Abstract:
A fuel injection valve designed for low pressure fuel injection system of internal combustion engines includes a valve needle and a movable valve seat and installs directly on a cylinder head. When the pressure of the cylinder increases, the valve seat can press the valve needle in opposite directions thereby preventing high-pressure gas to flow reversely into fuel system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is related to a fuel injection valve and in particular to one with a movable valve seat. 
     2. Description of the Prior Art 
     In conventional four-stroke internal combustion engines, the electromagnetic fuel injection valve is mounted in the intake manifold and the pressure at the outlet of the injection valve is lower or equal to the atmospheric pressure, so that a low pressure fuel injection system (about 2-3 kg/cm 2 ) will suffice for efficient working. 
     However, for two-stroke internal combustion engines, it is proposed to inject fuel or fuel-air mixture after the exhaust port is closed, in order to reduce the amount of fuel leaking into the exhaust pipe at the time of scavenging. Hence, it is necessary to mount the injection fuel valve on the cylinder. Although a high pressure injection system is workable in this case, it will increase the cost. If a low pressure injection system is used, it is necessary to use a mushroom valve in order to prevent the gas from flowing reversely into the fuel system, as described in U.S. Pat. No. 4,986,247, Kushibe et al 1/1991, and U.S. Pat. No. Re. 34,945 Sayer et al 5/1995. Although the air auxiliary fuel injection valve can promote the atomization of fuel, it is still impossible to obtain the optimum fuel distribution. 
     Therefore, it is an object of the present invention to provide an improved fuel injection valve which can obviate and mitigate the above-mentioned drawbacks. 
     SUMMARY OF THE INVENTION 
     This invention is related to an improved fuel injection valve and in particular to one with a movable valve seat. 
     It is the primary object of the present invention to provide an improved fuel injection valve which is low in cost in comparison with those adapted for use in high pressure fuel injection system. 
     It is another object of the present invention to provide an improved fuel injection valve which is mounted on the cylinder head for directly ejecting fuel or mixture into the cylinder. 
     It is still another object of the present invention to provide an improved fuel injection valve including a needle valve and a movable valve seat which will push the needle valve in an opposite direction to prevent high pressure gas from flowing reversely into the fuel system. 
     It is still another object of the present invention to provide an improved fuel injection valve which may be adapted to a single-hole or multi-hole ejecting orifice to mix air with fuel in correct proportions and obtain good dispersity. 
     It is still another object of the present invention to provide an improved fuel injection valve which is fit for use with liquid or gas fuel and the injection of which can be accurately controlled. 
     It is a further object of the present invention to provide an improved fuel injection valve which is externally connected to other fuel valve or air valve so as to mix fuel or fuel-air mixture into the cylinder. 
     Other objects of the invention will in part be obvious and in part hereinafter pointed out. 
     The invention accordingly consists of features of constructions and method, combination of elements, arrangement of parts and steps of the method which will be exemplified in the constructions and method hereinafter disclosed, the scope of the application of which will be indicated in the claims following. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an electromagnetic fuel injection valve according to the present invention; and 
     FIG. 2 is a sectional view of an automatically open-close fuel injection valve according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention can be applied to an electromagnetic fuel injection valve or an automatically open-close fuel injection valve as required. 
     With reference to FIG. 1, the electromagnetic fuel injection valve according to the present invention generally comprises a packing  1  made of elastomer, a sleeve  20  made of insulating material, a solenoid  2 , a spring  3 , a valve body  4 , a stator  5 , an armature  6 , a O-ring  7 , a valve seat  8 , and a valve needle  9 . 
