According to a team of mechanical engineers from Stony Brook University, only 10-16 percent of the fuel energy is used to drive the car during everyday usage – that is, to overcome the resistance from road friction and air drag and actually transport the vehicle forward. That amounts to a lot of energy being wasted. Hybrid cars recapture some of the energy usually lost in braking but the dissipation of vibration energy by shock absorbers in the vehicle suspension remains an untapped source of potential energy. To harvest this lost energy the researchers have designed and tested a shock absorber that can be retrofitted to cars to convert the kinetic energy of suspension vibration between the wheel and sprung mass into useful electrical power.
Unlike the regenerative shock absorber system designed by MIT researchers that uses the up and down movement of the suspension to drive an external hydraulic motor the mechanical engineers built and tested a 1:2 scale prototype that relies on magnetic flux to generate power, much like the Etive concept we looked at last year, which uses kinetic energy to charge mobile devices.
In the new regenerative shock absorber, rare-earth permanent magnets and high permeable magnetic loops are used to harvest energy and could help increase fuel efficiency and help cut pollution.
DesignThe device consists of two components - a hollow coil assembly and a magnet assembly that uses vibrational energy from the vehicle’s suspension to move up and down inside it.
The magnet assembly is made of ring-shaped permanent magnets and ring-shaped high magnetically permeable spacers stacked on a rod of high reluctance material. The magnets are arranged with like-poles of adjacent magnets facing each other to help push the magnetic flux outward. The magnetic assembly is encased in an outer cylinder made of high magnetically permeable material to further increase magnetic flux density in the coils.
The coil assembly is made of copper coils wound on a delrin tube. The coils were designed to align with the magnet stack and are connected to a rectifier set-up so, as the copper coils move inside the magnetic field, a voltage will be generated.
TestingTo test the prototype shock absorber’s voltage and power output on various road conditions the magnet assembly of the device was mounted in the mover of a vibration shaker, while to coil assembly was mounted to the top plate, which is fixed on the base of the vibration shaker. While simulating a range of road conditions an oscilloscope was used to measure the output voltage, both peak and RMS values, and also to view the output waveforms generated from the shock absorber. A multimeter was used to measure current output.
ResultsThe testing demonstrated that in typical driving conditions, traveling at a speed roughly equivalent to 45 mph (72.5 kph) the regenerative shock absorber was able to harvest 2-8 watts of power. The researchers told PhysOrg.com that they predict a full-scale system would be able to harvest approximately 64 watts per wheel. So with the regenerative shock absorbers put on all four wheels it should be possible to recover a total of around 256 watts under such driving conditions. Driving on rough surfaces such as a corrugated dirt track the system should be able to harvest considerably more.
Many hybrid vehicles harvest energy from braking to enhance the efficiency of the vehicle, but this is only intermittent. A system that captures energy through a vehicle’s suspension would be able to do so much more consistently resulting in greater fuel efficiency and reduced pollution. It might also means that cars will soon be swerving to hit potholes instead of avoid them.
The team is working to further improve the energy density and efficiency of the device. Their research appears in the paper, Design and characterization of an electromagnetic energy harvester for vehicle suspensions, which appears on IOP Science.