Torque Split & description of the MT/AT AWD system (Merged)

In other words, vdc is ok on road and in mild off road conditions.

When it comes to autos, I will leave it to others who know more about them.

You might be underselling VDC.

I would say it is brilliant on-road in difficult driving conditions with low friction surfaces. On high friction surfaces, it is only relevant if the driver exceeds the tyres' limit of adhesion. Off-road, it is superior to most other systems in shallow mud and on all types of sand but struggles on surfaces with variable levels of traction on steep grades.

The biggest body of evidence for this view is the almost universal adoption of VDC or a variant of it by vehicle manufacturers in vehicles that are intended mainly for on-road driving with occasional excursions in light to moderate off-road conditions.

Traditional 4 wheel drive technology is increasingly being reserved for industrial/trade vehicles or those that are manufactured with cost as the major consideration.

This is my opinion and should in no way be interpreted as being disrespectful of those whose opinions may differ. I believe in free speech. :)
 
My comments on vdc are confined to what it offers for off roading, which is minimal at best. I am not criticising what it can do in other situations
 
Given the front/rear split figures, it sounds like a WRX auto. Its a pity they didn't use a Forester and give us some off road data. Good find nevertheless.

The split correlates with some of the information I've read about the SVX 4EAT (JDM, EUDM - is there such a thing? and ADM), which i believe was the first VTD box (previous models had active torque split).
 
I believe you may be right. I remember reading something about that too. There was a very strong rear bias in the SVX.
 
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So sand ant mud and snow is not offroad ? Depends where you live i guess. With vdc off in those situations that i testedit it night and day difference in low speed. Thats why you all those forester do everything with good momentum.
 
Ok, so it does provide some improvements in mild off roading. So does having limited slip diffs. Have you compared back to back with a car with a viscous rear diff, or with upgraded diffs? If not, it would be interesting to see how each would go in circumstances where you have found vdc to be effective.
 
The torque split on the SG front:rear is about 50:50 in balanced situations. Of course, this will vary according to the conditions. IOW, for most the start point is around 50:50 (some models start at 60:40, and some at 45:55). Subarus do not have 'on demand' AWD. They have full time AWD.

Blather on the net about some Subarus having 90:10 is just that - blather. No Subaru has AWD that starts at 90:10.

It is all but impossible to even notice when the rear vLSD locks up, unlike any mechanical LSD. I have noticed it lock once in nearly 30 years of ownership and about 300K kms.
 
The reality is that I only had front wheel spin until I stopped, then I had wheel spin everywhere. I don't really care what the numbers were. I just wanted to get up that trail. I did, but I had to go up from the other side🙃
 
The problem with the auto box is that it’s permanent front wheel drive with an electronically activated clutch pack setup that sends power and torque to the rear wheels. This is why the lock up switch is such an effective mod.

As for the locker, as others have said, it’s locked all the time. Once one wheel rotates faster than the other via the larger outside ark of cornering, it is unlocked and allowed to freewheel.

If your Forester will not go places that a minivan would, there's something wrong with your Forester.

Or your driving technique in a vehicle with independent suspension all round.

Cheers

Bennie
 
The problem with the auto box is that it’s permanent front wheel drive with an electronically activated clutch pack setup that sends power and torque to the rear wheels.
That's not my understanding, Bennie. Do you have any reference for that?
 
I’d have to dig up the reference in the WSM, but that fuse under the bonnet for 2wd disables the mechanism that engages the rear wheels. The only way to do that is to have a permanent drive to the front wheels. No centre diff is going to do that for you.

That engagement mechanism, clutch pack or not, when it flogs out you only have front wheel drive.

This could be the earlier autos, but I’ve always through this was how the 4eat worked with its AWD.

Cheers

Bennie
 
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There is no fuse for "2WD" in either my SG manual or our SH 4EAT.
 
Manual never had them as they had a mechanical AWD device in the form of the centre diff, which is just a modified version of your front and rear diff.

Subaru must have done away with that fuse as they were either rarely used or they came up with a better AWD centre device.

Cheers

Bennie
 
There was an empty space for one in my 5MT manual Impreza (1993) IIRC.
 
I've got an empty fuse holder in the SVX that says Diff Lock. Not sure what it actually does..
according to google in boxes from a similar era it does in fact lock the Diff to 50/50. Might have to give it a try on dirt but a bit scared of breaking things at the moment.
 
I've got an empty fuse holder in the SVX that says Diff Lock. Not sure what it actually does..
according to google in boxes from a similar era it does in fact lock the Diff to 50/50. Might have to give it a try on dirt but a bit scared of breaking things at the moment.
make switch from it
 
The problem with the auto box is that it’s permanent front wheel drive with an electronically activated clutch pack setup that sends power and torque to the rear wheels. This is why the lock up switch is such an effective mod.

As for the locker, as others have said, it’s locked all the time. Once one wheel rotates faster than the other via the larger outside ark of cornering, it is unlocked and allowed to freewheel.



Or your driving technique in a vehicle with independent suspension all round.

Cheers

Bennie
That's the system that most AWDs are using but the electronic part of Subaru's AWD, as well as Audi's, is controlled via the Transfer Control Duty solenoid which only adjusts the torque distribution to the rear. Without such solenoid, there is proper torque bind or there is always torque to the rear, proving that all Subarus, and Audis, are AWD all the time (active AWD). It's actually a fool-proof system that gives owners torque bind or more torque to the rear when the solenoid wears out. So the electronic part is the control, not the activation. The ones that are electronically controlled are the ones that are reactive systems from Toyota, Honda, Kia, etc.

