Featured Speculative 2-speed EV transmission

Agreed. It has to make sense. If Toyota did it, I’d give it a try

 

Toyota is doing simulated gears for an EV.

 

Meaning what, exactly? Anything like actual gears that would change the torque/speed relationship from motor to wheels? Or just something to make the driver feel like there are shift points?

 

The latter, but with physical clutch pedal and shifter.
https://www.motortrend.com/news/toyota-lexus-bev-on-demand-manual-transmission-ev-tech/

Dodge had a true multi-speed transmission in an EV concept, but it looks like car going to market will have a two-speed like the Taycan.
https://www.caranddriver.com/news/a60076112/dodge-charger-banshee-ev-details-confirmed/

Continental AG has a two speed EV transmission. I think they supply Porsche.

 

To me, one of the real advantages of an EV is that it doesn't need to shift gears. Electric motors have wider RPM ranges, have torque all the way down to 0 RPM, and can reverse electronically.

It's only in something like an F1-type race car, or some other hyper-super-richstupid-car application where you'll be willing to ignore speed limits that this would even be worthwhile. Other than that, why add the extra complexity?

 

[QUOTE="Danno5060, post: 3446125, member: 206820" Other than that, why add the extra complexity?[/QUOTE]In a word, range.

Among the other causes when going faster, the motor itself can lose efficiency at higher rpms. A reason why the Taycan beats its EPA range is because it never actually shifts within the test cycles.

 

Certainly range is a big deal, but it has to be a difference maker, and cost and reliability will be the deciding factors.
Or perhaps it might allow for smaller batteries which would be good economically and environmentally

 

The spec you quote is the same that I find in the 2004 New Car Features manual on page TH-27, and what it really shows is that the torque behavior of the motor is pretty darned simple:

it's a straight line at 295 lb-ft (400 Nm) all the way from zero out to 1200 RPM. Right at 1200 RPM, it changes to a decreasing concave-up curve (the same shape as a y = k/x curve), right on until the limiting RPM for the motor, where it goes to nothing.



I got that image from L. David Roper's Physics of the 2005 Prius page, but it's recognizably the graph on page TH-28 of the NCF with numbers overlaid for clarity.

So why that sudden change from constant torque to decreasing torque at 1200 RPM (about 21 MPH, for gen 2)?

Well, the specs on page TH-27 also say MG2 is a 50 kilowatt motor. 1200 RPM is the very spot where 400 Nm of torque and 1200 RPM work out to 50 kW.

Below that speed, even at the maximum torque, the motor is at less than max power, so you get the max torque.

Above that speed, you can't have the max torque, because that would exceed the motor's power spec. Instead, you just slide down the y = k/x curve, the locus of all points where the RPM times torque works out to the 50 kW max power.

 

That edit shows both a torque increase as well as an RPM increase at the same time.

Yeah, no. I'm not buying that a transmission adds power to a mechanical system, (Unless there's another motor involved in the transmission.)

Whatever you've added to the Torque, you've gotta remove from the RPM, or vice versa.

 

Yes but: transmissions have long been a thing. They didn’t add power with traditional engines either. And yet they were considered useful.

addendum: ok see your point, something is not adding up in the graph, never mind.

 

Yeah, looks like any point on that added curve is both above and right of the original, so will have torque ✕ RPM coming out to more than 50 kilowatts.

Where's that power going to come from?

 

I think the Toyota transmission is also supposed to 'stall'. Talk about going after enthusiasts and not knowing their audience, I don't understand why Toyota is going all in on this.

 

Hyundai has come out with a similated "dual clutch" EV (no real multi-gear transmission). Not something I'd buy, but seems neat and terrible at the same time, at least to me.

For me, I like EV's, but I also like drving a manual. A two speed manual EV would be a dream come true for me, regardless of power.

Like I said, I like EV's. But I dislike how they feel. That's about the only thing I dislike about them in general. It's very dissengaged, more like an appliance. It's like the trigger on my drill. And adding noises and simulated gears just seems silly, kind of like when they put a flatplane crank in the Mustang yet made variously lengthed primaries to try to make it sound like a crossplane crank.

To me EV's are kind of like iPhones. They work and they work great, that's the point. But as an amateur radio operater, I get a bit of a grin when I'm able to get my antenna and radio setup just right to make that contact in Australia or some other country far away. I don't get the same feeling when making a phone call, even though admittedly cellphones are more practical.

 

A different maker than who?
I've only seen initial news about development of these two speed EV transmissions from 2 or 3 major auto part suppliers, not from an automaker. Porsche and Dodge could be using the same part.

 

Is it not the case that all the points of your added curve are both above and right of the original curve, and therefore have coordinates whose product exceeds 50 kW?

How should that be explained?

 

You increased total motor power output, without actually increasing its power capacity. A violation of Conservation of Energy.

Convert that chart to torque vs RPM at some other point, e.g. wheels. For Gear 1, the shape would be the same, just the axes scaled different.

For Gear 2, the torque cap is cut in half, RPM of the upper corner is doubled. At the right-hand end, the same k/x curve is continued out to twice the red-line RPM of the G1 curve. I.e. similar to having the same power motor without reduction gear, but doubling its red-line RPM.

In the operating range between the corner where Gear 2 changes from torque-limited to constant power, to where Gear 1 hits its red-line max RPM, they share the very same power curve.