Corey07850

Hi Guys

Haven't logged in since 2006 but figured this is a good place to start!

For the past few months I've noticed that the "SH-AWD" has been anything but "super"... Going around corners on wet/slippery roads I get the feeling that the rear wants to slide like it was a RWD car. I figured the tires were just worn so I had them replaced at around 55k. It's not something that has been in the front of my mind but the other day we had a nice pre-winter sleet storm in CT and I decided to take the car out for a spin at the parking lot at my office. Essentially I tried my best get the AWD/Traction Control to kick in by trying to induce a donut or two. The car would lose traction with no sign of the dash light indicating the car is trying to keep me from losing it.

Toward the end of last winter I had a car bump into my left rear wheel in a parking lot in a very low speed impact. I had a 4 wheel alignment done right after that with no adverse affects (car tracks straight, no steering wheel shimmy) but I have a feeling the light impact or the alignment may be playing a role.

Any idea of what to test? Is it possible that when they did the alignment they disconnected a sensor or something on the AWD system? Note that I have never had any dash indications for a malfunction/failure in the AWD system.

Here's hoping you guys have some ideas before I take her into the dealer!

Carbon2008RDX

Dealer time my fellow RDXer! Take it in. The SH-AWD is a complicated super proactive system so if it isn't working as it should, something is wrong. Only the dealer can tell you for sure.

Let us know the outcome.

MMike1981

this may be pretty cursory, but have you looked to see if power is getting sent to the rear wheels on the dash display? seeing that you have an 07, not sure if its a base model - if so, then u dont have that option.

additionally, one of the noted, i guess, benefits of SHAWD in the RDX was that the system actually lets the rear swing out a little bit as you may have been describing and let the TQ transfer rotate the car....but if this is essentially not happening and you are losing control with the VSA ON, then there could be an issue - (assuming your VSA is in fact ON/working - that may be the issue and not the actual SHAWD mechanisms)
- there was a review on youtube from a noted professional driving the RDX in snow stating as much as i write, at this time i cannot find it. Below may help you out some...

http://www.youtube.com/watch?v=Ae8rLIxZQMc
@ 6:31

wrestrepo

I believe that it is somewhat normal...doesn't the AWD send more power to the outside rear wheel in turns? wouldn't that induce oversteer or the feeling that you have a RWD?

Kaze66218

Well, the AWD idea you have is sorta wrong, I'll help you thru this. A FWD + RWD = AWD.

1. The FWD car has a toque biasing unit called a Differential. A differential in this case would send more power to the ouside wheel (AWD is not a prerequisite to transfer power while turnning)

--In the SH-AWD cars traditional front difs have been replaced by the ATTS unit. And is essentially 2 small A/T's.

2. The RWD car has a drive shaft that travels down the center of the car to a Rear differential from the engine.

--The Drive shaft in the SH-AWD couples the Transmission to the rear Dif, another set of electrionically controlled clutches.

The marriage of FWD to RWD:

3.The AWD car traditionally has 2 differentials and a coupling Driveshaft and depending on how it's setup the power is distibuted equally or to the rear on acceleration and to the front on decelleration. The traditional F/R differentials transfer power to the side with most grip. The end result is a dynamic power distribution while the vheicle trys to maintain traction.

--Ok I explained FWD/RWD/AWD all of them have Differentials in different setups. The main purpose of a Differential is to bias/ transfer power to a wheel that has traction. Now enter the SH-AWD The transfer of power is accomplished by a set of electronic clutches to transfer power to the wheel with the least traction, or while turning the outside wheel.

If I was picky, AWD in itself does not do this but the smaller componets of the bigger whole that does.

AWD is just power being sent to 4 wheels instead of 2, FWD or RWD.

The symtom that you discribe is typical of AWD vehicles as the car accelerates the power is transfered to the back and gives the sensation of losing traction or oversteer while turning.

This is not a cause for concern.

wrestrepo

No, it is not...

From the Acura website:

Though it has the same all-weather attributes of conventional all-wheel drive, Acura developed its revolutionary Super Handling All-Wheel Drive™ (SH-AWD®) system to enhance high-performance dry-road handling. By continuously directing engine power to match weight distribution, available traction, and other conditions, SH-AWD provides seamless power transitions and supreme agility. The result is enhanced high-performance cornering that simply can't be matched by front, rear, or conventional all-wheel drive systems.

