The centrifugal force acts on a body when it moves in the circular direction. The centrifugal force Fc takes effect in the centre of gravity on the vehicle and exerts force in a radial direction from the centre of the circular path towards the out side. It is directly proportional to the mass and driven speed of the vehicle and it rises with the decrease in corner radius.
The centrifugal forces supported by the cornering forces lead to transversal acceleration of the vehicle towards the centre of the curve. The tyre slip angle of different sizes occurs at the wheels depending on the strength of the centrifugal forces. The tyre slip angle increases with the increase in Transversal acceleration.
Differences in wheel load:
The differences in wheel load occur due to all the forces affecting the wheel above the road surface. These differences in wheel load reduce the possible cornering forces while the tyre slip angles remain the same. In the other case, the external forces and thus the cornering forces to be applied must be achieved by means of greater tyre slip angle. i.e. stronger turning, where required.
Following two fundamental negative effects on the vehicles can be seen on cornering.
- Swerving or Yawing and
- Inclination to outer edge of curve(rolling)
Swerving or Yawing can be largely prevented by the Electronic Stability Programme (ESP).
If the vehicle move not only in a positive linear direction along its longitudinal axis “x”, but rather it turns around the vertical axis “z”, this phenomenon is called Yawing. If this additional rotation takes place in the same direction as that of the vehicle longitudinal axis above the ground the vehicle over steers, otherwise it under steers.
The product of exterior forces and the cornering forces of the individual wheels with their lever arms at their center of gravity S gives the Yawing moment Mg.
The resulting forces of the cross wind on the surface point or the centrifugal forces affecting the centre of gravity of the vehicle lead to the vehicle rolling out of the curve.
The inclination of the rolling angle depends on the distance “r” of the centre of gravity to the instantaneous centre (rolling axis), spring rates of the suspension, and the stabilisers.
The instantaneous centre or rolling axis of the vehicle is the theoretical axis around which the vehicle turns with the rolling movement. The rolling movement Mw arises around the rolling axis from the force and the lever arm “r”. The higher the centre of gravity the greater the rolling movement and associated roll angle. This is why in engineering design , when loading the commercial vehicles attention must paid to have low location for centre of gravity.
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