2009 Acura TL SH-AWD.

Friday, August 29th, 2008

2009 Acura TL SH-AWD
After providing you with an exclusive first-drive of the all-new 2009 Acura TL and TL SH-AWD recently, Leftlane writer Gary Anderson has decided to go back and take a more extensive look at each model individually starting with the performance-oriented TL SH-AWD today and the standard TL next week.
In past years, Acura has attempted to capture enthusiasts who had cut their teeth on other Honda products by offering a Type S version of the TL, with more power and a tighter suspension in the same front-wheel drive chassis. With the all-new 2009 TL, Acura has dropped the Type S; the high-performance version of the TL now comes in the form of the SH-AWD model. This “Super Handling” version uses a high-tech all-wheel drive package to make a run around end, leaving the front-drive and rear-drive enthusiasts still butting heads in the middle of the field. In our view, this is a goal-scoring technology maneuver that may change the rules of the handling game.

We had the opportunity recently to test this strategic new Acura product on California’s gorgeous twisting coastal roads north of San Francisco, and then refresh our memory of the 2008 TL Type S in a quick loop drive near Sausalito. Our conclusions were two-fold: First, on every measure, the SH-AWD clearly outperforms the Type S that it replaces, but it delivers a different sort of driving experience. Second, the improvements in style and luxury shared with the standard TL have created a performance sedan that seems more likely to appeal to grown-up enthusiasts, rather than one to which young drivers will aspire.

What is it?
The Acura TL SH-AWD is an unabashed sports sedan, with a 3.7 liter all-wheel-drive VTEC engine producing 305 horsepower and 273 pound-feet of torque. Incidentally, that’s the most powerful engine Acura has ever built.

Power gets to the wheels through a paddle-controlled five-speed automatic transmission and an electronically controlled all-wheel-drive system that can vary torque not only front to back but between the rear wheels to provide optimum power to each wheel in any type of driving maneuver.
The SH-AWD also incorporates duct-cooled front brakes and a high-performance exhaust system which also provide the only design clues that it is different from the standard TL since in all other respects, the two models are identical.

What’s it up against?
Acura is going after the luxury sport sedan customer with the SH-AWD, compelling the engineers to benchmark it against the BMW 5-Series, Cadillac CTS, Mercedes E-class, Audi A6, Lexus GS 350, and Infiniti M35. That’s a tough crowd to match in a sedan that’s expected to sell for under $42,000.

Nevertheless, the product planners believe they’ve achieved their goal. Their qualitative evaluation scales of luxury and performance/emotional appeal show the new TL positioned beyond everything in the performance/luxury sedan category except the Audi A8 and BMW 7-Series. It’s worth noting that the TL SH-AWD is positioned to compete with larger cars than its identically-sized, less-powerful sibling, the standard TL.

Any breakthroughs?
Phew! There are so many innovations incorporated into the new SH-AWD that we can best discuss them under the subheads of drivetrain, suspension and engine.

Drivetrain
We’ll start with that “super-handling” all-wheel drive system, since that’s important enough that Acura names the car with it. The Acura engineers made two statements that summarize what they consider to be important. First, they say that the system is intended primarily to improve handling, rather than just enhance safety in wet or slippery conditions. Second, they make the claim that this system actually provides better handling than any car with traditional front-wheel drive or rear-wheel drive. Did you hear that, BMW?

So how does it perform this miracle? Standard all-wheel drive systems, intended primarily to improve handling safety, have some form of clutch between the front and rear wheels. This clutch allows power to be directed to the end of the car that has the most grip, overcoming any loss of grip due to weight shifts caused by acceleration or braking as well as differing road surfaces. If power needs to be reduced to stop a specific wheel from spinning, that is done by using the ABS system to brake that wheel. Though this does keep the car from rotating, it does it at the expense of loss of power.

The Acura system starts with a electronically-controlled multi-plate clutch between the front and rear wheels. Under normal cruising conditions, the system directs 90 percent of the power to the front wheels to maximize fuel efficiency by reducing drive-line power loss. Under acceleration and hard cornering, as much as 70 percent of the engine’s power is directed to improve handling and negate torque-steer. Given the range of power shifts, that capability gives the SH-AWD pretty much the best of both the front-wheel and rear-wheel drive world.

However, in addition to this capability, the Acura system has separate electronically-controlled multi-plate clutches between the rear differential and each of the rear wheels, which allows as much as 100 percent of the rear-wheel power to be directed to either wheel. Consequently, not only can power be proportioned between the front and rear of the vehicle, but it can also be proportioned between the rear wheels without the loss of power that would result from using wheel braking to minimize wheel slip.

This attribute is useful, of course, in situations where one wheel loses its grip and starts to spin, but its key advantage is that the outside rear wheel can actually be “overdriven” in tight curves. The result is that the wheel which is traveling the longest distance in the curve is actually turning faster than the other wheels, overcoming any tendency towards oversteer. More about this when we discuss our experience with the SH-AWD.

Suspension
Of course, any system that controls power to the wheels is going to work best if it doesn’t have to overcome significant amounts of body pitch and roll. The TL engineers have generally done a good job of balancing the springs, shock absorbers, and anti-sway bars to minimize weight shifts without sacrificing ride quality.

In recent years, to improve ride quality under all driving conditions, Acura has introduced a two-valve shock-absorber design. During normal cruising, both valves remained open, so that bumps encountered when driving in a straight line could be absorbed with a minimum of passenger discomfort. However, when cornering, one of the valves would shut so that shock movement was restricted to keep the vehicle level. Pretty nice: a soft ride on the straights, and a taut ride on the corners.

In the 2009 TLs, Acura has gone one better in the shock department, by introducing a new generation of dampers that have blow-off dual stage valves, which retain the two-level shock absorption capability but improve the response time, so that in a situation where a pothole is encountered on a tight curve, the bump will be cushioned without unsettling the car or passengers.

The result here is that the TL is getting most of the variable damper response now being built into high-end luxury cars through the use of sophisticated electronically-controlled shock absorbers, but at considerably less cost since the mechanical system is simpler to manufacture.

To take advantage of these handling improvements, in the SH-AWD, engineers built in more responsive variable electronic power steering assistance. This system increases assistance at low speeds to make parking lot maneuvers easier and reduces assistance at speed to maintain directional stability and improve feedback and turn-in response.

2009 Acura TL SH-AWD Gallery: