Chapter 3 - Cruise Control Systems

8/12/2019 Chapter 3 - Cruise Control Systems

1/25

CRUISE CONTROL SYSTEMS

CHAPTER 3


2/25

UNDERSTAND THE CRUISE CONTROL

SYSTEM

1. Control System Theory

2. Proportional Control System

3. Proportional Integral Derivative Control ( PID

Control )4. Integral Of Speed Is Distance

5. Derivative Of Speed Is Acceleration

6. Adaptive Cruise Control7. Radar Headway Sensor

8. Digital Signal Processor

9. Longitudinal Controller


3/25

introduction

CRUISE CONTROL SYSTEM

INPUT

setting buttons on

the steering wheel

gas pedal

brake

Clutch

the feedback

signal of the cruise

control

PROCESSOR

to control the

speed of the carby utilizing the

control system

theory.

OUTPUT

the throttle

position, which

is corresponding

to the actual

speed of the car

- Cruise control system control the speed of the car by maintaining theconstant speed set by the driver.- Therefore, cruise control system can help reduce drivers fatigue in driving

a long road trip.


4/25

There are usually 3-5 setting buttons on the steering

wheels for the input to the cruise control system

The ONbutton turns on the cruise control function.

The OFFbutton turns off the cruise control function.

The SET/ACCELbutton is to set the speed of the car to

the current speed that the car is driving at. Also, by tapping theSET/ACCEL button once can

increase the speed of the car by 1mph and so forth.

The RESUMEbutton is to set the speed of the car backto the last maintained speed, which is the speed rightbefore the cruise control is disengaged.

The COASTbutton is to decrease the speed of the car.


5/25


6/25

THE BRAKE AND THE CLUTCH are the other inputs to thecruise control system. When the pedal is pressed, the cruisecontrol system is disengaged, so the speed control of the car

is taken over by the driver in adjusting the gas pedal and thebrake.

The speed for the cruise control can be set by pressingthe GAS PEDAL to accelerate the car to the desired speed,

and then hitting theSET button. Also, when the cruisecontrol is engaged, the gas pedal overrides the set speedfrom the cruise control, so the car accelerates as long as thegas pedal is pressed.

Finally, the feedback signal from the measured speed ofthe car is taken into account of the input of the curse controlsystem. This input is closely related to the control system ofthe cruise control.


7/25

1.Control System Theory

A cruise control system needs to accelerate to the desiredspeed in a short time without overshooting the speed of

the car. Also, it needs to maintain the speed with littledeviation, when the car is driving up or down a steep hill.

The cruise control system in a vehicle is studied in details.

FIRST- control concepts in cruise control system areinvestigated.SECOND - simplified cruise control models aredeveloped and simulated.THIRD - an introduction to adaptive cruise control

system is presented. Fourth, modeling of adaptive cruisecontrol system in a traffic simulation is carried.FOURTHthe future development of the advancedadaptive cruise control system is presented


8/25

2. Proportional Control System

Proportional Control System

A proportional controlsystem is a type of linearfeedbackcontrol system.

Two classic mechanical examples are the toilet bowl

float proportioning valveand the fly-ball governor. The proportional control system is more complex

than an on-off controlsystem like a bi-metallic

domestic thermostat, but simpler than aproportional-integral-derivative(PID) control systemused in something like an automobile cruise control.
http://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Control_systemhttp://en.wikipedia.org/wiki/Ballcockhttp://en.wikipedia.org/wiki/Centrifugal_governorhttp://en.wikipedia.org/wiki/On-off_controlhttp://en.wikipedia.org/wiki/Thermostathttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/Cruise_controlhttp://en.wikipedia.org/wiki/Cruise_controlhttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/PID_controllerhttp://en.wikipedia.org/wiki/Thermostathttp://en.wikipedia.org/wiki/On-off_controlhttp://en.wikipedia.org/wiki/On-off_controlhttp://en.wikipedia.org/wiki/On-off_controlhttp://en.wikipedia.org/wiki/Centrifugal_governorhttp://en.wikipedia.org/wiki/Centrifugal_governorhttp://en.wikipedia.org/wiki/Centrifugal_governorhttp://en.wikipedia.org/wiki/Ballcockhttp://en.wikipedia.org/wiki/Control_systemhttp://en.wikipedia.org/wiki/Feedback


9/25

3. Proportional Integral Derivative

Control ( PID Control )

The PID controller is the most common form of feedback. PID controllers are today found in all areas where control is used.

The controllers come in many different forms.

There are standalone systems in boxes for one or a few loops,

which are manufactured by the hundred thousand yearly. PIDcontrol is an important ingredient of a distributed control system.The controllers are also embedded in many special purposecontrol systems.

PID control is often combined with logic, sequential functions,selectors, and simple function blocks to build the complicatedautomation systems used for energy production, transportation,and manufacturing.

Many sophisticated control strategies, such as model predictivecontrol, are also organized hierarchically.


10/25

Cont

PID control is used at the lowest level; the multivariable

controller gives the set points to the controllers at the lowerlevel.

It is an important component in every control engineers toolbox. PID controllers have survived many changes in technology,

from mechanics and pneumatics to microprocessors viaelectronic tubes, transistors, integrated circuits.

The microprocessor has had a dramatic influence on the PIDcontroller. Practically all PID controllers made today are based

on microprocessors. This has given opportunities to provide additional features like

automatic tuning, gain scheduling, and continuous adaptation.


