2005 Honda Accord Hybrid Sedan Tutorial

SEE ALSO: New Car Buyer's Guide for Honda

Released September 17, 2004

Introduction

Since the Accord's launch as a compact hatchback car in 1976, it has earned widespread acclaim as a leader in smart design, superb quality and world-class efficiency. In its 28-year history, the Accord has constantly re-invented itself, going from that original compact hatchback to today's premium mid-sized sedan and coupe. The seventh-generation Accord V-6, released in 2003, once again raised the bar for performance, safety and value in the mid-sized segment with a highly efficient and powerful 3.0-liter, 240-horsepower, SOHC VTEC V-6 engine, 4-wheel disc brakes and a standard anti-lock braking system (ABS) on all models, along with standard features such as air conditioning, power windows, mirrors and door locks, and an AM/FM/CD stereo system. In addition, the 7th-generation Accord was one of the first mid-sized sedans to bring luxury features such as a voice-activated navigation system, XM satellite radio and side curtain airbags to the premium mid-size segment.

In 2005, the Accord further establishes its role as a technology, performance and efficiency leader with the introduction of the Accord Hybrid, the world's first V-6-powered gasoline-electric hybrid vehicle. Boasting the highest fuel efficiency for a V-6-powered automobile, Accord Hybrid utilizes the third generation of Honda's exclusive Integrated Motor Assist (IMA) hybrid system featuring new Variable Cylinder Management (VCM) technology. By combining a high-output V-6 engine and IMA with VCM, the Accord Hybrid Sedan provides even more power - 255 hp versus 240hp in the regular Accord V-6 Sedan - while improving fuel efficiency to an estimated 30 mpg city / 37 highway - better than virtually all 4-cylinder mid-sized sedans and similar to that of the compact class Civic Sedan, already a benchmark for fuel efficiency in the compact car class.

Accord Sedan Accolades Car and Driver's 10Best List - The sixth and seventh generations of Accord have a current streak of 5 consecutive years on the publication's annual review of new cars. In total an Accord has been named to the list in 18 of 21 years the magazine has compiled this list, the most of any car in over two decades of the magazine's award. Automobile Magazine 50 Hottest New Cars (2003) Perfect 10 (1996) - One of 10 most significant cars between 1986-1996) Intellichoice 2003 - Best Overall Value, Mid-sized Car under and over $21,000 2000-2002 - Best Overall Value, Mid-sized Car under and over $20,500 Maxim Magazine 2004 Car of the Year - Accord 6-Speed EX V-6 Coupe Consumer Digest 2004 Best Buy, Family Car Edmunds.com Best Family Car (Comparison Test, 1/2003) 2004 Consumer's Most Wanted - Sedan under $25,000

The Honda Accord Hybrid Sedan is designed to show that a hybrid powertrain can be an important component in the mainstream of America's automotive landscape that provides exceptional fuel economy while still improving power, performance and comfort.

With the introduction of the 2000 Insight - America's first hybrid-powered car and still the leader of the EPA's annual fuel economy ratings - Honda has been at the forefront of hybrid technology. The company followed up the Insight with a hybrid version of America's best-selling small car, the Civic Hybrid, introduced in March 2002 as the first truly mainstream hybrid and the first application of hybrid technology to an existing, high volume vehicle. With the addition of the Accord Hybrid, Honda becomes the only car company in the United States with three hybrid models available to consumers.

While using a more powerful and efficient version of Honda's IMA system, the Accord Hybrid Sedan also incorporates new, leading edge technologies that engineers are also applying to Honda's main line of cars and trucks.

Among these advanced technologies are its Variable Cylinder Management (VCM) system that allows for deactivation of three of the engine's six cylinders during cruising. The system also features an Active Control Engine Mount (ACM) an Active Noise Control (ANC) system to eliminate the potential effects of three-cylinder operation on cabin noise and engine vibration. This same technology is also being applied on the all-new 2005 Odyssey minivan equipped with the available i-VTEC engine. In addition, the Accord hybrid utilizes a dual scroll hybrid air conditioning compressor that is both belt (engine) and electric motor driven, allowing for more efficient operation of the Accord Hybrid's dual zone automatic climate control system even when the engine is in idle stop mode.

