Abstract:
A fuel rail is provided for delivering fuel to a plurality of fuel injectors for a reciprocating piston internal combustion engine. The fuel rail includes an inlet tube for receiving pressurized fuel having at least one orifice. An outer tube forming and enclosing control volume is provided about the inlet tube. The outer tube has a plurality of injector outlets.

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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. In a step to further enhance fuel delivery, many spark ignited gasoline engines have gone to a system wherein there is supplied a fuel injector 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 dampeners. Dampeners with elastomeric diaphragms can reduce peak-to-peak pulsations to approximately 1-3 psi. However, added pressure dampeners 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 dampener. 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 dampeners. 
     SUMMARY OF THE INVENTION 
     To make manifest the above-noted and other manifold desires, a revelation of the present invention is brought forth. In a preferred embodiment, the present invention provides a fuel rail for a plurality of fuel injectors. The fuel rail includes an elongated inlet tube which receives pressurized fuel. The inlet tube is encircled by an outer tube which forms a control volume enclosing the inlet tube. Fluid from within the inlet tube passes through an orifice into the outer tube. The outer tube is fluidly connected with the injectors via injector outlets. 
     The present invention provides a fuel rail which provides dampening characteristics which minimizes or eliminates any requirement for separate fluid dampeners 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 shown in the accompanying drawings and detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a preferred embodiment fuel rail according to the present invention. 
     FIG. 2 is a sectional view of an alternate preferred embodiment fuel rail according to the present invention. 
     FIG. 3 is a partial sectional view of another alternate preferred embodiment of the present invention. 
     FIG. 4 is a partial sectional view of yet another alternate preferred embodiment of the present invention. 
     FIG. 5 is a sectional view of a positive pressure differential valve which can be utilized in an inlet orifice as shown in FIG. 1 or  2 . 
     FIG. 6 is a view taken along lines  6 — 6  of FIG.  3 . 
     FIG. 7 is a view taken along lines  7 — 7  of FIG.  4 . 
     FIG. 8 is a view taken along lines  8 — 8  of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a fuel rail  7  according to the present invention is provided. The fuel rail  7  has a generally elongated inlet tube  10 . The inlet tube has a first end  12  which is provided for the receipt of pressurized fluid therein. The inlet tube has an opposite blind end  14 . The inlet tube has three generally geometrically spaced orifices  16 . Enclosing the inlet tube  10  and forming a control volume thereabout, is an outer tube  20 . 
     The outer tube  20  has three geometrically spaced injector outlets  22 . The injector outlets  22  allow fluid within the outer tube  20  to communicate with a plurality of fuel injectors (not shown). The outer tube at its extreme ends has an installed plug  24 . The outer tube  20  at its front end has an angular plug  26  which seals the interior of the outer tube  20  and seals against the exterior of the inlet tube  10 . Fixedly connected by a press fit brazing, welding or other appropriate method to the outer tube  20  are three injector cups  28 . Supporting the inlet tube  10  within the outer tube  20  are three annular baffle plates  32 . The annular baffle plates  32  also function to bifurcate the interior of the outer tube  20  between the injector outlets  22 . The orifices  16  of the inlet tube are oriented generally opposite the injector outlets  22  of the outer tube  20 . 
     In operation, pressurized fluid is delivered to the inlet tube front end  12 . Fluid then exits the inlet tube  10  through the orifices  16 . Fluid flowing from the orifices  16  pressurizes the interior of the outer tube  20 . The opening and rapid closure of the injector adjacent to the blind end  14  will cause a pressure pulsation. The pressure pulsation will be dampened due to several factors. One factor is a relatively large volume of fluid within the interior of the outer tube  20  adjacent to the injector outlet  22 . Second, the orifice  16  acts as a convergent/divergent nozzle which further inhibits the propagation of pressure pulsations. Third, the baffle plate  32  inhibits the transmission of a pressure pulsation to the area within the outer tube  20  which is in the mid portion of the fuel rail  7 . Fourth, the wall thickness of the inlet tube  10  can be fabricated to be materially thinner than the material utilized to fabricate the outer tube  20 . 
     It has typically been found to be preferable that the volume of the fluid between the outer tube  20  and the inlet tube  10  between the two baffles  32  be at least equal to and preferably at least twice as large as the volume of the fluid within the inlet tube  10  between the two baffle plates  32 . 
