Alternatively, the activation of the stability control system can be triggered by an excess of estimated
sideslip angle, corresponding to a potential vehicle oversteer situation in comparison with the nominal conditions.
This makes AHK capable of preventing the build - up
of sideslip up to an extent.
The car with AHK on the other hand
minimizes sideslip making it much more stable on the corner exit.
As our entire starry neighborhood participates in the galaxy's grand rotation, we do a little 12 - mile - per - second
sideslip in Vega's direction.
Because of the
smaller sideslip angle in curves the test vehicle equipped with AHK was more stable on corner exits allowing the driver to apply throttle much sooner and gaining higher speeds on the straights.
AHK provides
maximum sideslip angle correction up to speeds of 220 km / h (137 mph).
Development and demonstration of yaw rate and
sideslip angle control algorithms based on the combination of front / rear and left / right torque vectoring to improve overall vehicle dynamic performance.
While doing so, the onset of oversteer is noticeable in good time and the linear increase of
the sideslip angle means that the vehicle remains stable,» noted BMW's release.
The reason is again with
the sideslip angle: The car without AHK develops sideslip in a curve which is still present at the exit of the curve.
The sideslip angle graph indicates the angle the vehicle makes with the current direction of travel.
This causes the vehicle to be angled to the actual direction of travel —
the sideslip angle.
The sideslip angle has a negative impact on the steering response of a vehicle and the steering effort that is required to change direction: If a driver decides to change direction in a curve while the vehicle is subject to oversteer and turns the steering wheel, because of the sideslip angle the vehicle's longitudinal axis has to cross the current direction of motion first before the vehicle body actually changes direction.
In oversteer
the sideslip angle amplifies itself ultimately ending in a spin.
The sideslip angle causes the vehicle's longitudinal axis to make a greater angle with the direction of travel axis of the slalom course than is strictly required for the maneuver.
AHK can steer the rear wheels far beyond what is possible with passive systems and because AHK does not rely on the build - up of forces acting upon the suspension and vehicle body but uses computer calculations based on the vehicle speed and steering angle instead, the system can counteract even before
the sideslip angle is actually built - up.
Steering the rear wheels into the curve forces the car's rear back towards the inside of the curve and moves the longitudinal axis back towards the direction of motion, reducing
the sideslip angle.
This on its turn increases the lateral acceleration and
sideslip angle, amplifying the steering even further.
The sideslip angle slows down the steering input.
The effect of the lateral force on
the sideslip angle is much lower for the vehicle with AHK.
The negative effect of
the sideslip angle is very evident in a high - speed slalom maneuver.
Minimizing
the sideslip does not only improve safety in curves.
It's obvious
the sideslip angle has a very negative impact on the handling of the car throughout the maneuver.
AHK can reduce
the sideslip angle from 4.5 degrees (without AHK) to well below 1 degree.
The sideslip points the vehicle's longitudinal axis towards the inside of the curve, amplifying the steering angle of the front wheels on the direction of motion.
AHK continues to reduce
the sideslip angle at even higher speeds but because it can not steer the rear wheels beyond 2 degrees the sideslip angle correction gradually decreases.
The higher the lateral acceleration becomes, the larger
the sideslip angle grows.
At low speeds
the sideslip angle is negligible and thus is AHK not active.
The angle between the car's longitudinal axis and direction of motion is
the sideslip angle.
Due to a limited degree of correction
the sideslip angle is not entirely neutralized by the AHK system; a small delay between steering input and output remains but the delay is very small.
There are three contributors to the slip angle of the wheels:
the sideslip angle of the car, the angular rotation of the car around the up axis (yaw rate) and, for the front wheels, the steering angle.
In other words, a much greater steering effort is required from the driver due to
the sideslip angle.
The key to improving the handling and stability in high - speed maneuvers is minimizing
the sideslip angle.
It's obvious that minimizing
the sideslip angle improves stability and vehicle safety.