1993 Acura Legend Sedan- Powertrain

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OVERVIEW

The planners and engineers set ambitious goals for the second-generation Legend powertrain: to provide substantially higher performance, with greater smoothness and quietness and no sacrifice in fuel efficiency. To accomplish this, they developed a longitudinal drivetrain with a 3.2-liter, 24-valve V-6 engine. Stronger, more refined manual and automatic transmissions, a more durable differential and a new mounting system were designed to match the increased power and torque of the engine.

3.2-LITER ENGINE

The engine development team was given a mandate to develop an engine with significantly higher performance and greater refinement than its predecessor, with no increase in weight or fuel consumption. A new V-6 was determined to be the right size and weight while producing enough power to achieve the intended goals. Given the acceleration and fuel efficiency targets they had in mind for the Legend, they saw no need for a large V-8engine.

The engine displaces 3206 cc with a bore of 90.0mm and a stroke 84.0 mm. The cylinder block, like all Acura engines, is made of aluminum alloy and equipped with cast-iron cylinder liners.

VALVETRAIN

The cylinder heads are cast from the same alloy as the block. There are two camshafts (one per cylinder bank), driven by a single synthetic belt, and four valves per cylinder. The second-generation valvetrain incorporates a pent-roof combustion chamber and valves in V-formation. Both exhaust and intake valves are actuated by a single rocker arm each, and the hydraulic lash adjusters are set into the valve end of each rocker arm.

DIRECT IGNITION SYSTEM

The platinum-tipped plugs are ignited by a direct ignition system, similar to that used in the Honda Formula One racing engine and in the NSX engine. Instead of the usual single coil, there is an individual coil for each spark plug. A sensor mounted behind one of the camshaft pulleys triggers the ignition.The system improves ignition reliability, helping achieve 60,000-mile intervals between spark plug replacement.

DUAL KNOCK SENSORS

Incorporation of knock sensors, one for each cylinder bank, helped the engineers program the ignition advance map closer to the optimum for fuel economy and driveability.The sensors also allow the Legend engine to run safely (though with a slight loss of power) should the tank be filled with gasoline of octane lower than the recommended premium unleaded fuel.

VARIABLE INDUCTION SYSTEM

A boost for both high-end power and low-end torque is provided by a Variable Induction System, improved from that in the previous Legend and similar to that used in the NSX. A complex two-level intake manifold, made of aluminum to save weight, provides three possible paths for air being inducted into the engine. The path is selected by three butterfly valves that are electronically controlled and actuated by intake vacuum. Up to 3200 rpm, air for the two banks of cylinders is strictly separated and is led through the longer of two intake paths for optimum resonance charge effect at low engine speeds. At 3200 rpm, the two larger butterflies open and air flows through the shorter path for best resonance effect in the midrange. Then at 3900 rpm, the third butterfly opens to provide a large plenum serving all cylinders. At this point the resonance effect is reduced, but an inertia ram-tuning effect takes over to boost high-end breathing and power output.

MANUAL TRANSMISSION

The standard transmission for the Legend Sedan is a rod-actuated, fully synchronized 5-speed manual with a pull-type, hydraulically operated clutch. To enhance reliability and durability, internal oiling of the manual transmission is provided by a built-in, forced lubrication oil pump. Also included is an oil cooler for the manual transmission, integrated with the engine's aluminum radiator to lower oil temperatures and extend transmission life. To reduce noise, this transmission has a large gear tooth contact ratio. To provide smooth engagement second gear utilizes a double-cone synchronizer. For easier, quieter engagement, reverse gear is also fully synchronized.

AUTOMATIC TRANSMISSION

The Legend Sedan's optional automatic transmission is an electronically controlled four-speed unit that features the unique Honda R&D-designed constant mesh automatic gearbox and a programmed lockup torque converter.All shifting and torque converter lockup functions are electronically controlled via the transmission's 32K microprocessor, which is integrated with the engine computer into a single ECU.

To help achieve smooth shifting, the ignition is programmed to retard momentarily during upshifts and downshifts in order to reduce engine torque on the transmission's shifting elements. The transmission also features a low-hold clutch. This system will hold the transmission in first gear, something drivers will find useful for trailer towing and for steep uphill or downhill driving.

The housings of the manual transmission, the optional automatic transmission and the differential are all cast in aluminum to help keep the weight of powertrain to a mlmmum.

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