Abstract:
An improved disk-valve fuel injector comprising a self-centering, floating valve seat insert disposed in a valve body. The valve seat insert includes a circular first valve seat and the body includes a circular second valve seat concentric with the first valve seat. A spring urges the valve insert into compliance with a disk-shaped valve head. The valve insert is able to adjust position in all three dimensions, allowing the disk head to mate precisely with both seats, thereby minimizing leakage when the valve is closed, improving metering precision, and extending the working lifetime of the valve head and valve seats.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to fuel injectors for internal combustion engines; more particularly, to fuel injectors having disk-shaped valve closures; and most particularly, to a fuel injector having a disk valve with a floating, compliant valve seat for improved valve sealing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fuel injectors having either ball-valve or disk-valve closures, referred to herein generically as “valves”, are well known. In principle, a disk valve injector configuration is superior to a ball-valve configuration in terms of flow capacity and dynamic range, attributes that are very beneficial in terms of required magnetic force from the actuator and breadth of range of engine that can be effectively serviced with a single design. Taken together, these attributes of a disk-valve closure can provide increased design efficiency and effectiveness and, more importantly, reduce overall cost. 
         [0003]    An important negative attribute of disk valving, however, particularly when a gaseous medium such as natural gas or hydrogen is metered, is leakage propensity. As a disk-valve injector generally employs relatively low lifts, compared to an equivalent flow ball-valve injector, very high flow/seal areas are required to satisfy necessary engine flow capacity. The relatively large seal area creates high sensitivities to surface imperfections and goodness-of-fit and contamination, with the slightest mismatch between disk and seat resulting in intolerable leak rates. Consequently, disk-valve fuel injectors have not enjoyed widespread use in automotive engine applications, especially in the nascent domain of gaseous fuels. 
         [0004]    What is needed in the art is an improved disk-valve fuel injector wherein the propensity for leakage, especially with gaseous fuels, is reduced. 
         [0005]    It is a principal object of the present invention to provide an improved fuel injector suitable for use with both liquid and gaseous fuels in internal combustion engines. 
       SUMMARY OF THE INVENTION 
       [0006]    Briefly described, an improved disk-valve fuel injector in accordance with the present invention comprises a self-centering, floating valve seat insert disposed in a valve body. The valve seat insert includes a circular first valve seat, and the body preferably includes a circular second valve seat concentric with the first valve seat. A spring urges the valve seat insert into compliance with a disk-shaped valve head. The valve seat insert is able to adjust position in all three dimensions, allowing the disk head to mate precisely and reliably with both seats, thereby minimizing leakage when the valve is closed, improving metering precision, and extending the working lifetime of the valve head and valve seats. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a cross-sectional elevational view of a portion of a prior art ball-valve fuel injector; 
           [0009]      FIG. 2  is a cross-sectional elevational view of a portion of a prior art disk-valve fuel injector; and 
           [0010]      FIG. 3  is an elevational cross-sectional view of an improved disk valve assembly in accordance with the present invention for use in an improved disk-valve fuel injector. 
       
    
    
       [0011]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]      FIGS. 1 and 2  are presented as representative of a portion of a prior art ball-valve fuel injector and a prior art disk-valve fuel injector, respectively, for comparison purposes. 
         [0013]    Referring to  FIG. 1 , prior art ball-valve fuel injector  10  comprises a valve body  12  having a seat insert  14  containing a tapered metering seat  16 . Valve body  12  is attached to an electric solenoid assembly  18  including electric windings  20  surrounding a spool  22  disposed in a stator  24 . An axial armature  26  is slidably disposed in a non-magnetic tube  28  passing through spool  22 . Armature  26  defines a pintle terminating in a ball valve head  30  that is matable with seat  16 . Energizing of windings  20  causes ball head  30  to be withdrawn from seat  16 , allowing passage of fuel  32  around ball head  30  and out of exit  34 . De-energizing of windings  20  causes ball head  30  to be re-seated on seat  16  by the force of return spring  36  disposed in a well in pintle  26  and by the pressure of fuel within injector  10 . 
         [0014]    Referring now to  FIG. 2 , prior art disk-valve fuel injector  110  comprises a valve body  112  having a valve seat insert  114  containing a first planar annular metering seat (“first seat”)  116 . Insert  114  is provided with longitudinal fluting  115  which is full-fitting on its outer diameter in bore  111  and yet permits flow of fuel past insert  114  when the valve is open. Valve body  112  contains a second planar annular metering seat (“second seat”)  116 ′ that ideally is coplanar with first seat  116 . A disk-shaped valve head  130  is freely disposed in a chamber  117  formed adjacent the first and second seats by ring insert  119  and has a planar surface  121  for mating with first and second seats  116 , 116 ′ during valve closure. An electric solenoid assembly  118  includes electric windings  120  surrounding a spool  122  disposed in a stator  124  defining a first magnetic pole piece. A second magnetic polepiece  126  is disposed in a non-magnetic tube  128  passing through spool  122 . Disk-shaped valve head  130  defines a free armature having axial travel within chamber  117  limited by seats  116 , 116 ′ in the valve closed position and the outer end  131  of polepiece  126  in the valve open position. Energizing of windings  120  causes head  130  to be withdrawn from seats  116 , 116 ′, allowing passage of fuel  32  both around and through head  130  and out of exit  134 . De-energizing of windings  120  causes head  130  to be re-seated on seats  116 , 116 ′ by the force of return spring  136  acting on disk head  130  and by the pressure of fuel within injector  110 . 