Combined, these technologies along with improvements in aerodynamics and weight saving features like an aluminum hood, allow the Accord Hybrid to achieve an estimated EPA fuel economy rating of 30 miles per gallon in the city and 37 mpg highway, up from an EPA-rated 21 city / 30 highway for the Accord EX V-6 Sedan - a fuel economy gain of 43 percent and 23 percent, respectively. The Accord's Integrated Motor Assist System (60%) accounts for over half the gains in city fuel efficiency, while Variable Cylinder Management (15%) and idle stop (25%) is responsible for the rest. During highway cruising, the VCM system (57%) provides the majority of the increase, while IMA (38%) and a lower drag coefficient and greater aerodynamics (5%) also contribute.

Accord Hybrid Highlights

• 3rd-generation Honda Integrated Motor Assist (IMA) system
• 3.0L i-VTEC V-6 engine
• Intelligent Power Unit (IPU) - Power Control Unit (PCU), Nickel Metal-Hydride (NiMH) battery pack, internal cooling system
• Idle Stop
• Variable Cylinder Management (VCM)
• Active Control Mount (ACM) engine mount system
• Dual Zone Hybrid Automatic Climate Control System

Unique Accord Hybrid Sedan Features

Exterior:

• Standard rear decklid spoiler
• Aluminum hood
• Unique front grille
• Exclusive, lightweight 16" alloy wheels with larger 215/60 R16 tires
• New combination AM/FM/XM radio antenna

Interior:

• Exclusive IMA digital readout
• Active Noise Control (ANC)
• New, illuminated steering wheel-mounted switches

Mechanical:

• 3.0L i-VTEC V-6 engine
• More powerful IMA system
  • 255 hp @ 6000 rpm
  • 232 lb.-ft. @ 5000 rpm
• Hybrid Idle Stop
• Variable Cylinder Management(TM) (VCM(TM))
• Dual scroll hybrid air conditioning compressor
• Active Control Engine Mount (ACM) system
• Modified 5-speed automatic transmission
• Electric Power Steering (EPS)
• Enhanced Traction Control System (TCS) with creep aid system
• Instant mobility flat tire repair system (IMS)

Unlike previous hybrid vehicles from Honda and other manufacturers, though, the focus for the Honda Accord Hybrid is not entirely on high fuel efficiency, but also on high performance. The use of Honda's new Variable Cylinder Management (VCM) system that deactivates the three of V-6 engine's cylinders to save fuel during cruising and deceleration allow Honda engineers to maximize fuel economy while the hybrid IMA system helps to increase peak power by 15 hp and 20 lb.-ft. of torque over the current Accord EX V-6. The Accord Hybrid Sedan improves on the current Accord V-6's 0-60 mph time by half a second (7.5 sec. vs. 8.0 for an Accord EX V-6). In addition, peak torque of 232 lb.-ft @ 5000 rpm is now spread out over a much flatter curve, which makes 90 percent available at engine speeds less than 4000 rpm.

Major Accord Hybrid Specifications
.	Accord Hybrid Sedan	Accord EX V-6 Sedan	Change from EX V-6
Engine displacement (cc)	2997	2997	.
Valve configuration	SOHC i-VTEC V-6	SOHC VTEC V-6	i-VTEC
Battery capacity	144V, 6.0 Ah	N/A	.
Horsepower @ RPM	255 hp @ 6000	240 hp @ 6250	+ 15 hp (6.3%)
Torque @ RPM	232 lb.-ft. @ 5000	212 lb.-ft. @ 5000	+ 20 lb.-ft (9.4%)
Transmission	New 5-speed AT	5-speed AT	Lighter, more compact
Wheelbase (in.)	107.9	107.9	.
Length (in.)	189.5	189.5	.
Width (in.)	71.5	71.5	.
Height (in.)	57.1	57.1	.
Passenger volume (cu. ft.)	102.7	97.7	+ 5 cu. ft. (5.1%)
Cargo volume (cu. ft.)	11.2	14.0	- 2.8 cu.ft (18.6%)
EPA Fuel Economy (mpg city / highway)	30 / 37 (estimated)	21 / 30	+ 9 mpg city (42.9%) + 7 mpg hwy (23.3%)
Driving range (based on hwy mileage)	633 miles	513 miles	+ 120 miles (23%)

Exterior Overview

When planning the current Accord Sedan, engineers were looking to put traditional Accord quality and reliability into a new package filled with more emotional appeal, and to employ sedan styling similar to popular luxury European sport sedans. The 2005 Accord Hybrid Sedan adds to this foundation design cues intended to help it achieve top-of-class fuel economy and to improve the car's aerodynamics and reduce its drag coefficient to a slippery 0.29. These additions include a rear decklid spoiler, lightweight 16" aluminum alloy aerodynamic wheels. Additionally, lightweight aluminum was used in the Accord Hybrid's hood, bumper frames and rear suspension knuckles, helping reduce overall weight.

