In a straight-line braking manoeuvre a vehicle can be subjected to a yawing moment due to different causes, such as a center of gravity lateral displacement from the vehicle center-line, dissymetries in braking forces, due to friction material tolerances, or an asymmetric behavior of left and right suspensions in vertical displacement and/or under loads. This yawing moment produces a deviation from the straight-line trajectory, whose entity is strictly related to the car directional stability. A numerical analysis of vehicle behavior during braking has been performed in order to find design criteria that allow either to reduce the yawing moment or to limit the car sensibility to unbalancing effects. The analysis has pointed out the influence of mass distribution and tyre characteristics on the braking directional stability of a light small car, with short wheel-base and high center of gravity and so with a great load transfer between front and rear axle. The entity of the yawing moment can be limited acting at design level on mass distribution in order to minimize the vehicle center of gravity lateral displacement from the center-line in all load conditions. Anyway the car sensibility to unbalancing moments can be reduced acting on tyre characteristics, in particular specifying the ratio between front and rear tyre concerning stiffness and using tyres with good lateral performances also at low loads.
Braking stability of lightweight small cars
Bremsstabilität von Leichtkleinwagen
1997
9 Seiten, 4 Tabellen
Conference paper
English
Braking stability of lightweight small cars
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