Energy Harvesting

Energy Harvesting in Automotive Powertrains

Modern automotive powertrains rely vastly on the use of smart electronic devices that can efficiently offer new potential in the ever increasing need for economical, less carbon-dependent vehicles. However, contemporary monitoring strategies lead to crowded, complex networks of these low-consumption devices, usually sensors and micro-controllers, which in turn, require a considerable amount of wiring for power transmission and data communication. Besides its physical weight that opposes the current trend for lightweight vehicles in view of the target for better fuel consumption and lower greenhouse emissions, several other issues arise regarding access to the nodes of this network for hard-wiring / maintenance, manufacturing costs for fitting it in limited space etc.

Energy harvesting applications
  • Energy Harvesting has recently attracted significant attention, partly due to the low power demand of electronic devices.
  • Autonomous sensors that could communicate wirelessly and power up locally (or even wirelessly) consuming the harvested ambient energy.
  • Applications vary from charging phones or mp3 players while a person is jogging, up to wireless sensors planted in train carriages.
Harvesting Energy from Mechanical Oscillations
  • Energy losses due to vibrations of parts are effectively translated to worse fuel consumption, let alone the risk of wear and fatigue.
  • Excessive vibrations also contribute to impaired passenger comfort in a variety of ways.
  • We consider exploiting this source of energy instead of simply rejecting it out of the powertrain system, as common palliatives and dampers do.
Operating Principle
  • There are three main categories in the state-of-the-art of energy harvesters, based on the operating principle of the power take-off system: piezoelectric, electrostatic and electromagnetic.
  • In the last one, Faraday’s law of induction provides the fundamental tool to predict the current flowing through an electric load Rl connected to the ends of a coil.
  • Two parameters are crucial in this multi-physics problem: the electromagnetic coupling coefficient and the magnet’s velocity amplitude.
  • Linear harvesters are tuned to the expected frequency of the vibrations such that they operate at resonance.
  • Real-life systems often experience unpredicted operating conditions that result in shifts in the realised frequency band, leading to linear harvesters underperforming.
  • Therefore, research on nonlinear harvesters attracts interest, given their attribute of a broader frequency response with higher amplitude peaks as well.

Figure 12. Sketch depicting the governing operating principle of electromagnetic energy harvesters