Powertrain

In balancing the seemingly contradictory goals of high fuel efficiency and high performance, Honda combined the 3rd generation IMA system with the all-new Variable Cylinder Management (VCM) system that alone generates substantial fuel savings when full engine power is not needed (as in highway cruising and deceleration). Working together, the two systems provide exceptional fuel efficiency benefits when the engine is not at full capacity, but mid-sized class-leading power when the car is at full throttle. Overall, the VCM system helps to maximize highway fuel economy while the IMA system helps to maximize city fuel economy.

The engine used on the Honda Accord Hybrid Sedan is primarily the same as that of the Accord V-6, but with a few modifications to save weight and to allow for the use of Honda's VCM system. Foremost among these changes is the implementation of Honda's advanced i-VTEC system in place of the VTEC system of the Accord EX V-6.

Without any help from the electric IMA system, this 3.0L engine provides 240 hp and 217 lb.-ft of torque, but utilizes some lighter weight materials than the original version used in the standard Accord EX V-6.

First introduced to North America in the all-new 2005 Odyssey minivan, Honda's innovative Variable Cylinder Management (VCM) system has now been engineered to maximize fuel economy in the Accord's 3.0L i-VTEC V-6 in concert with the IMA system. It works by monitoring speed and throttle action to determine if full engine power is required, if not - as in steady cruising or minor acceleration, the rear bank of three cylinders is deactivated. Further efficiency is achieved when the fuel injection system cuts fuel to the three active cylinders when the car is decelerating or braking - a feature similarly employed in most Honda vehicles.

Additional efficiencies are gained by the use of lightweight magnesium for certain engine parts, and the Accord Hybrid Sedan's engine incorporates a new engine head to manage the VCM system. A new airflow sensor and a 2-axis belt drive with an auto tensioner help to maintain maximum efficiency and prevent power losses due to friction.

IMA technology

The 3rd generation of Honda's Integrated Motor Assist system - which incorporates an ultra-thin electric motor (68mm) mounted between the gasoline engine and automatic transmission - is the largest and most efficient Honda has produced. The motor produces 10 percent more horsepower assist (12 kW total) than the Civic Hybrid and 26 percent more supplemental torque (100.4 lb.-ft. total). During regenerative braking when the motor acts as a generator for the IMA's battery pack, the generator also produces 12% percent more kW of power (14 kW total), and in both cases, the motor is more efficient, transferring 97.5 percent (vs. 94.6% in Civic Hybrid) of the available energy in assist mode, and converting 95.2 percent (vs. 93.6%) of renewable kinetic energy into electrical energy in charge mode. In addition, the Accord Hybrid's Nickel Metal-Hydride battery pack and integrated cooling system are more compact, yet more efficient than that in a Civic Hybrid Sedan.

Transmission

A specially modified version of the existing 5-speed automatic transmission was specified for the Accord Hybrid Sedan. This new transmission is more compact than that in an Accord EX V-6 Sedan and is specially designed to work with the IMA's electric motor to maximize the motor's ability to regenerate electricity during regenerative braking.

The transmission uses a high response lockup clutch torque converter for improved fuel efficiency while an integrated electric oil pump helps provide smooth and quick restarts of the engine after idle stops. With a slightly wider range of gear ratios than the automatic transmission in an Accord EX V-6, acceleration is quick from the line and the taller 5th gear helps conserve fuel during highway cruising.

IMA Operation

Though drivers will notice a different experience when it comes to the reduced frequency of fuel stops, the actual driving experience is virtually identical to that of a traditional Accord EX V-6. The complex processes that make the Accord Hybrid the fuel efficient car that it is would go unnoticed if not for the small IMA display integrated into the car's speedometer.

