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Plug-in hybrid brings Honda into sharper Clarity

Honda’s recently introduced Clarity plug-in hybrid sedan is the third variant of this revitalized and electrified nameplate. It joins the Clarity Fuel Cell, which debuted in December 2016 and the Clarity Battery Electric that arrived in the U.S. market in August 2017. The Plug-in Hybrid is the only one that’s available in all 50 states and the sole version customers can purchase.

The base Plug-in is $33,400 with a more upscale Touring model offering features like leather seats and satellite navigation ringing in at $36,600. Available by lease only, the Fuel Cell is just for California consumption and the Battery Electric version is currently offered only in a couple U.S. West Coast states at present. Honda will also offer the Plug-in in Canada.

The latest Clarity is currently the only passenger car that’s available with a choice of these three propulsion systems. Its overtly aerodynamic form may conjure up a sort of modern Tatra or Citroen, but the skirted wheelhouses (think 2000 Insight), scoops, air curtains, tall tail and full-figured shape are the result of careful CFD analysis and wind-tunnel work. While Honda engineers at the car’s U.S. media launch would not reveal a coefficient-of-drag number, the full underbody pan and wind-cheating shape would seem to indicate the Clarity Cd resides somewhere in the low 0.2x range.

Packaging and lightweighting

Work on the second-generation Clarity began in March, 2013. The car appears a tad ‘bloated’ because it has to accommodate a wide range of componentry. The “engine” compartment had to be large enough to fit a power control unit, the 181-hp (135-kW) four-stage synchronous electric motor and related hardware, the plug-in version’s 103-hp (77-kW) 1.5-L, LEV3 SULV20-certified Atkinson cycle 4-cylinder engine or the fuel-cell model’s stack. Compared to the previous generation FCV Clarity, Honda succeeded in developing a more power-dense fuel-cell stack for the new car that is 33% more compact.

The cabin had to be tall enough to package a large-capacity lithium-ion battery (25.5 kW·h for the electric, 17.0 kW·h for the plug-in hybrid) under the passenger floor. In the case of the fuel cell version, a small 1.7-kW·h lithium-ion “buffer” battery under the front passenger seat and a 6-gal (22-L) composite-reinforced/aluminum-lined, cylindrical hydrogen tank beneath the rear chairs.

Finally, the cargo bay needed to be roomy enough to house the fuel-cell’s bigger 31-gal (117-L) H2 tank or the second part of the full-electric’s 25.5 kW·h battery and the electric charger, while not unduly impinging on luggage space (an impressive 15.5 ft3 in the Plug-in) and enabling trunk pass-through and fold-down rear seats on the Plug-in version to handle longer objects.

With new Clarity’s larger footprint came added mass. To combat the weight gain, the company employed premium materials in key areas. Honda says that more than 40% of the Clarity’s structure utilizes super high-tensile steel. To be specific, there’s 1500 MPa material in the front door apertures and some roof sections and 980 MPa alloy in sections of the cabin floor, front load-path rails, rear bulkhead and roof crossmembers.

The hood, door outers, decklid, front fenders and front bumper beam are constructed of aluminum, and the front bulkhead is a resin-hybrid structure. Clarity’s rear bumper beam is a GFRP hybrid molding, the world’s first application says Honda. There’s more use of aluminum in the Clarity’s lightweight chassis, including a front strut and rear multilink suspension with forged aluminum control arms, cast-AL tie-rods, an AL subframe and a hollow die-cast front subframe.

To meet or exceed U.S. crash standards going forward, the Clarity employs a new ‘straight’ body frame structure to handle small-overlap front impacts, side impacts and rear impacts. The door B-pillars connect to a roof crossmember; this is why the Clarity does not offer a sunroof.

Shimizu’s greatest challenge

At the media preview in Northern California, we sat down with Clarity Development Leader Kiyoshi Shimizu, who expounded on the Plug-in’s basic mission of providing EV range sufficient to meet daily driving needs with the ability to handle longer routes without the range anxiety of a full-electric. For the record, that range is 47 mi (76 km) of EV range with a full charge and 340-mi (547-km) total range using the 7 gal of liquid hydrocarbons in Clarity’s fuel tank.

EPA estimates are 44 mpg city/40 mpg highway/42 mpg combined using the engine, or 110 MPGe of gasoline-equivalent electric-only operation. The Clarity operates in electric model most of the time, deploying the engine just to keep the battery charged or for bursts of power. 0-60-mph acceleration occurs in about 7.5 s.

The biggest engineering challenge, Shimizu -san said, was fitting the fuel-cell stack under the hood. Beyond that, his team had to tune the chassis to manage different weight distribution. The Battery EV model offers almost a 50/50 mass balance, while the Fuel Cell and PHEV versions are closer to the front-heavy bias of other Honda fwd sedans.

When asked why Honda had to create an all-new midsize platform for the Clarity triplets, with a footprint within inches of the all-new Accord, Shimizu explained that aside from some components not being able to fit in the Accord, company planners felt it was necessary to make an eco-aspirational design that would set the table for its electrified future.

The final challenge is, of course, getting Clarity owners to remember to plug it in. That, Honda says, takes just 2.5 h using a Level 2 32-A charger. But on a conventional 120-V house outlet, that stretches to 12 h.

58.2 mpg observed

Operated with console-mounted buttons, the driver can choose between Econ, Normal and Sport modes which provide increasingly sharper throttle mapping and acceleration response along with an associated reduction in fuel efficiency. At engine start, the Clarity always defaults to the Normal mode. A fourth mode is activated by pushing the HV button on the console, wherein the driver can choose to maintain the battery’s charge level, say during a long interstate trip, by running the engine more to save electric power for later use.

The steering wheel paddles aren’t used for shifting gears (the Clarity has no transmission) but adjust the amount of regenerative deceleration. Pushing the right paddle maximizes deceleration, pushing the left one minimizes it. And just like paddle shifters, after some seconds the regen braking function returns to the baseline setting unless Sport mode has been selected.

Thanks to a comprehensive noise-reduction effort with acoustic glass and triple-door seals, it’s an Acura-like quiet inside the Clarity, with no appreciable wind rush around the mirrors or the base of the windshield. There was no audible whirring or whining of electric motors. The only acoustic intrusions were some boom from the tires over aggregate surfaces and, later in the day, a very hard-working 4-cylinder engine trying to keep the system charged on a very steep, winding uphill grade.

On a fully charged battery and in 70°F weather, I headed out on a 120-mi (193-km) route that took me over foothills, valleys and varied hilly terrain at highway speeds in search of the 47-mi (76 km) all-electric plug-in range. Purposefully avoiding heavy accelerator pedal use that might cause the engine to fire up, this time the Clarity got only about 40 mi (64 km) of EV range before the engine kicked in.

Because the Clarity is so quiet while cruising, I didn’t even notice the engine running and had to rely on the dash readouts. Later in the day after several restarts, I saw an indicated 58.2 average mpg in Normal mode mixed driving after the initial EV range was depleted.

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This project has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° [609203].

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