Patent Publication Number: US-6665926-B2

Title: Method and apparatus for improved valve seating of a fuel injector by coining and a valve made thereby

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application filed pursuant to 35 U.S.C. §§120 and 121 and claims the benefits of prior application Ser. No. 09/606,409, filed Jun. 29, 2000, pending, which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus used to coin a valve seat in a fuel injector to improve seating between the valve seat and a needle in the injector. 
     BACKGROUND OF THE INVENTION 
     The metal-to-metal seal formed in a valve between a needle and a seat determines the accuracy at which the fluid flowing through the valve is controlled. Leakage results when the surfaces between the needle and the seat do not mate correctly. This leakage, no matter how small, is detrimental in systems where precise flow control is desired. 
     One of the uses of a fluid valve of the type to which the present invention relates is as a fuel injector for injecting a combustible fuel into a combustion engine. In the case of a spark-ignited, internal combustion engine for an automotive vehicle, the valve is typically under the control of an electronic control system and injects gasoline into the engine. 
     One of the chief reasons for using a fuel-injected engine is because of the ability to closely control the amount of fuel entering the engine. Close control over injected fuel is important for reasons of both fuel economy and exhaust emissions. When a fuel injector is closed, it should totally prevent fuel from leaking into the engine because such leakage can have undesired consequences. For example, even small amounts of leakage can adversely affect exhaust emissions in very significant ways. Certain countries now impose limits on the amounts of certain exhaust constituents that can be discharged to the atmosphere, and there is a trend toward making these limits even stricter. Accordingly, a commercially acceptable fuel injector is likely to have to comply with increasingly stringent limits on leakage. 
     The method and apparatus used to manufacture the needle and the seat greatly influence the accuracy and reliability of the fluid valve. Extremely costly manufacturing procedures could, of course, be invoked to ensure precise surface finishes and fits of the cooperating needle and seat by placing extremely small tolerances on the dimensions and surface finishes of the parts involved. Such activities would obviously increase the manufacturing costs, possibly to non-competitive prices for some companies. Alternate procedures that are less costly are therefore desirable. 
     One known method for surface finishing the needle and seat involves a grinding process. The mating surfaces of the needle and the seat are pressed into contact. Then, either the needle or the seat is rotated relative to the other. This grinding of the mating surfaces of the needle and the seat is performed in the presence of a slurry of fine-grained lapping medium. Vibrating the needle and the seat in the axial direction of the needle valve further complicates this known process. The vibration of these two valve elements is performed at the same frequency but at a different amplitude to impart a pumping action on the slurry. 
     Another method for manufacturing the needle and seat applies an axial compressive load to force the needle against the seat, coining the needle to the seat. The method described in U.S. Pat. No. 5,081,766 produces a valve that is capable of accurate and reliable fluid metering yet avoids expensive tolerance control on surface finishing and part dimensioning. The method disclosed by this patent involves the inclusion of an additional step in the manufacturing process, the coining step, but eliminates the necessity for stricter tolerances on surface finish and part dimensions. Accordingly, reconfiguration of existing manufacturing equipment and processes requires merely adding the coining step to reduce leakage through the injector. This coining step however does not involve the use of a coining die to coin a part. Rather, the coining step involves the application of axial compressive load to force a rounded distal end of the needle against a frusto-conical surface of the seat so that coining action occurs at an annular zone of surface contact between the needle and the seat. The force application is preferably conducted in a particular manner so that the needle is neither irreversibly bent nor buckled by the coining step. This step is conducted during the manufacturing process so that neither the solenoid nor the spring, which are parts of the operating mechanism in the completed injector, has an influence on the result of the coining. 
     Known manufacturing equipment typically comprises a fluid powered piston device to apply the axial compressive load. However, the compressive load is applied only one time during the manufacturing of the injector. If the needle and seat are laterally or rotationally displaced from one another after coining, the coining effect may be lost. It would be beneficial to develop a method of applying the compressive load multiple times during the manufacturing of the injector to form a better seal between the needle and the seat. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, a method for making a valve assembly is provided. The method comprises providing a first work piece having a longitudinal axis and a first end and providing a second work piece having a surface. The method also comprises the first work piece and the second work piece axially between a pair of aligned elements that are relatively movable toward and away from each other along the longitudinal axis of the first work piece. Additionally, the method comprises relatively moving the pair of aligned elements toward each other to axially clamp the first work piece and the second work piece and actuating the pair of aligned elements and delivering to the first work piece and the second work piece a controlled clamping force that acts to coin a zone of surface contact between the first end and the surface. Further, the method comprises repeating the actuating of the pair of elements a plurality of times. 
