Design and analysis of a d33 mode piezoelectric energy generator for vehicle braking system

A novel piezoelectric energy generator embedded in vehicle brake pads and excited by magnetic repulsion is developed. The generator is made of a cylindrical magnet and a piezoelectric stack. The generators are mounted on the backing plate of the brake pad through the perforated friction layer. Slotted brake rotor with embedded magnets is equipped to ensure the braking performance of the vehicle. During the braking process with slotted brake rotor, dynamic magnetic repulsion will be generated when the overlapping area of the embedded magnets in the brake pad and brake rotor is changing. The magnetic repulsion is generated when two magnets are close to each other, and the force is proportionally changing with the overlapping area of the two magnets. As a result of repulsion between the magnets, the piezoelectric stack will experience compressive forces, creating an electrical charge for generating energy. To illustrate the voltage generation, a mathematical model with experimental verification is established to calculate the electric charge and output voltage considering the charge dissipation. The energy harvesting process is evaluated by simulating the transient charging of the storage capacitor through the diode bridge, which was experimentally validated in literature. The influences of the dimensional and material properties of the piezoelectric stack, the vehicle speed, the magnetic repulsion, the diameter of the magnetic actuator, the capacitance of the storage capacitor and the distance between rotor center to the actuator on the root mean square (RMS) of the charging power are discussed. A total RMS power of 0.0710 W can be achieved with thirty-six generators embedded in both the inner and the outer brake pads within one brake caliper using APC850 (PZT4) material, and a total RMS power of 1.1226 W can be achieved using PMN-PT-B (PT = 0.3–0.33) material at 120 km h⁻¹ speed of the vehicle. This novel generator will be useful for efficient and practical energy harvesting applications during vehicle braking process.

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