make your EV more efficient, with a multi-gear transmission

[P-hack]

Electric motors have areas of operation where they are less than their peak efficiency, not unlike ICE's. The solution, modify the gear ratios in-flight (efficiently), of course. Tesla wanted to start with a two speed but didn't get the bugs worked out at those power levels I recon. The simplicity of direct drive is nice, but leaves a significant amount of efficiency on the table.

They claim 15% reduction in battery size (which translates into less weight and shorter recharge times)

Drive System Design: New three-speed transmission helps electric vehicles run farther, faster and more smoothly » Automotive World

[P-hack]

while reading some of the comments on the tesla forum, it is disheartening to hear the rank distaste and outright misinformation on using more than a single speed gearbox.

Most are outright oblivious as to what makes a machine efficient as far as I can tell, but for most motors the efficiency is largely a function of load (true for electric and ICE), and a higher gear that provides more engine load is going to help at higher speed, and a lower gear is going to help with hills and acceleration, and just having some ratio options means smaller motors (easier to load) and batteries for typical driving.

[P-hack]

and of course if you are serious about an efficient series setup, you need to pay attention to how your EV motor uses that power as well.

Vocis is road testing a multi-speed EV transmission - HybridCars.com

[Daox]

This is very true. In addition to downsizing your pack you can also downsize your motor as well. I looked into this when I was considering hybridizing my Paseo. I didn't have room in the engine bay for a large motor, so I had to eek out everything I could. Going through the gear box was the only way to achieve reasonable acceleration with the space I had to work with.

[P-hack]

just for a visual, I color coded a TDI bsfc chart in terms of lost efficiency from peak bsfc, the percentage losses are reasonably similar over much of the operating range.


compared to: (though this is a generalization, extreme low load is probably worse than indicated, i.e. https://www1.eere.energy.gov/manufac...s/10097517.pdf )

[user removed]

A transmission would also benefit regeneration.

regards
Mech

[niky]

We've known for quite a while that EVs could benefit from multi-gear transmissions. What's been missing are transmissions that can take the power of something like the Tesla Roadster.

[Ryland]

What is also missing is a transmission that can shift smoothly, without the sound of a gasoline engine and the vibration it's hard to tell when to shift an electric car, it's also hard to match motor RPM to wheel RPM so you increase the chances of grinding gears, these are small problems that could be taken care of with a very basic computer control and electronic shifting.
There are also transmissions that will handle the power, there are transmissions that will handle 1,000hp trucks and those have to deal with the vibrations of the engine!
As I understand it the area where Tesla had trouble is they tried to use a low cost, Geo Metro transmission and that blew up then realized that an over sized motor was cheaper then a transmission and made it simple.

[redpoint5]

I should think simple economics will dictate the design of cars to come. If it's cheaper to include a transmission and related shifting technologies than to build larger motors and batteries, EVs will soon receive them.

In the race to be first to market with EVs, transmissions may have been dropped to speed the development process. Perhaps future iterations will include them, or perhaps the cost, complexity, and reliability are hurdles the transmission cannot overcome.

[P-hack]

we've never really seen inexpensive pico-second controller timing and position sensing applied to a transmission, at least I haven't. But it seems very possible to make a reliable, efficient, fairly compact, and smooth shifting sliding mesh transmission with some authority over the traction motor during shifts as needed. such a transmission can theoretically rpm match the motor actively and even wait for teeth to be aligned before sliding into gear, then reapply power smoothly (user defined), and all very quickly, and cheaper and more efficient than dual clutch.