Abstract:
To increase the force to draw the armature of an electromagnetic valve gear for driving a valve for opening or closing a high-pressure liquid passage and to alleviate valve bouncing, the surface of the core with a coil embedded therein is shaped flat and the surface of the armature facing to the surface of the core is shaped convexly spherical, or the surface of the core is shaped convexly spherical and the surface of the armature is concavely spherical such that the curvature radius of the concavely spherical surface is larger than that of the convexly spherical surface, or the armature is composed by piling thin plates of different diameters such that the surface of the armature facing to the surface of the core forms an approximate convexly spherical surface, so that the gap between the surfaces of core and armature is smaller in the central part compared to that in the peripheral part of the surfaces. By this, the interference of the surfaces is prevented with smaller initial gap in the central portion of the faces even when the armature is installed aslant caused by insufficient accuracy of the component parts, and strong electromagnetic attraction can be secured because the smaller the gap is, the stronger the electromagnetic attraction is.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is related to an electromagnetic valve gear for driving an open/close valve to open or close a high-pressure fuel passage in order to control fuel injection timing and fuel injection quantity used particularly in the fuel injection equipment of an internal combustion engine.  
         [0003]     2. Description of the Related Art  
         [0004]     Electromagnetic valve gears have been known for driving by utilizing electromagnetic force an open/close valve to open or close a high-pressure fuel passage in order to control fuel injection timing and fuel injection quantity. The electromagnetic valve gear comprises a core with a coil embedded therein and an armature located adjacent to the core. The armature is attracted toward the core when magnetic flux generated by flowing electric current in the coil passes through the armature, thus a valve body connected to the armature is driven.  
         [0005]     As the electromagnetic valve gear is composed such that the valve body sits on the valve seat in the state the armature is attracted toward the core to close the fuel passage, there must be a gap between the core and the armature in the state the armature is attracted toward the core. It is required that this gap is as small as possible for securing strong electromagnetic attraction.  
         [0006]     However, heretofore, both of the surfaces of the core and the armature facing to each other have been shaped in a flat surfaces (see FIGS. 1, 3, 4, and 5 of Japanese Laid-Open Patent Application No. 2003-193939, and FIGS. 1, 2, and 3 of Japanese Laid-Open Patent Application No. 2002-98024, for example), and the valve gear has been composed to provide an enough initial gap between the surfaces of the core and the armature facing to each other so that the end surface of the armature does not interfere with the surface of the core facing to the end surface of the armature even when the armature is installed aslant caused by insufficient accuracy of the component parts, since it is difficult from the standpoint of accuracy of component parts to compose so that the gap is even allover the surfaces.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, there has been a limit to decreasing said initial gap in order to increase the electromagnetic attraction, and it has been difficult to provide an electromagnetic valve gear which is small in size and can exert strong electromagnetic attraction. The first object of the present invention is to solve this problem.  
         [0008]     Further, there has been a problem of occurrence of bouncing-when-closing of the valve body connected to the armature when the armature is attracted toward the core to allow the valve body to close the fuel passage and a problem of occurrence of bouncing-when-opening of the valve body when the valve body is allowed to open the fuel passage. To solve these problems is the second object of the present invention.  
         [0009]     The first object is attained by composing the electromagnetic valve gear such that the surface of said core facing to said armature is shaped into a flat surface, and the surface of the armature facing to said surface of the core with a small gap between the surfaces is shaped into a convexly spherical or convexly ovally spherical surface, so that the gap between the surfaces is smaller in the central part compared to that in the peripheral part of the surfaces.  
         [0010]     There may happen that, the periphery of the surface of the armature contact the surface of the core, that is, the interference of the surfaces of the armature and core occurs before the valve does not sit on the valve seat when the armature is attracted toward the core, which results in an incomplete closing of the valve, in the case the surfaces of the core and armature facing to each other are flat surfaces or curved surfaces facing with the same gap allover the surfaces, if the armature is installed such that the center axis of the armature is inclined to the center axis of the core caused by insufficient accuracy of component parts.  
