Patent Application
20060254563
The present invention relates to fuel rail assemblies for supplying fuel to fuel injectors of internal combustion engines; more particularly, to fuel rail assemblies for supplying fuel for direct injection of gasoline (DIG) or diesel fuel (DID) into engine cylinders; and most particularly, to an improved DIG/DID fuel rail assembled by precision placement and brazing of rail components without inducing stress in the final brazed assembly.
Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail assembly, also referred to herein simply as a fuel rail, is essentially an elongate fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating in any of various arrangements with a plurality of fuel injectors to be supplied. Typically, a fuel rail assembly includes a plurality of fuel injector sockets in communication with a manifold supply tube, the injectors being inserted into the sockets and held in place in an engine head by bolts securing the fuel rail assembly to the head.
Gasoline fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and direct injection (DIG), wherein fuel is injected directly into an engine cylinder, typically during or at the end of the compression stroke of the piston. Diesel fuel injection is also a direct injection type.
For purposes of clarity and brevity, wherever DIG is used herein it should be taken to mean both DIG and DID, and fuel cell rail assemblies in accordance with the invention as described below are useful in both DIG and DID engines.
DIG fuel rails require high precision in the placement of the injector sockets in the supply tube because the spacing and orientation of the sockets along the fuel rail assembly must exactly match the three-dimensional spacing and orientation of the fuel injectors as installed in cylinder ports in the engine. Further, a DIG fuel rail must sustain much higher fuel pressures than a MPFI fuel rail to assure proper injection of fuel into a cylinder having a compressed charge. DIG fuel rails may be pressurized to 100 atmospheres or more, for example, whereas MPFI fuel rails must sustain pressures of only about 4 atmospheres.
Efforts to form satisfactory DIG fuel rails by metal forming and welding have not heretofore been successful. The bending and welding processes can produce significant stresses in the formed parts, and even slight misalignments of components such as sockets mounted into the distribution tube can create even further stresses when the assembly is bolted to an engine head.
In response to these problems and requirements, DIG fuel rails typically are formed by precision casting followed by boring of various passages, or by precision/high cost machining of stainless steel. However, prior art cast fuel rails suffer from at least three serious shortcomings. First, they are expensive to manufacture, requiring multiple steps in casting, boring, and finishing. Second, they are typically an aluminum alloy, which is known to be subject to attack by some fuels. Desirable resistant alloys such as stainless steel are more costly to cast. Third, bolts securing a typical prior art fuel rail assembly to an engine head are typically offset from the centerlines of the fuel injectors, such that cylinder pressure on the fuel injectors exerts a torque on the bolts and the assembly which can result in progressive misalignment of the fuel rail with the injectors and potentially failure of the fuel injection system.
What is needed in the art is an inexpensive fuel rail for DIG engine fuel systems.
What is further needed in the art is a DIG fuel rail assembly formed of a non-reactive metal alloy such as stainless steel.
What is further needed in the art is a DIG fuel rail wherein the bolts securing the rail assembly to an engine head lie on the centerline of the fuel injectors.
It is a principal object of the present invention to provide an inexpensive, high-precision fuel rail assembly for use with a DIG or DID internal combustion engine.
Briefly described, a fuel rail assembly in accordance with the invention comprises a plurality of formed parts first assembled loosely on a precision fixture, then joined to fix relationships, containing braze filler metal (BFM), as for example, paste, preforms, or plating on all joints to form a “green” assembly, and fired in a brazing oven to produce a precision, fuel rail assembly formed from stainless steel parts.
A bracket defines a sole plate for the assembly, for attachment to an engine head in the region of direct injection fuel injectors. The bracket may be formed as a single, continuous element comprising all the fuel injector sites, or may be formed of a plurality of individual fuel injector brackets. Assembly is similar for either style. Flanged sockets for receiving the outer ends of the fuel injectors are attached to the bracket at locations corresponding to the fuel injector locations on an engine bank. Bolt holes are provided through the bracket on either side of each socket along the centerline of the sockets and fuel injectors. The bracket extends to one side of the sockets and is formed to support a fuel distribution tube. At least one saddle element is disposed between the bracket and the tube. A jump tube extends from the fuel distribution tube to each socket for supplying fuel from the distribution tube to each fuel injector.
Preferably, all components are formed of a non-reactive, brazable alloy such as stainless steel, for example, 304 stainless steel.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
Referring to
The centerline 148 of openings 124 and sockets 126 corresponds to the centerline of fuel injectors 114 in engine 112. Holes 150 are provided along centerline 148, preferably two such holes on opposite sides of each opening 124, for securing fuel 15 rail assembly 110 to engine 112 as by one or more bolts 152. Tapered adapters 116, which are formed preferably from a moldable, high-temperature polymer, may be installed between bracket 118 and engine 112, as shown in
It is an important advantage of a fuel rail assembly in accordance with the present invention that the mounting bolts lie along the centerline of the fuel injectors such that no bending torque is applied to the bolts by expellant pressures exerted on the fuel injectors. Further, the bolt line 148 is offset from the axis 149 of the fuel distribution tube, obviating steric hindrances present in some prior art fuel rails wherein the bolts are disposed under the distribution tube, a significant manufacturing and maintenance disadvantage.
Further, it is an important feature and object of a fuel rail assembly in accordance with the invention that the assembly be formed without internal stresses and that the assembly fit precisely onto an engine head wherein the fuel injectors have been inserted and are extending from their respective precision bores. Accordingly, the components of the fuel rail are assembled loosely onto a fixture simulating such an engine head, to assure proper orientations and positions of the components, then are secured to each other to prohibit further relative motion, and then are sealed to each other as by brazing.
Referring now to
Still referring to
a) installing a socket 126 onto each mandrel 168 and surface 166;
b) installing a bracket 118 onto sockets 126, surface 130, and against flange 164;
c) inserting a jump tube 146 into each socket side opening 142;
d) installing a fuel distribution tube 136 by inserting the other ends of jump tubes 146 into tube openings 144, and supporting installed tube 136 with brace 167;
e) engaging saddles 134 with flanges 132 and distribution tube 136;
f) joining, as for example by tack welding, all components together;
g) removing the tack-welded assembly from fixture 160;
Referring now to
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