11/25

FEEDBACK


12/25

4. Integral Of Speed Is Distance

The integral function to convert the input velocity

to distance.

The figure below shows the integrator block from

MATLAB Simulink convert the velocity to distance.


13/25

5. Derivative Of Speed(velocity) Is

Acceleration

The derivative function is to convert the input

velocity to acceleration.

The figure below shows the integrator block from

MATLAB Simulink convert the velocity toacceleration.

/Speed


14/25

6. Adaptive Cruise Control (ACC) (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 detectwhether 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.


15/25

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.

Adaptive cruise control (ACC) system takes the traffic flow into

consideration in controlling the speed of a vehicle. ACC system not

only maintains the pre-set speed of a vehicle, likes a conventional

cruise control system does, but it also maintains a constant distance

between the vehicle and the vehicle ahead by adapting the speed. Vehicle equipped with ACC system has a forward-looking sensor at

the front of the vehicle to detect the relative speed of the preceding

vehicle and the distance in between the two vehicles. Therefore, the

difference between an ACC system and a CC system is that ACC

system has the ability to adapt the speed of the preceding vehicle.


16/25

The ACC system consists of a series of interconnecting components andsystems. The method of communication between the different modules is via aserial communication network known as the Controller Area Network (CAN).

ACC Module The primary function of the ACC module is to process theradar information and determine if a forward vehicle is present. When the ACCsystem is in 'time gap control', it sends information to the Engine Control andBrake Control modules to control the clearance between the ACC Vehicle andthe Target Vehicle.

Engine Control Module The primary function of the Engine Control Moduleis to receive information from the ACC module and Instrument Cluster andcontrol the vehicle's speed based on this information. The Engine ControlModule controls vehicle speed by controlling the engine's throttle.

Brake Control Module The primary function of the Brake Control Module isto determine vehicle speed via each wheel and to decelerate the vehicle byapplying the brakes when requested by the ACC Module. The braking system

is hydraulic with electronic enhancement, such as an ABS brake system, and isnot full authority brake by wire.


17/25

Instrument Cluster The primary function of the Instrument Cluster isto process the Cruise. Switches and send their information to the ACC

and Engine Control Modules. The Instrument. Cluster also displays textmessages and telltales for the driver so that the driver has informationregarding the state of the ACC system.

CAN The Controller Area Network (CAN) is an automotive standardnetwork that utilizes a 2 wire bus to transmit and receive data. Eachnode 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 messageheader is a unique identifier that determines the message priority. Anynode on the network can transmit data if the bus is free. If multiplenodes attempt to transmit at the same time, an arbitration scheme isused to determine which node will control the bus. The message with

the highest priority, as defined in its header, will win the arbitration andits message will be transmitted. The losing message will retry to send itsmessage as soon as it detects a bus free state.


18/25

Cruise Switches

The Cruise Switches are mounted on the steering

wheel and have several buttons which allow thedriver to command operation of the ACC system.The switches include:

1. On- place system in the 'ACC standby' state2. Off - cancel ACC operation and place system in the

'ACC off' state3. Set + - activate ACC and establish set speed or

accelerate4. Coast- decelerate5. 'Resume- resume to set speed6. 'Time Gap +- increase gap7. 'Time gap - decrease gap


19/25

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 systementers '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.


20/25

ADAPTIVE CRUISE CONTROL


21/25

Adaptive cruise control is similar to conventionalcruise control in that it maintains the vehicle's pre-set speed. However, unlike conventional cruisecontrol, this new system can automatically adjust

speed in order to maintain a proper distancebetween vehicles in the same lane. This is achievedthrough a radar headway sensor, digital signalprocessor and longitudinal controller. If the leadvehicle slows down, or if another object is detected,

the system sends a signal to the engine or brakingsystem to decelerate. Then, when the road is clear,the system will re-accelerate the vehicle back to theset speed.


22/25

7. Radar Headway Sensor


23/25

The sensor of the ACC system detects the vehicle ahead throughthe use of either radar or lidar. Lidar is light detecting andranging, and it is a laser-based analog to radar. Also, Lidar is lessexpensive to produce and is easier to package. However, itperforms poorly in rain and in snow. The light beams of lidar are

narrower than water droplets and snowflakes, so it pushes downthe signal-to-noise ratio in bad weather. The bad weathersituation can be detected by the ACC system from the rapidsetting of windshield wipers, the activating of the anti-brakesystem, or the slipping of tires on turn.

On the other hand, the radar sensor in ACC system can detect

moving vehicle at distance up to 120 m or even 150 m in fog,heavy rain or other weather conditions. The radar typicallyoperates in the millimeter-wave region at 76-77 Ghz. These highfrequencies of the radar can reduce the antenna size, so the carmanufacturers can mount the radar inside a cars front grillewithout changing the shape or the construction of the vehicle.


24/25

i i l i l


25/25

8. Digital Signal Processor

The processor of a cruise control is a control system

designed to obtain the speed set by the driver. It plays animportant 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.

9. Longitudinal Controller

The longitudinal controller is the part of the automotive

adaptive cruise control system that decides the

minimum allowable separation from the car ahead and

when and how to adjust the car's speed (via throttle

control and/or braking)

Chapter 3 - Cruise Control Systems

Documents

Transcript of Chapter 3 - Cruise Control Systems