BoostLover

Sorry if repost but this is an impressive video showing application of full throttle in mid turn and how the car remains neutral (no understeer).

http://www.youtube.com/watch?v=vuUaq...eature=related

Unfortunately, this is the RL's version of SH-AWD, which has the acceleration device in front of the rear diff. The TL's SH-AWD does not have the accel device (someone please correct me with a source if I'm wrong).

Question: can the TL do this also, even without the acceleration device?

It's not a deal-killer for me but this would be hot; not even the Evo (IX) will avoid understeer if full throttle is applied mid turn - it'll understeer and then when the boost kicks in, it'll oversteer. Neutral would be a welcome change.

Bearcat94

I don't know what the "acceleration device" is, but the TL-SHAWD does do that - it can cause the outer wheel to turn upto 7% (??) faster.

That's my recollection anyhow.

You can look it up here:

http://www.hondanews.com/categories/733/releases/5197

TechnoCat

The acceleration device is just gearing. Think of how you can pedal a bicycle slowly but move quickly when in top gear. Out of curiousity, why do you think the TL lacks it?

Dry cornering is the strength of the TL AWD. As I've mentioned in some of my posts, it's first-reaction on slick surfaces that the SH-AWD suffers in comparison to a Torsen AWD (Audi) - e.g. starting from a stop or hitting a hydroplane opportunity - where it takes a second for the TL to actually engage enough rear torque to matter. But the performance-handling of the SH-AWD is far better than any other AWD I've been in.

George Knighton

I think it's called a transfer case on the TL. :-)

The transfer case of the TL serves the same purpose as the acceleration device on earlier versions of high performance SH-AWD, and some of us believe that listing the device as an acceleration device is more a translation problem than anything else.

I'd only believe that the RL acceleration device did something special if it had an acceleration device in addition to a transfer case.

George Knighton

The outer rear wheel can get up to 100% of the 70% total torque that is directed to the rear in extreme performance applications, depending on what the driver appears to the computer to be trying to accomplish.

Dopes6070

I believe the RL can vary the rear wheel acceleration where the TL/MDX/RDX is a fixed percentage


from wiki:
Yet another version of SH-AWD was introduced in late 2008 with the fourth generation 2009 Acura TL.[11] The Acura TL implementation of SH-AWD is actually mechanically more similar to the SH-AWD layout in the Acura MDX and RDX[12] in that the rear differential is over driven at a constant 1.7% faster than the front wheels[12], unlike the Acura RL, which, since its introduction in 2004[2][13], added an acceleration device[14] which can over drive the rear wheels up to 5.7% faster than the front wheels

BoostLover

^ Exactly. The acceleration device is *NOT* a transfer case; it is not gearing, either. It is present on the RL but not the TL, according to the wiki. I should have cited my source in my first post - apologies.

It's good to know the TL can maintain a neutral attitude in spite of mid-corner application of throttle.

CleanCL

iTrader: (4)

"SUPER HANDLING ALL-WHEEL DRIVE™ (SH-AWD®)

The 3.7-liter TL SH-AWD® features Acura’s Super Handling All-Wheel Drive™, which progressively distributes optimum torque not only between the front and rear axles but also between the left and right rear wheels. The benefits of the system are not only superior all-weather traction but neutral, accurate steering under power that is unmatched by front drive, rear drive or conventional all-wheel-drive systems.

By utilizing torque vectoring, and by rotating the outside rear wheel faster than the front axle speed while cornering, SH-AWD® helps to turn the vehicle through the corner- thus helping reduce understeer and improving handling balance and controllability. With cornering forces more evenly distributed between front and rear tires, overall cornering ability is increased. Also, rather than using only the steering angle of the front tires to turn the vehicle, the TL SH-AWD® model applies additional torque to the outside rear wheel to create a "yaw moment" that reduces understeer.

Vehicles with high power ratings using conventional front or rear drive systems generally use a limited-slip differential to help maintain traction under power. By linking inside and outside drive wheels, these systems tend to resist turning and can increase understeer-working against the front tires as they attempt to turn the vehicle. Conventional AWD systems work similarly to link the inboard and outboard tires and the front and rear axles that can create resistance to turning. Using torque vectoring to help turn the vehicle, SH-AWD® creates a more responsive, neutral and predictable platform while retaining the usual benefits of all-wheel drive."

http://www.hondanews.com/categories/733/releases/5197

So to answer the OP's question, yes, there is yaw control on the new TL.

