A HANDFUL OF . . . ENERGY!
Converting the shock absorbing movements into electric Energy to reduce fuel consumption: the idea is anything but a farfetched idea, and shows great potential
A suspension’s relentless work might not be quite so visible but its usefulness cannot be denied: in fact not only do they provide a comfortable ride, but also guarantee the correct road handling with their damping movement. Elastic elements – coil springs, torsion bars and hydraulic parts – combine with damping devices in keeping the wheels always in contact with the road surface, while the rest of the vehicle remains suspended above the ground.
Elastic elements dissipate very little energy and that is why they need to be linked to shock absorbers: if the mechanical energy accumulated by the coil springs is not dispersed by the shock absorbers, the suspensions will move with a counter-swinging movement that would be detrimental to both comfort and road handling.
The mechanical energy stemming from the movement of the suspension is then dissipated as heat: therefore, even if some of the elastic elements are slightly heated (i.e. coil spring, torsion bar etc.) most of the heat is dispersed by the shock absorbers.
Damping and power generation systems
Within the damping elements, mechanical energy is converted into heat and dispersed into the atmosphere, a situation that will soon be revolutionized by “energy harvesting” systems. Promising studies in this field underline the potential benefits behind mechanical energy converted into electricity, a process that allows a vehicle to store the energy generated by such systems to be used, for example, in Hybrid vehicles.
Everything is based on a fundamental property of electromagnetism, formalized in the Faraday - Neumann – Lenz Law: an electromagnetic coil immersed in a variable magnetic field creates electricity. This effect can be easily verified by connecting a wire coil to a tester and moving a magnet to and fro the coil itself; this is also reversible, in the sense that by inserting electricity in a coil, a magnetic field is created that can interact with that of the magnet, thus generating a force. But electricity flowing in a coil in turn creates a magnetic field that moves in the opposite direction compared to the one created by the magnet itself. Hi-fi speakers are an example of this type of action: a coil is attached to a membrane and is immersed in an electromagnetic field generated by permanent magnets: once the voltage coming from the amplifier enters the coil, a variable magnetic field is created which, combined with that of the magnetic group, creates a force that moves the coil, and consequently the membrane of the loudspeaker. Electric motors similarly take advantage of this interaction between magnetic fields to spin a rotor, converting electrical energy into mechanical energy.
Regenerative suspensions make extensive use of such devices: ZF Friedrichshafen and Levant Power, for example, are studying an interesting system that uses the pressure created by compressing the oil inside the shock absorbers. The fluid passes through a special rotary valve that not only regulates the oil flow but alos converts its pressure into a circular motion that drives an electrical generator. In fact, if an "electrical motor" operates as a generator, it will absorbs mechanical energy and its rotation will encounter more resistance: therefore electricity is produced at the expense of the kinetic energy produced by the suspensions. Since a generator can also function as a motor, it moves the Activalve (this is its name) to vary the damping action of the shock absorber, guaranteeing comfort and road handling. More similar to the way a speaker works, the patent filed by Intetronic Gresser, a German company responsible for creating a "shock absorber" providing a hydraulic damping system that operates simultaneously with an electromagnetic system. The first uses a piston immersed in oil: its movement sends the fluid in circulation and the damping rate depends on electronically controlled valves that allow more or less oil through. This adjustment, however, is activated only when the electromagnetic system is not sufficient: in average condition, the latter is in fact to be preferred, with a permanent magnet that runs through wire coils. This relative movement generates electricity (a bit like a speaker when the diaphragm moves due to an external force), which may be stored in batteries or used for on-board devices; once again generating energy this way will be at the expense of mechanical energy.
Further trials and experiments are underway at Virginia Tech and Stony Brook University, directed by Lei Zuo; it all started from an important fact: the fuel consumed by a car to win air resistance and friction is only 12/16% of the total, the rest being lost in heat and other waste. One of the patents relates to a system with permanent magnets, which slides inside a system of coils, much in the same fashion as seen above. The other has the appearance of a common shock absorber that contains a rack and a group of gears that convert the linear movement of the rack in a rotation that activates a generator able to produce about 80W.
Shortly on the market
These issues are already under the magnifying lens of a number of car manufacturers: 48 Volts electrical systems (we talked about it in the No. 6/2015 issue of Pneurama) lend themselves well to this use and Audi has already announced that its progressive switch to hybrid systems (something is in the pipeline already) will include suspension systems. Its eAWS system, ElectroMechanical Active Roll Stabilization, plans to split the anti-roll bars; the ends of the half-bars are connected to a three-stage planetary gear driven by an electric motor which can apply a torque of up to 1,200 Nm. Driving in "disengaged" mode, the electric group is blocked and the two half bars work as a classic anti-roll bar - favoring comfort and driving efficiency.
If an exciting ride is what you are looking for, the electric unit applies an opposing torsion that lifts the outer wheels and lowers the inner wheels (the correction is independently applied both at the front and at the rear), resulting in a neutral set up. The system also works as a generator: suspension movement turns the electric unit (at low speed or driving in a straight line, when anti-roll functions are not required) producing electricity: Audi states that driving on rugged terrain the energy requirements of the eAWS could practically be close to zero. The eROT (electromechanical rotary damper) replaces a traditional hydraulic damper that would normally release stored energy in the form of heat as the car travels over imperfections in the road. A strong lever arm moves up and down with each damper articulation and, using a set of gears, it creates a current that can be used to generate and store power in batteries, which can then be used later to power a number of components. According to Audi the system is able to generate between 3W (on a smooth highway) and 613W (on a poorly maintained country road) and is also able to reduce CO2 emissions by 3 g/km.