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Technical Paper

Post-Impact Dynamics for Vehicles with a High Yaw Velocity

Calculating the speed of a yawing and braked vehicle often requires an estimate of the vehicle deceleration. During a steering induced yaw, the rotational velocity of the vehicle will typically be small enough that it will not make up a significant portion of the vehicle’s energy. However, when a yaw is impact induced and the resulting yaw velocity is high, the rotational component of the vehicle’s kinetic energy can be significant relative to the translational component. In such cases, the rotational velocity can have a meaningful effect on the deceleration, since there is additional energy that needs dissipated and since the vehicle tires can travel a substantially different distance than the vehicle center of gravity. In addition to the effects of rotational energy on the deceleration, high yaw velocities can also cause steering angles to develop at the front tires. This too can affect the deceleration since it will influence the slip angles at the front tires.
Technical Paper

Determination of Critical Speed, Slip Angle and Longitudinal Wheel Slip based on Yaw Marks Left by a Wheel with Zero Tire Pressure

This article presents the results of an analysis of the yaw marks left by a car with normal pressure in all tires and then normal pressure in three tires and zero in one rear tire. The analysis is a continuation of research on influence of reduced tire pressure on car lateral dynamics in a passing maneuver, discussed in the SAE paper No. 2014-01-0466. Preliminary analysis of yaw marks has shown, that a wheel with zero pressure deposits a yaw mark whose geometry differs from the yaw mark made by a wheel with normal pressure based on which we could calculate: critical speed, slip angle and longitudinal wheel slip. The aim of the presented research was to analyze the yaw marks left by car with zero pressure in one rear wheel in order to check the possibility of determining the vehicle critical speed, slip angle and longitudinal wheel slip. It was reached by performing bench and road tests during which the vehicle motion parameters were recorded using GPS Data Logging System.