XC60 - Need information on AWD

[ra5040]

Many thanks for the info and advice.

First of all, I do have a spare set of wheels with winter tyres, but the point about tyres is well made!

I understand that the AWD system is quite complex (and also that it is similar to the Freelander, Evoque etc., having come from the same stable). I've looked at a bunch of Youtube videos and it's clear that in some cases where the car got stuck the driver really didn't know what to do.

There's a Volvo video that shows a 3-wheel spinning scenario http://www.youtube.com/watch?v=ZdvBqEwEfWU. It's clear that in this situation (it's clear because the guy says so ) that you need to apply more power to get torque on the non-spinning wheel, so I guess the rear diff must be some sort of limited slip differential ... and probably what the car does is to apply the breaks to the rear slipping wheel, so that torque is transferred to the non-slipping wheel.

However, in the video the guy doesn't say whether to leave DSTC on or to put it into sports mode ... or what sports mode actually does.

I'm one of these people who needs to understand how things work in order to work them properly. Also I'm just interested. Thanks for the technical information Clan ... but when you say that the differential is a normal one, what do you mean? Is it open, torsen or what ... ? What does a conventional front end mean? I presume the front also has a differential ... what kind? What happens when DSTC is on aor off in slip conditions (just basic slip like on snow or ice, with none or some wheels on gravel)? I understand the Haldex, pretty much, but I have no idea what kinds of differential are on the front and rear and how the breaking attempts to control the slipping.

As an example, the best we're going to get (if I understand it correctly) is 50% power split between front and rear. If the car applied breaking to both front wheels the engine would stall, so in taking off on a slippery surface if both front wheels are slipping there's nothing the car can do about it (except engage the Haldex). If one of the back wheels slip then presumably it can transfer some of the torque to the other wheel - but if that wheel starts to slip then there's nothing the car can do. So, as a driver, what do I do, or rather how do I know what to do? How does turning 'off' DSTC help (if it does)? Will the Haldex still engage if I do the usual thing of trying to take off in 2nd or 3rd gear?

I would rather find out now than when I'm stuck !

Thanks!!

[Crockers]

Jeez.....if Iwas that into off olading I'd have bought a Disco.

[richy2]

Yeah I must admit, these are design to be automatic and 'intelligent' with their AWD operation. the only advice I follow is that if I'm on really soft/muddy/icy ground I switch the DTSC off but only when going slowing, setting off or maneuvering, I'd be leaving it on when on road in fact don't think I've ever switched it off for road use even in winter.

Drive and forget, might sound less involved than some systems but I've found it to be very capable just letting it do it's own thing, if you have an auto box I do find outing that in sport mode also helps keep the gears a little higher, stops it up changing just when you are fighting for traction, you can also manually control the gears and also set off in Winter mode which is manually putting it into 3rd gear, on the auto box still.

[ra5040]

Originally Posted by Crockers

Jeez.....if Iwas that into off olading I'd have bought a Disco.

Quite right ... except that the Discovery costs 50% more, emits nearly twice the CO2 (so 4 times the road tax in this part of the world, quite apart from environmental issues), uses 50% more fuel (diesel in both), is slower and ...

BUT ... even if you did have a Discovery or Range Rover ... you would still need to know how to drive it offroad. So why the objection to finding out how best to drive the XC60?

[pauljoz]

Turn the DSTC off and you need to apply more throttle to get torque transfer.

Remember this and you will get stuck less often - possible further and deeper though :-)

[ra5040]

Hi,
I've finally got some answers from Volvo. Perhaps you may be interested:

• Front and rear differential mechanism –
o Standard diff mechanism, there is no limited slip in the units, all slip at the wheels is control electronically by the brakes
• DSTC effect on different wheel spin scenarios (one wheel spin, both wheels spinning on one axle, wheels spinning on one side of the car, 3-wheel spin)
o The DSTC system works in combination with the AWD Haldex system. So depending on the wheel(s) spinning different things will happen
1. One will spin (front wheel): DSTC system will: Apply the brake(intermittently) to the spinning front wheel, this will transfer power to the other front wheel with traction and reduce throttle opening, reducing power.
2. Both front wheel spinning: DSTC will reduce throttle opening to reduce power. Haldex system will: Detect difference in speed between the front and rear wheels(Front rotating faster), and engage drive to the rear wheels.
3. Both wheels spinning one side: DSTC will reduce throttle opening, and apply the brake to the spinning wheels to transfer torque to the wheels with grip. Haldex system is already engaged if front and rear wheels are spinning on one side.
4. 3 wheel spin: Systems will combine braking and AWD control to apply power to the wheels that have the most grip
o These scenarios can be difficult to explain, as each wheel will have a different amount of grip if moving over a very slippery surface, the system will look at the individual wheel speeds, and find the ones which are spinning fastest and use DSTC function, brakes, and AWD haldex unit to apply the power to the slowest moving wheels(Slowest rotating wheels have highest grip). The system keeps dynamically looking at the wheel speeds always changing to push power to the wheels with most grip.
• Effect of Sports Mode on DSTC
o In sport mode, Torque reduction is switched off, meaning that the wheels should be allowed to spin. It will not change the AWD system. Sport mode reduces the Active Yaw Control function, this is very useful in slippery conditions, so if the customers uses this to move off of a slippery surface, then it is good to switch it back on when they can. There is also a note on Sport mode in the owner’s manual, see attached, that the function is good for pulling away on slippery surfaces.
• How to take off on a slippery slope (DSTC on/off, 1st/2nd gear, throttle etc)
o This depends on how slippery the surface is and how steep the climb is. The AWD/DSTC system will attempt to apply the power to the wheels with the most grip, and will also reduce the throttle opening if the driver is applying to much power, but normal rules apply pulling away on snow, if customer thinks he could get better performance pulling away in second then this can be done. Also it is possible that switching off DSTC will help. In slippery conditions where power is needed, and if the customer has good vehicle control and experience then this can be used.
• Power to apply when there is wheel spin (for example, if only one wheel has traction but the car isn’t moving forward, should more power be applied?)
o The system will reduce the throttle opening if the wheels spin, so applying more power will not improve grip with DSTC switched on. To apply additional power to pull out of a 3 or 4 wheel slip DSTC will need to be switched off.
• Whether or not to use Hill Descent Control in slippery conditions
o Hill Decent Control is design for slippery downhill conditions so will provide the best grip
• Use of wheel chains
o front wheels only? If so, is there any way of preventing power to the rear wheels
o all four wheels?
1. We only have snow chains available for the front wheels, and there is no way to switch off power to the rear wheels.

