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TECHNICAL: Why not a 2+ Gear Box?

urbanscribe

Member
Aug 3, 2015
17
3
new york
one of features we like about our MS (and i assume MX) is the one speed gearbox and the lack of excessively complex 5/6/7 transmission gear box (ala PDK)
we think of the power being applied linearly and it works wonders.
the simplicity of a single gear also allows for no R&D wasted on recreating modern gear box/clutches/transmissions.

most of the torque and power is available right away (0-30mph - off the line neck snapping) and stays on for a long while.
ICEs (non turbos) get their max torque later in the RPM (5000+) so they need a gear box to keep maximum power available at all speeds

however,
MS power does fall off (let's say after 50MPH) and this is where we see the greatest acceleration disadvantage the MS has against fast ICEs
think all the drag races which start phenomenal as long as we cut it at 60mph where MS gets beaten towards the end of the quarter mile.

so:
why not FROM A TECHNICAL PERSPECTIVE have a 2+ gears transmission which would allow for the power/torque to come back (on the higher ration second gear) for better acceleration/quickness later on (above 50mph)?
 

DoctorJJ

Member
Nov 14, 2014
102
11
Oklahoma
They couldn't get a 2spd or any transmissions to hold up on the Roadster. They should have been able to, through utilizing torque management, which even ICE cars use, while the transmission shifts. Anyway, I think a better question would be, if it's traction limited down low right now, then why not use a higher gear ratio so that you keep the motor in a better torque driver higher into the mph range??
 

Saghost

Well-Known Member
Oct 9, 2013
8,217
7,010
Delaware
Weight and cost.

The thing is, while you can probably gain a few percent better motor efficiency at higher speeds from a multispeed transmission, you pay for it with a bunch of weight and complexity - and you lose efficiency in the transmission which may or may not be less than the the motor gain.

It's more likely that the EVs will gain more motor/inverter power instead - enough that they can stay torque limited through all their normal driving speeds.

The other thing you might see is an extension of what Tesla's doing now - higher gearing on rear motors than front to give the car most of the benefits of two gear ratios.
Walter
 

CurrentRide

Member
Jun 21, 2015
130
42
Charlotte, NC
How about just using different fixed gear ratios for the front and back motors? Software could control the relative power distribution at different speeds to improve efficiency.

Caveat lector: I am not an engineer.
 

green1

Active Member
Mar 25, 2014
4,548
1,121
Calgary, Alberta, Canada
How about just using different fixed gear ratios for the front and back motors? Software could control the relative power distribution at different speeds to improve efficiency.

Caveat lector: I am not an engineer.
That's a great idea, in fact it's such a great idea that it's exactly what Tesla is doing already with the D cars. That's why the 85D has more range than the 85 despite the extra weight of the second motor.
 

CurrentRide

Member
Jun 21, 2015
130
42
Charlotte, NC
So does the 85D have better acceleration at higher speeds than the S85? It seems that changing the gear ratio of the front motor could be a way to address the complaint that some members have had about highway passing power for the P85D.
 

EarlyAdopter

Active Member
Jun 24, 2012
2,821
2,048
Redmond, WA
Fun video, thanks. What mfr made that first gen 2-speed tranny they laughed about? And what came of that court case?

According to Wikipedia - Magna. As Marc mentions, Tesla won their lawsuit against them. They ended up going with BorgWarner for the single speed transmission.

Starting in September 2008 Tesla Motors selected BorgWarner to manufacture gearboxes and began equipping all Roadsters with a single speed, fixed gear gearbox (8.2752:1) with an electrically actuated parking pawl mechanism and a mechanical lubrication pump.[18]

The company previously worked with several companies, including XTrac and Magna International, to find the right automatic transmission, but a two-gear solution proved to be too challenging. This led to substantial delays in production. At the "Town Hall Meeting" with owners in December 2007, Tesla announced plans to ship the initial 2008 Roadsters with their interim Magna two-speed direct shift manual transmissions locked into second gear, limiting the performance of the car to less than what was originally stated (0 to 60 mph (0 to 97 km/h) in 5.7 seconds instead of the announced 4.0 seconds). Tesla also announced it would upgrade those transmissions under warranty when the final transmission became available.​

For the Model S, Tesla went in-house and makes the single speed reduction gear themselves.
 

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