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Discussion Starter #1 (Edited)
I've never been much of a gearing guy but I'm trying to understand how the Bolt does it. Check my understanding here

This says the right drive axel goes through the hollow motor shaft, 'right' being from looking at it from the drivers perspective



that shaft goes through the AC motor over to the differential shown here



The differential is so the two wheels can spin at different rates so you can do things like drive around curves.

Now the AC motor likes to spin faster than the wheels and we have torque to spare, so we have a single speed transmission that drops it from 7.05:1



via two shafts and four helical gears



Finally using the above two images, this view is top down from the front. Meaning, the two glycol connections are pointing horizontal toward the back of the car and the gearing is on our left, looking toward the front from the drivers position.

The only oil in the car is in this motor unit, in the picture above the black circular cap at the bottom of the picture is an oil pump which both circulates and cools the motor, the glycol going through a heat exchanger with the oil.

Here's a video showing it at the point they discuss the motor

Motor video

Rather a brilliant design, I like the oil which both cools and lubricates the motor and gearing.
 

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The drive shaft goes into a hollow coupler on the shaft end. It has them on both sides.
It's a very simple motor/generator design. The drive gear is on the motor shaft.
 

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Wonder if the motor turns the opposite direction of the wheels? I've got some experience with diesel driven pumps where we used speed increasers instead of reduction. Pretty much the same thing as this. Gear unit had water cooled heat exchanger that the oil was passed through. Have seen gear failure when the small oil pump fails or the filter gets clogged in the oil line. I say failure, but it actually a slow death and not complete failure. Just lots of gear wear and subsequent increase in noise. In our case, we couldn't hear the gear noise over the sound of the diesels. We caught the impending failure using acoustical listening devices as part of our preventative maintenance program. Pretty sure in a electric vehicle it wouldn't go unnoticed. Temperature monitoring is another way to pickup an oiling problem. Wonder if the Bolt has any such monitoring?
 

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Wonder if the motor turns the opposite direction of the wheels? I've got some experience with diesel driven pumps where we used speed increasers instead of reduction. Pretty much the same thing as this. Gear unit had water cooled heat exchanger that the oil was passed through. Have seen gear failure when the small oil pump fails or the filter gets clogged in the oil line. I say failure, but it actually a slow death and not complete failure. Just lots of gear wear and subsequent increase in noise. In our case, we couldn't hear the gear noise over the sound of the diesels. We caught the impending failure using acoustical listening devices as part of our preventative maintenance program. Pretty sure in a electric vehicle it wouldn't go unnoticed. Temperature monitoring is another way to pickup an oiling problem. Wonder if the Bolt has any such monitoring?
Considering the way the axle setup is attached it must spin the same direction when going forwards.
Look at the image in my other post. ^^^^^^^^
 

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I think that parallel-helical gear reduction should be stated as series helical gear reduction i.e. one gear set in series with the next gear set, and if the motor shaft wasn't hollow the differential would be completely useless. Parallel shaft helical gear reduction is a common phrase though, so maybe parallel shaft series helical gear reduction? Parallel shaft series helical gear reduction coaxial axle-motor rotor gear box assembly. Lol.

I also think the skinny countershaft that drives the far axle through the motor is also probably why the torque steer is so crazy on this beast, I'll bet the modulus of rigidity is way out of whack from right to left on this setup. Basically one axle is being driven through a torque tube, like you'd use on your air impact wrench to limit impact torque.

The motor and axle spin in the same direction in normal operation, the jack shaft with the corresponding mating helical gears should counter rotate, yeah?
 

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I think that parallel-helical gear reduction should be stated as series helical gear reduction i.e. one gear set in series with the next gear set, and if the motor shaft wasn't hollow the differential would be completely useless. Parallel shaft helical gear reduction is a common phrase though, so maybe parallel shaft series helical gear reduction? Parallel shaft series helical gear reduction coaxial axle-motor rotor gear box assembly. Lol.

I also think the skinny countershaft that drives the far axle through the motor is also probably why the torque steer is so crazy on this beast, I'll bet the modulus of rigidity is way out of whack from right to left on this setup. Basically one axle is being driven through a torque tube, like you'd use on your air impact wrench to limit impact torque.

The motor and axle spin in the same direction in normal operation, the jack shaft with the corresponding mating helical gears should counter rotate, yeah?
Torque steer is a result of the short/long shaft setup.
 

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Common misconception I think, but the shafts can be any relative length if they have the same modulus of rigidity, I learned that the other day reading somewhere, and some manufacturers put engineering effort into making sure the long axle is a fat wammer jammer to compensate.
 

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The motor and axle spin in the same direction in normal operation, the jack shaft with the corresponding mating helical gears should counter rotate, yeah?
I agree. Just looked at an animation and more pictures and came to the same conclusion.

 

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Common misconception I think, but the shafts can be any relative length if they have the same modulus of rigidity, I learned that the other day reading somewhere, and some manufacturers put engineering effort into making sure the long axle is a fat wammer jammer to compensate.
The issue is with the axle length in relation to the diff on the short side.
Most front wheel drive cars have always had the right front wheel setup as the drive output.
Somehow the length causes issue's inside the diffs output thought the sun gears. I haven't
been able to figure out any other reason and this is what is claimed by those crazy engineers >:)
 

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...and if the motor shaft wasn't hollow the differential would be completely useless.
Well the benefit of the hollow motor shaft is that it allows the differential to be co-axial with the motor, instead of having to drop it down below the motor to provide an unobstructed path to the drive wheels. It makes the whole drive unit a lot more compact.

It's really interesting to see how smartly these units are engineered these days.
 

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Discussion Starter #17
The issue is with the axle length in relation to the diff on the short side.
You're talking about the torque steer still?

Where unequal length driveshafts are used, their torsional stiffness must be made equal. This can be accomplished by making the shorter shaft hollow, and the longer shaft solid.

And I got it wrong in my post above, the glycol connections do point forward according to the animation video.

Still trying to figure it out, exactly. Problem with being a scientists/engineer is I can't stop until I perfectly understand it.
 

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You're talking about the torque steer still?

Where unequal length driveshafts are used, their torsional stiffness must be made equal. This can be accomplished by making the shorter shaft hollow, and the longer shaft solid.

And I got it wrong in my post above, the glycol connections do point forward according to the animation video.

Still trying to figure it out, exactly. Problem with being a scientists/engineer is I can't stop until I perfectly understand it.
Yes, we know what will REDUCE it ;) I was talking about the cause :x
 

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Discussion Starter #19
Yes, we know what will REDUCE it ;) I was talking about the cause :x
Ah, well my understanding is that it's due to how the two shafts react to the torque, they aren't perfect transmission mechanisms. There is a tensor absorption component, these are one of the losses that occur in the transmission (or gearbox in our case). Generally the shorter one would have a lower transmission loss (instantaneous torque) than the longer, hence a difference and therefore an imperfect alignment between the two wheels.
 

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Generally the shorter one would have a lower transmission loss (instantaneous torque) than the longer, hence a difference and therefore an imperfect alignment between the two wheels.
So you're saying that torque steer is due to the driveshafts twisting? They can't twist that much, you'd expect that by the time the wheels had revolved, say, once that the effect would have run its course.

I've never really experienced torque steer (don't have my Bolt yet) - is it a momentary thing or does it continue as long as you're accelerating?
 
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