At startup, the Accord Hybrid's engine runs at idle speed until the driver increases the throttle to begin accelerating. During acceleration, all six cylinders of the Accord Hybrid's 3.0-liter engine are active, with the IMA system helping if hard acceleration is required. If this is the case, the blue indicator bars in the Accord's IMA display will light to show that the IMA is in Assist Mode.

When the driver minimizes accelerator input at cruising speed, a number of fuel saving operations begin. First, the Variable Cylinder Management (VCM) system can deactivate the engine's rear bank of three cylinders to effectively cut fuel consumption in half. At the same time, the IMA's Intelligent Power Unit turns the IMA motor into a generator to begin regenerative braking and the IMA display's green bars illuminate to show the level of electrical energy being created. If, during cruising, power is required to maintain speed, the IMA motor will offer assist while the rear cylinders remain inactive.

As the vehicle begins to slow and the driver applies the brakes, more electricity is created through regenerative braking and the VCM system cuts fuel to the active front bank of three cylinders to further conserve fuel.
As the driver continues to apply the brake, the IMA system can completely idle-stop the engine when vehicle speed drops below 8 mph. An indicator in the instrument panel's tachometer flashes to alert the driver that the car is idle-stopped. When the driver releases the brake pedal, the IMA motor instantaneously spins the engine back into action with all six cylinders firing at idle speed. Occasionally, the idle stop feature is disabled when driving on a hot day and full air-conditioning power is needed by the hybrid air conditioning system. At all other times, idle stop can be activated once the vehicle speed exceeds approximately 10 mph.

Chassis Overview

The suspension and steering set up for the Accord Hybrid Sedan is essentially the same as that of the existing Accord EX V-6, except for the adoption of electric power steering (EPS) versus a traditional hydraulic power rack and pinion steering set up in the Accord EX V-6.

The 7th-generation Accord's 4-wheel double wishbone suspension continues to be one of the most sophisticated arrangements in the mid-sized sedan class. The front double wishbone suspension ensures accurate tracking at all vehicle speeds, while the rear 5-link double wishbone suspension mounted to the car's subframe helps to limit body roll during cornering and also isolates the cabin from road noise.

Electric Power Steering also contributes to higher fuel economy (engine power is not needed to pump the hydraulic system). While similar to the performance-oriented steering systems used in the Honda S2000 and the Acura NSX, the high-mounted EPS system in the Accord Hybrid is designed to provide complete steering operation during idle stop mode.

The Accord Hybrid Sedan also employs a similar braking system as to that of the Accord EX
V-6, which includes ventilated discs in the front and solid discs in the back. Braking is further enhanced by a standard 3-channel anti-lock braking system (ABS) and electronic brake distribution (EBD). Accord Hybrid has wider 215/60 R16 tires compared to those on the EX
V-6 Sedan.

Interior Overview

Continuing Honda's strategy of incorporating hybrid technology seamlessly into its mainstream vehicles, there are few interior differences between Accord Hybrid and an Accord EX V-6 Sedan. The main differences are the unique instrument panel meter display that shows the IMA system's charge and assist status, IMA battery charge levels, "ECO" light indicating VCM operation, along with trip and lifetime fuel economy readouts. Less obvious, but much more significant is Active Noise Control (ANC) - which helps to reduce the engine booming sound inherently created inside any engine that has cylinder deactivation, and a new hybrid air conditioning unit that is powered by a combination of the gasoline engine's drive belt and a supplemental electric motor depending upon cooling needs.

The Active Noise Control uses microphones in the front and rear of the passenger cabin to monitor the low-frequency "booming" noise created by three-cylinder engine operations. It then generates a counter-cycled sound wave through the car's audio system that effectively cancels the booming noise.

The hybrid air conditioning unit uses two air compressors, one connected to the gasoline engine and one connected to an electric motor. When full cooling is needed, as when a car is first started on a hot summer day, the HVAC control unit relies on both to create maximum cooling power. Under normal conditions, cooling is provided by either the belt-driven compressor attached to the 3.0-liter V-6 or the electric magnet driven compressor powered by the IMA battery. This allows the air conditioning system to work at virtually all times, even when the car is at idle-stop.

The Accord Hybrid Sedan features a standard leather-trimmed interior with heated front seats, an AM/FM/XM audio system with 6-disc in-dash CD changer, dual-zone automatic climate control, power windows, mirrors and door locks and a HomeLink remote system. The only factory option on the Accord Hybrid Sedan is the Honda Satellite-linked Navigation System with voice recognition.

