78 Tyre Asia April/May 2018
TECHNOLOGY
Professor (Dr) Luc G. Frechette of Quebec’s Universite de Sherbrooke’s Department
of Mechanical Engineering and Director of Research at the Centre in Nanofabrication
and Nanosystems (CRN2) is a renowned researcher in microengineering. His expertise
covers miniature systems for energy conversion, such as microfabricated heat engines,
fuel cells and vibration energy harvesting. His activities range from work on integrated
device development to microfluidics, heat and mass transfer studies. He is also involved
in developing Micro-Electro-Mechanical Systems (MEMS) sensors and actuators for
aerospace applications and microelectronics. In this interview to Tyre Asia he explains
in detail the practical application of his work in intelligent tyres to robotsMicro matters
Work on intelligent tyres is progressing
among many tyre manufacturers,
especially in the light of the need
to have speciality tyres for electric
vehicles. In this context can you explain
the details of the dynamic load sensors
that you have developed?
As a vehicle travels down the road, all the forces
required to guide its motion are transmitted through
the tyres, such as during braking, accelerating, and
manoeuvring. We proposed to monitor the forces
imparted on the tyres by measuring their deformation.
When a force is applied at the contact patch of the tyre
with the road, there is not only a local deformation,
but the entire tyre is affected. We noticed that the
sidewall and tread all around the tyre also deform as
a force is applied at the contact patch. This implies
that with only one (or a few) sensors located around
the circumference, we can continuously monitor the
forces seen by the tyre. We, therefore, first studied the
deformation field over the tyre to find the locations that
are the most sensitive to road excitation.
The tyre deformation can be measured by multiple
ways, such as piezoresistive strain gauges, piezoelectric
patches or capacitive sensors; the last two having been
evaluated in our work. The capacitive strain sensor
simply consists of two electrodes separated by a small
gap. Since the capacitance between the electrodes
is inversely proportional to the gap, it will vary when
stretched. By fixing the sensor onto the rubber, we can
therefore measure the tyre’s deformation. This requires
the sensor to be highly flexible, so the electrodes were
fabricated using a silver nanoparticle ink stamped onto
a flexible polymer film. We also tested the piezoelectric
approach by using Micro Fibre Composite patches,
which consist of thin piezoelectric fibres held between
two polyimide films with metallised electrodes. Both
were found to sense the loads from the road, validating
the proposed approach.How will the Capacitive Strain
Transducer and the Micro FibreComposite Transducer be incorporated
into tyres?
Currently, both types of sensors are fabricated on their
thin polymer films, and are then mounted on the tyre
with an adhesive. To protect the sensor from harsh
environmental conditions, it should be mounted on
the inside of the tyre, with careful attention to the
adhesion. Alternatively, the electrodes that form the
capacitive sensor could be stamped directly onto the
tyre inner wall, if this improves adhesion and eases
manufacturing.How can the introduction of sensors to
monitor the vehicle dynamics actually
work to ensure safety and comfort?Active control strategies for traction control, braking
and manoeuvring could use the load information to gain
precious fractions of a second to correct a dangerous
situation. For example, loss of lateral traction when
turning would be sensed as a change inside deformation
of the tyre, prompting the active braking or active
suspension system to react and avoid a loss of control.
In addition, noise coming from non-uniformities of the
road can also be cancelled before they are transmitted
to the cabin and perceived by the occupants. The
road-induced vibrations travel through the tyre,
the suspension, the car’s body and into the cabin as
acoustic noise. In this case, a feed forward algorithm
can use the measured load fluctuations on the tyre
to generate an opposite vibration further up in the
suspension that will cancel the road-induced vibrations.
This will reduce the noise generated in the cabin,
similar to a noise cancelling principle found in some
headphones.
Tracking the forces in the tyre, therefore, provides
unique knowledge of the vehicle’s interaction with the
road, even before the vehicle’s motion is affected.You bonded on the tyre CST using
printing electrodes. In the tyre
manufacturing process, when and
where can these sensors are embedded?TA News Bureau