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Power and Motion |
Another page of my website is devoted to long-range dual-mode
electric highway vehicles. Clearly, they can provide fast,
safe, convenient, flexible, portal-to-portal transportation, at low cost,
with no emissions. And they clearly could have unlimited range on electric
highways powered by clean, renewable and sustainable energy, supplied
by solar, wind, etc. RPM's flywheel
battery, described and illustrated in this link, and in my patents
"Minimal-loss Flywheel Battery and Related Elements" and "Robust Minimal-loss
Flywheel Systems" could be a vital part of these electric highways.
Technology that can enable electric highways has been in use for over a
century. Implementation for personal vehicles is hindered by institutional
barriers -- certainly not by technology, cost, safety, environment, sustainability,
or its potential market.
But lacking the electric highway infrastrure
those personal EVs (electric vehicles) require, let's consider an EV option
designed for our existing infrastructure: An ultra-light EV with
onboard batteries, an onboard battery charger that taps household power,
EV-integral PV (photo-voltaic solar cells on the EV's top surfaces) for
daylight charging and power assist, plus a human-powered pedal assist for
drivers who may want physical exercise during their trip. It can
be fun and healthy to drive, costing so little that trips would be free
compared to today's fuel-burning vehicles, and a great little low-cost
all-weather commuter car, that would also provide environment, energy,
and other great benefits.
Let's take a detailed look at it, and do some performance analysis.
Left:
A "see-through" view of a personal, 4-wheel ultra-light EV that seats 2.
PV can be applied on all top surfaces, that would collect about 500 watts
for several hours daily. Thin-film amorphous PV in window glass can
reduce glare and interior heat load from sunlight, comparable to conventional
tinted glass or reflective coatings that don't provide electric power.
Intelligent power electronics can enhance this EV, by providing infinitely
variable speed control, with synchronized non-conflicting proportional
regenerative braking.
With power electronics, its 2 rear wheels are each driven by a brushless regenerative motor-in-wheel, a special version of the motor described in my US Patent 4520300. Instead of conventional connection to tire rims, it has S-shape springs between the motor housing and rear wheel rim, and between the front wheel hubs and rims. So unsprung mass (only its tires and rims) is very low, and the motor-in-wheel is cushioned from road shock. This EV weighs 800 pounds or so. Its ultra-efficient motor has cruise control for any speed from zero to maximum. It also controls downhill speed, and regenerates power to charge the battery whenever decelerating. Optional pedal power supplied by a driver in a recumbent position (where we output the most power without tiring) to a generator (shown in red) can augment solar power. Effort level is selectable, like cardio workout gym equipment. As can be seen from the graphs below, a champion athlete can generate 370 watts almost indefinitely, a physically fit person 180 watts. So a driver, pedaling in daylight with 500 watts from PV, could travel indefinitely at about 35 mph, while trickle-charging the onboard batteries. This EV would be capable of traveling at speeds up to 60 mph, on mostly battery power, recharged by plugging into a garage power outlet. If provided in-transit power, via the 2 red extendable contacts shown, on electrified highways, it could maintain 60 mph indefinitely. We need to make the public aware of this simple, clean, very low-cost option, so politicians will come onboard, and permit the highway infrastructure for it.
Main motor and braking effort may be applied to the two rear wheels, by regenerative bi-directional motor drive and braking, plus a friction brake (as a parking brake, and backup mechanical brake). No motor clutch or gearshift or differential gear is needed. With 2 large diameter motors in the 2 rear rear wheels, no speed reducer is needed. If the batteries ever fail (and must be disconnected), the EV may be driven powered only by PV and/or pedal power. It can be driven forward or reverse at 0-15 mph on pedal power only.
Two red stripes are shown at the EV's rear left side. Early versions will have only an extension cord, to plug into 60 Hz outlets. Until we have electrified highways for EVs, they could be used as charging contacts, automatically extending to engage recessed electrified conductive charging strips, in a future home's garage.
