Patent Publication Number: US-6981663-B2

Title: Fuel injection valve

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fuel injection valve mainly used in an engine for a vehicle. 
   2. Description of the Related Art 
     FIG. 6  is a vertical section showing the whole construction of a conventional fuel injection valve disclosed in, for example, the Japanese Patent Publication (unexamined) No. 2002-3831. 
     FIG. 7  is a partial enlarged view for explaining the construction of an essential part (a magnetic path portion) of the fuel injection valve shown in  FIG. 6 . Hatching that indicates a section is omitted in  FIG. 7 . 
   When a microcomputer of the engine sends an operation signal to a drive circuit (not shown in the drawings) of the fuel injection valve, an electric current flows through a coil  13 , whereby magnetic fluxes indicated by lines of magnetic force  100  are generated in a magnetic loop formed of a stationary iron core  11 , a moving iron core  22 , a yoke  16 , and a housing  12 . Consequently, the moving iron core  22  is attracted toward the stationary iron core  11  by electromagnetic attraction stronger than spring force of a compression spring  14 . 
   As the moving iron core  22  is attracted toward the stationary iron core  11 , a valve element  21  integrated with the moving iron core also moves toward the stationary iron core  11 , thus fuel injection into the engine being carried out. 
   In  FIG. 6  or  FIG. 7 , reference numeral  17  designates a sleeve made of non-magnetic metal acting as a connecting member for connecting the yoke  16  and the stationary iron core  11 . 
   This sleeve  17  is composed of a cylindrical part in which the stationary iron core  11  is fitted, and a ring part being a ring-shaped protrusion formed on the outer circumference of an end of the yoke  16  side of this cylindrical part.  FIG. 7  clearly shows that the sleeve  17  is L-shaped in cross-section. 
   The ring part of the sleeve  17  is welded to the yoke  16  with the ring part being in contact with the yoke  16 , and the cylindrical part of the sleeve  17  is welded to the stationary iron core  11  fitted in the cylindrical part. 
   Therefore, the stationary iron core  11  and the yoke  16  are fixed through the sleeve  17  in their positional relation. 
   Numeral  17   a  indicates a portion where the ring part of the sleeve  17  and the yoke  16  are welded together, and numeral  17   b  indicates a portion where the cylindrical part of the sleeve  17  and the stationary iron core  11  are welded together. 
   As described above, in the conventional fuel injection valve, the sleeve  17  made of non-magnetic metal is disposed between the yoke  16  and the stationary iron core  11  in order to reduce magnetic leakage between the stationary iron core  11  and the yoke  16  to a minimum. The yoke  16  and the sleeve  17  as well as the stationary iron core  11  and the sleeve  17  are joined together by welding in order to seal fuel in. 
   In particular, it is necessary that the valve element of the fuel injection valve for in-cylinder injection (i.e., fuel injection valve for a vehicle) responds at a high speed, and therefore it is required to minimize eddy current generated in the sleeve  17 . 
   In such a fuel injection valve, a thickness t of the sleeve  17  is reduced to the minimum to minimize generation of eddy current. 
   In the conventional fuel injection valve of above construction, in the case where the sleeve  17  is thin, the welded portion  17   a  where the sleeve  17  and the yoke  16  are welded together is located near a magnetic path (i.e., path of the magnetic line of force  100 ) of the yoke  16 . Therefore the portion where temperature rises due to welding spreads partly to the magnetic path of the yoke, and this portion (i.e., inside of a semi-circle indicated by the broken lines in  FIG. 7 ) becomes a portion  16   a  of which magnetic characteristic is changed (hereinafter referred to as “magnetic characteristic change portion”) and in which magnetic flux density is decreased. 
   Electromagnetic stainless steel mainly used as a material for the yoke  16  in fuel injection valve tends to exhibit a sharp decrease in magnetic flux density when the temperature comes up to be not lower than 900° C. (for example, the magnetic flux density being 1.10 T at 900° C. comes to decrease to 1.02 T at 950° C.) as shown in  FIG. 8 , whereby the electromagnetic attraction generated in the moving iron core  22  also decreases. 
   In the case where the fuel injection valves are mass-produced, the magnetic characteristic in the magnetic characteristic changed portion varies depending on variation in welding temperature and welding position, which eventually results in variation in electromagnetic attraction generated in the moving iron core also varies. 
