ELECTRICITY GENERATING SHOCK ABSORBER
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Road vehicles can expend a significant amount of energy in undesirable vertical motions that are induced by road bumps, and much of that is dissipated in conventional shock absorbers as they dampen the vertical motions.
An electromagnetic linear generator and regenerative electromagnetic shock absorber is disclosed which converts variable frequency, repetitive intermittent linear displacement motion to useful electrical power. The innovative device provides for superposition of radial components of the magnetic flux density from a plurality of adjacent magnets to produce a maximum average radial magnetic flux density within a coil winding array. Due to the vector superposition of the magnetic fields and magnetic flux from a plurality of magnets, a nearly four-fold increase in magnetic flux density is achieved over conventional electromagnetic generator designs with a potential sixteen-fold increase in power generating capacity. As a regenerative shock absorber, the disclosed device is capable of converting parasitic displacement motion and vibrations encountered under normal urban driving conditions to a useful electrical energy for powering vehicles and accessories or charging batteries in electric and fossil fuel powered vehicles. The disclosed device is capable of high power generation capacity and energy conversion efficiency with minimal weight penalty for improved fuel efficiency.
We have been carrying out a proof-of-concept study to evaluate the feasibility of obtaining significant energy savings by using optimized regenerative magnetic shock absorber in vehicles. In addition to other potential applications, the use of such shock absorbers might allow for improved energy efficiency in electrical vehicles through the conversion of otherwise parasitic mechanical power losses into stored electrical energy, thereby leading to longer distances between battery recharges.
We recently carried out two experiments that validated a simplified eddy current damping model which, together with a “road bump” model (discussed further below), has been used to estimate the average power/energy recovery that might accrue for a 2500 lb automobile travelling on a “typical” road in the United States. The estimates are summarized in Table 1, and suggest that with a set of optimized regenerative shock absorbers, the average vehicle on the average road driving at 45 mph might be able to recover up to 70% of the power that is needed for such a vehicle to travel on a smooth
HOW IT WORKS
A conventional automotive shock absorber dampens suspension movement to produce a controlled action that keeps the tire firmly on the road. This is done by converting the kinetic energy into heat energy, which is then absorbed by the shock’s oil.
The Power-Generating Shock Absorber (PGSA) converts this kinetic energy into electricity instead of heat through the use of a Linear Motion Electromagnetic System (LMES). The LMES uses a dense permanent magnet stack embedded in the main piston, a switchable series of stator coil windings, a rectifier, and an electronic control system to manage the varying electrical output and dampening load.
The bottom shaft of the PGSA mounts to the moving suspension member and forces the magnet stack to reciprocate within the annular array of stator windings, producing alternating current electricity. That electricity is then converted into direct current through a full-wave rectifier and stored in the vehicle’s batteries.
The electricity generated by each PGSA can then be combined with electricity from other power generation systems (e.g. regenerative braking) and stored in the vehicle’s batteries. In turn, the electrical power can be used to recharge batteries or other efficient energy storage devices (e.g., flywheels) rather than be dissipated.
PLUG AND PLAY
The power generating shock absorber is the same basic size and shape, and mounts in the same way, as a standard shock absorber or strut cartridge.
An electronic control system monitors the requirements of each individual road wheel’s suspension and varies the dampening by quickly switching on or off individual stator coil rings. With all stator coil rings switched on the PGSA produces a strong dampening force which can then be varied for disparate road conditions by switching coils on and off as needed. This provides an added level of benefits in allowing the shock to be very soft in cruising situations (small, high-frequency movements) and instantly change to a sport shock in aggressive cornering situations (longer, lower-frequency movements). Further, the rebound and compression strokes can have different dampening values and application curves depending on performance requirements.
This application could conceivably produce over twenty watts per wheel in normal operation. City driving, with its varying road surface characteristics, as well as stop and go traffic’s font-to-back loading, will generate more power than driving on smooth roads at consistent speeds.
Manufacture of the Regenerative Shock Absorber will require a machined main shaft with embedded permanent magnet stack, astrong air-gap cylinder housing, high quality stator windings, and robust slide bearings. Other systems, such as microprocessor-controlled voltage, current, and dampening regulation, external casing, protective bellows, etc. will also need to be designed and tested.
LMES technology is already finding its place in ocean power generating systems. Its introduction into the automotive world is the next logical step. This technology can be applied to any type of vehicle that employs movable suspension technology and uses electricity in some form as its fuel.