Abstract:
A fuel injector seat for a fuel injector assembly, and more particularly for a high-pressure fuel injector assembly, having a number of features for minimizing the formation of combustion chamber deposits on the seat, providing a selected finish on a needle-sealing portion, and reducing sac volume. These features include positioning a transition portion between the needle-sealing portion and an orifice portion, positioning a sharp edge at the outlet of the orifice portion, and applying a coating to certain surfaces of the seat. This invention also relates to a fuel injector seat and method of manufacturing the fuel injector seat, and a method of evaluating when the transition portion is required between the orifice and needle-sealing portions for a particular seat arrangement.

Description:
CROSS REFERENCE TO CO-PENDING APPLICATION 
     This application claims priority to U.S. Provisional Application No. 60/131,251, filed Apr. 27, 1999, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a fuel injector assembly, and more particularly to a high-pressure fuel injector assembly which includes a seat having a number of features for minimizing the formation of combustion chamber deposits on the seat. This invention also relates to the arrangement and manufacture of a fuel injector seat. 
     BACKGROUND OF THE INVENTION 
     Fuel injectors are conventionally used to provide a measured flow of fuel into an internal combustion engine. In the case of direct injection systems, a high-pressure injector extends into the combustion chamber. Consequently, a downstream face of the fuel injector&#39;s seat is prone to the formation of combustion chamber deposits. It is desirable to minimize this formation of deposits in order to maintain the intended operation of the fuel injector. 
     For the intended operation, it is critical for the seat to provide a sealing surface for engaging a displaceable closure member, e.g., a needle of a conventional fuel injector assembly. In a first position of the closure member relative to the seat, i.e., when the closure member contiguously engages the seat, fuel flow through the injector is prohibited. In a second position of the closure member relative to the seat, i.e., when the closure member is separated from the seat, fuel flow through the injector is permitted. 
     In order to provide the sealing surface, it is known to provide the seat with a conical portion having a desired included angle. Conventionally, grinding tools with a conical shape are used to grind the conical portion. It is also known that the quality of a surface finish is related to the grinding velocity. In the case of conical shape grinding tools, the grinding velocity decreases toward the apex of the tools. 
     In the case of fuel injector seats having a small orifice, the velocity of the grinding tool at the edge of the orifice is insufficient. Thus, conventional grinding operations cannot provide a selected finish on conventional conical portions. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the seats in conventional fuel injectors, and provides a number of features for minimizing the formation of combustion chamber deposits. 
     According to the present invention, a transition portion is interposed between the conventional conical portion and the orifice, thus providing an additional volume in which the apex of the conventional grinding tool rotates. 
     However, excess sac volume, i.e., the volume of the fuel flow passage between the sealing band (i.e., the needle-to-seat seal) and the orifice, adversely affects the formation of combustion chamber deposits on the downstream seat. Thus, according to the present invention, the transition portion also minimizes sac volume. 
     Moreover, according to the present invention, a fuel injector seat is evaluated as to the necessity and configuration of a transition portion. This evaluation is based on different factors including orifice size and the included angle defined by the conical sealing portion. 
     Also, according to the present invention, an interface between the downstream face and the orifice is defined by a sharp edge. This facilitates dislodging combustion chamber deposits that may accumulate near the edge. 
     Additionally, according to the present invention, a fuel injector seat has a coating to control the formation of combustion chamber deposits in a first set of critical areas, and is uncoated in a second set of critical areas to facilitate the attachment and operation of the seat. 
     The present invention provides 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 positionable in the passageway between a first position occluding the passageway and a second position permitting fuel flow; and a seat contiguously engaging the needle in the first position, the seat having an upstream face, a downstream face, and a passage extending along an axis between the upstream face and the downstream face. The passage defining a portion of the passageway and including an orifice portion proximate the downstream face; a needle sealing portion proximate the upstream face and in fluid communication with the orifice portion; and a coating on select surfaces of the seat. 
