F2008-06-191
Development of High Pressure Fuel Pump for Direct Injection Gasoline Engine
Direct injection gasoline engine is growing in market as environmental engine for its advantage in power and fuel consumption. As a manufacture of automotive component and system, Hitachi introduced a high pressure fuel pump which enhances direct injection gasoline engines for higher power, better acoustics, and capability for ethanol fuel. This paper describes developing of fuel pump which realizes wide flow rate range with low noise emission, and capability for ethanol fuel, by introducing new construction of flow control valve, in combination with integrated relief valve and ethanol resistant material.
Conventionally, there were several structures of high pressure fuel pump in the market for direct injection gasoline engine. Due to increasing demand for less drive energy, smaller size, and low cost, single cylinder type with variable flow rate control became majority in the market. Single cylinder pump have benefit to meet those demands because of its simple structure; only 1 cylinder and 1 flow rate control valve. Yet, on the other hand, the challenge remained for increasing flow rate and decreasing noise.
Flow control valve, usually made by magnetic solenoid, controls output flow on every compression cycle, so it requires certain power to handle hydraulic force. Especially high flow rate pump needs high power for flow control valve, which consequently generates higher noise.
To overcome this trade-off between power and noise, new construction of flow control valve was designed. This unique structure has valve part integrated together with magnetic part which generates magnetic force to valve open direction. When at suction phase, magnetic part is pulled by valve which is motivated by hydraulic force, which then makes weak impact at stroke end. Compared to conventional flow control valve, which makes impact by magnetic force, impact noise is significantly reduced (-8dB compared to conventional Hitachi valve). On the other hand, it also has advantage to create large magnetic force to keep valve at open position. The reason is because magnetic part is sticked to its counterpart when valve is at open position. Since magnetic force works inverse proportion to the distance between 2 parts, it can create significant magnetic force when distance is nearly zero. Therefore, it makes easy to create high power to keep valve open with low drive current. Comparing to Hitachi conventional pump, drive current was reduced -80%, but valve open force was increased over +200%. As result, pump flow rate was increased +56% with nearly same package. Increased flow rate is also beneficial for ethanol fuel engine which requires more flow rate compared to gasoline fuel engine. It can be applied by using ethanol resistant material to pump parts. The construction of this flow control valve is unique for its concept that valve is normally closed, so that pump delivers fuel unless valve is controlled correctly. In order to avoid excess pressure at unexpected event, relief valve was integrated in pump.
Session: Fuel Injection II