Differential geek video
- Thread starter Yorkie Z
- Start date
Hope this works from phone in a taxi in Paris...
Ok so let me give my simple take on it and see if this helps.
Following the demo video it's clear to see that in an open diff arrangement power moves to the wheel, travelling furthest, be that driving or slipping. You can see that on any normal car which leaves a single traction line or one wheel spins out on ice/ gravel.
That I'll describe as 1WD. Adding a locking or limited slip device makes it up to 2WD.
Now looking at a 4x4 consider in basic form it would have 3 diffs., one in each axle and one between the front and rear axle (usually in the transfer case), for the same reasons that a car needs to allow 1 wheel to move more or slip, so does a 4x4 as each wheel has to move at different speeds when turning.
That in effect allows all drive to slip out of one wheel and again results in 1WD.
If we lock the transfer case or centre diff and split power equally to front and rear we get 2 open diffs. (One in each axle) and get 2wD.
If we now lock the rear axle and front axle all 4 wheels are equally powered and we get 4WD.
Hope that makes sense...
Next lesson we can see how different arrangements get around this using combinations of slipping diffs, locking diffs, torque vectoring and various braking technologies to stop wheels spinning out.
Ok so let me give my simple take on it and see if this helps.
Following the demo video it's clear to see that in an open diff arrangement power moves to the wheel, travelling furthest, be that driving or slipping. You can see that on any normal car which leaves a single traction line or one wheel spins out on ice/ gravel.
That I'll describe as 1WD. Adding a locking or limited slip device makes it up to 2WD.
Now looking at a 4x4 consider in basic form it would have 3 diffs., one in each axle and one between the front and rear axle (usually in the transfer case), for the same reasons that a car needs to allow 1 wheel to move more or slip, so does a 4x4 as each wheel has to move at different speeds when turning.
That in effect allows all drive to slip out of one wheel and again results in 1WD.
If we lock the transfer case or centre diff and split power equally to front and rear we get 2 open diffs. (One in each axle) and get 2wD.
If we now lock the rear axle and front axle all 4 wheels are equally powered and we get 4WD.
Hope that makes sense...
Next lesson we can see how different arrangements get around this using combinations of slipping diffs, locking diffs, torque vectoring and various braking technologies to stop wheels spinning out.
Cheers guys - in old skool serious 4x4's you need a real time understanding of this, locking and unlocking the diffs to get traction, steer and sometimes intentionally spinning wheels to clear mud or snow from them.
Get it wrong and you stop, roll or slide into something...
Get it wrong and you stop, roll or slide into something...
cj10jeeper said:
Actually it's not quite 1WD.
An open diff is always a force balance.
Say, for instance, that your engine has enough power, and the car has a classic 2wd setup with open diff.
1 wheel has a lot of grip (for instance 1000N to get the wheel to spin) and the opposite wheel has less grip (for instance 10N to get the wheel to spin).
The total maximum force propelling the car will be 20N, as the wheel with a lot of grip will always recieve the same torque as the wheel with less grip can put to the ground.
With an open diff you get a maximum of twice the propulsion force of the gripforce from the wheel with the least grip.
For 4wd with all open diffs it will be 4 times.
Obviously if 1 wheel has no grip (for instance freewheeling in the air), the total propulsion is 4x0...
I fully understand and agree your point. My illustration is a theoretical explanation in line with the simplistic video. Wasn't getting into torque and driving on nice tarmac roads
A car with a wheel on ice will just spin out. A cross axled 4x4 won't move even with the transfer case locked.
Lock the axles and hey presto we can move.
I've spent £20k on trick gear on 2 4x4's to overcome the on road useful open diffs
Edit - back to my beer and view:
A car with a wheel on ice will just spin out. A cross axled 4x4 won't move even with the transfer case locked.
Lock the axles and hey presto we can move.
I've spent £20k on trick gear on 2 4x4's to overcome the on road useful open diffs
Edit - back to my beer and view: