Honda Insight -- Integrated Motor Assist

9/15/2000 9:36:29 PM

In order to achieve their goal of making the Insight the world's most fuel-efficient gasoline-powered automobile, Honda engineers designed an entirely new gasoline-electric drive system called Integrated Motor Assist (IMA(TM)). The IMA system offers the advantages of a hybrid propulsion system -- low emissions and high fuel efficiency In addition, it offers several advantages generally not associated with such systems, such as simplicity, light weight and "transparent" operation (the driver does not need to alter his or her driving style to take into account the battery charge or driving range). Another advantage of the IMA system is its long-range driving capabilities -- the Insight can travel in excess of 600 miles on a single 10.6-gallon tank of gasoline.


  • World's lightest, most efficient 1.0-liter gasoline automobile engine
  • Meets California Ultra-Low Emission Vehicle (ULEV) standards
  • Offset cylinder bores minimize piston side-thrust friction
  • Compact, high-strength connecting rods
  • Low-friction pistons
  • Lightweight magnesium oil pan with integrated oil-filter bracket and AC-compressor bracket
  • Lightweight, plastic intake manifold, water-pump pulley and valve cover
  • Compact lean-burn VTEC(TM)-E cylinder head with single rocker-shaft valvetrain
  • Coaxial, low-friction roller-element rocker arms
  • Compact integrated exhaust manifold -- exhaust manifold is integrated into the cylinder head casting (world's first use on a gasoline automo-bile engine)
  • Nitrogen oxide adsorptive catalytic converter
  • Ultra-thin IMA electric motor assists gasoline engine during acceleration, functions as a generator to recharge the battery pack during deceleration and serves as the gasoline-engine starter motor
  • IMA Power Control Unit (PCU) efficiently controls electric power distribution, DC-DC voltage conversion and charging system
  • Idle-stop system
  • Compact nickel-metal hydride battery pack saves weight and needs no external charging system
  • Lightweight 5-speed manual transmission

The Insight's IMA system owes much of its remarkable performance to the application of numerous technologies developed by Honda over the past four decades, including lean-bum combustion, low-emission engines, variable valve timing, high-efficiency electric motors, regenerative braking, nickel-metal hydride battery technology and microprocessor control. In the IMA system, Honda engineers have optimized the performance of each of these technologies to create an efficient, lightweight and compact hybrid drive system that people can easily use and that does not require any changes in lifestyle. Here's how it works:

Primary motive power for the Insight is provided by the system's 1.0-liter, 12-valve, 3-cylinder, VTEC-E gasoline engine. Although the engine alone provides sufficient driving performance, even in sustained uphill driving, a permanent-magnet electric motor mounted between the engine and transmission provides power assistance under certain conditions, such as initial acceleration from a stop. And since the electric motor is used only for power assistance and not for primary motive power, it too can be made smaller and lighter relative to the full-size traction motors in other hybrid systems.

As the IMA gasoline engine enters its mid- to high-rpm operating range, the electric motor assist ceases and power is solely supplied by the engine, which is operating in its high-rpm 4-valve mode.

Power for the electric motor comes mainly by recapturing energy from the forward momentum and braking of the vehicle, rather than from the gasoline engine. When the Insight is coasting or its brakes are applied, and the vehicle is in gear, its electric-assist motor becomes a generator, converting forward momentum into electrical energy, instead of wasting it as heat during conventional braking (vented front disc/rear drum brakes are still the main means of braking). If the charge state of the IMA battery is low, the motor/generator will also rechai~ge while the Insight is cruising, however, the advantage of regenerative braking is that it eliminates the need for a large, on-board electrical generating system, like the ones used on most parallel hybrid gasoline-electric drivetrains.

This beneficial spiral of decreasing weight, reduced size and complexity and increased performance continues with the IMA nickel-metal hydride battery pack (a technology Honda pioneered in its EV PLUS electric car), which is also smaller and lighter in weight than the ones used in other hybrid systems. The batteries are located under the cargo compartment floor, along with the IMA system's Power Control Unit (PCU).

The IMA electric motor also functions as a high-rpm starter motor.

