Tesla with transmission will solve range and heating issues?

[Twiglett]

it all seems totally pointless.
The minor efficiency gains from being able to keep the motor at maximum efficiency would be lost in the extra weight, friction losses and huge cost increases.
There is a reason why most current BEV's are single gear - it make the most sense for 99% of the driving that most people do.

 

[deonb]

it all seems totally pointless.
The minor efficiency gains from being able to keep the motor at maximum efficiency would be lost in the extra weight, friction losses and huge cost increases.
There is a reason why most current BEV's are single gear - it make the most sense for 99% of the driving that most people do.

And if you're ok with extra weight and huge cost increases, just spend it in more batteries.

I bet you'll come out ahead. $5000 on batteries will increase your range by > 10%. No way a $5000 gear box does that.

 

[pmt32577]

The western world (although the US is much better) has been dominated by German cars to the detriment of the vast majority for far too long now. The promise (although seldom achieved) of being able to drive at 150+mph and the ability of a car to do this reasonably comfortably and safely means that cars are optimised against this measure. In practice, driving at high speed in a straight line is very quickly boring apart from the animal fear that a single mistake by yourself or the cars you overtake is going to kill you (my wife is German, I'm a brit, and I've done a fair bit of driving in Germany). In pretty much every other country driving like they do in Germany will get you banned or in prison. Therefore we end up driving round in cars that are optimised for conditions we almost never encounter. What is far more fun is acceleration, braking and going round corners quickly. I've had fast German cars and driving them around in UK conditions gives you the feeling that they are just waking up and getting interested and then you slow down. I've had a fast UK focused car - vx220 turbo which was a Vauxhall (General Motors) major tweak to a Lotus Elise, so like a cousin of a Tesla Roadster and had far more fun.

So, regardless of all the engineering issues others have mentioned, it is just the wrong idea philosophically.

 

[J1mbo]

Not sure if anything came of Antonov's 3-speed motor - they claim 14.7% improved efficiency.

 

[R3D-83]

Since peak efficiency is hard to achieve unless one deploys a high multi-ratio gear with its corresponding losses, let us settle for the practical aspect of keeping the motor efficiency at 4-5% off peak. With that assumption, I see the difference in motor efficiency from low rpm to high rpm in the range of +/- 4% in normal driving. Hence I don't think the multi-gear transmission with the added complexity is going to significantly improve the range of the BEV. I already have the milling noise, I don't need more gears with additional wear and tear, and maintenance.

For smaller city EVs it's probably meaningless to bother with any kind of transmission. But for larger, faster EVs (with a bigger range of speed) it makes sense in my opinion. The transmissions ought to be careless and generally they are. Most other cars (even the high power sport cars) don't have any issue with their transmission. In most cases the transmissions serve the entire life of the car without any serious repair (a few oil changes but that's it). I don't want to flame Tesla, but this is their "disability" that they haven't been able to design and/or manufacture a reliable gearbox. But it's not mission impossible, it could be done. And just a simple, 2 speed gearbox doesn't even need an auxiliary shaft (just an other pair of gears), so it wouldn't add a significant loss to the powertrain.

Not sure if anything came of Antonov's 3-speed motor - they claim 14.7% improved efficiency.

Thank for the article! I haven't read it yet but it sounds interesting!

 

[Lex]

But what of the engine "milling / cicada" sound ? Perhaps a transmission would have prevented this ? The motors right now seem to be consumable items, replaced at 20,000 miles or so...

The loaner P85+ that they gave me when my battery fried was starting to make the sound at 35,000 km (and who knows if it was on its 1st motor)....

 

[Gizmotoy]

For smaller city EVs it's probably meaningless to bother with any kind of transmission. But for larger, faster EVs (with a bigger range of speed) it makes sense in my opinion. The transmissions ought to be careless and generally they are. Most other cars (even the high power sport cars) don't have any issue with their transmission. In most cases the transmissions serve the entire life of the car without any serious repair (a few oil changes but that's it). I don't want to flame Tesla, but this is their "disability" that they haven't been able to design and/or manufacture a reliable gearbox. But it's not mission impossible, it could be done. And just a simple, 2 speed gearbox doesn't even need an auxiliary shaft (just an other pair of gears), so it wouldn't add a significant loss to the powertrain.

This is really the core of it, I think. Yes, the transmission bit Tesla in the past. Going without a transmission, at least in the near term, makes a ton of sense. Similarly, it'll eventually make sense to include one (or make one an option), especially as markets like Germany become more important to them. The issues are not insurmountable: there are today transmissions capable of handling the kind of torque the Model S produces.

They made the right decision to skip one for the Model S & X after the Roadster fiasco. And I suspect the same will be true for the 3. Generation 4 & 5, one of which may be a Roadster follow-up? I'm less sure.

 

[Soolim]

But what of the engine "milling / cicada" sound ? Perhaps a transmission would have prevented this ? The motors right now seem to be consumable items, replaced at 20,000 miles or so...

Is it the motor itself or the gear on the motor that is making the milling sound?

 

[Blue_Model_S]

Great video, but why did they put him right next to a restroom?!

Invest an hour watching this. Learn much, you will.

