Abstract:
An electric actuated control valve, such as an EGR valve, has a solenoid that can deliver useful force over a longer stroke for operating a valve element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to and benefit of provisional patent application serial No. 60/354,013, filed Jan. 31, 2002, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to electric-actuated control valves, such as valves for controlling flow of fluids in automotive vehicle engine systems. In particular, the invention relates to improvements for increasing the useful stroke of such a valve by enhancing the force vs. stroke characteristic of the valve actuator. Examples of such valves are exhaust gas recirculation (EGR) valves and fuel cell valves.  
         BACKGROUND OF THE INVENTION  
         [0003]    The actuator of certain control valves of automotive vehicle engine systems comprises a solenoid that comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve element to control flow through a passage of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve element, to bias the armature toward a position that causes the valve element to close the passage.  
           [0004]    The stator air gap is defined by an upper pole piece that is disposed at an upper end of the coil and a lower pole piece at a lower end of the coil. The pole pieces have respective annular hubs that fit into an interior space bounded by the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two hubs are spaced apart to define the air gap as a generally annular space within which the armature is centered and along which the armature can travel. Electric current in the coil creates magnetic flux that passes from one hub through a portion of the air gap to the armature, through the armature, and back across another portion of the air gap to the other hub. The flux creates an electromagnetic force on the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid against the resistance of the return spring. In order to operate the valve from closed to open, the solenoid must apply a force that is greater than the sum of the bias force being applied by the return spring and any other forces acting on the valve.  
           [0005]    For achieving improved control, it is desirable that the valve actuator be able to deliver increasing force over an increased stroke length. However, certain constraints that are imposed on certain automotive vehicles, especially mass-produced vehicles that are subject to governmental regulation, make it impossible, impractical, and/or uneconomical simply to use a larger solenoid. Accordingly, it is believed that a valve that is capable of delivering increasing force over an increased stroke length, without accompanying increases in size and weight that would be deemed unacceptable, would be useful to automotive vehicle manufacturers in complying with constraints imposed on the vehicles that they manufacture.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention relates to a valve that is capable of delivering increasing force over an increased stroke length, without accompanying increases in size and weight that would be deemed unacceptable.  
           [0007]    One general aspect of the invention relates to an electric-actuated control valve for controlling flow of fluid in an automotive vehicle engine system. The valve comprises a valve body comprising a passage having an inlet port for receiving fluid and an outlet port for delivering fluid. A mechanism selectively positions a valve element to selectively restrict the passage. The mechanism comprises a solenoid actuator comprising a bobbin having a tubular core of non-ferromagnetic metal and ferromagnetic pole pieces at axial ends of the tubular core. An electromagnet coil comprising a length of magnetic wire is wound on the tubular core between flanges of the pole pieces. The pole pieces form portions of a magnetic circuit for magnetic flux created by electric current in the coil and comprise hubs that protrude into the tubular core and have juxtaposed ends defining an air gap within the tubular core through which the magnetic flux passes between the pole piece hubs. The mechanism further comprises an armature that is guided for motion axially of the tubular core for positioning the valve element and that comprises ferromagnetic material for conducting magnetic flux created at the air gap when electric current flows in the coil to cause an axial component of electromagnetic force to be exerted on the armature for positioning the valve element.  
           [0008]    Another aspect relates to the solenoid actuator itself.  
           [0009]    Still another aspect relates to a method of making the valve and the actuator.  
           [0010]    The accompanying drawings, which are incorporated herein and constitute part of this specification, include a presently preferred embodiment of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic diagram of an engine system that comprises a valve in accordance with principles of the present invention.  
         [0012]    [0012]FIG. 2 is a cross section view, in elevation, of an exemplary embodiment of an actuator of the valve of FIG. 1 embodying the present invention.  
         [0013]    [0013]FIG. 3 is a graph plot for showing representative stroke length improvement that can be achieved with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    [0014]FIG. 1 shows an exemplary emission control system  10  having an electric exhaust gas recirculation valve (EEGR valve)  12  associated with an internal combustion engine  14  to control the flow of exhaust gas being recirculated from an exhaust system  16  of the engine to an intake system  18  of the engine.  
         [0015]    Valve  12  comprises a body containing a flow passage extending between a valve inlet port  20  communicated to exhaust system  16  and a valve outlet port  22  communicated to intake system  18 .  
