Patent Publication Number: US-8991783-B2

Title: Fuel injection valve for internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injection valve for an internal combustion engine and, in particular, relates to a plating coat structure formed on opposed faces of a stationary core and a movable core having a movable valve element. 
     BACKGROUND ART 
     A fuel injection valve used for an internal combustion engine for an automobile (hereinafter will be called as “engine”) comprises an electromagnetic coil, a movable valve element, a stationary core, a movable core and a spring (return spring), wherein end faces of the movable core and the stationary core are opposed to each other with a predetermined gap when the electromagnetic coil is not energized, and the return spring applies the spring load to the movable core and the movable valve element in the direction of valve-closing. The movable core is magnetically attracted toward the stationary core side against the spring force when the electromagnetic coil is energized and the movable valve element moves toward the stationary core side with the magnetic attraction to thereby make valve-opening. 
     Fuel is fed into a body of the injection valve from a fuel tank via a fuel pump and a fuel-feeding pipe, and is filled under pressure in a fuel passage from the inside of the hollow-stationary core to a seat portion in a nozzle body when the valve is closed. When the electromagnetic coil is energized with a fuel injection pulse signal, the valve opens only during the pulse time and fuel is injected. When the energization of the electromagnetic coil is turned off, the movable core is returned in the valve-closing direction together with the movable valve element by the return spring force and the movable valve element is pressed to the seat to make a valve-closing state. 
     Enhancement of a valve-closing response is of a key factor for enhancing a control accuracy of a fuel quantity of the electromagnetic injection valve. At the time when the fuel injection valve closes just after energization to the electromagnetic coil is turned off, it is known that a fluid resistance force (force due to a squeeze effect) occurs between the opposed faces of the movable core and the stationary core and that the fluid resistance force is caused by a fluid existing between the both opposed faces thereof so as to make interference against motion where the movable core removes from the stationary core. Such fluid resistance force tends to increase as the gap between the opposed faces of the movable core and the stationary core (so called fluid gap) decreases. 
     Conventionally, a variety of measures has been proposed for reducing such force due to squeeze effect. 
     For example, patent document 1 (JP-A-2003-328891) discloses that a protuberance is provided on the opposed face of a movable core with respect to a stationary core, and only this protuberance collides against the stationary core at the time of magnetic attraction so that portions other than the protuberance (non colliding portion) keep fluid gap. 
     Further, in place of such protuberance, patent document 2 (JP-A-2006-22727) discloses that an uneven surface of high-lying portions and low-lying portions is provided at least one of opposed faces of a movable core (armature) and a stationary core (namely, the upstream side end face of the armature and the downstream side end face of the stationary coil) by forming alternatively hard plating portions and non-plating portions on the core end face in a circumference direction thereof so as to keep fluid gaps on the low-lying portions by the height of the high-lying portions. 
     Still further, patent document 3 (JP-A-2005-36696) discloses that an annular collision face (a collision face with respect to a stationary core) with a limited width is provided on an annular end face of a movable core, and the collision surface is formed at an inner side with respect to a middle portion in the width direction of the annular end face of the movable core. Further, the document proposes to form tapered surfaces toward the inner side as well as the outer side from the collision surfaces and to apply anti wear plating on the annular end face. The proposed technology is intended to reduce squeeze effect by enlarging the fluid gap between the opposed faces of the movable core and the stationary core other than the collision surfaces through formation of the tapered surfaces. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: JP-A-2003-328891 
         Patent Document 2: JP-A-2006-22727 
         Patent Document 3: JP-A-2005-36696 
       
    
     SUMMARY OF THE INVENTION 
     Tasks to be Solved by the Invention 
     As disclosed in patent documents 1 or 3, in order to reduce squeeze effect when the movable core is magnetically attracted toward the stationary core (in other words, in order to increase the fluid gap between the stationary core and the movable core), the protuberances or tapered portions are provided on the opposed face of the movable core with respect to the stationary core, when the collision portions are limited partially where the movable core collides against the stationary core at the time of magnetic attraction, the collision load is concentrated on the portions where the collision portions locate. For this reason, in order to enhance durability (anti wear property) of the collision portions of the movable core and the stationary core, it is necessary to make a hard plated film comparatively thick on the collision portions. On the other hand, although it is desirable to make the gap between the opposed faces of the movable core and the stationary core (magnetic attraction surfaces) as small as possible from a viewpoint of magnetic attraction, if the plated film is thickened as above, the magnetic gap that is the sum of the protuberance and the film thickness enlarges. 
     In place of these protuberances, according to the arrangement of providing an uneven surface on at least one of opposed faces of a movable core (armature) and a stationary core by forming alternatively hard plating portions and non-plating portions on the annular end face in the circumference direction thereof, as shown in patent document 2, when forming the plated portions, a complicated work of masking for the non-plating portions is required that complicates the plating work. 
     The present invention has been invented in view of the above circumstances and is to provide a fuel injection valve for an internal combustion engine capable of enhancing valve-closing responsivity while maintaining durability (anti wear property) of the collision portion and valve-opening responsivity in the fuel injection valve of a type in which basically a collision portion (such as annular protuberance) confined to a partial area is provided on at least one of annular opposed end faces of a stationary core and a movable core. 
     Measure for Solving the Tasks 
     Basically, a fuel injection valve for an internal combustion engine using a solenoid valve according to the present invention comprises a stationary core and a movable core like those as above and is provided with collision portions on annular end faces of these cores opposed to each other, wherein the collision portions receive collision caused when the movable core is magnetically attracted to the stationary core side, and a non-collision portion is located in an area of an outer side or an inner side from the collision portion to keep a fluid gap. Further, the present invention is characterized in that the annular end faces of the stationary core and the movable core is provided with a plating having anti wear property, and at least one of the platings on the stationary core and the movable core is formed to be thicker on the collision portion and thinner on the non-collision portion. 
     In place of the above configuration, the present invention further proposes a configuration in which the annular end faces of the stationary core and the movable core like those as above are respectively divided into two of an inner side and an outer side in a radial direction thereof, the inner side takes on an area provided with a plating having anti wear property and the outer side takes on an area provided with non-plating, and an protuberance serving as the collision portions between the cores are coated by plating respectively, and the non-collision portion is formed by the non-plating area. 
     Advantages of the Invention 
     According to such configurations, at first, the height of the collision portion (the protuberance or the tapered tip portion) formed on at least one of the annular end faces (opposed faces) of the movable core and the stationary core can be reduced, and corresponding thereto, the plating thickness of the collision portion can be ensured sufficiently. Thereby, the responsivity (valve-opening responsivity) to magnetic attraction of the fuel injection valve (solenoid coil) can be maintained while preventing enlargement of a magnetic gap between the opposed faces of the movable core and the stationary core. Further, it is possible to thin the plating thickness on the area other than the collision portion of the opposed annular end faces or to provide the non-plating thereon, so that an enlargement of the fluid gap and reduction of squeeze effect can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross sectional view showing an entire configuration representing one example of a fuel injection valve to which the present invention is applied. 
         FIG. 2  is a partially enlarged vertical cross sectional view showing around the annular end face portion of opposed stationary core and movable core in the vertical cross sectional view of  FIG. 1 . 
         FIG. 3  is a partially enlarged vertical cross sectional view showing the annular end face portion of the stationary core and the movable core of a fuel injection valve according to a first embodiment of the present invention. 
         FIG. 4  is a partially enlarged vertical cross sectional view showing the annular end face portion of the stationary core and the movable core of a fuel injection valve according to a second embodiment of the present invention. 
         FIG. 5  is a graph showing a relationship between magnetic gap Gm between a stationary core and a movable core and magnetic attraction force G F . 
         FIG. 6  is a graph showing a relationship between fluid gap Gf between a stationary core and a movable core and fluid resistance force S F . 
         FIG. 7  is an enlarged vertical cross sectional view of a prime part showing a third embodiment of the present invention. 
         FIG. 8  is an enlarged vertical cross sectional view of a prime part showing a fourth embodiment of the present invention. 
         FIG. 9  is an enlarged vertical cross sectional view of a prime part showing a fifth embodiment of the present invention. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Preferred embodiments of the present invention as shown in the drawings will be explained. 
