Japanese Transmission in American SVX

[TomsSVX]

The difference between the JDM and USDM tranfer clutches...

USDM. The car is essentially FWD while the clutches engage the rear wheels when needed.

JDM- The car is essentially AWD except when the clutches release the car to make tight turns etc....

That is my understanding as of now.

Tom

[Nomake Wan]

Tom- Hate to disagree you here, but VTD is not 50/50 until you get into trouble. It's 35/65 until you get into a traction situation. So it operates like ours in terms of when to go 50/50... it's just which wheels are powered and how much that is the difference.

[b3lha]

Originally Posted by oab_au

The system that the rest of the world have is a compound planetary gearset that provides a 36% front / 64% rear torque split. This is due to the number of teeth on the pinions and sun gears that provide that split.

The drive comes in to the front sun gear, the rear wheel drive is from the rear sun gear. The front drive is from the carrier, so the torque split is fixed by the gear ratio. A multi plate clutch is between the rear sun gear and the carrier to bring the torque back to 50/50.

The US system is different because, you can't turn one set of wheels off, in the RHD system, to run it on a two wheel dyno.

Originally Posted by Trevor

Please keep the info on this one coming Harvey. You have started a very interesting and important thread.

Taken from this thread:
http://www.subaru-svx.net/forum/showthread.php?t=4496

There are some scans of the Aussie service manual in Harvey's locker

[Nomake Wan]

Yay, my translation was right! Multi-plate clutch system! Though it does say 35/65 split... I guess they're rounding that 36/64 number? Which also explains why the "FWD" fuse in the rest of the world is actually the "50/50" fuse.

Thanks Phil and Harvey!

[subaru-jin]

Awesome. Thanks for all the info.

My mechanic couldn't find anything wrong under the rear transfer case so he put it back together and it stopped making that noise. The only thing left is a little bit of noise from the aftermarket exhaust contacting the crossmember.

He did also mention that he saw that planetary gearset in there.

It ended up costing a great deal less than I had feared.

I'm happy now. The car drives great!

-Jim

[Nomake Wan]

Reviving this thread because I found quite a bit of information accidentally on a source I had around for a long, long time. Silly me for only reading the 4WS section of that site and not focusing on the JDM/VTD sections.

While there was lots of good info on the site, the best one relating to this topic is the following diagram (which closely resembles the one from 2001 I found on a Japanese website previously):



I can read a bit of it, but the real meat (the technical drawings) have text that's small enough that the kanji is very hard to make out. The gist of the article here (by the way, only half of the article is presented; the other half is missing from the site) is a history of Subaru transmissions. The beginning details all the workings of the 4EAT we know and love/hate (though they call it E-4AT), and then the third paragraph transitions to detailing the ECVT introduced on the Justy in '87. World's first continuously variable transmission. Dang it, Subaru, why do you always have to be ahead of the times!?

Anyway, why I believe only half the article is presented is because despite the ECVT being discussed in detail, all of the photos on that page refer to the E-4AT transmission. Specifically, they detail the VTD-4WD version that Japan used. Since it does in fact detail the VTD (and never once mentions the SVX), it makes me wonder if VTD was in fact found on the Legacy in 1989.

Upon doing research in that vein (thank you Wikipedia Japan), I have found that while the options the first-generation Legacy had were rather interesting, it did not come with VTD. In fact, the article states that the VTD installed in the SVX was a mere evolution of the ACT-4 and 4-channel ABS system used in the Legacy RS. Which would be true. So the theory that the SVX was the first VTD-equipped car holds true.

Not that I think it needs explanation, but the green box above the transmission illustration is an exploded view of the "center diff." It's actually called that.

In that diagram on the bottom-right, the transmission computer layout is incorrectly labelled as "ECU" but the diagram itself is indeed for the TCU. The battery charge sensor, throttle position sensor and ATF temp sensor feed into an Analog<->Digital converter, which then sends its signals to the TCU. The purely digital signals (speed sensor 1 (rear), speed sensor 2 (front), "range status," brake switch, ABS status, engine speed, diff lock switch) are fed to the TCU with no conversion. There is another factor entering the TCU, but the kanji is too small for me to read it (the bottom one). The TCU then makes a decision and sends a signal to Duty Solenoid C, which operates the multi-disc clutch mechanism (limited-slip). That's a complete translation of the lower-right diagram. Hopefully it will come in handy someday. I wish I had a larger scan!!

The lower-left one is even more interesting, and perhaps of interest to those who are analyzing the transmission computer's readouts (I'm looking at you, Phil! ). It's a Solenoid C duty graph. The X-axis is vehicle speed, the Y-axis is [Solenoid C] duty level, and the Z-axis is throttle position. Interesting... that really is all the information on it. Despite all the various inputs that are listed above as going into the TCU's decision for Solenoid C, the graph makes it seem like vehicle speed and throttle position are the only factors. Hm.

Below that is a diagram of the multi-plate clutch mechanism. Again, the scan is too small for me to read everything, but I'll do my best. The top and bottom pieces (U-shaped parts) are the slip plates. The bottom one is the rear, the top is the front. Sadly that's as much as I can read. The rest is kanji that's too blurry. The line between the front and rear (what the arrow is pointing to) is I think engine speed (the kanji for speed seems to be there). Grah.

The one above that is the diagram of the center diff. Seriously, it's called a center diff. Grah. This diagram is similar to the one on the site I found earlier, but sadly the image they had is missing so I only have this one to reference. The left-most line with the arrow pointing right is torque entering the transmission. The right-most line with the arrow pointing right is torque going to the rear wheels. The bottom two lines are Sun Gear 1 (left) and Sun Gear 2 (right). The upper-right item is the multi-plate limited-slip clutch mechanism. Immediately to the left of that are...where my lack of technical knowledge falters. They're listed as "Pinion #1 (right)" and "Pinion #2 (left)". No clue what that is supposed to represent, to be honest. Is that part of Duty Solenoid C? And finally, the line above "incoming torque" with the arrow pointing left is torque to the front wheels.

YIKES. Well that's everything... I could probably translate the whole article, but most of it is well-known stuff (power mode, non-power mode, manual mode) and ECVT stuff (unrelated). So right now, at 4:30 AM, I'm not going to bother. I just hope this has been an informative read at the least, and helpful assistance for future projects at most. Thanks for taking the time.

[b3lha]

Originally Posted by Nomake Wan

The lower-left one is even more interesting, and perhaps of interest to those who are analyzing the transmission computer's readouts (I'm looking at you, Phil! ). It's a Solenoid C duty graph. The X-axis is vehicle speed, the Y-axis is [Solenoid C] duty level, and the Z-axis is throttle position. Interesting... that really is all the information on it. Despite all the various inputs that are listed above as going into the TCU's decision for Solenoid C, the graph makes it seem like vehicle speed and throttle position are the only factors. Hm.

Thanks Nomake.

That certainly is interesting and useful to me. I haven't had any time recently to work on my project, but as soon as I do, I'll be looking to see if I can find the actual data in the TCU memory that implements that graph.

Phil.

[Nomake Wan]

You're welcome. I feel you on the "no time for hobbies" bit... I'm actually working today (30 minutes! I can still make it! ) and am supposed to be using my translation skills on a new Anime that came out about racing on the highway. Hahaha.