Regenerative Suspension Could Add to EV Range
Capturing the energy when a vehicle encounters a bump or dip in the road is a way to increase overall electric vehicle efficiency.
With electric vehicles (EVs) finally reaching the mainstream, automakers are keen to find ways to increase vehicle range. With the battery, power electronics, and electric drive motors already extremely efficient, and most EVs' aerodynamics nearing their optimum, the search is on to find other ways to reduce the energy consumption per mile traveled.
Image used courtesy of Gig Performance
One way studied for more than a decade is to use the motions and vibrations of the vehicle’s suspension system to generate electricity that can help recharge the EVs battery while driving through a regenerative suspension system.
Bumps in the Road
When a vehicle’s wheels encounter a bump on the road, its suspension system, consisting of a spring and damper working parallel to each other, stores the impact energy by compressing the spring. The energy is released to the vehicle body gradually as the spring expands, returning to its original length. The damper dissipates the energy by absorbing it, typically by forcing oil through an orifice within the shock absorber. If the road is particularly bumpy, friction within the shock absorber can heat the device, making it less effective at damping the suspension motion.
What if, however, the energy that heats the shock absorber could be captured, converted to useful electricity, and used to help charge the EV’s battery? One way that has undergone significant study is to collect the energy from the suspension motion through electromagnetic induction. An electromagnetic current can be induced by placing magnets on the moving suspension components near wire coils. This is particularly effective over large bumps and dips in the road when the suspension motion creates a significant amount of displacement of the magnets relative to the induction coils.
A second way to generate electricity from suspension motion is by using a piezoelectric energy harvester. Piezoelectric energy is created when certain crystalline materials are squeezed. Suspension devices have been developed that use the motions of the vehicle’s suspension. Testing has shown that piezoelectric harvesters can produce as much as three times the energy produced by electromechanical methods.
Piezoelectric energy can be made from small suspension motions and vibrations that occur on relatively smooth road surfaces.
Harvesting electricity from suspension motions using a small flywheel operated by an arm connected to the suspension. Image used courtesy of BMW patent application
BMW Flywheel Energy Harvesting
As reported by several media sources, BMW recently filed for a patent that describes a way to harvest electricity from suspension motions using a small flywheel device that is operated by an arm that is connected to the suspension. The arm actuates a disc connected through a one-way clutch to the flywheel. When a wheel encounters a bump, the suspension compresses, and the actuating arm spins the flywheel. Then, as the suspension rebounds, the arm moves in the opposite direction, and the one-way clutch engages a gear system that adds to the flywheel spin while multiplying the speed of the suspension motion. The flywheel is attached to a generator that produces electricity stored in an EV’s traction battery or used to run the vehicle’s electrical accessories in a traditional internal combustion engine (ICE) vehicle.
Roadkil 5000 converts vibrations from the roadway into electrical energy that can be stored in an EV battery. Image used courtesy of Gig Performance
Gig Performance Mechanical Energy Storage
Another company called Gig Performance is looking at ways to mechanically store the energy from suspension motion. The company’s Roadkil 5000 converts vibrations from the roadway into electrical energy that can be stored in an EV battery.
The Roadkil 5000 has a pair of arms used to convert the linear motion of the suspension system into rotational motion by moving the body (working as a generator stator) and a rotor in opposite directions. A planetary gear system enhances the spinning to increase the rotational motion, generating electricity whenever a bump is encountered.
Gig Performance claims its system can be used on a variety of vehicles, from a side-by-side ATV to a semi-truck. According to the company’s testing, when attached to a semi-truck, the unit can produce 4 kilowatt-hours (kWh) of energy over an 8-hour driving shift. The company is looking for manufacturers to further their development efforts.
Regenerative suspensions show a great deal of promise and, as EVs continue to grow, they will undoubtedly be adopted as one way to increase efficiency and range further.