     The present invention also provides a fuel injector seat. The fuel injector seat comprises an upstream face; a downstream face spaced from the upstream face; a passage extending along an axis between the upstream face and the downstream face, the passage including an orifice portion proximate the downstream face and a sealing portion proximate the upstream face; and a coating on select surfaces of the seat. 
     The present invention additionally provides a method of forming a fuel injector seat from a blank. The blank has an upstream face, a downstream face, and a perimeter surface extending between the upstream face and the downstream face. The method of forming the fuel injector seat comprises forming a passage through the blank, the passage extending along an axis between the upstream face and the downstream face; masking the perimeter surface of the blank; applying a surface energy reducing coating to the blank; and grinding a sealing portion of the passage proximate to the upstream face, the grinding removing the coating. 
     As it is used herein, the term “axis” is defined as a center line to which parts of a body or an area may be referred. This term is not limited to straight lines, but may also include curved lines or compound lines formed by a combination of curved and straight segments. 
     As it is used herein, the term “rate” is defined as a value that describes the changes of a first quality relative to a second quality. For example, in the context of describing a volume, rate can refer to changes in the transverse cross-sectional area of the volume relative to changes in position along the axis of the volume. The term “rate” is not limited to constant values, but may also include values that vary. 
     As it is used herein, the phrase “included angle” is defined as a measurement of the angular relationship between two segments of a body, when viewing a cross-section of the body in a plane including the axis of the body. Generally, the axis bifurcates the included angle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. 
     FIG. 1 is a cross-sectional view of a fuel injector assembly of the present invention taken along its longitudinal axis; and 
     FIG. 2 is an enlarged portion of the cross-sectional view of the fuel injector assembly shown in FIG. 1 which illustrates a seat and a swirl generator according to the present invention. 
     FIG. 3 is a graph illustrating engine flow decrease as a function of the ratio of orifice length over orifice diameter for different examples of fuel injectors. 
     FIG. 4 is a detail view of a seat portion that is indicated by IV in FIG.  2 . 
     FIG. 5 is a schematic illustration of the seat according to the present invention indicating the critical areas of the seat that are coated and the critical areas of the seat that are uncoated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a fuel injector assembly  10 , such as a high-pressure, direct-injection fuel injector assembly  10 . The fuel injector assembly  10  has a housing, which includes a fuel inlet  12 , a fuel outlet  14 , and a fuel passageway  16  extending from the fuel inlet  12  to the fuel outlet  14  along a longitudinal axis  18 . The housing includes an overmolded plastic member  20  cincturing a metallic support member  22 . 
     A fuel inlet member  24  with an inlet passage  26  is disposed within the overmolded plastic member  20 . The inlet passage  26  serves as part of the fuel passageway  16  of the fuel injector assembly  10 . a fuel filter  28  and an adjustable tube  30  are provided in the inlet passage  26 . The adjustable tube  30  is positionable along the longitudinal axis  18  before being secured in place, thereby varying the length of an armature bias spring  32 . In combination with other factors, the length of the spring  32 , and hence the bias force against the armature, control the quantity of fuel flow through the injector. The overmolded plastic member  20  also supports a socket  20   a  that receives a plug (not shown) to operatively connect the fuel injector assembly  10  to an external source of electrical potential, such as an electronic control unit (not shown). An elastomeric O-ring  34  is provided in a groove on an exterior of the inlet member  24 . The O-ring  34  is supported by a backing ring  38  to sealingly secure the inlet member  24  to a fuel supply member (not shown), such as a fuel rail. 
     The metallic support member  22  encloses a coil assembly  40 . The coil assembly  40  includes a bobbin  42  that retains a coil  44 . The ends of the coil assembly  40  are electrically connected to pins  40   a  mounted within the socket  20   a  of the overmolded plastic member  20 . An armature  46  is supported for relative movement along the axis  18  with respect to the inlet member  24 . The armature  46  is supported by a spacer  48 , a body shell  50 , and a body  52 . The armature  46  has an armature passage  54  in fluid communication with the inlet passage  26 . 
