Ing. Fabio Squadrani, Applus IDIADA, SPAIN

Mr. Danilo Mendes Pedroso, Applus IDIADA, SPAIN

Mr. Kenneth Mendoza, Applus IDIADA, SPAIN

Dr. Eng. Juan J. Garcia Bonito, Applus IDIADA, SPAIN

Mr. Juan Pablo Barles, Applus IDIADA, SPAIN

Mr. Antonio Rubio, Applus IDIADA, SPAIN

Mr. Antonio Jesus Contreras, Applus IDIADA, SPAIN

Mr. Jose Francisco Martinez, Applus IDIADA, SPAIN

Research and/or Engineering Questions/Objective:

The availability of big sets of data coming from brake durability tests paves the way for making predictions and decisions related to the noise coming from brakes. In this paper, the workflow for detecting brake squeal and all its main characteristics is presented.

Methodology:

Initially, a uniform set of data is generated, having a repetitive structure and format. This set of data will be used to train the machine learning algorithm. From the raw data coming from the vehicle data acquisition system, a spectrogram is mathematically generated, to graphically associate sound pressure level and noise frequency within the time domain. These spectrograms will be used to train the machine learning algorithm, which will be recognizing brake noise using the spectrogram images. The final objective is to detect squeal and to identify the frequency, sound pressure level, and subjective rating as well.

Results:

Once the algorithm is trained with thousands of brake noise events coming from real-life brake durability, brake noise is detected with a very high level of confidence. Currently, brake squeal is the noise being identified during this first phase of the project and is identified with a proper level of confidence, including frequency and SPL.

In the second phase of the project, the algorithm is also being evolved to associate a rating to the squeal noise event detected. The algorithm is capable to predict the subjective rating provided by a professional driver during standard driving or during specific noise research maneuvers.

Limitations of this study:

The real-time detection is currently under investigation and could affect the resolution of the spectrogram to be used to train the algorithm and to detect the brake noise. However, the current level of the study does not currently show any predictable problem that could arise when the machine learning algorithm is embedded within a real-time system.

Other brake noises should also be identified, even if less amount of data is available when compared with brake squeal.

Conclusion:

The study shows an alternative method for automatic noise detection and shows the possibility of automatically rating the brake noise. Real-time detection is also investigated and the results of its initial integration within embedded systems is shown.

Dr. Juan J. Garcia, Applus IDIADA, SPAIN

Mr. Bernat Ferrer, Applus IDIADA, SPAIN

Mr. Fabio Squadrani, Applus IDIADA, SPAIN

ABSTRACT

Research and/or Engineering Questions/Objective:

Vehicle bending and torsion due to fluctuating brake judder forces affects body vibration transmission at low frequencies. This dictates part of the annoyance perceived by the driver when brake judder occurs. Other sources of vehicle judder sensitivity may also be related to chassis stiffness and chassis-to-body hard points stiffness. However, the operational measurement of vehicle body bending and torsion stiffness reveals parameters of paramount importance for brake judder performance as well as for vehicle dynamic behaviour under transient loads.

Methodology:

The experimental methodology proposed in this work is based on the use of tri-axial accelerometer sensors located in six areas of the vehicle body. The simultaneous acquisition of the relative displacement of these location points when the vehicle is excited with operational brake judder loads makes it possible to calculate the global bending and torsion deformation experienced by the vehicle body.

Results:

The results show that the in-service measurement of vehicle body and torsion can be optimised to have similar error levels as those obtained in quasi-static conditions. Additionally, this bending and torsion stiffness information during braking application can be correlated with the associated operational Disc Thickness Variation (DTV) that produces the brake torque fluctuation.

Limitations of this study:

The acceleration data provided by the accelerometers attached to the vehicle body must have a very high signal-to-noise ratio in order to be used for bending and torsion estimation. This requires the use of high-quality low noise acquisition systems and sensors.

What does the paper offers that is new in the field in comparison to other works of the author:

This work reports a simple and robust experimental set up to measure the in-service overall vehicle body bending and torsion under fluctuating braking loads. Additionally, this bending and torsion stiffness information during braking can be correlated with the associated operational Disc Thickness Variation (DTV) that produces the brake torque fluctuation. Thus, a correlation can be established between DTV, judder induced vibration and vehicle body deformation.

Conclusion:

The information provided by the experimental methodology presented in this work allows the definition of the relationship between the operational vehicle body stiffness (bending and torsion) and the associated operational DTV causing the fluctuating braking loads. This information is of paramount importance for understanding and optimising vehicle body stiffness for vehicle performance improvement and for correlating simulation models of chassis dynamics.

Mr. Narcís Molina Montasell, Applus IDIADA, SPAIN

Dr. Juan Jesús García Bonito, Applus IDIADA, SPAIN

Mr. Amadeu Martorell Branchat, Applus IDIADA, SPAIN

Ing. Fabio Squadrani, Applus IDIADA, SPAIN

Research and /or Engineering Questions/Objective:

Brake creep groan and brake squeal are very distinct vibration and noise problems exhibited by brakes under certain braking conditions. Creep Groan is a low frequency (< 100 Hz) vibration induced by a stick-slip condition associated with the friction/velocity characteristic of the friction material. Creep groan can evolve into a resonant condition when a dominant suspension resonance is excited. This situation can induce high vibration levels both in the suspension and in the vehicle body, producing vibration annoyance.

On the other hand, squeal noise is a phenomenon that occurs at high frequencies (>1 kHz) and involves complex modes of the brakes, such as flexural vibrations of the brake disc. The excitation of the disc modes can be caused by the variability in the friction force due to surface roughness and to the bending modes of the pads. Squeal noise transmission is basically airborne. In general, creep groan and squeal are studied as independent events with no mutual interaction.

This work presents an investigation of how these two distinct brake phenomena can be related to each other during the operational use of a disc brake, as they can appear concatenated in time.

Methodology:

The vehicle under study is a medium-duty commercial vehicle equipped with an air disc brake system. The creep groan and the squeal dynamics occurring at the front axle are characterized in operational conditions by means of 14 tri-axial accelerometers on the brake caliper and 28 on the vehicle front axle. This experimental set up allows the time and frequency analysis of the evolution of the creep groan triggering, charging, and its unstable stage and the effect that the latter event might have on the activation of squeal generation. The analysis uses operational vibration data of the suspension and the brake system of the vehicle under creep groan and squeal conditions in combination with vibration measurements of the brake assembly only in a brake-dyno under squeal conditions.

Results:

This study confirms previous findings that show that the development of creep groan exhibits three stages: the triggering phase, the charging phase and the unstable stage. It is shown that the unstable stage involves the axle beam, the leaf springs, both front wheels and their respective brake calipers. For the brake under study, it is shown that during the unstable creep groan phase, the brake caliper housing exhibits a high deformation that limits the correct control of the pads positioning and orientation with respect to the disc. This situation induces a high mobility of the pads with little position control. The results suggest that this lack of control in the correct positioning and support of the pads, caused by the unstable creep groan phase, can facilitate the generation of squeal.

Limitations of this study:

The number of tri-axial accelerometers used in this type of analysis is considerable and thus it requires using a multichannel system for efficient tests.

What does the paper offer that is new in the field in comparison to other works of the author:

The paper reviews and confirms the existence of three main phases in creep groan generation for discs brakes and introduces an interpretation of how the final unstable stage of creep groan, apart from the typical vibration annoyance associated to it, can also be a squeal inducer for some brake caliper designs.

Conclusion:

This work shows that, for some disc brake caliper characteristics, the evolution stages found in operational brake creep groan, i.e., triggering, charging and instability phases, can occur concatenated with brake squeal. This association seems to be related to the fact that the unstable phase of operational creep groan produces high acceleration levels in the brake system that hinders the correct positioning and orientation control of the brake pads inside the caliper housing. This lack of control affects the duration of the unstable stage of creep groan and can promote the initiation of other noise problems, such as squeal.