In the VDA project group 370 the VDA recommendation “Electrical Parking Brake actuator – Layout and testing” was issued. Several car manufacturers, Tier 1 Brake suppliers and Tier 2 Brake component suppliers were participating and bringing in state of art expert knowledge. Thus international standards and informal/ internal specifications of the involved companies were harmonized and tailored to EPB systems. The content of the recommendation is on the one hand a description of the basis for the layout of the electrical parking brake actuator including the relevant influencing factors, and on the other hand the mapping of the related verification and validation tests.
A harmonization of both, the requirements base for EPB actuator layout and the related test concept, was achieved. Therefore, valid technical regulations and international standards, vehicle parameters and relevant operating and environmental conditions for achieving the hill-hold capability of the electrical parking brake are listed. For those, typical parameter values based on caliper integrated EPB solutions for passenger cars are named. The requirements resulting from operating and environmental conditions for the parking brake actuator design are defined as well.
Out of that the requirements for the wheel brakes and the base for a calculation method for the layout of the hill-holding capacity are derived.
The harmonized verification test concept comprises environmental tests, function and endurance tests. Additionally, for the verification of the hill-holding requirements, a test for determination of the static brake friction coefficients and a test for the verification of the hill-holding capability are proposed.
So it is the first time that a harmonized definition of the static brake friction coefficient as a characteristic value for EPB-applications, which is property of the brake and not the friction couple only, is published. Additionally, a qualified test to verify this characteristic value is presented. And also a harmonized hill hold verification test is introduced that improves the validity of the test results based on a dynamometer test with a high repeatability.