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2014 Acura RLX Sport Hybrid moves forward with three electric motors

The 2014 Acura RLX Sport Hybrid SH-AWD highlights

The 2014 Acura RLX Sport Hybrid SH-AWD highlights several important developments in the hybrid world, such as independent application of torque to each of the rear wheels. Credit: Wheelbase Media

Honda finally has its hybrid groove on.

The 2014 Accord Hybrid and the plug-in variant are impressive fuel conservers, but the technology also extends to the upper-crust Acura division where the new RLX Sport Hybrid SH-AWD blazes a fresh trail.

For most hybrids, the common industry practice is to use a single electric-motor assist (for each pair of driving wheels) that can function independently or in tandem with the gas engine, as the need arises. But in the all-wheel-drive Sport Hybrid's case, Acura has developed a unique three-electric-motor system.

To begin with, the rear-drive Twin Motor Unit (TMU) uses two 36-horsepower electric motors (one for each wheel). They operate exclusively as the RLX begins to slowly advance from a stop and during low-speed cruising for up to two miles. Then the 310-horsepower V6 engine (also used in the standard RLX) is engaged.

When accelerating slowly, both the V6 and the 35-kilowatt (47-horsepower) electric-motor companion in front take over from the TMU.

But when you aggressively depress the go pedal, the V6 and the three electric motors bring a combined 377 horsepower into play to drive all four wheels. The all-wheel-drive mode also seamlessly kicks in whenever slippery conditions are detected.

When decelerating, the electric motors convert braking energy to electricity, which is fed to the 360-volt lithium-ion battery pack located behind the rear seat. No worries, it consumes only a modest amount of trunk space.

The TMU also assists during cornering by apportioning additional torque to the outside rear wheel and at the same time eliminating or even reversing torque supplied to the inside wheel. This torque-vectoring effect noticeably helps the RLX pivot with certain precision, especially at higher speeds.

The V6 is assisted by a seven-speed automated manual transmission (with paddle shifters and no clutch pedal) that's integrated with the electric motor.

In city driving, the Sport Hybrid's fuel thriftiness earns a 28-mpg rating compared to 20 mpg for the front-wheel-drive gas-engine RLX, even though the hybrid weighs an extra 350 pounds. In highway driving, the Sport Hybrid improves on the base RLX's 31-mpg number by just a single mpg.

The powertrain is controlled through a nifty floor-console-mounted gear selector that replaces the traditional shifter. It includes buttons and switches for Drive, Neutral and Reverse and there's an electronic e-brake switch.

Whether in electric-only or gas-electric mode, the cabin is luxury-car quiet and comfortable under normal driving conditions. It's only when you unleash the powertrain's potency with your right foot that an aggressive engine growl becomes apparent.

The car's inherently sporty nature can be further amplified by pushing the "Sport" button on the gear-selector console, thus changing the RLX's orientation from fuel sipper to quasi-performance machine. At this point the entire powertrain springs into action, resulting in brisker acceleration and crisper shifts from the transmission, including throttle-blipping (rev-matching) downshifts. In fact, the transmission seems to "sense" the correct gear to select based on velocity and braking parameters so you're ready to go when getting back on the gas.

Speaking of braking, they're not as grabby as in other hybrids.

At an estimated base price in the low-$60,000 range, including an impressive assortment of luxury and safety bells and whistles, the Acura Sport Hybrid will cost at least $10,000 more than the base RLX when the hybrid arrives in early 2014. That's competitive with similar premium hybrids on the market, but on its technological merits alone, the Sport Hybrid shows the way forward.

What you should know: 2014 Acura RLX Sport Hybrid
Type: Four-door, all-wheel-drive full-size sedan
Engine (hp): 3.5-liter DOHC V6 (310), plus three electric motors (377, net)
Transmission: Seven-speed automated manual
Market position: Gasoline-electric hybrid vehicles are gaining in importance, especially for automakers wanting to offer V8 performance, but with four-cylinder fuel economy, for their upscale brands.
Points: One of the most advanced and complex hybrid powertrains on the market; Hybrid system similar that of upcoming NSX sports car; Fuel economy particularly impresses in city driving; Torque vectoring system aids turning; RLX styling an improvement over previous RL, but still a bit too low-key; Extra-quiet and comfortable interior.
Safety: Front airbags; side-impact airbags; side-curtain airbags; anti-lock brakes; traction control; stability control.
MPG (city/hwy) 28/32
Base price (incl. destination) $60,000 (est.)


Lexus GS 450h
Base price: $60,500
Luxury, power, impressive fuel efficiency are all in evidence on this Lexus.

Mercedes-Benz E400
Base price: $57,600
E400's hybrid system is more effective on highway than in city driving.

Infiniti Q70 hybrid
Base price: $58,000 (est.)
Former M35h makes 360 hp; uses a seven-speed automatic transmission. 

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