Branch connection in a high pressure fuel rail with gasket

A branch connection for a high pressure fuel rail including a passage through which high pressure fuel flows, and a plurality of through holes formed in the circumferential wall of the passage and including respective pressure receiving surfaces tapering radially outwardly from the passage. The branch connection comprises a branch element including a passage communicated with the passage of the fuel rail. The branch element includes a press head, at one end, engaged with the pressure receiving surface through a bowl-shaped seal so as to threadably secure the branch element to the fuel rail. The seal has a central hole, at least inner and outer peripheral edges of which are engaged with an end surface of the press head and the pressure receiving surface of the through hole in the fuel rail, respectively. The angle between the peripheral surface of the central hole in the seal and the pressure receiving surface is less than 90.degree.. The angle between the peripheral surface of the central hole and the end surface is also less than 90.degree.. The seal is made of metal and at least having a surface made of soft metal such as silver, indium, copper, brass, or aluminum.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to connection of a branch element such as a 
branch pipe or branch fitting to a high pressure fuel rail such as a high 
pressure fuel line or block and in particular, to a branch connection 
adapted to inject fuel to a gasoline engine and particularly, to deliver 
fuel under a pressure of greater than 1000 kgf/cm.sup.2 to a diesel 
engine. 
2. Description of the Prior Art 
A conventional branch connection is exemplified, for example, in FIGS. 12 
and 13. A main pipe 11 has an inner bore or passage 12. A plurality of 
conical or arcuate pressure receiving surfaces 13 are formed in the 
circumferential wall of the main pipe 11. A branch pipe 15 has a conical 
or arcuate end or press head 16 engaged in the corresponding pressure 
receiving surface 13 of the main pipe 11. A seal 14 is in the shape of a 
bowl and is disposed between the pressure receiving surface 13 and the 
press head 16. The seal 14 includes a central straight hole 14' and a bent 
wall 14" extending inwardly from the central hole 14'. Upon securement of 
the branch to the main pipe, a space 17 is defined by the bent wall 14" of 
the seal, the peripheral edge of the pressure receiving surface 13, and 
the passage 12. 
In such a connection, however, a high pressure of greater than 1000 
kgf/cm.sup.2 is applied to the seal 14 to provide two components P.sub.1 
and P.sub.2. The component P.sub.2 is a force (fluid pressure x sin 
.theta.) applied to separate the seal from the pressure receiving surface 
13. This force, together with vibration of an engine, causes fuel to enter 
between the seal 14 and the pressure receiving surface 13 and thus, leak 
from the main pipe. 
SUMMARY OF THE INVENTION 
In view of the problems encountered in the prior art, it is an object of 
the present invention to provide a connection wherein the component of a 
force as produced when a high pressure is applied to the seal is used as a 
force to press the seal against the pressure receiving surface of the main 
pipe so as to prevent fluid from entering therebetween and thus, leaking 
from the main pipe regardless of vibration. 
In order to achieve the above object, there is provided a branch connection 
for a high pressure fuel rail including a passage through which high 
pressure fuel axially flows, and a plurality of through holes formed in a 
circumferential wall of the passage and including respective pressure 
receiving surfaces tapering radially outwardly from the passage, the 
branch connection comprising a branch element including a passage 
communicated with the passage of th and a press head, at one end, engaged 
with the pressure receiving surface through a bowl-shaped seal so as to 
threadably secure the branch element to the fuel rail, wherein the seal 
has a central hole, at least inner and outer peripheral edges of which are 
engaged with an end surface of the press head and the pressure receiving 
surface of the through hole in the fuel rail, respectively, and wherein an 
angle between the peripheral surface of the central hole in the seal and 
the pressure receiving surface is less than 90.degree. . Additionally, an 
angle between the peripheral surface of the central hole and the end 
surface is less than 90.degree. . The seal is made of metal and at least 
having a surface made of soft metal such as silver, indium, copper, brass, 
or aluminum. 
With the present invention thus constructed, a high pressure of greater 
than 1000 kgf/cm, is applied to provide two components. One of the 
components serves to press the seal against the end of the press head and 
particularly the pressure receiving surface to improve the integrity of 
seal therebetween. Fuel is thus prevented from entering between the seal 
and the press head and the pressure receiving surface and leaking 
therefrom for a prolonged period of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 to 8, 1 is a high pressure main pipe made of carbon 
steel, alloy steel or stainless steel. The main pipe 1 has a relatively 
small diameter of approximately 20 m/m and a thickness of approximately 6 
m/m. The main pipe 1 includes a passage 2. A plurality of conical through 
holes 3a are formed in the circumferential wall of the main pipe 1 and 
include corresponding pressure receiving surfaces 3. Each through hole 3a 
tapers radially outwardly from the passage 2. The through holes 3a are 
communicated with the passage 2. A discrete, short joint 4 is placed in 
coaxial relation to the pressure receiving surface of each through hole 
3a. 5 is a branch pipe as a branch element including a passage 20. The 
branch pipe has a frustoconical press head 6 at one end. The frustoconical 
press head 6 extends through the joint 4 and has a press surface 6a 
engaged with the corresponding pressure receiving surface 3. A seal 8 is 
in the shape of a bowl and disposed between the press surface 6a and the 
pressure receiving surface 3. A nut 7 is fit around the branch pipe 5 
through a sleeve 28. The nut 7 is secured to a threaded hole 16 of the 
fitting 4. 
