Registreringsdatum: 15 mars 2007
|Postat: 2008-02-17 12:38:33 Rubrik: Motor / Drivlina (På engelska)
The standard engine on the NSX is an all-aluminum, 90-degree, 3.2-L (3179 cc), dual overhead cam, 4 valve per cylinder V-6 that produces 290 hp at 7100 rpm and 224 lb ft of torque at 5500 rpm. It is mated to a 6-speed close-ratio manual transmission. Redline is at 8000 rpm.
The optional electronically controlled 4-speed automatic transmission comes with an all-aluminum, 90-degree 3.0-L (2977 cc), dual overhead cam, 4 valve per cylinder V-6 with 252 hp at 6600 rpm and 210 lb ft of torque at 5300 rpm. Redline is at 7500 rpm.
An exclusive electronically controlled Variable Valve Timing and Lift Electronic Control (VTEC) system optimizes volumetric efficiency at both high and low engine speeds. A unique Variable Volume Induction System changes the configuration of the intake system with varying engine speeds, working with the VTEC system to broaden the torque curve and increase peak power output. The 3.2-L engine boasts a stainless steel exhaust header system to improve engine breathing.
ENGINE BLOCK, CYLINDER HEADS, CRANKSHAFT, PISTONS
To achieve both light weight and durability, the engine block is made of aluminum alloy. While cast iron cylinder liners are used on the 3.0-L engine, the cylinders on the 3.2-L V-6 are made using advanced metallurgical technique called Fiber Reinforced Metal (FRM), in which an a ultra lightweight alumina-carbon fiber is cast into the traditional aluminum alloy for enhanced rigidity. This process not only allows displacement to be increased without increasing bore centers, it provides outstanding cooling characteristics.
The 3.2-L engine has cylinder bore surfaces consisting of a 0.5 mm-thick layer with fibers of carbon and alumina (aluminum oxide, or Al203) in the aluminum alloy. In production, the cylinder block's aluminum alloy is poured around cylinder cores composed of these two fibers. The cores absorb the molten aluminum during the casting. After casting, the cylinders are bored to a slightly smaller diameter than the outside diameter of the cores, leaving a tough, wear-resistant, composite cylinder wall integral with the block but reinforced by the fibers. The process allows larger bores within the same external block dimensions and bore spacing, and makes open-deck block construction possible. This is appropriate for the 3.2-L NSX engine's higher performance level. The elimination of iron cylinder liners, allows a weight reduction of 2.4 kg for the larger displacement engines.
In the 3.0-L engine, conventional aluminum pistons are used. However, because aluminum-on-aluminum is not an ideal combination for durability with a piston sliding in a cylinder, the 3.2-L aluminum pistons are given an iron coating. The piston crown has been reshaped to improve heat resistance, and the pin diameter enlarged to cope with the higher power output.
The crankshaft on the NSX engine is a forged unit made of a special high-strength steel to cope with the high power output of both engines.
The cylinder heads are low-pressure cast aluminum. To increase flow into the combustion chamber in the 3.2-L engine, the intake valves have been increased by 1 mm to a 36 mm diameter. Even though the valve diameter was increased, a unique cup shape was incorporated into the valve head to allow it to maintain the same weight. To further increase air flow, by creating a gentle radius leading from the intake port into the combustion chamber, a special four-angle valve-seat machining process is used - a process typically reserved for racing applications. The head gasket on the 3.2-L V-6 is now made of stainless steel to ensure a positive seal with the new FRM cylinders. The combustion chamber for both engines is a pent-roof design with generous squash area to promote swirl and enhance combustion efficiency. The spark plug is centrally located for optimum flame propagation and features a platinum tip for improved durability and longer service life.
TITANIUM CONNECTING RODS
The connecting rods are made of a specially patented titanium alloy. While titanium rods are common in Formula One and other race engines, this is the first application of titanium rods in a production car. Compared to a steel connecting rod for the same engine, these titanium rods each weigh 190 g less and are significantly stronger. To cope with the increase in power, the 3.2-L engine's piston pin diameter has been increased by 1 mm ( from 22 mm to 23 mm), while the crankshaft pin diameter was increased by 2 mm ( from 53 mm to 55 mm).
To accommodate the larger crankpin diameter, the connecting rod bolts were moved 1 mm farther apart and incorporate a new, high-strength design. The rod bolts used are actually stronger, yet 1 mm smaller in diameter and 20 percent lighter than those previously installed. .
VARIABLE VALVE SYSTEM TIMING AND LIFT ELECTRONIC CONTROL (VTEC)[/b]
Without question, the Variable Valve Timing and Lift Electronic Control (VTEC) system is recognized as a breakthrough in engine technology. It convincingly solves the age-old trade-offs between low-end torque and high-end power.