   Hence a problem exists in that injection quantity characteristics of the produced fuel injection valves vary largely between one product and another. 
     FIG. 9  is a graphic diagram showing variation in injection quantity characteristic of the conventional fuel injection valves. In the drawing, the axis of abscissas indicates a drive pulse width (msec) of an injection signal impressed on the fuel injection valve, and the axis of ordinates indicates a fuel injection quantity (mm 3 ) per injection. 
   As shown in  FIG. 9 , the variation in injection quantity characteristics of the conventional fuel injection valves ranges approximately 10% between the uppermost and lowermost injection quantities. 
   SUMMARY OF THE INVENTION 
   The present invention was made to solve the above-discussed problem and has an object of providing a fuel injection valve for a vehicle capable of suppressing variation in injection quantity characteristic by individual products due to magnetic characteristic changed portion produced by heat generated at the time of welding the sleeve and the yoke together. 
   A fuel injection valve according to the invention includes: a valve section consisting of a cylindrical moving iron core that reciprocates in axial direction in response to fuel injection signal, a valve element integrated with the mentioned moving iron core at one end and provided with a valve seat at the other end, and a plate provided with orifices that are opened and closed as the mentioned valve seat comes in contact with the orifices and parts therefrom; and a solenoid section consisting of a cylindrical stationary iron core disposed facing the mentioned moving iron core in axial direction, a cylindrical yoke disposed on the outer circumference of the mentioned moving iron core, a non-magnetic metal sleeve where the mentioned stationary iron core and the mentioned yoke are joined into one body by welding, a housing forming a magnetic loop with the mentioned stationary iron core, moving iron core and yoke, a coil that is disposed on the outer circumference of the mentioned stationary iron core and gives axial electromagnetic attraction to the mentioned moving iron core, and a compression spring to urge spring force that moves the mentioned valve element toward the mentioned plate. 
   Furthermore, the mentioned moving iron core of the fuel injection valve according to the invention is provided with a radial recess of a predetermined width and a predetermined depth on the outer circumference thereof at a position facing a magnetic characteristic change portion produced in the mentioned yoke due to heat generated when the mentioned sleeve and the mentioned yoke are welded together. 
   In the mentioned fuel injection valve according to the invention, since the moving iron core is provided with a radial recess having a predetermined width and a predetermined depth on the outer circumference thereof at the position facing the magnetic characteristic change portion produced in the mentioned yoke due to heat generated at the time of welding the mentioned sleeve and yoke together, magnetic fluxes passing through the moving iron core detour and flow through underside of the recess (i.e., on the side where the stationary iron core is not disposed). 
   This makes it possible to reduce number of magnetic fluxes passing through the magnetic characteristic change portion of the yoke and prevent the influence of the variation in magnetic characteristic, and it is possible to suppress the variation in injection quantity characteristic of the products caused by the magnetic characteristic change portion due to the heat generated at the time of welding the sleeve and the yoke together. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view showing a construction of a whole fuel injection valve according to Embodiment 1 of the invention. 
       FIG. 2  is a partially enlarged view for explaining a construction of an essential part of the fuel injection valve according to Embodiment 1. 
       FIG. 3  is a graphic diagram showing injection quantity characteristics of the fuel injection valve according to Embodiment 1. 
       FIG. 4  is a partial enlarged view for explaining a construction of an essential part of a fuel injection valve according to Embodiment 2. 
       FIG. 5  is a graphic diagram for explaining advantages of the fuel injection valve according to Embodiment 2. 
       FIG. 6  is a longitudinal sectional view showing a construction of a whole fuel injection valve according to the prior art. 
       FIG. 7  is a partial enlarged view for explaining a construction of an essential part of the fuel injection valve according to the prior art. 
       FIG. 8  is a graphic diagram showing the relation between magnetic flux density and temperature of electromagnetic stainless steel used in a yoke. 
       FIG. 9  is a graphic diagram showing variation in injection quantity characteristic of the fuel injection valve according to the prior art. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiment 1 
     FIG. 1  is a vertical section showing construction of a whole fuel injection valve according to Embodiment 1, and  FIG. 2  is a partial enlarged view for explaining a construction of an essential part (magnetic path portion) of the fuel injection valve according to Embodiment 1 shown in  FIG. 1 . Hatching that indicates a section is omitted in  FIG. 2 . 
   A fuel injection valve  1  according to this embodiment is comprised of a solenoid section  10  and a valve section  20  as shown in  FIG. 1 . 
