Regarding the development of passenger cars the aspects comfort and environment are important objectives nowadays. Due to the regulation of the EU a low limit was set for the fleet consumption of new passenger cars and light commercial vehicles of automobile manufactures. Therefore vehicles have to be optimised continuously with regard to the efficiency of the powertrain and the reduction of the driving resistances. Previous studies showed that it is important to analyse the efficiency by considering additional driving cycles which are closer to reality in comparison to the NEDC. Driving resistances can be broken down into the steady-state resistances of aerodynamic drag, powertrain drag, rolling resistance and climbing resistance, plus the inertial resistance. The brake drag torque of the wheel brake is related to the rolling resistance and occurs in the so called offbrake-mode when the brake is not applied and there is a friction contact between the pad and disc due to an unfavourable constellation of piston clearance (pad and finger side) and dynamic runout. At the department of automotive engineering comprehensive studies were carried out concerning the brake drag torque of different floating caliper brakes. First results showed a high temporal dependency of the brake drag torque within a test cycle. So further research of the department considers two directions:
A robust axial displacement measurement system for analysing the brake component movement is used to capture the clearance and hence the geometric conditions in the wheel brake during a complete test cycle. The clearance then can be related to the brake drag torque. Further investigations with the described system and a special test setup which allows the application of lateral forces show how the detaching of the pads or (in general) the clearance behaviour of the wheel brake after a deceleration or simulated cornering affects the brake drag torque. An additional measurement system to determine the force conditions is used to measure the force distribution in the pads in the offbrake-mode. So there are two analytic tools described to optimise and control two major influence factors - geometric and force conditions - on the brake drag torque.
Heimann, Stefan* - Ilmenau University of Technology; Augsburg, Klaus - Ilmenau University of Technology