2017 Chevy Bolt EV Cd 0.312

[freebeard]

IMHO it's about the torque curve. Single speed is possible, reverse is a non-issue.

Electric torque is flat to a 'knee' where is starts to drop off, so if it's geared to only use a limited RPM range you won't hit a wall. But, per Jack Rikard, a single speed motor will need twice the power at lower RPMs.

Hence why I'm hoarding a 68hp electric to replace a 36hp gas engine.

[sendler]

Production EVs always have a gear reduction and a differential. So the Bolt has two different reductions to choose from with a computerized clutch instead of just the one. It's not like it has a five speed slush box. A starting gear and an everything else gear with a compound planetary gear set and a clutch instead of just a simple planetary gear that other EVs already have.
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Better performance and efficiency for a very minimal weight and cost gain.

[NeilBlanchard]

Originally Posted by sendler

So it seems the Bolt will have a multi speed transmission.
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https://en.wikipedia.org/wiki/Chevrolet_Bolt
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Huh?

It has a reduction gear with a differential, and the right side half shaft passes through the tubular motor shaft.

[redpoint5]

Originally Posted by NeilBlanchard

Huh?

It has a reduction gear with a differential, and the right side half shaft passes through the tubular motor shaft.

Why does the motor need a differential? It powers both wheels right, so shouldn't it just turn at the speed it turns?

Can I get a layman's interpretation for what you just said. I think you are saying it doesn't have multiple or adjustable gearing...

[redpoint5]

Originally Posted by rmay635703

An electric AC motor as it stands in the volt is over 91% efficient across its operational range.

What motor speeds are considered the operational range, and are you sure it maintains 91% efficiency across that range?

Electric motors do not maintain efficiency across their functional ranges and can benefit from gear selection to keep them at their peak efficiency RPM.

[sendler]

Electronic precision shift is mentioned again here. What ever that really means we will have to wait and see.
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The single high capacity electric motor produces 200hp and 266lb ft (360Nm) of torque and is mated to Chevrolet’s first Electronic Precision Shift System, a shift-by-wire system that saves space and according to the company, manages to offer “precise feel and delivery of power and torque”.
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Chevrolet Details 2017 Bolt’s Long-Range Electric Powertrain In Detroit, Gets 200HP
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[Daox]

A differential allows the front tires to rotate at different speeds. This is necessary while cornering to maintain stability and reduce tire wear as the outer tire spins faster than the inner tire.

[NeilBlanchard]

Originally Posted by redpoint5

Why does the motor need a differential? It powers both wheels right, so shouldn't it just turn at the speed it turns?

Can I get a layman's interpretation for what you just said. I think you are saying it doesn't have multiple or adjustable gearing...

I don't think the Bolt EV has variable or multiple gears. Unless it had two motors, it needs a differential.

The motor shaft is a tube. The output is on the left end, and it has a reduction gear to a shaft just behind the motor, and then another reduction gear driving the ring gear on the differential. The differential is concentric with the motor - and so the two half shafts that drive the front wheels are also concentric with the motor. The right side half shaft passes through the motor tube/shaft. So the motor and gear box are centered between the front wheels, and the two half shafts between the u-joints and CV joints are equal length.

Here is a semi-transparent image:



Of the gears they show, I cannot see where this could be variable. The caveat is the portion of the gearbox housing behind the transparent bits.

[freebeard]

Tesla and the Toyota/Lexus HSD MGR3 use a single motor and an open differential. Arcimoto use twin motors ganged together. Possibly for packaging or availability issues.

There is discussion on EVTV about making an aftermarket limited-slip differential for the Tesla, to save reverse engineering the Tesla traction control.