   The solenoid apparatus  10  is comprised of a coil  13 , a stationary iron core  11 , a yoke  16 , a housing  12 , a sleeve  17  made of non-magnetic metal acting as a connecting member for connecting the stationary iron core  11  and the yoke  16 , a compression spring  14  to give spring force that urges a valve element integrated with a moving iron core described later, a rod  15  for positioning and fixing the compression spring  14 , and so on. 
   The valve apparatus  20  is comprised of a valve element  21 , a valve main body  24  in which the valve element  21  is fixedly accommodated, a moving iron core  22  integrated with one end of the valve element  21 , a valve seat  21   a  disposed at an end of the valve main body  24 , a plate  23  having plural orifices, and so on. 
   Numeral  30  is a fuel supply pipe for supplying high-pressure (for example, not lower than 2 Mpa) fuel to the fuel injection valve  1 , and numeral  31  is a fuel flow opening of the fuel supply pipe  30 . 
   Because the engine for vehicle has plural cylinders, plural fuel injection valves are arranged in a direction crossing the drawing (i.e., direction perpendicular to the drawing) respectively conforming to the cylinders, and the longitudinal direction of the fuel supply pipe  30  is arranged in a direction crossing the drawing (i.e., direction perpendicular to the drawing). Numeral  33  is a mesh portion of a filter, and numeral  34  is a filter holding member. 
   The fuel injection valve  1  is disposed between the fuel supply pipe  30  and a cylinder head  40  of the engine through seal members  51  and  52 , and mounted on a washer  53  by axial and downward load. 
   When a microcomputer of the engine sends an operation signal to a drive circuit (not shown) of the fuel injection valve  1 , an electric current flows through the coil  13 , and magnetic fluxes are generated in a magnetic loop comprised of the stationary iron core  11 , moving iron core  22 , yoke  16  and housing  12 . As a result, the moving iron core  22  is attracted to the stationary iron core  11  by electromagnetic attraction stronger than the spring force of the compression spring  14 . 
   As the moving iron core  22  is attracted to the stationary iron core  11 , a valve seat  21   a  being an end of the valve element  21  integrated with the moving iron core  22  parts from a valve seat face of the valve main body  24 . When a space is formed between the valve seat  21   a  and the valve seat face of the valve main body  24 , high-pressure fuel is injected into the cylinders of the engine through the orifices of the plate  23 . 
   When the microcomputer stops sending the operation signal from the drive circuit (not shown) of the fuel injection valve  1 , there is no electric current flowing through the coil  13 , and the attraction that has attracted the moving iron core  22  to the stationary iron core  11  vanishes. 
   As a result, the valve element  21  is urged to move toward the plate  23  by the spring force of the compression spring  14 , and the valve seat  21   a  is pushed against the valve seat face of the valve main body  24 , and thus the injection of fuel is lost. 
   Referring now to  FIG. 2 , numeral  61  is a thrust (axial) air gap. In this portion (i.e., in the thrust air gap  61 ), electromagnetic attraction works between the stationary iron core  11  and the moving iron core  22 , and the stationary iron core  11  attracts the moving iron core  22 . 
   Since the moving iron core  22  moves a certain distance in axial direction, it is required that the thrust air gap  61  is longer than a traveling distance of the moving iron core  22 . 
   Numeral  62  is a radial air gap, and this air gap is secured between the moving iron core  22  and the yoke  16  in order to prevent the moving iron core  22  from touching the yoke  16  at the time of traveling the moving iron core  22  in the axial direction. 
   As described in the background of the invention, the sleeve  17  made of non-magnetic metal is comprised of a cylindrical part into which the stationary iron core  11  is fitted and a ring part constituting a ring-shaped protrusion formed on the outer circumference of an end on the yoke  16  side of the cylindrical part. As a result, the sleeve  17  is L-shaped in cross-sectional on a plane spreading through the axis A. 
   The ring part of the sleeve  17  is joined to the yoke  16  by laser welding with the ring part being in contact with an end face of the stationary iron core  11  side of the yoke  16 , and the cylindrical part of the sleeve  17  is joined to the stationary iron core  11  fitted therein by laser welding. 
   Accordingly, the positional relation between the stationary iron core  11  and the yoke  16  is fixed through the sleeve  17 . 
