HIGH- PRESSURE FUEL RAIL

Abstract: Brazing strength at a connection is made great, and fatigue stress in the vicinity of a connection on a side of a branch connecting body (2) is effectively dispersed by a diameter expansion portion (3) contiguous to an inclined wall (3'), so that in the event of repeated, sudden changes in a supply pressure of a high pressure fluide in the installation and vibrations or relative dimensional changes of mating parts and so on, cracking in the vicinity of the connection on the side of the branch connecting body (2) is effectively prevented to eliminate troubles such as fuel leakage. In a fuel rail, one or more through holes provided in an axially extending peripheral wall portion of a main pipe (1) and communicating to a flow passage in the pipe are stepped in cross section or made in the form of a dish-shaped seat (1'') having an inclined surface. A portion near the end on the branch connecting body (2) side defines the diameter expansion portion (3) leading to an inclined wall toward a tip end of the branch connecting body (2), and a tip end of the diameter expansion portion (3) makes a connecting head portion (2''), which has a cross sectional shape completely matching that of the dish-shaped seat (1''), so that the connecting head portion (2'') is made to engage with the dish-shaped seat (1'') and engaging portions of the former and the latter are subjected to brazing to be connected to each other.

Description: TECHNICAL FIELD The present invention relates to a high-pressure fuel rail which supplies fuel under high pressure more particular reaching 1000 kgf/cm 2 or more in a diesel internal combustion engine. BACKGROUND ART A conventional high-pressure fuel rail of this kind for a branching connector is shown in Fig. 7, where a main tube 11 acts as a fuel rail provided with a channel 11'. A hole 11" extends through the wall around the main tube 11, and is in communication with the channel 11' in the main tube. The hole 11" is of simple circular cross section. A branch tube 12 acting as a branching connector is inserted in the hole 11". The branch tube 12 has a connection end 12' which is neither enlarged nor shrunk. Under this condition, the connection end 12' is brazed at 13 to the main tube, thus forming a connection structure. In this connection structure built by the prior art technique, fluid under high pressure amounting to 1000 kgf/cm 2 or more is constantly and repeatedly supplied. The pressure is rapidly changed. Vibrations are given especially from the engine. The ambient temperature is elevated and lowered, causing the relative dimensions of the opposite members (the opposite seat surfaces) to vary. Especially, where the diameter of the branching connector is small compared with the diameter of the main tube 11, when the main tube is brazed to the branching connector, local heating deteriorates the mechanical strength near the brazed portion 13. As the tubes get fatigued due to vibrations, cracks are easily produced. As a result, leakage of the fuel may occur frequently. By GB-1 397 493 is known a pipe connection for high pressure fuel injection pipes. However the connection is made through a mechanical joint and is not appropriate to avoid cracks due to fatigue stress. By US 5 358 168 is known a brazed fitting for use as a hydraulic coupling for pressurized fluid, but the brazed portion is not sufficient to withstand high stress of high pressure constantly and repeatedly supplied as stated above. US 5 120 084 which is considered to be the closest prior art, proposes a mechanical connection of a branching connector onto a fuel rail comprising a joint piece and a nut providing a concavo-convex fitting. In view of the foregoing problems with the prior art technique, the present invention has been made. It is an object of the invention to provide a connection structure for a branching connector used in a high-pressure fuel rail, the connection structure having a connected portion in which two components are brazed together firmly. The connection structure is further characterized in that stress in the branching connector near the connected portion due to fatigue is effectively dispersed. If the connection structure is placed in position and repeatedly supplied with fluid under high pressure which varies rapidly, or if the relative dimensions are varied by the variations in the pressure of the supplied fluid, application of vibrations, or temperature variations, cracks are effectively prevented from being produced in the branching connector near the connected portion. This eliminates the possibility of leakage of the fuel. DISCLOSURE OF THE INVENTION In order to achieve the foregoing problem, the present invention provides a high-pressure fuel rail according to claim 1. In one feature of the invention, the aforementioned connection head portion is formed by having the connection head portion or a sleeve fitted thereover. The connection head portion is formed integrally with one end of the branching connector. Alternatively, the outer surface of the connection head portion forms an enlarged portion extending to the inclined wall toward the front end. Since the present invention is constructed in this way, the above-described seat portion formed by the fuel rail is totally brought into abutting engagement with the connection head portion of the