[jeb]

Haven't been here much lately but I thought you guys would like this article. I thought it quite interesting.

http://blogs.youwheel.com/2015/03/31/acura-sh-awd-comprehensive-analysis/

 

[Dnick]

That is an interesting read. Here's a pertinent excerpt from it: EDIT: This sounds totally wrong..... especially last sentence.

EDIT: I believe the above info in that article is very inaccurate, especially the point about VTM-4 being "effectively pure FWD after 18MPH". This is just an incorrect understanding of how VTM-4 works by the author of that article; which is very unfortunate, because it reads like it was written by an authority on the subject ("NOT!").
If the author was not totally misunderstanding how VTM-4 operates, then he truly mis-stepped in his attempt to explain his understanding.... because this does not read right at all.

:act060: :act047:

 

[henni]

Joe has posted several comments similar to this one, makes one wonder how many RLs today have a burned out VTM-4

 

[xrdad]

There is a misunderstanding in the description...

The RL is still very much an AWD vehicle long after 18MPH.. (if memory serves, up to 70MPH).

What it won't do after 18MPH is LOCK the dif.

Big difference!

 

[Dnick]

^^^^^^
.... that was my understanding as well. I posted that extracted bit to see if anyone else might think this info (as well based as it sounds) might be a bit off base with respect to the VTM-4 info.
Sounds like it is ONLY talking about locked mode.

..... as a matter of fact, not that I re-read it, it sounds totally wrong (especially last sentence). I'm going to edit that to flag that point.

 

[jeb]

Heh... Interesting...

 

[jeb]

There is a misunderstanding in the description...

The RL is still very much an AWD vehicle long after 18MPH.. (if memory serves, up to 70MPH).

What it won't do after 18MPH is LOCK the dif.

Big difference!

Do you have a source on that up to 70mph claim?

I don't see that anywhere here, http://www.ridgelineownersclub.com/Variable-Torque-Management-VTM-4-Explanation

Our explanation makes it sound like its very much fwd while cruising or even when vtm4 lock is activated after 18mph.

 

[xrdad]

I'm going to find the source of that asap.. stay tuned!

(1st hand experience though = driving on an icy hwy or on a frozen lake, my RL does not have the front end sliding all over on acceleration like my Civic does... it's obviously still in 4wd mode, well above 18MPH. Although that is not an engineering document, it's as real as it gets. Now, I just need to find documented proof!)

 

[speedlever]

Don't confuse normal automatic VTM-4 action with manual VTM-4 lock action. In the latter case, lock begins decreasing after 6mph until it is fully disengaged by 18mph. It will re-engage as speed begins to drop below 18 mph again. Automatic VTM-4 action has no speed limit that I am aware of. And yes, it is mainly FWD in cruise... until the ECU detects conditions that cause it to direct power to the rear wheels.

But in that condition (manual lock), you will be in 1,2 or R and will have pressed VTM-4 lock in order to manually engage the lock. The primary purpose for this is to direct the full amount of power available to the rear wheels right off the bat. In automatic mode, the amount of power going to the rear wheels varies based on conditions including the amount of throttle input detected.

So where you may not want to nail the throttle to get out of a slippery place (in normal, automatic mode), engage manual VTM-4 lock to creep out with maximum rear wheel assist.

I have never heard of the 70mph limit on normal VTM-4 actuation. I would be curious to see that documented too.

 

[jeb]

That is an interesting read. Here's a pertinent excerpt from it: EDIT: This sounds totally wrong..... especially last sentence.

EDIT: I believe the above info in that article is very inaccurate, especially the point about VTM-4 being "effectively pure FWD after 18MPH". This is just an incorrect understanding of how VTM-4 works by the author of that article; which is very unfortunate, because it reads like it was written by an authority on the subject ("NOT!").
If the author was not totally misunderstanding how VTM-4 operates, then he truly mis-stepped in his attempt to explain his understanding.... because this does not read right at all.

