Installing tyre pressure monitoring systems (TPMS) in passenger vehicles has been mandatory in the United States since 2008, and will come into force in the EU on the 1st of November 2014. These legislations are made to enhance traffic safety as faulty, particularly low, tyre inflation pressure can cause fatal accidents by causing tyre overheating and excessive strain. In addition, correct tyre pressure helps in reducing rolling resistance, noise, tyre wear, fuel consumption, and CO2 emissions. It also increases vehicle control and tyre life.

One of the biggest challenges that face the vast majority of TPMS is the energy source, which is in most cases a coin Lithium battery. As such, various attempts have been made to introduce different energy harvesting systems within tyre-TPMS assembly in order to promote a battery-free TPMS. Harvestable energies dissipated within rolling tyres primarily include vibration energy, thermal energy, and strain energy. The latter mainly exists within the tyre contact patch area, which is a deformed area at all times and occupies approximately 8% of the treadwall area in passenger vehicle tyres. In this study, the energy harvesting potential from a 14-inch car tyre (#175/65/R14) using a Piezo Fibre Composite (PFC) element is investigated. The strain energy in the PFC element which is adhered firmly onto the tyre inner surface is predicted by finite element analysis (FEA) tyre strain results. The amount of the generated electric charge due to the PFC element deformation is then calculated by applying basic piezoelectric equations found in IEEE piezoelectric standards.

The FE tyre model is constructed of three major rubber components including tread, main body, and apex as well as various material properties in reinforcement – i.e. cap ply, steel belt, carcass, bead, and bead reinforcement. Visco-hyperelasticity properties of rubber are considered and elastic behaviour assumption has been made for the reinforcements. The tyre was fitted to a rigid rim, representing the boundary condition of the tire. Then the tyre was inflated to 2.4 bars as the standard rated pressure for this tyre. A vertical load of 4000 N, i.e. the car load share, was applied to the tyre by a rigid/flat road and the tyre was forced to spin around its axis in a steady-state dynamic analysis step at the required constant speed.  This enabled the best location to install the piezoelectric element to be determined as well as to estimate the strain energy that can be scavenged by the piezoelectric element attached to the tyre inner liner.

The predicted strain energy distribution in the tyre inner liner showed good agreement with the measured strain distribution. As a result, the likely optimal location of the piezoelectric element was identified to provide the highest possible scavenged strain energy. The flexible PFC element was then adhered to the tyre inner liner and integrated with a TPMS to produce a battery-free system. The predicted amount of scavenged strain energy was shown to be sufficient to power the TPMS. This was confirmed by results obtained from the physical system when tested.