FUEL INJECTOR HAVING FLAT SEAT AND NEEDLE FUEL SEAL

Abstract: An electromagnetic fuel injector (10) has a raised seat (20) with which the needle tip (32) coacts to open and close the injector (10) as the injector (10) is operated. The raised seat (20) has an annular transverse seating surface (22) surrounding a hole (24) through the seat member (14). The hole (24) through the seat member (14) has a frusto-conically shaped surface (24a) immediately contiguous the annular seating surface (22), and the tip (32) of the injector needle (12) is conically shaped. The cone angle of the needle tip (32) is greater than the cone angle of the frusto-conically shaped hole (24a) in the seat member (14), and the needle tip (32) and the annular transverse surface (22) of the seat (20) are almost parallel so that the needle tip (32) seats on the annular transverse surface (22) of the seat (20) at the rim of the frusto-conically shaped hole (24a) when the injector (10) closes. The seat (20) is softer than the needle (12) so that the seal is initially good and becomes better as the injector (10) is operated.

Description: This invention relates generally to electromagnetic fuel injectors. More specifically it relates to a new and unique flat seat and needle fuel seal in an electromagnetic fuel injector. The fuel injector that is illustrated in U.S. patent 4,610,080, commonly assigned, is representative of one known type of fuel injector. The needle has a rounded tip that seats in a frusto-conically shaped hole that is centrally located in a seat member that disposed at the tip end of the injector. A guide member is affixed to the interior face of the seat member and comprises a hole that is accurately aligned to the frusto-conical hole in the seat member. As the needle is displaced by operation of the injector's electromagnetic solenoid, the hole in the guide member guides the needle axially into and out of seating engagement with the frusto-conical hole in the seat member. The guide member has several holes that are located radially outwardly of its central guide hole, and these several holes serve to convey fuel past the guide member and toward the seat member. The present invention relates to a new construction for the seat member and the needle wherein the two are constructed to have what are essentially flat parallel mating surfaces that provide a good initial seal when the injector closes and whose interface plastically conforms during continued operation of the injector to produce an even better seal. The invention provides improved sealing over the life of the injector, de-sensitizes the fuel flow vs. stroke characteristic of the injector, and reduces the alignment sensitivity resulting in reduced dependency on precision manufacturing operations. The invention also provides a particle trap that can reduce the chances of a foreign particle falling between the needle and seat. US-A-1 821 272 discloses a raised seat. CH-A-225 227 discloses a cone angle of needle tip greater than cone angle of seat, FR-A-2 328 854 discloses different hardnesses of needle and seat. However, the particular combination of features and interrelationships described in the characterizing clause of claim 1 are not found in the known art. The foregoing features, advantages, and benefits of the invention will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention in accordance with the best mode contemplated at the present time in carrying out the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view, having portions broken away, of a fuel injector embodying principles of the invention. Fig. 2 is a fragmentary enlarged view of a portion of Fig. 1. Fig. 3 is a fragmentary enlarged view taken in circle 3 of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENT The construction of the fuel injector 10 that is shown in the drawings is like that contained in U.S. patent 4,610,080 except for the needle 12 and the seat member 14. The seat member comprises a frusto-conically shaped inside wall 16 and a flat transverse wall 18. Disposed centrally on wall 18 within the confines of wall 16 is a raised seat 20. Seat 20 has a flat transverse seating surface 22 which is of circular annular shape. Surface 22 bounds a through-hole 24 which comprises a frusto-conically tapered portion 24a and a circular cylindrical portion 24b. A needle guide member 26 is affixed to the rim of seat member 14 and comprises a circular hole 28 that is precisely aligned with hole 24. Needle 12 fits very closely within hole 28 so as to be accurately guided for axial travel to and from seat 24. Member 26 also contains several through-holes 30 in radially outwardly spaced relation to hole 28, and in the condition of the injector portrayed in Figs. 1 and 2 showing needle 12 unseated from seat 24, fuel can flow through these holes 30, and through member 14, exiting via hole 24. The tip end 32 of needle 12 is conically shaped. Its cone angle is greater than the cone angle of hole portion 24a so that when the tip end of the needle seats on seat 20, the seating contact is with surface 22 just at the rim of portion 24a. For purposes of illustration in the drawing Figs., the cone angle of the needle tip is somewhat smaller than is actually the case in the actual embodiment of injector. By way of example, if surface 22 lies in a flat plane that is exactly perpendicular to the axis of the needle, the cone angle of the needle tip may be 88 degrees plus or minus one and one half degrees. Thus, the needle tip surface and the seat surface may be considered as two flat and nearly parallel surfaces. In accordance with further principles of the invention, needle 12 is made of a hardened stainless steel while seat member is made of a softer stainless steel, such as 416 stainless steel. The result of such construction is that a newly fabricated injector will have good initial sealing of the needle to the seat when the injector closes, and the sealing will improve as the injector is operated. This attribute is achieved in conjunction with several other attributes. One, there is reduced lateral alignment sensitivity which can ease manufacturing considerations, such as reduced tolerances and reduced surface finish requirements. Two, there is reduced flow vs. lift sensitivity due to a more efficient fluid flow path resulting in improved linear range capabilities and decreased minimum operating voltage. Yet another feature of the invention is the provision of a well 34 around seat 20. The well provides a particle trap around the seat and reduces the chances of minute foreign particles falling between the needle and the seat.

Claims: An electromagnetic-operated fuel injector (10) of the type comprising an injector body having a fuel passage terminating at a tip end at which fuel is emitted, a seat member (14) disposed at said tip end, said seat member comprising a transverse wall containing a hole (24) through which fuel passes, a needle (12) having a tip end (32) that coacts with said seat member to open and close said hole in response to operation of the fuel injector, and a needle guide member (26) that is coaxial with said seat member, said needle guide member having a hole (28) that guides said needle and one or more additional holes (30) through which fuel passes through said needle guide member toward said seat member, characterized in that said seat member has a seat on said transverse wall that is raised toward the tip end of said needle, said seat comprises an annular surface (20) surrounding the hole in said seat member, the surface portion (24a) of the hole in said seat member that is immediately contiguous said annular surface is of a frusto-conical shape, the tip end (32) of said needle is of a conical shape whose cone angle is greater than the cone angle of the frusto-conical surface portion (24a) of the hole in said seat member so that when said needle is operated to close the hole in said seat member, an annular shaped portion of the conically shaped tip end of the needle seats on said annular surface of said seat at the rim of said frusto-conical surface portion of the hole in said seat member, and the tip end of said needle and said annular surface of said seat have different hardnesses. An electromagnetic-operated fuel injector as set forth in claim 1 characterized further in that said seat member transverse wall comprises an annular well (34) surrounding said seat member hole. An electromagnetic-operated fuel injection as set forth in claim 2 characterized in that said hole (24) in said seat member (14) is separated from the well (34) by an annular surface (20) that is spaced above the bottom of the well, the surface portion of the hole in said seat member that is immediately contiguous said annular surface being of frusto-conical shape, said needle (12) having a tip end (32) that is of a conical shape and cone angle greater than the cone angle of said frusto-conically shaped surface portion of said hole in said seat member.

Inventors: WIECZOREK, DAVID PAUL
Applicants: SIEMENS AKTIENGESELLSCHAFT
Application year: 1990
Main classification: F02M61
IPC codes: F02M61, F02M51