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Would adding a 2 speed transmission increase range?

Would adding a 2 speed transmission increase range?

One of the biggest differences in range I see between a car with an ICE and an electric car is as you increase your traveling speed, your range in an electric car is dramatically reduced.

For example, if you get 300 miles per charge going 65mph, you likely only get 150 miles per charge traveling at 90mph. In an ICE, if you get 300 miles on a tank going 65mph, you likely get around 280 miles on a tank going 90mph.

I know there is a lot of math to account for. Drag coefficients at the different speeds, weight, grade of road and so on. What I was wondering, if you were to put a 2 speed transmission in an electric car, and have it shift at around 60mph, then aside from the additional torque gained, you’d also be running the motor at half speed (assuming the gear change was 2:1). Would the motor still draw the same amount of power as while the RPMs were reduced, the load was increased, or does the increased load not effect the draw as much? I’d assume that having that transmission would reduce the recharge rate of regenerative breaking as slowing would only spin the motor half as fast when it’s in second gear.

Thoughts?

Cnixon | 04. februar 2020

Doesn't the Porsche do this?

Earl and Nagin ... | 04. februar 2020

One might be able to get a very small improvement but possibly no more than would be lost in the transmission.
Electric motors tend to be very efficient across a very large speed range, starting at slow speed (like zero rpm). This means that one can get higher speeds by simply making the motor larger (which doesn't add much to the weight or cost). There is a slight improvement that can be gained as an electric motor reaches its optimal output which could be improved with a different gear, however, Tesla achieves some of this with its dual motor vehicles where one motor is optimized for high, cruise speeds while the other is more optimized for slower acceleration.
We see the big penalty with ICE because the ICE is so inefficient at stop-and-go driving which often happens with slower, city driving.
The big hit to any car is that the drag increases with the velocity squared. That's why your range at 90 mph is so much worse than at 65 mph.

TeslaTap.com | 04. februar 2020

Adding a transmission will actually reduce the range.

The Taycan has a 2-speed transmission. The Taycan is also the least efficient EV you can currently buy and has a lower top speed than the Model S and far less range. There can be many issues, but the extra weight and extra inefficiency of having extra gears for an extra transmission are partly to blame.

Now that extra transmission does provide a bit more torque at higher speeds, while Tesla accomplishes a similar effect by using two different gear ratios between the front and rear motors.

PrescottRichard | 04. februar 2020

I’d happily give up top speed for range too. Anything over 90 is not needed :)

Do you have a link for your ‘In an ICE, if you get 300 miles on a tank going 65mph, you likely get around 280 miles on a tank going 90mph.’? I’m skeptical.

Transmissions are heavy and complicated. The benefits of NOT having one apparently outweigh the pro of having one in Tesla’s opinion apparently :) E&N pointed out that electric motors behave differently enough that a transmission isn’t needed or as helpful.

Yes, Porsche does have a 2 speed tranny on one of the two motors. Oddly enough it isn’t the most efficient electric car even with this in place.

jordanrichard | 04. februar 2020

you would be robbing Peter to pay Paul. A 2 speed tranny would only add weight which affect range. Then there is the additional cost.

TeslaTap.com | 04. februar 2020

One main reason ICE cars have transmissions and the rush for more gears is the internal combustion engine has a specific RPM where it is the most efficient. The longer you can keep it near that sweet spot, the more efficient the car becomes. With today's computer controls, it can make shifts to maintain optimum efficiency. That's also one reason manual transmissions are rarely available - they are just not as efficient as a good automatic anymore.

science-isbetter | 04. februar 2020

Earl and Nagin: Just a nit.

"The big hit to any car is that the drag increases with the velocity squared."

We can say that we have a high Reynolds Number and in that case the Drag Force is proportional to the velocity squared. But the situation may need more analysis. The *POWER* needed to overcome the aerodynamic drag is proportional to the cube of the speed, while the *ENERGY* expended is proportional to the square of the speed. However, current (and consequently power) increases decrease the capacity of a battery.

It's hard to know if the increased power required of a Tesla battery puts it into the reduced capacity regime. But in any case, the effect is likely to be worse than the speed squared.

I know your point was that increased speed is more important than what a gear box would do. But the effect of speed on range is likely worse and your point is even more important.

