Abstract:
An injector seat assembly for a fuel injector is provided. The injector seat assembly includes an injector seat having a longitudinal seat channel and a longitudinal channel axis extending therethrough. The injector seat is constructed from a first material. An insert is fixedly inserted into the longitudinal seat channel. The insert has a longitudinal insert channel and a longitudinal insert channel axis extending along the longitudinal seat channel axis. The insert is constructed from a second material, different from the first material. A method of constructing the injector seat assembly is also provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a valve seat for a fuel injector which includes a deposit resistant material in areas on the valve seat where deposits detrimental to injector performance can form. 
     BACKGROUND OF THE INVENTION 
     Fuel injectors are used in internal combustion engines to provide a measured amount of fuel to each combustion chamber. The tips of the injectors protrude into the combustion chamber, and are exposed to a high temperature atmosphere containing fuel and air. Fuel in the presence of air at elevated temperatures reacts with metal in the injector, typically stainless steel, which is used to form the injector tip. The product of this reaction is a hard residue adhering to all surfaces wet with fuel and exposed to elevated temperatures and air. These surfaces include critical surfaces such as the inside of the fuel orifice all the way up to the sealing band of the seat, including the transition cone. The deposits on these surfaces restrict flow and distort the pattern and atomization of the injector fuel spray, resulting in higher emissions and reduced running stability of the engine. 
     Although combustion systems have been designed to reduce tip temperatures and to provide a cleansing air flow across the injector tip, making conditions for deposit less than optimal, deposits still form on the injector tip due to the reaction of the fuel with the stainless steel of the tip. 
     It would be beneficial to develop an injector surface exposed to fuel and air at elevated temperatures which is constructed from a material which retards or prevents the formation of deposits on the surface. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, the present invention discloses a fuel injector having an inlet, an outlet, and a passageway providing a fuel flow conduit from the inlet to the outlet. The fuel injector comprises a needle and an injector seat assembly. The needle is positionable in the passageway between a first position occluding the passageway and a second position permitting fuel flow. The injector seat assembly includes an injector seat having a longitudinal seat channel and a longitudinal channel axis extending therethrough. The injector seat is constructed from a first material. An insert is fixedly inserted into the longitudinal seat channel. The insert has a longitudinal insert channel and a longitudinal insert channel axis extending along the longitudinal seat channel axis. The insert is constructed from a second material, different from the first material. 
     Additionally, the present invention discloses an injector seat assembly comprising an injector seat having a longitudinal seat channel and a longitudinal channel axis extending therethrough. The injector seat is constructed from a first material. An insert is fixedly inserted into the longitudinal seat channel. The insert has a longitudinal insert channel and a longitudinal insert channel axis extending along the longitudinal seat channel axis. The insert is constructed from a second material, different from the first material. 
     Further, the present invention discloses a method of manufacturing an injector seat assembly comprising providing a valve seat blank having a longitudinal seat channel extending therethrough; installing an insert into the longitudinal seat channel; and forming a longitudinal insert channel in the insert, the longitudinal insert channel being co-axial with the longitudinal seat channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate a presently preferred embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. In the drawings: 
     FIG. 1 is a side profile view, in section, of a downstream end of a fuel injector utilizing a valve seat assembly according to the present invention; 
     FIG. 2 is a side profile view, in section, of a valve seat blank according to a preferred embodiment of the present invention; 
     FIG. 3 is a side profile view, in section, of a valve seat insert according to the preferred embodiment of the present invention; 
     FIG. 4 is a top plan view of the valve seat insert taken along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a side profile view, in section, of a machined valve seat assembly according to the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the drawings, like numerals are used to indicate like elements throughout. As shown in FIG. 1, a fuel injector  110  has an inlet  12 , an outlet  14 , and a passageway  16  providing a fuel flow conduit from the inlet  12  to the outlet  14 . The fuel injector  110  includes a needle  18  positionable in the passageway  16  between a first position occluding the passageway  16  and a second position permitting fuel flow past the needle  18  and past a valve seat assembly  100  for flow through the passageway  16 . 
     A valve seat blank  10  for the valve seat assembly  100  is shown in FIG.  2 . An insert  20  for insertion into the valve seat blank  10  is shown in FIGS. 3 and 4. The insert  20  is inserted into the valve seat blank  10  to form the valve seat assembly  100 , shown in FIG.  5 . The valve seat assembly  100  is inserted in the fuel injector  110  proximate to the tip (not shown). 
     Referring to FIG. 2, the valve seat blank  10  includes an upstream side  102  and a downstream side  104 . As used herein, “upstream” is defined to mean a direction toward the top of the figure referenced and “downstream” is defined to mean the bottom of the figure referenced. Preferably, the valve seat blank  10  is constructed from stainless steel, although those skilled in the art will recognize that the valve seat blank  10  can be constructed from other materials as well. A longitudinal channel  110  extends therethrough, preferably along a longitudinal seat axis  112 . The longitudinal channel  110  includes a channel wall  114 , and a diameter  115 . The channel wall  114  extends downstream from a location between the upstream side  102  and the downstream side  104  of the valve seat blank  10  to the downstream side  104  of the valve seat blank  10 . Preferably, the channel wall  114  is generally parallel to the longitudinal seat axis  112 . 