         [0015]    Generic ball-valve and disk-valve fuel injectors  10 , 110  are representative of the nearest prior art. The injectors are presented side by side to provide a visual assessment of the comparative difference in seal length or diameter. The ball injector seal diameter is defined by the length of mating surface of metering valve  10  and seat  12 . In the disk injector the corresponding area is defined effectively by the nominal value of the metering annulus  113 , which is sealed by the disk head  130 . Comparatively speaking, in the case of these two injectors, which target equal flow, the seal diameter of the disk-valve injector is nearly three times larger than that of the ball-valve injector. Typically, engine and vehicle manufacturers specify permissive leakage at &lt;0.5 cc/min, which is challenging even for small seal widths and ball-valve injectors; the larger the seal width/diameter, the more difficult to comply with this requirement. With such large seal width/diameter in a disk-valve injector, any imperfection in mating of either the disk surface  121  or the valve seats  116 , 116 ′ can easily be large enough to cause the injector to exceed this specification. 
         [0016]    Note that prior art valve seats  116 , 116 ′ are concentric circular surfaces which ideally are absolutely coplanar as reference surface  138  to permit sealing of disk surface  121  against both, simultaneously and completely. However, in manufacturing practice it is extremely difficult to machine the two surfaces to an acceptable level of coplanarity. 
         [0017]    The sensitivity of a disk-valve injector to leakage as a result of such non-coplanarity may be reduced by providing a three-dimensionally compliant interface between the disk head and one of the valve seats which facilitates conformal and preferential mating of the sealing surfaces. The present invention is directed to an arrangement that provides such a compliant interface. 
         [0018]    Referring now to  FIG. 3 , a lower valve seat assembly  200  is shown for use in an improved disk-valve fuel injector  210  in accordance with the present invention. Valve seat assembly  200  replaces prior art valve body  112  and prior art valve seat insert  114 , as shown in  FIG. 2 , to form such an improved fuel injector  210 . 
         [0019]    Assembly  200  comprises a valve body  212  having a stepped bore defined by a smaller-diameter bore  211   a  and a larger-diameter bore  211   b , separated by a tapered ball seat  250  which may be fluted  252  to permit flow of fuel. An improved valve seat insert  214 , comprising a ball-shaped portion  254  and a cylindrical portion  256 , floats in bores  211   a , 211   b  and is urged against ball seat  250  by a spring  258  disposed in bore is  211   b . Cylindrical portion  256  is fluted  260  and is cup-shaped at the free end, forming a circular first valve seat  216 . Valve body  212  is also relieved  262  along reference surface  238  to form a circular second valve seat  216 ′, the improved seats  216 , 216 ′ being analogous to prior art seats  116 , 116 ′. Reference surface  238  is machined to be highly planar, thus providing second seat  216 ′ as a reference stop for disk valve  130  upon closure of fuel injector  210 . 
         [0020]    The desired compliance of first seat  216 , to allow first seat  216  to be absolutely coplanar with second seat  216 ′, is provided in accordance with the present invention as follows: 
         [0021]    Floating valve seat insert  214  is suspended by compression spring  258 . Ball head  254  is retained by tapered ball seat  250  in such fashion that axial travel of insert  214  is restricted to a predetermined magnitude. Ideally, floating seat insert  214  is held against tapered ball seat  250  by compression spring  258  such that first seat  216  protrudes by about 10 μmeters beyond second seat  216 ′. 
         [0022]    Additionally, the diametral clearance of cylindrical portion  256  within bore  211   a  facilitates compliance, and preferably is limited to less than about 50 micrometers to preclude cocking or switching of the floating insert within the bore. This diametral clearance allows floating seat insert  214  to be rotated slightly about the center of ball  254  as may be needed to bring seat  216  into coplanarity with seat  216 ′. 
         [0023]    The force generated by spring  258  is preferably less than about 75% that of return spring  136  ( FIG. 1 ), so that disk valve head  130  is still forced against second seat  216 ′ as well as against floating first seat  216  when solenoid assembly  118  is de-energized. First seat  216  is depressed by the amount of the intentional protrusion within bores  211   a , 211   b  and rotated about the center of ball  254  as just described to be flush and coplanar with second seat  216 ′ by the force of closure spring  136 , thus providing a reliable seal of sealing surface  121  on both seats  216 , 216 ′. 
         [0024]    An important secondary benefit of this arrangement is that seat insert  214  oscillates within bores  211   a , 211   b  with every cycle of solenoid assembly  118  and disk head  130 . The consequent protrusion of seat insert  214  beyond second seat  216 ′, as described above, and the spring backing of seat insert  214  provides impact kinetic energy attenuation for disk head  130  as it nears second seat  216 ′ which is, as noted above, a fixed reference for the valve head. This feature reduces noise generated by actuation of the injector  210 , increases working lifetime of the disk head and valve seats, and thereby increases long-term precision of fuel injection amount. 
         [0025]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have the full scope defined by the language of the following claims.