The Role of Handling Characteristics in Driver Assistance Systems with Environmental Interaction

1
The Role of Handling Characteristics in Driver
Assistance Systems with Environmental Interaction

• Eric Rossetter
• Dynamic Design Lab
• Stanford University
• 6/29/2000

2
Overview

• Introduction
• Vehicle Control with Virtual Forces
• Effects of Handling on System Performance
• Stability Analysis
• Conclusions

3
Introduction and Motivation

• Current Driver Assistance Systems
• ABS
• Traction Control
• Stability Control Systems
• Problem No Collision Avoidance
• In 1996 almost 30 of all fatal accidents
  involved collisions with fixed environmental
  objects
• Goal To create safe vehicle behavior in the
  presence of obstacles

4
Control with Virtual Forces

• Use controls to apply a virtual force to the
  vehicle
• Previous Work
• Reichardt and Schick
• Electric Field Analogy
• Hennessey et al
• Virtual Bumpers

Lane Keeping System
5
Our Approach to Driver Assistance Systems

• Use a potential field framework
• Leave the driver in the loop
• Do not cancel the vehicle dynamics

High Hazard
Low Hazard
6
Vehicle Equations of Motion
Controlled Terms
Uncontrolled Terms
7
Control Law
Write equations of motion in the form
Given a potential function V(w)
Road Fixed Coordinates
8
Control Law

• System is Passive
• Kinetic plus Artificial Potential Energy is
  Bounded
• Vehicle is now coupled to the environment
• Performance depends on handling characteristics

e
Simple Lane Keeping
9
Closed Loop Performance

• Apply virtual force at the center of gravity
• Desired behavior for understeering vehicles
• Instability for oversteering vehicles

2
10
Closed Loop Analysis

• Jacobian linearization about a constant
  longitudinal velocity
• Two eigenvalues associated with vehicle handling
• Two eigenvalues associated with environmental
  coupling

e lateral position y heading angle
11
Closed Loop Analysis Results

• Oversteering Vehicle
• Always Unstable
• Critical Speed ? 0
• Understeering Vehicle
• Stable below a critical speed
• Critical speed is large 100 mph
• Can the oversteering case be stabilized?

12
Stabilizing the Oversteering Vehicle

• Shift the application point of the virtual force
• Stabilize by negating the adverse rotational
  effects
• A convenient location is the neutral steer point
• No steady state yaw rate

Neutral Steer pt.
F
virtual
13
Results of Shifting the Virtual Force

• Stable under a critical speed
• Changing the application point alters the dynamic
  behavior

14
Conclusions

• Handling influences stability in any system that
  couples the vehicle to the environment
• Applying virtual forces at the center of gravity
  creates instability for oversteering vehicles
• Shifting the application point
• Stabilizes oversteering vehicles
• Alters the behavior of the vehicle