Abstract:
An electromagnetic actuator for a fluid pressure control valve in a fuel injector for an internal combustion engine is disclosed. The actuator comprises a valve body having an opening therein and a bore extending at least partially therethrough. A control valve having an armature attached thereto is inserted into the bore in the valve body. A magnetic core, encircled by windings, is located in the opening in the valve body. A valve spring biases the armature away from the magnetic core. The windings, when energized, produce a magnetic circuit that includes the valve body, magnetic core, armature, and retainer ring to attract the armature towards the magnetic core.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to electromagnetic actuators for a control valve of a fuel injector for internal combustion engines. 
     2. Background Art 
     Co-pending U.S. patent application Ser. No. 10/197,317, filed Jul. 16, 2002, entitled “Electromagnetic Actuator and Stator Design in a Fuel Injector Assembly” now U.S. Pat. No. 6,565,020, discloses an injector assembly for an internal combustion engine wherein a plunger body, a valve body and nozzle assembly are arranged in a linear, stacked relationship. The valve body encloses a magnetic core. The magnetic core is surrounded by windings that are energized to create a magnetic circuit, which creates a magnetic force that draws an armature connected to a control valve towards the magnetic core to close the control valve. The magnetic core has a generally E-shaped cross section having a central inner portion and outer portions. The magnetic circuit comprises the central portion of the magnetic core, the armature, and the outer portions of the magnetic core. 
     The co-pending patent application and U.S. Pat. No. 6,565,020 are owned by the assignee of the present invention. 
     The separate magnetic core components of the design of the co-pending patent application are assembled with the valve body prior to assembling the control valve and valve actuator. It would simplify manufacture of the fuel injector if the magnetic core could be made integral with the valve body. Such a core design also would be more economical to manufacture than a magnetic core with separate components. 
     SUMMARY OF THE INVENTION 
     The electromagnetic actuator of the invention is adapted for use with a control valve module described in the co-pending application identified above. 
     The actuator of the invention comprises a modular valve body having an opening therein and a coaxial bore extending at least partially through the valve body. A control valve, having an armature attached thereto, is inserted into the bore in the valve body. A magnetic core, encircled by windings, is inserted into the opening in the valve body. A valve spring biases the armature away from the magnetic core, and a retainer ring holds the windings and the magnetic core in the opening in the modular valve body. The windings, when energized, produce a magnetic circuit that includes the modular valve body, magnetic core, armature, and retainer ring to attract the armature towards the magnetic core. 
     The valve body of the actuator of the invention comprises an integral part of the magnetic circuit, unlike the magnetic core of generally E-shaped cross-section in the design disclosed in the co-pending application. The invention simplifies the manufacturing and assembly process and reduces the cost of the fuel injector. If the inner portion of the core is formed by laminated windings, the magnetic performance of the actuator is enhanced. 
     In accordance with one embodiment of the invention, both the inner and outer magnetic core portions are made as a part of the valve body, which eliminates the need for a separate inner core portion. The core windings are held in place by a retainer ring. In accordance with another embodiment of the invention, the retainer ring can be eliminated if the armature is sized to overlie the core windings. Thus, the windings can serve the secondary function of a retainer. Such a design would be useful if the resulting increased mass of the armature is not detrimental to the effective performance of the injector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing the overall assembly of an injector that incorporates the electromagnetic actuator of the invention; 
     FIG. 2 is an enlarged partial cross-sectional view showing the stator design and electrical connector of the invention; 
     FIG. 3 is a cross-sectional view of one embodiment of the valve body having an integral magnetic core; 
     FIG. 4 is a cross-sectional view of another embodiment of the valve body having an integral magnetic core wherein a retainer ring for the windings is eliminated; and 
     FIG. 5 is a perspective view of a round laminated core. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, an injector assembly, including the actuator of the present invention, includes a relatively small pump body  64 . A central pumping cylinder  66  in body  64  receives plunger  68 . A cam follower assembly  70  includes a follower sleeve  72  and a spring shoulder element  74 . The follower assembly  70  is connected to the outer end of plunger  68 . The cylinder  66  and plunger  68  define a high-pressure cavity  78 . The plunger is urged normally to an outward position by plunger spring  80 , which engages the shoulder element  74  at the outer end of the plunger. The inner end of the spring is seated on a spring seat  81  of the pump body  64 . 
     The cam follower assembly  70  is engageable with a surface  71  of an actuator assembly shown at  73 , which is driven by engine camshaft  75  in known fashion. The stroking of the piston creates pumping pressure in chamber  78 , which is distributed through an internal passage  82  formed in the lower end of the pump body  64 . This passage communicates with the high-pressure passage  84  formed in valve body  86 . The opposite end of the passage  84  communicates with high-pressure passage  88  in a spring cage  106  for needle valve spring  92 . 
     The spring  92  engages a spring seat  94 , which is in contact with the end  96  of a needle valve  98  received in a nozzle element  100 . The needle valve  98  has a large diameter portion and a smaller diameter portion, which define a differential area  103  in communication with high-pressure fuel in passage  88 . The end of the needle valve  98  is tapered, as shown at  102 , the tapered end registering with a nozzle orifice  104  through which fuel is injected into the combustion chamber of the engine with which the injector is used. 
