Measuring and Characterizing Brake System Performance During Race Track/High Energy Driving Conditions 2005-01-0790
Recent years have seen an increased emphasis on producing automobiles with a ‘performance’ image, and a corresponding level of performance capability. Greatly increased engine power and cornering ability naturally lead to the need for increased braking capability. With more and more vehicle programs developing, validating and advertising their performance at the racetrack, the need arises for objective means of measuring brake performance and differentiating between brake system configurations under these driving conditions.
One of the greatest challenges of measuring brake performance during racetrack driving conditions is coping with the wide range of braking conditions and driving styles incurred. Rapid brake applies and releases, and brake modulation make it very difficult to get a meaningful measure of brake output. Furthermore, a steadfast desire to maintain brake cooling airflow as design representative as possible, and to insure the safe operation of the test vehicle prevents the use of torque transducer wheels for directly measuring brake torque. Racetrack operation also prevents the use of any other sort of measuring device requiring the use of slip rings protruding from the center of the wheels of the test vehicle for this same reason.
To address these issues, measurements were made of vehicle deceleration and brake system pressure over the course of multiple laps of a closed-loop racetrack. Vehicle deceleration was related to brake system pressure with a term called ‘Brake Hydraulic Pressure Deceleration Gain (BHPDG)’, or ‘Decel Gain’ (DG) for short. By examining how this relationship changed with brake lining temperature and over time, it was possible to detect and measure brake fade. Statistical analysis on these data allowed for data sets from different brake configurations to be compared.
A method of measuring and representing apply system runout is also covered, as are methods of graphically representing the large quantity of data typically gathered during a race track event. Examples from multiple test vehicles are used to depict the occurrence of brake performance issues at the racetrack such as mechanical and temperature-related fade and apply system runout. Examples are also used to depict ‘good’ performance.