enlarged portion extending to the inclined wall of the branching connector, and they are brazed and connected together. The total abutting engagement permitted by the cross-sectional shapes of the engaging portions increases the area of the brazed portions. Furthermore, the directions of the abutting surfaces increases the brazing strength at the junction. At the same time, fatigue stress in the branching connector near the junction is effectively dispersed by the enlarged portion and also by the inclined wall whose diameter varies gradually. Accordingly, if the connection structure is repeatedly supplied with fluid under high pressure which varies rapidly, or if the relative dimensions are varied by the variations in the pressure of the supplied fluid, application of vibrations, or ambient temperature variations, cracks are effectively prevented from being produced in the branching connector near the junction. This eliminates the possibility of leakage of the fuel. In addition, if the diameter of the branching connector is small compared with the diameter of the tube of the fuel rail, advantages can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cutaway cross section of a connection portion formed by a branch tube associated with a connection structure of a branch connector used in a high-pressure fuel rail according to the present invention; Fig. 2 is a view similar to Fig. 1, but showing another example; Fig. 3 is a view similar to Fig. 1, but showing a further example; Fig. 4 is a front elevation of a branch connector formed by a branch metal fixture; Fig. 5 is a partially cutaway cross-section of a connection portion formed by a branch metal fixture, showing a still other example; Fig. 6 is an exploded, partially cutaway cross section of a yet other example of the invention; and Fig. 7 is a partially cutaway cross section of a connection structure of a branching connector used in a conventional high-pressure fuel rail. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention are hereinafter described by referring to the drawings. In Figs. 1-6, a main tube 1 serves as a fuel rail and is provided with a channel 1'. The main tube is a pressure piping made of carbon steel having a diameter of less than about 30 mm, a thick-walled steel tube consisting of stainless steel, or composite tubular member fabricated by fitting a corrosion-resistant inner tube 1 1 as made of stainless steel, as shown in Fig. 2. One or more holes 1" extend vertically through the wall of the main tube surrounding the channel, and are in communication with the channel. The holes 1" are axially spaced from each other. The cross-sectional shape of each hole 1" is shaped like a staircase to form a dished seat portion 1"', as shown in Fig. 1 or 5, or each hole forms a dished seat portion 1" having an inclined surface, as shown in Fig. 2 or 3. The fuel rail may also be formed as a fuel block 1-1, as shown in Fig. 3. Indicated by 2 is a branch tube (Figs. 1, 2, and 3) acting as a branching connector. Similarly, a branch metal fixture 2 1 (Figs. 4 and 5) forms a branching connector constituting a further example. The diameters of the branch tube 2 and branch metal fixture 2 1 are less than about 20 mm. These tube and fixture are made of the same kind of steel piping member or steel member as the main tube 1. One end of the branch tube 2 or branch metal fixture 2 1 is so shaped that an enlarged portion 3 extending to an inclined wall 3' is formed. The diameter of the tubular enlarged portion 3 gradually increases toward the front end. A connection head portion 2"' is formed integrally with the front end of the enlarged portion 3. The connection head portion 2"' totally conforms in cross-sectional shape with the seat portion 1"'. The head portion is brought into abutting engagement with the seat portion 1"'. Under this condition, the abutting portions are brazed together at 4, thus forming a connection structure. Where the branch metal fixture 2 1 is used, a high-pressure fuel injection tube 5 is placed at the other end of the branch metal fixture by a nut 6. In the examples shown in Figs. 1-5, one end of the branch connector 2 is shaped so as to have the integral connection head portion 2"'. The present invention is not limited to these examples. The invention can also be constructed as shown in Fig. 6. Specifically, instead of forming the connection head portion 2"' integrally with the end of the branch connector 2, a separate sleeve 2a having an enlarged portion 3 extending to an inclined wall 3' may be mounted on the outer surface of the branch connector 2. The diameter of the tubular enlarged portion 3 gradually increases. The sleeve 2 is at a distance corresponding to the depth of the dished seat portion 1''' from the end of the branch connector 2 and fitted over the branch connector 2. The sleeve 2a and the branch connector 2 may be previously brazed together. Alternatively, when brazing to the seat portion 1"' at 4 is done, they may be brazed together, thus forming a connection body. In this structure, in the present invention, the diameter (D) of the enlarged portion 3 is about 1.1-1.5 times the diameter (d) of the branch tube or branch metal fixture in connection with the relation of the diameter (D) of the enlarged portion 3 to the vibration-resistance, the easiness with which the enlarged portion is machined, the