A Laudable Technical Achievement for Hybrid Die-Hards
James Riswick, New and Used Car Editor
The Acura RLX has had a rather inauspicious rookie year. After its initial public introduction, the subsequent reviews were, as one Acura representative plainly described, "positive to neutral. Nobody hated it."
Not exactly a standing ovation, and as we concluded in our Acura RLX road test, "Acura is going to have a tough time keeping its flagship on customers' radar."
The 2014 Acura RLX Sport Hybrid is a much-needed new player on a struggling team. It faces an uphill battle for reasons we shall explain later, but its revolutionary powertrain and other innovative technologies nevertheless deserve attention and even praise. If the RLX Sport Hybrid is at the very least a glimpse into Acura's future, there is plenty of light on the horizon.
A New Kind of Hybrid
This is not a hybrid as you've come to know them. There is a gasoline-fueled engine, a battery pack and some electric motors to be sure, but their novel arrangement and execution result in far more than simple fuel savings.
It starts with the same 3.5-liter direct-injected V6 with i-VTEC and cylinder deactivation found in the regular, front-wheel-drive RLX. Output is almost identical at 310 horsepower and 273 pound-feet of torque. The road forks from there.
Instead of the base car's traditional six-speed automatic, or even a CVT (continuously variable transmission) as found in many gasoline-electric cars, the RLX Sport Hybrid features a seven-speed dual-clutch automated manual (DCT) that makes its debut in a Honda-Acura product. Though touted for the performance benefits of its quick shifts, the DCT was ultimately chosen because it leaves plenty of room for an electric motor.
Integrated within the DCT and connected to the front wheels via a clutch is a 35-kilowatt (47 hp) electric motor. Like those found in most other hybrid applications, this motor supplements the V6 during acceleration, provides regenerative braking and resupplies the 1.3-kWh lithium-ion battery pack with electricity.
Electric All-Wheel Drive
From there, things get really interesting. Though the RLX Sport Hybrid wears the same Super Handling All-Wheel Drive (SH-AWD) badge as the MDX, TL and old RL, the system it refers to here is entirely different.
Rather than the mechanically based system that uses a conventional driveshaft to send power to the rear wheels, the Sport Hybrid uses a pair of 27-kilowatt (36 hp) electric motors. Packaged together in what Acura calls a Twin Motor Unit (placed where the differential would be), each motor sends power to its own rear wheel.
Like the original SH-AWD that introduced the term "torque vectoring" to many a car enthusiast's lexicon, the Twin Motor Unit delivers more torque to the outside wheel while cornering for sharper turn-in, reduced understeer and the general feeling of a car implacably glued to the road. Imagine the way a tank turns and you'll be on the right track: no pun intended.
The results are amplified in this new SH-AWD iteration, as the electric motors can create an even greater torque difference through the use of regenerative braking. In other words, one side can accelerate while the other is braking. Torque vectoring even occurs when the throttle isn't applied, so you get the same corner-taking abilities regardless of what your right foot is doing.
On the twisting coastal roads north of San Francisco, the RLX Sport Hybrid indeed stuck with tenacity, demonstrating a neutral character that gives way to rear-biased, effortless torque as you power out of a corner. An Audi A6 Quattro that Acura provided for comparison purposes felt almost antiquated. Understeer may have been similarly quelled, but the swift kick from behind was missing. So, too, was the whip-around effect afforded by torque vectoring.
The Most Powerful Acura Ever
The Twin Motor Unit is more than a handling aide, however, as it also works in concert with the front axle's V6-motor combo to provide a combined output of 377 hp and 377 lb-ft of torque. That makes the RLX Sport Hybrid the most powerful production Acura ever built.
The elaborate ballet among its power sources that occurs during acceleration and deceleration (and sometimes both simultaneously) can be broken down into several driving modes. When launching with light or moderate throttle, power comes from the rear motors only, momentarily creating a rear-wheel-drive car. The engine and front motor join the party once the car is under way. Cruising at lower speeds is handled by the rear motors, while the engine alone carries the load at highway speeds. All four wheels are also engaged when the car senses slippery conditions.