     The spacer  48  engages the body shell  50 , which engages the body  52 . An armature guide eyelet  56  is located on an inlet portion  60  of the body  52 . An axially extending body passage  58  connects the inlet portion  60  of the body  52  with an outlet portion  62  of the body  52 . The armature passage  54  of the armature  46  is in fluid communication with the body passage  58  of the body  52 . a seat  64 , which is preferably a metallic material, is mounted at the outlet portion  62  of the body  52 . 
     The body  52  includes a neck portion  66  that extends between the inlet portion  60  and the outlet portion  62 . The neck portion  66  can be an annulus that surrounds a needle  68 . The needle  68  is operatively connected to the armature  46 , and can be a substantially cylindrical needle  68 . The cylindrical needle  68  is centrally located within and spaced from the neck portion so as to define a part of the body passage  58 . The cylindrical needle  68  is axially aligned with the longitudinal axis  18  of the fuel injector assembly  10 . 
     Operative performance of the fuel injector assembly  10  is achieved by magnetically coupling the armature  46  to the end of the inlet member  26  that is closest to the inlet portion  60  of the body  52 . Thus, the lower portion of the inlet member  26  that is proximate to the armature  46  serves as part of the magnetic circuit formed with the armature  46  and coil assembly  40 . The armature  46  is guided by the armature guide eyelet  56  and is responsive to an electromagnetic force generated by the coil assembly  40  for axially reciprocating the armature  46  along the longitudinal axis  18  of the fuel injector assembly  10 . The electromagnetic force is generated by current flow from the electronic control unit (not shown) through the coil assembly  40 . Movement of the armature  46  also moves the operatively attached needle  68  to positions that are either separated from or contiguously engaged with the seat  64 . This opens or closes, respectively, the seat passage  70  of the seat  64 , which permits or inhibits, respectively, fuel from flowing through the fuel outlet  14  of the fuel injector  10 . The needle  68  includes a curved surface  78 , which can have a partial spherical shape for contiguously engaging with a conical portion  72  of the seat passage  70 . Of course, other contours for the tip of the needle  68  and the seat passage  70  may be used provided that, when they are engaged, fuel flow through the seat  64  is inhibited. 
     Referring to FIGS. 1 and 2, an optional swirl generator  74  can be located proximate to the seat  64  in the body passage  58 . The swirl generator  74  allows fuel to form a swirl pattern on the seat  64 . For example, fuel can be swirled on the conical portion  72  of the seat passage  70  in order to produce a desired spray pattern. The swirl generator  74 , preferably, is constructed from a pair of flat disks, a guide disk  76  and a swirl disk  78 . The swirl generator  74  defines a contact area between the seat  64  and the body  52 . The guide disk  76  provides a support for the needle  68 . 
     The needle  68  is guided in a central aperture  80  of the guide disk  76 . The guide disk  76  has a plurality of fuel passage openings that supply fuel from the body passage  58  to the swirl disk  78 . The swirl disk  78  receives fuel from the fuel passage openings in the guide disk  76  and directs the flow of fuel tangentially toward the seat passage  70  of the seat  64 . The guide disk  76  and swirl disk  78  that form the swirl generator  76  are secured to an upstream face  602  of the seat  64 , preferably, by laser welding. 
     Fuel that is to be injected from the fuel injector  10  is communicated from the fuel inlet source (not shown), to the fuel inlet  12 , through the fuel passageway  16 , and exits from the fuel outlet  14 . The fuel passageway  16  includes the inlet passage  26  of the inlet member  24 , the armature passage  54  of the armature  46 , the body passage  58  of the body  52 , the guide disk  78  and the swirl disk  80  of the swirl generator  76 , and the seat passage  70  of the seat  64 . In a high-pressure, direct injection system, fuel is supplied from the inlet source in an operative range approximately between 700 psi and 2000 psi. 
