Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2002-06-13
2004-05-18
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S467000, C138S030000
Reexamination Certificate
active
06736111
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an internal combustion engine fuel injection system and more particularly, to a fuel injection system having a fuel rail with integral pressure damping and over-pressure compensation. In one embodiment, the pressure damping system is adapted to an Air Pressure Direct Injector (APDI) fuel injection system.
BACKGROUND OF THE INVENTION
Modern automotive fuel systems typically employ fuel injection systems that precisely control the flow of fuel from the fuel tank to each of the engine's cylinders. In a typical fuel injection system, fuel pressures operate in the range of 300-450 kPa, or even higher. Fuel enleanment to the cylinders and cylinder-to-cylinder maldistribution can occur when fuel flow and fuel pressures are not carefully controlled. Fuel enleanment (not enough fuel delivered to the cylinder) occurs when the amplitude of fuel pressure pulsations measured in the fuel rail varies with engine speed. This has the effect of changing the average fuel pressure while the injector is open, thereby changing the rate of fuel flow for the same injector. Cylinder-to-cylinder maldistribution (uneven apportionment of fuel between cylinders) occurs when the pressure oscillations at the injectors differ from one cylinder to the next during the injector event under constant engine speed and load. The resulting difference in average fuel pressure during the injector event causes variations in cylinder-to-cylinder fuel delivery. Either condition is undesirable and can cause higher emission levels, rough engine operation and a loss in fuel economy.
A typical “direct injector” fuel injection system wherein a metered fuel spray is delivered directly into the combustion chamber incorporates a plurality of electromagnetic injectors mounted in a fuel rail. The fuel rail receives fuel, under pressure, from a high-pressure pump, and delivers the fuel to the injectors. The rail also serves to position each injector so as to aim the injected fuel spray at a precise spot in the combustion chamber. In a typical direct injector fuel injection system, each injector, when pulsed open, simultaneously meters and delivers fuel to the associated combustion chamber. In an Air Pressure Direct Injector (APDI) system a staged injector, comprised of two separate injectors, is constructed to separate the fuel metering event from the fuel delivery event. The staged injector includes a fuel injector for fuel metering and an air injector, coupled in series and immediately downstream of the fuel injector, for the timed delivery of a charge of air along with the metered fuel to the combustion chamber. The APDI system delivers fuel to the fuel injector at approximately 800 kPa and air, through a separate delivery channel, to the air injector at approximately 650 kPa.
In operation, the two injectors of the staged APDI injector are pulsed, slightly out of phase. First, the fuel injector is opened to meter the fuel charge. Then, the air injector is opened to deliver a charge of air along with the charge of metered fuel to the combustion chamber.
In a typical direct injector fuel injection system, each injector is programmed to pulse or open every other revolution of the engine crankshaft. During an injector opening event in a direct injector fuel injection system, the measured fuel pressure in the fuel rail can instantaneously drop by more than 30 kPa, then can increase by more than 50 kPa after the injector closes. For a typical four cylinder engine operating at 2000 RPM, the combined injectors pulse at a rate of 66 pulses per second. In such injector-based systems, these pulses, dropping then raising the pressure in the rail, cause high frequency pressure waves of significant amplitude to propagate through the fuel rail(s) potentially causing erratic delivery of fuel to the cylinders. This condition is aggravated even further in an APDI system where a pair of injectors, firing out of phase, each at 66 pulses per second, induce pressure pulsations into the fuel rails.
In the past, vehicle manufactures have incorporated several types of pressure-damping devices to reduce pressure pulsations in the fuel rails. One such pressure-damping device is a spring diaphragm, similar to a regulator, attached to the fuel rail or the fuel supply line. One acknowledged problem with the spring diaphragm is that it provides only point damping and can lose function at low temperatures. Other problems associated with the use of the spring diaphragm are that it complicates the rail or fuel line, adds more joints susceptible to leakage, can permeate hydrocarbons through the diaphragm, necessitates additional hardware cost, and in many cases does not provide adequate damping.
Another pressure damping device known in the art is an internal rail damper. Two stainless steel shell halves are welded together to form a damper having a sealed airspace filled with trapped air disposed between two compliant sidewalls. The damper shells have relatively large flat or nearly flat sides that flex in response to rapid pressure spikes in the fuel system. The compliant sidewalls absorb the energy of the pressure spikes and reduce the wave speed of the resultant pressure wave thereby reducing the amplitude of the pressure spikes inside the fuel rails during injector firing events. The damping device is disposed inside the fuel rail and must be hermetically sealed and impervious to gasoline. Although internal dampers have excellent damping properties, a known disadvantage is that it requires the use of end supports to properly position the dampers. These support structures are often difficult and expensive to make due to the intricate slots, grooves and keys required to receive the damper and maintain proper positioning. Also, the fuel rail itself must be specially designed to accommodate the support structures and damper. This may lead to larger fuel rails than are otherwise needed. Other disadvantages include additional assembly time and the further expense of rail end plugs and o-rings.
A third pressure-damping device known in the art is a metal fuel rail having flat, flexible walls. The flexing fuel rail is provided with large flat surfaces, designed to flex in response to rapid pressure spikes in the fuel system. As pressure pulses occur, the elastic walls function to dampen the pressure pulsations. A rigid wall section to which the mounting hardware and injectors are necessarily affixed accompanies the flexing wall. While this type of construction serves to dampen the fuel pressure spikes generally, it does not serve to manage the out-of-phase pulses generated by a staged APDI injector. Nor does it have a means for protecting against over-pressure spikes that could permanently distort the flexible walls.
There exists a need in the art for a fuel rail assembly having an internal damper with a means for protecting the damper against over-pressure spikes. Moreover, there is a need in the art for such a damper for use in an APDI system wherein damping can be provided for the out-of-phase pulsing of the APDI staged injector. Finally, there is a need in the art for such a fuel rail assembly constructed substantially from sheet metal components thereby reducing manufacturing cost, simplifying assembly, and saving weight.
SUMMARY OF THE INVENTION
The present invention generally includes a pressure damping fuel rail with integral over-pressure protection for use with fuel injected internal combustion engines. When used with an APDI fuel system, the present invention further provides a means for balancing the pressure pulsations induced by air delivery and fuel delivery systems.
The invention comprises, in one form thereof, a pressure damping fuel rail assembly for use with an APDI system including a lower fuel rail having outwardly formed injector cups for receiving a select number of fuel injectors, a damper cover, and a flexible damper sandwiched between the rail and cover to form a fuel chamber between it and the fuel rail for the delivery of pressurized fuel to the injectors, and an air chamber between it
Braun Charles W.
Haynes Kern E.
Delphi Technologies Inc.
Griffin Patrick M.
Moulis Thomas N.
LandOfFree
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