Historically, vehicle brake feel has usually been evaluated in a subjective manner. If an objective measure was used, it was pedal force versus the deceleration rate of the vehicle.
Stopping distance is almost always used to characterize vehicle braking performance by the automotive press. This represents limit braking performance, but ignores braking performance under normal driving conditions experienced by customers most of the time. Evaluation of pedal feel by the press is generally limited to subjective adjectives such as “mushy”, “positive”, and “responsive”.
A method will be presented, which is being used by General Motors, to translate customer brake feel expectations into objective performance metrics. These metrics are correlated to actual subjective ratings and are used to set objective, measurable requirements for performance. Having objective requirements allows the use of math based computer models to design systems early in the vehicle development process, which have a high likelihood of satisfying customers.
An index has been established which combines various braking feel parameters, with appropriate weighting, to give an overall number which correlates well to customer perception of brake system performance. This number is referred as to the “Brake Feel Index” (BFI).