Using Automatic Transmissions

[Cobb]

Are we talking about a typical 4 speed automatic or a fancy tip tronic transmission complete with paddle shifters?

Most Ive seen are dc that use a stock manual tranny and no clutch that is shifted from time to time. Most AC setups are direct drive to the axles. I guess it depends on the rpms of the motor used vs axle speed at desired rpms rather any gear reduction is needed.

As a former electric wheelchair user I know the gearless brushless motors always had problems were as the 2 and 4 pole with worm and helesphere(SP?) cut gears had no problems at all. 4 pole had better battery life vs the 2 pole.

Originally Posted by Ryland

A guy in our local EV club has an automatic transmission in his Porsche 911, he's building a control box to make it shift so that it works properly

[oil pan 4]

Originally Posted by Cobb

Most Ive seen are dc that use a stock manual tranny and no clutch that is shifted from time to time.

Yes I believe most DC set ups are connected straight on to the transmission input shaft. Its cheaper, simpler and it works fine for most people.
I would go with a clutched DC motor to retain the ability to burn a little rubber and shift on the fly as needed.

[gone7]

Hey, oil pan 4, how's that regen braking working for you?

[oil pan 4]

I would never use regen braking.
Electric golf carts, forklifts and floor tugs dont use it, why should I?
My plan is to scale up what I know works.
No need to reinvent the wheel...
I do occasionally blaze new trails, but not here.

[gone7]

Almost everyone must be missing the point here. I will simplify.

An electric motor has most of its torque right from the start, with hardly any reason to change speed. However, depending on tire rotational speed versus the top speed of the motor, there may need to be some sort of speed matching technology (a transmission) to keep things running efficiently. Changing tire rpm versus motor speed appears to signify a need for a go-between technology. Further, starting from a stop is better handled by a lower gear, especially if one is using a lower-powered motor and a heavier vehicle. Another factor involved in vehicle power is that even a tractor trailer might not use much power once it is moving.

So the obvious question is about bolting an electric motor directly to an existing transmission, and in particular, an automatic. And also obviously, what happens when one does so.

[MetroMPG]

What happens when you bolt an e-motor to an automatic with a torque converter is: your efficiency (range, power to the wheels) goes down and complexity goes up.

That's the answer, simplified.

A manual gearbox is best.

[Ryland]

Another guy in our electric car club tried using an automatic transmission, I think it was a Toyota Corrola and found that his range was 40% worse then the same set up with a manual transmission, he said his car was also pretty slugish.
If you want the vehicle to shift automaticly why not use something like an Arduino that can over ride the throttle, have a speed sensor on the motor shaft and the output shaft of the transmission and some solinoids to shift in to neutral, match the speed for the gear it needs to shift in to and shift in to that gear without the use of a clutch, that way you keep the driveline lighter weight and simple and you don't wear out the syncros in the transmission.

A lot of EV's like mine have a single speed gear box, others like my parents use the manual transmission but are driving in 2nd gear most of the time ad 4th gear on the highway.

[gone7]

Those are excellent pieces of information. It would therefore appear that some sort of electrically actuated shifting would be the best. That way one might get rid of the clutch expense and complexity, and still have an automatic shift based upon controller input.

By the way, what is the comparison of loss between an ICE and a motor? Did the suggestions take that into consideration? For instance, we know an ICE setup is pretty inefficient to begin with. Would simply swapping for a motor gain signigicantly?

[oil pan 4]

I would run a GM T-5 (non-world class) on 4.10 gears with 30 or 31 inch load range C tires.

Also auto transmissions put off a lot of heat, they have external coolers.
Any heat produced by the system is just power that never made it to the rear wheels.
I have had several T-5 transmission vehicles, I could always drive them long distance and put my hand on the transmission afterwards, inferred temp gun never registered over 140'F on one. It also didn't have any kind of cooling system.
Dont try that with an auto transmission.

You don't need "some sort of electrically actuated shifting", you can shift a standard transmission with out the clutch as long as it has syncros. No one showed me how to do it, I read on the internet that it could be done so I tried it and it works.
I have never met one that I couldn't at least up throught the gears with out the clutch.

Still set on using an auto?

[mechman600]

TheSGC in this forum is currently completing a 2001 Civic EV, but his first EV was a 1996 Civic with an automatic:
Civic Electric Car Conversion
He would have all the answers.