       FIG. 1  is a vertical cross sectional view showing an entire constitution representing one example of a fuel injection valve to which the present invention is applied, and  FIG. 2  is a partially enlarged vertical cross sectional view showing around the annular end face portion of opposed stationary core and movable core in the vertical cross sectional view of  FIG. 1 . 
     A fuel injection valve main body  100  comprises a hollow stationary core  107  having a fuel passage  112  therein, a yoke  109  serving also as a housing, a nozzle body  104 , a movable core  106  and a valve element  101 . With regard to the movable core  106  and a movable valve element  101 , the needle shaped-valve element  101  is inserted through a middle aperture of the movable core  106  in a cylindrical shape with a bottom so as to enable to move relative to the movable core in an axial direction thereof. At the upper side of the valve element  101 , a flange  101 A is provided integrally with the valve element, and the flange  101 A is supported on the inside of the bottom of the movable core  106 . 
     The inside of the stationary core  107  is provided with a spring  110  that applies the spring load to the valve element  101  in a valve-closing-direction, namely, toward a seat portion  102 A provided at the lower end side of the nozzle body  104  and an adjustor  113  for adjusting the spring load of the spring. The spring  110  is disposed between the adjustor  113  and the upper surface of the flange  101 A of the valve element  101  to apply the spring load to the valve element  101  in the valve-closing direction. 
     A buffer spring  114  is disposed between the outside of the bottom of the movable core  106  and a valve element guide member  105  fixed at the upper side of the nozzle body  104 . The force of the buffer spring  114  is set to be sufficiently smaller than the spring  110 . 
     When the movable core  106  is magnetically attracted to the stationary core  107  side by energizing the electromagnetic coil  108 , the valve element  101  is lifted up together with the movable core  106  to do valve-opening operation. In contrast to that, when the energization to the electromagnetic coil  108  is turned off, the valve element  101  is press-returned in the valve-closing direction (toward the seat  102 A) by the force of the spring  110 , and the movable core  106  also receives the press-returned force via the flange portion  101 A of the valve element  101  and moves together with the valve element  101 . 
     The stationary core  107 , the yoke  109  and the movable core  106  serve as constitutional elements for a magnetic circuit. 
     The yoke  109 , the nozzle body  104  and the stationary core  107  are joined by welding. The electromagnetic coil  108  sealed by resin mold is incorporated within the yoke  109 . 
     At the top end of the nozzle body  104 , an orifice plate  102  provided with the seat  102 A and an orifice (illustration is omitted) serving as an injection hole is fixed by welding. The movable core  106 , the valve element  101 , an upper side valve guide member  105  and a lower side valve guide member  103  are incorporated inside the nozzle body  104 . 
     The fuel passage in the injection valve is constituted by the inner flow passage  112  in the stationary core  107 , a plurality of holes  106 A provided in the movable core  106 , a plurality of holes  105 A provided in the guide member  105 , the inside of the nozzle body  104  and a plurality of holes  103 A provided in the guide member  103 . 
     A resin cover  111  is provided with a connector portion  111 A for supplying an excitation current (pulse current) to the electromagnetic coil  108 , and a part of a lead terminal  115  insulated by the resin cover  111  positions in the connector portion  111 A. 
     When the electromagnetic coil  108  is energized by an external drive circuit (not illustrated) via the lead terminal  115 , the stationary core  107 , the yoke  109  and the movable core  106  constitute a magnetic circuit, the movable core  106  is magnetically attracted against the force of the spring  110 , and collides with the downstream side end face of the stationary core  107 . At this moment, the valve element  101  is also lifted up by the movable core  106  and removes from the seat  102 A to make an open valve condition, and the fuel in the injection valve main body that is pressurized in advance (more than 10 MPa) by an external high pressure pump (not illustrated) is injected via the injection hole. 
     When excitation of the electromagnetic coil  108  is turned off, the valve element  101  is pressed to the seat portion  102 A side by the force of the spring  110  to thereby make a close valve condition. At the time of closing the valve element  101 , although the valve element  101  collides with the seat portion  102 A, the movable core  106  moves slightly relative to the valve element  101  due to inertia force against the buffer spring  114 , thereafter the movable core  106  is returned to a position where the same comes into contact with the flange portion  101 A of the valve element  101  by the force of the buffer spring  114 . Through these operations, rebounding of the valve element  101  at the time of collision is suppressed. 