DonS | 04. februar 2020

Despite the above comments that a transmission makes efficiency worse, ZF is building a product line around being able to increase EV efficiency. Maybe using a small motor with a transmission can save energy compared to a powerful motor that does not need a transmission?

tessnme | 04. februar 2020

Telsa gears the front and back motors differently and divides the load depending on speed. A two speed solution without a transmission.

jordanrichard | 04. februar 2020

DonS, it is too early to state as fact that this transmission by ZF will do as you/they are saying. ZF is creating this to stay relevant. We are going to see more and more traditional suppliers try to adapt their long standing products/experience applicable to EVs. ZF has seen the writing on the wall, and what I believe to be their core business, transmissions, are being eliminated.

TeslaTap.com | 04. februar 2020

I suspect for single motor EV vehicles a transmission could help with efficiency. One problem is the torque is so great on an EV, a two-speed transmission has to be far more robust than an ICE transmission. So the cost goes up, and the weight goes up. Perhaps the cost and weight of adding a second motor are about the same as the 2-speed transmission. The second motor gives you AWD and redundancy without the transmission complexities. I wish ZF well, but on the surface, it doesn't seem like the smart move.

Earl and Nagin ... | 04. februar 2020

@science,
Good points. I stand corrected.
I'll add that, perhaps the most valuable thing about the 2 speed transmission from Porsche is that it made at least one friend in the boardroom - The transmission division gets a little revenue from the Taycan.

blue adept | 04. februar 2020

The more complexity you introduce into a system the more you increase its inherent operational drag detracting from both its efficiency and performance as a result.

The fewer the gears the better.

andy.connor.e | 04. februar 2020

The short answer is No.

blue adept | 05. februar 2020

@andy.connor.e

+1

Unfortunately "No" is never good enough of an answer.

bp | 06. februar 2020

Whether it's with a transmission or other solution, finding ways to increase energy efficiency while operating at high speeds would have a huge impact on long distance range.

Extending range by adding batteries is expensive - and adds weight.

If Tesla can figure out a way to increase energy efficiency at highway speeds, they'd likely accept some increase in complexity and weight if it meant they could reduce battery pack size (which reduces weight and cost).

Unlikely we'd ever see a traditional gear-based transmission - there are other technologies they could use instead.

And with increasing competition, Tesla won't be able to rely solely on battery improvements or increased motor efficiency.

andy.connor.e | 06. februar 2020

They do know a way to increase highway efficiency. Its called the air suspension. Reduce the distance between the bottom of the vehicle and the road.

finman100 | 06. februar 2020

the competition "burns" 49 kWh for every 100 miles. is that the "competition" referred to here?

https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=42383

There are are more efficient EVs out there and most have a T on the hood. The Hyundai Kona is VERY close. but that's about it.

blue adept | 06. februar 2020

Tesla's are internationally acknowledged//recognized as being THE most technologically advanced, critically engineered vehicles on the road today, checking boxes that no one was even aware could be checked, and yet some think that they are...lacking...in some way?

Are you kidding me?

Believe me, if there were a way to do it better Tesla will be the ones to think of it.

andy.connor.e | 06. februar 2020

adding more complicated parts to gear an electric motor is not more efficient or economical. All you are doing is making the car more expensive.

Tesla2018 | 06. februar 2020

The original roadster was planned to have a 2 speed transmission. However when they started testing it overheated and had other problems so that's why they went with the one speed.

rsmith | 07. februar 2020

The motors spin at up to 18,000 RPM. It is tough to make a multi gear transmission that will handle the torque AND handle the high RPM.

David N | 08. februar 2020

“Would adding a 2 speed transmission increase range?“

No

billtphotoman | 08. februar 2020

@TeslaTap.com - This makes sense to me. I suspect the equivalent weight and cost in extra battery capacity would be more effective. It will be interesting to see what the battery capacity the tri-motor Plaid model S is.

jordanrichard | 08. februar 2020

Porsche, by putting in a 2 speed transmission, only added cost, complexity and weight. This was just to help with it’s 0-60 time at the figurative and literal expose of range/efficiency.

Yodrak. | 08. februar 2020

"... at the figurative and literal expose of range/efficiency."

I expect that you meant to write 'expense of range/efficiency', because gears and shifting mechanisms incur losses in the transfer of power, as well as adding weight and cost to the car.

andy | 08. februar 2020

@jerry I didn’t know that. It’s another act of genius in the overall system.

In general the electric motor has such significant advantages over legacy technology that it would be shame to add mechanical complications to the elegant simplicity.