     Referring to FIG. 2, an alternate preferred embodiment fuel rail  107  is provided. The fuel rail  107  has an inlet tube  110 . The inlet tube  110  has a first portion  112  at its front end. The first portion  112  penetrates an end wall  116  of the fuel rail. The end wall  116  can optionally be made thick enough that it supports the inlet tube  110 . Connected to the inlet tube first portion  112  is an inlet tube second portion  118 . The inlet tube second portion  118  will typically be fabricated from a very thin wall low carbon or stainless steel having a thickness in the range of 0.005 to 0.020 inches. It is typically preferable for the inlet tube first portion  112  to be fabricated from a metal having a wall thickness materially thicker than the second portion  118  to allow the inlet tube first portion  112  to have strength in its connection to and penetration of the end wall  116 . The wall thickness of the inlet tube  110  is also provided for attachment fluid fittings. 
     At an extreme opposite end on the inlet tube second portion  118 , there is provided an orifice  120 . The orifice  120  is sized so that there is generally a positive pressure differential between fluid within the inlet tube  110  and fluid which has escaped through the orifice  120  into an area adjacent to the inlet tube  110  outer diameter. The inlet tube  110  has an enclosed control volume formed thereabout by an outer tube  124 . The outer tube  124  has its opposite end close by a blind end  126 . The outer tube  124  has a series of injector outlets  128 . Fixably connected to the outer tube  124  adjacent the injector outlets  128  are injector cups  130 . Only two injector cups  130  are shown. 
     In other embodiments not shown, there will be three or four injector cups in total and in some cases even six. In the fuel rail shown in FIG. 2, the thin wall of the inlet tube second portion  118  is materially thinner than the wall of the outer tube  124  which will be in the neighborhood of thirty to forty-five thousands of an inch in thickness. Connecting brackets and associated hardware (not shown) will be fixably attached by brazing, welding or other suitable techniques to allow the fuel rail  107  to be connected to an internal combustion engine (not shown). 
     The thinness of the inlet tube second portion  118  allows it to deflect to dampen pulsations caused by the opening and closing of the injectors (not shown) associated with the various injector cups  130 . The orifice  120  as previously mentioned is sized so that regardless of flow there through, a generally positive delta pressure is maintained between the fluid within the inlet tube  110  and the outer tube  124 . 
     Referring to FIGS. 3 and 6, another alternate preferred embodiment fuel rail  207  is provided. The inlet tube  219  is fabricated similar to prior inlet tube  118  except that it has a blind end in tube  110 . Additionally, the inlet tube  219  has an orifice  230  which is adjacent to an injector outlet  128 . This configuration provides an advantage in that the orifice  230  can be injected or inserted through the injector outlet  128 . Additionally, to provide for more flexure to alleviate pressure pulsations the inlet tube  219  is given a polygonal cross sectional shape. In other embodiments (not shown), the inlet tube may be triangular or other various rectangular or polygonal shapes. 
     Referring to FIGS. 4 and 7, a fuel rail  307  is provided. Fuel rail  307  has an inlet tube  310 . The inlet tube  310  can be radially supported by supports  316  which are formed in an outer tube  320 . Additionally, the inlet tube  310  has an inverse parabolic end  324 . The outer tube  320  has stamped or formed supports  336  which axially support the inlet tube  310 . The radial supports  316  have an almost flower shape providing opening  340  between the adjacent axial supports  336  to allow the free flow of fluid throughout the outer tube  320 . 
     Referring to FIGS. 5 and 8, a positive pressure differential flow valve  500  is provided which can be utilized in the fuel rails shown on FIGS. 1 through 4. Differential valve  500  has a body  502 . The body  502  has integral stamped or added guides  503 . The body  502  has an inlet orifice  504  and an outlet orifice  506 . The body has an outward taper from the inlet orifice  504  to the outlet orifice  506 . The length of guides  503  has a generally constant diameter. 
     Biased by spring  508  is a valve member  510 , which is centered by the guides  503 . The valve member  510  has a partial flow orifice  512 . As the valve member moves towards the outlet orifice  506 , an increased flow area exists between the valve member  510  and the valve body  502 . 
     When an injector opens, the flow of fluid to the injector through one of the damper outlets causes a lowering in pressure in the outlet  506  causing the valve member  510  to be urged against the biasing of spring  508 . Upon closing of the solenoid valve, fluid pressure at the outlet  506  will increase, urging the valve member  510  to reposition itself rightwardly. The positive pressure differential valve  500  functions to preserve a condition wherein there is a positive pressure differential between the fluid pressure at the inlet  504  versus the outlet  506 . 
     While preferred embodiments of the present invention have been disclosed, it is to be understood that they have been disclosed by way of example only in that various modifications can be made without departing from the spirit and scope of the invention as it is explained by the following claims.