     Referring to FIG. 2 in particular, the seat passage  70  of the seat  64  extends between the upstream face  602  of the seat  64  and a downstream face  604  of the seat  64 . The seat passage  70  includes an orifice portion  608 , a needle sealing portion  612 , and a transition portion  614 . The needle sealing portion  612  is disposed proximate to the first face  602 , the orifice portion  608  is disposed proximate to the downstream face  604 , and the transition portion  614  is interposed between the orifice portion  608  and the needle sealing portion  612 . 
     The orifice portion  608  has a first transverse cross-sectional area relative to the longitudinal axis  18 . That is to say, the first cross-sectional area can be measured in each of the imaginary planes that are oriented orthogonally to the longitudinal axis  18  as it extends through the orifice portion  608 , or it can be measured in each of the imaginary planes within the orifice portion  608  that are parallel to the downstream face  604 . It is most frequently the case that the downstream face  604  is oriented substantially orthogonal to the longitudinal axis  18 , and the longitudinal axis  18  consists of a straight line extending throughout the entire fuel injector assembly  10 . Consequently, the first cross-sectional area can be measured in each of the imaginary planes that are both oriented orthogonally to the longitudinal axis  18  and parallel to the downstream face  604 . 
     The first transverse cross-sectional area can be substantially uniform throughout the orifice portion  608 . For example, the first transverse cross-sectional area can be a circle having a diameter D and orifice portion  608  can extend along the longitudinal axis  18  a distance L. Thus, in the most frequent case described above, the orifice portion  608  comprises a right circular cylinder. Through experimentation, it has been determined that desirable operating characteristics for the fuel injector assembly  10  are achieved when the ratio of the length L to diameter D, i.e., L/D, for the orifice portion  608  approaches, but is not less than, 0.3. FIG. 3 is an empirical data plot of flow changes due to deposit formation as a function of the L/D ratio. 
     The needle sealing portion  612  has a second transverse cross-sectional area relative to the longitudinal axis  18 . That is to say, the second cross-sectional area can be measured in each of the imaginary planes that are oriented orthogonally to the longitudinal axis  18  as it extends through the needle sealing portion  612 , or it can be measured in each of the imaginary planes within the needle sealing portion  612  that are parallel to the upstream face  602 . It is most frequently the case that the upstream face  602  is oriented substantially orthogonal to the longitudinal axis  18 , and the longitudinal axis  18  consists of a straight line extending throughout the entire fuel injector assembly  10 . Consequently, the second cross-sectional area can be measured in each of the imaginary planes that are both oriented orthogonally to the longitudinal axis  18  and parallel to the upstream face  602 . 
     The needle sealing portion  612  is formed by a grinding tool so as to provide a selected finish. The contour of the needle sealing portion  612  can be described by the shape of each second transverse cross-sectional area and the rate that the second transverse cross-sectional area decreases throughout the needle sealing portion  612 . The second transverse cross-sectional area can have a first area in the imaginary plane that is proximate to the upstream face  602 , and decrease at a first rate to a second area in the imaginary plane that is distal from the upstream face  602 . As discussed above, this rate may be constant or variable. In the case where the shape of each second transverse cross-sectional area is a circle having a diameter that deceases at a constant rate, as is illustrated in FIG. 2, the shape of the needle sealing portion  612  is that of a truncated right cone with an included angle  624 . Of course, different shapes for the needle sealing portion  612  can be obtained by varying the shape of the second transverse cross-sectional areas or by varying the rate at which the second transverse cross-sectional areas change. 
     The transition portion  614  has a third transverse cross-sectional area relative to the longitudinal axis  18 . That is to say, the third cross-sectional area can be measured in each of the imaginary planes that are oriented orthogonally to the longitudinal axis  18  as it extends through the transition portion  614 , or it can be measured in each of the imaginary planes within the transition portion  614  that are parallel to the upstream face  602 . It is most frequently the case that the upstream face  602  is oriented substantially orthogonal to the longitudinal axis  18 , and the longitudinal axis  18  consists of a straight line extending throughout the entire fuel injector assembly  10 . Consequently, the third cross-sectional area can be measured in each of the imaginary planes that are both oriented orthogonally to the longitudinal axis  18  and parallel to the upstream face  602 . 