     When the plunger  68  is stroked, pressure is developed in passage  88 , which acts on the differential area of the needle valve and retracts the needle valve against the opposing force of needle valve spring  92 , thereby allowing high-pressure fuel to be injected through the nozzle orifice. Spring  92 , located in the spring cage  106 , is situated in engagement with the end of the pocket in the spring cage occupied by spring  92 . A spacer  110 , located at the lower end of the spring cage  106 , positions the spring cage with respect to the nozzle element  100 . A locator pin can be used, as shown in FIG. 1, to provide correct angular disposition of the spacer  110  with respect to the spring cage  106 . 
     A control valve  112  is located in a cylindrical valve chamber  114 . A high-pressure groove  116  surrounding the valve  112  is in communication with high-pressure passage  84 . When the valve is positioned as shown in FIG. 2, the valve  112  will block communication between high-pressure passage  84  and low-pressure passage or spill bore  118 , which extends to low-pressure port  120  in the nozzle nut  122 . 
     The nozzle nut  122  extends over the valve module  86 . It is threadably connected at  124  to the lower end of the pump body  64 . 
     The connection between passage  84  and groove  116  can be formed by a cross-passage drilled through the valve body  86 . One end of the cross-passage is blocked by a pin or plug  126 . 
     The end of control valve  112  engages a control valve spring  128  located in valve body  86 . This spring tends to open the valve and to establish communication between high-pressure passage  84  and low-pressure passage  118 , thereby decreasing the pressure acting on the nozzle valve element. 
     Valve  112  carries an armature  132 , which is drawn toward stator  130  when the windings of the stator are energized, thereby shifting the valve  112  to a closed position and allowing the plunger  68  to develop a pressure pulse that actuates the nozzle valve element. 
     The stator  130  is located in a cylindrical opening  134  in the valve body  86 . The valve  112  extends through the central opening and valve chamber  114  in the stator assembly. The windings of the stator assembly extend to an electrical terminal  136 , which in turn is connected to an electrical connector assembly  138  secured to the pump body  64 . This establishes an electrical connection between a wiring harness for an engine controller (not shown) and the stator windings. 
     A low-pressure passage  140  is formed in the pump body  64 . This communicates with a low-pressure region  142  at the stator assembly and with a low-pressure region  144 , which surrounds the valve body  86 . Fluid that leaks past the plunger  68  during the pumping stroke is drained back through the low-pressure passage  140  to the low-pressure return port  120 . 
     The interface of the upper end of the spring cage  106  and the lower end of the valve body  86  is shown at  146 . The mating surfaces at the interface  146  are precisely machined to provide flatness that will establish high-pressure fluid communication between passage  88  and passage  84 . The pressure in spring cage  106 , however, is at the same pressure that exists in port  120 . This is due to the balance pressure port  148 , seen in FIGS. 2,  3  and  4 , whereby the chamber for spring  128  communicates with the low-pressure region surrounding the valve body  86 . 
     The interface between the upper end of the valve body  86  and the lower end of the pump body  64  is shown in FIG.  2 . The upper surface of the valve body  86  and the lower surface of the pump body  64  are precisely machined to establish high-pressure fluid distribution from passage  82  to passage  84 . The seal established by the mating precision machined surfaces at each end of the valve module  86  eliminates the need for providing fluid seals, such as O-rings. 
     The assembly of the pump body  64 , the valve module  86 , the spring cage  106  and the nozzle element  100  are held in stacked, assembled relationship as the nozzle nut  122  is tightened at the threaded connection  124 , seen in FIG.  1 . The module, the spring cage and the nozzle element can be disassembled readily merely by disengaging the threaded connection at  124 , which facilitates servicing and replacement of the elements of the assembly. 
     The valve body contains a cut-out portion or opening  152  into which is fitted a bobbin  154  containing a plurality of windings  133 . The windings  133  are electrically connected to the conductor  136 , which in turn is electrically connected to connector assembly  138 , as mentioned above. This provides electrical communication of the windings with the engine control system (not shown) for controlling the operation of the fuel injector. A magnetic inner core portion  137  is also inserted into the cut-out portion  152 . A retainer  135  is inserted into the cut-out portion  152  to retain the bobbin  154 . 
     In the design of the co-pending patent application identified above, the magnetic circuit comprises a magnetic core of generally E-shaped cross-section. The valve body is not included as part of the magnetic circuit. However, in this invention, the valve body  86  is part of the magnetic circuit M, as shown in FIGS. 2,  3  and  4 . This design is advantageous because it eliminates separate magnetic core components and allows, as in the case of the design of FIG. 2, a larger diameter wire and more turns to be designed into a same-size valve body compared to a conventional E-section core. 
     The valve spring  128  normally biases the control valve  112  to an open valve position. To close the control valve  112 , the engine controller energizes the windings  133 , which produces a magnetic flux circuit that flows through the magnetic core portion  137 , the valve body  86 , the retainer  135 , and the armature  132 . The magnetic circuit M creates a magnetic force that draws the armature  132  towards the stator  130 . 
