The field of the present invention is fuel rails for internal combustion engines and in particular, fuel rails for reciprocating piston, spark-ignited internal combustion engines.
In the past three decades, there have been major technological efforts to increase the fuel efficiency of automotive vehicles. One technical trend to improve fuel efficiency has been to reduce the overall weight of the vehicle. A second trend to improve fuel efficiency has been to improve the aerodynamic design of a vehicle to lower its aerodynamic drag. Still another trend is to address the overall fuel efficiency of the engine.
Prior to 1970, the majority of production vehicles with a reciprocating piston gasoline engine had a carburetor fuel supply system in which gasoline is delivered via the engine throttle body and is therefore mixed with the incoming air. Accordingly, the amount of fuel delivered to any one cylinder is a function of the incoming air delivered to a given cylinder. Airflow into a cylinder is effected by many variables including the flow dynamics of the intake manifold and the flow dynamics of the exhaust system.
To increase fuel efficiency and to better control exhaust emissions, many vehicle manufacturers went to port fuel injection systems, where the carburetor was replaced by a fuel injector that injected the fuel into a port which typically served a plurality of cylinders. Although port fuel injection is an improvement over the prior carburetor fuel injection system, it is still desirable to further improve the control of fuel delivered to a given cylinder.
To further enhance fuel delivery, many spark-ignited gasoline engines have gone to a system where a fuel injector is supplied for each individual cylinder. The fuel injectors receive their fuel from a fuel rail, which is typically connected with all or half of the fuel injectors on one bank of an engine. Inline 4, 5 and 6 cylinder engines typically have one bank. V-block type 6, 8, 10 and 12 cylinder engines have two banks.
One critical aspect of a fuel rail application is the delivery of a precise amount of fuel at a precise pressure. In an actual application, the fuel is delivered to the rail from the fuel pump in the vehicle fuel tank. At an engine off condition, the pressure within the fuel rail is typically 45 to 60 psi. When the engine is started, a typical injector firing of 2-50 milligrams per pulse momentarily depletes the fuel locally in the fuel rail. Then the sudden closing of the injector creates a pressure pulse back into the fuel rail. The injectors will typically be open 1.5-20 milliseconds within a period of 10-100 milliseconds.
The opening and closing of the injectors creates pressure pulsations (typically 4-10 psi peak-to-peak) up and down the fuel rail, resulting in an undesirable condition where the pressure locally at a given injector may be higher or lower than the injector is ordinarily calibrated to. If the pressure adjacent to the injector within the fuel rail is outside a given calibrated range, then the fuel delivered upon the next opening of the injector may be higher or lower than that preferred. Pulsations are also undesirable in that they can cause noise generation. Pressure pulsations can be exaggerated in a returnless delivery system where there is a single feed into the fuel rail and the fuel rail has a closed end point.
To reduce undesired pulsations within the fuel rails, many fuel rails are provided with added pressure dampers. Dampers with elastomeric diaphragms can reduce peak-to-peak pulsations to approximately 1-3 psi. However, added pressure dampers are sometimes undesirable in that they add extra expense to the fuel rail and also provide additional leak paths in their connection with the fuel rail or leak paths due to the construction of the damper. This is especially true with new Environmental Protection Agency hydrocarbon permeation standards, which are difficult to satisfy with standard O-ring joints and materials.
It is desirable to provide a fuel rail wherein pressure pulsations are reduced while minimizing the need for dampers.
To make manifest the above-noted and other desires, a revelation of the present invention is brought forth. In one preferred embodiment, the present invention provides a fuel rail for a plurality of fuel injectors. The fuel rail includes a sealed housing having an inlet for receiving fuel. The housing has at least first and second outlets for delivering fuel to fuel injectors. A first chamber forming a first control volume is provided having an inlet connected with an interior of the housing. The first chamber forms a vapor space for the housing inlet. A second chamber is provided providing a second control volume. The second control volume has an inlet to the first control volume forming a vapor space for the first control volume.
The present invention provides a fuel rail with damping characteristics that minimize or eliminate any requirement for separate pressure dampers to be added to the fuel rail.
Further features and advantages of the present invention will become more apparent to those skilled in the art after a review of the invention as it is shown in the accompanying drawings and detailed description.
Referring to
The sealed housing 10 also has an inlet 24 with an orifice approximately 8 mm in diameter. The inlet 24 can be encompassed by a pressure fitting (not shown) which is fluidly connected with a pressurized fuel delivery line.
In the embodiment shown, the fuel rail has three injector outlets 30. Brazed or otherwise fixably sealably attached to the injector outlets 30 are three injector cups 32.
Bifurcating the sealed housing is a baffle plate 40 which can be made of materials similar to that of the sealed housing 10. In the embodiment shown, the baffle plate, has its perimeter 42 sealably engaged with an extreme end 44 of the leg 16. The baffle plate 40 also connects with a generally U-shape channel member 46. The U-shape channel member 46, in cooperation with the baffle plate 40, forms a first control volume or chamber 50. The chamber 50 has an inlet 52 with a filling chamber 54 of the sealed housing 10. The peripheral edges 56 of the channel member 46 are sealably and fixably connected to an underside 58 of the baffle plate 40.
