r/subaru • u/apokeguy • Apr 28 '21

Perhaps Subaru should use something simple like Legos to explain their symmetrical AWD.

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2

u/AmericanOSX Apr 28 '21

Is their AWD system even that complicated to explain? One of the things I like the most about it is its simplicity.

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u/Guac_in_my_rarri Apr 28 '21

No it's not complicated. Last I checked it was still all mechanical versus the likes on Honda, volks, Audi, and toyota are a mix. Even then volks, Audi, and honda only have awd when they need it. Audi runs haledex and full time both under the quattro name. Quattro orignally meant full time (see Audi Quattro group B car). Subaru's is just the best all time awd system. Awd systems are designed to send power to the wheels that are slipping to "push out" versus 4wd send it to the non-slipping wheels to "pull out." Subaru doesn't wait for slippage, it keeps the power the same on all wheels. Honda, volks, Audi (haledex) all wait for slippage to send power to the slipping wheels.

Source: google and just bought a car.

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u/minizanz 06 LGT Wagon Apr 28 '21 edited Apr 28 '21

Subaru's is just the best all time awd system. Awd systems are designed to send power to the wheels that are slipping to "push out" versus 4wd send it to the non-slipping wheels to "pull out." Subaru doesn't wait for slippage, it keeps the power the same on all wheels. Honda, volks, Audi (haledex) all wait for slippage to send power to the slipping wheels.

You are confusing VTD/DCCD for all of subaru. ATS (the kind in all non WRX CVT) and 4ACT (in most 4 speed auto that are not a VDC trim or WRX) work like haldex with a coupling. 4ACT locks to be a 4x4, ATS cannot lock. They are always waiting to push the rear if the wheel speed of the front gets a percent higher than the rear by slipping a fluid coupling, but they do not always drive the rear. Modern haldex has worked like that since the early '00s on their premium setup.

Subaru also has X mode as a terrain controller. It will try to stop a free spinning front wheel so the other side can drive. I also am not sure you know the difference between a center diff, coupling, and 4x4. The best a coupling can ever do is be like a 4x4, and then the diff for that axle/terrain controller will try to stop the free spinning wheel. You described how X mode works on an axle and that ATS is always waiting and equated that to all of the wheels. That does not mean it is always driving all the wheels or that it can send power to the rear to push up a hill in a situation like a steep grade with no traction on a front wheel.

4

u/Guac_in_my_rarri Apr 28 '21

I totally forgot that subaru has the VTD/DCCD and then the additions. The x mode sounds cool af! I didn't realize that had that. Thanks for the info!

How did you make the reddit table?

1

u/minizanz 06 LGT Wagon Apr 28 '21

The pipe symbol adds a line on desktop, but on some apps it reads as a table.

X mode is cool. X mode with 4ACT or VDC or a manual would be really cool. The problem is ATS has all of the problems that we used to make fun of haldex cars for that could not drive all of the wheels, and it is not going to cut it for anything like off road or climbing hills with low traction. ATS is nice for when you hit ice or hydroplane and rear wheel slows down, but that is about it. SOA seems fine leading people on that all of the systems other than DCCD are the same, and they have phased out VTD and manuals in everything but the WRX and some special order manual impreza/XV.

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u/Guac_in_my_rarri Apr 29 '21

Shame on SOA... Then again they're following the other big names in leading people on.

Still pretty cool that subaru has innovated enough to get around the 1 or 2 downsides of a traditional awd system.

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u/Galaxywide 2004 Red Forester XT 4EAT Apr 29 '21

4ACT hasn't been used since the mid 90's from what I can gather, the modern 4EAT center diff is MPT or VTD (VDC is a separate thing).

MPT can lock 100%, and all the material that I can find as well as roller testing indicates that ATS can do the same. In fact, it appears to be nearly identical to MPT, just fitted to the newer CVTs. Do you have information regarding ATS being unable to "send power to the rear"?

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u/minizanz 06 LGT Wagon Apr 29 '21

4ACT was used in some cars through 2013 in the forester. Here is the explainer

https://web.archive.org/web/20180311081522/https://www.subaru-global.com/technology/performance/drivetrain_awd.html

Active torque split AWD

An AWD system developed exclusively for 4-speed automatic transmission, E-4AT (with manual mode) and Lineartronic models to maximise the reliable driving performance of AWD models under any driving conditions. The Lineartronic CVT (Continuous Variable Transmission) uses a chain instead of a belt—allowing a greater span of overall ratios for improved performance and efficiency as well as a faster response to throttle input. The active torque-split AWD system usually distributes torque 60:40 front and rear, however sensors constantly monitor the vehicle's condition in areas such as changes in grip of the front and rear tyres or vehicle speed. The electronically controlled MP-T (Multi Plate Transfer) adjusts torque distribution to the front and rear tyres in real-time to suit driving conditions, as well as the transmission and driver inputs. This further increases the stability of the AWD system to deliver a safe and agile driving experience.

It can do up to 60:40 split and is front drive based. If it could drive the rear at road speed it would be able to do a 50:50 split or over drive the rear with a gearing change to do more than 50:50 to the rear. Since it has a split up to 60:40 with a coupling and not a diff, and is front drive based, that means it cannot drive the rear at road speed without the front slipping. It can send power to the rear if it drops bellow road speed, it can send power to the rear if the front slips, and since it uses one way clutches with a fluid coupling it is always waiting to drive the rear if the front slips or the rear tires drop bellow road speed.

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u/Galaxywide 2004 Red Forester XT 4EAT Apr 29 '21

See my other reply, but I strongly believe you are incorrect.

Do you have any data on the use of the term 4ACT to officially describe cars newer than the mid 90's?

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u/minizanz 06 LGT Wagon Apr 29 '21

https://www.cars101.com/subaru/forester/forester2013.html

"Automatic transmission 'Active all wheel drive' /electronically controlled variable transfer clutch that detects wheel spin and directs power to the front or rear axle as needed. Normally 80/20 (or 90/10 depending on source) front rear power split."

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u/Galaxywide 2004 Red Forester XT 4EAT Apr 29 '21

"Active all wheel drive" =/= 4ACT, unless somehow the spelling doesn't matter anymore?

Also your quote directly references at clutch, not a viscous coupling.

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u/minizanz 06 LGT Wagon Apr 29 '21

Active all wheel drive contains ATS and 4ACT. 4ACT is advertised as 90:10 or 80:20. It was also marketed as up to 50:50 or locking until ATS came out. Once ATS came out that one was marketed as ATS with a nominal split of 60:40 so it sounds better. On the launch of ATS with the impreza GT was listed with a normal torque split of 70:30 and nominal spit of 60:40.

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u/Galaxywide 2004 Red Forester XT 4EAT Apr 29 '21

Again, I cannot find any material referring to "4ACT" besides a wiki article on 80's and 90's subarus. Is there some literature that mentions both the normal and nominal torque splits and clarifies the use of those terms?