[Westyman]

A bit o/t this but it all sounds so familiar to my past working life dealing with wheelslip on railway vehicles - i.e. Preventing wheels locking when braking. Steel wheels on steel rails is a whole lot different to rubber tyre on Macadam but similar scenarios to those in ra5040's post had to be considered. If this then that.....etc
I found Volvo's response interesting.

[JJJ]

Hi there, this is my first post on this forum - and I'm with ra5040.

Presently driving a - mostly Volvo XC90 - 2007 Freelander 2 Si6, I am also considering a late previous generation Volvo XC60 as replacement.

Part of this selection process consist of EXACTLY the info that the OP was looking for - thanks for that footwork. After all, we both know how well a LR2 works offroad.

According to some sources, i.t.o. drivetrain layout, the XC60 is basically a clone of this car, with a different skin. But it works differently.

My efforts to find out HOW differently, led me to registration on this forum.

E.g. is it possible to lock the rear wheels in 4x4 instead of waiting for the Haldex to kick in. Surely that should give better control than waiting for wheel speed difference detection, no matter how fast?

I noticed that Volvo responded that there is no way to disable the rear wheels. I am not convinced that this is true.

The Haldex clutch of my LR2 recently started "biting" - the effect is similar to driving on a hard surface with difflock on, with the rear wheels fighting each other. I googled across a temporary fix to pull the Haldex fuse in the boot of the car. I did so, and the issue was gone, as the Haldex is now "open". I could now drive the car to a repairer without causing more damage.

Studying a downloaded owner manual of the XC60, I noticed that there is a fuse in Fusebox A: Allwheel Drive Control Module (F29). I would at least pull that and see what it does. There is ALWAYS some bypass - just not advertised.

E.g. in dune trips across Namibia, the issue of DSC/ESP - which cuts applied throttle and cannot be disabled via a user function on some vehicles - is bypassed by disconnecting one of the wheel speed sensors. Seeing as the TC control unit realizes there is one wheel it knows nothing about, it disables itself. At least now you can maintain the required 80km/h plus approach speed up the dune to get to the top.

If there is any new information on this topic - since 2013 - e.g. possibly Haldex update from GEN4 to GEN5 (my LR2 is still on GEN3) I would appreciate any inputs.

[Tannaton]

Originally Posted by Crockers

Jeez.....if Iwas that into off olading I'd have bought a Disco.

I had a very smug moment a few years ago towing a Discovery with horsebox attached out of a muddy field with my 160k mile 2003 XC90.

To be honest the issue was tyres, the Disco had summery road type tyres and my 90 is shod with Cooper Discoverer (but only MS2's not the mud terrain type STT's)

[Tannaton]

Originally Posted by JJJ

Hi there, this is my first post on this forum - and I'm with ra5040.

Presently driving a - mostly Volvo XC90 - 2007 Freelander 2 Si6, I am also considering a late previous generation Volvo XC60 as replacement.

Part of this selection process consist of EXACTLY the info that the OP was looking for - thanks for that footwork. After all, we both know how well a LR2 works offroad.

According to some sources, i.t.o. drivetrain layout, the XC60 is basically a clone of this car, with a different skin. But it works differently.

My efforts to find out HOW differently, led me to registration on this forum.

E.g. is it possible to lock the rear wheels in 4x4 instead of waiting for the Haldex to kick in. Surely that should give better control than waiting for wheel speed difference detection, no matter how fast?

I noticed that Volvo responded that there is no way to disable the rear wheels. I am not convinced that this is true.

The Haldex clutch of my LR2 recently started "biting" - the effect is similar to driving on a hard surface with difflock on, with the rear wheels fighting each other. I googled across a temporary fix to pull the Haldex fuse in the boot of the car. I did so, and the issue was gone, as the Haldex is now "open". I could now drive the car to a repairer without causing more damage.

Studying a downloaded owner manual of the XC60, I noticed that there is a fuse in Fusebox A: Allwheel Drive Control Module (F29). I would at least pull that and see what it does. There is ALWAYS some bypass - just not advertised.

E.g. in dune trips across Namibia, the issue of DSC/ESP - which cuts applied throttle and cannot be disabled via a user function on some vehicles - is bypassed by disconnecting one of the wheel speed sensors. Seeing as the TC control unit realizes there is one wheel it knows nothing about, it disables itself. At least now you can maintain the required 80km/h plus approach speed up the dune to get to the top.

If there is any new information on this topic - since 2013 - e.g. possibly Haldex update from GEN4 to GEN5 (my LR2 is still on GEN3) I would appreciate any inputs.

All Volvo's with traction control have a disable DSTC (or more specifically "Spin Control") function. On earlier models (like P1 XC90) it is a button on the dash, on later models (like XC60) it's inconveniently in a menu but this disables the mechanism for the traction control to override the commanded throttle - i.e. for use on viscous surfaces like sand and mud. Applies equally to 2WD and AWD cars.