A Batteryless Full Energy Harvesting System for Inside-Engine Temperature Sensors

This paper presents a full energy harvesting system for harvesting mechanical energy from internal combustion engines to power low power autonomous sensor systems inside of the engine to record and wirelessly transmit the piston temperatures. Due to the reciprocating movement of the pistons, sensors cannot be connected to the cars electrical system by wires and thus are usually powered by batteries. Changing those batteries is a time consuming process since large parts of the engine needs to be taken apart to get to the pistons. This is the reason why we present a system that uses a piezoelectric nano generator (PENG) based on flexible PVDF to convert a small amount of the mechanical energy of the pistons to electrical energy. A power management system (PMS) including a maximum power point (MPP) circuit maximizes the power output of the harvester and supplies a regulated dc voltage to the sensor. The MPP circuit used in this design has a very few components, thus keeping its own power consumption low. It requires a minimum input voltage of 3V and a minimum power of 1.4µW during operation. During startup, a power of 4µW is required for a short time until the input capacitor of thre PMS is charged to 1.8V. Measurements show an increase of up to 44% of harvested power while also allowing higher output voltages compared to the same power management system without an MPP circuit. A prototype to emulate the movement of the pistons was built and tested with the PENG and PMS. At 600rpm, data transmission is possible every 90 seconds with 3.5µW harvested power.