The combustion pressure in diesel engine cylinder rises intensely and the maximum pressure is extremely high compared with a gasoline engine, because of the differences in the combustion methods (see Diesel Engines and Gasoline Engines (2) ). As a result, diesel engines generally produce more noise, vibration and harshness (NVH) than gasoline engines, and this is a major complaint among diesel users. Isuzu is making efforts to reduce the NVH to the level of gasoline engines by making full use of the latest technology.
Pilot Injection System to Reduce Combustion Pressure
|The sudden rise in combustion pressure is a major source of diesel engine noise. By the development of the common rail high pressure injection system and electronic fuel injection, flexible and precise control over the injection timing and amount have been made possible. The fuel pressure rise can be controlled by smoothing the combustion process by pilot injection, a method in which a small amount of fuel is injected and ignited just before the main fuel injection process.|
Increased Rigidity of Engine Structure
The maximum cylinder pressure in diesel engine is considerably high and the pressure rise during combustion is very rapid, causing the engine vibration and noise. Also, diesel engine components such as the piston are solidly built in order to endure the high pressure and pressure increase ratio. The extra weight of these components translates into increased inertia, the scale of vibration. It is possible to control noise generation by reforming the engine structure to absorb vibration and to reduce the overall level of vibration. Moreover, vibration travels from the piston to the connecting rod, crankshaft and engine block. This form of vibration can be attenuated by employing a ladder frame structure with a more rigid crankshaft bearing.
|A secondary balancer is used to help smooth out the vibrations characteristic of four-cylinder engines.|
|Pairs of gears or scissors gears, working side by side with the same numbers of teeth, help to reduce mechanical engine noise byreducing the gear play.|
|The two sides of the flywheel, which face the engine and the transmission respectively, are each fitted with a spring and damper to absorb driventrain vibration caused during changes in speed.|
|A silencer installed in the intake pipe reduces the air noise drawn into the engine.|