Chas2

The RDX and MDX have a different SH-AWD system than the RL. I have noticed in the literature, that the RDX/MDX rear diffs are constantly overdriven by 1.7% whereas the RL has an "acceleration device" which can overdrive the rear axle up to 5.7%. With the deletion of the RL's variable speed acceleration device, to me, the RDX/MDX system is inherently less complex, lighter and probably more reliable as a result.

Does the deletion of the acceleration device mean that the RDX/MDX have an improved version, essentially version 2.0, of SH-AWD? Has Acura found that they can achieve the same handling ends with a less complex and probably lighter SHAWD layout?

Or is it just because we have the "flagship" vehicle, and therefore our SH-AWD is "more" capable?

Does any one understand why the change was made?

Apologies if this has been discussed before, but I could not find any posts directly addressing this difference.

From the RL technical literature at hondanews.com

"Positioned at the front of the RL rear drive unit, the Acceleration device typically passes torque rearward to the rear axle at very close to a one-to-one ratio. In cornering, however, the Acceleration device's output shaft spins faster than its input shaft.

The Acceleration assembly uses a compact planetary gearset to achieve its speed increase. Hydraulic actuators operate clutch packs that control the planetary gearset. When the input shaft is locked with the planetary gear carrier, there is no ratio change (this is the straight-line mode). During cornering, the carrier is coupled with the case, and the output shaft speed increases up to five percent. A speed sensor at the hypoid gear, downstream of the Acceleration device provides a feedback loop to the SH-AWD Electronic Control Unit to ensure that the system is working properly. "

From the RDX technical literature at hondanews.com

"The rear drive unit of the RL sedan has a clutch and planetary gear set, called the "acceleration device," that can increase the speed of the rear axle up to 5.7%. In contrast, the RDX's rear driveshaft is constantly overdriven by 1.7% - and the resulting overdrive effect is regulated by the left and right rear clutch packs. The difference in the chosen rear axle speed increase is due to the differing handling dynamics of the two vehicles. The RDX achieves the desired SH-AWD™ cornering characteristics with less outside rear wheel speed increase. A matched pair of direct electromagnetic clutch systems, one on each side, controls the power delivered to each rear wheel."

Take a look at the TOV RL underbody analysis video to see that acceleration device housing.

http://www.vtec.net/articles/view-ar...icle_id=452729

black label

The system on the RL is the more advanced and sophisticated version of SHAWD. The RDX/MDX are confined to 1.7% overdrive of the outside rear wheel (no more or no less) where as the RL can overdrive the wheel by UP TO 5% (anywhere from 0-5%). The RL also gets the carbon fiber reinforced propeller shaft.

TampaRLX-SH

I would expect the SHAWD systems would have to be different. If I remember correctly, the SHAWD system input also include yaw & pitch sensors. The RL having a lower center of gravity, and different grip than the SUVs and would likely trigger different responses in the SHAWD. The input of these vehicles' different dynamics would likely require different output of the SHAWD system. I expect the SUV SHAWD systems had to be 'tuned' differently that the RLs.

Chas2

Well, yes you are right there. The Direct Yaw Control System--though not pitch--while many of us think we are flying in our RLs, I don't think we are quite there yet-- is what controls the amount of torque sent to the individual rear wheels. I expect that you are right that the two SUV platforms handle similarly, and that the RL handles quite differently than an SUV thereby accounting for the different designs.

I just figured that maybe Honda learned from a couple of years with the RL and found it could achieve similar handling, while eliminating weight and complexity, and perhaps increasing inherent reliability. Our cars are so heavy, despite all the aluminum in our cars, even in the body parts, plus the carbon fiber drive shaft, all to save weight. I do not know, but can only guess that all the high strength aluminum is a lot more expensive to manufacture than the steel those SUVs are made of.

TampaRLX-SH

Yeppers Chas, our RLs do indeed have a lot of detailed engineering that is rarely appreciated. I found out more details on aluminium components, underbody details and the SHAWD system on European sites and in Japan. The Honda Legend gets thorough disclosure of it's attributes, while our RL gets trees and rocks in the adverts.

I knew I read yaw or pitch sensors, but maybe only yaw. A car does pitch however, such as braking or accelerating from a stop. But that likley is less a factor in the twisties.

You must be an aviation enthusiast based on your comments. My yaw and pitch comes from 13 years at sea!

Check out Honda Legend on Google Videos...you will likely see some of the informative overseas demos on the Honda Legend technology & construction.

jhr3uva90

That's because we don't know what "pitch" and "yaw" mean.

Chas2

Imagine three lines running through an airplane and intersecting at right angles at the airplane's center of gravity.

