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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, along with public transit vehicles,
could have unlimited range on electric highways, powered by clean, renewable
and sustainable energy, supplied by solar, wind, geo-thermal,
ocean-wave, hydro, etc. and RPM's (Regenerative Power &
Motion's) flywheel
battery, described and illustrated in this link, and in my patent pending
entitled "Minimal-loss Flywheel Battery and Related Elements." Conducted
power, 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
4 to 10 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. Although
it's not for everyone, it can be fun and healthy to drive, and a great
little low-cost all-weather commuter car, that can afford 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. Crystalline
PV can be applied on opaque top surfaces. Thin-film amorphous PV
in window glass can reduce glare and interior heat load from sunlight as
good as conventional tinted glass or reflective coatings. Intelligent
power electronics can enhance this EV, by providing infinitely variable
speed control, with synchronized non-conflicting proportional regenerative
braking.
With power electronics, wheels may be driven by a brushless regenerative motor, described in my US Patent 4520300 for a "Brushless Ultra-efficient Regenerative Servomechanism." This 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. Its speed control has a selected deceleration profile, if an abrupt lower speed setting is entered, and prevents downhill speedup while conserving energy, without brake wear.
Forward and reverse drive, and speed settings, may be entered via levers mounted on the EV's steering column, so the driver's feet can be used exclusively for pedaling when desired. Proportional regenerative braking can be controlled by force on another lever, perhaps mounted to the steering wheel, controlled by the driver's other hand, or in the usual auto hand-break location. A preferable alternative requires sensing pedal drive chain force. If forward pedal rotation augments motor power, for both forward and reverse drive, reverse pedal force can be used for proportional braking, as with many bicycles. Note that, with this method, the top of the drive chain is in tension while pedaling forward, and the bottom is slack. Conversely, with reverse pedal force, the top is slack and the bottom is in tension. A tension sensor at the bottom of the chain can transmit a proportional braking signal to power electronics before friction braking occurs, so the motor regeneratively applies braking, proportional to the reverse pedal force. Normal braking effort (not reaching levels that activate friction braking), to control downhill speed and distance to the car ahead, is entirely regenerative.
Power supplied by driver effort can augment motor torque, thru pedals which crank a drive sprocket. It drives a chain, coupled to a driven sprocket. Several crank and driven sprocket diameters may be selected, by a lever mounted to the steering column, or in the usual auto gear-shift location, to provide speed ratios varying over a range of about 10-to-1, by a standard derailleur gear-shift. The driven sprocket is coupled to a free-wheeling ratchet mechanism, so that the pedals cannot be driven by the wheels (which could be dangerous). This safety feature, and the derailleur shifting, is common on many bicycles.
A reversing gear-shift/clutch, driven by the ratchet, can drive the EV's left rear wheel. It may have 3 states: Forward, Off, and Reverse. Forward and Reverse may be controlled by the same forward/reverse lever used for bi-directional motor control. In forward drive, its gear ratio may be about 1-to-3 (speed increase to wheel). In reverse drive, its gear ratio may be 1-to-1. Its 3rd (neutral) state decouples the chain from the wheel and its drive motor. Alternatively, the motor might be driven in only one direction, and forward/reverse wheel torque controlled by the same reversible gearing used for the pedals. With this alternative, the driven sprocket would be connected to the motor through a ratchet.
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 (for panic stops, as a parking brake, and for backup). No motor clutch is needed. With a motor for each rear wheel, no differential gear is needed. If the batteries ever fail (open), the EV may be driven by PV and/or pedal power, albeit at lower speeds. With no electric power, the EV can be driven forward at 0-15 mph and reverse at 0-5 mph, by pedal power, and decelerated by its friction brake.
It is important that all braking action while driving the EV be controlled by a single lever, perhaps where one of the driver's hands grips the steering wheel, or in the usual location of a parking brake lever, so no time is lost searching for it. A light force on the brake lever may control proportional regenerative braking, in EVs with electronic speed control. It over-rides speed control in EVs with power electronics, and does not conflict with speed settings. Electronic speed and brake control is far easier and less costly to synchronize than mechanical. More force by the driver, on the brake lever, activates friction braking.
Lower cost, conventional dc motor drive, without electronic control, can also be used. Speed of dc motors, having permanent-magnet rotors, varies in proportion to voltage: To increase speed, just increase motor voltage -- to decrease speed, reduce voltage. The motor will act as a generator for high speeds and low supply voltages.
For example, by switched connection of only four 12-volt batteries, motor voltages of 0, 12, 24, and 48 volts can be selected. Switching from 48 to 24 volts will result in regenerative braking from full speed to half. Then, switching to 12 volts will result in regenerative braking from half speed to quarter speed. Shorting the motor terminals (0-volts) will result in strong braking action that is not regenerative. Shorted at high speed, it can cause very hot motor windings. Changes are abrupt, and not continuously variable, with this "low-tech" control. And command synchronization is not so easily included. But most drivers may become accustomed to its response, and will be able to accommodate it.
With 2 motors -- each coupled to respective left and right wheels -- no differential gear is needed. Since each (along with its power electroncics) can be smaller, with half the power rating of a single motor, total cost for 2 is only a bit more. But total EV weight and cost could be a bit less.
