Vehicle Dynamics

What is Vehicle Dynamics?

to get to vehicle dynamics we first look at Dynamics,
is a fork ( branch ) of classical mechanics that deals with forces and their impacts on Motion.

so Vehicle Dynamics is the study of vehicle motion, i.e. it’s movement changes in response

Why do we need it?

Apart from needing it for vehicles in general why EVs in general.

• High motor torque
  EVs Having the higher torque react differently upon acceleration over ICE vehicles
• Heavy Battery mass
  The centre of gravity and the vehicle load balance all depend on the immense weight of the batteries
• Software-controlled behaviour
  since most evs rely on systems like drive by wire and have a lot of software controlled aspects , sometimes including the power delivery it impacts the dynamics
• Safety, comfort, and efficiency challenges
  self explanatory

Vehicle Motions

• Longitudinal
  • Traction/Driving Force: Generated by the engine and transmitted through tires.
  • Braking Force: created upon braking to decelerate the vehicle
• Lateral
  • Centripetal Force: Keeps the vehicle on a curved path
  • Cornering Force: Generated by tire deformation.
• Vertical
  • Normal Force: Reaction force from the ground
  • Aerodynamic downforce: enhances grip at high speeds.
• Rotational:
  • Roll
  • Pitch
  • Yaw

Core Factors affecting the Vehicle Dynamics?

1. Distribution of Mass

2. Geometry and Kinematics of Moving Components and Tires

3. Most Contributing Subsystems: Suspension, Steering Frame, Aerodynamics

4. Aerodynamic Forces

Basic Principles and Concepts to Deal with when studying Vehicle Dynamics

1. Newton’s Laws of Motion
   the three laws serve as the foundation of all dynamic analysis

2. Forces acting on a vehicle
   refer vehicle motion ⬆

3. Tire Dynamics
   tires being the primary interface between the vehicle and the road:
   Rolling resistance
   Grip: the frictional force that allows tires to transmit acceleration, braking and cornering forces
   Slip Angle: The angle between the direction a tire is pointing and the direction its travelling, which influences the cornering perform
   Tire Models: help predict behaviour (e.g., magic formula/ Pacejka model)

4. Vehicle motion types
   refer vehicle motion again ⬆

5. Key performance metrics
   Stability: Ability to maintain control under various conditions.
   Handling: How the vehicle responds to driver input.
   Ride Comfort: Minimizing vibrations and shocks for passengers.
   Traction: Capability to transmit forces to the road without slipping.

6. Vehicle frames of reference
   Analysis requires a reference system ( coordinate system )
   Global Frame: Fixed reference system (ex: Earth’s surface )
   Vehicle Frame: Moves with the Vehicle, with:
   Longitudinal axis (x-axis): Forward/backward
   Lateral axis (Y-axis): left/right centripetal forces while cornering
   Vertical (Z-axis): up/down think of riding over a pothole.

7. Aerodynamics
   Drag Force: Opposes vehicle motion, proportional to speed squared.
   Lift Force: Acts vertically, potentially reducing tire grip.
   Downforce: Improves grip, especially in performance vehicles.

8. Suspension dynamics
   The suspension system supports vertical loads and improves ride quality.
   Springs and Dampers: Absorb shocks and maintain contact with the road.
   Roll Centre: Affects vehicle stability during cornering.

9. Vehicle stability
   Under Steer: Front tires lose grip first; the vehicle tends to go straight.
   Over Steer: Rear tires lose grip first; the vehicle tends to spin.
   Neutral steer: Ideal balance between front and rear grip.

Key aspects of vehicle dynamics.

the major components of vehicle dynamics are:

• Longitudinal dynamics ( Braking and Acceleration )
• Ride characteristics ( Vertical dynamics or suspension characteristics )
• Lateral and handling dynamics ( steering system performance)
• Noise, Vibration and Harshness