     In another embodiment illustrated in FIG. 3, the magnetic core portion  137  is an integral part of valve module  86  thereby further reducing the number of components. The bobbin  154  containing the windings  133  is inserted into opening  134  in valve body  86 . In this case, the magnetic circuit M includes the valve module  86 , the retainer  135 , and the armature  132 . This eliminates the need for a separate magnetic core. 
     In yet another embodiment illustrated in FIG. 4, the separate retainer ring shown in the previous figures has been eliminated. A press fit maintains the bobbin  154  in place in the control valve body  86 . The modified armature  132  can be used with a separate magnetic core portion  137  (as shown in FIG. 2) or with an integral magnetic core (as shown in FIG. 3) producing magnetic circuits M that travel through the valve body  86 , magnetic core portion  137 , and armature  132  or the valve body  86  and armature  132 , respectively. 
     FIG. 5 illustrates another example of a magnetic core that can be used with the present invention. The magnetic core portion  137  shown in FIG. 5 comprises a laminated, wound, flat strip, preferably of high magnetic saturation metal. The laminated core minimizes the formation of eddy currents that are detrimental to the performance of the fuel injector. The eddy currents slow down the demagnetization process. Natural oxides that form on the metal strip reduce the formation of eddy currents by electrically isolating the rolled strip windings. Further eddy current reduction can be obtained by coating the strip with a nonconductive coating prior to rolling the metal strip. 
     Unlike the injector design of the co-pending patent application identified above, the magnetic core of each of the embodiments of the present invention does not have an outer circuit to conduct the magnetic flux. The valve body provides the outer path for the magnetic flux flow. The core diameter can be slightly increased to compensate for the reduction in the pole face area. In the case of the design of FIG. 3, the retainer ring shown at  135  completes the magnetic circuit between the armature and the valve body. Unlike the design of the co-pending patent application, the valve body and the core of the design of FIGS. 3 and 4 are not separate components since the valve body is part of the magnetic circuit. This eliminates parts from the overall assembly and simplifies assembly procedure while reducing cost further. Integration of the outer core portions with the valve body makes it possible to increase the volume of the magnetic wire windings. As previously mentioned, the design of the invention has the further advantage of enabling the designer to use larger diameter wire and more turns with the available module size. Since magnetic forces are proportional to the product of the amperage and the number of turns in an unsaturated state, the design of the present invention provides a higher force with lower resistance. 
     In the embodiment of the invention shown in FIGS. 1 and 2, the valve body, which is magnetized, is made from a high strength material, typically a high carbon steel, that provides fatigue resistance to high stress resulting from high injection pressure. High injection pressure is required for diesel fuel injection. The core portion  137  of FIG. 2 is made of magnetized material of high coercivity and high permeability and is retained in place against the adjacent surface of the valve body  86  by mechanical and magnetic forces. When the windings  133  are not energized, the residual magnetism of the valve body due to the high coercivity of the valve body retains the core in contact with the valve body. This complements the retention forces of the retainer ring and the bobbin, the latter being press-fitted in opening  134 . 
     When the coils are energized, the air gap at  131  between the core and the valve body, seen in FIG. 2, is smaller than the air gap  139  between the armature and the core. Because of the larger air gap at  139 , the magnetic forces will pull the armature toward the core. The force on core portion  137  at air gap  139  always will be less than the force at air gap  131  between the core and the valve body. Thus, a contact force between the core portion  137  and the valve body always will retain the core portion  137  securely in place when the magnetic circuit is either energized or non-energized. 
     The core and the bobbin can be encapsulated with a polymer, if that is desired, to form a more permanent assembly. This configuration may be desirable in some instances when high forces due to pressure or vibration tend to cause the magnetic core to move. 
     In the embodiment of FIG. 2, the magnetic circuit is completed as the magnetic flux travels through the valve body, through the retaining ring and through the armature. The armature and the retaining ring are soft magnetic alloys, which maximizes the magnetic performance. The magnetic force that closes the control valve is created at the air gap  139  between the armature and the core. A second air gap exists between the inner surface of the retaining ring and the outer surface of the armature. This air gap is designed with a minimum clearance so as to minimize the energy losses as the magnetic flux traverses the air gap. This is true also of the air gap between the retainer ring  135  and armature of FIG.  3 . 
     The retaining ring  135  has a dual function of conducting magnetic flux and retaining the bobbin. This is desirable because more volume within the space limitations of the design is then made available for the magnetic windings rather than having an additional part to accomplish the retention function. Furthermore, in the case of the designs of FIGS. 1,  2  and  3 , the mass of the armature is reduced because of the presence of the retaining ring  135 . This improves the dynamic behavior of the design since the reduced mass makes it possible to improve the valve response to commands issued by the engine control system. In those instances, when the reciprocating mass of the armature is less important and the reduction of the number of components of the design is more critical, the armature  132  may be made as indicated in FIG.  4 . This concept can be used also, of course, in the case of the embodiments of the invention illustrated in FIGS. 1 and 2. 
     Although embodiments of the invention have been disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications and equivalents thereof are intended to be covered by the following claims.