Article by: Bernat Ferrer, Project Manager, Braking Systems in Applus IDIADA.
Brake durabilities on public roads are one of the main activities for the development and validation of OEM’s vehicles in terms of brake noise research and friction material wear.
Many routes have been defined worldwide, and some of them have been turned into brake NVH verification standards. European, American and Chinese markets are clear examples, with both city traffic and mountain road patterns. The scope of this article is to describe a complete correlation of the worldwide public road brake durability standards, in order to get global ratios defining the equivalence between each test location.
The Complete Study Includes:
USA: 1. Los Angeles (city traffic)
Europe: 2. Barcelona (city traffic) and 3. Mojácar (mountain road)
China: 4. Yellow Mountain (mountain road) and 5. Shanghai (city traffic)
For each location, a specific route is defined and local drivers (skilled in NVH evaluations) are selected to accumulate mileage. In this way, local driving styles are taken into account for the comparison.
This work includes a full objective parametrization of each route and mileage accumulation, focusing on the driving profile description (brake applications, speed, deceleration ranges), squeal noise (frequency, loudness, and occurrence) and parts wear (friction material volume worn-out). Route severity criteria, coming from a combination of the braking energy and power outputs, are also introduced. Overall, the routes and fields of study are compared with reliable ratios that provide a complete understanding of the different markets.
A total of 4,000 km is performed per location, keeping an initial mileage for brakes burnishing and maintaining (when possible) dry climate conditions. The initial disc runout is checked and fixed under a referenced value, in order to prevent unexpected wear and the generation of squeal due to the mounting conditions.
The instrumentation mounted on the vehicle is in accordance with brake durability purposes: sensors for the objective NVH recognition, as well as for general driving outputs. Therefore, wheel microphones and caliper accelerometers are mounted for squeal noise detection; brake hydraulic pressure and disc temperatures for brake actuation characterization; vehicle speed, lateral acceleration, longitudinal deceleration, ambient temperature and humidity for the route profile description.
For data acquisition and its treatment, IDIADA’s own tools are used to record and analyze the squeal noise outputs. On the one hand, the dbBrake is the hardware mounted for the on-vehicle activities; on the other, the dbSoft is the software used to manage and generate all results.
To ensure the validity of the results, the same vehicle model has been used on each location: a front-wheel-drive D-segment car with automatic transmission. In addition, new brake components (calipers, discs, and pads) —selected from the same production batch— are retrofitted prior to each activity. Specifically for the linings, a low steel friction material is chosen for both front and rear axles. Furthermore, a previous study of compressibility is carried out; the pads with the lowest dispersion are the ones chosen in order to reduce the uncertainty in wear and noise.
Having introduced the study and explained the methodology, the main results will be presented in the next section, which will deal with brake usage, the severity of the routes and, finally, the analysis itself of the encountered brake noises.