The transitions among these modes are commendably seamless. Specifically, when the engine automatically starts or stops (be it at a light or under way), electronically controlled engine mounts help eliminate vibration, while the Active Noise and Sound Control systems quell uncouth noises. The engine noise that does filter into the cabin is not only subdued, but possesses the sort of pleasing audible qualities we've come to expect from Honda engines. In contrast, a Lexus GS 450h is loudly unpleasant when pushed, with a more intrusive engine start-up made worse by a droning CVT.
A Pedal That Pushes Back
Paired to the Sport Hybrid SH-AWD system is a new Reactive Force pedal designed to increase the likelihood of matching the EPA-estimated 30 mpg combined (28 city/32 highway) by adding varying degrees of resistance to the gas pedal. Just as a variable-assist power steering system will increase effort as speeds rise, the Reactive Force pedal retards its reactions at lower speeds to benefit fuel economy and in slippery conditions to maintain traction. It will also push against the driver's foot should the available collision-sensing and -mitigation technologies detect an impending crash.
For those who don't relish the thought of such HAL 9000 powers, the Reactive Force pedal is deactivated when Sport mode is engaged (another item unique to the Sport Hybrid). Other parameters altered in Sport include enhanced SH-AWD involvement, additional engine intervention for more power, disabled cylinder deactivation and auto stop-start, and an increased tendency to downshift with accompanying throttle blipping. The latter is of particular note, as the RLX does a bang-up job of dropping down a gear or two under braking, limiting the need to utilize the wheel-mounted paddle shifters.
Unfortunately, the electric power steering system is unchanged when Sport is activated. The effort remains too light, with a detached feel and a lack of feedback that ultimately lets down the truly impressive handling capabilities produced by the trick electric hybrid system. It would be nice if the car's reactions could be felt through the hands as well as through the seat of your pants.
Unique Interior Features
Unlike other hybrids, the 2014 Acura RLX Sport Hybrid maintains the styling of its gasoline-only sibling. Subtle "Hybrid" and "SH-AWD" badges are the easiest tell, while keen eyes may spot the tiny LED foglights encased in orange markers on the lower fascia.
The handsome, well-crafted cabin is carried over as well, save for two key elements: an electronic gear selector on the center console and a head-up display. The gear selector is odd, and it's ergonomically awkward to use and bizarre in concept. There are push buttons for Park, Neutral and Drive, but Reverse is engaged with a switch you pull up. The standard head-up display (a first for Acura) features a power-distribution graphic. Perhaps it's a tad distracting, but it's fascinating to visualize the electric SH-AWD system doing its business.
Not surprisingly, there is another key difference found in the trunk, where space is eaten up by the battery pack. It's not a terrible penalty, though, as the remaining 12 cubic feet are only 3.3 less than the base car and, according to Acura, still capable of accommodating four golf bags.
Is It the RLX Savior?
In the end, this top-of-the-line RLX lives up to the "Sport" in its name. Its novel marriage of gas engine and electric motors proves that the term "hybrid" doesn't have to be solely associated with fuel misers. The idea of this concept being adapted for use in the forthcoming Acura NSX is tantalizing as well. Its biggest hurdle is the fact that hybrids are associated with fuel misers, and their buyers are principally concerned with three words: miles per gallon. Torque vectoring might as well be a greeting in Klingon.
The RLX Sport Hybrid's EPA estimate of 30 mpg combined is a definite improvement over the base RLX's 24 mpg estimate. It's also better than the Infiniti M35h (29 mpg) and Mercedes-Benz E400 Hybrid (26 mpg), and falls only a rather insignificant 1 mpg short of the Lexus GS 450h. Yet a Lincoln MKZ Hybrid is good for an EPA-estimated 45 mpg combined, while the Lexus ES 300h manages 40.
With that in mind, the Sport Hybrid doesn't seem destined to bolster the languid sales of the regular Acura RLX. It still possesses the same anonymous styling and a less prestigious badge than most of its competitors in the midsize luxury sedan segment. So while the 2014 Acura RLX Sport Hybrid may be a laudable technological achievement, it will likely have a tough time getting well-heeled buyers to appreciate it.
Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.
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