Introduction to Vehicle Dynamics

What is Vehicle Dynamics?

Vehicle dynamics describe how a vehicle moves and how the forces and moments acting upon it influence that motion. It helps engineers understand and assess vehicle handling under various driving conditions such as braking, acceleration, steering, or cornering, as well as under external influences like uneven roads or crosswinds. During vehicle dynamics evaluations, parameters such as accelerations, angular velocities, and vehicle speeds are measured to better understand the vehicle’s behavior during these maneuvers. A stable vehicle is controllable and therefore safe under all driving conditions. These motions can be described using six degrees of freedom.

Areas of vehicle dynamics

To evaluate all aspects of vehicle dynamics, the field is commonly divided into three subcategories, each focusing on one axis of motion:

Longitudinal dynamics

Lateral dynamics

Vertical dynamics

Longitudinal dynamics primarily concern acceleration — including the effects of the powertrain, braking, aerodynamic drag, and fuel consumption. Lateral dynamics focus on steering behavior, cornering stability, and rollover protection. Vertical dynamics mainly focus on driver comfort as well as pitch and roll. For high performance cars it also includes aerodynamics and maximizing tire potential.

Testing and evaluation

To understand, quantify, and improve vehicle behavior and performance, it must be tested, measured, and evaluated using various methods and techniques.

Test methods

Common test methods include constant-radius cornering, lane-change maneuvers, sine-sweep tests, and obstacle avoidance. Each targets a different aspect of vehicle handling.

Methodology

To obtain meaningful data for these tests, various measurement techniques are used. These include velocity measurement, side-slip angle detection, pitch and roll angle measurement, and angular velocity recording.