The heart of the VTEC system is a unique camshaft and rocker arm system. For each cylinder's set of two intake (or exhaust) valves, there are three rocker arms and three corresponding lobes in the camshaft. The two outboard lobes each have a profile suited for low- to mid-rpm operation. The third or center camlobe has a dramatically different profile designed for Ionger duration and higher lift. This lobe profile is designed to optimize breathing and hp production at high engine speeds. At low engine rpm, the valves are operated by the outboard lobes. During high-speed operation above 5800 rpm, the VTEC computer sends a signal to a spool valve, which in turn delivers engine oil to small pistons in the rocker arms. Oil pressure causes the pistons to slide, locking all three rocker arms together. Once locked, the rocker arms are forced to follow the center cam lobe, increasing top-end performance. The crossover from low lift to high lift occurs in 0.1 seconds and is virtually undetectable to the driver.
VARIABLE VOLUME INDUCTION SYSTEM
In addition to VTEC, the NSX engine also uses a Variable Volume Induction System. This system uses a separate intake air plenum, located beneath the main intake manifold. This second plenum is separated from the primary manifold by 6 butterfly valves, which open between 4600 and 4900 rpm and are actuated by manifold vacuum.
When the valves open, the added volume of the secondary plenum creates a higher resonance frequency, which in turn creates a sonic pressure wave. This sonic pressure wave hits each pair of intake valves just as they open, promoting more rapid and complete cylinder filling. This system was designed to work in concert with VTEC to improve both low-end torque and high-rpm power.
Programmed Fuel Injection (PGM-FI) ensures that each cylinder receives the precise amount of fuel necessary for the present load and speed conditions. This system has been specially tailored to the unique capabilities of the induction and VTEC systems. An air-assist mechanism aids fuel atomization for better combustion at low temperatures. To provide additional fuel for the new 3.2-L V-6, the flow rate of the injector has been increased by 15 percent.
ONBOARD DIAGNOSTIC SYSTEM (OBD-II)
An onboard diagnostic system incorporated into the engine-management-electronics system records and stores information on engine systems and operation. These can be retrieved through the diagnostic port to facilitate maintenance and repair.
The NSX features a lightweight, highly efficient exhaust system. On the 3.2-L V-6, the exhaust manifold is made of stainless steel header pipes, rather than a cast-iron manifold, for improved performance and lighter weight. Increased flow from this configuration is a key contributor to 20 additional hp drawn from this engine.
The catalytic converters displace 1.14 Ls and are close to the engine for quick converter light-up and a consequent reduction in emissions without any sacrifice in power output. The overall weight of the unit has also been minimized by using spherical joints in the exhaust system rather than conventional flexible tubes.
DIRECT IGNITION SYSTEM
To ensure a hot, stable spark at high rpm operation, the ignition system has a coil mounted atop each spark plug, a design similar to that used in Formula One racing engines.
A compact, close-ratio six-speed manual transmission is designed to provide short shift throws and quick, precise response. Dual-cone synchronizers are used on first through fourth gear to reduce shift load from 40 to 50 percent for quicker, smoother shifting. Reverse gear is also eqipped with synchromesh. To increase performance while maintaining excellent fuel economy, the five first ratios have been lowered while sixth gear is seven percent higher than fifth gear in the previous NSX. A reverse lock-out solenoid ensures proper gear selection when shifting into sixth gear. The transmission is also designed for outstanding durability in the high-performance application.
To handle the high torque and power output of the 3.2-L V-6, a dual-mass flywheel clutch system was developed. The design involves a split flywheel that incorporates a grease-lubricated wide-angle torsion mechanism. Gear rattle is effectively minimized because the system is specially tuned to the NSX drive system. Clutch performance is maximized by a high performance friction material on the low-inertia mass clutch disc while the relocation of the torsion mechanism to the flywheel side helps retain a light clutch feel.
SPORTSHIFT AUTOMATIC TRANSMISSION
The optional SportShift four-speed automatic transmission allows the driver the option of letting the transmission shift automatically in a conventional manner or selecting each gear manually by means of a fingertip-control shift lever on the steering column. Inspired by advanced Formula One transmissions, this dual-mode system was created to give the driver of an automatic the same sporting performance feel of a manual. Unlike some other similar systems, this one allows the driver to keep both hands on the wheel while selecting a gear. This feature adds to the safety of the vehicle by allowing the driver to concentrate his full attention on the road ahead.
The shift quadrant (PRNDM21) is depicted on the tachometer. SportShift mode is engaged by selecting the M, or manual, position. In M mode, the shift position is illuminated in a window to the right of the shift quadrant. To shift up, the fingertip control lever is moved up, and to shift down, the lever is moved downward. The CPU (central processing unit) is programmed to prevent any downshift that would cause the engine to over-rev.
Precise automatic transmission shift programming has resulted in minimal shift shock when downshifting during deceleration, maximizing the potential of the Traction Control System (TCS) and drive-by-wire throttle system.
The automatic is also equipped with a programmed lockup torque converter to improve fuel economy and reduce slippage. In the SportShift manual mode, lockup is available in second, third and fourth gear during both acceleration and deceleration.
The drive-by-wire throttle system replaces a conventional throttle cable arrangement with an all-electronic ystem that senses the throttle pedal position and relays that information to a computer. The computer, in turn, performs the actual throttle activation instantaneously. The system works by means of a throttle pedal sensor, a throttle angle sensor, an electronic control unit and a step motor to control throttle opening and provide fail-safe throttle operation. It works in harmony with the TCS to provide a broad range of control. This system also helps to enhance the precision of the cruise control system.