     Now, embodiments with regard to structural examples of the downstream side annular end face  107 A of the stationary core  107  and the upstream side annular end face  106 A of the movable core  106  as shown in  FIG. 2  will be explained with reference to  FIGS. 3 through 9 . 
       FIG. 3  is a partially enlarged vertical cross sectional view (around the portion indicated by symbol P in  FIGS. 1 and 2 ) of an prime portion showing the annular end face portions of the stationary core and movable core of the fuel injection valve according to a first embodiment of the present invention. 
     In the present embodiment, among the opposed annular end faces  107 A and  106 A of the stationary core  107  and the movable core  106 , an annular protuberance  106 C constituting the collision portion against the stationary core  107  is provided on the annular end face  106 A at the movable core  106  side. The annular protuberance (collision portion)  106 C is provided at an inner side from the middle position in the width direction of the annular end face  106 A.  FIG. 3  shows a condition where the movable core  106  is magnetically attracted to the side of the stationary core  107 . Areas of non-collision portions for keeping fluid gap Gf are constituted by the areas of the outer side and the inner side from the annular protuberance  106 C representing the collision portion. 
     The annular end faces  107 A and  106 A of the stationary core  107  and the movable core  106  are applied with platings  30  and  31  having anti wear property. The plated coatings are of non magnetic materials, for example, constituted by such as hard chromium coating or electroless nickel coating. In the present embodiment, the thickness of the plating  30  at the stationary core  107  side is formed uniformly, on the other hand, the thickness of the plating  31  at the movable core  106  side is formed in such a manner that the coating thickness t 1  at the collision portion (protuberance portion)  106 C is maximized, the coating thickness t 1 ′ at the area of non-collision portion outside the collision portion is formed thinner than t 1  and the thickness thereof is continuously (in sloping manner) decreased toward the side of outer diameter Do of the movable core  106 . 
     The magnetic gap Gm at the time when the movable core  106  is magnetically attracted to the stationary core  107  (valve-opening time) is expressed by the total sum (Gm=h+t 1 +t 2 ) of the height h of the collision portion (protuberance portion)  106 C, the plating thickness t 1  on the collision portion at the movable core  106  side and the plating thickness t 2  at the side of the stationary core  107  opposed thereto. The magnetic gap Gm at the time of valve-closing is determined by adding to the above total sum the separated distance between the collision portions of the movable core and the stationary core. Further, the fluid gap Gf is a value obtained by subtracting the plating thickness from the magnetic gap Gm. In the present embodiment, the most part of the non-collision portion is located outside (outer diameter side) from the collision portion and the area is larger than other area thereof because the part is located at the outer side. For this reason, a force due to squeeze effect acting on the area of the non-collision portion becomes large, and which causes to reduce the responsivity. Since the plating thickness t 1 ′ at the non-collision portion is made thinner than the plating thickness t 1  at the collision portion (t 1 ′ is made to decrease continuously), the fluid gap Gf between the movable core and the stationary core at the non-collision portion located outside from the collision portion satisfies a relationship of fluid gap (Gf)&gt;height h of collision portion (protuberance portion)  106 C. 
     When enumerating a specific numerical example of the above, for example, in the case where the outer diameter of the movable core  106  is about 10 mm, the inner diameter thereof is about 5 mm and the width W of the annular end face is about 2.5 mm, and when setting the height h of the collision portion as in the range of 10˜25 μm (herein 20 μm), the plating thickness t 1  at the collision portion as in the range of 10˜20 μm (herein 15 μm), the plating thickness t 2  at the stationary core  107  as about 10 μm and the plating thickness t 1 ′ at the outer diameter position of the movable core as below 5 μm, wherein the plating thickness t 1 ′ is of the non-collision portion outside from the collision portion and is continuously decreased from the thickness at the collision portion toward the outer diameter of the movable core, it is preferable to determine the magnetic gap Gm as about 45 μm and the fluid gap Gf as about 25 μm˜30 μm. When setting and determining the size relationship as above, the fluid gap can be increased by about 5˜15 μm in comparison with those not using the present invention. Since the fluid resistance force due to squeeze effect is inversely proportional to a cube of size of the fluid gap, even when the fluid gap increase is of about 5 μm, an advantage of reducing the force due to squeeze effect can be obtained. 
