XC60 D4 AWD rear wheel torque

[window]

I posted on another area of web site which was the incorrect. Thanks Nigel Day. So forgive me for posting the same thing twice.

Can anybody help?
In normal operation modes the maximum torque that will be transmitted to the rear wheels is 5%.
In "off road mode" has anybody any idea what the maximum torque is that can be transmitted to the rear wheels? I had a problem with wheels spin and I have been trying to clarify the situation with Volvo Customer Service for a month now with success.

[HamDenFede]

I dont think the off-road mode changes anything related to the torque distribution, as the system does not work that way. If so, the dynamic mode should also change power to the rear wheels, to make it RWD biased (e.g. like the BMW X3), which would change the driving dynamics substantially. But this is not the case either. Unfortunately.

To my knowledge the off-road mode sets the ride height (only with air suspension), lightens the steering, shows a compass in the driver display and activates the hill decent control. Maybe there is more.

The Haldex system is by design made to be FWD biased with 95% torque sent to the front wheels. This only affects the driving dynamics, but should not affect the AWD capabilities, as the system works electronically and senses many many times (read somewhere that it was up to 200 times) each second, whether any wheel looses grip and start to spin, and instantly changes the power distribution to the wheels with grip.

I'm not an engineer and the above explanation may be too simple, so maybe someone else can tip in with a few more details.

[Roosterb]

Off road mode also makes the accelerator much less sensitive.

[JC888]

Interesting, mine is a S90 but the salesman told me the system can distribute up to 50% torque to the rear wheels.

[Ringthane]

Snipped from the interweb:

“a BorgWarner Generation 5 coupling distributes torque as required based on on-going sensor inputs; as much as 50 percent of the torque can be distributed to the rear wheels when necessary.”

[Philip Fisher]

Dont forget that any 4x4 system without a locking centre diff will just spin away the power on the wheel with the least grip. Once you defeat the traction control (by being heavy on the throttle) then the mechanics and physics of any system will just spin away on one wheel.

Be light with the throttle, maybe use a touch of left foot braking, let the traction control do it's thing and it should get you out of most situations.

[Quacker]

The Haldex system, as previously mentioned, can send as much as 50% of the available torque to the rear wheels.
I can compare this to various vehicles I have a do own but to put it into perspective I have to compare it with the Honda CRV, which has a similar design of system, except that the Honda rear drive is really just an assist system, built very lightly and capable of only around 15% torque delivery.

In practical terms the Honda system is barley capable, and often fails to push the car forwards when the front wheels are on a slippery surface and the rears on tarmac, when the car is facing up a fairly steep hill. The Volvo has no such problem.

In my case, I have a bit of land that goes down a steep grassy bank that does require hill descent control to safely get to the bottom of, and then one must pick a suitable day and time of day. The CRV has barely enough engine torque in first gear [manual transmission] to get back up anyhow, but it is so steep that the weight transfers to the rear of the car. That means that the front tyres will lack traction but there will be plenty for the rears. Unfortunately the clutch pack in the back axle of the Honda which engages the back axle does not have the torque capacity to handle the torque required for rear end traction, so about 50 yards up the slope the clutch pack has already slipped enough to heat the oil in the diff [It only holds 1.5 litres] until the system throws oil temperature warning lights on the dash and cuts all transmission to the rear.
I've never ever had another 4wd vehicle do that and fail to get up the hill. It would easily reverse up, except that reverse is too high geared and the car lack oomph to do so.

The Volvo with its 50% transmission just sails up there, whether giving it some welly from the bottom or using the toque multiplying effect of the torque converter to go nice and slowly. Or any way in between. Repeatedly.

I do believe that the next new Honda will have a substantially beefed up 4wd system, possibly with the same 50% capability as Haldex.

Heavy duty systems can actually transmit 100% to either end if required, and even to one wheel, which may be needed in some twisty rock-crawling situations which are not pertinent to this kind of crossover mild 4wd car.

[Quacker]

Originally Posted by Philip Fisher

Dont forget that any 4x4 system without a locking centre diff will just spin away the power on the wheel with the least grip. Once you defeat the traction control (by being heavy on the throttle) then the mechanics and physics of any system will just spin away on one wheel.

Be light with the throttle, maybe use a touch of left foot braking, let the traction control do it's thing and it should get you out of most situations.

The Haldex clutch pack is, effectively, acting as your centre diff and apportioning torque to where it is most effective, in partnership with traction control.
Land Rover Discovery Sport and latest Evoque do not have a physical differential either in the centre or, fairly surprisingly perhaps, across the rear axle. Yet they are surprisingly capable vehicles. in demanding conditions.
They have stopped using Haldex in favour of the relatively new GKN system.

[Haldex]

Originally Posted by HamDenFede

To my knowledge the off-road mode sets the ride height (only with air suspension), lightens the steering, shows a compass in the driver display and activates the hill decent control. Maybe there is more.

From the user's manual:

OFF ROAD
Maximise the car's traction when driving in difficult terrain and on poor roads.
The drive mode provides high ground clearance, steering is light, all-wheel drive and the function for low speed control with hill descent control (Hill Descent Control) are activated. Start/Stop function is deactivated.

All wheel drive activated- meaning the front/rear torque distribution is locked at 50/50. The torque distribution is also locked at 50/50 when at standstill. Once in motion- if no slip is detected- the torque distribution is reverted to 95/5..

[Philip Fisher]

Originally Posted by Quacker

Land Rover Discovery Sport and latest Evoque do not have a physical differential either in the centre or, fairly surprisingly perhaps, across the rear axle.

You mean that they don't have a "locking" centre and cross axle diff I assume?

They would have to have a cross axle and centre diff or they would be undriveable.....