Thread: All wheel drive vs 4 wheel drive vs ?

OK we are probably reading it the same way but tripping over descriptions.

I'm saying that the rear drive shaft is permanently driven so that whenever the gearbox output is turning, so is the rear diff. The rear diff of course is still a differential and relies on either TC or the e-locker to manage slip when traction is uneven between left and right.

The front drive shaft default to not being driven. It requires a clutch to transfer torque from the TC or rear shaft (unclear technically which bit). However it's "1:1" in the sense that the front shaft and rear shaft cannot be driven at different speed other than if the clutch slips such that the front shaft goes *slower* than the rear. Now think about that for a sec. When do you ever have a situation where the front wheels should be spinning slower than the rears? Never. Front wheels need more speed than rears because their turning radius is larger. There's no centre differential function whatsoever and the clutch doesn't make up for that.

So it's like an automatic switch between RWD and traditional 4WD without the centre diff. Because it's automatic you don't have to get out and lock hub and you don't have to worry about wind-up etc.

The precursors to this that I've seen (eg Haldex) were all front-wheel-drive based with torque sent to the rear as needed. That makes much more sense from a clutch vs differential perspective.

We are in furious agreement TB.

The engagement is 1:1 but the amount of torque delivered could be variable (don’t know if this system supports that). If torque was variable to the front it will give the Defender a far more dynamic driving style with a rear bias and only the right amount of torque to the front, reducing under steer which is the killer of most simple all wheel drive systems.

Sure it’s another thing to go wrong and wear out but they’re generally known to be extremely reliable systems.

Originally Posted by DiscoJeffster

The engagement is 1:1 but the amount of torque delivered could be variable (don’t know if this system supports that). If torque was variable to the front it will give the Defender a far more dynamic driving style with a rear bias and only the right amount of torque to the front, reducing under steer which is the killer of most simple all wheel drive systems.

You gotta remember that without a centre differential, there's no way to drive the front shaft faster than the rear. That means this system makes understeer *worse*, just like it does in old-school part-time 4WD.

And because the rear is permanently driven, the only scenario where the front could be using more torque that the rear in this system is when the rear has lost traction and the front has all the grip.

If its used in the Defender to reduce fuel burn, then the front wheels would be programmed to only be used when absolutely necessary, one would presume.

In the Jag link in a previous post,there is no mention of fuel burn, just vehicle handling.

Interesting they also admit to looking at all the other manufacturers systems, which seems to point to them wanting to copy something another manufacturer has already designed and uses, but couldn't find anything that would suit their application,and what they wanted to do.

Originally Posted by scarry

...In the Jag link in a previous post,there is no mention of fuel burn, just vehicle handling.

I also find it interesting that JLR makes a big deal out of the Jaguar's system but is deathly quiet about that in the Defender. One reason might be that we long-term owners can be challenged by anything that wasn't in the Series 1 Land Rover . We tend to be a bit luddite-ish and conservative.

Originally Posted by one_iota

I also find it interesting that JLR makes a big deal out of the Jaguar's system but is deathly quiet about that in the Defender. One reason might be that we long-term owners can be challenged by anything that wasn't in the Series 1 Land Rover . We tend to be a bit luddite-ish and conservative.

It is advertised as a remote area go anywhere off road touring vehicle.
So adding more complications may put people off.

They did beat their chests about it having 85 PCB's,but that seems to have quietened down as well.

It looks like a Haldex type system that's been used in all wheel drives for years.
It drives well, relatively cheap to manufacture and torque can be apportioned to influence driving characteristics, ie. great on something like a Golf but IMO it's not a 'serious' 4wd system, where you sometimes need the driveline locked to proceed.