Inside Honda's IMA System

By Bill Siuru

Honda has long been a leader in applying advanced automotive technologies to increase fuel economy and reduce emissions. In the gasoline crisis days of the early 1970s, Honda introduced its Civic CVCC with its pace-setting Compound Vortex Controlled Combustion (CVCC) engine technology. A few decades later, Honda was the first automaker in America to have a hybrid electric vehicle (HEV) in its dealers’ showrooms.
The two-seat Honda Insight hybrid electric vehicle debuted in late 1999 as an early 2001 model…quite an accomplishment since, with the exception of Toyota, most of the rest of the industry is just now getting serious about hybrids. In 2003, Honda introduced its second generation HEV, the five passenger Honda Civic Hybrid.

Both Honda models are parallel hybrid configurations – in other words, the wheels are powered by both the internal combustion engine and an electric motor. These two Honda Integrated Motor Assist (IMA) systems feature a smaller-than-normal gasoline engine and a thin, pancake-type electric motor/generator located between the engine and transmission. Their fuel-thrifty internal combustion engines – a 1.0-liter three-cylinder in the Insight and a 1.3-liter four-cylinder in the Civic – provide all the power needed for most driving situations. When additional power is needed, such as when passing or climbing grades, the integrated electric motor/generator performs in ways similar to a supercharger, seamlessly kicking in to supply added power. The motor/generator also functions as a high-speed starter and as a generator for battery charging during regenerative braking.

Unlike the hybrid configurations used by Toyota and Ford, Honda’s hybrids cannot operate solely on battery power as pure electric vehicles under specific driving circumstances. Still, Honda’s IMA fits the longstanding definition of a true integrated full hybrid, designed from the ground-up to enable vehicles to run super-efficiently on shared internal combustion and electric power. Those who cast it as a “mild” hybrid do so incorrectly. The simpler and less costly “mild hybrids” being developed by some automakers typically use an integrated starter/generator that automatically shuts down an engine when a vehicle stops, then seamlessly starts it up when it’s time to go again. The result is a modest improvement in fuel economy of maybe 10 percent, an important achievement in an era where any bump upward in fuel economy is a good one, but a world apart from the 40, 50, and 60+ mpg fuel economy achieved by a full hybrid system like Honda’s IMA.


Honda hybrids achieve these significant fuel economy numbers through several means. Primarily, the motor/generator’s ability to augment internal combustion power allows the use of a smaller displacement engine with a commensurate decrease in fuel usage. Regenerative braking also recoups energy upon deceleration that would otherwise be wasted or simply dissipated as heat during braking. Electricity created in this process is stored in the batteries for use as electric power is needed. Automatically shutting down the internal combustion engine while idling, such as at traffic lights, also saves fuel. Reduction of vehicle weight through use of lightweight materials plus improved aerodynamics and decreased rolling resistance also serve to improve fuel economy.

VARIATIONS ON A THEME
The IMA system used in the Honda Insight features a 1.0-liter, three-cylinder VTEC-E (Variable valve Timing and lift Electronic Control) gasoline engine that produces 54-horsepower. The ultra-thin, permanent magnet, three-phase synchronous electric motor/generator sandwiched between the engine and transmission adds 13 horsepower (10 kilowatts) as needed. This adds up to a total of 67 horsepower, which gives sprightly, if not neck-snapping, performance. The best part is the EPA numbers: 60 city/66 highway miles-per-gallon with the five-speed manual and 57/56 mpg with the continuously variable (CVT) automatic transmission.


The larger Civic Hybrid uses a 1.3-liter, four-cylinder with advanced technologies like VTEC, Dual-point Sequential Ignition (i-DSI), two spark plugs per cylinder, a lean NOx (oxides of nitrogen) catalyst system for emissions reduction, and various friction-reducing techniques. This IMA powerplant capably produces a combined 93 horse-power. Like in the Insight, an ultra-thin, brushless DC motor/generator assists the internal combustion engine. Because of the high torque characteristics of electric motors, especially at low speeds, torque is increased by an impressive 66 percent at 1000 rpm. At an EPA rating of 46 urban/51 highway mpg with a five-speed manual transmission, this sedan gets up to 650 miles on a tank of gas. Civics equipped with a CVT automatic achieve a fuel economy rating of 48/47 mpg.

