[2cycle]

There should be no reason mechanically that a simple 2 speed couldn't be made. I'm not quite sure what the shift delay problem is all about. A cassette style transmission doesn't need much more than a handful of milliseconds to unload enough torque to smoothly lock the next gear.
I don't know who Tesla had build the prototypes but if it wasn't a cassette style they were likely doomed from the beginning. You don't have to be an engineer to see that coming.
Another thing about the Tesla power curve, if your shifting past 9500 rpm your not helping yourself out. It looks like the power peaks near 9000 rpm and any transmission mechanically should handle that no problem.
My bet is it was a money thing. They already went so far over initial predicted cost that they made the call.

[Duncan]

The initial post said
"As soon as it had reached 40mph its all over"
If I am reading the specs right peak power is about 80 mph and the bugger has still got
150 Kw at its governed top speed (125 mph)
The torque curve shows constant torque from zero to 60 mph
I suppose you could increase the rear wheel torque by gearing it down and then changing up a gear but you would want to run to 12,000rpm then change down to 7000rpm
Now this is all with the stronger motor but it does beg the question of why you would need a gearbox at all

[Duncan]

2cycle
Why would you change at 9500 rpm ?
at that rpm you are only about 3% below peak power,
you have a wonderful flat power band
from 6000 rpm to 11000 rpm you are within 7% of max power
The initial flat torque curve takes you through the part when you cannot use all of the power then you still have 150 kw at a highly illegal max speed

[Duncan]

Sorry to keep messing about

But another look at the Tesla power curve showed that gearing the thing lower may (tyres permitting) increase its acceleration up to 40 or 50 mph but then it is power limited and that flat power curve means that adding gears could only help a tiny little bit and then above 110 mph

[JRP3]

Originally Posted by 2cycle

My bet is it was a money thing. They already went so far over initial predicted cost that they made the call.

Yes, the cost, the need to get a product to market, and the realization that by increasing the power they really didn't need a two speed at all.

[2cycle]

Originally Posted by Duncan

The initial post said
"As soon as it had reached 40mph its all over"
If I am reading the specs right peak power is about 80 mph and the bugger has still got
150 Kw at its governed top speed (125 mph)
The torque curve shows constant torque from zero to 60 mph
I suppose you could increase the rear wheel torque by gearing it down and then changing up a gear but you would want to run to 12,000rpm then change down to 7000rpm
Now this is all with the stronger motor but it does beg the question of why you would need a gearbox at all

Maybe the term "it's all over" wasn't really a good term. I've been looking for the link online to see the dyno tests and the comparison to the Chevy but no luck so far. Anyway, their graph overlay of the Tesla compared to a V-6 Chevy Camaro showed the Tesla having great torque to the rear wheels up to 40 mph then a linear decent. Once the Chevy shifts to second gear the torque to the rear wheels was already surpasing the Tesla and remained higher than the Tesla all the way to peak speed which is likely pretty close between the cars seeing as the Camaro was only a V-6 model.
When we set up a trans ratio you need to know the powerband as compared to the desirable rpm drop upon shift. The tesla can overrev quite a bit as noted on their simple graph but the real numbers would need to be looked at to find the true sweet spot. Look at it this way, if the peak power is 250 hp, and 1500 rpm past peak is 230, and 1500 rpm before peak is 230, then you will accelerate much faster if you shift down 3000 rpm and make another run through the power peak area rather than let it keep running a downhill slope.

[Buckster]

Surely it would react better to a torque converter type arrangement, a simple two cone system would suffice and could be built lightly while retaining reliability, it would remain a one speed transmission but by shifting up the drum at a preset point would reduce rpm. There are multiple ways to manipulate a torque converter.

[2cycle]

was reading tid bits from the article again and came across the cost comparison "in California" to a gas burner. They were charged crazy amounts to charge the car at night. The few days they spent driving (500 miles I think) they spent $45 on electricity. They equate that to driving a car that gets 33 mpg, not that tough to find when you can settle for a 2 seater, my friends new Corvette gets 30 mpg.

How does Cali figure they are helping anything by charging 3 times what the rest of us pay for electricity. Why is being green mostly for the rich minority?

[gor]

Originally Posted by 2cycle

There should be no reason mechanically that a simple 2 speed couldn't be made. I'm not quite sure what the shift delay problem is all about. A cassette style transmission doesn't need much more than a handful of milliseconds to unload enough torque to smoothly lock the next gear.
I don't know who Tesla had build the prototypes but if it wasn't a cassette style they were likely doomed from the beginning. You don't have to be an engineer to see that coming.
Another thing about the Tesla power curve, if your shifting past 9500 rpm your not helping yourself out. It looks like the power peaks near 9000 rpm and any transmission mechanically should handle that no problem.
My bet is it was a money thing. They already went so far over initial predicted cost that they made the call.

absolutelly no reason - torque - same and in a same range as 6 syl car they shown and go lower...
-doesn't has to have 4 gears... or change it often...
- what's wrong with the regular clutch? wouldn't have to worry about motor deceleration - clutch and wheels would take care of it : )
p.s. - pict: tq&power curves from the net;

pps. top speed is drag, effort & hp limited - whatewer it is; final rpm at wheels: 24’’, 1000rpm=71.3mph; 2000 =142.6

[gor]

Originally Posted by 2cycle

I picked up a car magazine this weekend because it had done a multi day test session with the Tesla. The guy really liked it for stoplight to stoplight fun. He mentions the lack of top speed but also reminds us that top speed is rarely used and was worth the trade off of the off the line punch.
They showed some interesting numbers that were either chassis dyno figures or onboard dyno figures. It pretty much shows what I thought all along, it has great off the line torque to the rear wheels but as soon as it gets past 40 mph it's all gone and heading down hill quick. They showed a comparison to the V-6 Camaro and as soon as the Camaro shifts to second gear the torque to the wheels as already more than the Tesla is at that point during a sprint. When you campare the weight specs you will see that the Tesla is more than 1000 lbs lighter, that's where the performance comes from. After reading that write-up I would have to say a 2 or 3 speed tranny would surely make the torque to the rear wheels show better but the weight would slow it down off the line to gain the top speed and it wouldn't be worth it.

according to data http://www.teslamotors.com/performan...and_torque.php

Sport:
288 HP (215kW) @ 4,400-6,000 rpm
395 lb-ft (400 Nm) @ 0-5,100 rpm
Overall Final Drive
8.28:1


Size - rear
225/45 R17


125 mpg: wheel rpm= 1683.82

------------
torque (acceleration) rises until 45mph and than going down, HP after 53mph down

max torque at: 5100 24.97*0.0029735/8.28=45.73mph
max hp at: ... =53.803mph