Subaru Forester Owners Forum banner

2013 AKA 2014 Forester AWD questions

('14-'18) 
15K views 24 replies 12 participants last post by  clarkjw 
#1 ·
Just ordered a 2.0i-S CVT from a dealer in Japan. I am an engineer but I still cannot understand half of what I read on the internet about the AWD design. The dealer speaks only Japanese. Can anyone reply to the following:

1) Does this model have front, center, and rear differentials, each with equal torque to both output shafts?
2) Does the center differential have a computer-controlled multi-plate clutch (MPT) between the front and rear output shafts?
3) Is the MPT clutch controlled progressively (not just binary engaged/disengaged)?
4) Regarding X-mode - if both left-hand side wheels are on ice (zero traction) and both right-hand side wheels are on dry pavement, will there be any torque to the right-hand side wheels?

Thanks
 
#2 ·
Hope you don't mind, I've tweaked your thread title to attract those that have deciphered the tech stuff on the forthcoming Forester.

The model years can be confusing with many markets defining the model years (MY) differently. Your MY13 is North America's MY14.

I'm sure we'll get a response soon.

Welcome and Cheers
Doug
 
#3 ·
You do have a front, center and rear differential, all of which are open differentials (well, the center is technically a MPT, discussed later). The actual torque split is unknown, but it is most likely the same as other Subaru's with the CVT transmission- 60% front, 40% rear (60/40). Putting it in Manual mode (or low for those who do not have paddle shifters) locks the AWD system at 50/50 split for power.

Torque side to side is equal however unless slip is detected.

The center differential is a MPT, and it is a computer controlled MPT (computer actuates a pump to increase/decrease pressure I believe). It is progressive too. It actually is completely capable of sending all the power to the front or rear, but it will never do that while driving (you have to insert a fuse to make it 100% FWD, and do some computer tuning yourself to make it 100% RWD).


As to X-Mode, if the left hand wheels have 0 traction, and the right hand are on pavement, it will transfer power to the right side. Even with X-Mode off, it will still transfer power using the VDC system. X-Mode is a more aggressive power transfer system that builds on the VDC system present in earlier foresters (09-13 US Model Year, or 08-12 Model Year for you).

This is a nice practical demonstration of the capabilities of Symmetrical AWD.

New Forester Test #2 - YouTube
 
#25 ·
Any Update on 2014 CVT Default Torque Split?

...The actual torque split is unknown, but it is most likely the same as other Subaru's with the CVT transmission- 60% front, 40% rear (60/40)...
Dear Loscaldazar -- I'm posting here primarily to provide a link to my new thread. I recently requested an update on this issue at http://www.subaruforester.org/vbulletin/f89/torque-split-default-2014-cvt-models-183729/#post1937665. Any new information available would be appreciated. -- clarkjw
 
#5 ·
To LOSCALDAZAR

Thanks for your reply.

Could you explain how the torque split front to rear can be 60/40?

As I understand it: If we drive down a straight dry road with no wheel slippage, then I assume MPT to be disengaged. I also assume there will be no traction-related application of any of the brakes. I also assume that with MPT disengaged the center differential is a “normal” design that has equal torque to both output shafts (same as the front and rear differentials). In those conditions, the torque will be equal to all four wheels. I guess we could call this a 50/50 torque split front to back.

If any wheels are slipping and MPT is engaged and locked up, the front-to-rear torque split is determined mainly by tire traction. For example, if the front wheels have no traction, all the torque will go to the rear wheels (a 0-100 split).
 
#6 ·
The MPT is always engaged. If the MPT were to be disengaged, the car would be 100% FWD (as there would be zero pressure on the clutch plate). Pressure is then increased to send power to the rear, and decreased to keep more power at the front. The clutch essentially only works one way (more pressure=more rear torque).

So the AWD system on CVT/4EAT doesn't so much as transfer power front to rear, as it does take power away before it reaches the front wheels, to send to the back wheels. Power goes center then to rear and front at the same time.

This isn't to be confused with how many competitors AWD systems work. In Honda's for example, power is sent to the front wheels, then the power is taken away from the front wheels when the rear need it. So the power goes Front to center to rear in its transfer.