         [0011]     To prevent this, it is necessary to provide an enough gap between the surfaces. According to the present invention, the gap between the surfaces is larger in the central part than in the peripheral part of the surfaces because the surface of the armature is shaped into a convexly curved surface. Therefore, even if the armature is installed inclined by the same angle that may happen in a prior art, the interference of the armature and core does not occur. It means that the gap between the surfaces in the central part can be decreased without the occurrence of the interference when it happens that the armature is installed aslant caused by insufficient accuracy. Accordingly, it is possible to compose the valve gear so that the electromagnetic attraction is increased compared to the case of prior art.  
         [0012]     The first object can be attained also by the invention recited in claim  2  to  5 , according to which the surface of the core is shaped into a flat surface and the surface of the armature is shaped such that the central part thereof is a flat surface and the surface outer side from the flat surface is a convexly spherical or convexly ovally spherical surface connecting tangentially to the flat surface, that is, so-called crowning is executed, or the surface of the armature is shaped into a convexly spherical or convexly ovally spherical surface with its central part removed to be formed into a flat surface; or the surface of the armature is shaped into a flat surface and the surface of the core is shaped into a convexly spherical or convexly ovally spherical surface; or the surface of the core is shaped into a convexly spherical or convexly ovally spherical surface and the surface of the armature is shaped into a concavely spherical or concavely ovally spherical surface such that the curvature radius of the concavely spherical surface of the armature is larger than that of the convexly spherical surface of the core; or the surface of the core is shaped into a flat surface and the armature is composed of thin plates piled in the moving direction of the armature such that there is provided a part in which the thin plates are piled such that the nearer to the surface of the flat face of the core, the smaller the plate in diameter.  
         [0013]     Next, the second object of the present invention can be attained by composing such that at least one passage hole is provided the armature, the passage hole having a tapered portion broadening toward the surface of the core facing to the surface of the armature. With this composition of the armature, when the armature is attracted toward the core and the valve connected to the armature closes the high-pressure fuel passage, the fuel rapidly compressed in the gap between the surfaces of the core and armature can escape through the passage hole, so that the occurrence of bouncing-when-closing of the valve connected to the armature and supported by a spring is prevented or the bouncing is alleviated.  
         [0014]     When the electromagnetic attraction is released and the armature is drawn back from the core side by the spring together with the valve connected to the armature to open the valve, the bouncing-when-opening of the valve is harder to occur when there is some resistance for the valve to move back. When the passage hole is of constant cross-sectional area, although the occurrence of valve bouncing-when-closing can be suppressed, the occurrence of valve bouncing-when-opening is rather conduced. Through making the passage of fuel through the passage hole easier when closing the valve than when opening the valve by forming each of the passage hole to have a tapered portion broadening toward the surface of the core, the occurrence of valve bouncing-when-closing is prevented or suppressed without excessively conducing to the occurrence of valve bouncing-when-opening.  
         [0015]     The second object can be attained also by composing such that the diameter of the thin plate located remotest from the surface of the armature facing to the surface of the core is about the same as that of the thin plate facing to the surface of the core, and at least one passage hole penetrating through the piled thin plates except said thin plate located remotest from the surface of the armature is provided such that the passage hole is open toward the surface of the core at the thin plate facing to the surface of the core and is closed by the remotest thin plate.  
         [0016]     In this case, the fuel compressed in the gap between the surfaces of the core and armature by rapid attraction of the armature toward the core bends the thin plate located remotest from the surface of the armature to escape through the passage hole, as a result the occurrence of valve bouncing-when-closing is prevented or suppressed. When the armature is drawn back from the surface of the core side to open the valve, the fuel below the armature does not pass through the passage hole because the passage hole are closed by the thin plate located remotest from the surface of the armature. Therefore, the occurrence of valve bouncing-when-opening is not conduced. Further, eddy current loss is decreased by composing the armature of piled thin plates. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a sectional view of the electromagnetic valve gear of the first embodiment according to the present invention in the state the valve gear is mounted to the fuel injection equipment for opening or closing the high-pressure fuel passage thereof with the open/close valve installed.  