   In addition, numeral  17   a  indicates a portion where the ring part of the sleeve  17  and the yoke  16  are welded together, and numeral  17   b  indicates a portion where the cylindrical part of the sleeve  17  and the stationary iron core  11  are welded together. Laser welding joins these welded portions so that fuel may be sealed in. 
   Austenitic stainless steel being a low-permeability non-magnetic material is used as the sleeve  17  in order to prevent rust and minimize magnetic leakage between the stationary iron core  11  and the yoke  16  to a minimum. 
   The thickness t of the sleeve  17  is reduced to the minimum because it is necessary to reduce eddy current generated in the sleeve  17  as small as possible in order to provide rapid response of the magnetic fluxes generated in the magnetic loop comprised of the stationary iron core  11 , moving iron core  22 , yoke  16 , and housing  12 . 
   Melting temperature at the welded portion  17   a  where the sleeve  17  and the yoke  16  are welded together is higher than 1540° C., which is the melting point of iron, and temperature of the portion near the welded portion  17   a  of the yoke  16  (the portion surrounded by a broken-lined semi-circle in  FIG. 2 ) also rises to approximately 1000° C. through heat conduction of metal. 
   It is this portion that acts as the magnetic characteristic change portion  16   a  where magnetic flux density becomes low and of which magnetic characteristics vary between one product and another. 
   In this embodiment, number of the magnetic fluxes passing through the magnetic characteristic change portion  16   a  (i.e., number of the magnetic lines of force  100 ) is reduced, whereby variation in magnetic characteristic in the magnetic characteristic change portion  16   a  of the yoke  16  gives less influence on the variation in number of the whole magnetic fluxes. Consequently, it is arranged such that the variation in electromagnetic attraction generated in the moving iron core  22  is suppressed. 
   For that purpose, a portion having strong magnetic resistance is formed by providing a recess (groove)  22   a  having a predetermined width and a predetermined depth on the outer circumference of the moving iron core  22  at a position facing the magnetic characteristic change portion  16   a.    
   As a result, the magnetic fluxes passing thorough the moving iron core  22  detour and flow through underside of the recess  22   a  (i.e., on the side where the stationary iron core  11  does not exist), and this makes it possible to reduce number of the magnetic fluxes passing through the magnetic characteristic change portion  16   a  of the yoke  16  and avoid the influence of the variation in magnetic characteristic in this portion. 
   In addition, it is desirable that width of the recess (groove)  22   a  is larger than axial length of the magnetic characteristic change portion  16   a.    
   It is further necessary to arrange the radial depth of the recession (groove)  22   a  so that decrease in electromagnetic force due to the reduction in number of the magnetic fluxes caused by the provision of the recess (groove)  22   a  on the outer circumference of the moving iron core  22  does not brings about any trouble when the fuel injection valve is put into practical use. 
     FIG. 3  is a graphic diagram showing injection quantity characteristics of the fuel injection valve according to this embodiment. In this diagram, the axis of abscissas indicates a drive pulse width (msec) of an injection signal impressed on the fuel injection valve, and the axis of ordinates indicates a fuel injection quantity (mm 3 ) per injection. 
   As compared with  FIG. 9 , while the variation in injection quantity characteristics of the conventional fuel injection valves ranges approximately 10% between the uppermost and lowermost injection quantities, the variation range is improved to the extent of only 6% in the fuel injection valve according to this embodiment. 
   According to Embodiment 1, the variation in injection quantity characteristic varying with each individual product of the mass-produced fuel injection valves is reduced, which makes it possible to produce fuel injection valves of stabilized and uniform quality. 
   As described above, the fuel injection valve according to the invention includes: a valve section  20  consisting of a cylindrical moving iron core  22  that reciprocates in axial direction in response to fuel injection signal, a valve element  21  integrated with the mentioned moving iron core  22  at one end and provided with a valve seat  21   a  at the other end, and a plate  23  having orifices that are opened and closed as the mentioned valve seat  21   a  comes in contact with the orifices and parts therefrom; and a solenoid section  10  consisting of a cylindrical stationary iron core  11  disposed facing the mentioned moving iron core  22  in axial direction, a cylindrical yoke  16  disposed on the outer circumference of the mentioned moving iron core  22 , a non-magnetic metal sleeve  17  where the mentioned stationary iron core  11  and the mentioned yoke  16  are joined into one body by welding, a housing  12  forming a magnetic loop with the mentioned stationary iron core  11 , moving iron core  22  and yoke  16 , a coil  13  that is disposed on the outer circumference of the mentioned stationary iron core  11  and gives axial electromagnetic attraction to the mentioned moving iron core  22 , and a compression spring  14  to urge spring force that moves the mentioned valve element  21  toward the mentioned plate  23 . 
