Any link to an explanation of the drive system?

[PackardV8]

The engineering team designed the Bolt EV’s electric motor with an offset gear and shaft . . . . Combined with a 7.05:1 final drive ratio, . . . Power delivery is controlled by Chevrolet’s first Electronic Precision Shift system. This shift and park-by-wire system sends electronic signals to the Bolt EV’s drive unit to manage precise feel and delivery of power and torque, based on drive mode selection and accelerator inputs.

http://media.chevrolet.com/media/us.../us/en/2016/Jan/naias/chevy/0111-bolt-du.html

The above extract from the Chevy site is just gibberish. I'm fairly good at understanding technical writing, but that ain't. There's no mechanical details, but seques into an attempt to make electronic/drive-by-wire controls, which have been around in ICE applications forever, into a breakthrough Chevy just invented.

jack vines

 

[NeilBlanchard]

Seems clear enough to me - a fairly odd style, maybe.

 

[PackardV8]

Seems clear enough to me - a fairly odd style, maybe.

One more try. Through what mechanical means does the power get from the motor to the wheels? Yes, they state an offset shaft and a reduction gear, but that's a pretty slim explanation. I was hoping for a bit more detail.

Power delivery is controlled by Chevrolet’s first Electronic Precision Shift system. This shift and park-by-wire system sends electronic signals to the Bolt EV’s drive unit

Very much ado about nothing; electric shifting has been used in ICE vehicles for decades. There's nothing I can see the Bolt doing there that others haven't. The Bolt shifter looks and feels pretty much like the BMW ICEs.

jack vines

 

[LeftieBiker]

Most EVs use a single reduction gear in what is essentially a differential to send power from a single motor/generator through the two drive axles. Think of it as a one speed "transmission" that is always engaged. Reverse is accomplished by reversing the motor.

 

[JeffN]

Here are the technical details:

http://papers.sae.org/2016-01-1153/

There is a link on the right side of the page to a free preview of the paper which shows most of the content of the paper (5 of the 8 pages).

 

[SeanNelson]

...electric shifting has been used in ICE vehicles for decades. There's nothing I can see the Bolt doing there that others haven't. The Bolt shifter looks and feels pretty much like the BMW ICEs.

Well of course the difference is that in an ICE vehicle the shift-by-wire system has to use solenoids to physically move the gears around. In the Bolt, the "transmission" has a fixed gearing so the shifter doesn't do anything to it at all. All the shifter does is instruct the motor controller to run the motor forward or backward, or (in "Neutral") to not apply any power at all.

All the fancy talk is just marketspeak which can safely be ignored.

 

[PackardV8]

Here are the technical details:

http://papers.sae.org/2016-01-1153/

There is a link on the right side of the page to a free preview of the paper which shows most of the content of the paper (5 of the 8 pages).

Many thanks, Jeff; that's exactly the technical detail I was looking for. I knew it was out there, but just hadn't hit upon it.

jack vines

 

[DanCar]

How does one get a copy?

 

[JeffN]

If you go to the SAE link I posted earlier and look on the right side of the browser page you will see a link for buying a download PDF of the paper for $27 or thereabouts.

 

[ScooterCT]

I know it's not Bolt-specific, but there is a Tesla parts maker who did a wonderful video on EV drive trains. I found it really educational in general. Parts certainly don't apply to the Bolt.

https://evannex.com/blogs/news/how-does-an-electric-car-work

 

[NeilBlanchard]

Seems clear enough to me - a fairly odd style, maybe.

One more try. Through what mechanical means does the power get from the motor to the wheels? Yes, they state an offset shaft and a reduction gear, but that's a pretty slim explanation. I was hoping for a bit more detail.

Power delivery is controlled by Chevrolet’s first Electronic Precision Shift system. This shift and park-by-wire system sends electronic signals to the Bolt EV’s drive unit

Very much ado about nothing; electric shifting has been used in ICE vehicles for decades. There's nothing I can see the Bolt doing there that others haven't. The Bolt shifter looks and feels pretty much like the BMW ICEs.

jack vines

Okay, that I can answer - here's a picture:

And here's the similar Spark drivetrain:

The motor is on the right side (as you sit in the driver's seat), and the reduction gear and differential are compact. The KEY thing to know is the motor has a TUBE - and the right side drive shaft passes through that tube. So, the two half shafts are equal length, so this minimizes torque steer.

 

[SeanNelson]

The motor is on the right side (as you sit in the driver's seat), and the reduction gear and differential are compact. The KEY thing to know is the motor has a TUBE - and the right side drive shaft passes through that tube. So, the two half shafts are equal length, so this minimizes torque steer.

I'm clueless about drive train design, so take this for the very little that it's worth... I know they designed the drive unit to minimize torque steer, but since the differential is not centered within it that means that there has to be an unequal length in either the driveshafts internal to the housing and/or the external shafts that run between the CV joints. Perhaps that's the source of whatever torque steer there is.

It would probably be infeasible to put the differential in the exact center since the motor inevitably takes more space than the gearbox does - the only way to do that would be to artificially extend the length of the housing on the gearbox side and that would doubtless have a bunch of other negative consequences that would outweigh the benefits.

 

[LeftieBiker]

The thing is, though, that the Bolt doesn't, according to test drives I've read, have minimal torque steer. It has significant torque steer. So somewhere they got the drive balance wrong. I've driven FWD cars with and without torque steer, and there is nothing fun about the car trying to turn while accelerating hard.

 

[NeilBlanchard]

The half shafts are equal length. The shaft through the motor tube doesn't affect this.

I had two short test drives, and never noticed torque steer.

 

[devbolt]

The half shafts are equal length. The shaft through the motor tube doesn't affect this.

I had two short test drives, and never noticed torque steer.

The Torque steer issue rears it's ugly head under excessive acceleration. You likely won't ever encounter it during normal driving circumstances. Our Highlander Hybrid also exhibits Torque steer under the same circumstances, but to a slightly less severe level. So the Bolt is not necessarily unique in this regard.