     The transition portion  614  can be formed by a grinding tool, a drill bit, etc. The contour of the transition portion  614  can be described by the shape of each third transverse cross-sectional area and the rate that the third transverse cross-sectional area decreases throughout the transition portion  614 . The third transverse cross-sectional area can decrease at a second rate from the second area of the second transverse cross-sectional area to the first transverse cross-sectional area of the orifice portion  608 . As discussed above, this rate may be constant or variable. In the case where the shape of each third transverse cross-sectional area is a circle having a diameter that deceases at a constant rate, as is illustrated in FIG. 2, the shape of the transition portion  614  is that of a truncated right cone with an included angle  626 . Of course, different shapes for the transition portion  614  can be obtained by varying the shape of the second transverse cross-sectional areas or by varying the rate at which the second transverse cross-sectional areas change. 
     The transition portion  614  provides a volume which receives the tip of the grinding tool forming the needle sealing portion  612 . Thus, only portions of the grinding tool that are driven at a sufficient grinding velocity contact the needle sealing portion  612 , thereby producing at least a minimum selected finish over the entire surface of the needle sealing portion  612 . 
     When the transition portion  614  is conically shaped, the included angle  624  of the needle sealing portion  612  is preferably greater than the included angle  626  of the transition portion  614 . The included angle  624  can be approximately 15° greater that the included angle  626 , e.g., the included angle  624  of the needle sealing portion  612  can be approximately 105° and the included angle  626  of the transition portion  614  can be approximately 90°. Of course, different combinations of included angles can be used provided that the needle sealing portion  612  sealingly conforms to the surface  78  of the needle  68 , and the transition portion  614  facilitates providing a selected finish on the needle sealing portion  612 . For example, it has been found that when the included angle  624  is approximately 104° and the included angle  626  is approximately 85°, flow stability is improved. If the included angle  626  is increased into the range of approximately 95° to 100°, flow stability decreases and deposit removal, perhaps as a result of cavitation, improves. 
     In addition to providing a transition between the needle sealing portion  612  and the orifice portion  608 , the transition portion  614  minimizes the sac volume, i.e., the volume of the seat passage  70  from where the surface  78  of the needle  68  contiguously engages the needle sealing portion  612  to the orifice portion  608 . For example, a transition portion  614  having the shape of a right circular cylinder would undesirably increase the sac volume as compared to a right cone, such as illustrated in FIG.  2 . 
     Referring now to FIGS. 2 and 4, the interface at the junction of the downstream face  604  and the orifice portion  608  can be a sharp edge to facilitate the dislodging of combustion chamber deposits that form on the downstream face  604 . In particular, a sharp edge prevents the formation of combustion chamber deposits on the downstream face  602  from continuing to accumulate on the orifice portion  608 . That is to say, the pattern of deposit formation does not extend from the substantially flat surface of the downstream face  604  onto the substantially cylindrical surface of the orifice portion  608 . Instead, a continued build-up of the deposits at the interface of the downstream face  604  and the orifice portion  608  results in a formation that can be readily dislodged by the high pressure spray of fuel passing through the orifice portion  608 . According to the present invention, a sharp edge can be defined by an interface comprising an annular chamfered edge  606  connecting the perpendicular surfaces of the downstream face  604  and the orifice portion  608 . The chamfered edge  606  can extend for approximately 0.02 millimeters and be oriented at 45° with respect to each of these perpendicular surfaces. 
