[Robert.Mauro]

@Robert.Mauro what WAS that clunk in the 3rd video at 5:14?
I have to say the palisade just looks out of its element on a bumpy gravel road. I'm sure their engineers are correct that its designed for a wheel to spin like that but it certainly doesnt make that a better system lol

My Primitive front skid plate slamming the center of the rut.

 

[pcampbell]

So when the clutches lock up they run in 50/50 ? Why doesn't it do this all the time by default-- is it more wear and tear on the multi plate clutch system? Economy?

Is 50/50 front/rear the most it can send to the rear? Thanks

 

[Robert.Mauro]

The power is biased slightly front for better driving dynamics based on the weight distribution of the car. Subaru's videos and literature show power being transferred either direction (most of these were made during the days of the TR690 being their only CVT in production cars), though others claim that's not how the system works. Our TR690 is different than the TR580, so, the differences may be there. One day, I hope to get a conclusive answer.

 

[pcampbell]

I wonder if we put the Ascent on a dyno that can load the individual wheels differently, it we could get some more info. My dyno guy has a hub dyno although I don't know if he can load up the wheels individually.

 

[Robert.Mauro]

We could just plug into the computer and watch... I can't find my OBD dongle to try, and I'm not sure if the latest revision of ActiveOBD reads the data for the Ascent.

 

[hokiefyd]

So when the clutches lock up they run in 50/50 ? Why doesn't it do this all the time by default-- is it more wear and tear on the multi plate clutch system? Economy?

That's a question of mine as well. If we have a wet clutch that can shift between a nominal 40% or 50% power to the rear axle, I guess that means a wet clutch is slipping at least part of the time. Intuitively, I would guess the clutch is "engaged/locked" under a 50/50 scenario, and only partially engaged at anything less than 50% power to the rear...but it may not be that simple.

 

[Robert.Mauro]

I'm not the best at explaining this... I hope to find a good video on it one day to share with everyone.

Helps prevent the lighter rear from spinning around the front on turns, or pushing the front on turns. Dynamically allocates more power to the rear as needed, in situations where doing so won't initiate a slip.

Our front is heavier, and, has an Active Torque Vectoring system, meaning, it's slowing a wheel around a turn to match the speed it should travel.

Imagine flooring a rear wheel drive car with a light rear end (cough; Mustangs for decades) around a sandy or slippery turn. That little bit more power in the rear can cause it to slide (nowadays, Mustangs use the computer and somewhat better weight balancing, to help prevent slip). Switching to "slightly pulling" instead of "equal" or "slightly pushing" or a Mustang's/RWD's "only pushing" helps alleviate that.

 

[Ponch]

No, it's considerably different, and here's how.

1. Front differential is inside the CVT (and manuals), with zero directional changes (one shaft goes to the front differential, and in the opposite direction, the output shaft goes to the rear differential). There's no 2, 3, or 4 90° turns. There's no separate gear box. That allows more power to be transmitted to the wheels, less stress points in the drivetrain, and easier ability to control where power goes.
2. The system is designed to put higher amounts of power to the rear end continuously (and we have a beefy rear end designed to handle it - even beefier in the Premium, Limited and Touring). Honda, for instance, does not, because their system is a part time system. People who decided to push the system, forcing it to be engaged for a little more than their "part time" plans, ended up with burned out rear differentials. Honda's solution to that was to have the computer limit power to the rear even more.
3. Subaru's system is symmetrical. That means the system isn't fighting torque steer like all the rest. Instead, it only has AWD chores to deal with. It makes it more able to deal with shuttling power to retain tire grip, and, because it's ALWAYS on AWD, proactive in helping prevent vectoring based slip from ever starting.
4. Subaru's system is ALWAYS on. While systems like Nissan's are 100% front, 0% rear for most driving, and Hyundai's are 80-100% front, 20-0% rear, Subaru's is 60/40 under normal driving. Anyone who's driven on the beach with a 2WD/4WD vehicle knows that the same amount of power that makes a 4WD vehicle move, can be the same amount of power to make that same vehicle spin wheels in 2WD mode. NOT breaking grip is considerably better than losing grip and a system trying to correct it.
5. Subaru has spent decades building and learning how to make what's arguably one of the best AWD systems on the market, while most other systems are 2WD systems with tacked on components to shuttle some power to the rear.

And in the case of our TR690, there's more. Besides the chain based CVT nature of the system, we don't have the normal collection of gears. We've got primary and secondary reduction gears, a transfer gear, and that's virtually it. Heck, even forward and reverse are not done with gears. Power transfer from engine to differentials is very simple with very few parts.

There's a reason Subaru's system continuously beats the rest in test after test. For instance, other cars do flat ground roller tests, Subarus get tested on inclines.

Does Subaru use locking, torsen or limited slip differential? How is the transferase designed to differentiate? Just wondering.

 

[Ponch]

I'm not the best at explaining this... I hope to find a good video on it one day to share with everyone.

Helps prevent the lighter rear from spinning around the front on turns, or pushing the front on turns. Dynamically allocates more power to the rear as needed, in situations where doing so won't initiate a slip.

Our front is heavier, and, has an Active Torque Vectoring system, meaning, it's slowing a wheel around a turn to match the speed it should travel.

