• Introduction

The aim of this project is to implement a strain sensor in the automotive tire. This sensor will provide an advanced disturbance signal to a controller used to minimize vibrations transmitted through an automotive suspension. The Active Structural Acoustic Control (feedforward LMS control) will be used to reduce road noise in the passenger car (inside the cabin).

• Feasibility of extracting a reference signal from tire vibrations

The concept of using the vibrations on the tire to extract a reference signal for active road noise control is validated. For this aim, the coherence between the dynamic response of the tire and a reference force sensor is determined in a quarter-car test bench when the wheel is subjected to a real road force excitation. The laboratory quarter-car suspension test bench used to conduct the experiments is shown herein.

A Polytec PSV 200 Laser Doppler Vibrometer (LDV)  is used to measure the out-of-plane velocity on the tire surface to help determine if a signal coherent with the reference force sensor can be obtained through tire dynamic sensing. To do so, the coherence between the signal obtained by the LDV and the one obtained by the reference force sensor is calculated in the quarter-car test bench when the wheel is subjected to a real road force excitation. Coherence between the sidewall tire out-of-plane velocity and a reference force sensor is shown in the below video.

• Strain sensing configuration

For better sensitivity, the best locations for strain transducers will be where the largest strain levels are obtained. The strain is computed based on Kirchhoff-Love plate theory where the tire sidewall is assumed to be separated into several sections of radial plates. This assumption is verified by using a benchmark Macro-Fiber Composite (MFC) to measure the strain on the tire sidewall.

It is concluded that the optimal position for a radial strain sensor in the sidewall of the tire is in the middle of the tire sidewall. However, for circumferential strain sensing, it is preferable to place it near the inner radius of the tire sidewall, although a mid radius location is also acceptable. In addition, the sidewall circumferential strain showed larger strain level than the sidewall radial strain.

• Design and fabrication of a Printed Capacitive Strain Transducer (CST)

Although the benchmarking MFC transducer can potentially provide the strain information required to provide the reference signal to the active road noise control system, this type of sensor cannot be practically integrated into the tire because of its rigidity, cost and limited durability to harsh exploitation conditions.
In this work, a new type of flexible transducer has been implemented and evaluated for its capacity to fulfill the requirements for this application, which are cost effectiveness and easily embeddable. The approach consists Capacitive Strain Transducer (CST) which exhibits a change of capacitance between interdigitated electrodes fixed to a flexible substrate that is subjected to strain.

The CST is implemented using a UV-curable polyurethane (PU) prepolymer as an adhesive layer to efficiently transfer silver nanoparticle (AgNP) ink pattern onto the target substrate using a stamping technique. This direct stamping method has been applied to fabricate a CST made of 5 micron-thick interdigitated electrodes without any residual layer. The thick electrodes fabricated using the direct stamping of metal nano ink might help enhance the durability of the sensor and allow large deformations (details in the references at the bottom of the page).

• Implementation of the CST

Rather than LDV measurements that are limited to the outside sidewall of the tire, the CST is implemented behind the sidewall and the tread, inside the tire.

The strain sensing performance of the CST is evaluated by comparing it to the reference force sensor, considering various locations and orientations of the CST. As a result, the strain level in the tire tread area was larger than the strain level in the tire sidewall, and also the sidewall circumferential strain level from inside was higher than the sidewall circumferential strain level from outside. Furthermore, the sidewall circumferential strain was higher near the inner radius of the sidewall and showed larger strain level than the sidewall radial strain. The response of the CST in the tire tread is given in the video below and compared to a reference force sensor.

Finally, in order to get a complete picture on the potential of using the CST as a reference sensor for active road noise control, where coherence is critical, a study is carried out at a given position for different amplitudes of applied forces for the tread CST.

It can be seen that coherence levels in the order of 0.9 can be achieved up to 100 Hz for an applied force of 17 N, and up to 250 Hz for an applied force of 25 N, for the tread CST.

• Active Structural Acoustic Control (feedforward LMS control) on the quarter-car suspension

• Noise reduction in the quarter-car test bench using the reference force sensor and the Capacitive Strain Transducer 

• Project presentation at Actuator21 conference 

• Acknowledgement
  The authors gratefully acknowledge the support of AUTO21 Network of Centres of Excellence (Canada).

• References

1. Hassan Hariri, Patrice Masson, Luc Frechette, Road Noise Reduction inside car cabin using Active Structural Acoustic Control (ASAC), International Conference and Exhibition on New Actuator Systems and Applications 2021, Germany
2. H. Hariri, L. Frchette, P. Masson, J. Kim, W. S. Kim ‘’Performance Validation of Printed Strain Sensors for Active Control of Intelligent Tires’’, Journal of Applied Acoustics, 2017
3. J. Kim J, W. S. Kim, ”Stretching silver: printed metallic nano inks for stretchable conductor applications”, IEEE Nano Magazin, 2014.