     A sealing cone  116  is located in the valve seat blank  10  between the upstream side  102  and the channel wall  114 . The sealing cone  116  is generally centered around the longitudinal seat axis  112  and tapers generally downstream and inward toward the longitudinal seat axis  112 . Preferably, the sealing cone  116  has a cone angle α of approximately 104 degrees relative to the longitudinal seat axis  112 , although those skilled in the art will recognize that the cone angle α can be other sizes as well. The sealing cone  116  mates with a reciprocating valve needle (not shown) which seats in the sealing cone  116  in a closed position to seal the longitudinal seat channel  110  preventing pressurized fuel in the injector from flowing through the longitudinal seat channel  110 . 
     Referring now to FIGS. 3 and 4, the insert  20  includes an upstream end  202  and a downstream end  204 . Preferably, the downstream end  204  includes a beveled face  205  for reasons that will be explained. The insert  20  also includes an outer wall  206  which extends generally from the upstream end  202  to the beveled face  205  and has a diameter  208 . The insert  20  also includes a longitudinal insert axis  212  extending therethrough. Preferably, the insert  20  is constructed from a ceramic material that retards or is resistant to the formation of deposits thereon. 
     To form the valve seat  100  shown in FIG. 5, the downstream end  204  of the insert  20  is inserted into the longitudinal seat channel  110  through the upstream end  102  of the valve seat insert  10  and the sealing cone  116 . The beveled face  205  of the downstream end  204  engages the sealing cone  116  and guides the insert  20  into the longitudinal seat channel  110 . The beveled face  205  helps to prevent the insert  20  from cocking at an angle during insertion. Preferably, the insert  20  is inserted into the longitudinal seat channel  116  such that the upstream end  202  of the insert  20  is flush with the interface between the downstream end of the sealing cone  116  and the upstream end of the longitudinal seat channel  110 . Preferably, the insert  20  is sufficiently long so that the entire beveled face  205  extends beyond the downstream end  104  of the valve seat blank  10 . Preferably, the diameter  208  of the insert  20  is larger than the diameter  115  of the longitudinal seat channel  116 , forming an interference fit between the outer wall  206  of the insert  20  and the channel wall  114  of the valve seat blank  10 . Those skilled in the art will recognize that, in order for the insert  20  to fit into the longitudinal seat channel  116 , the valve seat blank  10  is preferably heated to temporarily expand the valve seat blank  10  and enlarge the longitudinal seat channel  116  sufficiently to enable the insert  20  to be inserted therein. The valve seat blank  10  is then cooled to reduce the longitudinal seat channel  116  and securely retain the insert  20  therein. Those skilled in the art will recognize that other methods of securing the insert  20  to the valve seat blank  10 , such as tapering the longitudinal seat channel  116 , welding the insert  20  to the valve seat blank  10 , upsetting material from the valve seat blank  10  over the insert  20 , or heat treating the valve seat blank  10  and insert  20 , forming a molecular bond between the valve seat blank  10  and the insert  20 . 
     Once the insert  20  is inserted into the longitudinal channel  116 , the insert  20  is machined. A longitudinal insert channel  210 , shown in FIG. 5, is machined along the longitudinal insert axis  212 , which is preferably co-axial with the longitudinal seat axis  112 . The downstream end  204  of the insert  20  which protrudes beyond the downstream end  104  of the valve seat blank  10  is machined smooth with the downstream end  104  of the valve seat blank  10 , forming a sharp edge of the longitudinal insert channel  210  at the downstream end  204 . 
     The upstream end  202  of the insert  20  is machined to form a transition cone  214  transition cone  214  extends from the upstream end  202  to the longitudinal insert channel  10  at an angle relative to the longitudinal insert axis  212 . Preferably, the angle is approximately 85 degrees, although those skilled in the art will recognize that the angle can be more or less than 85 degrees. The transition cone  214  is preferably the same transition cone disclosed in U.S. Provisional Patent Application No. 60/131,251, filed Apr. 27, 1999, for which US utility application Ser. No. 09/559,748 was filed on Apr. 27, 2000, now U.S. Pat. No. 6,311,901 issued on Nov. 6, 2001 and assigned to the assignee of the present invention, the disclosure of which is incorporated by reference herein in its entirety. 
     Those skilled in the art will recognize that the steps of manufacturing the valve seat assembly  100  can be performed in other orders than those recited above, while providing the same end product. 
     The insert  20  is located in the valve seat assembly  100  in the longitudinal seat channel  116  where deposits tend to form as a result of combustion. The material from which the insert  20  is preferably constructed retards or prevents deposits from forming in the longitudinal seat channel  116 , allowing the longitudinal seat channel  116  to remain its desired size and allowing a desired amount of fuel to flow through the longitudinal seat channel  116 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiment described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined in the appended claims.