Vehicle Speed < 25 mph
An ACC system fault is detected
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Presented by:
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Cruise Control Devices
1. Introduction

Every day the media brings us the horrible news on road accidents. Once a report said that the damaged property and other costs may equal 3 % of the world’s gross domestic product. The concept of assisting driver in longitudinal vehicle control to avoid collisions has been a major focal point of research at many automobile companies and research organizations. The idea of driver assistance was started with the ‘cruise control devices’ first appeared in 1970’s in USA. When switched on, this device takes up the task of the task of accelerating or braking to maintain a constant speed. But it could not consider the other vehicles on the road.
An ‘Adaptive Cruise Control’ (ACC) system developed as the next generation assisted the driver to keep a safe distance from the vehicle in front. Advanced Cruise Control is also known as adaptive, active or intelligent cruise control, is an addition to conventional cruise control systems. ACC not only maintains the driver-set vehicle speed, but also adjusts the vehicle's speed to that of a preceding vehicle, helping to maintain a pre-selected headway time to the vehicle ahead. ACC uses a frontal radar/laser sensor to detect vehicles in front and subsequently adjusts the vehicle's speed and headway by controlling fuel flow or by slightly braking. Active braking carried out by ACC can usually reach up to maximally 30% of the vehicle’s maximum deceleration. When a stronger deceleration is needed, the driver is warned by an auditory signal. Once the preceding, slower vehicle has moved out of the lane, the vehicle's speed will return to the driver-set cruise speed.
The first ACC systems that were introduced to the market in the late 1990’s were a rather expensive option for top-of-the line vehicle models. Today, ACC can be found on a much wider range of vehicle models. However, the equipment rate within the entire vehicle fleet is still very low. Most of the ACC systems now available function for speeds above 30 km/h, have a detection range of 120m to 150m, and allow for a manually set headway time between 1 and 3 seconds This system is now available only in some luxury cars like Mercedes S-class, Jaguar and Volvo trucks the U.S. Department of transportation and Japan’s ACAHSR have started developing ‘Intelligent Vehicles’ that can communicate with each other with the help of a system called ‘Co operative Adaptive Cruise Control’ .this paper addresses the concept of Adaptive Cruise Control and its improved versions.
2. Adaptive Cruise Control (ACC)
2.1 Principle of ACC

ACC works by detecting the distance and speed of the vehicles ahead by using either a Lidar system or a Radar system .The time taken by the transmission and reception is the key of the distance measurement while the shift in frequency of the reflected beam by Doppler Effect is measured to know the speed. According to this, the brake and throttle controls are done to keep the vehicle the vehicle in a safe position with respect to the other. These systems are characterized by a moderately low level of brake and throttle authority. These are predominantly designed for highway applications with rather homogenous traffic behavior. The second generation of ACC is the Stop and Go Cruise Control (SACC) whose objective is to offer the customer longitudinal support on cruise control at lower speeds down to zero velocity.
The SACC can help a driver in situations where all lanes are occupied by vehicles or where it is not possible to set a constant speed or in a frequently stopped and congested traffic. There is a clear distinction between ACC and SACC with respect to stationary targets. The ACC philosophy is that it will be operated in well structured roads with an orderly traffic flow with speed of vehicles around 40km/hour. While SACC system should be able to deal with stationary targets because within its area of operation the system will encounter such objects very frequently.
2.2 Constituents of an ACC System
1. A sensor (LIDAR or RADAR) usually kept behind the grill of the vehicle to obtain the information regarding the vehicle ahead. The relevant target data may be velocity, distance, angular position and lateral acceleration.
2. Longitudinal controller which receives the sensor data and process it to generate the commands to the actuators of brakes throttle or gear box using Control Area Network (CAN) of the vehicle.
3. Sensor Options
Currently four means of object detection are technically feasible and applicable in a vehicle environment. They are
1. RADAR
2. LIDAR
3. VISION SENSORS
4. ULTRASONIC SENSOR
The first ACC system used LIDAR sensor.
3.1 LIDAR (Light Detection and Ranging)
Lidar is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar radar technology, which uses radio waves instead of light, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal.
The first acc system introduced by Toyota used this method. By measuring the beat frequency difference between a Frequency Modulated Continuous light Wave (FMCW) and its reflection.
There are several major components to a lidar system:
1. Laser
2. Scanner and optics
3. Receiver and receiver electronics
Fig.1.Range estimation using FMCW-LIDAR
A company named Vorad Technologies has developed a system which measured up to one hundred meters. A low powered, high frequency modulated laser diode was used to generate the light signal.
Most of the current acc systems are based on 77GHz RADAR sensors. The RADAR systems have the great advantage that the relative velocity can be measured directly, and the performance is not affected by heavy rain and fog. LIDAR system is of low cost and provides good angular resolution although these weather conditions restrict its use within a 30 to 40 meters range.
3.2 RADAR (Radio Detection and Ranging)
RADAR is an electromagnetic system for the detection and location of reflecting objects like air crafts, ships, space crafts or vehicles. It is operated by radiating energy into space and detecting the echo signal reflected from an object (target) the reflected energy is not only indicative of the presence but on comparison with the transmitted signal, other information of the target can be obtained. The currently used ‘Pulse Doppler RADAR’ uses the principle of ‘Doppler effect’ in determining the velocity of the target.
3.2.1 Pulse Doppler RADAR
The block diagram of pulse Doppler radar is as shown in figure.2.
The continuous wave oscillator produces the signal to be transmitted and it is pulse modulated and power amplified. The ‘duplexer’ is a switching device which is fast-acting to switch the single antenna from transmitter to receiver and back. The duplexer is a gas-discharge device called TR-switch. The high power pulse from transmitter causes the device to breakdown and to protect the receiver. On reception, duplexer directs the echo signal to the receiver. The detector demodulates the received signal and the Doppler filter removes the noise and outputs the frequency shift ‘fd’.
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