Manta,
(photo at left) was developed and built by MIT students. It's a good
example of an EV powered by integral PV, with 1 or 2 onboard batteries
to improve acceleration and enable regenerative braking.
Its PV can provide 800 watts, for several hours, on a sunny day, for battery charging and drive power.
Manta, and other cars like it, are designed to meet racing rules. Powered by their PV, with no help from external power sources -- not even for battery charging -- they are not intended to be commuter cars per se. But they provide tangible evidence of capabilities their PV, aerodynamics, light-weight body, and electric motor can offer.
The
solar electric powered car at left was developed and built by students
at the University of Arizona. Its photo is a link to their
website.
A brushless motor is shown, as described in my US Patent 4520300 "Ultra-efficient Brushless Regenerative Servomechanism." It has 99% motor efficiency, 95% controller efficiency, and very long service life without maintenance.
A cross-sectional view of this motor is shown here.
I built this version almost 20 years ago, and have test data that shows it will provide reliable service for at least that time span. It is a type of motor known as coreless, because the stator windings are not placed in laminated iron core slots. Instead, they are formed to have radial segments in an axial magnetic field provided by neodymium-iron-boron or ferrite magnets. These magnets are placed in a non-magnetic disk, such as aluminum or fiber composite, attached to the rotor shaft, in a ring array, with alternating polarities. Each disk holds an even number of magnets, whose fields are aligned with the other disks.
Hall sensors, exposed to the magnetic field edge, provide sinusoidal feedback signals in phase with their associated stator winding. The stator windings are formed, then embedded in a thermally conductive epoxy, to support the conductors and enhance heat transfer to a flush outside surface beneath the EV. Two or three phases may be used. A dozen or more poles (equal to the number of magnets in a disk) would be best for a direct wheel drive. The maximum wheel speed is several hundred rpm. A 20-pole motor, at a shaft speed of, say, 840 rpm, has a 140 Hz electrical frequency.
The alternating axial magnetic field pattern from the rotor magnets rotates with the rotor. With stator current varying sinusoidally with rotor position, the magnetic field from stator winding current rotates in synchronism with the rotor. So the rotor is not subjected to a varying magnetic field, and therefore does not incur hysteresis or eddy loss. Stator winding eddy loss is minimized by proprietary eddy blocking (with fine, individually insulated multi-strand stator windings) and bucking (by forming the winding so that end-to-end emf of each strand is equal to every other) techniques. At maximum speed, motor efficiency can be 99%. Controller efficiency is about 95%.
Left:
A photo of my motor-controller-charger prototype/demo. A power cord is
shown here, which plugs into 115-volt 60-Hertz outlets, to supply a battery
charger, that's packaged with the motor controller. Batteries (4 in series,
12-vdc each) are housed in the covered plastic tray.
Control signals, generated in the control box shown, respond to a 0 to 6000-rpm speed setting, a 0 to maximum torque proportional regenerative brake command which over-rides the speed setting, plus forward/coast/reverse direction commands. Battery current is monitored by a minus10-adc to plus 10-adc analog meter, with zero center position. Battery voltage is monitored by a 0 to 100-vdc analog meter. Both meters are shown installed on the controller.
Advantages of my motor, over dc motors with brush commutators: Mine has no brushes; nor their friction and wear; nor their spark hazard in explosive environments; nor their dust contamination of clean environments. Mine can have efficiency ~99%, and practically no idling losses. Mine has no rotor heating; and thus needs no flow-through air; so it can be totally enclosed and non-ventilated. Mine regenerates power when decelerated -- and even when reversed!! Reversing almost any other motor at full speed results in a very high current, that burns motor insulation.
Advantages of my motor, over variable-speed induction motors with electronic power control: Mine is more efficient. Electronics to control mine costs less. Mine has no tendency to instability in regenerative braking mode.