Two red stripes are shown at the EV's rear left side. They are charging contacts, and extend to engage recessed electrified conductive charging strips, in the home's parking garage. You don't need another chore that you may forget to do (inserting a charger "paddle" into an EV that can be seen at many General Motors showrooms, and removing the paddle before you enter the EV). Contacts that automatically extend to tap household power, when the EV is parked in the garage and the key is removed, can be inexpensive and very reliable. They automatically retract when the key is inserted.
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.
Conversely, our illustration at the top of this page focuses on a likely combination of power inputs for a practical commuter car, in a scenario that may even include a solar powered home.
In that illustration, the garage door is shown open, to show the external (household power) charging setup. It supplies ubiquitous residential power at 115 volts, 60 Hz. Or, if the house has clean, renewable solar/wind power capability, it may be supplied power at 115 volts dc. RPM's flywheel battery, to store solar/wind power, is safely housed beneath the round steel cover plate shown flush with the concrete slab garage floor surface.
To prevent children from contacting the power strips, besides recessing them, they can be equipped with a sliding cover, or connected so that they are energized only when the EV's weight closes an insulated pressure switch. Automatic extend and retract would be a convenient and low cost feature. Battery charging from household (or electric highway) power is controlled by the EV's small and light weight ~500-watt onboard charger. An EV with 4 onboard batteries, having 2400 watt-hour capacity, can be charged in ~5 hours, in the garage, or by ~500-watt PV parked in sunlight.
Left:
A functional schematic of onboard EV equipment. PV (phovoltaic) output
leads, from solar power converters on all the vehicle's top surfaces, including
at least the fixed windows, are connected directly across the batteries.
A discretionary shunt load regulates PV charging.
After batteries are fully charged, PV output current, inherently limited to a nominal 2.5 amps dc in this example, will provide limited over-charge current that equalizes individual cell charge. This also helps to break down sulphate layers that tend to form on lead-acid battery plates. To prevent gross battery over-charge, PV current can be diverted to an interior ventilator or air conditioner, when requisite battery charge state is reached. Clearly, PV output power is wasted, if not used or stored, when it is available.
A brushless motor is shown, as described in my US Patent 4520300 entitled "Ultra-efficient Brushless Regenerative Servomechanism." It has 99% motor efficiency, 95% controller efficiency, and very long service life without maintenance.
But the motors need not be brushless. Power electronics, for reversible variable speed control and regenerative braking, using dc motors having commutator brushes, are well known, and have been available for decades.
A cross-sectional view of the brushless regenerative motor, described
in my US Patent 4520300, is shown at right.
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 essentially 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 can be 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. This version provides higher power in a smaller motor size, than one coupled directly to the wheel.
Back again to the first illustration, at top of page: Optimally, the home's roof also is covered by building-integral PV solar panels. And RPM's flywheel is installed under the reinforced concrete floor slab in the garage. Its electronics cabinet (the flywheel's power interface with the home's dc power buss) can be seen, hung on the garage's interior wall. This cabinet also affords convenient power system monitoring, by viewing its low power display built into it. Another page of my website describes how this can enable stand-alone building-integral on-site solar and wind power.
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, 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). There is data showing that, if batteries are deep discharged frequently, and not recharged promptly (as would be the case for this type of use), they will begin failing after only 2 years or so. That is costly, for 10 batteries.
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, and a lower cruising speed, is better suited to an EV with a human-powered 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 batteries or less.
Weight of 4 batteries would be about 200 pounds, and total weight (including passengers and parcels) could be 1000 pounds or so. The EV chassis and drive train could weigh and cost less, power electronics would cost less; and the EV would be more nimble, driven from PV and pedal power. If a passenger rarely is included in it, a lighter vehicle, with narrow, large diameter wheels, and smaller frontal area, may well be a better choice, especially for short urban trips.
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 0.12 (large area, sloped PV windows, and narrow large-diameter
tires, help achieve this). 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
or lithium-ion batteries may be serious candidates, and higher efficiency
PV with 800 watts output may be worth the higher cost for this market segment.
Drivers weighing more than 160 pounds would have incentive to achieve commensurate
fitness and physical output capability.
On battery power only, its cruising range would be about 70 miles at 45 mph -- and 55 miles at 60 mph. 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).
Peak wheel thrust at 10-kw is 320 pounds up to 15 mph, 160 pounds up to 30 mph, and 80 pounds up to 60 mph. Drive power is 1.5-kw at 45 mph and 2.75-kw at 60 mph.
Achieving low aero drag, with adequate interior ventilation during high driver pedal effort, will be a major challenge. It will probably have movable louvers that result in a higher drag coefficient when open, at speeds up to about 35 mph (where rolling friction considerably exceeds aero drag).
With such light EVs, crash safety (with much heavier vehicles) is always a concern. Even with crumple zones, side crash bars, etc. its driver and passenger are generally more safe in a heavy vehicle. But it would be far safer than a bicycle, and would not carry fuel like today's autos, that may be grossly as dangerous as an incendiary bomb. And today's driver, stalled in high speed traffic, if unable to quickly re-start the auto's engine, is in serious trouble and danger; whereas the redundant drive in our EV, besides augmenting power, can provide a "pedal home" capability if electric power fails.
This EV's main features and benefits are summarized below:
Several excellent websites describe other combinations of muscle power and electric motors, batteries, and solar cells, in various EVs. The performance achievable with such combined power sources, with low-cost EVs, indicates they can contribute much to convenient, flexible, and practical personal urban transportation, on a global basis. For example, see Marvin Johnson's great website about his global solar/muscle power EV tour.
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