Compared to a comparable internal-combustion-powered drivetrain, like that in a Honda Civic, the Insight's IMA system boasts an impressive 24-percent improvement in efficiency in combined-mode city and highway driving, while meeting California's stringent Ultra-Low Emission Vehicle (ULEV) standard.

Primary motive power for the Insight is supplied by a 1.0-liter, 12-valve, 3-cylinder VTEC engine linked to a 5-speed manual transmission. Built with lightweight materials, such as aluminum, magnesium and plastic, this super-efficient engine weighs only 124 lbs. and is the smallest and lightest 1.0-liter production gasoline automobile engine in the world.

Some of the advanced technologies used in the Insight's IMA gasoline engine include its compact VTEC-E cylinder head, nitrogen-oxide adsorptive catalytic converter, integrated cylinder head and exhaust manifold, and plastic-resin intake manifold, valve cover and water-pump pulley. Magnesium alloy is used to make the oil pan, and the IMA engine also boasts numerous advanced friction-reduction techniques that help minimize frictional power loss.

Fuel induction is via an advanced version of Honda's sequential programmed fuel injection, and the ignition is a direct type with individual ignition coils for each cylinder and long-lasting iridium-tipped spark plugs.


Displacement 995 cc
No. of Cylinders: 3
Bore and Stroke: in. (mm) 2.8 x 3.2 (72 x 81.5)
Weight: lbs.(kg) 124 lbs. (56.2)


73 @ 5700 rpm
(67 @ 5700 m gasoline engine only)


91 @ 2000 rpm
(66 @ 4800 rpm gasoline engine only)
Compression Ratio: 10.8:1
Valvetrain: 12-valve VTEC-E
Fuel Economy: tba
Emissions: ULEV

The IMA gasoline engine's 3-cylinder engine block is a highly compact, aluminum-alloy die casting. An unusual feature of the engine's design is that the crankshaft axis has been shifted, or offset, 14 mm, relative to the cylinder-bore axis. In other words, the crankshaft does not sit directly under the cylinder. This was done in the interest of minimizing friction caused by the side thrust of the pistons against the cylinder walls, just after top-dead-center, as each piston begins its descent on the firing stroke.

In a conventional engine, piston-side thrust and the friction it generates are the result of the crankshaft's resistance to turning at this point. This resistance is the result of the small angle formed by the crank throw relative to the centerline of the piston and cylinder. The IMA engine's cylinder bores are offset to be over the crank throw at this point, so the piston and connecting rod push straight down, thereby minimizing side force on the piston.

Cylinder-bore offset in the IMA engine accounts for as much as a three-percent reduction in internal friction.

Borrowing the technology from Honda's high-performance S2000 sports car, the IMA engine uses special compact, high-strength, forged-steel, carburized connecting rods. Carburization toughens the rod's surface so that it resists crack formation. Carburizing allowed Honda engineers to reduce the cross section of the connecting rods, thereby reducing their weight (always a penalty in a reciprocating engine) by 25 percent, while increasing their strength by more than 50 percent.

In the interest of friction reduction, Honda engineers specffied a new lightweight aluminum-alloy piston design for the IMA engine. The pistons have a minimal skirt area and the surface of the skirt has been shot-peened. Shot-peening is a process in which a metal part, such as a piston or connecting rod, is blasted with shot-like particles, creating uniform, microscopic dimples on the surface. This dimpled surface is better able to retain a lubricating oil film. Shot-peening the IMA engine's pistons accounts for another 1.5- to 2.0-percent reduction in internal friction.

The Insight IMA engine features a magnesium-alloy oil pan. Like a cast-alu-minum pan, the Insight's magnesium pan adds stiffness to the engine block, helps muffle engine noise and also helps to cool engine oil, but it is 35 percent lighter than aluminum. The magnesium alloy specified for the Insight engine's oil pan is a new type that exhibits less thermal-induced expansion and contraction (creep) at high temperatures, so the oil pan remains oil tight.

Honda engineers designed additional weight-saving measures into the Insight's magnesium oil pan by incorporating the engine oil-fflter bracket, AC-compressor bracket and an engine-block stiffener into the casting.

The intake manifold used on the Insight's 1.0-liter engine is made out of plastic resin instead of aluminum alloy. The entire manifold weighs only 2.2 pounds, roughly half the weight of a comparable aluminum manifold. The individual pieces that make up the manifold, such as the intake runners, plenum chamber and throffle-body mounting, are permanently connected with a vibration-welding technique.

Additional weight-saving engine components made with plastic resin indude a 0.39-pound water-pump pulley, a 0.2-pound air-intake tube and a 0.88-pound valve cover.

Much of the IMA engine's fuel efficiency comes from its newly designed VTEC-E (Variable Valve Timing and Lift Electronic Control for Economy) cylinder head and valvetrain, and advanced combustion technology. Earlier versions of the VTEC-E system have been used on other high-mileage Honda automobiles, including the Civic HX Coupe and Civic VX Hatchback. The new version is more compact, operates with less friction and features an expanded stratified charge area within the combustion chamber. These features, combined with the engine's advanced fuel-injection mapping, a NOR-control catalyst and the Lean Air-Fuel Sensor (LAF), help it to achieve its high fuel efficiency without sacrificing driveability.

The engine's LAF Sensor is designed to detect air-fuel ratios as lean as 25:1. The fuel-injection Electronic Control Module uses this data, along with engine rpm, crankshaft angle, throttle angle, car mass, coolant temperature and valve position, to maintain a lean air-fuel ratio below 2500-3200 rpm (depending on throttle position and engine load).

The VTEC-E engine can burn such a lean mixture partly because of a strong air-fuel swirl created in the combustion chamber, created by the mixture's entry through only one of two intake valves during low-rpm operation. Although the overall air-fuel mixture is lean, optimized injection timing, along with the vortex, creates a "stratified" charge -- the air-fuel ratio is richer near the spark plug and leaner toward the combustion chamber periphery. The richer mixture ignites more readily and creates a fast-burning, stable flame that promotes more complete combustion.

Above 2500 to 3200 rpm, the VTEC-E engine activates both of its intake valves. The additional valve area of 4 valves per cylinder (2 intake and 2 exhaust) satisfies the high-rpm breathing and power requirements of the engine.

The IMA engine's single overhead camshaft (SOHC) cylinder head uses a compact chain drive in place of a toothed belt, and features a new compact, low-friction VTEC valvetrain that uses a common shaft for both the intake and exhaust rocker arms. Placing all the rocker arms on one shaft eliminates the need for a second rocker-arm shaft, so the valve mechanism can be more compact.

An additional advantage of this design is its narrower included valve angle that better centralizes the stratified air-fuel charge around the spark plug for quick light-off and more complete combustion.

The VTEC rocker arms are a new, compact, low-friction design, adapted from the S2000 roadster, with the VTEC switching mechanism located coaxially with the roller elements. This new design reduces the reciprocating mass of the valvetrain, for more reliable high-rpm operation, and also allowed Honda engineers to reduce valve-spring load by 30 percent.

Another innovative feature of the IMA engine's aluminum VTEC-E cylinder head is its integrated exhaust manifold. The individual exhaust-manifold runners are part of the head casting, just like the exhaust ports. The shape and length of the manifold runners is optimized for efficient flow, and the system offers the advantages of faster heat transfer to the catalyst, for faster lightoff. Eliminating the need for a separate exhaust manifold also increases manufacturing efficiency, and offers greater compactness and lower engine weight. The IMA engine is the world's first production gasoline engine to use an integrated exhaust manifold.

Lean air-fuel ratios improve fuel economy and reduce hydrocarbon, carbon monoxide and oxides of nitrogen; however, conventional 3-way catalysts are not very effective in converting NOx into normal nitrogen when excess oxygen is present. To keep NO2 emissions within ULEV levels, Honda engineers added a new, nitrogen-oxide-adsorptive catalytic converter. The catalyst uses a proprietary mixture of platinum and other metals to attract NOx molecules to its surface (adsorption) during lean-air fuel mixture combustion. Then, when the IMA engine is operating with a richer air-fuel ratio, the catalyst combines these NOx molecules with the hydrocarbons and CO present in the exhaust to form water vapor, carbon dioxide and nitrogen. The engine's nitrogen-oxide-adsorptive catalyst plays an important role in helping the Insight achieve ULEV emission standards.

