What Tree Huggers Can Teach Us

What Tree Huggers Can Teach Us
By Don Terrill © -

Hybrid cars may not be a symbol of power, but they are high tech. and can teach us a lot about getting the most out of our race cars. My favorite is the Honda Insight. See if you can pick out any speed tips from the Insight's engine description:
  • 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)
  • Horsepower: 73 @ 5700 rpm(67 @ 5700 m gasoline engine only)
  • Torque: 91 @ 2000 rpm(66 @ 4800 rpm gasoline engine only)
  • Compression Ratio: 10.8:1
  • Valvetrain: 12-valve VTEC-E
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.

Check out this great site on the Honda Insight

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