George Knighton

Be careful believing Wikipedia automatically.

It is we who write the Wiki articles, and sometimes people write things they're not always sure about, and sometimes there are even troll editing instances that will not be noticed for a while.

I'd believe Honda before I believed Wiki. :-)

How does the acceleration device work if it is not a transfer case with mechanical gears? It seems to me it would have to contain some Torsen type gears if there is no transfer case in addition to the acceleration device.

But what do I know.

CleanCL

iTrader: (4)

Here is the description of the "Acceleration Device" found in the RL.

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

The Acceleration Device 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 traditional straight-line acceleration mode). During cornering, the carrier is coupled with the case, and the output shaft speed increases up to 5.7-percent. A speed sensor at the hypoid gear (located downstream of the Acceleration device) provides a constant feedback loop to the SH-AWD™ system's Electronic Control Unit (ECU) to ensure that the system is working properly."

http://www.hondanews.com/categories/755/releases/5160

CleanCL

iTrader: (4)

TL SH-AWD operating parameters include:
* Up to 90-percent of available torque can be transferred to the front wheels during normal cruising.
* In hard cornering and under acceleration, up to 70-percent of available torque can be directed to the rear wheels to enhance vehicle dynamics.
* Up to 100-percent of the torque sent to the rear axle can be applied to either rear wheel, depending on conditions.

RL SH-AWD operating parameters include:
* During straight-line cruising and moderate cornering below half throttle, up to 70-percent of engine torque is delivered to the front wheels.
* In full-throttle straight line acceleration, up to 40-percent of the power is sent to the rear axle.
* In hard cornering, up to 70-percent of available torque goes to the rear wheels for enhanced chassis balance. Up to 100-percent of this torque can be applied to the outside rear wheel, which also can also be overdriven up to 5.7-percent by a built-in acceleration device.

CleanCL

iTrader: (4)

So I take back my original statement, the correct answer to the OP's question: The TL does not have the same ability as the RL to overdrive the outside rear wheel during a full throttle turn.

Bearcat94

But in the TL the outside rear wheel CAN be over-driven (i.e. speeded up):

http://www.hondanews.com/categories/733/releases/5197



IOW - it does the same thing as the RL, but maybe by a different method and/or amount. Right??

BoostLover

I think you're right it does the same thing as the RL but not by the same amount.

The original question was in regard to the car's attitude when applying heavy throttle mid-corner. I was concerned that b/c the TL doesn't have the Accel. device, it wouldn't be able to maintain its neutrality under that condition.

BoostLover

This is a very good point.

JM2010 SH-AWD

The SH-AWD TL does overdrive the outside rear wheel during aggressive cornering.

Just stab the throttle in one mid-turn and you'll see. No understeer; if anything, it feels like it cuts an ever shorter radius.

BoostLover

Solid. I'm super happy that Honda/Acura builds a high-performance, AWD, manual transmission sedan that's actually comfortable to drive 100 miles a day.

winstrolvtec

The accleration device acts similar to variable gearing in allowing the rear wheels to spin at a faster rate than the front. This has nothing to do with the amount of torque transfer ability. It is just the rate that rear tires spin in relation to the front, whatever the amount of torque applied. Under the same exact handling condition, provided that it is fairly aggressive, the RL's rear wheels will spin faster even if the same exact amount of torque is applied to the rear wheels of the TL. Perhaps this allows it to behave more nuetral but much of that depends on how the vehicle's suspension is designed and other characteristics.

The RL being heavier and having a softer ride and suspension would benefit more from this extra ability as it would likely be giving up grip. The TL does overdrive the rear wheels in relation to the front but at a lower fixed rate instead of a variable one. I assume the RL's SH might feel slightly more fliud allowing it to handle almost as well while maintaining better ride quality and being heavier. Where the TL might feel choppy at times but with more grip and probably a more traditional and predictable handling feel instead.