The IMA electric motor operates in parallel with the system's gasoline engine, supplying an additional 25 lb.-ft. of torque in assist mode. This eliminates the need for a separate, heavy electric drive motor. The high-efficiency, permanent-magnet motor has a maximum output of 10 kilowatts. The motor's ultra-thin design -- only 2.3 inches wide -- allows it to be mounted directly between the engine and transmission. The IMA electric motor's high torque characteristics at low speeds makes it ideal for assisting the IMA engine during low-rpm acceleration, thereby increasing overall efficiency during normal driving.

The motor also functions as the generator for the IMA system, thereby saving the additional weight of a separate unit, and as a high-rpm strter, quickly spinning the engine up to its idle speed. If the IMA system battery charge is low, a separate 12-volt battery and starter motor will start the engine.

Another innovative feature of the IMA system is the use of the electric motor to damp engine-idle vibration by application of reverse torque to the crankshaft. The reverse torque pulses are exactly in phase and opposite the 60-degree torque fluctuations of the gasoline engine. As a result, the Insight's LMA gaso-line engine is remarkably smooth throughout its operating range.

The IMA system's idle-stop feature saves fuel and minimizes emissions when the Insight is stopped by temporarily shutting off the gasoline engine. The system is automatically engaged when the driver places the gear selector in neutral and takes his or her foot off the clutch. A green "Auto Stop" light indicates when the feature is operating. When the driver pushes the clutch pedal and engages the transmission, the IMA motor immediately restarts the gasoline engine.

The JMA feature will not operate if the battery state of charge is low, or the engine has not warmed up, or if the air conditioning is operating. When the economy mode is selected, the idle-stop feature will work; however, it will periodically keep the engine idling so that the air conditioning can maintain a comfortable cabin temperature.

Also, if the transmission has not been shifted out of first gear, for example in slow-moving traffic, then the idle-stop feature will keep the engine running so that it will be ready to accelerate, and to conserve electrical energy.

The IMA system is controlled by the Power Control Unit (PCU), which is locat-ed under the cargo-area floor, along with the battery pack, high-voltage inverter, DC to DC converter, Electronic Control Unit (ECU) and two cooling fans. The PCU controls the flow of electricity between the lMA motor and battery pack, supplying energy to the assist motor when needed, and it also regulates the system's nickel-metal hydride batteries and controls the idle-stop feature.

Electrical power for the IMA system is produced by the IMA motor during regenerative braking and when cruising, and is stored in a bank of nickel-metal hydride batteries. Since the motor's power consumption when it is assisting is not as great as that of a full-time drive motor, the battery pack is also smaller and lighter. The pack consists of 120 D-sized with a total output of the system is 144 volts and 6.5 amp-hours.

Honda engineers designed a completely new 5-speed manual transmission for the Insight. Like the rest of the Insight, its new transmission is designed to be as lightweight and as compact as possible, and is sized to the power requirements of the IMA system. The new transmission weights just 91 pounds and is 9.25 pounds lighter and almost a half an inch shorter than the current Civic manual transmission.

In order to minimize power loss within the transmission, the gears have been carefully machined to reduce rotational mass. The transmission's lubricating system has also been redesigned to provide more efficient lubrication with a smaller oil capacity, thereby saving additional weight and size.

The transmission's shift linkage operates smoothly, with minimal effort, thanks to the use of shortened synchronizer sleeves and a redesigned reverse-gear mechanism. A neutral switch built into the transmission tells the IMA idle-stop feature when the transmission is in neutral.

Transmission Gear Ratios

First Gear: 3.461:1
Second Gear: 1.750:1
Third Gear: 1.096:1
Fourth Gear: 0.857:1
Fifth Gear: 0.710:1
Reverse Gear: 3.231:1
Final Drive: 3.208:1