Rotation around the front-to-back axis is called roll.
Rotation around the side-to-side axis is called pitch.
Rotation around the vertical axis is called yaw.

Works the same for a boat, although the roll and pitch, and to a lesser extent, yaw, is necessarily limited (by sinking)

Works the same for a car, only roll and pitch angles are really limited!

http://www.nasm.si.edu/exhibitions/g...TF/HTF541B.HTM

RL06tech

Different systems for different aplications. The RL's is more complex and thus more "sophisticated" but that certainly does not imply that the SUV's systems are inferior. The effect is the same. The RL's variable system gives it more flexibility. As far as the extra percentage, it may be due to the RL' greater tendency to understeer or simply to give it additional higher speed capability. Whatever the reason, it just works! And its a bragging point since no one else has it. Audi is copying the system in their next AWD generation. As we know imitation is the biggest form of flattery, since Audi "invented" the AWD luxury sedan, the act has even more "props" to it

GoHawks

The question is WHY ISN'T ACURA FIGURING OUT A WAY TO MARKET THIS BETTER? You know Audi will.

Come-on guys. Take an ad out on the TiVo showcase, get the message out. Something!!!

TampaRLX-SH

It's almost like there was infighting between Honda and Acura. Honda develops the Legend and showcases SHAWD (and many other features). Honda does OK with sales of the Legend with expected volumes. Honda promotes the attributes of the Legend in an intelligent, informative and factual manner.

Acura turns their nose up to the rebadged Legend, as does the North American market. But does Acura attempt to bring it's bastard child into the light? Nooooo. Maybe a connection, maybe not. But only true fans know of the bastard childs secret powers. Acura markets the RL detached from its attributes and expects consumers to become aware of the RL by Gamma Rays.

Now Acura is all abuzz with SHAWD and how wonderful it is on the RDX and MDX. 'SHAWD is the new shiznit!' (Sorry Bob, I am using that in my staff meetings too... )

But where? WHERE oh WHERE did SHAWD come from? That bastard Honda Legend! But Acura did not design it, Honda did, how COULD we proclaim it on the RL???

Tune in tomorrow for another episode of "As the Driveshaft Turns!" <cheesy organ music>

Acura's marketing boardroom would not know how to cash a winning Lotto ticket.

jhr3uva90

There was an article in the Wall Street Journal last year about how a few years ago, Honda in Japan proposed a certain preliminary design for the 2004 Acura TL to Acura in California. Acura turned down that design, so Honda Japan used it for another car: the Legend. Then Honda in Japan pushed that car on Acura in California to sell as the new Acura RL. So basically, Acura is forced to sell a car that has a design that they rejected earlier. That, in my opinion, is why the RL is being treated like a bad stepchild. Meanwhile, the RDX and MDX were designed in California and manufactured in North America. The "biological children" (non-stepchild) are being treated better than the stepchild. Personally, I don't think Acura corporate (CA) cares that much if the RL sells well. Meanwhile, the Acura salespeople at the dealerships don't have much incentive to sell the car, since their commissions are not proportional to the cost of the car. For the same effort, and Acura salesperson at a dealership can sell a TL and get virtually the commission as an RL. To top it off Acura used what power they had to initially release ONE type of RL (in other words, it too two years for them to offer an RL without a navigation system) with far fewer options than its competitors and you have our present situation. I still love my car, though!

gavine

That's it...I'm going to re-badge my RL with "Honda Legend". Does anyone know where I can get the Legend insignias?

I think that would be pretty cool. I predict that I will get more buzz about it than with "Acura RL" on it. People will be intrigued...no doubt.

jftjr

I *really* want a pitch control on my RL... I keep grabbing for the collective and wanting to pull up, but I haven't managed to find a shop to install that option.

Dammit, it's 2007. When I grew up and watched The Jetsons and Space:1999 I was promised flying cars -- and they aren't here yet! Who can I sue?

Chas2

The 2G Legend was the last time there was anything resembling a collective, in the Legend/RL lineage, and pulling up on that would give you a lot more yaw than pitch!

neuronbob

Nah. Just debadge it, then people will think it's a Lexus. Watch their jaws drop when you tell them what you're actually driving!

Sorry to hijack the thread.

jhr3uva90

Actually, I have a friend who swears up and down I have a Lexus. I keep having to tell her it is an Acura.

Qest

Acura literature and advertisements are often mistaken, wrong, and/or incomplete. Thus, around 80% of the reviews I read of the RL when it was introduced explained that SH-AWD is unique in its ability to shift torque left and right between the rear wheels.

jhr3uva90

You mean it isn't unique?

Chas2

What other systems do this? I would be interested in looking at those systems. This is really the first AWD system I have had experience with.