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Old 07-25-2013, 01:36 AM   #11 (permalink)
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All you need is to alter the electric motor speed to match the transmission's speed between shifts... electronic rev matching. Should be even easier with an electric motor than a gasoline motor.

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Old 07-25-2013, 02:16 AM   #12 (permalink)
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yah and with enough resolution it can wait to shift till the teeth line up, no load. Goodby constant mesh/synchros/dogs. Hello nice efficient sliding mesh, again, without the crashes.

EDIT: forget the lining the teeth up bit, it is probably fine to just have pointy gear teeth ends instead.
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Old 07-25-2013, 08:46 AM   #13 (permalink)
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I seem to remember the Chevy Spark having a transmission.
So far the only EVs I've driven that have transmissions have been home built EV's.
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Old 07-25-2013, 11:54 AM   #14 (permalink)
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Here's a twin motor, 4-speed electric drivetrain, with a twist:

Green Car Congress: Oerlikon Graziano launches 4-speed electric drive; up to 15% efficiency increase

Quote:
The 4SED, based on Graziano’s original eDCT, uses two traction motors in a very compact powertrain which provides four speeds to allow running closer to peak efficiency – approximately 90 percent. The result is an overall efficiency improvement of up to 15 percent, which translates into increased range or improved performance for the vehicle.

“The design of the gearbox is very simple”, says Paolo Mantelli, Head of Oerlikon Graziano Performance Automotive. “The transmission’s unique configuration uses two input shafts, each driven by its own electric motor. The two motors replace the twin clutches and the synchronizers, allow pre-selection of the next gear before the previous one has been disengaged, and can synchronize shaft speeds”. The use of the traction motors also permits a reduced set of software algorithms compared to a normal automated gearbox, and since there are no hydraulics, there is no need for valve control.
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Old 07-25-2013, 12:38 PM   #15 (permalink)
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Those are still constant mesh though. Dual clutch (or dual motor) is designed for "smoothness".

Back in the 1930's Chevy introduced constant mesh and a couple years later they came out with cone synchronizers.

Prior to that they used a much much simpler and more efficient "sliding mesh" gear engagement, where the teeth of the gears slid in and out of each other for engagement/disengagement and the rest of the gears are not rubbing against each other and their bearings all the time. Sliding mesh also had significantly fewer parts.

Good drivers (the ones who could rpm match manually) didn't have a problem with sliding mesh, but for everyone else it became known as a "crash box".

I don't know what the state of the art is, but it seems time for the efficiency of sliding mesh and electronic synchronization, especially if an electric motor is the input. The load (amps?) is actively set to zero, an actuator puts it in neutral, then rpm-matches (back EMF?) to the next gear, actively. It should be fast (though not air-shifter fast) and smooth, and the software can record the output torque prior to the shift and re-apply an appropriate torque immediately following the shift for smoothness, or just set most efficient torque for that rpm, because feeling when a car shifts isn't such a hardship that it should compromise efficiency, is it?

Dual clutch is obviously, to me anyway, a luxury with a significant number of extra parts compared to a single clutch, when transmissions don't even really need a clutch except to get rolling, or don't even need one at all with an electric motor.

They claimed 15%, and added a second motor that cannot be used with the first simultaneously, great, I know we can do better.

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Old 07-25-2013, 05:16 PM   #16 (permalink)
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I'd think the planetary gear system is ideal for a simple 3-speed EV gearbox. The gears are in constant mesh and can take high loads.

Toyota already uses that at the core of their Hybrid Synergy Drive system in the Prius, where it is augmented with extra motors and generators to mimic CVT operation while having superior efficiency around the 3 base gearings. Either that or a planetary system without the gizmo's would seem right as a EV transmission.
The Toyota setup makes for smooth transitions. It also makes for license fees or lawsuits for anyone who uses it without their permission, though Antonov claims it is the other way round.

The most succesful car to use planetary gears was the Ford model T btw.

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