Ross1 | 08. februar 2020

OP: No it wouldnt help.
How do I know this?
Because I asked the same question about 2015/16, and the experts on this forum answered it for me.

nukequazar | 09. februar 2020

@blue adept, have you looked under the hood of a modern car vs, say, a 40-year-old car? Modern cars are incredibly more complex and incredibly more efficient. I don't think car companies would spend all that time and money if an old 2-stroke 4-banger with a carburetor was more efficient.

"blue adept | February 4, 2020
The more complexity you introduce into a system the more you increase its inherent operational drag detracting from both its efficiency and performance as a result.

The fewer the gears the better."

blue adept | 09. februar 2020

@nukequazar

Yes, actually, I have and what I've found is increased complexity of the onboard diagnostic and engine management systems in the form of additional input sensors and monitors but, IMHO, it is all at the sacrifice of actual performance increases and pollution mitigation strategies with the focus turned more towards concealing // masking the emissions than eking out better fuel efficiency.

But then burning fuel, like gasoline, has never been particularly efficient given that, of all the potential chemical energy in it, around only 14-30% is converted into energy that actually moves the car whereas the rest is lost to idling, parasitic losses, heat, and friction.

Plus, moving the injectors into the head behind the valves (to provide additional cooling which allows for the use of cheaper valve material / metal) only ensures the increased reduction of complete air-to-fuel mixture and resultant combustion.

Then, on top of that, you've got doltards like Trumptato wanting to lower fuel-economy standards even more:

https://www.cnet.com/roadshow/news/fuel-economy-standards-heavier-cars-s...

Which means that ICE automakers will be even less focused on increasing overall efficiency and / or fuel-to-power conversion.

The more complexity you introduce into a system the less efficient it becomes.

mbowden | 10. februar 2020

Only the Cybertruck could possibly use a 2 speed gearbox to improve moderate to hard level off-road efficiency, but I doubt enough people plan on using it in such a manner to make it worth while.

andy.connor.e | 10. februar 2020

Not even on the cybertruck would it provide any advantage.

Techy James | 10. februar 2020

Yes Porsche did this and they have currently the worst EPA rating of all EV's based on Battery Pack size and EPA rated range for full charge. So besides the obvious consideration that more complexity, you would be adding an extra maintenance item that would add to cost for production plus cost to ownership as you would have to add maintenance.

blue adept | 10. februar 2020

*eeking

jordanrichard | 10. februar 2020

I have seen the service schedule/sheet for a Taycan and it is almost as minimal as a Tesla,

blue adept | 10. februar 2020

The primary consideration for offroad or load hauling capability is the availability of 'torque' and electric motors, unlike ICE's which have to build up torque over the course of their RPM range, have 100% torque as soon as you step on the pedal with the only variation being dependent on just how fast you want that torque applied to the pavement or terrain.

Diesels are marginally better than standard ICE's, but they are still no match for electric motors and have to build up torque with increasing RPM's as well.

The point being that a second gear, or two-speed transmission, on an electric motor is pointless and unnecessary.

andy.connor.e | 11. februar 2020

The 2-speed transmission on an EV serves no purpose for speeds less than ~155mph. Where the 2 speed transmission comes in is that electric motors have an efficiency curve at extremely high RPMs. At those speeds you could save 5% or more efficiency but really i dont see that happening because of the additional moving parts. The whole point of an electric motor is that the physics of it allow for no gears. Why wouldnt you want that. Speeds of 155mph are impractical so if anyone like Porsche makes a 2-speed transmission they are clearly not building a practical car. You can see that in the vehicles efficiency.

blue adept | 21. februar 2020

Tesla's Roadster 2.0 has a reported 250 mph top speed and, according to the last thing I've heard out of Straubel and others (from way back in '08), will be achieving that speed with a single-gear transmission because they, essentially, kept grenading their previous 2-speed transmission designs:

https://www.tesla.com/blog/engineering-update-powertrain-15

https://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-th...

So it'll be ready to eat everyone's lunches, dinners, deserts and even bedtime snacks when it hits the streets and do it, by all current indication, with a single-speed / gear transmission, ergo, despite what other EV manufacturers (Porsche) might contend, I don't see any reason what Tesla should take a step back from the progress they've already made and others are attempting to compete with.

Again, 'the more complexity you introduce into a system the less efficient it becomes.'