Isuzu 3LA, Руководство пользователя

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VIII. Isuzu Technology: L-Series Direct Injection
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L-Series Diesel 49
Despite the very small differences in bore and stroke, the engines are virtually identical in other respects. Isuzu insists
new DI L-Series still offers OEMs a single engine family with high component commonality in both three and four
cylinder configurations.
The compact and lightweight L-Series feature one-piece, cast iron blocks and heads, and overhead valve design with
two valves per cylinder. The block is deep skirted for strength, rigidity and durability. Unit injection pump housings are
cast into the blocks. The engine water jacket is formed with a one-piece casting core to eliminate irregular cooling
passages.
The ductile iron crankshaft is underslung to the block with five main bearings for the 4LE2 and four main bearings for
the 3LD2. The flame-hardened, chilled casting camshaft is mid-mounted in the block and it is gear driven. The
camshaft is a one-piece design.
Low noise and vibration were very active design themes for the L-Series. A single camshaft actuates unit pump
injectors as well as intake and exhaust valves. Valves are actuated through forged steel push rods and aluminum die
cast rocker arms. Gears are helical and the number of gears in the gear train is only three and this permits a smaller gear
cover with a lower profile and reduced forward noise emissions.
Finite element analysis (FEA), modal analysis and acoustic intensity techniques were used to evaluate every engine
component and determine the contribution to the overall noise level. FEM was used to develop spherical cylinder block
sidewalls and to optimize bulkhead ribs. Integral camshaft journal bearings featured on the L-Series had a tendency to
lower rigidity of the engine block but this was overcome by numerous FEMJ iterations.
Other L-Series noise reduction features include the use of auto thermatic type pistons, an oil pan constructed of
vibration damped steel sheet on the 3LD2, crankshaft balancers and an optimized fuel injection system. There is no
difference in noise level comparing the DI and IDI at no load and only a 2 dB(A) difference at full load. Fuel injection
lines from the unit pumps to the injectors are short and all the same length. Additionally, the fan or blower speed can
also be lowered for an extra measure of noise reduction. Isuzu feels it has accomplished something with respect to
sound quality as well as sound level.
Both the 3LD2 and the 4LE2 direct injected diesels are naturally aspirated and feature Isuzu's new "Cobra" combustion
chamber, which uses an interesting high swirl conservation strategy. The aim is twofold. First, reduce the peak
temperature in the premixed combustion stage to lower combustion noise and NOx emissions. A two-spring injector is
vital to achieving this part of the rate shaping. Second, promote vigorous, fast mixing in the diffusion combustion stage
- after top dead center - to lower smoke and particulate matter emission and to improve fuel consumption.
The unit injection pump is driven by the camshaft lobes that have a concave-shaped cam profile and this determines
rate shaping throughout the combustion cycle. A lower initial injection rate in the premix stage and a higher rate in the
diffusion stage provides a more complete and efficient burn.
So most of the fuel is actually injected during the combustion diffusion stage via a high-pressure nozzle with small
holes to minimize fuel particle size and new combustion chamber design optimized through the use of computational
fluid dynamics (CFD) analysis. The entire combustion cycle is reduced in length, but it is characterized by relatively
higher swirl in the later stages.
Tier 2 compliance is the real driving force here, but fuel consumption should be lower 10 to 15 percent. The overall
efficiency of the DI L-Series engines is demonstrated by a heat rejection rate that is 20 to 25 percent lower than the
comparable IDI engines. Users may be less interested in fuel consumption lately, but the overall improvement in
efficiency cannot be overlooked.
The engine lube oil filler and level gauge, oil filter cartridge, unit injection pumps, and injection nozzles are all located
on the right side of the engines. The L-Series reputation for leak-free operation should be continued, always a strong
point for Isuzu. The fuel system is also self-bleeding and self-priming, meaning that should the operator run out of fuel,
he can just add fuel and restart the engine.
Summing up features of the new DI L-Series, high engine performance and efficiency, compliant with Tier 2
regulations; low noise and pleasant sound quality, low fuel consumption, low heat rejection, compact envelope size,
one side service access, high reliability. And don't forget, the same footprint as the IDI versions.