The seal 8 is made of relatively soft metal such as silver, indium, copper, 
brass or aluminum, or matel plated or cladded with these metals. The seal 
8 has a central hole 8'. Upon securement of the branch to the main pipe, 
the inner and outer peripheral edges of the central 8' are situated 
against an end surface 6' of the press head 6 and the pressure receiving 
surface 3 of the main pipe 1, respectively, as shown in FIG. 3. An angle 
.alpha. formed between the central hole 8' and the end surface 6' of the 
press head 6 is preferably less than 90.degree. . 
Such an angle is established for the reasons as will be described with 
reference to FIG. 4A. A high pressure P of greater than 1000 kgf/cm, is 
applied at right angles to the surface of the central hole 8' to provide 
two components P.sub.1 and P.sub.2. The component P.sub.2 serves to press 
the seal 8 against the pressure receiving surface 3 under a pressure of P 
x sin.alpha.. Such a force causes the seal 8 to come into close contact 
with the pressure receiving surface 3 to improve the integrity of seal. 
Fuel, if not properly sealed, may enter between the seal 8 and the 
pressure receiving surface 3 and leak from the main pipe. 
This is also the case with the end surface 6' of the press head 6 and the 
seal 8 shown in FIG. 4B. In this case, the end surface 6' of the press 
head 6 is contacted with the seal 8 under a pressure of P x sin .beta.. 
In the foregoing embodiment, the central hole 8' has a flat conical wall 
with the angle .alpha. between the peripheral surface of the central hole 
6' and the pressure receiving surface and the angle .beta. between the 
peripheral surface of the central hole 8' and the end surface 6' of the 
press head 6 being less than 90.degree. . Alternatively, the central hole 
8' may have two or three surfaces angled relative to one another as shown 
in FIG. 5 or FIG. 6. In these cases, the angles .alpha. and .beta. are 
less than 90.degree. . 
Still alternatively, the central hole 8' may have an arcuate surface as 
shown in FIG. 7. In such a case, the angle .alpha. formed between the 
pressure receiving surface 3 and an imaginary line extending from 
connection X between the inner peripheral edge of the seal 8 and the end 
surface 6' of the press head 6 to connection Y between the outer 
peripheral edge of the seal 8 and the pressure receiving surface 3 is less 
than 90.degree. . The angle formed between the imaginary line and the end 
surface 6' of the press head 6 is also less than 90.degree. . 
Referring to FIG. 8, the press head 6 and the pressure receiving surface 3 
are arcuate in shape. In this case, the angle formed between the outer 
periphery of the press head 6 or the inner periphery of the pressure 
receiving surface 6 is less than 90.degree. . This embodiment also falls 
within the scope of the present invention. 
FIG. 9 is a vertical sectional view showing the principal part of another 
embodiment of the present invention. In this embodiment, a branch element 
is in the form of a branch fitting 5'. The main pipe serves as a fuel 
rail. The branch fitting is used to prevent interference with other 
components when a branch pipe is bent with large curvature. The branch 
fitting may be in the form of an elbow joint or may include a constant 
pressure valve, a damping valve, a feed valve, or a discharge valve. 
In the embodiment shown in FIG. 9, the branch fitting 5' serves as a branch 
element connected to the main pipe 1. The branch fitting 5' has a 
frustoconical press head at one end as in the foregoing embodiments. The 
branch fitting 5' has a threaded wall 25 for threaded engagement with a 
threaded hole 16 of a joint 4. The branch fitting 5' is thus engaged with 
the pressure receiving surface 3' of the main pipe 1 through the seal 8. A 
locking nut 24 is threaded onto the other end of the branch fitting 5' 
through a sleeve 23. 
With this arrangement, a branch pipe 5' may extend in a direction parallel 
to the longitudinal axis of the main pipe 1. 
FIG. 10 is a vertical sectional view showing the principal part of a 
further embodiment of the present invention. In this embodiment, a locking 
nut 26 is used to connect the branch pipe 5 as a branch element to the 
main pipe 1 as a fuel rail. The locking nut 26 is centrally extended to 
provide a boss 27. The locking nut 26 has a thread 26' on its inner 
periphery. The joint 4 has a corresponding thread 16' on its outer 
periphery. While the thread 26' of the locking nut is threadably engaged 
with the thread 16' of the joint, the boss 27 presses down an annular 
projection 21a to cause the press surface 6a to engage with the pressure 
receiving surface 3 through the seal 8. 
FIGS. 11A and 11B are views showing a fuel block as a fuel rail, in lieu of 
the main pipe. A thick block 30 has a pair of passages 31 and 32 through 
which high pressure fuel flows. A plurality of mounting holes 33a to 33d 
and 34a to 34d are formed in the block 30 to communicate with the passages 
31 and 32, respectively. These mounting holes 33a to 33d and 34a to 34d 
have respective pressure receiving surfaces 3 as in the foregoing 
embodiments. The mounting holes 33a to 33d and 34a to 34d also have 
threaded inner peripheral surfaces. 
When the fuel block 30 is used as a fuel rail, a locking nut 7 is threaded 
to the threaded inner peripheral surface of each mounting hole to secure 
the branch element to the block. This results in engagement of the press 
surface 6' of the press head 6 with the pressure receiving surface 3 
through the seal 8. 
With the branch connection of the present invention thus far described, a 
high pressure is applied to the seal to provide two components. One of the 
components serves to press the seal 8 against the press head and 
particularly the pressure receiving surface 3 due to the shape of the 
central hole 8' of the seal 8 and contact of the inner and outer 
peripheral edges of the seal 8 with the press head 6 and the pressure 
receiving surface 3, respectively. This substantially improves the 
integrity of seal and thus, prevents entry and leakage of fuel for a 
prolonged period of time if vibration is produced due to repeated flow of 
high pressure fuel. The branch element can thus be safely connected to the 
main pipe or fuel block.