chapter 3 - cruise control systems
TRANSCRIPT
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CRUISE CONTROL SYSTEMS
CHAPTER 3
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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
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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.
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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.
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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.
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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
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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 -
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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.
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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.
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FEEDBACK
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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.
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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
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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.
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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.
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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.
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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.
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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
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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.
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ADAPTIVE CRUISE CONTROL
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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.
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7. Radar Headway Sensor
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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.
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i i l i l
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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)