This document describes an adaptive cruise control (ACC) system for an automobile. It discusses the functions of ACC which automatically controls speed based on traffic conditions while maintaining a safe distance from the vehicle ahead. It outlines the inputs and outputs to the ACC system including radar/laser signals, throttle position, and brake status. It also describes the control panel interfaces, design metrics for testing, and how the ACC algorithm adapts the vehicle's speed and braking based on the distance to the preceding vehicle.

1. Case Study of an Embedded
System for an Adaptive Cruise
Control (ACC) in a Car

2. • Embedded
Systems in
Automobiles
• What is ACC
System, its
functions and
requirements?
• Working, ACC
Algorithm and
Hardware
Architecture

3. Embedded Systems in
Automobiles
• Automobiles have many
Embedded Systems called
ECU’s.
• A car may have the following
types of ECU’s embedded in
it.
• Engine control, Speed control
and braking systems, Safety
systems, Infotainment
systems etc.

4. Types of
ECU’S

5. Adaptive Cruise Control System
(ACC)
Function
• It automatically controls the speed of
the car where the speed is preset by the
driver and the system takes the control
of throttle and adjusts the speed of the
car depending on the traffic
conditions(by measuring safe distances).
• Its also called as Intelligent Cruise
Control(ICC)
Application
• This type of technology is commonly
used in automobiles, aviation electronics
and defence aircrafts for cruising

6. Requirements
Inputs and Outputs
Control Panel, Signals and
Notifications
Design Metrics, Test and
validation conditions

7. Inputs and
Outputs
• Inputs:
1. Present alignment of Radar (or laser)
beam emitter.
2. Delay interval in reflected pulse with
respect to transmitted pulse from
emitter.
3. Throttle position.
4. Speed from speedometer.
5. Brake status for brake activities from
brake pedal.
• Outputs:
• Transmitted pulse at regular intervals
• Alarms
• Range and speed messages
• Brake control
• Output to pedal system for applying
emergency brakes and driver for taking
charge of cruising from ACC system

8. Control Panel, Signals
and event notifications
• Control Panel:
• Switch cum display for ‘ON’, ‘OFF’,
‘RESUME’, ‘COAST’ and
‘SET/ACCELERATE’.
• The driver activates or deactivates, the
ACC system by pressing ‘ON’/‘OFF’
respectively.
• S/he sets the cruise speed by
‘SET/ACCELERATE’ switch. The driver
hands over or resumes the ACC by
pressing ‘COAST’ or ‘RESUME’
respectively.
• A switch glows green or red as per the
status when ACC activates.
• Signals and event notifications:
• User commands given as signals from
switches/ buttons. User control inputs
for ACC on, off, coast, resume,
set/accelerate buttons.
• Brake event (Brake taping to disable the
ACC system, as alternative to “cancel”
button at front panel.
• Safe/Unsafe distance notifications.

9. Design metrics, Test and
Validation conditions
• Design Metrics:
• Resolution: 2m inter car distance
• Performance: Safe distance setting 75m
to 200m.
• Process Deadline: Less than 1s response
on observation of un-safe distance of
front end car.
• User interface: Graphics at LCD or touch
screen display on LCD.
• Test and Validation Conditions:
• Test in dense as well as light traffic
conditions.
• Tested on plains, hills and valley roads.
• All user commands must function
correctly.

10. Working
• An ACC car system moves in a cruise
mode at a preset speed. A radar or laser
emits signals at regular intervals. These
signals are reflected from the vehicle in
front. When reflected signal received
earlier than expected from minimum
safe distance, it notifies the presence of
another vehicle to the system. The ACC
system then decelerates and the car
slows down. It accelerates again to the
preset speed when condition permit.
• New systems apply the brakes also and
deploy a Collision Mitigation Braking
(CMB) system. The CMB alerts the driver
if the object is at less than 100m
distance. If the driver still doesn’t
react, the system retracts, locks the
seatbelts and brakes hard.

11. Adaptive control
algorithm adapts and
functions
• An adaptive control means an
algorithm, the parameters in
which adapts to the present
status of the control inputs in
place of constant set of
mathematical parameters in
algorithmic equations.
• For an ACC system, an
adjustable system sub-unit
generates output control
signal to throttle valve.

12. • The desired pre-set cruise velocity V(t)
desired pre-set distance d(set) and safe
pre-set distance d(safe) are the inputs to
index of performance measurement sub-
unit. The measured cruise velocity v and
distance d has inputs to index of
performance computing sub-unit. The
comparison and decision sub-unit has
inputs of set performance parameters and
observed performance parameters. It sends
outputs which are inputs to adaptive
mechanism sub-unit. The adaptive
mechanism sub-unit sends outputs, which
are inputs to adjustable system.

13. Class diagrams
• ACC system measurements of
front end car range, distance
and error estimations and
adaptive control can be
modeled by 2 class diagrams
of abstract classes, Task_ACC
and Task_Control .

14. • Task_ACC is an abstract class, derived to measure the range and errors. Task_ACC
extends to Task_Align, Task_Signal, Task_ReadRange and Task_Algorithm.
• Task_Control is an abstract class derived to measure the range and errors. This includes
Task_Brake, Task_Throttle and Task_Speed.
• Task_Algorithm interfaces Task_Brake, Task_Throttle, Task_Speed and Task_ReadRange.
• There are 2 ISR objects, ISR_ThrottleControl and ISR_BrakeControl.

15. ACC Hardware
Architecture
• An automotive embedded system based
control unit use the microcontroller and a
separate microprocessor. The ACC embeds the
following hardware units:
• A microcontroller runs the service routines and tasks
except the Task_Algorithm. The microcontroller has
stores temporary codes and stack. ROM saves the
application codes and RTOS codes for scheduling the
tasks.
• CAN(Controller Area Network) interfaces ACC system
with the other embedded systems of the car.
• Transceiver for transmitting pulses through an
antenna hidden under the plastic plates.
• Stepper motor based alignment unit and throttle
control unit