         [0016]    Valve  12  further comprises an electromagnetic actuator  24 , namely a solenoid, which is under control of an engine control system  26  to control the extent to which valve  12  allows exhaust gas to be recirculated through the flow passage in the valve body. In the closed position of valve  12  that blocks exhaust gas recirculation, a preloaded return spring within the valve body is resiliently biasing a valve element to close on a valve seat in the flow passage, closing the flow passage to flow of exhaust gas between ports  20  and  22 .  
         [0017]    As engine control system  26  delivers increasing electric current to actuator  24 , a point is reached where the current is sufficiently large to create sufficient force for overcoming the spring bias. Further increases in current increasingly open the valve.  
         [0018]    The improvement that is achieved by the present invention is accomplished through actuator  24 , detail of which appears in FIG. 2.  
         [0019]    Actuator  24  comprises stator structure  28  associated with an electromagnet coil  30  to form a portion of a magnetic circuit path. The stator structure comprises an upper pole piece  32 , disposed at one end of the actuator coaxial with a centerline CL, a lower pole piece  34  disposed at the opposite end of the actuator coaxial with centerline CL, and an outer cylindrical shell  36 . All three pieces  32 ,  34 ,  36  comprise ferromagnetic material.  
         [0020]    Upper pole piece  32  comprises a circular end wall  40  and an annular walled hub  38  that extends interiorly from an interior face of end wall  40 . The junction of the hub and flange comprises a chamfer  42  between a radially outer surface of hub  38  and the interior face of end wall  40 . The chamfer ends at a shoulder  43  in the outer hub surface, and beyond that shoulder the outer hub surface continues axially as a circular cylindrical surface  44 . Beyond surface  44 , the outer hub surface continues as a frustoconical surface  46 , finally ending at a narrow flat end face  48  that is perpendicular to centerline CL.  
         [0021]    The radially inner surface of hub  38  comprises a circular cylindrical counterbore  50  extending into the hub from face  48  as far as an internal shoulder  52 . The radially inner hub surface continues axially from shoulder  52  as a chamfer  54 , and then as a circular cylindrical bore  56 , finally ending via a chamfer  58  at an end face  60  that is perpendicular to centerline CL. Counterbore  50  and bore  56  thereby form a blind hole in pole piece  32  that is centered on centerline CL.  
         [0022]    Lower pole piece  34  comprises a central hub  62  and a circular flange  64  that girdles hub  62  intermediate opposite axial ends of hub  62 . One portion of hub  62  that extends from an interior face of flange  64  comprises an annular wall. The junction of flange  64  and that annular wall comprises a chamfer  66  extending between the interior face of flange  64  and the outer surface of the hub wall. From chamfer  66 , the outer surface of the hub wall continues as a circular cylindrical surface  68  ending at an end face  70  that is perpendicular to centerline CL. The portion of hub  62  extending from the exterior face of flange  64  comprises an annular wall whose radially outer surface is a circular cylindrical surface  72  beginning at flange  64  and ending at a shoulder  73 . From shoulder  73 , the outer wall surface continues as a circular cylindrical surface  76  and ends at an end face  78  that is perpendicular to centerline CL.  
         [0023]    Lower pole piece  34  further comprises a through-hole that forms the inner hub surface and comprises a circular cylindrical counterbore  80  extending from end face  70  and ending at an internal shoulder  82 . A circular cylindrical bore  84  extends from shoulder  82  to end face  78 .  
         [0024]    Pole pieces  32 ,  34  are assembled to a non-ferromagnetic tube  88 , one pole piece at one end of the tube, the other pole piece at the opposite end. Tube  88  has a circular cylindrical shape of uniform radial thickness. One end of tube  88  fits over hub  38 , being centered on surface  44  and axially abutting shoulder  43 . The other end of tube  88  fits over the upper end of hub  62 , being centered on surface  68  and abutting chamfer  66 .  
