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Dipl.-Ing. Laszlo Boros, Research Associate, Robert Bosch GmbH; Dr.-Ing. Simon Peter, Research Associate, Robert Bosch GmbH; Dr.-Ing. Xi Nowak, Research Associate, Robert Bosch GmbH; Dipl.-Ing. Christopher Kneissl, Research Associate, TU Graz, Inst. of Automotive Engineering; Prof. Dr.-Ing. Peter Fischer, Professor, TU Graz, Inst. of Automotive Engineering


Effects of disc thickness variation and out of roundness on electromechanical brakes Laszlo Boros1, Simon Peter1, Xi Nowak1, Christopher Kneissl2, Prof. Dr. Peter Fischer2 1 Robert Bosch GmbH, Robert-Bosch-Campus 1, 71272 Renningen, Germany 2 Institut für Fahrzeugtechnik, TU Graz, Inffeldgasse 11/2, 8010 Graz, Austria Abstract. Imperfections in the brake geometry, such as the disc thickness variation (DTV) or the out of roundness (OOR) of drum brakes are well examined in the context of hydraulic brake systems in passenger cars. Geometric imperfections can cause discomfort due to brake torque oscillations, chassis vibrations and brake pedal pulsations. These effects also influence the interactions between the basic brake and the actuation mechanism and vice versa. Electromechanically actuated brakes (EMB) have some unique properties in that respect. For example, the actuator motor inertia is directly coupled to the brake pad by a relatively stiff gearing. In contrast, the coupling of a hydraulic brake system to the foundation brake is different, leading to different stiffness and damping properties. This paper examines these differences and their consequences, especially regarding the vibration load on the EMB gears and bearings. A theoretical analysis shown in the paper predicts some challenges in the design and endurance testing of future EMBs. First experimental results obtained with eccentric drums and electromechanical brake actuation partly confirm the theoretical analysis. The measurements also raise some questions about the relative motion of the brake shoes in a rotating eccentric drum. Even if the brake shoes are mounted in a floating manner, the friction at the lower and upper abutment prevents the shoes to follow freely the eccentric movement. Small eccentricities may be completely adsorbed by deformations, without any sliding motion of the brake shoes. Additional sensors on the brake shoes are used to gather information about the motion relative to the backplate. The results indicate that a deeper analysis of DTV, OOR and other geometry imperfections must be conducted for EMB-s in passenger cars. Their effect may have to be considered in future endurance test specifications.

EuroBrake 2023

Low frequency NVH




Paper + Video + Slides


Mr. Tobias Loss, Robert Bosch GmbH, GERMANY

Dr.-Ing. Simon Peter, Robert Bosch GmbH, GERMANY

Dipl.-Ing. Armin Verhagen, Robert Bosch GmbH, GERMANY

apl. Prof. Dr.-Ing. Daniel Görges, German Research Center for Artificial Intelligence (DFKI), GERMANY

Current electric vehicles (EVs) already perform most braking maneuvers by recuperation using the electric powertrain. In order to generate additional benefits regarding cost, weight, brake dust emission and design freedom, there might be the option to omit the brake system and solely brake by recuperation. The potential elimination or downsizing of the friction brakes results in multiple questions concerning deceleration capabilities, availability of brake torques as well as driving dynamics. Especially for EVs with the electric motor located centrally at the axle, wheel individual braking interventions may not be possible without additional measures.

This study investigates the brake torque requirements for the rear axle of an electrically driven urban vehicle with rear axle drivetrain. The focus of the analysis is targeted on wheel individual brake torque generation as such differential brake torques may be relevant for state of the art (SoA) driving safety and electronic stability control (ESC) interventions.

In order to examine the wheel individual brake torque requirements a Simulink based software in the loop (SiL) simulation environment for vehicle dynamics is utilized. It simulates the dynamic behavior of vehicles with focus on the brake system. The main feature is the integration of software in the loop control algorithms of an ESC system with powertrain, vehicle behavior and electronics also being included. To maintain expert knowledge and application effort, a simulation model and ESC software of a SoA series production urban EV is used.

This model is applied to a vehicle test catalogue for ESC software release covering maneuvers that allow testing of different driving stability functions. Based on the simulation results and supported by real world measurement data, the most critical driving maneuvers concerning the amount of differential brake torque, its direction and dynamics are identified. The test catalogue includes driving scenarios such as acceleration on inhomogeneous surfaces. In case of a vehicle equipped with a conventional open differential the maximum drive torque of the entire axle is limited by the lower friction wheel. Wheel individual brake applications can increase this drive torque. Such intervention may not be possible in vehicles without a conventional brake system topology. As a result, acceleration on such surface is restricted. Further maneuvers examined are dynamic cornering situations that may require wheel individual brake torque to ensure driving stability and safety. An in-depth analysis of the SoA vehicle behavior and its control strategy is necessary to understand potentials and limitations of EVs with non-conventional brake topologies.

EuroBrake 2021





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