Validation of the Electric Parking Brake EPB-Si: Hydraulic Pressure Overlay functionality

The automotive sector is currently in a transition phase driven by the aim of reducing C02 and pollutant emissions. The sector is looking for continuous improvement and evolution intending to provide new technologically and innovative products to the customer. This innovation policy also concerns the enhancement of traditional products which are redefined through all the phases of design and production. In this context take place the development of a historical product as the Drum Brake which was renewed to fit this changeover with the Electric Parking Brake Simplex Integrated (EPB-SI), which consist of a motor gear unit (MGU) controlled by an Electronic Control Unit (ECU) in addition to a mechanical part (Sic-M). The reasons why this product nowadays is interesting in the automotive sector is because it preserves all the advantages of the classic drum brake, as fewer costs and less maintenance compared to the competitors and, in addition to that, in the hybrid and electric vehicles it allows to reduce the pollutant emission and to recover energy from the regenerative braking. This thesis is developed in the R&D team of the company “Continental” in Cairo Montenotte (SV) as part of the System Testing Team. The aim of the project is the study and the characterization of the functionality "Hydraulic Pressure Overlay" (HPO) included in the verification and validation process of the EPB-SI. The HPO is a software's functionality of the ECU included in the Standard VDA requested by many customers. The functionality introduces a pressure pre-load to help the electric parking brake EPB operation. The implementation is tested in different ways using different types of test benches to obtain an overview of the response of the system to this phenomenon. Two different types of testing approaches were followed considering the system level and the component one. System and component levels were analysed through a characterization test to study the phenomenon, to obtain an indication of the system's performances in terms of forces and to evaluate the durability of the component. Moreover, for the system level, a functional test is also performed to evaluate the software functionality and define the correct application time of the pressure signal. The obtained results show, for the system level, that HPO functionality introduces a positive delta between the Initial Force and the Force after the release of pressure. This offset lasts for the entire duration of the test. This step, in terms of adjuster force, is influenced mainly by pressure. The force performances remain competitive compared to the defined limits for the entire duration of the test. For what concern the component level, all the components under test overcame the estimated break limit. Furthermore, with the functional test, the functionality was verified, and the critical conditions were recognized in terms of application time. This leads to the definition of the minimum application time and the delay time between the pressure pre-load signal and the EPB application.