Performance of anti-lock Braking System Equipped Passenger Vehicles - Part II: Braking as a Function of Initial Vehicle Speed in Braking Maneuver 2002-01-0307

This paper presents the results of original research conducted to evaluate the braking characteristics of passenger vehicles equipped with anti-lock braking systems (ABS) as a function of vehicle speed at the beginning of a braking maneuver. The conditions studied in this paper are for braking on a dry, level roadway without any steering input. The objective of the paper is to study the effect of vehicle speed on the braking systems of common vehicles currently in-use. Comparisons are made between ABS and locked-wheel braking for each vehicle.

The subject of this paper is part of the general topic of passenger vehicle dynamics and stability. Knowledge of how a vehicle performs under a variety of braking conditions is important for a variety of applications such as 1) intelligent vehicle highway systems, 2) vehicle stability and control, 3) vehicle dynamics, and 4) accident reconstruction. To date, a number of studies have been performed to study the locked-wheel braking characteristics of passenger vehicles, but few studies have been published relative to how ABS-equipped vehicles perform as a function of speed while emergency braking. Of interest is a better understanding of how typical passenger vehicles equipped with anti-lock brakes behave as a function of vehicle speed at the start of a braking maneuver.

In our paper we present data obtained utilizing state-of-the-art data-acquisition systems for determination of vehicle speed effects on braking for a group of passenger vehicles equipped with ABS. We also present reduced and plotted data for the group of vehicles tested. The results provide an excellent understanding of how a variety of passenger vehicles equipped with anti-lock brakes perform as a function of initial vehicle speed during real-world braking conditions.

We found that ABS braking average deceleration is a significant function of vehicle speed. Surprisingly, higher vehicle speeds resulted in overall improved ABS braking under the test conditions that included speeds to about 115 kph (32 m/s.) In general, ABS tended to degrade braking performance relative to locked-wheel braking at speeds of about 35 kph (10 m/s) or below. One vehicle exhibited reduced braking performance relative to locked-wheel braking at speeds below 50 kph (14 m/s) while another did not exhibit any reduction in braking relative to locked-wheel braking even at speeds as low as 18 kph (5 m/s.)

The ABS Index of Performance (the ratio of ABS braking to locked-wheel braking,) ABSIP, varied as a function of speed and from vehicle to vehicle. ABSIP varied as little as 20% for one vehicle to as much as 37% for another as a function of speed.

The locked-wheel braking of one vehicle does not necessarily indicate the locked-wheel braking of another vehicle on the same surface under the same conditions. Likewise, ABS emergency braking of one vehicle does not necessarily indicate ABS emergency braking for another vehicle on the same surface under the same conditions.