Safety Overview

The Accord Hybrid Sedan retains all of the Accord's class-leading safety technology, including dual-stage, dual-threshold front airbags, dual front side airbags and side-curtain airbags to protect front and rear passengers in the unlikely event of a rollover impact.

In addition to the advanced passive safety technology of the Accord Hybrid Sedan, it also utilizes the same active systems as all Accord V-6 sedans. This includes four-wheel disc brakes with a three-channel anti-lock braking system, electronic brake distribution, and a 2nd-generation traction control system (TCS).

New with the Accord Hybrid Sedan is the car's Instant Mobility System, which replaces a traditional spare tire with a flat tire repair kit. The elimination of a spare tire provides an extra covered storage compartment within the car's trunk. The Accord's IMS provides a convenient and quick process to repair most flat tire situations.

Retail Gas Prices in the United States (August 6, 2001 to Present)

After a brief decline in prices at the end of 2001, retail gasoline prices have been rising steadily to a peak of 2.02 per gallon of regular (87 Octane), unformulated unleaded gasoline during the 2004 Memorial Day weekend. This is even more profound in states like California, where emissions regulations require further refinement of the gasoline sold. In California, the reformulated regular unleaded gasoline is currently going for $2.19 per gallon after reaching a peak of 2.33. Though the gas shortage of the mid-1970's was more substantial on an inflation-corrected basis, this is the first time in the history of the United States that gasoline prices have topped $2.00 nationwide.

At current prices in California, using an average of 15,000 miles driven in a year, Accord Hybrid Sedan drivers would reduce their fuel expense over $350 per year compared to a traditional Accord EX V-6 ($997/year vs. $1,369)*.

* 33 combined mpg (Hybrid) vs. 24 mpg (Accord V-6). SOURCE: US Department of Energy

Hybrid powertrains were developed originally to enhance fuel efficiency, and the IMA system in the Accord Hybrid is no different in that regard, helping the V-6 sedan achieve an estimated 30 mpg city / 37 hwy. What sets this iteration of Honda's Integrated Motor Assist apart from previous systems is the fact that along with the increase in fuel efficiency comes a marked gain in horsepower, torque and performance - making the Accord Hybrid Sedan the industry's first high performance hybrid car, delivering the power of a high-performance V-6 engine with the fuel efficiency of a 4-cylinder car.

Along with excellent fuel efficiency, the combination of this Accord's 3.0L i-VTEC V-6 engine with Variable Cylinder Management and Honda's 3rd generation IMA system produces 255 horsepower (+6.3% over an Accord EX V-6) and 232 lb.-ft. of torque (+9.4%). Internal testing shows the IMA's motor assist helps the Accord Hybrid improve its 0-60 mph time to 7.5 seconds versus 8.0 seconds for Accord EX V-6 Sedan, with the powertrain producing torque in a constant, flat manner - 90 percent of peak torque (232 lb.-ft) available below 4000 rpm.

Accord Hybrid Powertrain Highlights

• Peak power: 255 hp @ 6000 rpm, 232 lb.-ft. @ 5000

3.0L V-6 engine

• Lightweight, durable aluminum alloy block
• Single Overhead Cam (SOHC) head with i-VTEC
• Magnesium head cover
• Variable Cylinder Management (VCM)
• 4-valves per cylinder
• Programmed Fuel-Injection (PGM-FI)
• 6500 rpm redline
• Active Control Engine Mount System (ACM)
• Idle-stop feature

Integrated Motor Assist (IMA) Electric Motor

• 3rd-generation of Honda's patented gasoline-electric hybrid system
• Thin (68mm), brushless DC motor (vs. 65 mm in Civic Hybrid)
• Peak assist: 16.1 hp / 100 lb.-ft of torque (vs. 13hp / 46 lb.-ft. in Civic Hybrid)
• Peak generation: 14 kW (vs. 12.6 kW in Civic Hybrid)
• Maximum electrical current: 120 Volts (vs. 75V in Civic Hybrid)
• Intelligent Power Unit - Power Control Unit, Nickel-Metal Hydrid (Ni-MH) battery pack and Integrated cooling system
• Regenerative braking
• Improved 5-Speed Automatic Transmission

3.0-Liter SOHC i-VTEC V-6 engine

At the heart of the Accord's power plant is the same 3.0L V-6 engine as that in the Accord EX V-6, but with a few modifications to reduce space and weight and to allow for the installation of the IMA motor and new VCM system. This 60^o V-6 engine is designed to require only minimal maintenance, including oil changes every 10,000 miles and its first scheduled tune-up at 105,000 miles.

