Accord Goes Hybrid
Honda uses Integrated Motor Assist technology and cylinder deactivation to bring the first V-6 hybrid to market.
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 years 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 highvolume 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 fuel 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).
|Packaging the 3.0L V-6 and IMA system under the Accord’s hood was a challenge (above). Honda engineers developed an IMA electric motor that was only 2.7 in. (68 mm) wide. It bolts between the gasoline engine and compact 5- speed automatic transmission (below). The hybrid system fits in the same cradle as the conventional 3.0L V- 6 and automatic trans.|
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 Dual Scroll hybrid compressor can shift from belt-driven to electricmotor when the engine is at idle. The electric motor also enhances the compressors ability to provide proper climate control at all times. |
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.
While the Hybrid system isn’t designed to launch or run exclusively on the electric motor (like the Toyota Prius) there are specific times (during deceleration and at cruising speeds) when it does run electric-only.
German says that the best use of the electric motor is to eliminate the usage of low efficiency engine operation. At very low loads the engine efficiency is bad, but at high loads it is good. So it doesn’t necessarily need the electric motor at launch. The electric motor will assist the engine when the car is accelerated at full throttle. The hybrid Accord share no parts with Civic but is an evolution of the same concepts. “If you look at the parts for the power converter, they have a whole different capacitor and condenser,” German says, “but it’s the same basic theory.”
The third-generation Power Control Unit (PCU) uses a new computer chip that quickens the unit’s response and a new inverter and DC/DC converter help contribute to the IMA’s overall power increase.
A Sanyo-supplied battery pack stores up to 144 volts in a bank of 120 1.2v nickel-metal hydride cells that are about the size of a AA battery. Honda claims a 45 percent gain in output efficiency over the last generation battery. The battery pack is continuously cooled by an integrated cooling system, mounted directly to the battery, that flows cabin air over the pack, recirculating the air through a small vent in the package shelf.
| The only visible difference in the interior is an IP with a readout under the speedometer that shows when the system is charging and discharging as well as a mileage readout and a small green light that shows when the system is running at its best economical efficiency.|
The Accord hybrid features a new 5-speed transmission that is 60 mm thinner than the transmission in the standard V-6 Accord. A new lockup clutch converter shortens shift response during acceleration and more immediate start-ups after idle stop come with the help of an integrated electric oil pump that constantly pumps oil through the torque converter.
The hybrid Accord only weighs 127 lb. more than a standard V-6 model thanks to an aluminum hood, decklid and rear knuckle suspension components. The hybrid gets an exclusive rear fascia, rear spoiler, hybrid badging, exclusive 16-in. aluminum wheels and a roof-mounted antenna. An exclusive IP includes an IMA status display under the speedometer. The display used bar graphs to show when the battery is assisting the engine (blue) and when the battery is being charged (green). There is also an mpg readout and a small green light that comes on when the vehicle is being driven at its best economical efficiency.
All 2005 Honda Accords, including the hybrid, will have side airbags and side curtain airbags as standard equipment as part of Honda’s “Safety for Everyone” initiative. This core suite of advanced safety features, announced last October (which also includes ABS) will be standard on a full range of Honda and Acura vehicles with the exception of a small number of specialty vehicles.
The hybrid Accord will be marketed as a premium option selling for about $30,000 dollars, or about $3,400 more than a comparably equipped Accord V-6. The hybrid goes on sale December 3, and Honda expects to sell 20,000 units in calendar-year 2005.
The hybrid Accord is built at Honda’s Sayama, Japan, assembly plant on the same line with other Accords.
Modifications were made to the assembly plant to facilitate the sub-assembly of batteries and surrounding electronic control units, including space and equipment to do testing. Honda builds the IMA in-house, with the other components sourced from Japan. The hybrid powertrain fits in the same cradle as the standard V-6 with the electric motor and transmission added to the engine at the plant. A power-assist device was added to the assembly line to help with the installation of the battery. The battery pack and power control unit are assembled in the plant as a module that is bolted to the back of the rear seat.
Though Honda currently has no plans to do so, if it were to decide to build the hybrid Accord in North America, similar changes would be required to the Marysville, Ohio, assembly plant. Honda also adds that U.S. workers are not used to the complexity of producing as many different models on the same assembly line, compared to their Japanese counterparts, so there would need to be some extra training.
German says that there could also be a supplier issue with the battery.
“If we were going to build hybrids in the U.S.,” German says, “then Sanyo would have to set up an operation over here to supply it. The whole volume of hybrids is going to take off in the next year with the (Lexus) RX400h and the Accord hybrid and then it will take another year or two and we’ll see how things shake out.”