Evaluation of system’s behaviour as static camber angle is changed

The evaluation of the total force in Figure 6.43 confirms what was already found in this paragraph:

There is a large increase in force as steering starts, then it fluctuates and finally it stabilizes to a final value for both tests. The front axle has higher frequency peaks in its stabilization phase compared to the rear one, what’s interesting between the two is how the forces are distributed between the two axles, the short vehicle will have the two axles with comparable values, a clearer difference between the two will be present for the long wheelbase vehicle. The front axle will be more loaded than the rear one by a good margin, this reflects the different weight distribution between the two vehicles.

Figure 6.45: Lateral acceleration variation as the camber angle is changed, magnified in the second graph

Like in previous cases, analysis on side-slip angle and lateral acceleration gives a good idea on how the vehicle behaves overall during the manoeuvre, these graphs are important because they give an idea on how the system changes with camber, the differences in values between the different configurations are small but the trend that each parameter follows is clear, both side-slip angle and lateral acceleration will increase as the camber value moves towards more negative values.

The opposite happens towards positive values, the shape of the curve is basically the same between all the configurations, results are found in Figure 6.44 and 6.45.

Figure 6.46: Camber angle variation as static camber is changed, experienced in the front wheels

Camber angle will slightly change from the static value as the manoeuvre occurs, by watching the graph in Figure 6.46 it is possible to split the camber analysis in three different phases:

1. A first phase before the start of the step steering motion where camber is equal to the static camber value set.

2. A second phase representing the step steer itself, in this phase the system will try to react to the steering motion, this results in an oscillation of the camber values shown by a sinusoid.

3. A final phase where the camber reaches the value that will keep during the corner, when the steering wheel is set at the defined angle.

For the front wheels, there are some differences between the left and the right wheel, the most loaded wheel is the outer one, in this case the right wheel, on this side the camber value will basically go back to the static camber value after the oscillation. The inner wheel will instead move towards more positive angles, this is mainly related to the roll angle experienced by the vehicle. The rear axle experiences what was found in all the other cases, the rigid axle will make the inner wheel move towards positive values and the outer towards negative values, comparing Figure 6.46 and 6.47 it is possible to understand how a suspension with camber recovery reacts compared to a suspension typology where camber recovery is not possible. When evaluating the inclination angle, it is possible to have a better representation of how the wheels actually vary in angle. When comparing Figure 6.48 with Figure 6.46 it is possible to see that after the steering motion the inclination angle will change.

Figure 6.47: Camber angle variation as static camber is changed, experienced in the rear wheels

Camber angle variation could not catch this phenomenon, mostly due to the fact that reference systems changed before and after the steering phase. By keeping the reference system fixed to the one that defines the ground it is possible to evaluate how much the angle changes.

Left to right variations are comparable and the difference from the neutral condition is almost

symmetrical for positive and negative variation. The stabilization phase is almost identical between the three cases.

Figure 6.48: Inclination angle variation with static camber variation, for the front axle

On the rear axle, shown in Figure 6.49 it is possible to see that differences between the conditions studied are negligible, the main change is on the static value at the beginning. Distance between left and right curve is halved after the stabilization phase, compared to the initial difference. At the beginning only weight may affect this angle: As the vehicle will be steered, the roll angle will load more one side changing the relationship between left and right angle.

Toe angle results to be not affected by the value of static camber, the variation between the different tests is very minimal, both in values and shape.

Figure 6.49: Inclination angle variation with static camber variation, for the rear axle

Computation of forces along the duration of the test gave interesting results, as it is shown in Figure 6.50: In term of values there is a small difference between the three tests, what is important to catch is the inversion of trends between front and rear axle. On the front, the total force in the axle will increase as the static camber moves towards positive values; The opposite happens on the rear axle,

when camber moves to positive values lateral force will decrease on the rear axle. Negative camber will move the lateral load from the front to the rear and vice versa, this will likely affect the understeering or oversteering behaviour of the vehicle.

Figure 6.50: Lateral force variation experienced by the front and rear axle as camber angle is changed