For drivers, one of the most important attributes of any vehicle is brake feeling, yet it is one of the least understood, with a confusing array of adjectives and definitions when it comes to subjective evaluation. The impact of objective measurement systems and methods, where testing is controlled by the driver’s right foot, and resulting pedal load, stroke and vehicle deceleration are measured, has been limited to say the least. Add to this the recent introduction of two new braking systems giving three distinct methods of providing the brake actuation: vacuum boosters, brake-by wire, and electromechanical brake boosters. The vacuum and electromechanical boosters are similar in approach, boosting the driver demand, whereas brake-by-wire takes the braking signal and separately applies the brakes. One of the first OEMs to use brake-by-wire was Toyota in 1998 with the Prius. The main driver behind this was to increase the range of their electric/hybrid vehicles by recuperating the braking energy. This required blending the regenerative and foundation brake and decoupling the brake pedal from the hydraulic system. Then in 2013 Bosch introduced the iBooster, here again it had advantages for regenerative braking, but also for ADAS support and packaging. These systems have seen rapid growth in recent years as the drive to reduced CO2 increases, and as the need to reduce non tailpipe emissions strengthens. However, the main function of these systems is still to control the deceleration of a vehicle, and as such they must provide the same level of brake feeling as a conventional vacuum booster equipped vehicle. This case study looks at the equipment and methods required to quantify brake pedal characteristics and compares the three differing methods of brake generation. To do this an AB Dynamics braking robot system was used to provide controlled and repeatable pedal inputs and to record the resulting decelerations. The inputs to the brake pedal consisted of three differing applications: slow and fast applies and fixed position, and where applicable, with and without regeneration. The measured objective data was analysed, and a comparison made compering the three different systems. This was then compared to the subjective evaluation of each vehicle, and links drawn between the objective data and the subjective evaluation to establish a quantitative assessment of brake feeling.

Anthony Best Dynamics Ltd.: Mr. Allan Johnstone