Noise Reduction in Gasoline DI Engines 2011-01-0930

We developed a novel method for reducing the engine noise associated with the high-pressure fuel system in gasoline direct-injection (DI) engines. We focused on the level of noise at idle running speed, because at the idle state, engine noise is the only noise source to the driver. The dominant vibration source of the high-pressure fuel system was fuel pulsation from the high-pressure fuel pump and activation noise of the solenoid-drive injector. To reduce the noise of the idling engine, we focused on the vibration transmission path from the high-pressure fuel system to the cylinder head, which results in noise radiation from the engine block. Next, we focused on the radiation noise associated with the pressurization event of the high-pressure fuel pump. To reduce the vibration transmission from the high-pressure fuel system to the cylinder head, the fuel rail and the injector were isolated from the cylinder head by avoiding metal-to-metal contact. Furthermore, to reduce the radiation noise associated with the pressurization event of the high-pressure fuel pump, the fuel pump pressurization event was skipped periodically; that is, the pump pressurizes fuel intermittently.

The isolation method eliminated the transmission path from the vibration source (high-pressure fuel system) to the radiation source (cylinder head). Mid-frequency noise in the 1 to 3 kHz range was reduced by 5 dB by isolating the fuel rail from the cylinder head with rubber-like damping material. Moreover, high-frequency injector ticking noise above 5 kHz was reduced by 3 dB by suspending the injector from the fuel rail. The intermittent pressurization control method skipped the high-pressure fuel pump pressurization event periodically. The noise reduction effect was the minimum 5.8 dB (A) at 1.6 kHz and the maximum reached up to 7.5 dB (A) at 1.6 and 10 kHz. These two methods significantly reduced the level of noise radiation associated with a high-pressure fuel system in a gasoline DI engine.