     In contrast to the above example, when the plating thickness of the movable core  106  is made almost the same (uniform) as the thickness t 1  at the collision portion over the entire region (comparative example), with regard to the fluid gap Gf, since a relationship of Gf=h (the height of the collision portion) stands, when the numerical conditions except for the movable core are set as in the above, since the fluid gap Gf becomes 20 μm which is smaller than the fluid gap 25 μm˜30 μm in the above embodiment, this results in an increase of squeeze effect (fluid resistance force) S F . 
     Here, as shown in  FIG. 6 , the smaller the gap Gf between the opposed faces of the movable core and the stationary core is, the larger the fluid resistance force becomes (S F ∝1/Gf 3 ), however, according to the present embodiment, since the fluid resistance force S F  can be reduced without increasing the magnetic gap Gm, the squeeze effect can be reduced. By the way, as shown in  FIG. 5 , the smaller the magnetic gap Gm is, the larger the magnetic attraction force G F  becomes (G F ∝1/Gm 2 ). 
     According to the present embodiment, the operation responsivity of the movable core from turning off energization to the electromagnetic coil until the valve-closing can be improved and the delay of valve-closing can be improved by 20%˜50% in comparison with the comparative example. This improved advantage can contribute to higher dynamic range and higher fuel pressure that are particularly required for recent engines. 
     Particularly, according to the present embodiment, it is possible to satisfy the conditions for reducing the magnetic gap (enhancement of magnetic attraction force) by decreasing the height of the collision portion (protuberance portion) and for decreasing the fluid resistance (reduction of fluid resistance force: squeeze effect) while keeping a sufficient thickness of the plating at the collision portion in view of durability thereof. 
     A method of varying the plating thickness, in the case of electrolytic plating such as hard chromium, can be executed by an arrangement of plating electrodes being set in such a manner that the plating current density is set higher at a portion where the plating thickness is desired to be thicker than at other portions and the plating current density is set lower at a portion where the plating thickness is desired to be thin than at other portions. For example, from the viewpoint of the positional relationship between one (electrode positioned at the side to be plated) of the plating electrodes and a portion to be plated, since it can realized by positioning the electrode closer to a portion where thick plating is desired than a portion where thin plating is desired, no complexity is accompanied in connection with the plating work. The plating current density and plating current flowing time can be set arbitrary depending on the plating thickness. 
     Incidentally, the annular protuberance  106 C and the structure of the plating  31  of which thickness varies as above can be provided at the stationary core  107  side instead of the movable core  106  side. Further, in contrary to the above first embodiment, the annular protuberance  106 C can be provided at the outer side from the middle position in the width direction of the annular end face, and the plating  31  can be formed from the collision portion (annular protuberance  106 C) toward the inner side in the width direction of the annular end face in such a manner that the thickness thereof continuously decreases. 
     FIGS.  4  and  7 ˜ 9  are vertical cross sectional views showing prime parts of other embodiments of the present invention, and the same reference numerals as in the previous embodiment show the same or equivalent elements as those therein. Further, in FIGS.  4  and  7 ˜ 9 , the fuel injection valve is shown in valve closed condition, namely, the condition where the movable core  106  is separated from the stationary core  107 . 
       FIG. 4  is a second embodiment of the present invention, in which the thickness of a plating  30  on a downstream side-annular end face  107 A of the stationary core  107  is also continuously decreased with a gradient from the inner side toward the outer side like the side of the movable core  106 . The constitution other than the thickness of the plating  30  is the same as of the first embodiment. 
       FIG. 7  is an enlarged vertical cross sectional view showing prime portions of a third embodiment of the present invention. 
     In the present embodiment, a collision portion  106 F provided on the movable core  106  is formed by an annular portion  106 F provided at the inner side from the middle position in the width direction of the annular end face  106 A. Further, this annular portion  106 F is formed with a plane annular width between an outside tapered portion  106 D and an inside tapered portion  106 E, which will be explained later. 