The system determines the ideal distribution of power to the front and rear wheels, and between the rear wheels based on an analysis of wheel speed, steering angle, lateral G-force and yaw rate.
For better fuel economy, up to 90% of the power is sent to the front wheels when cruising in a straight line.
As weight shifts to the rear of the RDX during hard acceleration, the SH-AWD system transfers up to 45% of engine power to the rear wheels to take advantage of available rear-wheel traction.
In a curve under hard acceleration, 70% of torque can be directed to the rear—all of which can go to the outside wheel to improve cornering by directing power where weight has shifted.
The system reduces understeer and increases stability by turning the outside rear wheel slightly faster than the rest of the wheels, rotating the vehicle through the turn.

so, thanks but no thanks....

Mr Marco

^^^STFU! Kaze is one smart cookie. You, on the other hand, have mastered the art of cut and paste.

wrestrepo

yes, he must be really smart telling me I was wrong when what I said is exactly what Acura says about their AWD system...don't let a fact get in the way of your feelings...

VietNinjaJ30A1

That video you posted makes me wish it snowed in central Texas

MMike1981

i have to admit, shawd is alot of fun if you can do it safely

Kaze66218

@all, its all good Marco. Sometimes people get in a hurry and miss read or dont fully understand. He is entitled to his views. Well I appreciate the support, but west doesn't realize that we both said the same thing if you reread the posts. Even if he did cut and paste that info nothing I have said is to the contrary to Acura.

Again big bird style. Sunny days, wishing those clouds away....

AWD is a dynamic system where power is distributed to front or rear proportionally. SH is the system that replaces the traditional (AKA conventional) differentials and biases the power to the outside wheels.

Furthermore: Acura did not invent AWD nor is it any different than AWD as it would be unaptly named or misleading and is a case of massive consumer fraud.

The type SH Honda Preludes were the foundation of Acura's SH-AWD, yet explain to me how a FWD car biases the outside wheel to turn and is again a FWD(not AWD) where an ATTS unit replaced the differential. Also If he highlighted the 70 percent he sealed it because in a corner or straight, the car biases the rear on any AWD vehicle, even SH-AWD, that is accelerating but it is the SH (ATTS) unit biasing the outside wheel.(Although certain conditions have to be met it still applies power to a wheel with traction first, then once both wheels have traction the outside wheel receives power.)

@west, If anything a question mark at the end of a sentence means either you are unsure or don't know and asking a question.

So your answer is no AWD does not transfer power to outside wheel. That is the job of the differentials, and since Acura has SHAWD, these traditional difs are replaced with ATTS units. The SH/ ATTS units bias the power as long as traction is present at both wheels.

@OP again there is no reason to worry as this is a common occurrence with any AWD vehicle

Just wait Acura is gonna barrow another trick from the preludes again, in a few years i wouldn't be suprised we see Acura SH-AWD 4WS(4 wheel steering)

wrestrepo

It was (in my mind) understood that we were talking about the Acura AWD (SH-AWD). BBoards are a bitch because they do not incorporate "rhetorical question" or a "sarcastic comment" option. It's all good.

MMike1981

which would seem right on target for them, as they are far behind just even infiniti. before they start worrying about what wheels should turn, how bout they apply their 'advanced' line to a transmission of this decade and new powerplants. i think thats a better place to start


honestly, if acura didnt have SHAWD, what do they have

XLR8R

Corey07850, you have been driving the RDX for years now. If it doesn't feel right to you, then something very well may need attention. If you were doing doughnuts in the snow and could not make the VSA light even flash, that doesn't sound quite right. The VSA light should flash and you should hear the system working as it applies individual brakes and transfers torque under throttle.

Mike's idea is good. Can you read the SH-AWD display? It should show torque transfer under throttle. Otherwise try disabling the VSA. Press the VSA button for about 3 seconds until it beeps. The VSA light should come on to show it's disabled. Turn it back on and see if the light goes out. VSA problems should definitely give you plenty of lights and warnings to look at .

Actually, the purpose of a differential is to allow driven wheels to rotate at different speeds when turning. The outside wheel must be allowed to rotate faster, because it is traveling farther. In doing so an open diff will always send more torque to the wheel rotating faster. In snow or under hard corner acceleration, the wheel with the least traction (spinning faster) will get the torque. This is counter-productive; an open diff won't get you out of snow or a corner very well, because the wrong wheel is getting power. VSA or stability control counters this by appling individual brake to the spinning wheel -- tricking the diff into powering the other side.

However, it requires a limited slip differential (LSD) to limit the slipping of the wheel with the highest rpm, by progressively locking the wheels together, thereby maintaining up to 50% torque to the wheel with the most traction -- that is the one rotating slowest. Mechanical LSDs have been around a long time, such as GM's "Positraction".

What the traditional LSD can't do is apply more torque to the slower wheel or the outside wheel when turning (torque vectoring). That is where Honda's Super Handling LSD comes in. It uses electronically controlled clutches to apply more than 50% torque to the outside wheel, thereby yawing the nose of the car into the turn -- hence "Super" handling. However, SH torque vectoring is only active during turning with throttle applied.

