In recent years there has been a shortage in energy supply like fossil fuel and concerns about environmental issues. Considering only 10-16% of fuel energy burned by the engines is used to drive the vehicles, we developed an innovative energy harvesting absorber to regenerate electricity from vibrations in the suspension system usually wasted as heat in oil shock absorbers. The regenerative absorbers can be designed with the same size and shape to replace the conventional absorbers without changing structure of the conventional suspension system, which helps improve 2-4% fuel efficiency.
This electromagnetic energy-harvesting shock absorber is based on our unique concept of a mechanical motion rectifier (MMR). The MMR can directly convert irregular reciprocating oscillation vibrations into regular unidirectional steady high generator rotation resulting in high energy conversion efficiency. Three bevel gears are used, and two of them are mounted on the shaft of pinion gear with two one-way bearing. The one-way bearing is used to transmit motion in one direction. Through the engagement and disengagement of two one-way bearings, at any instant the pinion shaft will be engaged with one of the bevel gears, and thus the generator will be rotated in one direction, no matter which direction the suspension is moving. Such MMR design is actually analogous to semiconductor diode which rectifies an AC voltage. It can solve the fundamental challenge of vibration energy harvesting due to irregular oscillatory motion, offering significant advantages as followings.
(1) Higher energy conversion efficiency: Several proof-of-concept MMR-based shock absorbers for various vehicle duty loads were tested on a SUV and achieved a higher energy conversion efficiency of 60-80% with high power density.
(2) Controllable suspension damping: The damping constant of the generative absorber can be conveniently adjusted for various vehicle dynamics by changing the electrical load or adjusting the charging circuit connecting with the motor.
(3) Better suspension dynamics: In the MMR based design, the generator rotates in one direction, and inertia acts as a flywheel to temporally store the kinetic energy at higher speed and reduce rotational fluctuation. The suspension dynamics, including both the ride comfort and road handling, can be much better.
(4) Higher reliability: Since almost all the components, including bevel gears and generator, except the rack pinion, rotate uni-directionally, the impact force, backlash, and friction loss and further fatigue or failure can be lessen than those in the traditional bi-directional designs.
(5) Retrofit integration: the characteristics of excellent damping and power density enable the energy-harvesting shock absorber to be retrofit into existing space of the vehicles. Actually the proof of concept prototype we build for passenger car is even lighter than the oil shock absorbers. The energy harvesting shock absorbers can also be directly integrated with the existing electrical system of the vehicle to charge the battery without changing the alternator’s electronics.
The regenerated energy from the regenerative absorbers can be used to charge the existing 24V battery, to maintain the operation of alternator driven by the engine and to provide electricity for need of on-board electrical devices like lights, ignition, power steering, fans, etc.