     At least, the tapered portion  106 D is formed so as to incline in the direction opposite to the stationary core  107  from this annular portion  106 F toward the outer diameter of the movable core  106 . The non-collision portion between the cores is formed by this tapered portion. On this tapered portion  106 D, the plating  31  is formed so that the thickness thereof continuously decreases from the collision portion (annular portion)  106 F toward the outer diameter side the movable core. The thickness of the plating  31  on the collision portion  106 F and on the inner side therefrom is made thicker than that on the outer side. 
       FIG. 8  is an enlarged vertical cross sectional view showing prime portions of a fourth embodiment of the present invention. 
     In the present embodiment, the collision portion and the structure of the tapered portion (non-collision portion) are inverted as those in the third embodiment. Namely, the collision portion provided on the movable core  106  is formed by an annular portion  106 F′ provided at the outer side from the middle position in the width direction of the annular end face  106 A. Further, this annular portion  106 F′ is formed with a plane annular width between an outside tapered portion  106 D′ and an inside tapered portion  106 E′, which will be explained later. 
     At least, the tapered portion  106 E′ is formed so as to incline in the direction opposite to the stationary core  107  from this annular portion  106 F′ toward the inner diameter of the movable core  106 . On this tapered portion  106 E′, the plating  31  is formed so that the thickness thereof continuously decreases from the collision portion (annular portion)  106 F′ toward the inner side of the movable core. 
     Further, the annular collision portions ( 106 F,  106 F′) at the side of the movable core and the tapered portions ( 106 D,  106 D′,  106 E,  106 E′) as shown in connection with the third and fourth embodiments can be provided at the side of the stationary core instead of at the side of the movable core. 
       FIG. 9  is an enlarged vertical cross sectional view showing important portions of a fifth embodiment of the present invention. 
     In the present embodiment, the collision portion (annular protuberance)  106 C provided on the annular end face  106 A of the movable core  106  is provided at the inner side from the middle position in the width direction of the annular end face. 
     The annular end face  106 A of the movable core  106  is divided in radial direction into two parts as an inner side and an outer side, the inner side is provided with an area  31  for forming a plating of anti wear property and the outer side is provided with an area  41  of non-plating. The annular protuberance  106 C serving as the collision portion is coated by the plating  31 , and the non-collision portion is constituted by the non-plating area  41 . 
     Further, the annular end face  107 A of the stationary core  107  is also divided in radial direction into two parts as an inner side and an outer side, and the inner side is used as an area  30  for forming a plating and the outer side is used as an area of non-plating. 
     Further, instead of the fifth embodiment, the collision portion (annular protuberance)  106 C can be provided at the inner side from the middle position in the width direction of the annular end face. In this instance too, the annular end face  106 A of the movable core  106  is divided in radial direction into two parts as an inner side and an outer side. The outer side is provided with an area  31  for forming a plating of anti wear property and the inner side is provided with an area  41  of non-plating. The annular protuberance  106 C serving as the collision portion is coated by the plating  31 , and the non-collision portion is constituted by the non-plating area  41 . Further, in this instance too, the annular end face  107 A of the stationary core  107  is also divided in radial direction into two parts as an inner side and an outer side, the outer side is provided with an area  30  for forming a plating and the inner side is provided with an area of non-plating. 
     With the above respective embodiments too, it is possible to satisfy the conditions for reducing the magnetic gap (enhancement of magnetic attraction force) by limiting the height of the collision portion (protuberance portion) and for increasing the fluid gap (reduction of fluid resistance force: squeeze effect) while keeping a sufficient thickness in view of durability thereof with regard to the plating at the collision portion. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           30 ,  31  . . . Plating,  100  . . . Fuel injection valve,  101  . . . Valve element,  106  . . . Movable core,  106 A . . . Annular end face at movable core side,  106 C . . . Annular protuberance (collision portion),  106 D,  106 E . . . Tapered portion,  106 F . . . Collision portion,  107  . . . Stationary core,  107 A . . . Annular end face at stationary core side.