 

[GuyGadois]

I am not an engineer and have no training in this but could it work if you have a dual engine that one of the engines would run as though it is a second gear and the power could transfer to that engine as speed increases. Maybe it already does this. All I know is that it works really well right now. No need to make this thing faster (IMHO)

GG

 

[R3D-83]

Is it the motor itself or the gear on the motor that is making the milling sound?

It's the gearbox. The gears and/or bearings make that noise while the tiny metal particles are scratching them.

 

[cbin97]

They put a switch to effectively act like a tranny in this Monster, Translogic 180: Zombie 222 Electric 68 Mustang - YouTube you switch it on at 70mph and it resets the torque and the horse power. They get 0-60 in 1.9 out of that thing, but only 50 mile range. Made for drag strip, not range.

 

[MP3Mike]

They put a switch to effectively act like a tranny in this Monster, Translogic 180: Zombie 222 Electric 68 Mustang - YouTube you switch it on at 70mph and it resets the torque and the horse power. They get 0-60 in 1.9 out of that thing, but only 50 mile range. Made for drag strip, not range.

No the switch triggers an over-drive gear box. (They mention it is a Gear Vendors overdrive unit.)

So obviously someone can make gear boxes that handle the torque...

 

[cbin97]

No the switch triggers an over-drive gear box.

You are right, good catch.

 

[CurrentRide]

could it work if you have a dual engine that one of the engines would run as though it is a second gear and the power could transfer to that engine as speed increases. Maybe it already does this. All I know is that it works really well right now. No need to make this thing faster (IMHO)

GG

I too am not an engineer, and I asked this very question a few months ago. The reported answer (which I did not verify) was that dual motor vehicles have different gearing for the front and rear motors, with software adjustable power distribution depending upon the relative speed. It would seem that this strategy would benefit overall performance more than overall efficiency, even if point efficiency (depending on rpm) could be improved. It might improve acceleration at higher speeds to change the gearing of one of the motors, but at the cost of efficiency at other speeds. Like all engineering questions, it would involve compromises. (I think that) I trust Tesla to have considered these questions and made appropriate compromises for these passenger vehicles we love.

 

[mjdurack]

The Tesla cars have very large motors typically in excess of 300kW . They have these large motors so that their performance is astounding and people buy them because of this. Most of the time the cars are only using 10kW of power or less so the electric motor is running relatively inefficiently (<75%). Gears can improve this. Gears can also allow a smaller motor to be used while maintaining similar 0-100kph acceleration and this can in itself improve efficiency.
It is a reasonably well held belief that gears can improve range of BEVs by 15-20% . The commercial difficulties are associated with the torque interruptions when using big steps which come with small numbers of gears, and the complexity that comes with larger numbers of gears. This behavior is compounded by the need to change gears during braking. When you improve range by 20% you can maintain range and reduce the battery pack from 100kWh to 80kWh saving around $5,000. As the industry matures, BEVs become more common, and production numbers increase we will see gears in most BEVs . It is highly likely that they will be CVTs.

 

[gavine]

But what of the engine "milling / cicada" sound ? Perhaps a transmission would have prevented this ? The motors right now seem to be consumable items, replaced at 20,000 miles or so...

The loaner P85+ that they gave me when my battery fried was starting to make the sound at 35,000 km (and who knows if it was on its 1st motor)....

Are motor replacements still prevalent? I remember seeing a lot of them early-on, but I'm pretty sure Tesla has mitigated the problem on newer cars. I don't have any data, but it seems the topic is not discussed here like it used to.

 

[jelloslug]

As an engineer, I have always wondered why Tesla don't go with multi-gear transmission, just like ICE cars. The advantage is that the electric motor only needs to output very low RPM in order for the car to achieve highway speed. That means less electrical power is needed overall, and the range can be extended greatly even if the battery capacity is unchanged at 70 or 90 kwh. The heating issue of battery and electric motor is also greatly reduced, which means Tesla can do aggressive driving for much longer. On top of all that, the top speed of Tesla will probably reach 190 mph instead of the current 155 mph limit. You can pretty much solve multiple major issues of electric car by adding multi-gear transmission.

Any idea on why Tesla cars are still stuck with single-gear transmission?

As an engineer also, I question your credentials based off of your post.

 

[Matias]

Tesla nearly went to bankruptcy because of original Roadster's two speed transmission.

 

[P100DHG.]

As an engineer, I have always wondered why Tesla don't go with multi-gear transmission, just like ICE cars. The advantage is that the electric motor only needs to output very low RPM in order for the car to achieve highway speed. That means less electrical power is needed overall, and the range can be extended greatly even if the battery capacity is unchanged at 70 or 90 kwh. The heating issue of battery and electric motor is also greatly reduced, which means Tesla can do aggressive driving for much longer. On top of all that, the top speed of Tesla will probably reach 190 mph instead of the current 155 mph limit. You can pretty much solve multiple major issues of electric car by adding multi-gear transmission.

Any idea on why Tesla cars are still stuck with single-gear transmission?

My BMW M3 had a 155 mph limit and that wasn't because that was the top speed, I'm sure of it. My brothers S4 has a 155mph too speed. The M5 and M6 have a top speed of 160mph. The 90D has a top speed of 155mph and so does the P100D. My best guess is this is for insurance reasons or regulatory reasons not because it can't go faster. Also could be simply because it's had to find a tire rated at higher speeds.