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Multiple Speed Transmission

4

Description

The Model S should offer an option for a auto or manual multi-gear transmission not just one single gear.  A five or six speed gear box might mean a more efficient and faster car.

Competitive/Pricing/Notes

A tranny might also allow Tesla to use a smaller electric motor since it wouldn’t have to turn such a large gear, this may improve range and efficiency.  Auto makers like Detroit Electric and  Brammo motorcycles have already incorporated  six speed transmissions in there vehicles and Brammo explains why they don’t use a single speed gearbox https://www.youtube.com/watch?v=WzGaDIMlOy4

The Model S is a great car but if its gonna be competing with the big boys the single speed gearbox doesn’t seem the way to go.  If you watch any race with the model S it usually wins when the other car is about to pass with it after they leave the starting line.  This seems due to the one speed gearbox, it has extremely acceleration up to about 95mph and then falls flat.    Also a transmission would reduce the rpm’s of the motor during highway drives therefore improving range

Editor: This would add weight, cost, and complexity to the existing system, and consume some luggage space.

Status

Unknown.



Category: Tags: entered 7-Jun-2013

6 Comments

Why? You want to shift like the red car in this video? ;-)
http://www.youtube.com/watch?v=VLCdP6sMN9k

No use for a gear box. If the RPM band turns out to be too narrow, they could tweak the (single) reduction gear and/or improve the motor to support more RPM. So far, there is no real-world evidence that this is a problem, except in the heads of some ICE nuts that have not yet arrived in the EV age...

Update: Smaller electric motor is *not* more efficient, more like the other way around. Similarly, higher RPM (within some RPM band) does *not* equal lower mileage in an electric motor. That's counter-intuitive to someone who has grown up with ICEs, and it goes to show once again how inherently more suitable electric motors are for driving auto mobiles, than ICEs.
This seems like strictly an engineering question, the sort for which Tesla engineers are among the best in the world (and probably better than any owners on this site).
The Tesla roadster started with a two speed transmission, but that was abandoned and simplified when it kept breaking under full acceleration.

The only purpose of a transmission and clutch is to allow an engine or motor to idle or run at a speed where it can generate some torque and power. Bog down an ICE and it will run very badly, so the transmission is essential. In contrast, an electric motor is perfectly happy to pull with full torque at zero revolutions per minute. There is probably a practical upper limit on revs, but it's very high since there are no reciprocating parts with inertia that has to be reversed periodically.

I recall reading that Morgan has an electric roadster in which they have implemented a five speed transmission (or similar). But I think Morgans tend to be built more for the nostalgia fanatics among us rather than for practical modern uses.
I'm pretty sure that the extra weight of a gearbox would be better used to increase the size of the motor, if a greater top end (and greater accelleration to get there) is desired.  Not to mention reliability and maintenance issues resulting from having the additional moving parts.

But the clincher is that yes they did want to have two gears in the roadster, and no it wasn't possible to make one that could handle the torque of a powerful electric motor.  Clearly Brammo is "right" about providing gears, but until we see multiple electric cars racing against each other we're not going to find out the ideal optimal solution for power delivery.

 
So what if the Tesla starts to fall behind above 100 mph?  Other than Germany or a racetrack, there's just not a useful purpose for designing a passenger vehicle for optimum performance over 100 mph.  Tesla's single speed electric motor is ideally suited for how we drive our cars every day - stop and go, speeds under 100 mph.  The only Tesla I could see needing performance at really high speeds is the new Roadster and they are probably engineering a solution for that (which will cost $$$).
Think "elegant simplicity."