Aluminum alloy block

Like all Honda engines, the 3.0L i-VTEC engine used in the Accord Hybrid is built around a lightweight and durable aluminum alloy block that provides significant weight and long-term corrosion benefits over traditional iron blocks. The 60¹ V-6 block incorporates extra brackets to allow the mounting of the VCM's magnesium composite head cover and the IMA motor.

To further enhance durability, each cylinder contains cast-iron liners, while the crankshaft and each of the two camshafts are made of forged steel designed to minimize friction.

i-VTEC Engine with Variable Cylinder Management

One major improvement new to this engine is the implementation of the advanced version of Honda's variable valve-timing and lift electronic control (VTEC) system or i-VTEC. i-VTEC adds a level of "intelligence" to the legendary VTEC system by adding a Variable Cylinder Management (VCM) system that switches between six- and three-cylinder combustion. When high output is required, such as during startup and acceleration or when climbing hills, the engine operates on all six cylinders to deliver superior performance. During cruising and at low engine loads, the system idles the rear bank of three cylinders for improved fuel efficiency and reduced emissions. Further, the idled cylinders remain sealed, alleviating the pumping losses associated with intake and exhaust and giving fuel economy a further boost.

Variable Cylinder Management helps maximize fuel efficiency by making the Accord Hybrid's 3.0L V-6 engine effectively run on only three cylinders when the power needs are minimized, yet it can still seamlessly provide the full power of all six cylinders during hard acceleration or other high load situations. When full power is needed, i-VTEC instantly opens the valves and sends fuel to the three previously idled cylinders. When combined with the IMA motor, output peaks at 255 horsepower.

The Accord Hybrid's VCM system is similar to the VTEC-controlled Cylinder Idling System used on Civic Hybrid, but is more sophisticated. Where the Civic Hybrid's cylinder idling deactivates three of the engine's four cylinders during deceleration only to help improve regenerative braking efficiency, the Accord's VCM system, is able to deactivate the engine's rear bank of three cylinders during a variety of driving situations, including steady-speed cruising, light acceleration and braking. Thus, improving fuel efficiency, reducing emissions and making regenerative braking more efficient.

VCM Operation

The Accord Hybrid's i-VTEC V-6 engine features a Variable Cylinder Management (VCM) system that improves fuel economy by idling three of the Odyssey's six cylinders during cruising and deceleration. VCM deactivates the rear bank of cylinders by using the VTEC (Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while cutting fuel at the same time.

The rear bank of cylinders was chosen for deactivation because the front bank is best positioned for cooling performance. Idling the rear bank also helps to maintain the temperature of the catalytic converter beneath the cylinder heads, helping to maintain optimum emissions performance. The Accord Hybrid's spark plugs continue to fire even when the cylinders are deactivated. This minimizes plug temperature loss and prevents fouling induced from incomplete combustion during cylinder re-activation. Further, sparking in air alone results in higher voltages than in a fuel-air mixture because of the higher insulation resistance. Therefore, iridium-tipped spark plugs are used for their high resistance to wear at high voltages.

i-VTEC VCM System Designed for Rapid Switching at Low Engine Speeds

In a conventional VTEC system, hydraulic pressure pushes a single synchronizing piston, which is in turn pressed back by a return spring. The VTEC system locks the valvetrain's rocker arms to allow additional valves to open and increase engine breathing. Such systems require relatively high engine speeds since hydraulic pressure is used to push the spring. VCM, however, demands switching at low rpm. This is achieved by creating a hydraulic circuit with two systems, each capable of providing the hydraulic pressure required to push the synchronizing piston in the required direction. This design thereby allows switching from six cylinders to three cylinders in low-speed ranges. To achieve responsive switching to six cylinders when the driver quickly opens the throttle under hard acceleration or driving up hill, the system employs a new three-way solenoid spool valve to control the oil pressure for switching. These enhancements result in highly responsive VCM switching regardless of engine speed.