         [0018]      FIG. 2  is a sectional view of the electromagnetic valve gear of the second embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0019]      FIG. 3  is a sectional view of the electromagnetic valve gear of the third embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0020]      FIG. 4  is a sectional view of the electromagnetic valve gear of the fourth embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0021]      FIG. 5  is a sectional view of the electromagnetic valve gear of the fifth embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0022]      FIG. 6  is a sectional view of the electromagnetic valve gear of the sixth embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0023]      FIG. 7  is a sectional view of the electromagnetic valve gear of the seventh embodiment according to the present invention in the state as is in  FIG. 1 .  
         [0024]      FIG. 8  is a graph showing an increase in attraction force of the electromagnetic valve gear of the present invention compared to that of a conventional electromagnetic valve gear.  
         [0025]      FIG. 9  is a drawing for explaining the working of the electromagnetic valve gear of the seventh embodiment when the armature is attracted toward the core to close the valve.  
         [0026]      FIG. 10  is a graph showing the state the occurrence of valve bouncing-when-closing is prevented in the case of the sixth and seventh embodiments.  
         [0027]      FIGS. 11A and 11B  are representations for explaining why the initial gap between the surfaces of the core and armature can be reduced.  
         [0028]      FIGS. 12A and 12B  are sectional views of another two embodiments of the armature according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     A preferred embodiment of the present invention will now be detailed with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only not as limitative of the scope of the present invention.  
         [0030]      FIG. 1  to  FIG. 7  are sectional views of the electromagnetic valve gear of the first to seventh embodiments according to the present invention in the state the valve gear is mounted to a fuel injection equipment for opening or closing the high-pressure fuel passage thereof with the open/close valve installed.  
         [0031]     Referring to  FIG. 1 , reference numeral  1  is an electromagnetic valve gear,  10  is an open/close valve device, and  30  the pump case of a fuel injection pump.  
         [0032]     Said electromagnetic valve gear  1  includes a core  3  with a coil  4  embedded therein and an armature  5  covered with electromagnetic valve cases  2 ,  9  and mounted to said pump case  30 . Reference numeral  6  and  7  are plastic sealing agents. Said open/close valve device  10  is composed of a valve seat member  11 , a valve body  12  fitted into said valve seat member  11  for reciprocation, a fixing member  13  for fixing said valve seat member  11  to make it contact closely to the bottom  33  of the valve device mounting part of said pump case  30 , the fixing member  13  being screwed in the pump case  30 , and a spring  14  is accommodated in said fixing member  13  for pushing said valve body  12  downward.  
         [0033]     Said armature  3  is fixed to said valve body  12  by means of bolts  8 . Reference numeral  15  shows the seating part of the seat member  11  onto which the seating part of said valve body  12  sits when the valve closes. Reference numeral  31  is a high-pressure fuel passage communicating to the plunger chamber and fuel sump near the nozzle needle valve of the fuel injection equipment not shown in the drawing, and  32  is a low-pressure fuel passage communicating to a fuel tank not shown in the drawing.  
         [0034]     When electric current is flowed in the coil  4  of the electromagnetic valve gear  1 , the armature  5  is attracted toward the core  3 , the valve body  12  connected to the armature is lifted upward to sit on the seating part  15  of the seat member  11  to close the high-pressure fuel passage  31 . When the valve is closed, the fuel in the high-pressure fuel passage, plunger chamber, and fuel sump near the nozzle needle valve is trapped within a closed space, and the fuel in the space is compressed by the movement of the plunger of the injection pump to be injected from the fuel injection nozzle into the cylinder.  
         [0035]     When electric current to the coil  4  is cutoff, the electromagnetic attraction is released, the valve body  12  is pushed down together with the armature  5  by the spring force of the spring  14  until the bottom end of the valve body  12  reaches the bottom  33  of the valve device mounting part of the pump case  30 , and the valve is opened at the seating part  15 . When the valve is opened, the high-pressure in said closed space in the fuel injection pump is communicated to the low-pressure fuel passage  32  to be returned to the fuel tank, the fuel pressure in the fuel injection pump decrease, and fuel injection ends.  
         [0036]     The valve body  12  is provided with a central hole  12   a  and lateral hole  12   b  which communicate to the spring room  16  formed between the valve body and fixing member  13 . The fuel leaked from the sliding portion of the seat member  11  and valve body  12  enters the spring chamber where the spring  14  is accommodated and flows out to the armature chamber  9   b  through a space  17  between the fixing member  13  and the valve body to be returned therefrom to the fuel tank through piping not shown in the drawing.  