That is an older video from before Acura improved the electronic stability functions of the system and combined them with SH-AWD. I am sure there were many reasons for not using it on other models or at least the TL but one theory is that VSA has since been fully cooperative with SH-AWD starting with the intro of the MDX. It is believed that this was not the case with the early model RL, so mid turn and throttle off situations, it relied on the acceleration device to maintain stabilty before VSA (brakes only) kicked in if necessary and now C-VSA can direct any available torque where it's needed as detected before (and if) the brakes need to be applied but it's mostly speculation, don't quote me on any of this.

I came across something I have never heard or realized before regarding C-VSA in this video in the link. I know VSA used braking to emulate vectoring on the front differential being open but I had always assumed it was just for poor driving conditions and slippage. It may just be the way it's worded and said but it sounds like it is used as an active function for dry handling as well, braking the inner front wheel as well as torque transfer to the rear and outside rear wheel to further reduce understeer and help keep it nuetral. Another reason why the acceleration device wouldn't necessarily need to be used in the TL strictly for handling.

http://www.acura.com/Features.aspx?m...ability_assist - click on the view video link in orange text

BoostLover

Good to know. Yet another reason to upgrade the front brakes - VSA sounds like it would be very taxing on them during cornering work.

CleanCL

iTrader: (4)

I think that would be the best choice of words, it overdrives in a different method than the RL. Just from personal experience, this car is extremely neutral in WOT during a hard turn.

NOX 3.2

http://www.topspeed.com/cars/automot...m-ar16052.html

George Knighton

Thank you for digging that up.

It sounds like an expensive little piece of equipment.

It seems to me that the TL's system is a very reasonable one for most of us who are enthusiastic drivers.

Not being able to "overdrive" might lead a casual ready to misunderstand that his TL will be using a lot of torque on the outside wheel to point the nose toward the apex, as the car understands the apex from the driver's input.

I think we're misunderstanding the use of the word "overdrive" in this scenario. The other poster intends for "overdrive" to refer to the X-multiplication of RPM, not to the application of the percentage of total available torque.

After digesting all this, I think I understand why the TL does not have the acceleration device, and why it performs perfectly well with the clutch pack and transfer case.

I would still prefer to be driving the TL instead of the RL in an enthusiastic scenario, even if the RL had a six speed.

Exactly. I hope you'll understand why it took some of us a while to understand this. :-)

The TL's VSA does the same thing, but it's a last resort after SH-AWD. I have felt it only once, while navigating a corner in the Mid Atlantic blizzard this season. I disagree that it happens faster than the driver can realise, since I could definitely tell what the car was doing.

During cornering work, I think I'd turn off VSA and simply allow the SH-AWD to do its stuff.

And if you're cornering-working so hard you are worrying about brake pads, you'd better worry 'bout high temperature brake fluid, too. :-)

With a Honda representative watching at the scene, it was hard for me to tell how much of a brake feel problem was caused by the modulator allowing air into the system and how much of it was caused by burned brake fluid. This was in a track test against Crown Vics and Impalas at an invitational event designed to show departments that the front drive cars were every bit as capable as their traditional purchases.

Once you start driving your cars well beyond its assumed parameters, all kinds of things start showing up that people didn't think about.

Be aware that the track scene I describe was with an Accord 6-6 HFP Coupe. I feel a lot more confident with the TL 6-6, and although I am sure the modulator still lets some air into the system as the ABS is used over and over again, it is a problem much easier to solve than it was in the earlier cars.

I think that for VSA and ABS to work completely properly for the average driver, they are going to work in a way that requires some attention and maintenance if you're at the track.

winstrolvtec

I was thinking of a function that is more in line with an active torque vectoring brake ability for handling, specifically on the front wheels (but also the rear) used as an active function with SH even before a full blown VSA brake intervention occured. Basically, the brakes would vector on the front inner wheel to spin up the outer front wheel in conjunction with the normal rear outside wheel function under SH-AWD, allowing active vectoring on all four wheels. All as a proactive handling function and not a last resort safety feature.

The video is a little vague, so I am wondering if VSA lightly brakes the inner front wheel in addition to the standard rear function of SH for handling without spin or wheel loss required. We know the front differential is open and that the front wheels are capable of electronic vectoring and the rear is capable of mechanical and electronic vectoring so I don't see why not but I have never heard of any official type of confirmation.