Electric motors used in electric vehicles are not efficient at all speeds, but instead are only efficient at a narrow range of speeds. It turns out that electric motors have what’s called an efficiency motor curve that shows a graphical representation of how efficient a motor is different speeds. The range a motor is efficient at is directly related to its diameter.
Figure 1 shows an efficiency curve of a large, medium and small diameter motors. The large motor is very efficient at low speeds but cannot reach highway speeds. The small motor is very efficient at highway speeds, but very inefficient at city speeds. And the medium motor at city speeds.
Figure 3 shows an aerodynamic force curve that demonstrates that a car traveling at highway speeds sees 3 times more air flow resistance than traveling at city speeds. If this is so, then why are all highway capable electric cars travel distance’s roughly the same at both highway and city speeds? The small motor curve shows the problem, at city speeds the small motor is less than 40% efficient.
Figure 2 shows three different sized motors together and by switching them on and off independently at the speeds they are efficient at we could build a compound motor that would be efficient at all speeds. This means an electric car could be travel 3 times farther at city speeds than at highways speeds.
Figure 4 shows three different sized motors on a single axel. But there is a problem. If we activate one motor the other two will act as generators and stop the first from turning.
But there is a novel solution to this problem. Figure 5 shows that if all the electric coils are placed on sliders then we can physically move the coils away from the magnets when not in use. This will allow one motor to work unimpeded by the other two.
This compound motor uses each motor as a different “gear”. A worm gear is used to move the coils away from and towards the magnets.
Figure 5-8 shows how the different “gears” are activated.
Figure 9 shows electric motors how permanent magnets always have magnets placed on one side of the electric coils. These motors can be as efficient as 75-85%. We need better than that.
To increase the efficiency further we placed magnets on both sides of the coils (figure 10). What this does is it forces the magnets to push on both the south and north poles of the coils, not just one pole. This greatly increases the torque output without increasing the electricity used.
For the 2nd and 3rd gear motors the design uses two sets of coils (figure 11). The number of magnetic poles a motor has directly affects its magnet flux strength. By replacing large coils with two sets of smaller coils we can again increase the efficiency. These two sets of coils can also be activated alternately in series or in parallel to achieve further gearing.
ABOUT THE ENTRANT
Type of entry:individual
Number of times previously entering contest:never
Chad's favorite design and analysis tools:AutoCAD and Autodesk Inventor
For managing CAD data Chad's company uses:None
Chad is inspired by:I aspire to create environmentally helpful devices and designs.
Software used for this entry:AutoCAD, 3D Studio Max, Autodesk Inventor