         [0037]     When the valve is closed by the sitting of the valve body  12  on the seating part  15  of the seat member  11 , there must be a gap G between the surfaces of the core and armature, otherwise the surfaces of the core and armature interfere with each other and the valve body  12  does not sit completely on the seating part  15 .  
         [0038]     The smaller the gap between the surfaces of core and armature is, the stronger the electromagnetic attraction of the core to attract the armature is. However, it may happen that the armature is installed such that the center axis of the armature is aslant to the center axis of the core because of insufficient accuracy of component parts.  
         [0039]     It may happen that the valve body  12  does not sit completely on the seating part  15  when said gap is small caused by insufficient accuracy of component parts. Therefore the dimensions of components parts must be determined to secure a good margin in initial gap to evade said interference. The electromagnetic attraction is decreased by the value corresponding to the margin in initial gap. By shaping the surface of the armature into a convexly spherical surface, said margin in initial gap can be reduced. This is recognized by comparing  FIG. 11A  and  FIG. 11B . In  FIG. 11A  is shown the case the both of the surfaces of the core and armature are flat and the initial gap between both surfaces is S 0 . In this case, the periphery of the surface of the armature  5  contacts the surface of the core when the armature inclines by an angle θ. In the case the surface of the armature  5  is shaped into a convexly spherical surface as shown in  FIG. 11B , there remains gap S 1  when the armature inclines by the same angle of θ. Accordingly, it is possible to reduce said margin in initial gap to a large degree.  
         [0040]     However, when the curvature radius of the convexly spherical surface is too small, the electromagnetic attraction does not increases, instead decreases because of increasing gap in the peripheral part even if said margin in initial gap is reduced. So the curvature radius is desired as large as possible. But it becomes necessary to increase said margin in initial gap when the curvature radius is increased in order to evade the interference of the surfaces of core and armature. With this taken into consideration, the relation between the range of gap that can be set initially without inducing the interference of surfaces with required electromagnetic attraction kept and the electromagnetic attraction in the case the surface of the armature is flat or convexly spherical is shown in  FIG. 8 , in which the abscissa is initially set gap and ordinate is electromagnetic attraction. It is recognized from  FIG. 8  that electromagnetic attraction can be increased by shaping the surface of the armature into a convexly spherical surface.  
         [0041]      FIG. 2  shows the second embodiment. The surface of the core  3  is flat and the surface of the armature  5  is shaped such that the central part is flat and peripheral part is spherical connecting tangentially to the flat surface of central part, that is, so-called crowning is executed. Other than that is the same as the case of  FIG. 1  and explanation is omitted. As the diameter of the flat part of the armature is decreased in this embodiment, said margin in initial gap can be decreased and similar effect as in the case of the first embodiment of  FIG. 1  can be obtained.  
         [0042]      FIG. 3  shows the third embodiment. The surface of the armature  5  is shaped into a convexly spherical surface and the surface of the core  3  is shaped into a flat surface. Other than that is the same as the case of  FIG. 1  and explanation is omitted. It is easily understood that with this embodiment similar effect as in the case of the first embodiment of  FIG. 1  can be obtained.  
         [0043]      FIG. 4  shows the fourth embodiment. The surface of the core  3  is shaped into a convexly spherical surface and surface of the armature  5  is shaped into a concavely spherical surface such that the curvature radius of the concavely spherical surface is larger than that of the convexly spherical surface. Other than that is the same as the case of  FIG. 1  and explanation is omitted. It is easily understood that with this embodiment similar effect as in the case of the first embodiment of  FIG. 1  can be obtained.  
         [0044]      FIG. 5  shows the fifth embodiment. The surface of the core  3  is flat and the armature is composed of thin plates piled such that there is provided a part in which the thin plates are piled such that the nearer to the surface of the flat face of the core, the smaller the thin plate in diameter. Other than that is the same as the case of  FIG. 1  and explanation is omitted. As the diameter of the thin plate  5   b  located nearest to the core  3  to face the surface of the core directly is small, said margin in initial gap can be decreased and similar effect as in the case of the first embodiment of  FIG. 1  can be obtained. In addition, eddy current loss is reduced with this embodiment.  