         [0025]    The assembly of pole pieces  32 ,  34  and tube  88  forms a bobbin on which magnet wire is wound to create coil  30 . Ends of the wire are led through a plastic overmold  86  and a clearance opening (not shown) in flange  40  where they can be attached to electric terminals in a cap of the valve actuator (also not shown). The cap terminals protrude externally from the cap material where they are bounded by a surround of cap material to form a connector adapted for mating connection with a wiring harness connector for connecting the coil to control system  26 . The plastic overmold  86  separates the wound coil wire from direct contact with end wall  40  of upper pole piece  32 , and is believed useful in damping vibrations. Although not shown in the drawing, a thin layer of insulating plastic or paper may be disposed around tube  88  and similar thin insulating sheets disposed over the interior face of end wall  40  and that of flange  64  for insulation between the coil wire and the metal parts of the stator structure.  
         [0026]    A sleeve bearing  90 , carbon steel for example, is fit to surface  84  to provide guidance for axial travel of an armature  92  of actuator  24 . Such an insert may not always be needed, and replaced by a sleeve of thin non-magnetic material. Armature  92  is guided only on lower pole piece  34  and not the upper pole piece.  
         [0027]    Armature  92  comprises ferromagnetic material having a circular cylindrical outer surface  94  guided by the inner surface of bearing  90 . The axial length of the armature overlaps the hubs of both pole pieces. At its lower end armature  92  comprises a valve actuating stem  96  that protrudes from lower pole piece  34 .  
         [0028]    An air gap is present between confronting ends of hubs  38  and  62  within space bounded by coil  30 . Armature  92  is disposed in the air gap between juxtaposed ends of the pole piece hubs. When coil  30  is energized by electric current, magnetic flux passes from one hub across one portion of the air gap, through that portion of the armature disposed at the air gap, through another portion of the air gap, and to the other hub. Exterior to coil  30 , the magnetic circuit is completed from one pole piece to the other through shell  36 . Flanges  40  and  64  have matching circular edges, and shell  36  is fit to those edges.  
         [0029]    The end of armature  92  disposed at the air gap has a shape that is believed beneficial in concentrating flux without saturation to improve the force vs. travel characteristic of the actuator. A frustoconical counterbore  95  is present in the end face of the armature, creating a raised annular rim  97  that bridges much of the distance between the confronting ends of the hubs of the respective pole pieces. Rim  97  is the portion of the armature through which the magnetic flux is conducted between the pole pieces at the air gap and comprises a circular radially outer surface and a frostoconical tapered radially inner surface. Rim  97  has a widening taper in the direction from the tapered wall of hub  38  toward hub  62  of pole piece  34 .  
         [0030]    In the closed position of valve  10 , the preloaded return spring (not shown) is resiliently biasing the valve element to close the flow passage between ports  20  and  22 . That spring forms an element of the internal valve mechanism, functioning via the valve element to resiliently bias armature  92  to an initial position along centerline CL when no current flows in coil  30 .  
         [0031]    As electric current begins to increasingly flow through coil  30 , the magnetic circuit exerts increasing electromagnetic force urging armature  92  in the downward direction as viewed in FIG. 1. Once the force is large enough to overcome the bias of the preload force of the return spring, armature  92  begins to move downward, similarly moving the valve element and opening valve  10  to allow flow between the two ports. The position to which the armature is displaced, and hence the extent to which the valve is allowed to open, is controlled by the electric current in coil  30 . The actual control strategy for the valve is determined as part of the overall engine control strategy embodied in engine control system  26 .  
         [0032]    Solenoid  24 , as described above, endows armature  92  with a longer useful stroke in comparison to certain other valves, as shown by Figure.  
         [0033]    [0033]FIG. 3 is a graph plot showing armature force as a function of armature displacement for two different valves. The graph plot  100  is for valve  12  while the graph plot  102  is for a similar valve that has a solenoid different from solenoid  24  of valve  12 . It is evident that for a given amount of current in the respective coils, valve  12  delivers force that is not only larger, but that is delivered over a larger range of armature displacements. Both plots are characterized by the presence of hysteresis. For the example given, the useful stroke length has been almost doubled, with only about a 12% increase in volume of the actuator.  
         [0034]    It is believed that the improvement provided by the invention arises because the coil is wound directly on tube  88 , instead of being wound on a synthetic bobbin that is assembled to a stator. Such direct winding provides closer coupling of the armature to the stator. Certain features of the stator, such as the various chamfers, avoid saturation in certain portions of the magnetic circuit.  
         [0035]    While the foregoing has described a preferred embodiment of the present invention, it is to be appreciated that the inventive principles may be practiced in any form that falls within the scope of the following claims.