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Electric Vehicles Research
Posted on October 8, 2010 by  & 

Tyre pressure monitoring systems & energy harvesting

Worldwide adoption of tyre pressure monitoring systems
Optimal operation of tires is even more critical with electric vehicles. Although the first tyre pressure monitoring systems (TPMS) appeared in the mid-80's as a feature of top-range luxury vehicles, it is only in recent years that they have seen widespread adoption worldwide.
Most drivers in the USA must recognize the symbol below, a warning light incorporated in dashboards of all new vehicles after 2007 (although phase in started in 2005), that informs drivers on whether tire pressure is getting dangerously low.
The adoption of TPMS's in the USA stemmed from safety issues that received a lot of attention at the end of the 90's, and accidents that could have potentially been avoided if there was a way to make sure tire pressure wasn't under a critical level.
On the other hand Europe and East Asia are also slowly making the use of TPMS's mandatory, albeit for different reasons, taking a more environmental slant in the reasoning behind their adoption. According to Transense, a car that has tyres that are 20% underinflated has an increased rolling resistance of 12%, reducing tyre lifetime by up to 50% and leading to increased fuel consumption by 6%.

Issues with TPMSs using batteries

Companies developing TPMS's include Continental AG, Schrader Electronics and SmarTire Systems. The research into battery-less TPMS's is gaining attention due to two major issues relating to the use of batteries on these monitoring systems:
  • Car manufacturers require a lifetime for batteries used in TPMS's between 7 and 10 years. But batteries eventually do run out, presenting car owners with a non-functioning TPMS, a safety issue and replacement costs to the consumer.
  • As use of TPMS's becomes mandatory, there is concern about the effects of the hundreds of millions of additional batteries introduced into the environment.
Such issues have led to efforts in developing battery-less TPMS's and technologies like energy harvesting are a perfect match for this application.

Energy harvesters for TPMSs

Battery-less TPMS's have been developed by Transense and VisiTyre. STE Engineering has developed a system that has reduced power consumption by 3 orders of magnitude, making their device much more efficient and also compatible with energy harvesters that would provide small amounts of power.
Transense is using a surface acoustic wave (SAW) based technology with licensees including companies such as Honeywell and Michelin. SAW systems measure pressure with temperature compensation and can either be attached to wheel (e.g. back of valve or to run-flat system), embedded in the wheel or can be embedded / attached to the tyre itself.
Visityre on the other hand is using an electromagnetic closed-coupling technology. The device the company has developed along with a visualization of the magnetic field of the device's coil are shown in the pictures below
VisiTyre's pick up coil.
Source: VisiTyre
Visualization of the VisiTyre coil's magnetic field. Image courtesy of Paul Nylander, University of California Irvine.
The Hong Kong Applied Science and Technology Research Institute (ASTRI) has a wide range of activities on the field of energy harvesting but one of the more interesting applications is the development of a TPMS based on a piezoelectric vibration energy harvester.
For more attend: Future of Electric Vehicles which uniquely covers the whole electric vehicle market - land, sea, air whether hybrid or pure EV - with emphasis on future breakthroughs.
Top image source: Recycle This

Authored By:

Principal Analyst

Posted on: October 8, 2010

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