     Additionally, the present invention provides a coining apparatus. The coining apparatus comprises a frame, a first clamp having a first work piece receiving portion, and a second clamp axially aligned with and opposing the first clamp. The second clamp has a second work piece receiving portion. One of the first clamp and the second clamp is connected to the frame. The coining apparatus also comprises a vibrator attached to the frame, distal from the one of the first clamp and the second clamp connected to the frame and a cylinder connecting the vibrator and the other of the first clamp and the second clamp. The cylinder includes a rod reciprocally extending therefrom. The rod is connected to one of the vibrator and the other of the first clamp and the second clamp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. In the drawings: 
     FIG. 1 is a partial view taken in cross-section of a valve mounted on a coining apparatus during the manufacturing process; and 
     FIG. 2 is a schematic of the preferred embodiment of the coining apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a fluid valve assembly  10  having an upstream end  10   a,  a downstream end  10   b,  a longitudinal axis  11  extending therethrough, a valve body  12  housing an elongated needle  20  and an annular valve seat  30 . As used herein, the terms “upstream” and “downstream” refer to directions toward the top and bottom of FIG. 1, respectively. In the drawings, like numbers indicate like elements throughout. The valve body  12  has a hollow portion defined by an inner surface  14 . The needle  20  and the seat  30  are coaxially received along the longitudinal axis  11  in the hollow portion of the valve body  12 . Although the fluid valve assembly  10  is preferably part of a fuel injector and a fluid used in the fluid valve assembly  10  is preferably a fuel, such as gasoline, those skilled in the art will recognize that the fluid valve assembly  10  can be other than a fuel injector and the fluid can be other than a fuel. 
     An annular element  40  is interposed with the seat  30  and a first annular shoulder  16  of the valve body  12 . A valve guide  50  is secured between the seat  30  and a second shoulder  18  formed on the inner surface  14 . The valve guide  50  has a central hole through which the needle  20  extends. Fluid can exit the valve assembly  10  via an orifice  34  in the seat  30 . 
     The seat  30  includes a generally frusto-conical surface  32 , which extends generally downstream and toward the longitudinal axis  11 . The seat  30  also includes an orifice  34  at the downstream end of the frusto-conical surface  32  and along the longitudinal axis  11 . Preferably, the seat  30  is constructed from a metal, such as stainless steel. A downstream end  22  of the needle  20  has a convex surface  24  that engages the frusto-conical surface  32  of the seat  30  when the needle  20  is in a closed position. Also preferably, the needle  20  is constructed from a metal, such as stainless steel. An armature  60  is connected to an upstream end  26  of the needle  20 . The armature  60  has an outer surface  62  that slidably engages a portion of the inner surface  14  during operation of the fluid valve assembly  10 . 
     During operation of the fluid valve assembly  10 , the needle  20  is axially reciprocally displaced toward and away from the seat  30 . Contact between the convex surface  24  and the frusto-conical surface  32  forms a seal to block the flow of fluid through the orifice  34 . The effectiveness of this seal is determined by the tightness of the contact between the convex surface  24  and the frusto-conical surface  32 . Surface irregularities and misalignment between the convex surface  24  and the frusto-conical surface  32  have adverse effects on the contact tightness, especially where the contact is metal-to-metal. 
     When the completed fluid valve assembly  10  is in use, pressurized liquid fuel that has been introduced into the upstream end of the injector fills the annular space surrounding the needle  20  within the body  12 . Circumferentially spaced through-holes (not shown) in the valve guide  50  serve to convey the fuel from the annular space to fill depression defined by the frusto-conical surface  32  with pressurized fuel in a conventional manner. 
     FIG. 1 illustrates the seated condition wherein the convex surface  24  of the needle  20  has an annular zone of sealing contact with the frusto-conical surface  32  to thereby close orifice  34 , and hence prevent pressurized fuel from being emitted from the fluid valve assembly  10 . This condition represents the closed condition of the fluid valve assembly  10 . 
     It is in this closed condition that the convex surface  24  and the frusto-conical surface  32  are coined together according to the method of the present invention. The coining is conducted at a station  2  of the assembly line on which the injectors are assembled. FIG. 1 represents the-fluid valve assembly  10  at the station  2 . Essentially the station  2  comprises a suitable fixture  301  for supporting that much of the fluid valve assembly  10  as is portrayed, preferably in an upright orientation. The station  2  has a mechanism, which is capable of axially clamping the needle  20  and the seat  30  in such a manner that an axial compressive load can be applied to the needle  20  and the seat  30  in a controlled manner. 