The latest entry in Honda’s stable is the 2005 Accord Hybrid with its V-6 IMA system, a 240+ horsepower package that provides better performance than the conventional V-6-equipped Accord, with the benefit of four-cylinder Civic fuel economy. To maximize fuel economy, this model also incorporates Honda’s new Variable Cylinder Management (VCM), which deactivates three of the six cylinders under low-load conditions without sacrificing performance.


In most states, Honda’s hybrids are certified as SULEVs, or Super Ultra Low Emission Vehicles. Because of the credits offered toward Zero Emission Vehicle mandates in California and certain Northeastern states, Honda equips its hybrids in these markets with a zero evaporative emission fuel system and additionally warrants the emission control system for 150,000 miles, making these certified Advanced Technology – Partial Zero Emission Vehicles (AT-PZEVs), the cleanest-running category of vehicles outside of fuel cell and battery electric vehicles.

A nickel-metal-hydride (NiMH) battery pack is used in Honda hybrids. The hybrid vehicle battery features stable output characteristics regardless of the state-of-charge status and is also extremely durable, designed to last 10 years under normal driving conditions. The brains of the IMA system is the Power Control Unit (PCU), which precisely controls the motor assist, regenerative braking, and battery charging functions, including both the NiMH battery pack and the conventional 12-volt battery used for lighting and power accessories. Just one example of the PCU’s function is illustrated during the power assist mode, when the PCU determines the amount of auxiliary electric power needed based on throttle opening, various engine parameters, and battery state of charge.

GETTING TECHNICAL
Clearly, that’s enough information for most people to digest. But if you’re a “gearhead” and you must know the specifics about how Honda’s IMA works, read on.



Operating in the motor mode, the IMA motor/generators starts the gasoline engine and instantly spins it up to 1000 rpm. As a back-up, this job can be handled by the Honda’s conventional 12-volt starter if, for example, the battery module state-of-charge is too low, the car is operating in extremely cold or hot weather, or in the unlikely event the IMA system fails. Direct current from the battery module is converted to AC electric power by the motor drive module (MDM). This electricity is supplied to the IMA motor/generator operating in motor mode for accelerating, climbing hills, and other high load conditions. For maximum acceleration, both the IMA motor/generator and gasoline engine are used. Under light acceleration, the motor/generator provides only partial assist in an amount determined by load and throttle position. Once cruising, the Honda hybrid is propelled solely by the gasoline engine. If the battery module state-of-charge is low, some of the engine’s output drives the IMA motor/generator operating in generator mode for recharging. If fully charged, a small output is still used for the vehicle’s 12-volt accessories and battery.


The gasoline engine is switched to the fuel cut mode when slowing down. The IMA motor/generator in the generator mode is driven by the vehicle’s wheels. The MDM converts its AC output into DC power for both battery module charging and the 12-volt system while slowing the vehicle. Partial charging occurs if brakes are not applied, while applying the brakes results in greater deceleration and electricity generation. Regeneration continues until engine speed drops to about 1000 rpm and when the transmission, either manually or automatically, is shifted into neutral. The engine will be shut down if the battery module state-of-charge is sufficient, although the engine may idle for a short time before stopping if it’s not clear that a stop is imminent. The engine will continue to run at a fast idle if battery charging is required.



Additionally, the gasoline engine is shut off when propulsion power is not needed unless air conditioning is required. The engine automatically stops when vehicle speed is below 19 mph and brakes are applied, or when speed is less than 3 mph. It will also stop when the transmission is in any gear, except first, before slowing down, or when the transmission is in neutral and engine speed drops below 1000 rpm. The engine is restarted when the accelerator is applied again, a gear is selected with the clutch disengaged on manual transmission vehicles, the brake pedal is released during deceleration, or the battery module’s state-of-charge drops below a threshold level. Idle stop will not operate if the engine has not yet warmed up, the transmission is in reverse, the battery module is not sufficiently charged enough for the IMA motor/generator to restart the engine again, or the system detects stop-and-go traffic conditions.