         [0045]      FIG. 6  shows the sixth embodiment. In this embodiment, at least one passage hole is provided to the armature  5  in order to attain the object to prevent the occurrence of valve bouncing-when-closing in addition to increase the electromagnetic attraction through decreasing the margin in initial gap. When the armature  5  is attracted toward the core  3  to lift the valve body  12  to close the high-pressure fuel passage  31 , the fuel in the gap between the surfaces of the core  3  and armature  5  is compressed rapidly, and the valve body  12  supported by the spring  14  begins to oscillate due to the impact of the rapid compression. By allowing the fuel in the gap to escape through the passage hole  5   a , the impact is relieved and the occurrence of the oscillation is prevented or suppressed. That is, the occurrence of valve bouncing-when-closing is prevented or suppressed. The passage hole  5   a  is formed to be broadened upwardly in a cone shape so that the fuel in the gap can escape through the passage hole easily. Best result was obtained with the cone angle of about 60°.  
         [0046]     In  FIG. 10  is shown valve bouncing. As to valve bouncing, there are bouncing that occurs at valve closing and bouncing that occurs at valve opening. The valve bouncing-when-closing induces fluctuation in injection rate at fuel injection beginning, and the valve bouncing-when-opening induces deterioration in sharpness of the end of fuel injection. Both of these affect the fuel injection control and engine performance.  
         [0047]      FIG. 7  shows the seventh embodiment. In this embodiment, the armature  5  is composed of piled thin plates as in the case of  FIG. 5 , but composed such that the diameter of the thin plate  5   c  located remotest from the core  3  is about the same as that of the thin plate  5   b  located nearest to the core  3 , and at least one passage hole  5   a  is provided to penetrate the thin plates except the remotest thin plate  5   c , the hole passages  5   a  being closed by the remotest thin plate  5   c  near the periphery thereof.  
         [0048]     When the armature  5  is attracted toward the core  3  to lift the valve body  12  to close the high-pressure fuel passage  31 , the fuel in the gap between the surfaces of the core  3  and armature  5  is compressed rapidly. The thin plate  5   c  remotest from the core  3  is bent by the pressure of the compressed fuel as shown in  FIG. 9  and the fuel escapes through the gap developed by the bending of the thin plate  5   c . Therefore, the occurrence of valve bouncing-when-closing can be prevented or suppressed as in the case of the embodiment of  FIG. 6 . When the armature  5  moves down together with the valve body  12  connected to the armature  5  to open the high-pressure fuel passage  31 , the passage hole  5   a  is closed by the thin plate  5   c  located at the bottom.  
         [0049]      FIG. 12A  and  FIG. 12B  show respectively still another embodiment of the armature  5 . In the embodiment of  FIG. 12A , after the top face of the armature  5  is shaped into a convexly spherical surface  52 , the central part is removed to form a flat surface  51  to provide the initial gap G between the surface of the core  3  and the flat surface  51 .  
         [0050]     In the embodiment of  FIG. 12B , the top face of the armature  5  is shaped to consist of two convexly spherical surfaces  53 ,  53  by rotating a machining circle  54  around the center of the armature  5 . The gap G is formed between the tops of spherical surfaces  53 ,  53  and the core surface.  
         [0051]     As has been described in the foregoing, according to the present invention, as the initial gap between the core and armature can be reduced, the electromagnetic attraction can be increased. Further, by providing passage hole to the armature such that the fuel in the gap between the surfaces of the core and armature can escape from the gap through the hole easily when the armature is attracted toward the core and the fuel below the armature is rather difficult or impossible to flow through the passage hole toward the gap side when the armature drawn back from the core side, the occurrence of bouncing-when-closing of the valve for opening or closing the high-pressure fuel passage of a fuel injection equipment can be suppressed or prevented without enhancing valve bouncing-when-opening.  
         [0052]     According to the present invention, an electromagnetic valve gear can be provided, which can be used for controlling injection timing and fuel injection quantity of fuel injection equipment, with which the electromagnetic force by the core to attract the armature can be increased and valve bouncing-when-closing can be prevented or suppressed.