     FIG. 1 illustrates two elements of the station&#39;s mechanism, a first clamp  300  and a second clamp  310 . The clamps  300 ,  310  are arranged coaxially along the longitudinal axis  11  and so that the parts to be clamped, the needle  20  and the seat  30 , can be placed coaxially between the clamps  300 ,  310 . The clamps  300 ,  310  are then relatively moved toward each other along the longitudinal axis  11  so that clamping occurs in the manner presented in FIG.  1 . In this regard first annular shoulder  16  circumscribes an opening sufficiently large to allow for through-passage of the upstream end of second clamp  310  into abutment with the annular element  40 . The armature  60  allows the downstream end of the first clamp  300  to abut the upstream end  26  of the needle  20 . Preferably the abutment surfaces for the parts involved are flat and smooth, as shown. 
     FIG. 2 shows, schematically, an apparatus according to the instant invention used to coin the convex surface  24  and the frusto-conical surface  32 . A piston assembly  100  has a cylinder  110  in which a piston (not shown) reciprocates in a known manner. Two rods  120 ,  122  are attached to the piston and extend out of the cylinder  110  in opposite directions. The piston assembly  100  may be any known pneumatic or hydraulic piston assembly that will provide sufficient load to coin the convex surface  24  and the frusto-conical surface  32  together. The piston assembly  100  is secured to a frame  101  in any known manner. 
     A vibrator  200  is connected to one of the rods  120 ,  122 . Alternatively, the vibrator  200  may be interposed with the rod  122  and the first clamp  300  or placed in contact with the second clamp  310 . The vibrator  200  is preferably any known mechanical vibrator, but electro-mechanical vibrators, such as a piezoelectric device or a magnetostrictive device, are equally acceptable. The vibrator  200  in the preferred embodiment operates at a frequency of 50 Hz, but other frequencies are possible. 
     The valve assembly  10  is secured between the two clamps  300 ,  310 . These clamps  300 ,  310  are mounted to the frame  101  in a known manner to permit movement relative to each other and to the frame  101 . As shown in FIG. 1, the first clamp  300  has one portion that contacts one end  26  of the needle  20  and another portion that contacts the rod  122 . The second clamp  310  has a portion that engages the annular element  40 . 
     The needle  20 , the seat  30  and annular element  40  become work pieces once the clamps  300 ,  340  secure them. Coaxial alignment of the needle  20  relative to the seat  30  and the valve body  10  is maintained by the cooperation between the inner surface  14  of the housing  12 , the outer surface  62  of the armature  60 , the needle  20  and the valve guide  50 . Therefore, no external guides are needed to maintain proper alignment of the needle  20 , the seat  30  and annular element  40  during the coining operation. 
     To coin the convex surface  24  and the frusto-conical surface  32 , the piston assembly  100  is actuated such that the rod  122  is displaced in a direction F to transmit an axially compressive coining force onto the convex surface  24  and the frusto-conical surface  32 . This force is applied for a predetermined amount of time and then released. Simultaneous to the application of the force F, the vibrator  200  is actuated. The vibrator  200  displaces the rod  120  in a reciprocating, vibrating manner as indicated by arrow V in FIG.  2 . The vibration of the rod  120  is transmitted to the needle  20  via the piston, the rod  122  and the first clamp  300 . This vibration has the effect of applying the coining force to the surfaces  24 ,  32  multiple times. The conformance of the convex surface  24  and the frusto-conical surface  32 , one to the other, increases with each such application of the force. The guidance of the needle  20  and the manner in which the coining force is applied avoids irreversible bending or buckling of the needle  20 . 
     The process that has just been conducted on the fluid valve assembly  10  coins the annular zone of sealing contact between the convex surface  24  of the seated needle  20  and the frusto-conical surface  32 . By way of example, the needle  20  and the seat  30  should have approximately the same hardness, Rockwell C 56-60, and that of clamps  300 ,  310  should be at least that hard, Rockwell C 58-60 for example. The force that is applied should not irreversibly bend or buckle the needle  20 . For a needle  20  having a length of 28-30 mm, a diameter of 2 mm and a radius of 1.18-1.32 mm for the downstream end  22 , a maximum force of about 490 pounds has been successfully used. 
     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 embodiment disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined in the appended claims.