The Driving Dynamics analyses the forces that acts on the moving vehicle. The combination of all Forces that offset the vehicle during driving movement is monitored for its effectiveness. These forces are influenced by the following parameters.

  • Vehicle weight
  • Acceleration
  • Deceleration (Braking)
  • Road conditions
  • Cornering and
  • Air flow


X- Longitudinal Axis.
1 – Acceleration and Deceleration
2 – Rolling (Snaking)

Y- Transfers Axis
3 – Transfers Vibrations
4 – Pitching (nosing)

Z – Vertical Axis
5 – Lifting, Lowering.
6 – Yawing (swinging)

 

Co-ordinate System
There are total of six forces acting on the freely moving body. One for each of the three co- ordinate system and rotational forces around these three axes.
According to the three coordinates these forces are sub divided as

  • Longitudinal dynamics
  • Transfers dynamics and
  • Vertical dynamics.

Longitudinal Axis:
The longitudinal axis passes through the vehicle corresponds to X axis in the co-ordinate system. It is directed towards the direction of Travel. In this axis speed and Acceleration as regarded as positive and Brakes and Deceleration are defined as negative. The Tensional vibrations around these Axes are referred as “Rolling” or “Snaking”.
Transverse Axis:
The Y Axis of the Co-ordinate system is termed as transverse axis. This Axis is arranged vertically to the direction of the moving vehicle. In this system the movement to the left is regarded as positive. Linear vibrations along these axis are referred as” Shaking” or Transversal Vibrations, tensional vibrations are termed as “Pitching” or “Nosing”.
Vertical Axis:
Vertical Axis Z is located at right angle to the longitudinal and transverse axes and points upward. Lifting and Lowering are referred for linear vibrations, “Yawing” or “Swinging” for torsional vibrations

LONGITUDINAL VEHICLE DYNAMICS:
Longitudinal vehicle dynamics is a sub area of Driving Dynamics. It deals with all the forces exerted in the longitudinal direction of the vehicle. To move the vehicle we should overcome the road resistance. Similarly the body with mass and volume possess some resistance to the motion. This overall resistance is divided in to 4 major components.

  • Rolling resistance
  • Climbing resistance
  • Acceleration Resistance and
  • Aerodynamic drag

Depending upon the driving situation the intensity of the individual road resistance varies. When designing a vehicle attempts are made to reduce these road resistance in order to improve the efficiency of the vehicle and to lower the fuel consumption.
Rolling Resistance FR occurs when the wheels rolls on the wheel surface. It is determined by the vehicle weight and Rolling resistance co-efficient μR. The Rolling Resistance co-efficient depends on the type of the Tyre and the road surface. The higher the vehicle weight or wheel load the greater the rolling resistance co-efficient.

FR = μR . GR = μR . M . g

The rolling resistance is composed of

  • Rolling friction
  • Flexing work
  • Air friction in the Tyre
  • Friction in the wheel bearing

The rolling resistance can be reduced using the following measures.

  • Selection of right tyres
  • Proper wheel alignment and
  • Regular check on Tyre inflation

 

 Load dependency of the Rolling Resistance Co-efficient

 

 ROLLING RESISTANCE CO-EFFICIENT: With decrease in Tyre pressure and increase in vehicle load the Rolling resistance Co-efficient increases and hence the rolling resistance power to be overcome.

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