Acura RLX shows advanced rear-steer, engine technology

  • 11-Dec-2012 02:52 EST
aei-AcuraRLX.jpg

New RLX is conservatively styled, but the sculpted silhouette conveys a luxury image.

Acura has a new flagship model, the RLX, and it will be making its debut in spring 2013 as a 2014 model. If the name is new but sort of familiar, the answer is that the car is a replacement for the RL.

The RL had been the Acura flagship, but in truth such models as the MDX, TL, TSX, and RDX were far and away the Acura sales leaders. A flagship often is not a brand's best-seller, but it is expected to “get noticed.” When the flagship isn’t making a sizable dent in the market in which it competes, however, something is sure to be done. The RLX first appeared as a “concept” at the 2012 New York Auto Show last spring and just recently as a production-intent model at the Los Angeles Auto Show.

This is a familiar Honda approach to introducing a new model, with the company disclosing some of the more significant technical changes in the process. In this case, the new technology is significant, and although the jewel-like strip of LED headlamps is visually obvious, what are under body and hood are not, although they have major effects on improved handling and performance.

Electric rear steering

What drew considerable attention was Honda’s newest approach to electric rear steering, a system with a separate computer-controlled electric motor at each wheel. Named Precision All Wheel Steer (P-AWS), the system can change toe up to plus/minus 2º at each rear wheel, working in conjunction with the vehicle’s electronic stability system, and of course, under all cornering conditions with the driver-controlled steering.

The motors operate independently, based on the computer analysis of the road situation and what rear steering can improve cornering. On a turn, for example, they might set an inside wheel to toe out, and an outside wheel to toe in. P-AWS responses are effective over a wide range of operating conditions, from low-speed maneuvers in tight areas and parking, to cruising on twisty roads.

The car has four-wheel-disc brakes and a premium suspension—double-wishbone front, multilink rear, with “amplitude reactive dampers.” These are shock absorbers with an internal spring for anti-roll and a second piston-valve that slides along the piston rod and comes into play when road inputs exceed the 10 mm (0.4 in) range of the primary piston. Acura also uses them on the RDX, introduced earlier in 2012.

At this stage, all-wheel drive is not part of the RLX picture, but in a few months there will be an RLX sport hybrid with even more technology including a version of Acura’s Super Handling AWD and reportedly, a dual-clutch transmission. Acura has projected it will deliver “triple 30” fuel economy numbers, that is 30 mpg city, 30 mpg highway, and so 30 mpg combined, along with 370-hp (276-kW) powertrain performance.

The conventional RLX EPA fuel economy numbers are 20 mpg city/31 mpg highway, a measurable boost from the RL’s 17/24. Extensive use (55%) of high-strength steel for the body, and aluminum for such parts as the hood and door skins, reportedly helped reduce mass by 270 lb (122 kg) to just under 3900 lb (1769 kg).

Direct-injection, I-VTEC, VCM

The new engine apparently gets most of the fuel economy credit. It is a direct-injection 3.5-L V6, and although that’s a bit less displacement than the 3.7-L V6 of the RL, the performance numbers actually are slightly better: 310 hp (231 kW) and 272 lb·ft (370 N·m) vs. 300 hp (224 kW) and 271 lb·ft (369 N·m) for the outgoing 3.7-L. What’s more important is the combination of I-VTEC (intelligent valve timing and lift electronic control) with VCM (variable cylinder management), Honda’s cylinder deactivation system.

The long-used V6 VCM had deactivated cylinders in two different stages, from six to four and/or three cylinders. VCM was very effective on the Accord, worth about three mpg, which brought the V6 automatic right up to the 34 mpg highway number of the four-cylinder model with manual transmission. However, there was an NVH issue during much of the operation in the three-cylinder mode, hence the frequent switch to operation on four cylinders to smooth out the engine. But—the highway numbers notwithstanding—that did affect fuel economy.

Instead, Honda now is using electronically controlled diaphragm engine mounts that are activated to quell the NVH on both V6 Accord and RLX, so the V6 can operate in three-cylinder mode much more often. The Accord mounts system operates at 28 volts, the RLX “higher,” according to Acura engineering. The actual number will be announced “later,” AEI was told.

Because the VTEC is “intelligent,” it not only changes timing and valve lift for improved low-end torque (from about 2000 rpm) but also does instant torque calculations, using rpm, throttle position, load, etc. So it continues to make timing and lift changes throughout the operating range and integrates the data into the cylinder count during VCM operation.

The engine is bolted to a six-speed automatic, an upgraded version of the one that had been used in the RL.

Honda has not yet released detailed specifications for the RLX but said that the wheelbase was stretched 2 in (50 mm) from the previous 110.2 in (2800 mm), although overall length is about the same as the RL's—196.1 in (4981 mm). A brief check at the LA Auto Show indicated that the rear-seat legroom, listed at 38.8 in (986 mm), was indeed the primary beneficiary of the modest wheelbase stretch.

The body was engineered with Honda’s ACE II system, a second generation of Advanced Compatibility Engineering. The front-end structure design approach is intended to disperse energy in the full range of frontal crash tests. Honda said it expects ACE II will enable the RLX to be an IIHS (Insurance Institute for Highway Safety) Top Safety Pick and receive a "Good" rating in the new IIHS small overlap frontal crash test as well as five stars in NHTSA’s NCAP (New Car Assessment Program).

Every car in the luxury flagship class comes with a complement of electronic safety technologies, and the RLX has a long list, including active cruise control with low-speed following, forward collision warning and mitigation, lane departure warning and lane keeping assist, blind spot monitoring, and a multiview rear camera.

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