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.