The MPT system is Subaru takes torque/power from the "line of power" before it reaches the front wheels. There will be a fuse in the engine bay, in which you can put a fuse to completely disengage the MPT and make it 100% FWD. There are also mods for the 4EAT (not sure about the CVT) to "lock" the MPT in a 50/50 transfer. And then if you tinkered around with the duty solenoids and so on, you could find a way to get the pump to put enough pressure on the clutch to send all the power to the rear.

Make more sense?
 
#7 ·
LOSCALDAZAR, Yes, great, thank you. It seems that the automatic (CVT) version has only two differentials, not three. I re-read the document at http://www.subaruforester.org/vbulletin/f63/subaru-awd-explained-45312/ more carefully and sure enough - Section 1 is the manual, LSD version with a center differential. Section 2 is the automatic, MPT version and it has no mention of a center differential in either the diagram or the text. The dealer told me (I think) that there were three differentials with CVT but that was probably just lost in translation. I appreciate the time you spent on this.
 
#8 ·
The fuse to disable the MPT on older Subarus doesn't really do anything on a VDC equipped Subaru. When I had a rear tire blowout I put the fuse (located inside cab) in but it didn't disengage the rear wheels. I know because a donut spare tire spins very easily in winter conditions!
 
#17 ·
2013 AKA 2014 Forester AWD - some answers

Since my last post I have gotten a better understanding of the AWD system in this Japanese 2013 model Forester. I want to share the attached with you all. This info comes from a discussion with our dealer's mechanic, plus reviewing a lot of new material on the web. Confidence is fairly high, but not 100%.

A few notes:
> The mechanic was clear that there is a hydraulic torque converter and not a clutch, next to the engine. Another clue: A Subaru video at at 10:42 seconds mentions "no torque converter lock-up", so there you go.
> Wheel nut torque should be 10 Kg meters (98 Newton-meters or 72 foot-pounds). Note that these are 19mm lug nuts.
> Tires are rotated in a simple X pattern: swap the right-front with the left-rear.
> The mechanic said the car will move with traction on one wheel only. I have low confidence in this (maybe in X-mode only). If the attached drawing is correct, it's all up to the computer.
> I have now received the new Forester and I like it a lot - sort of a cross between a truck and a video game. I was surprised by an apparent downshift when going slowly up a steep hill. In all other cases the CVT adjusts slowly and you never feel a shift. Maybe the torque converter is unlocking?
> If the attached is correct, this is not AWD all the time. Auto companies spew a lot of hokum but very little information.

Will have to wait till next winter to see if Forester can get us up the steep hill to our house. The VW Polo left us stranded at the bottom a few times during snowstorms last year.
 

Attachments

#19 ·
It's a schematic. The drive is symmetrical as I understand it, but the doodle doesn't represent the 3rd dimension well which allows all those things to exist symmetric in a plane.

BTW. I'm not sure about the 50/50 in low for us USDM owners. I tried to get clarification of that. It's true of the SH, for sure; it's there in the manual. The manual says nothing about power split in L. The Fast Lane video does imply that in XMode it tries to keep things split evenly.
 
#23 ·
I respectfully disagree, that diagram poorly represents the beauty of our AWD in the Subaru, which is why most of us bought one :) The diagram shows pretty much a 4WD system minus the transfer case [plus one MPT].

The OP was curious about how the AWD system works in the Subaru and it is worth knowing really how that works and looks as it is unique and brilliant. The front differential is behind the engine, in front of the transmission. I do not believe it is considered a transaxle, at least in the auto. The manual may be different since they share the same lube oil.

Pic one shows a basic diagram of the Subaru AWD.

Pic two shows a picture of a bare Subaru drivetrain.

Pic three shows the drivetrain of the Suzuki Grand Vitara, similar to the drivetrain of your schematic/diagram from earlier posts.

You can google up Subaru drivetrain images and gaze upon tons of pics of our drivetrain. It really is pretty well laid out. In fact, it is very much like the Porsche 911 AWD system, only entirely backwards! lol Which is interesting since both Subaru and Porsche had a history in airplane building[Subaru] or at least supplying engines and parts [Subaru and Porsche]. If you want to see a pretty wild AWD drivetrain, google up images of the Nissan GTR R35 drivetrain :icon_eek: Functional, yes. Beautify, not so much.
 

Attachments

You have insufficient privileges to reply here.
Top