Center locking diff?

[87-Z28]

Don’t need this.

https://en.wikipedia.org/wiki/Differential_(mechanical_device)

When you have this.

Differential allows for different rotations out of a splitter. Or…a differential in rotation. Advanced transfer case in 4A, and while the rear axle output is fixed, it does allow for a differential on the front output. You can use 4A on dry pavement without issue. That wouldn’t possible without a differential…unless of course you only went straight.

written by a human. Or at least I think he is… he does like to weld, maybe he is an AI robot welder… either way I like the response.

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[CalvinT]

I would say wikipedia has not kept up. Look at that history, ends in 1958. Not sure when (Porsche in the 959 of the 1980's comes to mind) exactly but eltro-mechanical (mostly wet clutch packs) have been doing differentiation for a while now.

I wonder how the EV world is doing it, since most of it is single motor on front, rear, or both axles. Even the quad motor systems have to differentiate via computer/motor control.

I'd say Wikipedia is up to date. A differential is a mechanical device. Nothine more, nothing less.

The Porche 959 didn't have a center differential. It had wet cluch pack that acted like one in how it split power between the front and rear axles. So they have a simulated center differential and not an actual differential.

Many manufacturers have gone to simulating the function of a differential without actually having one.

 

[crenca]

I'd say Wikipedia is up to date. A differential is a mechanical device. Nothine more, nothing less.

The Porche 959 didn't have a center differential. It had wet cluch pack that acted like one in how it split power between the front and rear axles. So they have a simulated center differential and not an actual differential.

Many manufacturers have gone to simulating the function of a differential without actually having one.

Incorrect. A differential is what a differential does, differentiation, not any particular mechanical implementation of said differentiation.

It's a copy machine, not a "Xerox"

 

[Brian_B]

The failures on flat tow are usually transmission overheat since the trans oil pump isn't moving.

Getting pulled out of a ditch, or very slowly down a back road to recovery won’t hurt.

Going 70 down the interstate for miles and miles definitely will

 

[indio22]

Yes an no. In 4H or 4L the transfercase is 'locked'. In 4A 4wd engages and disengages as required automatically (with no differential) when needed. There is no true transfercase differential in any drive mode

Yeah unless the Bronco 4A clutch pack is providing a kind of slipping torque to the front axle, it seems more of a binary on/off decoupler. Unlike a typical vehicle differential that provides torque to both axles even while turning at different rates. In the most general sense both approaches could be said to allow different rotations, but otherwise are significant different in design and behavior.

On a related note, years ago I recall an aftermarket company offered a kind of vicious coupler that could be installed on a tcase front output (the front driveshaft had to be shortened as part of the install). It allowed enough slippage while still transmitting torque to use a part-time tcase full-time on pavement. I want to say those things had a habit of eventually failing though.

 

[CalvinT]

t's a copy machine, not a "Xerox"

It's neither. It's an adding machine. The differential is the spider gears and rotating cage. The crown and pinion gears just provide input to the differential. A differential (rotating cage with spider gears) adds or subtracts. It doesn't multiply. That's the job of the crown and pinion gears. In auto mechanic terminology the entire assembly is called a differential.

The fire control computer I worked on when in the Navy (MK-68, Mod 8) was an electro-mechanical analog computer. It solved the fire control problem in three axis, north/south, east/west, and vertical. It generated a target model internally and compared it to the position indicated by radar. It used three disk-ball integrators to calculate velocity in each axis. Each integrator had a differential that would add or subtract the calculated position from the measured position.

Imagine a regular differential that's in almost all autombiles. The axle shafts would be inputs, the drive shaft was the output. One input to one axle would be the calculated postion, the input to the other axle was the measured position. They'd rotate as the target moved. The output (spider cage) was the error. If calculated and measured positions matched, the spider cage didn't move. If they didn't match the spider cage rotation would represent the error which went into a feedback loop to correct the solution.

(My brain hurts after having to remember all that.)

 

[dgorsett]

It's neither. It's an adding machine. The differential is the spider gears and rotating cage. The crown and pinion gears just provide input to the differential. A differential (rotating cage with spider gears) adds or subtracts. It doesn't multiply. That's the job of the crown and pinion gears. In auto mechanic terminology the entire assembly is called a differential.

The fire control computer I worked on when in the Navy (MK-68, Mod 8) was an electro-mechanical analog computer. It solved the fire control problem in three axis, north/south, east/west, and vertical. It generated a target model internally and compared it to the position indicated by radar. It used three disk-ball integrators to calculate velocity in each axis. Each integrator had a differential that would add or subtrack the calculated position from the measured position.

Imagine a regular differential that's in almost all autombiles. The axle shafts would be inputs, the drive shaft was the output. One input to one axle would be the calculated postion, the input to the other axle was the measured position. They'd rotate as the target moved. The output (spider cage) was the error. If calculated and measured positions matched, the spider cage didn't move. If they didn't match the spider cage rotation would represent the error which went into a feedback loop to correct the solution.

(My brain hurts after having to remember all that.)

I examined with interest the firing control analog computer at the USS Bowfin sub in Pearl Harbor 25 years ago, my head still hurts.

I see that black and white video of the differential made of tinker toys once aa year and forget 5 minutes later.

Now, it all makes sense, until it doesn't

 

[crenca]

Yeah unless the Bronco 4A clutch pack is providing a kind of slipping torque to the front axle, it seems more of a binary on/off decoupler.

Well, according to the "power distribution gauge" it does vary the amount of torque (and thus is allowing 'slippage' in the clutch pack itself) to the front axle. At high steering angles (say, a tight right turn out of a parking lot) the gauge indicates less forward then rear for example. This seems to correlate with the butt dyno as well off-road, where say I'm in sand (low traction) and have a high steering angle, the rear is digging in - where as if I straighten the wheel out, or leave wheel turned and manually select 4H, then the both axles are digging.

Regardless, even if did not have this capability the computer manipulates it such that it would still be a differentiating device, even if not as elegant one such as the usual mechanical diff that splits torque evenly across the axle at all times while at the same time allowing differing wheel speeds.

 

[SierraBronco]

Yeah unless the Bronco 4A clutch pack is providing a kind of slipping torque to the front axle, it seems more of a binary on/off decoupler. Unlike a typical vehicle differential that provides torque to both axles even while turning at different rates. In the most general sense both approaches could be said to allow different rotations, but otherwise are significant different in design and behavior.

On a related note, years ago I recall an aftermarket company offered a kind of vicious coupler that could be installed on a tcase front output (the front driveshaft had to be shortened as part of the install). It allowed enough slippage while still transmitting torque to use a part-time tcase full-time on pavement. I want to say those things had a habit of eventually failing though.

Well, according to the "power distribution gauge" it does vary the amount of torque (and thus is allowing 'slippage' in the clutch pack itself) to the front axle. At high steering angles (say, a tight right turn out of a parking lot) the gauge indicates less forward then rear for example. This seems to correlate with the butt dyno as well off-road, where say I'm in sand (low traction) and have a high steering angle, the rear is digging in - where as if I straighten the wheel out, or leave wheel turned and manually select 4H, then the both axles are digging.

Regardless, even if did not have this capability the computer manipulates it such that it would still be a differentiating device, even if not as elegant one such as the usual mechanical diff that splits torque evenly across the axle at all times while at the same time allowing differing wheel speeds.

 

[Brian_B]

Well, according to the "power distribution gauge" it does vary the amount of torque (and thus is allowing 'slippage' in the clutch pack itself) to the front axle. At high steering angles (say, a tight right turn out of a parking lot) the gauge indicates less forward then rear for example. This seems to correlate with the butt dyno as well off-road, where say I'm in sand (low traction) and have a high steering angle, the rear is digging in - where as if I straighten the wheel out, or leave wheel turned and manually select 4H, then the both axles are digging.

Regardless, even if did not have this capability the computer manipulates it such that it would still be a differentiating device, even if not as elegant one such as the usual mechanical diff that splits torque evenly across the axle at all times while at the same time allowing differing wheel speeds.

This is correct - 4A T-case can vary the torque to the front. The clutch pack has a sliding ball enagement (Sierra's video shows that) - the more the ball slides forward, the more the clutch grips, the more torque goes to the front.. all the way until you have full engagement - total 50/50 split front/rear. It has no control over which wheel - it just relies on the open diff to take care of that, which is how you can still turn without totally binding up -- unless you hit the locker (do not do that).

The Part Time T-case is binary - it's either off entirely, or full 50/50 split and it's totally locked front to rear, there's no in between.

 

[Brian_B]

I examined with interest the firing control analog computer at the USS Bowfin sub in Pearl Harbor 25 years ago, my head still hurts.

I see that black and white video of the differential made of tinker toys once aa year and forget 5 minutes later.

Now, it all makes sense, until it doesn't

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