   In the mentioned fuel injection valve according to the invention, the mentioned moving iron core  22  is provided with a radial recess  22   a  of a predetermined width and a predetermined depth on the outer circumference thereof at a position facing a magnetic characteristic change portion  16   a  produced in the mentioned yoke  16  due to heat generated when the mentioned sleeve  17  and the mentioned yoke  16  are welded together. 
   As a result, the magnetic fluxes passing through the moving iron core  22  detour and flow through underside of the recess provided on the outer circumference of the moving iron core  22  (i.e., on the side where the stationary iron core is not disposed). This makes it possible to reduce number of magnetic fluxes passing through the magnetic characteristic change portion of the yoke  16  and prevent the influence of the variation in magnetic characteristic, and it is possible to suppress the variation in injection quantity characteristic of the products caused by the magnetic characteristic change portion  16   a  due to the heat generated at the time of welding the sleeve  17  and the yoke  16  together. 
   Embodiment 2 
     FIG. 4  is a partially enlarged view for explaining a construction of an essential part (magnetic path portion) of a fuel injection valve according to Embodiment 2. Hatching that indicates a section is omitted in  FIG. 4 . 
   In the fuel injection valve according to the foregoing Embodiment 1, since the moving iron core  22  is provided with a recess  22   a  having a predetermined width and a predetermined depth on the outer circumference thereof and radial thickness of the moving iron core  22  is reduced, there is a disadvantage that magnetic fluxes are blocked and electromagnetic force decreases in this portion. 
   This disadvantage is overcome in the fuel injection valve according to Embodiment 2 by employing a magnetic material as the valve element  21  so that the magnetic lines of force  100  also pass through the upper part of the valve element  21 . 
   Thus, the upper part of the valve element  21  and the moving iron core  22  act as parallel magnetic paths, which makes it possible to prevent decrease in number of magnetic fluxes due to provision of the recess  22   a  on the outer circumference of the moving iron core  22 . 
   In addition, the valve seat  21   a  at the lower part of the valve main body  24  comes in contact with the plate  23  provided with the orifices, and therefore martensitic stainless steel being an abrasion resistant magnetic material is employed as the valve seat  21   a.    
     FIG. 5  is a graphic diagram for explaining the advantages of the fuel injection valve according to Embodiment 2. 
   In the fuel injection valve according to the foregoing Embodiment 1, variation in injection quantity characteristic of the mass-produced fuel injection valves is reduced by providing a recess  22   a  on the outer circumference of the moving iron core  22  and preventing the magnetic fluxes from passing through the magnetic characteristic change portion  16   a  of the yoke  16 . 
   However, as shown in  FIG. 5 , electromagnetic force of the solenoid section  10  is lower than that in the conventional valve by approximately 20% due to reduction in number of magnetic fluxes passing through the magnetic path. 
   On the other hand, in the fuel injection valve according to Embodiment 2, the valve element  21  is made of a magnetic material, whereby upper part of the valve element  21  and the moving iron core  22  act as parallel magnetic paths. Therefore, the decrease in number of magnetic fluxes is prevented. As a result, as shown in  FIG. 5 , the solenoid section  10  exhibits restoration in electromagnetic force by approximately 16% as compared with that of the foregoing Embodiment 1. 
   As described above, in the fuel injection valve according to Embodiment 2, the variation in injection quantity characteristic of the mass-produced fuel injection valves is reduced by providing the recess  22   a  on the outer circumference of the moving iron core  22 , thereby preventing the magnetic fluxes from passing through the magnetic characteristic change portion  16   a  of the yoke  16 . Furthermore, employing a magnetic material as the valve element  21  and utilizing the upper part of the valve element  21  and the moving iron core  22  as parallel magnetic paths prevent the decrease in number of magnetic fluxes. This results in quite a small decrease (approximately 4%) in electromagnetic force of the solenoid section  10 . 
   Consequently, in Embodiment 2, it is possible to achieve a fuel injection valve in which variation in injection quantity characteristic is small and decrease in electromagnetic force of the solenoid section is very small. 
   While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.