Honda is finally bridging the hybrid-technology gap.
When the first Honda Insight beat the first Toyota Prius
to market a decade and a half ago, Big H created a new vehicle segment
in the U.S. and catapulted gas-electric vehicles into the mainstream. We
probably don’t need to tell you that sales of such fuel sippers
subsequently exploded or that the Prius became the darling of the
segment, likely because it offered buyers the double bonus of having a
back seat and not looking like a bionic tadpole.
But, technology aficionados that we are, we can’t help wondering if the
cars’ guts had something to do with the Prius’s dominance. Honda’s
hybrid system, dubbed Integrated Motor Assist, was very simple, whereas
Toyota’s Hybrid Synergy Drive was more complex. It didn’t help that, in
the intervening years, Honda pretty much stood pat with IMA while the
rest of the industry released ever more intricate and efficient designs
similar to Toyota’s, with the Chevrolet Volt plug-in coming in as the
hybrid-tech high-water mark. Well, until now.
Honda is back at the bleeding edge of hybrid technology, introducing a
flurry of innovative systems across its product lineup. For starters,
the new Honda Accord plug-in and regular hybrids share a groundbreaking and Honda-exclusive powertrain design that lacks a transmission.
The system is anything but simple, yet it’s seamless and works very
well in day-to-day operation. Further, the reborn 2015 Acura NSX will
debut with its own hybrid powertrain with two electric motors driving the front wheels and a twin-turbo V-6 and another electric motor spinning the rears.
TMU Ain’t Just an Airport in Costa Rica
When the subject of this story, the Acura RLX Sport Hybrid SH-AWD—or “SH
SH-AWD” for short—was announced, many thought that it would share its
hybrid guts with the NSX, only in reverse. That isn’t the case, except
perhaps philosophically. The only common bit between the two cars is
what Acura calls the twin motor unit (TMU). In the RLX SH SH-AWD, the
TMU is fixed to a rubber-isolated subframe at the rear axle and is what
enables the RLX hybrid to offer four-wheel drive via two identical 36-hp
electric motors that are coupled together by a planetary gearset and
produce 54 lb-ft of torque.
Below 78 mph, each motor can supply
torque to its assigned wheel
independently via yaw-inducing torque vectoring, or the two can work in
concert to contribute thrust or braking. Above 78 mph, the TMU can still
perform the torque-vectoring trick, but it ditches its acceleration and
deceleration duties. Controlled via electronics and connected to the
rest of the powertrain only via wires, the TMU means there’s no
driveshaft. It’s unique among torque-vectoring differentials in that it
can deliver torque to one tire while the other pulls torque (or, put
another way, produces negative torque) and feeds the energy into the
regenerative braking system.
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