     The valve body  4  is formed with a first cylindrical recess  41  at an end and a second cylindrical recess  42  at another end and coaxial with the first cylindrical recess  41 . The solenoid  2  is fitted on the sleeve  20  which is in turn arranged within the first cylindrical recess  42  of the valve body  4 . The valve seat  8  is a tubular member fitted in the valve body  4  and having a first portion  81  arranged in the first cylindrical recess  41  of the valve body  4  and a second portion  82  extending out of the second cylindrical recess  42  of the valve body  4 . The first portion  81  of the valve seat  8  is made of non-magnetic metallic tubular member. The outer end the second portion  82  of the valve seat  8  is formed with outlets  10 . The armature  6  is fitted within the valve seat  8  and formed with an axial hole (shown but not numbered). The stator  5  is arranged in the valve seat  8  and provided with a spring  3  at an end urging against the armature  6 . The valve needle  9  is made of hardened steeland has two sets of four circumferential ridges to be concentric with the valve seat  8  and enabling passage of fuel. The structure of the valve needle  9  is well known in the art and considered a part of the invention. The valve needle  9  is inserted into the second portion  82  of the valve seat  8  and has an end threadedly engaged with the axial hole of the armature  6 . The O-ring  7  is fitted between the valve body  4  and the valve seat  8 . 
     As electric current passes through the solenoid  2 , magnetic lines of force will be generated to go through the valve body  4 , the stator  5 , the armature  6  and the valve seat  8  thereby forming a magnetic field which will attract the armature  6  to contact the stator  5  and therefore opening the valve needle  9  to enable fuel to flow out of the outlets  10 . The valve needle  9  will be opened after supplying electricity for a time period of {fraction (2/1000)} sec. If the fuel pressure is constant, the amount of fuel injected out of the injection valve is proportional to the time. 
     When no more electric current flows through the solenoid  2 , the spring  3  and the fuel pressure will push the valve needle  9  back to engage closedly with the valve seat  8  thereby stopping injection. 
     The above injection must be accomplished in a very short time, because if the pressure in the cylinder is higher than the fuel pressure, the injection will be stopped and the valve seat  8  will be pushed to move against the valve needle  9  thereby pushing the armature  6  to contact the stator  5 . The higher the pressure in the cylinder is, the larger the engaging force is between the valve needle  9  and the valve seat  8 , so that the high pressure gas will not flow reversely into the fuel system. If the pressure in the cylinder is lower than the fuel pressure, the valve seat  8  will be pushed by the fuel pressure and the elastomer  1  to its original position. 
     Referring to FIG. 2, the automatically open-close fuel injection valve according to the present invention comprises a rear cover  11 , an elastomer  12 , a spring  13 , a valve body  15 , a valve needle  16 , and a valve seat  18 . The valve body  15  is formed with an axial through hole and a branch passage in communication with the axial through hole. The valve seat  18  is fitted in the valve body  15  and has outlets at the outer end. A portion of the valve seat  19  extends out of the valve body  15  and keeps in air-tight manner therewith. The valve needle  16  has a set of four circumferential ridges to be concentric with the valve seat  18  and enabling passage of fuel. The structure of the valve needle  16  is well known in the art and not considered a part of the invention. The valve needle  16  is arranged within the valve seat  18  and has a recess at an end in which is mounted the spring  13 . The cover  11  is engaged with the rear end of the valve body  15 . The elastomer  12  is fitted between the valve seat  18  and the cover  11 . 
     When fuel or air-fuel mixture enters into a valve chamber  17  of the valve seat  18  through the branch passage  14 , the fuel pressure will push the valve needle  16  to move away from the outlets of the valve seat  18  thereby enabling fuel to be injected into the cylinder. 
     When the fuel pressure is lowered to a predetermined value, the spring  13  will push the valve needle  16  to close the outlets of the valve seat  18 . 
     When the pressure in the cylinder increases, the valve seat  18  will be forced to push the valve needle  16  to contact the rear cover  11 . The higher the pressure is in the cylinder, the higher the engaging force is between the valve seat  18  and the valve needle  16  thus preventing the high pressure gas from flowing reversely into the fuel system. When the pressure in the cylinder decreases, the elastomer  12  will push the valve seat  18  back to its original position. 
     It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. 
     While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.