By timing displayed volts and amps, while accelerating and decelerating my motor, drive and regeneration efficiency can be calculated, with no need for a dynamometer load.
Left:
A photo of the motor parts prior to assembly.
Photo includes motor mounting brackets attached to 2 fixed aluminum end plates, black 2-phase stator windings in radial slots cut in 5 phenolic rings (note crossovers at inner and outer diameters of rings, 4 winding terminals on each ring, and 2 linear Hall sensors in ring at top of array), black cylindrical magnets in 5 aluminum rotor rings, iron rotor rings at each end (to complete magnetic path for axial field), the motor's outer aluminum spacer rings, plus signal and power cord and connector (which connects to controller).
Rotor rings, including iron rings at each end, have keyed inner shoulders, which are attached to the rotor shaft when assembled. They maintain angular and axial position of each ring. Self-aligning ball bearings support the motor shaft at each end.
A few years ago, some partners and I built and tested a motor-in-wheel version. We included a 5-to-1 planetary gear speed reducer. So at a 900 rpm wheel speed, motor speed is 4500 rpm. That version provides higher power with a smaller motor diameter, than one coupled directly to the wheel.
Electronic collision avoidance was developed at least 30 years ago. Various implementations have been successfully demonstrated, and shown on TV viewed by millions. Since typical car bodies are mostly steel, radar has worked well for the "eyes" of those systems. The EV proposed here, to minimize weight, would have a body that's mostly fiber composites. Ultrasound "eyes" would be preferable to radar, to detect them, and steel bodies, even in rain and snow. If rear transponders are used, then either implementation will work, but a compatability standard would need to be adopted.
EV Performance Analysis
Let's consider the same representative EV model used in my electric
highway vehicle webpage:
Gross vehicle weight with full load = 1500 pounds
Coefficient of rolling friction = 0.01 (15 pounds
drag for 1500 pounds weight)
Aerodynamic drag coefficient = 0.1
Frontal area subject to aero drag = 20 square feet
Peak motor power = 20 kilowatts (about 26 horsepower)
Battery storage capacity = 6 kilowatt-hours (battery
pack weight ~ 500 pounds)
Maximum battery power ~ 40 kilowatts (available for up
to 30 second bursts)
EV may have 10 square meters integral PV that generates ~ 500 watts
for ~ 5 hours per day. The PV's peak voltage may be
about 220 vdc, and its maximum current may be about 2.5 amps. It's
connected directly across 200 vdc battery terminals..
Based on motor power, and a representative torque/speed relation, wheel
thrust at 20kw is:
651 pounds at EV speeds from 0 to 15 miles per hour
325 pounds at EV speeds from 15 to 30 mph
162 pounds at EV speeds from 30 to 60 mph.
These thrust computations are the electromechanical equivalent of a
3-speed transmission, which shifts to 2x wheel/motor
speed ratio at 15 mph, and 4x at 30 mph. Fradella's motor does it by
contact shifting. Motor/generator efficiency at maximum
speed can be over 99%. Almost all loss occurs in stator conductors.
Heat transfer in the motor is by conduction, with no air flow through the
motor.
Power to overcome rolling friction (watts) =
(2 watts/mph.lb.)(Rolling friction coefficient)(Total pounds car weight)(mph
car speed)
Power to overcome aerodynamic drag (watts) =
(.005 watts/sq.ft. mph3)(drag coefficient)(sq.ft. frontal
area)(mph car speed)3
Computed results, over a vehicle speed of 0 to 60 mph, for that larger 4-seat EV, are shown in the next two figures.
Left:
A graph, of power needed to overcome the sum of rolling friction and aerodynamic
drag, at speeds from 0 to 60 mph, for our representative EV. At 60
mph, rolling friction consumes about 1.5-kw; aero drag about 2.5-kw; and
they total about 4-kw.
