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. Bernat Ferrer, Applus IDIADA, SPAIN

The Adaptive Cruise Control (ACC) is one of the main ADAS functionalities of the automotive industry. It automatically regulates the vehicle speed in order to keep a safe and constant longitudinal distance gap with the vehicles ahead. The development of its requirements and calibration parameters, are key to achieve not only the safety but also the comfortableness of the complete system.

This study considers many of the scenarios that an ACC system is usually challenged to develop and calibrate its main parameters: deceleration with decreasing target speed, target vehicle cut-out, approaching a slower target vehicle, etc. In order to characterise these events, some metrics have been defined, willing to objectivize the vehicle and system performance: longitudinal braking deceleration, acceleration overshoots, jerk, vehicle reaction delays, etc. Signals coming from vehicles instrumented with sensors and tested at IDIADA proving ground tracks, have been acquired for the corresponding analysis. Different vehicle segments and systems were assessed to generate a complete user profile study.

The final vehicles performances were also evaluated subjectively, by experienced drivers under all the above-mentioned driving scenarios. Mainly focused on the longitudinal deceleration behaviour, the different concepts of the brake control (beginning, ending, quality, delays, etc.) have been used as parameters for its comparison with the metrics analysed.

All in all, this study presents interesting and objective methods of evaluation for the ACC systems, supported by the experienced users’ evaluators. This may finally be used as a tool for stages of development and calibration, as the subjective inputs compared with objective metrics provide valuable information of the best system practices.