Metal treatment – Stock – Carburized or nitrided
Reexamination Certificate
2002-06-26
2004-01-20
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Carburized or nitrided
C148S328000, C148S326000, C148S579000, C148S230000, C239S584000, C239S533200
Reexamination Certificate
active
06679953
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to fuel injector assemblies and, more particularly, to a method for assembling and hardening a ball plug in a counterbore of a fuel injector nozzle assembly.
BACKGROUND OF INVENTION
As is known in the art, the nozzle assemblies of fuel injectors contain drilled passages that must be plugged after machining.
FIG. 1
illustrates a cross-section of one such prior art counterbored passage
10
formed into the body
12
of a fuel injector nozzle
14
. The body
12
is made, for example, from H13 steel and is hardened (for example, core hardened and gas nitrided by means of processes well-known in the art). The core hardening and gas nitriding process infiltrates the crystalline structure of the steel body
12
to an average depth, as can clearly be seen in the areas
16
.
After the core hardening and gas nitriding process is performed, a ball plug
18
is press fit into the counterbored passage
10
. The ball plug
18
may be made, for example, from annealed 52100 steel. The press-fitting operation employs enough force to squeeze the distal end of the ball plug
18
into the reduced diameter section of the passage
10
counterbore, causing tearing of the ball plug
18
material in the process. This results in the distal end of the ball plug
18
not forming a tight seal with the walls of the passage
10
, as can be seen at the gaps
20
.
During operation of the fuel injector nozzle
14
, the passage
10
is filled with fuel, which reaches a relatively high pressure (25 ksi or 375 lbf, for this prior art injector) during an injection event. The existence of the gaps
20
significantly increases the surface area upon which this pressure acts, resulting in an unacceptable failure rate of ball plugs
18
being forced out of the passage
10
.
There is therefore a need for a method for assembling and heat treating a ball plug in a counterbore of a fuel injector nozzle assembly which significantly increases the pressure required to force the ball plug
18
out of the passage
10
. The present invention is directed toward meeting this need.
SUMMARY OF THE INVENTION
According to the method of the present invention, the ball plug is press fit into the counterbored passage of a fuel injector nozzle assembly prior to hardening of the fuel injector nozzle assembly. A core hardening and gas nitriding process is then applied to the assembly, causing the ball plug to expand and the passage diameter to shrink. This results in a greatly increased seal between the ball plug and the passage, and substantial elimination of the gaps experienced therebetween in prior art fuel injector nozzle assemblies.
REFERENCES:
patent: 3641802 (1972-02-01), Segro
patent: 6286769 (2001-09-01), Gunji et al.
patent: 408074707 (1996-03-01), None
Barnhart Curt M.
Cheung Angelina Y.
Foreman Gary A.
Hamilton Dan N.
Jackson Stephen C.
Cummins Engine Company, Inc.
Woodard Emhardt Moriarty McNett & Henry LLP
Yee Deborah
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