:act060: :act047:

I don't see any issue with what he said really, if he just added... "until wheel slip is detected" at the end.

 

[speedlever]

Except that I've only seen 18mph mentioned in terms of manual VTM-4 lock disengagement. I have no idea when VTM-4 tails off during normal acceleration in normal (auto) mode.

I think the author was confusing auto and manual VTM-4 lock operation a bit. Regardless, I think his basic point is valid as to the reason for a limited time engagement of VTM-4 lock due to heat and wear.

 

[jeb]

I have no idea when VTM-4 tails off during normal acceleration in normal (auto) mode.

You're right, it's kinda vague.

"At higher speeds, the front wheels are capable of providing the desired thrust with excellent handling so torque delivered to the rear wheels automatically diminishes with speed."

Source: http://www.ridgelineownersclub.com/Variable-Torque-Management-VTM-4-Explanation

 

[Dnick]

I don't see any issue with what he said really, if he just added... "until wheel slip is detected" at the end.

Except that's not all we get from VTM-4 Jeb.

There are 3 functional 'modes' of activation.
The first, already discussed by Speed is the "Lock Control" mode. We know what that does, and that it's limited to 1st/2nd/R gears & to 0-18MPH, with the amount of torque to rear wheels being reduced as 18MPH is approached (zero "Lock" to rear wheels after that... this is only the "Lock" function that ends at that speed).

The second is Limited Slip Differential or LSD mode. This is as Jeb alluded to; where differences in speed & acceleration between front & rear wheels triggers increasing levels of torque to rear wheels, depending on how much difference (front to rear) is detected.

The third is Vehicle Acceleration Torque Control or VATC mode. THIS is what has been overlooked completely by the description in that "primer". This is when the amount of torque to be delivered to the rear wheels is calculated based on the acceleration of the vehicle, as is determined/calculated in the VTM-4 unit. This is a significant element of our VTM-4, and is always active & automatic. (I will admit I am curious how the VTM-4 unit senses/calculates acceleration)

So, if you are driving straight & flat on dry roads & at a constant speed (zero acceleration), then yes, a minimum amount of torque will be delivered to the rear wheels (which is zero). If you want to call that "essentially" FWD, then OK... but that is a very temporary & fleeting state. That is the only time when this "steady state" of no triggers for torque distribution exists; and VTM-4 is active even then, but just not sensing any "torque diversion" triggers. All other times the VTM-4 unit will be varying the amount of torque to the rear wheels based on the circumstances being sensed & calculated by the system. I will say it would be nice to see a chart showing just how much torque goes to the rear wheels under what conditions (quantified). The diagrams in the SM are only conceptual & without numbers.

Lastly, I agree with Speed's suggestion that the author was confusing VTM-4 with VTM-4 Lock-Mode. Otherwise I would question his comment that ".... the VTM-4 system cannot deliver power to the rear wheels for a long period."

Edit: 'Just saw the link to the Gary Flint VTM-4 Explanation..... thanks for that Jeb. Much more authoritative & complete.

 

[jeb]

I will admit I am curious how the VTM-4 unit senses/calculates acceleration

Throttle position sensor perhaps?

 

[csimo]

If you're interested in what the next-generation Ridgeline will get you need to read the section about the Acura TLX. The Ridgeline will NOT have the torque vectoring features, but that's essentially the same system that will be used.

 

[eurban]

I posted a comment at the end of the article about the apparent error in his VTM4 description. He has revised what he previously said to this:
"This changes the way how the rear wheel drive unit work fundamentally. Now the clutch pack is 100% responsible for transmitting power to the rear wheel. It works in the same way as the GKN Twinster. Wear and heat generated from friction become a big concern, therefore the VTM-4 system cannot deliver power to rear wheels for a long period. In fact, after the vehicle reaches the speed of 18mph and in constant-speed status, the clutches in the VTM-4 will completely disengaged, which means the vehicle is effectively in pure FWD mode under this condition (during acceleration, the VTM-4 can still kick in and provide temporary torque to the rear wheels)."