Note that power on a sunny day of 500 watts, from the EV's PV surface, if the only power available, would support sustained cruising speed on a level grade to about 15 mph, without discharging the batteries. Added pedal power, from an average fit cyclist, can increase continuous speed to 20 mph. It can increase speed to 35 mph or so, but only for the several seconds that even a very fit cyclist may be able to output about 1-kw.
Range at a cruising speed of 60 mph, from 6-kwh onboard batteries only, would be about 90 miles. During daylight hours, the installed PV can extend it to about 100 miles. Parked in the sun, its PV can provide a full battery charge in 12 hours (in ~ 2 days of sunlight).
Left:
A graph, of car speed vs. time to reach it, starting from zero mph. This
EV would accelerate, on a level grade, to 60 mph in less than 20 seconds
-- not a "hot-rod" but probably acceptable to many EV commuters and travelers.
Four onboard batteries could supply the 20-kw acceleration power.
But with only 4 batteries, this EV's range on battery power would be 35
miles.
The considerations presented here, and by the cyclist data below, strongly indicate that a lighter weight EV, like the ultralight EV described above, is better suited to an EV with a human-powered pedal option.
For example, if we consider a 1000-pound total weight, and select a
40 mph cruising speed, total power needed is ~1-kw (compared to 4-kw for
a 1500-pound EV at 60 mph). PV and sustained pedaling power can sustain
~35 mph without discharging the batteries. Considerable data from cyclists
is available. It's compiled in the chart at right:
Note that the time scale is logarithmic. Also note that a champion 160-pound athlete can output 1.5-hp for several seconds, while a physically fit person can output about 1-hp.
The athlete can sustain about 0.5-hp for well over an hour, while the
fit person can sustain about 0.25-hp. A driver wanting to power his
vehicle more from his pedaling will probably choose to have 4 onboard 600
watt-hour batteries or less.
.
This
lighter "fitness version" EV (front and side view images at left) might
have only 2.5 kwh onboard battery capacity. Its aero drag coefficient
could be 0.1 (large area, sloped PV windows, and narrow large-diameter
tires, help achieve this), higher when ventilated. Its frontal area
could be 12 square feet (with a bit less head-room, and a bit more recumbent
driver sitting position than shown in the image at the top of this page).
With less batteries, there would be more dependence on PV power.
Nickel-metal-hydride, lithium-ion batteries, and ultracaps may soon cost
less, and higher efficiency PV with 800 watts output may be worth the higher
cost for this market segment.
On battery power only, its cruising range would be about 70 miles at 45 mph -- and 55 miles at 60 mph. This range is not reduced much, for night driving, with ultra-efficient LED head-lights and tail-lights. In daylight, on PV and pedal power only, a fit driver could maintain 35 mph, and achieve occasional 45 mph bursts.
With 10-kw peak motor power, this EV can accelerate to 15 mph in 2 seconds, 30 mph in 7 seconds, and 45 mph in 20 seconds (mostly on battery power).
Aero drag will increase when interior ventilation is needed, during
high driver pedal effort. But that's no problem at speeds up to about 35
mph (where rolling friction considerably exceeds aero drag).
This EV's main features and benefits are summarized below:
My other 8 webpages also cover sustainable technology I've worked on; to improve our environment; increase building and vehicle safety; lessen global dependence on fossil fuels and nuclear energy (and their serious negative consequences); and provide far more convenient and reliable UPS (Uninterruptible Power Supplies). To view them, please click on any of the links below.
Comparison of RPM's flywheel battery with others -- a somewhat detailed study
Brief Summary of RPM's Business Plan -- what we've done and plan to do for the future
RPM's Resources -- our people, tangible properties, office and lab facilities, etc.
Technology: Public and Business Policy
RPM's UPS can enable future distributed on-site solar/wind power, and more
I greatly value your interest in this exciting venture.
If you have comments or suggestions, email me at fradella@earthlink.net
Edited April 2, 2002