     Referring to FIG. 5, coatings that lower surface energy or reduce surface reactivity can also control the formation of combustion chamber deposits. Certain surfaces of the seat  64  can be coated, however, the presence of a coating can adversely affect certain critical surfaces of the seat  64 . For example, coatings can reduce the effectiveness of the seat to needle seal, or can hinder the connection of the seat  64  with respect to the body  52 . An injector seat blank, i.e., a seat  64  comprising the upstream face  602 , the downstream face  604 , and the rough passage  70  (prior to grinding the needle sealing portion  612 ), is coated or plated. Masking can be used to prevent applying the coating on an outer circumferential surface of the seat  64 . Masking can also be used to prevent the application of the coating to a portion of the downstream face  604  that is proximate to the outer circumferential surface. These masked areas can subsequently be used for attaching the seat  64  with respect to the body  52 . Grinding for the needle sealing portion  612  removes the applied coating in the area of the critical sealing band. Thus, the seat  64  is coated in the areas most necessary to inhibit deposit formation, and is uncoated in the critical sealing band area and in seat attachment area. The coating can be a carbon based coating, such as that sold under the trade name SICON, which can be applied by conventional vapor deposition techniques. The coating can also be fluoro-polymer based, aluminum based, or a ceramic. The contiguously engaging needle  68  can also be coated or can be uncoated. 
     The method of forming the fuel injector assembly  10  includes forming the seat  64  having the upstream face  602 , the downstream face  604 , and the seat passage  70  extending between the upstream face  602  and the downstream face  604 . The method further comprises forming the orifice portion  608  and the transition portion  614  within the passage  70 . Before applying a coating to the seat  64 , the needle-sealing portion  612  can be rough formed and the sharp edge interface  606  can be formed between the downstream face  604  and the orifice portion  608 . The orifice portion  608 , the rough formed needle-sealing portion  612 , and the transition portion  614  can be formed in any order, and by any technique, e.g., drilling, turning, etc. Moreover, any combination of the orifice portion  608 , the rough formed needle-sealing portion  612 , and the transition portion  614  can be formed concurrently by one operation, or all can be formed in a single operation. Next, the seat  64  can be masked and the coating applied to the seat  64 . Thereafter, the seat  64  can be unmasked, and the selected finish on the needle sealing portion  612  can be formed by grinding. Alternatively, the needle sealing portion  612  can be formed with the selected finish in a single step, i.e., without separately rough forming the needle sealing portion  612 . The transition portion  614  provides the volume for the grinding tool that is necessary to form the selected finish on the needle-sealing portion  612 . And as discussed above, the transition portion also minimizes sac volume. The seat  64  is now ready to be mounted with respect to the body  52  of the fuel injector assembly  10 . 
     A number of factors are evaluated to determine the necessity of providing the transition portion  614  between the orifice portion  608  and the needle sealing portion  612 . These factors include the first transverse cross-sectional area of the orifice portion  608 , the included angle of the needle-sealing portion  612 , and the selected finish to be provided on the needle-sealing portion  612 . 
     The finish, or surface texture, of a material is a measurement of roughness, which is specified as a value that is the arithmetic average deviation of minute surface irregularities from a hypothetical perfect surface. Roughness is expressed in micrometers. 
     For a rotating grinding tool, linear velocity varies as a function of the radial distance from the axis of rotation. Therefore, if the finish produced by a rotating grinding tool at a radial distance corresponding to the edge of the first transverse cross-sectional area is too rough, a transition portion  614  according to the present invention is necessary. 
     The transition portion  614  provides a volume that is relatively near to the axis of rotation for a rotating grinding tool, and in which the grinding tool does not contact the seat  64 . Thus, only those diameters of a rotating grinding tool that move with a sufficient grinding velocity are used to provide the selected finish on the needle-sealing portion  612 . 
     According to the present invention, for a needle-sealing portion  612  having an included angle of approximately 105°, a transition portion  614  is necessary when the ratio of the first transverse cross-sectional area over the first area of the second transverse cross-sectional area is less than 0.5. 
     Of course, if the needle-sealing portion  612  is to be formed by a technique using something other than a rotating grinding tool, or the shape of the second transverse cross-sectional areas are not circular, the necessity of a transition portion  614  will be determined by evaluating the quality of the surface finish at the interface between the needle-sealing portion  612  and the orifice portion  608 . 
     While the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.