The 2014 Accord Hybrid: Taking Hybrid Tech to a New Level

Gary S. Vasilash

While many hybrid systems use the internal combustion engine as a primary way to turn the wheels, Honda engineers have cleverly decided to not only have a highly efficient engine, but to use it mainly as a generator and to make use of electric motors to power the wheels.

Here’s something you rarely—or ever—hear from a program chief engineer about a development program: “We challenged ourselves repeatedly, and we failed repeatedly.” Sure, you may hear the part on the left side of the comma, but rarely the right, at least not so openly, as there would be a tendency to provide a little spin to mitigate the notion of failure.

But Koji Ninomiya of Honda R&D, who headed up the development of the 2014 Accord Hybrid, makes the statement, and adds, “But we didn’t change our goal.”

And that goal was to create “the world’s best” hybrid system in a midsize sedan. Given the level of competition—from the Toyota Camry to the Ford Fusion to the Hyundai Sonata to the Kia Optima—that’s a serious challenge. But given that when the car is launched it has the best EPA estimated fuel economy rating for city driving—50 mpg—and given that one of the primary purposes of a hybrid powertrain is to optimize city driving, where stopping and starting is problematic for achieving fuel economy in conventional powertrain setups, arguably Ninomiya and his colleagues achieved their goal. (The other two numbers are 45 mpg highway and 47 mpg combined.)

“Fuel economy wasn’t the only thing we achieved,” Ninomiya says, noting that thanks in large part to the high-output drive motor they developed, the Accord Hybrid also provides “smooth and responsive driving.”

The system developed by Ninomiya and his team is called the “Intelligent Multi-Mode Drive” (i-MMD). It is a different hybrid approach than Honda’s own Integrated Motor Assist system, used, for example, in the Civic Hybrid, which has an electric motor positioned between the internal combustion engine and the transmission, with the motor primarily providing a supplement to the engine during acceleration, powering the car during cruising if the conditions are right, and acting as a generator to replenish the batteries during braking. It is different than the approach used by makers of other hybrids, such as the Prius, which uses a planetary gear system (“Power Split Device”) to orchestrate the output internal combustion engine and two motor/generators in the powertrain.

Not only is the i-MMD different, but Ninomiya suggests that it is as important a Honda powertrain development as the CVCC engine and the VTEC valve control system.

The CVCC system was developed by Honda R&D in the early 1970s, when emissions became a world-wide concern. Rather than relying on catalytic converters, as other vehicle manufacturers did, Honda engineers determined that there could be fundamental changes to the combustion process such that CO, NOx and HC could be significantly reduced. Realize that back then, Honda was but a nascent automobile manufacturer, not a company that was thought of in the context that it is today. This meant that the engineers had to do some clever engineering while staying cognizant of the fact that they couldn’t come up with a solution to emissions that would necessitate a change in the company’s engine manufacturing infrastructure.

What they did, in effect, was develop a lean combustion approach that made use of a prechamber in the head that mixed the air and fuel and ignited it prior to being vented into the main cylinder. “CVCC” stands for “Compound Vortex Controlled Combustion,” with the “compound” relating to the main and auxiliary combustion chambers; the “vortex” to the swirl generated in the main chamber by the jet from the prechamber; and the “controlled combustion” to the engine’s ability to, well, control the combustion.

The consequence of this development was that because complete combustion occurred in the engine, it wasn’t necessary to have a catalytic converter. The 1975 Civic was certified by the EPA as meeting the requirements of the then-new Clean Air Act. Not only wasn’t it necessary to have the additional device, but the CVCC engines could run on gasoline that was leaded or unleaded; unleaded fuel was necessary for the performance of catalytic converters. In the early days, not all gas stations had unleaded gas available. It wasn’t a problem for Honda. In large part because of the CVCC, Honda became an established and respected OEM.

The VTEC development—for Variable Valve Timing & Lift Electronic Control—occurred in the following decade, originally undertaken for the 1989 Acura Integra. The valve timing approach had originally been taken in order to achieve improved fuel efficiency. But the Honda R&D goal was to improve performance across the entire engine power band. While the program for the Integra originally called for developing a 1.6-liter engine that would produce 140 hp, or 10 hp more than was the norm for that size engine at the time, a determination was made to develop one that could produce 160 hp at a maximum 8,000 rpm, which was 20% higher than the then-maximum 6,800 rpm.

Not only did they have to develop a reliable valve operating system, but it was necessary to make changes to the components, as regards size (the diameter of the intake valve went from 30 mm to 33 mm) and/or materials (to handle the heat, the exhaust valve was made of a newly developed nickel-based steel that was alloyed with molybdenum, titanium and tungsten).

The VTEC technology proved to be so important that it was used for the NSX supercar as well as for the Accord and Civic.

Honda engineers are not strangers to hybrid technology. The first hybrid on American roads was not, as some think, the Toyota Prius, but the first-generation Honda Insight in December, 1999. In 2002 it produced the Civic Hybrid, which is the first application of hybrid powertrain technology in an existing mass production vehicle, an approach that has subsequently been used by several automakers. In 2004, it launched the first-generation Accord Hybrid, which was the first mass-produced V6-based hybrid. 2009 saw the second-generation Insight, which was, at the time, the world’s most affordable hybrid. In 2010, the sporty CR-Z hybrid was released to the U.S. market.

But for the 2014 Accord Hybrid, things were going to be different, which led to the powertrain that is being deployed in the car that is essentially the ninth-generation Accord sedan (which was launched in September 2012) with a few non-powertrain-related changes. For example, visibly there are changes like blue accents to the upper grille and head- and tail-lamps and a trunk lid spoiler. Structurally, there is an all-aluminum front subframe—an assembly of die castings and stampings—that is 8.8 lb. lighter than the steel-and-aluminum assembly it replaces.

The real change comes in the powertrain.

There is an all-new 2.0-liter inline four-cylinder, 16-valve i-VTEC Atkinson cycle engine. It produces 141 hp @ 6,200 rpm and 122 lb-ft of torque @ 3,500 to 6,000 rpm. The aluminum block has cast-in iron cylinder liners. The head is pressure-cast aluminum alloy. The included angle between the intake and exhaust vales is 3.4°; this narrow valve angle contributes to a flatter, compact combustion chamber that reduces the amount of unburned hydrocarbon emissions.

There are two electric motors. Primarily is a 124-kW AC synchronous permanent-
magnet propulsion motor that is linked to the drive wheels. The torque of this motor is 226 lb-ft. The propulsion motor also works as a generator when the car is decelerating and braking. The second electric motor is driven by the gasoline engine to create electrical energy for the propulsion motor; it also acts as an engine starter when the vehicle is in idle-stop mode.

There is an “integrated power unit” (IPU) that is located behind the rear seat of the car; it contains a 1.3-kWh lithium-ion battery and DC-DC converter.

The car doesn’t have a conventional transmission. Nor does it have a torque converter. What it has is referred to as an “Electric Continuously Variable Transmission” (E-CVT). The E-CVT works by coordinating the interactions and operations of the gas engine and the electric motors. There is a clutch that is engaged when the engine is powering the wheels. When car is operating on electric power via the propulsion motor, not only is the engine shut off, but the clutch disengages so that efficiency losses associated with mechanical friction in the engine are taken out of the system.

For the most part, this hybrid system operates in a way that the 124-kW motor is doing most of the powering of the wheels and the engine is used to produce electricity via the generator motor. To be sure, the engine operates at times, such as when going at highway speeds and then accelerating to pass. But by and large, the motive power comes from the motor.

Which, for a hybrid, is absolutely remarkable.