XLR8R

This is not the case in the RDX. There is no ATTS in the front. It has an open front differential common to most FWD cars. The VSA/ABS system applies individual brake to a spinning front wheel, reducing it's rpm so the open diff will send torque to the other side. It performs this individual braking on the rear wheels as well, but is augmented by active torque distribution of the limited slip rear diff.

The active torque distribution system and its clutches, both front to rear and rear left to right is contained entirely within the rear differential.

Kaze66218

I really enjoyed this forum.

Example 1:
A car squats back the power goes to the back, the car squats forward the power is sent to the front. Rolls left sent left, rolls right sent right.

Example 2:
In every situation the weight was transferred to on Sid of the car "reinforcing" traction. Put a car on a Jack lift one side higher than the other and I'll bet my life savings that the opposite side of the car just got heavier due to weight transfer. Simple concept.

Kaze66218

I hope this helps

@everyone hold your fire,

@xcl8r read page 303 in the RDX user manual. It clearly states info that you may want to know in the shortest amount of words. I wanted to pull up a part diagram but this will do. http://www.rdxforum.com/pdf/2007_RDX.pdf

BTW it is sort of a safety issue the idea you have on brakes, the internal parts of the transmission handle this and is priority in a situation where power needs to be diverted and does the redirecting and bleeding of power. Granted one system is a contengincy for the other, I will give you that.

I'm not the type to be condisending or slinging mud/flamer.

I mention 2 a/t's because one interefaces with the engine and the other isn't exactly a A/T but follows the function and acts as a front diff very similar to a Prelude type SH ATTS unit did.

Acura RDX iVTEC SiR SH-AWD 4WS anyone? Wait that'd be the Halo Warthog...FTW. Makes me wanna paint mine Halo greenish gray metallic.

Do it Acura I DARE YOU!

XLR8R

OK, One more time: the purpose of a differential is to allow driven wheels to rotate at different speeds when turning.

I don't know what you call a "traditional" differential. There are two kinds of diffs: open and limited slip.

Open diffs are common on FWD cars, including most sport compacts. The open diff knows nothing of body roll or traction. All it sees is wheel rpm. It will send more torque to the wheel with greater rpm. In a normal turn, the open diff will send more torque to the outside wheel as it is rotating faster. But apply throttle in a hard turn -- such as a sport compact on an auto-X course -- and the resulting body roll will lift the inside wheel, reducing its traction and allowing more spin. The open diff will send more torque to the spinning inside wheel. This is the drawback to open diffs. The sport compact will struggle to exit the turn as the inside wheel with the least traction is getting most of the torque -- but not specifically because of body roll or traction -- only because it is spinning faster.

To demonstrate that, put the same FWD open diff half on ice and half on dry pavement. The wheel on ice will spin much faster and take up to 100% of the torque. The wheel with traction on pavement may not turn at all -- the car struggles to move.

Most manufacturers, including Acura, now employ ABS as traction control to individually brake the spinning wheel on open diffs. This slows the lifted inside wheel in the hard corner or the spinning wheel on ice, below the rpm of the other side and the open diff will now send torque to the desired side. In the case of the sport compact auto-Xer; braking in order to accelerate is not ideal. That's why Quaife sells LSDs for sport compacts.

In a more real world case of a FWD car in snow, the traction control will use ABS to brake the spinning wheels alternately, forcing the open diff to shift torque left and right with each wheel spin -- and the car claws its way along. ABS braking of open diffs is common now and typically called "electronic limited slip" or "electronic differential lock".

The Acura RDX has an ordinary FWD transaxle with an open front differential. Front traction control is provided by individual braking. There is no ATTS unit or anything similar on the front transaxle. If the SH-AWD rear diff is disabled the RDX reverts to common FWD. The RDX also employs ABS braking to limit wheel spin on the rear, but it is augmented by active torque transfer of the SH-AWD unit. The SH-AWD can transfer torque both to the front open diff and to the rear, as well as between the rear wheels left and right.

Both the Subaru and the Mitsubishi Evo you refer to do not have open diffs. Those cars have LSDs both front and rear -- that is why they perform so well. I believe if you understood the function of an open differential you would then appreciate why an LSD such as Honda's ATTS or Positraction is a great improvement. Your repeated belief that "A wheel with less traction will receive less torque..." is the source of your confusion regarding open differentials. Your question "Why spin a wheel that has no traction, when all you'll do is bury yourself in mud, snow,sand?" has a simple answer. That is precisely what open differentials do. Drop the "traditional differential" thing. Get your terms right. Research open differentials.

I really don't wish to argue this -- I just don't like to see mis-information on this board.

uhh, OK then.