That’s Honda’s IMA in its smaller displacement versions as we know it today, although the latest V-6 IMA variant operates somewhat differently (a story for another time). It’s always possible that Honda could add a twist or two with a next-generation hybrid system, but with its Integrated Motor Assist powerplant providing such an admirable coupling of performance and fuel economy, it isn’t likely anytime soon. Plus, the IMA powerplant has proven to be quite scaleable, so expect to see it widely used on other Honda and Acura models in the future.

Ethanol or Gas?

By Bill Siuru, JR.
Millions of clean-running alternative fuel vehicles are plying American roads, ready and waiting to fill their tanks with ethanol fuel. These are flexible-fuel vehicles, or FFVs, marketed by Ford, General Motors, DaimlerChrysler, Isuzu, Mazda, and Mercedes-Benz since the late 1990s. FFVs are so-named because they can operate seamlessly on any mixture of E85 (a blend of 85 percent ethanol and 15 percent unleaded gasoline) or straight unleaded gasoline from the same tank.

Ethanol, or ethyl alcohol, is a clean burning fuel typically produced from corn, although other grains like wheat or barley can also be used. These feedstocks are abundantly available in this country. Besides its advantages as a renewable and domestically available biofuel, ethanol combustion in engines also results in modest reductions of harmful hydrocarbon and benzene emissions, as well as reduced carbon dioxide, a greenhouse gas.

Hmmm… domestically produced by American farmers and producers, lower emissions, and a huge number of vehicles with tanks a-waiting. So why is there such a monumental disconnect that finds millions of FFVs on the highway and only about 175 stations nationwide where drivers can fill up on E85?

This dichotomy is good example of what can occur when technology outpaces society’s ability to apply its use, in this case primarily due to economics and, unfortunately, politics. It’s also an example of how government incentives and subsidies can have unintended consequences. Lessons learned from the FFV experience should be examined and applied as the nation embarks on a path that will find us potentially using a much more technically challenging and expensive alternative fuel: hydrogen.

The dilemma can be traced directly to the Alternative Motor Fuels Act (AMFA) passed by Congress in 1988, a law that gives automakers incentives to develop and market vehicles that use fuels other than gasoline. Manufacturers can receive a credit of up to 1.2 miles-per-gallon for each FFV produced that can be applied toward meeting their Corporate Average Fuel Economy (CAFE) requirements. Unfortunately, there is no corresponding incentive to encourage development of a refueling infrastructure, which brings us to the nearly nonexistent E85 refueling infrastructure today.

Establishing an E85 infrastructure presents a significantly larger challenge than getting engines to run well on E85. Since alcohol fuels like ethanol cannot be moved readily through existing petroleum distribution pipelines, it must be transported by barge, rail, or truck. Contrasting this, modifying an engine to run on E85 is not that difficult, requiring a fuel sensor for detecting the real-time ratio of ethanol to gasoline being supplied to the engine at any given point in time and optimizing engine and fuel settings for this mixture. Items like stainless steel fuel tanks, Teflon-lined fuel lines, and modified injectors must also be used to ensure compatibility with ethanol since it’s a much more corrosive fuel than gasoline.

From a vehicle standpoint, the AMFA incentive is a resounding success. Manufacturers driven by the additional CAFE credits made more than a million FFVs last year and expect to produce twice as many in 2004.

Chevrolet Silverado, 5.3-liter V-8
Chevrolet Avalanche, 5.3-liter V-6
Chevrolet Suburban, 5.3-liter V-8

Chevrolet Tahoe, 5.3-liter V-8
Chrysler Sebring, 2.7-liter V-6
Dodge Caravan and Grand Caravan, 3.3-liter V-6

Popular models that can run on gasoline or E85 range from the Ford Explorer and Chevrolet Silverado to the Dodge Stratus and Mercedes-Benz C320. These vehicles are available in many, but not all, states, so check with your local dealer or your dealer’s fleet department to confirm availability in your area.

Still, while the vehicle end is a success, all this has not accomplished the AMFA’s primary intended goal of reducing the nation’s dependence on imported oil, not to mention significantly decreasing C02 emissions. According to the National Highway Traffic Safety Administration (NHTSA), extending these credits without expanding the availability of E85 actually increases petroleum consumption and greenhouse gas emissions. That’s because FFVs operating almost entirely on gasoline effectively decrease the CAFE for this FFV fleet by about 1.2 mpg. The credits given for the unused ethanol equates to somewhere between 20 to 56 million additional barrels of oil used annually.