Imagine flooring a rear wheel drive car with a light rear end (cough; Mustangs for decades) around a sandy or slippery turn. That little bit more power in the rear can cause it to slide (nowadays, Mustangs use the computer and somewhat better weight balancing, to help prevent slip). Switching to "slightly pulling" instead of "equal" or "slightly pushing" or a Mustang's/RWD's "only pushing" helps alleviate that.

Understeer and oversteer. Rear wheel drives are prone to oversteer when they lose traction and even then. I had a 1983 Camaro with a 400 small block chevy in it. The oversteer could be harrowing under certain conditions. On the other hand, on decreasing radius turns if one learned how to use the throttle, speed could be increased. FWD cars tend to oversteer or plow. That can be bad too under certain conditions. AWD eliminates a lot of the drama.

 

[mtmra70]

Does Subaru use locking, torsen or limited slip differential? How is the transferase designed to differentiate? Just wondering.

The Ascent, or Subaru? If Subaru, it varies.

 

[Robert.Mauro]

Does Subaru use locking, torsen or limited slip differential? How is the transferase designed to differentiate? Just wondering.

Yes, but not in the Ascent or any of the other ATS systems. We have two open differentials, and one center multiplate clutch pretending to be a differential. Left to right power shuttling is done by applying rotational resistance to a wheel that's slipping, using the individual brake channels, which forces power to the other side.

Now, on the STI, things are considerably different. It uses a driver controllable electromagnetic multi-plate transfer clutch and mechanical, locking limited slip differential. The front differential is a helical type limited slip differential, and the rear differential is a TORSEN limited slip diff.

The WRX comes in two flavors, depending on whether it's a manual (6 speed manual, with viscous coupling) or an automatic (TR690 CVT with ATS). It has an open rear differential.

 

[laufu]

The WRX comes in two flavors, depending on whether it's a manual (6 speed manual, with viscous coupling) or an automatic (TR690 CVT with ATS). It has an open rear differential.

Hi Robert

When did Subaru remove VTD from the CVT WRX?

 

[Robert.Mauro]

Hi Robert

When did Subaru remove VTD from the CVT WRX?

My understanding is that the TR690 in the WRX has the VTD system, and I even alluded to that a day and a half ago to a tech that was looking at swaps vs rebuilds...

But, I keep hearing otherwise.

I'm pretty sure I'm correct and the current WRX has the VTD system paired in its TR690.

I should probably check it's service manual one day.

It is, in effect, a type of ATS.

 

[denissh]

I think he cowered all AWD types

 

[Robert.Mauro]

I think he cowered all AWD types

Yep. Jason agrees with me/I agree with him.

 

[Sprintguy]

I love the engineering explained channel, He is amazing to listen to. What was left out was, what about when the vehicle does not need AWD? Dealing with Jeeps for long time I can tell you that the viscous coupling is always trying to move power to the axle it is controlling, usually minimal transfer. So I would believe that when the vehicle does not need all wheel use the split would be more of 80% 20% until utilized. The ascent Uses the VTS , The wet clutch will inherently transfer power even when not being used so then again possibly 80:20 split until locked. The wet clutch will never be fully locked. The same scenario happens during torque converter lock up in the newer style lock up clutch torque converters (always some slip when locked). The combination of the clutch material and plates along with the fluid keeps the friction material from burning up when locked (slippage occurs by design). Now we are forgetting that there is the all important rear differential. This I would speculate is designed and geared to allow the use of this style of system without causing undue stress of the wet clutch assembly. The ascent does not need a limited slip (torsen or helical) type diff. The ABS/ESP control unit will modulate the brakes at each wheel to apply pressure to the wheel slipping which in turn transfers power to the wheel not slipping (or has traction). This style of limited (loosely stated) slip control has been in use on many different vehicles.

Carl

 

[Robert.Mauro]

Hi Carl, he covered all of that. We don't have a viscous coupling, and we have 60/40 bias under normal driving, not the less effective 80/20 of others.

 

[hokiefyd]

I understand our coupling is electronically controlled, so the computer controls the clutch engagement and can tailor it to whatever environment it senses at the moment (accelerating, turning, stopping, wheel slip, etc.). A viscous coupling is generally more mechanical in nature and its engagement is usually pretty linear with speed differences. It can't be quite as proactive.

 

[Sprintguy]

Hi Carl, he covered all of that. We don't have a viscous coupling, and we have 60/40 bias under normal driving, not the less effective 80/20 of others.

So what you are saying is that the TCM / CVT module is always engaging the rear wheels through the clutch. I can only imagine that in straight ahead conditions or The module uncouples the rear for cornering? I have been trying to figure out the system , but alas Shop Key does not have too much system function and strategy info on the Ascents . What I do know is that the Front diff ratio is 4.111:1 and the rear diff is 4.444:1 and when the clutch is engaged the final gear ratio out of the CVT is at 1.08:1 . Kinda useless info but cool how Subaru uses 2 different gear ratios to make up for the .08 underdrive of the clutch assembly.

Carl

 

[hokiefyd]

The ratio of the transfer gear to the front differential (internal to the CVT) is 1.08:1. That's why the front and rear ring-and-pinion ratios are slightly different. I don't think that has a direct relationship with the AWD clutch.