Limit range (driving dynamics)

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In driving dynamics, the limit area is the area of lateral acceleration shortly before the adhesion limit is reached . The maximum lateral acceleration determines the speed at which a curve with a given radius can just be negotiated. The former depends on the condition of the road surface, the tires and the suspension setup.

In the case of cars , the entire usable lateral acceleration range is divided into a linear range that relates to the relationship between steering wheel angle and lateral acceleration, the transition range and the limit range.

conditions

To strengthen active safety, the border area should not be too narrow and be announced in good time, e.g. B. by the progressive increase in the steering wheel angle over the lateral acceleration. This is at a understeering of the vote self-steering behavior of the case of the front axle out the slip limit reached. There should not be "an abrupt change in driving behavior so that the driver is not overwhelmed with his compensatory control."

Vehicles in which the rear axle first reaches the slip limit oversteer . They become unstable and the resulting large sideslip angle must be "caught" by active counter-steering or reduced by braking interventions by the vehicle dynamics control (ESP).

In the case of motorcycles , the incline is a measure of the utilization of the frictional connection. Compliance with the maximum possible angle of inclination is "sensed" in racing by the distance between the knee protector and the road. The limit range is essentially dependent on the tires on the front and rear wheels. Since the front wheel is more difficult to control than the rear wheel, the limit area should be indicated by the slip angle of the rear wheel.

Stationary lateral dynamics

The limit range on a dry road in modern cars is far above the "normal driving range" of around 4 m / s 2 lateral acceleration, corresponding to an inclination of around 22 degrees for two-wheelers, which is rarely exceeded by customers. The further increase is essentially a question of tire technology, which must also take into account the conflicting goals with rolling resistance or wet grip. What is technically possible here was explored on the near-series research vehicle Mercedes F400 with tilting technology , in which a lateral acceleration of up to 1.28 times the acceleration due to gravity was achieved. Racing vehicles achieve a multiple of this lateral acceleration. This requires special rubber compounds in the tires and aerodynamic downforce . The maximum lateral acceleration increases with the speed.

The maximum lateral acceleration is significantly lower on a wet or slippery road surface. The transition area is correspondingly small and therefore more difficult to perceive for the driver, e.g. B. only on the steering wheel torque. In general, the smaller the slip angle at which the maximum lateral force of the tires occurs, the narrower the limit area is . On a dry road, this maximum is between 8 and 12 degrees for car tires and around 5 degrees for slicks.

Disruptions

Since both the front and rear axles are close to the frictional connection limit in the limit area, even small disruptions can become noticeable through major changes in driving behavior. A load change or light braking on vehicles with a low rear axle load (e.g. Audi TT 8N ) can be enough to trigger oversteer. The same applies to rear-wheel drive vehicles when accelerating on a slippery road in a curve.

literature

  • Manfred Mitschke, Henning Wallentowitz: Dynamics of motor vehicles . Springer, 2004, ISBN 978-3-662-06803-8 .

Web links

Wiktionary: border area  - explanations of meanings, word origins, synonyms, translations
  • Achim Kuschefski: Grip. (PDF; 738 KB) Institute for Bicycle Safety e. V., August 2010, accessed on January 14, 2019 .

Individual evidence

  1. ↑ Erich Schindler: Driving dynamics: statics, basics of steering behavior and their application for vehicle control systems . expert verlag, 2007, ISBN 978-3-8169-2658-0 , p. 9 . : ( limited preview in Google Book search)
  2. ↑ Klaus Becker (Ed.): Making subjective driving impressions visible . expert verlag, 2000, ISBN 3-8169-1776-3 , p. 44 ( limited preview in Google Book search).
  3. ↑ Volker Schindler, Immo Sievers (ed.): Research for the car of tomorrow: the future is created from tradition . Springer, 2008, ISBN 978-3-540-74150-3 , pp. 258 Fig. 18 ( limited preview in Google Book search).
  4. ↑ a b Michael Trzesniowski: race car technology. 2nd Edition. Vieweg and Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0857-8 .