The Acceleration and climbing resistance also contributes to the overall road resistance on the moving vehicle.
Accelerating and Deceleration:
When the vehicle moves on acceleration, mass inertia forces arise in the opposite direction of the acceleration. As deceleration is negative acceleration the inertia forces have their effect with the direction of the movement of the vehicle. The proportion of inertia forces in the overall road resistance is called Acceleration resistance.
Translational and Rotational:
The Acceleration resistance is divided in to 1) Translational Part and 2) Rotational part. A Translational part resulting from the total mass of the vehicle and a rotational part arises due to the mass inertia of the rotating components of the vehicle drive unit. The rotational part is relatively insignificant as regard to the total road resistance.
The climbing resistance is the proportion of the overall road resistance that is influenced by the Topography (Ref. fig)
A: Forces on upward inclined.
B: Forces during Acceleration.
a: vehicle Acceleration
m: Mass of the vehicle.
αST: Upward inclination angle
G: vehicle weight
FST: Climbing resistance
FT: Acceleration resistance
The down ward force FST works against the direction of the travel of the vehicle when the vehicle moves upwards on the inclined plane and when driving downhill it works in the direction of the movement of the vehicle. It is proportional to the gross weight of the vehicle and the inclination angle of the inclined plane on which the vehicle is moving.
FST = G . SinαST
Here αST specifies the inclination angle.
Acceleration resistance is influenced by the inertia forces. The greater the vehicle acceleration ie.the faster the change in speed the greater the force required to over come the acceleration resistance. Similar way the Accelerating force FT (Translational force) also rises with the mass “m” of the accelerated vehicle.
FT = -m . a
On Braking or Deceleration the inertia forces continue to push the vehicle in its direction of movements. It is very significant factor in the case of commercial vehicles due to heavy mass.
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