[CroDriver]

Originally Posted by WarpedOne

Form over substance eh? Lets all sing khumbaya and ignore the facts?

You came forward with:


Facts are that Tesla Motors spent over 10 million $, tried 2 different transmission suppliers and suffered over a year of delays trying to produce a reliable 2 speed transmission that could handle those 14k rpm, be lightweight and efficient enough. And reliable. And quick.

In my book that counts for wanting it badly. They wanted it so badly that they almost failed as a company. There is a saying around here that goes something like "If there isn't any, even army can't take it".

Now, If you know of such a transmission by all means point it out. I (and many others) want to know of it also.

As far as I know the 2 speed they have used was a standard Honda transmission with only two gears left inside. If a Honda transmission could take it I don't see a reason why they couldn't make a custom transmission for their needs.

Modern superbikes can spin to 17.000 RPM





I know that they haven't much torque but their transmissions are very light. I'm pretty sure that it IS possible to make a transmission for a high speed - high torque AC motor.

[WarpedOne]

As far as I know the 2 speed they have used was a standard Honda transmission with only two gears left inside.

?!?!?
Where did you get that info?

[CroDriver]

Originally Posted by WarpedOne

?!?!?
Where did you get that info?

I really can't remember. I think that I "know" that for years but I don't know where I got that info from.

Just did some googling but didn't find any usable info

[WarpedOne]

I don't know what they've used for their first prototype. Motorcycle transmission makes sense for such a thing as it is only a proof of concept. For the first prototype the main issue is availabilty.

Direct from Darryl Siry:

Update: Tesla VP Darryl Siry contacted us to clarify the issue with the original X-Trac gearbox. Apparently the problem was not one of actual durability of the transmission itself. Tesla evidently spec'ed out a two speed unit with no clutches. The design intent was to do clutch-less shifting and manage the torque output of the motor during the shifts. Unfortunately the rotational inertia of the motor made this plan unworkable as the torque output couldn't be changed fast enough. According to Siry there were never actually any mechanical failures of the X-Trac transmission, it was simply a matter of Tesla not being able to get their control strategy to work adequately with the hardware. Subsequently Tesla contracted Magna to develop a dual clutch two speed gearbox. Unfortunately, this is the design that had durability issues leading to Tesla's ultimate decision to revise the motor for more power and go with a single speed unit for production. The vehicles running with the interim single speed gearbox are actually using the original X-Trac box with the lower gear locked out (for prototypes) or removed entirely (early production cars). - Sam

That "couldn't be changed fast enough" was about 4 seconds IIRC.

[Bowser330]

The members on the Tesla forums actually explained the issue with the transmission more clearly so I understand that it wasn't just about a 14,000 rpm transmission....The problem looks to be more specifically the gearing drop from ~12,000rpm down to 7,000rpm...

Warpedone touched on that with the D. Siry quote:

...Unfortunately the rotational inertia of the motor made this plan unworkable as the torque output couldn't be changed fast enough...

As you would expect there really hasn't been any large need for a single gear drop like that for this application or any other that I know of...so there hasn't really been much r&d on it... Its not that it cannot be done..There are way more advanced technologies out there than a 2 speed EV specific gearbox...patience warped one.

There were also some good ideas on the Tesla forum...(paraphrasing)
(1) Why shift at 120000rpm? It would make more sense for a 9000rpm shift (81mph) down to 7000rpm (9-7..is a down shift that is handled by Porsche GT3 cup cars)

(2) Why not just have a sequential shifting transmission that can blip the gears down in milliseconds down 2 steps instead of one 12-9-7 or something like that.

Both valid ideas.

[CroDriver]

Originally Posted by Bowser330

(2) Why not just have a sequential shifting transmission that can blip the gears down in milliseconds down 2 steps instead of one 12-9-7 or something like that.

Wasn't the two speed transmission in the Tesla a sequential? A sequential gearbox is the only reasonable solution IMO. A automatic transmission with a torque converter is not very efficient.

And I think that the problem was not a slow transmission (or gear change mechanism). The motor (or motor controlling) was the problem.

The design intent was to do clutch-less shifting and manage the torque output of the motor during the shifts. Unfortunately the rotational inertia of the motor made this plan unworkable as the torque output couldn't be changed fast enough. According to Siry there were never actually any mechanical failures of the X-Trac transmission, it was simply a matter of Tesla not being able to get their control strategy to work adequately with the hardware.

So Tesla wanted to make a clutch-less two speed gearbox. In this case the motor has to prepare itself for the next gear. When shifting from the first to second gear it must lower the RPM to a exact figure to make a clutch-less shift possible.

Since Tesla uses a AC motor I think that this shouldn't be a major problem for them...

[Bowser330]

Originally Posted by CroDriver

Wasn't the two speed transmission in the Tesla a sequential? A sequential gearbox is the only reasonable solution IMO. A automatic transmission with a torque converter is not very efficient.

I think the idea was...12-9-7 as quickly as possible..that is three speeds with two shifts:
(1) 12,000rpm to 9000rpm
(2) 9000rpm to 7000rpm

I agree with you CroDriver, I am also a bit confused by this quote:

According to Siry there were never actually any mechanical failures of the X-Trac transmission, it was simply a matter of Tesla not being able to get their control strategy to work adequately with the hardware.

[WarpedOne]

Since Tesla uses a AC motor I think that this shouldn't be a major problem for them...

It is not only you guys that are confused by this. I get many comments along the line that it should be easy/doable to slow down the motor. Even from 14.000 to 7.000 rpm. Even when the rotor weighs about 50 pounds. Even in only half a second.

The problem lies in their controller. Is it possible that while the controller tried to stop the motor and absorb all that energy in half a second (about 50 kW of power) some huge current spikes occurred that some part of their electronics just couldn't handle? Maybe not under all possible circumstances?

Remember the controller is air-cooled and can overheat. What if the controller already overheated and it had to absorb that surge of power while down-shifting? Ten times in a row? You cannot write into owners manual something like "When the controller overheats you should not down-shift". Car costs 100.000$ It has to work under all "normal" circumstances. Repeatedly.

[major]

Originally Posted by WarpedOne

Even from 14.000 to 7.000 rpm. Even when the rotor weighs about 50 pounds. Even in only half a second.

Hi Warped,

Why would they be trying to go from 14kRPM to 7k when the peak power is back at 7 or 8k?

The problem lies in their controller. Is it possible that while the controller tried to stop the motor and absorb all that energy in half a second (about 50 kW of power) some huge current spikes occurred that some part of their electronics just couldn't handle?

And why would they try to "absorb" that energy in the controller? Simply dump it back into the battery. The controller surely is capable of converting 50kW and the battery capable of 50kW short term charge.

I've seen heavier rotors decelerate faster than this with the dyno connected to the shaft with similar or smaller size inverters (controllers). It is not an insurmountable problem with the physics. But may present some unique control challenges.

I don't know the specifics about the Tesla transmission or the development they did. But if they couldn't validate the transmission, they did the right thing releasing it direct drive. Seems like a well performing vehicle to me

Regards,

major

[Batterypoweredtoad]

50lbs isnt that much. I doubt that is much different than most manual transmission ICE vehicles when you account for flywheel, clutch, crank, pistons, etc... Add in the fact that you can use some electronic control to slow the motor and I'm surprised they couldn't make it work. On the flip side they are a small operation, so I bet they pay big bucks for r@d instead of having people beg them to use their product.