Subaru Ascent Forum banner

21 - 35 of 35 Posts

·
Administrator
Joined
·
8,832 Posts
@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.
 

·
Registered
Joined
·
167 Posts
Discussion Starter #22
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
 

·
Administrator
Joined
·
8,832 Posts
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.
 

·
Registered
Joined
·
167 Posts
Discussion Starter #24
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.
 

·
Administrator
Joined
·
8,832 Posts
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.
 

·
Registered
2020 CWP Touring
Joined
·
540 Posts
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.
 

·
Administrator
Joined
·
8,832 Posts
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.
 

·
Registered
Joined
·
77 Posts
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.
 

·
Registered
Joined
·
77 Posts
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.
 

·
Administrator
Joined
·
8,832 Posts
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.
 

·
Administrator
Joined
·
8,832 Posts
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...
6841


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.
 

·
Administrator
Joined
·
8,832 Posts
21 - 35 of 35 Posts
Top