We already know that Subarus are AWD all the time but since the TCU codes are closed-source, we can only use whatever we can measure. That's where FreeSSM or any SSM comes in. According to FreeSSM, 1A on the solenoid = 100% torque transfer to the rear, which rarely happens. 0.16A is approximately 42% transfer to the rear. One must think that when the solenoid is out, it would give 0A and no transfer to the rear but that is where the mechanical fail-safe of the design comes in. The solenoid just completes the AWD circuit and without it, there is nothing limiting the torque transfer to the rear, hence the torque bind. FreeSSM proves also that the system is not only active but extremely dynamic.

These data have already been discussed and documented extensively in subaruoutback.org. There results below from ntippet can be replicated by Subaru dealerships when you ask them to do it for you:

Discussion Starter • #38 Oct 22, 2011 (Edited)

Alright I have a whole new set of measurements ready.

I will need to classify these into categories from now on.
The TCU Stratgey Has Very Dynamic AWD Control
But we already knew this right?

Transfer Solenoid % engagement is directly affected by:
-Wheel Speed
-Gear Selection
-Throttle Position

These are the first set of measurements I took for the Transfer Solenoid.
From now on I will be referring to them as:
Static Control
This is what the TCU outputs when the vehicle is stationary with no throttle input.
Gear | Duty Cycle | Amperage
P - | 5% | .01A
R - | 42% | .16A
N - | 5% | .01A
D - | 42% | .16A
3 - | 42% | .16A
2 - | 42% | .16A

1 - | 55% | .27A

I then stated the following:

- Full lock up is achieved in 2 ways:
- 1: 100% Throttle Engagement
- 2: TCU detects front wheel slippage from the wheel speed sensors (speed differential between the front and rear wheels)
- This delivers a maximum of 95% duty cycle and 0.95 A to the solenoid.

Clarification
1: Vehicle stationary, in gear, 100% throttle - This can also be called a stall test, requires high brake input to hold the vehicle stationary.
2: This test I will have to confirm once the snow files, I know it will increase %, but by how much is the question...

Now we move into the next category of measurements.
From now on I will be referring to them as:
Dynamic Control
I have only taken the % duty cycle, posting the V & I is redundant.
This is how the transfer solenoid is controlled in the real world, driving down the road.

4th-TCC Engaged
WOT - 43%
Cruise - 38% @ 60 MPH
Decel - 41%

4th-TCC Off
Did not get these measurements, would have had to eliminate the TCC temporarily to get this.

3rd
WOT - 52%
Cruise - 38% @ 50 MPH
Decel - 42%

2nd
WOT - 60%
Cruise - 42% @ 30 MPH
Decel - 43%

1st
WOT - 95% - drops off to 80% & lower as speed increases beyond 1-2MPH
Cruise - 44% @ 10 MPH
Decel -

The highest I could get the duty cycle to jump was in 1st gear full throttle @ about 1-2 MPH.
From here the faster the car travels the more the duty cycle drops off.
Once any speed is measure through the wheel speed sensors values drop off 5-10% or more.

Another interesting note:
If a change in the Correction of Transfer Duty Ratio has been set in FreeSSM it will make the change across the board under all conditions.
The key:
Every 1% change in FreeSSM results in an equivalent 1% change of duty cycle for this solenoid.


The FWD impression is when the centre diff wears out due to donuts, uneven tire wear, etc. Where the wet clutch isn't as effective in holding torque anymore. That's the extreme, though, as the Transfer Control Duty solenoid fails first and when binding is felt on high traction surfaces, the owner should replace the the solenoid immediately to save the centre MPT diff. The same feeling is felt when the viscous centre diff of manual transmission wears out completely. Cheers.

EDIT: I formatted the results differently so they are easier to see.

EDIT 2: My brother experienced the solenoid failure first hand on his BP5's 4EAT so he initially went to a non-Subaru workshop and the mechanics all said, "What happened? It's like the centre diff is locked fully like some 4x4s!" They had to call in a Subaru mechanic to diagnose the issue. The mechanic explained that with the solenoid failure, the mechanical system just isn't controlled and would send the same amount of torque to both axles all the time. I drove the car before that and felt like going off-road, haha.

EDIT 3: FreeSSM can adjust the average amperage for each gear. I have discussed this with some Subaru mechanics and they said that raising the first gear average from 55% to 60%, which they can do, then using the diff lock mod, which they won't do, will significantly increase the TorqueMasters locker performance significantly. Some PNW mechanics are already doing the mod, they said.
 
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The FWD impression is when the centre diff wears out due to donuts, uneven tire wear, etc. Where the wet clutch isn't as effective in holding torque anymore
And this is why my thinking was/is that they’re permanent front wheel drive with an attached AWD device.

Cool programming around the lock and shift points etc. It would be good to have a switch to completely disengage the rear when in car parks with the rear locker ;)

Cheers

Bennie
 
@El_Freddo IF(I don't know)the only damage is the solenoid after 60k, it may be worth driving in FWD whenever you don't need the rear wheels helping move you forward. I do have a friend that drives his Outback in FWD 8 months a year other than when he needs it for offroading. He's driven like that for over 80,000km and it seems fine. I've ridden in it up some really steep roads with +15cm of snow. Roads we'd never make it up with FWD only and all season tires.
*I have no idea how hard the solenoid is to replace. But if you can do it without opening things up, I'd be willing to replace it on a regular maintenance cycle to ensure it doesn't fail at a really bad time.
 
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