diameter of the main tube 1, and other factors. Where the factor is less than 1.1, the vibration-resistance is poor. On the other hand, where the factor exceeds 1.5, it is unreasonable or difficult to machine the enlarged portion. Furthermore, where the fuel rail is the main tube 1, the rigidity of the main tube deteriorates. In connection with the fatigue stress-dispersing effect, the length (L) of the inclined wall 3' is 1-5 times the diameter (d) . If the length is less than the diameter, the dispersing effect is poor. On the other hand, where the ratio is in excess of 5, the dispersing function is almost hardly affected and meaningless. Furthermore, in connection with the brazing strength, the easiness with which the enlarged portion is machined, and the fatigue stress-dispersing effect, the ratio of the length (1) of the enlarged wall 3 to the diameter (d) is 1/4 to 1. If the length is less than one quarter of the diameter, a fillet exhibiting good stress-dispersing capability is not well formed, or sufficient brazing strength is not obtained. If the length is in excess of the diameter, it is unreasonable or difficult to machine the enlarged portion. The inclined wall 3' may be formed by an outwardly directed, mild, arc-shaped surface according to the need. INDUSTRIAL APPLICABILITY As described thus far, a connection structure for a branching connector used in a high-pressure fuel rail according to the present invention has the sleeve (2a) fitting over the branching connector. The main tube (1) is mounted on the side of the fuel rail, or the holes (1") extend through the block (1-1). The branch tube (2) or branch metal fixture (2 1 ) forms the connection head portion (2"') on the side of the branching connector in the hole 1". The sleeve (2a) is similar in shape with the connection head portion. The sleeve is totally brought into abutting engagement with the dished seat portion (1"') by the connection head portion (2"), and they are brazed together at 4. The total abutting engagement permitted by the cross-sectional shapes of the engaging portions increases the area of the brazed portions. Furthermore, the directions of the abutting surfaces increase the brazing strength at the junction. At the same time, fatigue stress in the branching connector near the connected portion of the branch tube (2)or of the branch metal fixture (2 1 ) can be effectively dispersed. Accordingly, if the connection structure is placed in position and repeatedly supplied with fluid under high pressure which varies rapidly, or if the relative dimensions are varied by the variations in the pressure of the supplied fluid, application of vibrations, or ambient temperature variations, cracks are effectively prevented from being produced in the branching connector near the connected portion. This eliminates the possibility of leakage of the fuel. In addition, if the diameter of the branching connector is small compared with the diameter of the tube of the fuel rail, advantages can be obtained. Moreover, during an overhaul, dust is prevented from intruding through the junction. In this way, the connection structure for the branching connector used in the high-pressure fuel rail is quite useful.

Claims: High-pressure fuel rail comprising a branching connector brazed thereto, said fuel rail comprising: a main tube (1) provided with a channel (1') and having a peripheral wall; at least one hole (1") extending vertically of said main tube through said peripheral wall and in communication with said channel in said main tube; a dished seat portion (1‴) having a staircase-shaped cross section or an inclined surface, said dished seat portion being formed by a portion of the main tube (1); an inclined wall (3') near a front end of said branching connector; an enlarged portion (3) extending to said inclined wall (3') toward said front end of said branching connector and having a front end; and a connection head portion (2‴) formed around the front end of said enlarged portion (3), said connection head portion (2‴) totally conforming in cross-sectional shape with said seat portion, said head portion being brought into abutting engagement with said seat portion (1‴), engaging portions of said head portion and said seat portion which abut against each other being brazed and connected together; wherein said enlarged portion (3) has a diameter (D) which is approximately 1.1-1.5 times as large as diameter (d) of the branch tube (2) or branch metal fixture (2 1 ), wherein said inclined wall (3') has a length (L) which is 1-5 times as large as diameter (d) of said inclined wall and wherein said enlarged portion (3) has a length of (1) and the ratio of said length (1) of said enlarged portion to the diameter (d) of the branch tube is 1/4 to 1. A connection structure for a branching connector in a high-pressure fuel rail as set forth in claim 1, wherein said connection head portion has a connection head or sleeve (2a) fitted thereover, said connection head portion being formed integrally with one end of said branching connector, said sleeve having an outer surface forming the enlarged portion extending to the inclined wall toward the front end.

Inventors: USUI MASAYOSHI, USUI, MASAYOSHI
Applicants: USUI KOKUSAI SANGYO KK, USUI KOKUSAI SANGYO KAISHA LTD.
Application year: 1995
Main classification: F16L41
IPC codes: F02M55, F16L41