Accord goes hybrid: Honda uses integrated motor assist technology and cylinder deactivation to bring the first V-6 hybrid to market

Automotive Industries, Nov, 2004 by John Peter

It all started with introduction of the Honda Insight in December 1999. The little city scooter may have been more science experiment than commuter car, but it featured an all-aluminum body and Honda's first generation Integrated Motor Assist (IMA) technology. Honda followed that with the hybrid Civic in 2002, the first North American hybrid to be built off of an existing mainstream platform. Dan Bonowitz, vice president, American Honda Motor Company Inc., says that this marked the first time that customers could walk into a dealership and choose a hybrid powertrain as an option. And many have. This year, the Civic Hybrid posted three consecutive months (May, June and July) of record sales, only dropping off as Honda struggled to keep up with demand. Bonowitz says that there are two hybrid camps right now, those who want to be seen and those who are flying under the radar.

"The future of hybrid technology is headed squarely down the path first cut by the Civic Hybrid almost three yeats ago," says Bonowitz.

And that path has led to the latest hybrid offering from Honda, available December 3, 2004. That's when Honda will introduce an optional hybrid powertrain on the high-volume mid-size Accord sedan.

The Accord hybrid is powered by Honda's third generation IMA technology. While the previous generations focused on fuel economy over performance, the third generation IMA combines both performance and furl economy. The Accord posts Civic-like mileage at an estimated 30 mpg city/37 mpg highway, combining the V-6 and electric motor to produce 255 hp, 15 more than the standard Accord V-6. Honda engineers say that carves about a half second off of the 0 to 60 time (7.5 versus 8.0).

Torque is 232 lb.ft., with 90 percent available below 4,000 rpm.

"The electric motor really fills in the lower rpm torque curve," says John German, manager of environmental and energy analyses. "There isn't a lot of power from the electric motor, but it can develop its maximum torque at very low rpm. Our engines can't do that. It's a good fit."

The hybrid uses the same 3.0L V-6 iVTEC with Variable Cylinder Management (VCM) found in the 2005 Odyssey minivan with the addition of magnesium valve covers and intake manifold to reduce weight. VCM utilizes the Variable Valve-Timing and Lift Electronic Control system to idle the rear bank of cylinders during cruising or low engine loads. VCM monitors throttle position, vehicle speed, engine speed and automatic transmission gear selection along with other factors, determining whether the vehicle is cruising or decelerating. As the cylinders are idled, the system controls ignition timing and turns the torque converter on and off, suppressing the torque-induced jolt caused by switching from three-to six-cylinder operation. Honda engineers chose to deactivate the rear bank because the front bank is in the best position for cooling performance. The rear bank also helps to maintain catalytic converter temperature allowing for optimum emissions performance.

The VCM system is relatively new to Honda, appearing about a year ago in the Inspire (the Japanese Accord) and most recently in the Honda Odyssey minivan. The standard V-6 Accord won't get the VCM engine.

VCM has shown a 10 to 12 percent improvement in highway mileage for the Odyssey. German says that while VCM adds to the fuel mileage equation in the hybrid, it's the synergy of the two systems that adds the greatest benefit, making it hard to determine just how much of a difference the VDM system is making.

"We're using the electric motor to extend the envelope of three-cylinder operation," German says. "Do you assign that benefit to VCM or to the electric motor?" German says that a big issue in utilizing VCM is the noise and vibration caused by running on three cylinders--especially an unbalanced three cylinders.

An Active Control Engine Mount (ACM) uses sensors that alert the ECU to direct ACM actuators to vibrate in sync with the engine, to keep the vibration from being transmitted to the passenger compartment. If any vibration reaches the interior, an ANC controller with cabin-mounted microphones (front and rear) detects the noise and instructs the vehicle's audio system to emit an opposite sound wave through the car's audio speakers, canceling out the noise.

The IMA brushless DC electric motor has a peak assist of 16.1 hp and adds up to 100 lb.ft. of torque due, in part, to a new internal permanent magnet. Peak generation is 14 kW and maximum electrical current is 120v. The 68 mm-thin electric motor, mounted between the engine and 5-speed automatic transmission also serves as a generator during braking and deceleration, recapturing kinetic energy and recharging the IMA's battery pack during regenerative braking. It also provides power to the dual scroll hybrid A/C compressor. The dual scroll compressor is actually two smaller compressors, one is belt driven by the engine while the other is run off of the electric motor. The compressors can work independently or together depending on the cooling needs of the vehicle. When the A/C system is forced to use both compressors, the idle-stop function is deactivated.