Anti-lock Brake System

Group 2

Presenters: Christan Balnius,Zain Kazim, Mark Pulver

Demo Given by: Brian Lawnichak

Unique Feature: Distributed Control System (DCS)

• Enhances modularity of system• Components of DCS

– Manager– Wheel Monitors– Wheel Cylinder Gnomes

http://members.tripod.com/~waterdragon/boygnome.gif

What DCS Supports

• Functionality of DCS– Computes, recognizes, and responds to

rapid deceleration– Encapsulates per-wheel activity

• Sample scenario description– Manager receives brake signal– Manager signals Wheel Monitors– Wheel Monitors compute deceleration– Wheel Monitors signal Gnome

Key Model: State Diagram

• High-level state diagram showing concurrent processes

• It is key because– Shows the major components of system– Highlights concurrency

We will decompose this further…

High-level State Diagram

Key Model Revisited

• Now focusing on the Manager, which is the top level of the DCS

• Manager is key because– Handles error testing– Responds to signals from vehicle– Sends signals to wheel monitors as

appropriate• State diagram highlights this behavior

Manager State Diagram

Critical Properties

• Safety properties– If ABS fails, mechanical braking still works– ABS activity never leads to spins

• Liveness properties– If the car speed drops below 15 mph while

braking, ABS becomes idle– If a skid is detected above 15 mph, pressure

is modulated on the wheel

Promela and XSpin

• Verification Technique– Modeled our state diagram in Promela– Verified safety and liveness properties

through use of LTL invariants– Assertion and reachability tests were also

performed

Safety Property Verification

• If ABS fails, mechanical braking still works

• [](Error -> (Power Off | Brake Not Pressed | <>(Main Brake Valves Open, Relief Valves Closed)))

• XSpin verified that this property holds

Liveness Property Verification

• If the car speed drops below 15 mph while braking, ABS becomes idle

• [](Below Activation Speed -> <>(Wheel Monitors Idle))

• XSpin verified that this property holds

Demo of Prototype

• High-level features of User Interface:– Independent control of wheel speed and

acceleration– Changeable environmental factors– Feedback on system-wide conditions with

indicator lights– Per-wheel information readout

Scenario 1

• Single-wheel skid– Press ignition button to start engine– Increase system speed to 30 m/s– Press brake button– Decrease the speed on wheel 3 to 20 m/s

Scenario 2

• Change-of-surface skid– Press ignition button to start engine– Increase system speed to 30 m/s– Press brake button– Initiate a panic brake by increasing system

brake pressure to 200 kg– Change road type from “Pavement” to

“Gravel”