Vehicle Dynamics - Fundamentals and Modeling Aspects

Introduction

• Vehicle dynamics involves various engineering disciplines such as classical mechanics, physics, and more.
• Focuses on ground vehicles with wheels and tires.
• Key components: driver, vehicle, load, and environment.
• Goal: improve safety, comfort, and reduce road wear.

Driver

• Can influence the vehicle through steering, acceleration, braking, and gear shifts.
• Receives feedback from vehicle vibrations and sounds.
• Driver simulation in labs uses ideal models.

Vehicle

• Vehicles categorized by ISO, including cars, buses, trucks, and trailers.
• Complex dynamics modeled through calculations, testing, and simulations.

Load

• Affect vehicle dynamics, e.g., truck behavior changes with load.
• Challenges in modeling dynamic loads (e.g., liquid loads).

Environment

• Road irregularities, friction, and climate impact dynamics.
• Reproduction of environmental effects in testing is difficult.

Road Modeling

Deterministic and Random Profiles

• Road models provide height and friction data.
• Deterministic models include bumps, potholes, and sine waves.
• Random profiles characterized statistically, often using power spectral densities.

Tire Dynamics

Tire Development

• Progression from vulcanization to modern pneumatic tires.
• Run-flat tires allow driving post-deflation.

Tire Forces and Torques

• Contact patch transmits normal and friction forces.
• Forces and torques measured for dynamics modeling.
• Complex models (e.g., FTire) simulate tire behavior.

Contact Geometry

• Defines interaction between tire and road.
• Calculations involve contact point velocity and dynamic rolling radius.

Drive Train

Components

• Includes engine, clutch, transmission, and differentials.
• Different configurations for power distribution among wheels.

Wheel and Tire Dynamics

• Influenced by torques and external forces.
• Dynamic models simulate wheel behavior under different conditions.

Suspension Systems

Purpose and Components

• Supports vehicle weight, maintains alignment, and reduces shock effects.
• Types include coil springs, torsion bars, and air springs.

Examples of Suspension Systems

• Multi-purpose: double wishbone, McPherson, multi-link.
• Specific: semi-trailing arm, twist beam.

Force Elements

Standard Force Elements

• Springs and dampers absorb and control forces.
• Anti-roll bars reduce body roll.

Dynamic Force Elements

• Tested through frequency domain analysis.
• Advanced models mimic real-world behaviors.

Vertical Dynamics

Goals

• Optimize ride comfort and safety.
• Influence of body suspension and damping on dynamics.

Basic Tuning

• Simplified models used for initial studies.
• Quarter car models evaluate suspension performance.

Longitudinal Dynamics

Dynamic Wheel Loads

• Defined by forces at front and rear axles.
• Static and dynamic loads affect vehicle behavior.

Maximum Acceleration

• Limited by tilting and friction conditions.
• Aerodynamics play a significant role at high speeds.

Driving and Braking

Single Axle Drive

• Acceleration varies between front and rear wheel drives.

Braking Stability

• Locked front wheels offer more stability than rear.

Optimal Force Distribution

• Aims for equal skid resistance across axles.

Lateral Dynamics

Kinematic Approach

• Tire models predict vehicle path without lateral slip.

Steady State Cornering

• Evaluates vehicle stability and steering tendencies.

Mechatronic Systems

Electronic Stability Control (ESC)

• Integrates various systems to maintain vehicle control.

Steer-by-Wire

• Uses electronics for steering control, improving safety and performance.

Driving Behavior

Standard Driving Maneuvers

• Steady state cornering and step steer input assess vehicle control.

Different Rear Axle Concepts

• Various designs impact vehicle handling and stability.