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TU Graz

TU Graz




As the name suggests, TU Graz is located in the centre of Graz, the second biggest city in Austria. With eight institutions of higher education, Graz is a real student city and is regarded as one of the cities of central Europe and the European Union with the highest quality of life.




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16 July 2021


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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



Effects of disc thickness variation and out of roundness on electromechanical brakes, EB2023-TCH-004, EuroBrake 2023


Paper + Video + Slides


Dipl.-Ing. Severin Huemer-Kals, TU Graz, AUSTRIA

Prof. Jurij Prezelj, University of Ljubljana, SLOVENIA

Mr. Máté Tóth, TU Graz, AUSTRIA

Dipl.-Ing. Dominik Angerer, TU Graz, AUSTRIA

Dipl.-Ing. Manuel Pürscher, TU Graz, AUSTRIA

Mr. Federico Coren, TU Graz, AUSTRIA

Mr. Martin Zacharczuk, Mercedes-Benz AG, GERMANY

The nature of friction within a vehicle’s disk brake system can cause a wide range of different noise phenomena. Especially high-frequency brake squeal was examined during the last decades. Numerous publications treat squeal phenomenology and its mitigation. Increasing shares of electrified powertrains, automatic driving functions such as park assists and further increasing quality demands have now shifted the research interest more and more towards low-frequency phenomena.

One of these low-frequency phenomena is creep groan. Defined by its main frequency below 200 Hz, creep groan is characterized by a highly non-linear behavior: Global stick-slip transitions in the disk/pad contacts repeatedly excite the whole brake and axle system. Different bifurcations or even chaotic behavior occur.

To ensure good creep groan behavior, defined assessment procedures and rating criteria are necessary. Currently, the German Association of the Automotive Industry recommends a combined rating via the subjective perception of trained test drivers and the objective, A-weighted sound pressure level. This practice could be improved with a more sophisticated objective rating: By considering the human perception, objective and subjective ratings would correlate even better.

One possible approach towards an enhanced objective creep groan rating could therefore use psychoacoustic metrics. In 2009, this idea was formulated for the psychoacoustic loudness and the tonality of creep groan by Abdelhamid and Bray.

The present work seizes this suggestion and provides additional psychoacoustic evaluations of full-vehicle creep groan signals. Based on measured accelerometer signals, a novel procedure for the psychoacoustic evaluation of structure-borne noise was applied: Optimized FIR filter transfer functions were used to compute equivalent sound pressure signals from the accelerometer data, with the equivalent signals resembling the measured signals but lacking unwanted noise. Both the measured and the simulated signal were then evaluated and compared regarding their psychoacoustic behavior.

Results reveal the value of the equivalent sound pressure signal: Whereas loudness and sharpness were found very similar and tonality rather arbitrary for both measured and equivalent sound pressure signal, roughness and fluctuation strength showed strong differences between the signals: Here, only the accelerometer-based, equivalent sound pressure provided easily interpretable characteristics. The proposed method also compared psychoacoustic characteristics for different creep groan bifurcations.

Possible applications comprise an enhanced objective rating of low-frequency noise phenomena, the detection and classification of creep groan bifurcations, or the possibility to estimate creep groan cabin noise based on simulative results during early development stages. Therefore, this study provides another step towards silent automotive brake technology.

EuroBrake 2021




The Psychoacoustic Characteristics of Non-Linear Automotive Disk Brake Creep Groan: a Method Based on Accelerometer Data, EB2021-STP-011, EuroBrake 2021

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