In another embodiment (not shown), the baffle plate can be provided by a U-shape channel member having side legs extending upward parallel adjacent to the side legs 18.
The fuel rail 7 is provided with a second control volume or second chamber 60 which is substantially larger than the first control volume 50. The second control volume 60 provides a secondary vapor trap having an inlet 62 with the first control volume 50.
The inlets 52, 62 in a preferred embodiment will have a length-to-diameter ratio equal or greater than two, and an orifice diameter between 1.0 and 4.0 mm to provide for capillary action between the various control volumes.
In operation, fuel is delivered into the sealed housing 10 through the inlet 24. Air or vapor within the housing is entrapped within the first chamber 50 and the second chamber 60. The air within the chambers 50 and 60 acts as a damper to lower pressure pulsation caused by the rapid opening and closing of fuel injectors (not shown) which are positioned within the injector cups 32. The inlets 52 and 62 ensure that fuel vapor, which condenses upon cooling, will return into the filling chamber 54 when the engine is turned off.
The providing of fuel vapor chambers 50, 60 also helps to ensure that there is air within at least the second chamber 60 which will act as a damper for the pulsating fuel injectors regardless of a potential inclined position of the vehicle or an operational state of the engine that the fuel rail 7 is presenting fuel to.
In another embodiment (not shown) there can be multiple first chambers 50, each one being associated with an inlet to the second chamber 60. The occasional misalignment of the inlets 52 and 62 also aid in the prevention of liquid fuel entering into the second chamber 60.
The tubular member 115 is supported within the sealed housing 110 by radially extending arms 118. Inserted within the tubular member 115 is a tubular member 120. The tubular member 120 forms a first control volume or vapor chamber 124. Tubular member 120 is substantially supported and positioned within the tubular member 115 by two radially extending arms 126. Tubular member 120 has an inlet opening 128, generally adjacent a second end of the sealed housing 110, with a filling chamber 132 of the fuel rail.
The tubular member 120 also has a flared opening 136. The opening 136 provides an inlet for the second chamber 116 to the first chamber 124. The opening 136 is positioned on an upper portion of the second chamber 116.
The fuel rail 107 also has an inlet 140 and injector cups 144 which are positioned adjacent injector outlets 146. Again, vapor or air entrapped within the second chamber 116 and first chamber 124 act to dampen pulsation caused by the rapid opening and closing of injectors (not shown) placed within the injector cups 144.
Referring to
The damper 217 has a lower arcuate wall 222 that forms a semi-conic pocket with respect to its opposite ends 220. Generally along an apex of the lower wall 222 is a vent 224. Vent 224 has a side wall 228, which aids in the formation of droplets of vaporized fuel within the fuel rail 207. The damper 217 also has an upper arcuate wall 230. Between the upper wall 230 and the lower wall 222, a damping control volume or vapor pocket is formed by the damper. The upper and lower walls will preferably, in their free form, have a formed radius or diameter greater than that of the tubular member 210. Therefore, upon insertion within the tubular member 210, the damper 217 opposite ends will spring outward and generally, by spring force, be self retaining within the housing 210. In most instances, mounting devices and methods such as connectors, fasteners, clips, retainers, adhesive application or a tacking and brazing operation will not be required to retain the damper 217 in position.
In operation, fuel will typically compress the air captured in the semi-elliptical pocket formed by the lower wall and approach a level which is below that of the vent 224. The vent 224 will have a length-to-diameter ratio equal to or greater than two, to promote capillary action. The volume of the air above the fluid level 234, with the addition of the air within the damper 217, will act as a damping force upon the fuel, in response to pulsations caused by the opening of the various fuel injectors. Fuel may leak past the opposite ends 220 and enter into a control volume 236, which is formed between the upper wall 230 and the housing tubular member 210. Air entrapped within this space will further add to the damping capacity of the damper. And, if by chance, control volume 236, is in a solid (full) condition, air will still be entrapped within the control volume 238 formed between the lower and upper walls 222, 230.
In the prior manufacturing process, a fuel rail would typically have the components of a fuel rail housing with first and second end caps. Additionally, adjacent to the injector outlets formed in the rail housing, there were attached injector cups. In the prior fabrication process, the rail housing and the injector cups and one of the end caps were connected and brazed together. The damper was fabricated separately from the housing and its injector cups. The damper was connected with attachment clips. The damper and attachment clips were inserted into the open end of the housing. The attachment clips were used to connect the damper within the housing. The other end cap of the housing was welded to the housing using a laser weld process in order to minimize the conduction of heat to other components. The fuel was then ready for leak tests.
With the fuel rail 207, an insertable damper can be installed within the housing without the use of fasteners or clips or retainers. The injector cups and end caps can be attached to the housing in one brazing operation. The fuel rail is now prepared for final leak tests. The laser welding of one of the end caps can be eliminated.
Referring to
Referring to
The present invention has been shown in various embodiments. It will be apparent to those skilled in the art of changes and modifications which can be made without departing from the spirit or scope of the invention as it is encompassed by the following claims.
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