Is the humvee transfer case an open transfer case?

[thoner7]

How else would it remain in 4 wheel drive all the time and not ruin road performance?

I know every truck I've ever had, when in 4x4, can't turn for snot on pavement or gravel.

 

[Bulldogger]

The NP242 (most common HMMWV TC) allows selection of Locked and Unlocked differentials. At highway speeds we run in High (unlocked), off road we put it in High Lock or Low (which is locked).
It does produce TC binding to run on clean pavement/flat ground with the TC locked, and the tech manual tells us anytime we have been offroad in Lock for a long period or the truck seems to be fighting itself, to reverse 50-100 feet to unwind the tension.
That's my understanding.
BDGR

 

[Action]

We don't lock all 4 wheels on. We are only locking the front and rear propshafts.

 

[Mogman]

Action is right, there is a differential in the transfer case that allows a variance in front and rear axle speeds while still actually delivering power to both the front and rear axles (full time 4wd) , when in H or L lock it "locks" the diferential in the transfer case forcing the front and rear drive shafts to spin at the same speed.

 

[jrtoffroad]

I did a little research and it appears it's just an open diff when unlocked. Similar to the Jeep 242, but without a 2wd option and much heavier duty. I was a little surprised it's only an open diff and not some type of limited slip, because of how capable it is unlocked. Just like in low, a little application of the brakes when a tire is in the air works great to maintain progress.

 

[Action]

I did a little research and it appears it's just an open diff when unlocked. Similar to the Jeep 242, but without a 2wd option and much heavier duty. I was a little surprised it's only an open diff and not some type of limited slip, because of how capable it is unlocked. Just like in low, a little application of the brakes when a tire is in the air works great to maintain progress.

“open diff when unlocked”?
The hmmwv diff is always the same. It does not care where the shifter is. Power will take the path of least resistance.

 

[jrtoffroad]

“open diff when unlocked”?
The hmmwv diff is always the same. It does not care where the shifter is. Power will take the path of least resistance.

Sorry for any confusion. I was speaking about the differential inside the transfer case. Open with in H, locked in HL. I thought it might be a torsen (similar to the axle diffs) or a viscous coupling as used in a NP249.

Yes, the front and rear torsen differentials don't care about the transfer case shifter position.

 

[thoner7]

I guess that makes sense. More like AWD in High and the true 4x4 in low.

 

[thoner7]

Another question..... What's the Gearing of H and Low? Is high 1:1?

 

[jrtoffroad]

Another question..... What's the Gearing of H and Low? Is high 1:1?

Correct. High is 1:1 and Low is 2.72:1.

 

[thoner7]

Crazy question but does anyone know if there's a ring and pinion setup that 1:1 or close to it? (For the diffs)

 

[Coug]

Crazy question but does anyone know if there's a ring and pinion setup that 1:1 or close to it? (For the diffs)

Not likely, as that would require a redesign of the diffs in order to fit the gears.

The bigger question is "Why?"

you're talking about increasing the output speed by a factor of 2.5-3 times faster, but also drops the input by the same ratio when driving lower speeds. That puts a lot of stress on everything before it in the drivetrain, and would be like cold molasses trying to accelerate. These things are slow to begin with, but you wouldn't even be able to drive up a gentle slope without putting the transfer case in low range. Closest equivalent I can come up with is trying to floor it when you're already doing 55mph (if in a 3 speed). Sure, you accelerate, but not much.

 

[thoner7]

The simple answer to "why" is..... Electric motor.

 

[Coug]

Still not seeing the reason to go to a 1:1 rear end gearing.
If it's supposed to be a direct drive motor for the wheels, then just eliminate the differential completely and do independent motors for each wheel.
If it's supposed to directly replace the engine, but still be hooked up through the transmission and transfer case (or even eliminate the transmission and go straight to transfer case) it should be really easy to find a motor with higher RPM ratings than the original diesel motor.

So which motor/drivetrain is it that you are considering as a power plant?

 

[Coug]

btw, the differentials are AMC 20. If you do a search for replacement gears, you likely won't find anything that's geared as high as the HMMWV already is. Because of the portal hubs, the end gear ratio is pretty low, but the differential is only about half of the gearing.

Looking around, the highest gears I see readily available are 3.31:1, and lowest are 4.88:1

Depending on series, the HMMWV should be 2.56:1, 2.73:1, or 3.08:1

You'd have to find a completely different diff to do higher.

 

[Mogman]

btw, the differentials are AMC 20. If you do a search for replacement gears, you likely won't find anything that's geared as high as the HMMWV already is. Because of the portal hubs, the end gear ratio is pretty low, but the differential is only about half of the gearing.

Looking around, the highest gears I see readily available are 3.31:1, and lowest are 4.88:1

Depending on series, the HMMWV should be 2.56:1, 2.73:1, or 3.08:1

You'd have to find a completely different diff to do higher.

BTW you will never see a even gear ratio differential, as in 1:1 or 2:1, etc, the reason is with an odd ratio say 2.56:1 every tooth on the ring gear comes in contact with every tooth on the pinion as it makes multiple turns, if for say the ratio was 1:1 then the teeth on the ring gear would come only in contact with the same teeth on the pinion every revolution which would lead to uneven gear wear and a noisy differential.
That is also why the portal hubs are not simply 2:1

 

[thoner7]

Still not seeing the reason to go to a 1:1 rear end gearing.
If it's supposed to be a direct drive motor for the wheels, then just eliminate the differential completely and do independent motors for each wheel.
If it's supposed to directly replace the engine, but still be hooked up through the transmission and transfer case (or even eliminate the transmission and go straight to transfer case) it should be really easy to find a motor with higher RPM ratings than the original diesel motor.

So which motor/drivetrain is it that you are considering as a power plant?

I'm still considering options, but there's basically Tesla motors and Danfoss motors at this point. Tesla motors can't replace the transfer case bc of the gearing, and they can't replace the diffs, ie direct drive, because of the disk brake locations on the humvee. Cost becomes prohibitive with two motors rather than one too.

 

[Coug]

I'm still considering options, but there's basically Tesla motors and Danfoss motors at this point. Tesla motors can't replace the transfer case bc of the gearing, and they can't replace the diffs, ie direct drive, because of the disk brake locations on the humvee. Cost becomes prohibitive with two motors rather than one too.

There does appear to be someone that's done disc brake relocation to the spindle.

As for the "cost prohibitive" part, it's going to cost more than the HMMWV did to convert everything to electric, so if the price difference between one larger motor and multiple smaller motors is an issue, then you might want to rethink the entire project, as things like this never go as planned and within initial budget.

The aerodynamics of the truck, as well as the weight, mean you're going to have to put in a pretty large power pack in order to have any realistic range.
Of course, if you live in a city and don't ever plan to drive very far then range isn't an issue.

It really depends on your end goals for the truck though.

 

[Action]

I was just thinking of the 1:1 diff..,,,
Wouldn’t the ring gear and pinion gear need ti be the same size? That ain’t gonna happen !

 

[jrtoffroad]

How fast do you want to go? I assume you're planning to keep the telsa transmission? What tire size are you running?

If you're running 37" tires, 2.56 gears, 1.92 hubs, and re-gear the tesla trans with a 4.5 ratio you'll have a max speed of 90mph @ a motor speed of 18000 rpm. That would be assuming you remove the t-case and run the tesla trans outputs directly to the diffs, OR run through the t-case in 1:1 high range. Personally though I'd lose the 242 t-case, and use the telsa trans as your tcase.

Quick edit: I have no idea what the HP output of the tesla motor is at 18000 rpm, I just saw that listed as the max rpm. Might not be reasonable to actually run that high.