EV transmissions are coming

I know that is how it is on the Tesla(at least the Roadster) and on some BEV concepts. Leaving the brake pedal for friction pedal keeps designing the brake system easy. The exactness of that pedal position could probably be made as easy to hit as they want. The free wheel glide is a great tool for maximizing efficiency in the real world.

Some car companies realize this. The smart ED has paddle shifters for controlling the amount of regen braking. So does the ELR and next Volt. The eGolf doesn't have the paddles, but gives the driver control through a traditional style shifter. You can choose regen braking hard enough to trip the brake lights or none at all until the brake pedal is pressed.

Animal scientist here. So the Prius is able vary the voltage going to the MG, correct? No physical gear ratios are changing, so do the differing voltage inputs change the motor's efficiency curve?

What is back EMF?

PS: Came across so older news of the subject. One article claiming 15% improvement with a 3 speed.
New multi-speed Electric Vehicle transmission improves EV performance and range
Antonov's 3-speed transmission for electric vehicles boosts efficiency by 15 percent

 

So 6 years ago they developed this improvement and we have heard nothing since?
15% over what? Was it a DC or AC motor?

A DC motor I might believe. The efficiencies sounded rather low for an AC.

 

I am asking how much more of a loss this supposedly efficiency building transmissions are sustaining. I thought a traditional manual at high speeds (high output rpm has more friction and higher losses) had a drop through a transaxle and final gear to the axle in the neighorood of 8%-15%. i know there is new tech, but I didn't think any automatics really were much lower. Now if a motor just goes through a final gear (single speed) transmission losses will be lower. Simply the transaxle gears rotating in the transmission fluid causes a loss of power. Ofcourse someone could have invented one that is far more efficient that I haven't seen so if there is this low friction transmission I wanted to hear about it. The volt transmission is about as low as you can get in bev mode, having only an extra univeral gear that is eather clucthed to one or two motors, then going through a final gear to the axle. Still this is less efficient than the single gear leaf, i3, or model S when accounting for weight and aerodynamics (it could be something other than the motors and transmissions).

 

Good questions:

I'll cite some papers to fetch for more details but this is a quick summary:

• back EMF - back Electro Motive Force, is the voltage induced by a spinning motor that resists the voltage trying to push current through the motor. We say "back" because it is backward to the voltage-current trying to spin the motor. The faster the motor spins, the stronger this 'reverse' voltage. Ordinarily a motor will reach a point where no more current can be pushed into the motor at a fixed speed and constant load because the back EMF blocks further current.
• voltage double and triple - to get more speed (or power,) the voltage has to increase to overcome the back EMF. It also means the motor can spin faster without getting larger and heavier.
• motor losses - tend to come from higher currents leading to resistance heating and magnetic induced currents in the magnetic structures. Any conductor that comes into range of a changing magnetic field will generate small 'eddy' currents that suck energy from the motor and heats it up. Slower motor speeds lead to higher currents, larger conductors, and weight.
• pulse-width modulation - a $10 phrase meaning the power is turned ON and OFF fast enough that it throttles the power to the motor. As the rotor of the motor turns through 360 degrees, there phases (i.e., angles) where voltage moves the rotor forward. To modulate the power, the voltage is turned ON later at each of these rotor angles and OFF earlier within each phase. When starting to spin at low speeds, the ON/OFF periods happen within the phase. Otherwise the current would be too high leading to more heat than mechanical power.

With luck, see if you can find:

1. Development of Electric Motors for the TOYOTA Hybrid Vehicle "PRIUS" Kazuaki Shingo, Kaoru Kubo, Toshiaki Katsu, Yuji Hata.
2. Development of New-Generation Hybrid System THS II - Drastic Improvement of Power Performance and Fuel Economy Koichiro Muta, Makoto Yamazaki, Junji Tokieda, SAE 2004-01-0064
3. Development of the Hybrid Vehicle and its Future Expectation Shinichi Abe, SAE 2000-01-C042
4. Google "Argonne Prius"
5. Google "Battelle Prius" or "ORNL Prius"

Bob Wilson

 

The coils (three-phase) are static. The rotating magnetic field is formed by the permanent magnets in the shaft. If no current to/from the coils, an open circuit, no torque at the motor shaft, so it rotates freely, 'neutral' coasting - if some current is drawn, it makes regen braking, true.

Bob has gone deeper in the previous post