VCM monitors throttle position, vehicle speed, engine speed, automatic-transmission gear selection, and other factors to determine if the vehicle is cruising or decelerating. During cruising and deceleration, VCM deactivates the three cylinders on the rear bank of the engine. To further enhance control, the system also simultaneously determines whether engine oil temperature is suitable for VCM switching and whether catalytic converter temperature will remain in the proper range. While idling the cylinders, the system controls ignition timing, and turns the torque converter lock-up on and off, thereby suppressing torque-induced jolting during the switch from six to three cylinder operation. The result is a smooth, seamless switch between three and six cylinder modes that is nearly unnoticeable to the driver.

For cylinder deactivation operation, the synchronizing piston moves to isolate the valve-lift rocker arms from the deactivated cylinders' rocker arms. The deactivated cylinder rocker arms are operated by zero-lift cams that deactivate the cylinders by closing the intake and exhaust valves.

Active Control Engine Mount System (ACM)

Due to the inherent increase in engine vibration when VCM has deactivated the rear bank of cylinders, an Active Control Engine Mount system (ACM) is used to minimize the effects of engine vibration. The system uses sensors that alert the Electronic Control Unit (ECU) to direct ACM actuators to move in synch with the vibration, thereby eliminating the vibration being transmitted to the passenger compartment. Additionally, an Active Noise Control system (ANC) works in cooperation with the ACM. An ANC controller with front and rear microphones in the passenger cabin detects the booming noise associated with cylinder deactivation and instructs the audio system's speakers to emit an opposite sound wave. (See the Interior section for more information on ANC.)

Idle stop

As with previous versions of Honda's hybrid powered cars, the IMA system incorporates an idle-stop feature that temporarily turns off the gasoline engine when the vehicle comes to a stop from speeds over 10 mph. In this situation, the IMA's ECU monitors the closed throttle, speed and brake pressure to determine the driver is bringing the car to a stop. The engine is turned off when the car's speed drops below 10 mph (16 km/hr). When the brake pedal is released, the IMA's motor restarts the engine and power is available immediately.

Unlike the idle-stop feature in the Insight and Civic Hybrid, the Accord Hybrid system continues to operate even while the car's automatic climate control system is in use. This is made possible by the introduction of a new hybrid air conditioning system, which uses air compressors powered by both the gasoline engine's drive belt and IMA electric motor (see Interior). Idle-stop is unavailable only when the car is first started on an extremely hot day when maximum cooling is required.

IMA System

The 3rd-generation IMA system is the largest and most efficient to come out of Honda's hybrid development program. As with previous versions, the IMA system consists of an ultra-thin DC brushless electric motor mounted between the gasoline engine and the automatic transmission, and an intelligent power unit (IPU) that stores electric power in a compact battery box and controls the flow of electricity to and from the electric motor. Also new with this generation of the IMA is the mounting of a 15cc air compressor to the electric motor which provides increased cooling capacity to the Accord Hybrid's dual-zone automatic climate control system (see Interior).

IMA Electric Motor

Providing supplemental power boost to the V-6 engine, the IMA's electric motor is designed to provide up to 12 kW (16 hp) and 136 Newton-Meters (100 lb.-ft) of additional power and torque to the Accord Hybrid's engine. Mounted between the engine and the Accord Hybrid's 5-speed automatic transmission, the IMA motor is an ultra-thin (68 mm) DC brushless design and provides a substantial amount of low-end torque to aid in hard acceleration and hill climbing.

In addition to providing supplemental motive power, the IMA motor acts as a generator during deceleration and braking to recapture kinetic energy and recharge the IMA's battery pack during regenerative braking, and provides power to the dual scroll hybrid A/C compressor used in the Accord's dual zone hybrid automatic air conditioning system (see Interior).

For this third generation of IMA motors, a new internal permanent magnet was designed to increase output density and make the motor more efficient than previous motors. At startup, the Accord hybrid provides 26 percent more starting torque than the Civic Hybrid. During driving, the motor provides a 20 percent increase in horsepower assist and more than doubles peak torque (100 lb.-ft. from 46 lb.-ft) compared with the Civic Hybrid's IMA motor; and it is more efficient, now converting 97.5 percent (versus 94.6 percent efficiency of Civic Hybrid IMA) of the available electricity into motive energy in assist mode.