Dodge Ram, 4.7-liter V-8
Dodge Stratus, 2.7-liter V-6
Ford Explorer, 4.0-liter V-6

Ford Exlporer Sport Trac, 4.0-liter V-6
Ford Taurus, 3.0-liter V-6
GMC Yukon, 5.3-liter V-8

Several solutions to this so-called CAFE loophole have been proposed. One calls for Congress to amend the existing AMFA law to only allow CAFE credits when automakers can certify that their AFVs actually use the alternative fuel. In effect, though, this would penalize the auto industry unfairly since automakers have done their part in developing and marketing FFVs. This strategy could potentially sour automakers’ interest in all AFVs and drastically reduce future investment in other fuel alternatives including hydrogen.

Additionally, if automakers no longer have incremental CAFE credits as an incentive for producing FFVs, they will most certainly stop making them since the incremental cost of making FFVs is now being absorbed in return for the CAFE credits. A more viable solution may be incentives for fuel providers to ensure that adequate fueling facilities are readily available anywhere AFVs are sold. Potentially, this could be federal income tax investment credits for each new alternative fueling site, which would cover most of the cost and thus make establishing these fueling sites attractive.

The infrastructure problem is com-pounded because ethanol is not a petroleum-based product, thus the petroleum industry has shown little interest in offering it. Indeed, ethanol is viewed as a competitor. In the U.S., three producers dominate the ethanol market and the largest, Archer Daniels Midland, controls nearly 40 percent of that market. Because there are so few producers, some fear the potential that supplies could be artificially limited and prices potentially manipulated upward. Additionally, an unintended consequence is that food prices could increase if it turns out that it’s more profitable to convert farm products to fuel rather than food.

GMC Yukon XL , 5.3-liter V-8
GMC Sierra, 5.3-liter V-8
Mercedes-Benz C240 Sedan and Wagon, 2.6-liter V-6



Mercedes-Benz C320 Sedan and Coupe, 3.2-liter V-6
Mercury Mountaineer, 4.0-liter V-6
Mercury Sable, 3.0-liter V-6

The ethanol lobby carries substantial clout in Washington and so has been able to obtain subsidies that distort the true market price of this alternative fuel. Since 1996, crop subsidies alone have been worth nearly $30 billion to the ethanol industry. Ethanol opponents make the case that these subsidies are taking money from taxpayers and giving it to the few ethanol producers, and thousands of corn farmers, without replacing any petroleum or even providing a cleaner fuel. Since ethanol receives a tax subsidy, a gallon of ethanol is taxed 5.3 cents less than a gallon of gasoline, which means that less tax revenue is funneled into the Highway Trust Fund for repairing and replacing roads and bridges. On the other hand, ethanol proponents suggest that with military assets protecting the flow of imported oil, the true price of gasoline is significantly distorted as well.

In use, most people will not be able to discern the difference between driving on E85 and regular gasoline. While ethanol does produce fewer BTUs (less energy) than gasoline, it has a significantly higher octane rating than un-leaded gasoline (100-105 octane versus 85-90). Testing of Ford FFV engines show about a 5 percent increase in horsepower when operating on E85. However, offsetting this is that drivers will notice a 5 to 15 percent decrease in fuel economy, depending on ambient temperatures and driving conditions.

This disparity could be improved if FFVs were optimized for E85, which is presently not the case – another consequence of the absence of E85 availability. Because of lower miles-per-gallon and the now higher per-gallon cost for E85, vehicle operating costs will go up. Currently, ethanol demands higher pump prices because this alcohol fuel is more difficult for refiners to blend with gasoline and also more expensive to ship into areas where corn is not grown.

What could make E85 the fuel of choice for motorists in the absence of government mandates? The best answer is the economics of the marketplace. If the price of gasoline climbs to a point where it equals or exceeds E85, drivers will soon be demanding E85 for their FFVs and traditional fuel suppliers will see a profit in meeting the demand. Such interest could be accelerated by an oil shortage such as a disruption of oil from the Mideast, something this country has seen before.

In a sense, you might even say the millions of FFVs on American roads today are as much an emergency energy resource as the millions of barrels of oil in the nation’s Strategic Petroleum Reserve. That’s food…or rather, fuel…for thought.