Vehicle Drifting

Inspired by cornering manoeuvres in races, another vehicle control skill has emerged in 1970s in Japan where the driver tends to intentionally cause the vehicle to turn at a condition which requires counter-steering, i.e. steering towards a direction away from curvature centre of the path. For such a condition to develop, a large negative side-slip angle is needed for the car body to be generated. Commonly, this is achieved by applying large driving or braking torques to the rear wheels to cause an intentional drop in rear lateral forces, and consequently large rear slip angles. Such a condition may be viewed as an induced over-steering.

It is important to note that such vehicle control skills are not only helpful as hobby or sport, but also inspire engineers to develop stabilizing control strategies to mitigate an undesirable condition from the safety point of view. Understanding the vehicle's motion in such manoeuvres helps developing better control frameworks and better design of vehicles and assistive control systems (ADAS), making the passenger vehicles less prone to instabilities.

This research aims to introduce a mathematical definition for drifting of vehicles. A necessary kinematic condition for enabling negative body side-slip angle at centre of the front wheel during a left-hand turn is identified as drifting indicator. Dynamics of the drifting motion is investigated by means of planar vehicle models in steady-state, focusing on Rear Wheel Drive (RWD) vehicles. Drifting point is identified as an unstable equilibrium point of the nonlinear system. The equilibrium point is made stable by means of direct control only over yaw velocity, as a single key stabilising objective, and using the steady-state model as feedforward. A four-wheel planar dynamic simulation model is used together with a combined slip tyre model to investigate the accuracy of the proposed analysis. Steady-state RWD drifting motion is achieved by using the proposed method, validating the proposed dynamics analysis. Finally, the drifting metric is used to measure the amount of drifting achieved during a manoeuvre and its effectiveness is observed.

Keywords: Vehicle Drifting; Nonlinear Vehicle Dynamics; Drift Equilibrium Point; Drift Stabilisation; Yaw Rate Control.