IMA Intelligent Power Unit (IPU)

Power for the IMA system is controlled through the Accord Hybrid's Intelligent Power Unit. Located directly behind the rear seatback, the IPU consists of the Power Control Unit (PCU) - or the IMA's brain, a rechargeable Nickel Metal-Hydride battery module, and an integrated cooling unit.

• Power Control Unit (PCU) - Electronically controls the flow of energy to and from the IMA's electric motor. Using the latest in computer chip technology, the PCU's response time is quickened over previous versions, and a new inverter and DC/DC Converter help contribute to the IMA's overall increase in peak power.
• Battery Pack - Energy for the IMA motor is stored in a bank of Nickel Metal-Hydride cells. This bank of 120 1.2V units stores up to 144 Volts of electrical energy for the IMA motor, as in previous versions. But a new SANYO dual module casing reduces weight from previous hybrid battery packs and also allows it to increase efficiency of the electrical flow.
• Integrated Cooling Unit - To offset the heat generated by the constant flow of electricity to and from the battery pack, an integrated cooling system is mounted directly on the battery pack's outer box. Interior cabin air is continually flowed over the battery pack, and recirculated via a small vent placed on the rear parcel shelf.

Regenerative braking

A key to the long-term viability of hybrid-powered vehicles is their ability to recapture kinetic energy via regenerative braking and store this energy as electricity in rechargeable battery packs. Accord Hybrid is no different, as its IMA electric motor also acts as a generator to recharge its battery pack during steady cruising, deceleration/coasting and braking.

Accord Hybrid's efficiency in generating electricity from braking energy is enhanced by a more efficient IMA motor/generator, the ability of the engine and transmission to minimize friction through the VCM system and a modified 5-speed automatic transmission. Exploiting these friction-saving features during electricity generation, the IMA motor is able to convert 95.2 percent of the available kinetic energy into electricity to store in the IMA's rechargeable battery pack. This is an improvement of almost two percentage points over the previous Civic Hybrid's generator efficiency (93.5%).
This greater efficiency is achieved through more efficient cooperation between the transmission and the IMA motor, and a more sophisticated the idle stop feature that cuts fuel to the engine and reduces excess friction losses due to engine idling.

5-Speed Automatic Transmission

To increase performance through quicker shifts and a wider range of gear ratios and to aid the IMA system's ability to recapture kinetic energy through regenerative braking, Accord Hybrid employs a new 5-speed automatic transmission.

Sixty millimeters thinner than the version of 5-speed transmission used on the current Accord EX V-6, this transmission contributes to improved fuel efficiency through a new lockup clutch torque converter that shortens shift response during acceleration, more immediate startup after idle-stops by using of an integrated electric oil pump, and smoother ride during hard acceleration. While a new long torsion damper works with the VCM system to increase the rpm range during which VCM is activated to further contribute to improved fuel economy.

Integrated Electric Oil Pump

In order to generate the hydraulic pressure necessary to shift gears through its torque converter, most automatic transmissions experience a lag between shifts while the engine spins the drive shaft and the counter-spinning torque converter spins to create oil pressure. The Accord Hybrid eliminates this lag, which subsequently improves fuel efficiency, by using an integrated electric oil pump to constantly pump oil through the transmission's torque converter. This is particularly important for the Accord Hybrid when restarting after an idle stop when the gasoline engine is providing no power to the drive shaft.

High-response lockup clutch torque converter

In addition to the electric oil pump which maintains consistent pressure within the transmission, the torque converter itself employs an advanced, compact design that improves shift response time to one-third of that in the Accord EX V-6's automatic transmission. Regardless of gear, or vehicle speed, shift engagement takes place in less than half a second, which results in smoother acceleration and improved fuel economy.

In combination with the integrated oil pump, this new high-response lockup clutch torque converter helps improve city fuel economy by more than 1.5 mpg

Internal testing shows Accord Hybrid achieving an estimated fuel economy rating of 30 miles per gallon in the city and 37 mpg highway, up from an EPA-rated 21 city / 30 highway for the 2004 Accord EX V-6 Sedan - a fuel economy gain of 43 percent and 23 percent, respectively. The Accord's Integrated Motor Assist System (60%) accounts for over half the gains in city fuel efficiency, while Variable Cylinder Management (15%) and idle stop (25%) is responsible for the rest. During highway cruising, the VCM system (57%) provides the majority of the increase, while IMA (38%) and a lower drag coefficient and greater aerodynamics (5%) also contribute.