Patent Application
20060249604
The present invention relates to fuel injectors for internal combustion engines; more particularly, to fuel injectors for direct injection of fuel into the cylinders of such engines; and most particularly, to an improved seat and director plate assembly for a fuel injector wherein a fuel volume of fuel accumulated past the seat is reduced.
Fuel injected internal combustion engines are well known. In direct-injected engines, the injection tip of the fuel injector extends into the combustion chamber and includes a perforated plate, known in the art as a “director plate,” for dispersing and directing fuel injected from the injection valve. In a conventional engine fuel injection system, the injection tip of the injector extends into a plenum or rail of the engine's intake manifold where the injected fuel is mixed with intake air before being discharged into the engine's combustion chamber.
As is well known in a direct injected engine, the configuration and positioning of a director plate with respect to the injection valve and the top of an engine piston are critical elements in the most fuel-efficient distribution of fuel into the firing chamber. A typical fuel injection valve includes a beveled circular seat and a reciprocably-actuated ball that seals against the seat in a circular sealing line.
A known problem in prior art fuel injectors is that the volume of fuel remaining between the valve ball and the director plate can be oxidized and polymerized by residual heat when an engine is shut down, leading to unwanted deposits on the valve and director plate. Further, any residual fuel outside the valve after each injection event must be displaced by the next succeeding injection event. A relatively large fuel residue can adversely affect the injection spray pattern and atomization intended by the director plate. Therefore, in prior art fuel injectors the valve seat typically is relatively thin below the sealing line to permit the director plate, which is co-planar with the axial end of the seat in this region of the plate, to approach the ball, thus minimizing the residual volume of fuel. However, experience has shown that a thin valve seat is vulnerable to mechanical deformation from the seat being inserted into the injector and to thermal deformation from welding of the seat in place during manufacture thereof, thus spoiling the uniformity of a circular sealing line and permitting additional fuel to leak past the valve ball during shutdown.
What is needed in the art is a fuel injector having a thicker seat that will not deform during welding, but at no increase in residual fuel volume.
It is a principal object of the present invention to reduce fuel leakage past a fuel injection valve during shutdown, without increasing the volume of residual fuel between the injection valve and the director plate.
Briefly described, an improved fuel injection valve and director plate assembly in accordance with the invention includes an annular beveled valve seat, a valve ball for forming a circular sealing line against the seat, and a perforated director plate. With reference to the thickness of a prior art seat at the radius of the sealing line, the improved seat is substantially thickened in an axial direction to provide greater mass of seat material and hence reduced vulnerability of the seat to thermal distortion from welding. Thus, a circular sealing line is assured after welding of the seat into the fuel injector assembly. To obviate an increase in residual fuel volume that would result from displacing the director plate from the valve by the added thickness of the seat, the central portion of an improved director plate is made concave from the outer portion such that the actual fuel-directing portion of the director plate is spaced from the valve ball as in the prior art relationship, thus preserving the desirably small prior art volume of residual fuel after valve closing.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
When valve ball 14 is sealed against face 20, a space 32 is formed among the seat, the ball, and the director plate. The volume of this space is known in the art as the SAC volume of a fuel injector. As noted above, it is desirable to minimize the SAC volume 32. In the prior art, this is achieved by minimizing the axial thickness of seat 12 to nearly the point at which director plate 16 interferes with ball 14. As noted above, a relatively thin seat as shown in
Referring to
Novel assembly 110 differs from prior art assembly 10 in the following ways.
Valve seat 112 is thicker than seat 12 by an amount 150 which preferably is at least about twice the thickness 25 of prior art seat 12 or more between sealing line 22 and axial face 26. Thickening the valve seat in this fashion increases the mass of the valve seat and thereby prevents the valve seat from being thermally deformed by welding during assembly of improved fuel injector 118. Further, thickening of the valve seat creates a second beveled face 121 defining a conical exit opening significantly longer along the cone surface than prior art face 21. Improved seat 112 terminates at an axial face 126.
An immediately-obvious disadvantage of improved seat 112 is that the greater thickness 150 and longer length of face 121 creates a potentially much larger SAC volume for fuel injector 118. To obviate this effect and provide a SAC volume 132 equal to SAC volume 32, the preferably-planar central portion 119 of improved director plate 116 is axially displaced from the preferably-planar peripheral portion 117 by a distance equal to increased thickness 150. Preferably, a transition portion 152 is formed at an angle 154 from surface 126 which is equal to the cone angle of face 121. Thus, the central portion 119 is spaced from ball 114 identically with the spacing of portion 19 from ball 14, and therefore SAC volume 132 may be made the same as SAC volume 32. Of course, the SAC volume of improved fuel injector 118 may be varied as may be desired by varying the distance that central portion 119 is displaced from peripheral portion 117.
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 full scope defined by the language of the following claims.
