Hybrids are not something new for Honda, but the system in the forthcoming 2014 Accord plug-in hybrid (PHEV) is several giant steps from the type introduced in the 1999 Insight and merely upgraded since. It also includes some very different approaches from the plug-in Toyota Prius, Chevrolet Volt, and Ford Fusion Energi.
The question of appropriate all-electric range for a PHEV is controversial. The Accord rating is 10-15 mi (16-24 km) vs. the Volt at about 35 mi (56 km), Prius at about 12 mi (19 km), and the Fusion Energi's reported 20 mi (32 km). Based on the size of the lithium-ion battery pack, 6.75 kW·h (vs. 5.2 kW·h for the Prius PHEV), the range estimate would seem to be conservative, although the Prius is smaller, lighter, and more aerodynamic than plug-ins and HEVs based on non-dedicated platforms. What apparently has set EV limits for PHEV newcomers is the high cost of lithium-ion batteries and the needs to keep the retail prices at more attractive levels and recharge times short.
Although the Accord PHEV will include a 120-V built-in charger and perform a full recharge in 3 h, a 240-V charge capability will be available and do a full recharge in under 1 h. The electric plug is an SAE J1772 compatible type.
The engine is one of the entries in Honda’s new Earth Dream series. It’s a 2.0-L Atkinson cycle four-cylinder (late intake valve closing) rated at 137 hp (102 kW). Unlike the 2.4-L in the non-hybrid, it doesn’t have direct fuel injection but does use an i-VTEC variable valve timing and lift system. The electric traction motor is rated at 124 kW, but with the engine the combination peak rating is 196 hp (146 kW) and 226 lb·ft (306 N·m).
As a 2014 model, the Accord PHEV will not go on sale until early next year. That Honda chose to lead with a plug-in is interesting, because a less-expensive hybrid-only is scheduled to arrive next summer. The PHEV, shown at a press introduction for the 2013 Accord sedan and coupe, was a pre-production model, and as a result, detailed specifications were not available.
Honda has said the Accord PHEV will top 100 mpg-e (equivalent), including a start with full charge, so the electric range is factored into the EPA window sticker numbers. AEI tested the PHEV on a brief drive with the EV range fully depleted and engine warmed up. So it was running as a pure hybrid and recorded 41.4 mpg on a 10-mi (16-km) drive. Although Honda has not released official hybrid-only figures, a Honda engineer informally told us that he would have expected we would have exceeded 50 mpg. Well, perhaps with a longer run, but that was the limit of the opportunity we were given.
The Honda hybrid power flow is unique, nothing like the acceleration assist-only system the company has used exclusively since the 1999 introduction of the Insight and later on other Honda models. The Accord PHEV has a two-motor design—one starter-generator and one traction motor within what forms an electric CVT (continuously variable transmission).
The system operates in one of three power flow modes: pure EV, hybrid, and direct drive from the engine—through a clutch into a helical gearset in the CVT-E and into the transaxle. A shaft-within-a-hollow-shaft system and an electromagnetic clutch are packaged within the CVT-E housing, Honda engineers said, but a cutaway or exploded version was not available for inspection. The direct drive from the engine is by engaging the electromagnetic clutch located between the engine (with starter-generator) and the traction motor.
An advantage of this system is that, in direct drive, at the cruising speeds that are beyond the hybrid operation, there are no energy conversion losses (from the gasoline engine used to produce electricity to power the traction motor) as in other two-motor hybrids. That is, the engine transfers power through the clutch and the gearset in the CVT-E into the transaxle.
The direct-drive mode from the engine is engaged by locking the clutch at the most efficient combination of road speed and load, so at higher road speeds in particular, the Accord PHEV should deliver better fuel economy than with a conventional hybrid system. The car reportedly will run in EV mode up to about 60 mph (96 km/h). A Honda engineer told AEI that the direct-drive clutch could lock in at as low as 45 mph (72 km/h) depending on load conditions.
There also are "sub-modes,” entered by pressing the control panel EV button. If just pushed quickly, it will switch from EV mode (if available) to hybrid. This would save battery energy for later EV operation or for future electric motor assist under high load. If held briefly, the button engages a power split to use the engine to recharge a range-depleted battery pack. This permits a driver heading for a mountainous area to restore the battery charge for performance assist.
The battery pack contains 100 prismatic-shape cells, supplied by a joint venture between Honda and GS Yuasa, a Japanese battery maker with worldwide distribution. The pack, behind the rear seat and just above the suspension, is cooled by a fan system that uses cabin air.
The underhood electronics center is cooled by a liquid system, with its own radiator in the left front (adjacent to the primary radiator) and an electric pump to maintain circulation. The car has an electronically controlled regenerative hydraulic braking system adapted from the Fit EV, which Honda claims improves regenerative efficiency 5%.
Although the hybrid system and battery pack add weight, the PHEV includes a lot more aluminum than the regular Accord: the front subframe, brake pedal, hood, rear bumper beam, and a specific 17-inch aluminum wheel. Additionally, the interior acoustic materials are a lightweight type, and the spare tire is replaced by a puncture repair kit.
The Accord PHEV is unlikely to match the Cd numbers of a dedicated hybrid like the Prius, but much was done, such as installing underbody covers (powertrain and cabin areas), a rear spoiler, and those specific 17-inch wheels, which come with aero wheel covers.
Although gasoline engine-only Accords sold in the U.S. are made in the company’s Marysville, OH, plant, the PHEV is an exception. It will be produced at a Honda plant in Sayama, Japan.