Abstract:
An automotive emission control valve, such as an EGR valve, has a solenoid for operating a valve element. The solenoid has a stator and an armature. A pole piece of the stator is cooperatively associated with a wall of the armature and comprises a channel that is annular about, and concentric with, a centerline of armature motion. In radial cross section the channel is defined by radially inner and outer walls that form an open throat for the channel, allowing an end portion of the armature wall to move within the channel as the armature is displaced along the centerline. Various constructions for the inner and outer walls are disclosed, including tapers for both walls.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to electric-actuated automotive emission control valves, such as exhaust gas recirculation (EGR) valves, and in particular to a solenoid actuator for such emission control valves. 
     BACKGROUND OF THE INVENTION 
     An EGR valve may comprise a solenoid as an electric actuator. The solenoid 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 member to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature to a position that causes the valve member to close the passageway. 
     A known solenoid-actuated EGR valve comprises a stator having an upper pole piece that is disposed at an upper end of the coil and a lower pole piece at the lower end of the coil. The pole pieces have respective annular walls that fit into the open center of the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two walls are spaced apart within the open interior of the coil, and their construction and arrangement define an annular air gap disposed circumferentially around the armature. Electric current in the coil creates magnetic flux that passes from one wall across the air gap to the armature, through the armature, and back across the air gap to the other wall. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid. Certain changes in coil current will change the magnetic flux spanning the air gap, and possibly also how that flux acts on the armature. Shaping of the interface between each pole piece and the armature is a factor in achieving a desired relationship of armature displacement to coil current. 
     In an EGR valve, knowledge of the relationship of armature displacement to coil current is essential to a control strategy that accurately meters exhaust gas into the engine intake system. 
     Accordingly, improvements in the solenoid that would enable desired response to be achieved are seen to be useful, especially as increasingly strict emission regulations become effective, and smaller amounts of exhaust gas need to be metered with increasing precision. 
     It would also be desirable to provide a basic solenoid construction that can be adapted by designers to create various models of valves possessing desired functional characteristics conforming to various customer specifications. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an object of this invention to provide improvements in solenoid actuators, especially those used in smaller automotive emission control valves such as EGR valves, so that more precise control can be achieved. 
     One general aspect of the invention relates to an mission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises a wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises an inner wall disposed radially inward of the armature wall and an outer wall disposed radially outward of the armature wall. One portion of the air gap flux is conducted from the outer wall to the armature wall, another portion of the air gap flux is conducted from the inner wall to the armature wall, and at least one of the pole piece walls has a radial thickness that changes as a function of its location along the centerline. 
     Another aspect relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises an annular wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises a channel that is annular about, and concentric with, the centerline and that, in radial cross section, has an open throat that faces the armature and is arranged to allow an end portion of the annular wall of the armature to be disposed within the channel for certain displacements of the armature along the centerline. 
     A further aspect of the invention relates to a solenoid actuator that comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises a wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises an inner wall disposed radially inward of the armature wall and an outer wall disposed radially outward of the armature wall. One portion of the air gap flux is conducted from the outer wall to the armature wall, another portion of the air gap flux is conducted from the inner wall to the armature wall, and at least one of the pole piece walls has a radial thickness that changes as a function of its location along the centerline. 
     A still further aspect relates to a solenoid actuator that comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux and that comprises an annular wall spaced radially from the centerline. The stator comprises a pole piece that is cooperatively associated with the armature wall and that comprises a channel that is annular about, and concentric with, the centerline and that, in radial cross section, has an open throat that faces the armature and is arranged to allow an end portion of the annular wall of the armature to be disposed within the channel for certain displacements of the armature along the centerline. 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments 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 
     FIG. 1 is a cross section view, in elevation, of an exemplary embodiment of the present invention comprising an emission control valve including a solenoid actuator. 
     FIG. 2 is a half-section view of a pole piece of the solenoid of FIG. 1 shown by itself. 
     FIGS. 3,  4 , and  5  are respective half-section views of other embodiments of the pole piece. 
     FIG. 6 is graph plot illustrating representative characteristic traces of force vs. armature displacement for solenoids embodying the various pole pieces. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an exemplary EEGR valve  10  that comprises a housing assembly  12  provided by a shell  14  having an open upper end that is closed by a cap  16 . Shell  14  further comprises a flat bottom wall  18  that is disposed atop a flat upper surface  20  of a base  22  with an spacer  25  between them. Fasteners  23  secure the shell to the base. Base  22  comprises a flat bottom surface  24  that is adapted to mount on a flat mounting surface of a component of an internal combustion, such as a manifold not specifically shown in the drawing. 
     Valve  10  comprises a flow passage  36  extending through base  22  between an inlet port  38  and an outlet port  40 . With valve  10  mounted on the engine, inlet port  38  is placed in communication with engine exhaust gas expelled from the engine cylinders and outlet port  40  is placed in communication with the intake flow into the cylinders. 
     A valve seat element  42  is disposed in passage  36  proximate inlet port  38  with the outer perimeter of the seat element sealed to the passage wall. Valve seat  42  has an annular shape comprising a through-hole. A one-piece valve member  44  comprises a valve head  46  and a valve stem  48  extending co-axially from head  46  along an imaginary centerline CL of the valve. Head  46  is shaped for cooperation with seat element  42  to close the through-hole in the seat element when valve  10  is in closed position shown in FIG.  1 . 
     Valve  10  further comprises a bearing member  50  that is basically a circular cylindrical member except for a circular flange  52  at its lower end. An upper rim flange of a multi-shouldered deflector member  53  is axially captured between flange  52  and a shoulder  54  of base  22 . Deflector member  53  is a metal part having a clearance hole for stem  48  and a shape that does not restrict exhaust gas flow through passage  36 , but at least to some extent deflects the gas away from stem  48  and bearing member  50 . 
     Bearing member  50  further comprises a central circular through-hole, or through-bore,  56  with which stem  48  has a close sliding fit. Bearing member  50  may comprise a material that possesses some degree of lubricity providing for low-friction guidance of valve member  44  along centerline CL. 
     Valve  10  further comprises an electromagnetic actuator  60 , namely a solenoid, disposed within shell  14  coaxial with centerline CL. Actuator  60  comprises an electromagnetic coil  62  and a polymeric bobbin  64 . Bobbin  64  comprises a central tubular core  66  and flanges  68 ,  70  at opposite ends of core  66 . Coil  62  comprises a length of magnet wire wound around core  66  between flanges  68 ,  70 . Respective terminations of the magnet wire are joined to respective electric terminals mounted side-by-side on flange  68 , only one terminal  72  appearing in the view of FIG.  1 . 
     Actuator  60  comprises stator structure associated with coil  62  to form a portion of a magnetic circuit path. The stator structure comprises an upper pole piece  74 , disposed at one end of the actuator coaxial with centerline CL, and a lower pole piece  76  disposed at the opposite end of the actuator coaxial with centerline CL. Shell  14  comprises a side wall  78 , a portion of which extends between pole pieces  74 ,  76  to complete the stator structure exterior of the coil and bobbin. 
     An annular air circulation space  80  is provided within shell  14  axially below actuator  60 . This air space is open to the exterior by several air circulation apertures, or through-openings,  82  extending through shell  14 . The shell side wall has a lower ledge  86  on which the outer margin of lower pole piece  76  rests and an upper ledge  88  on which the outer margin of upper pole piece  74  rests. Cap  16  comprises an outer margin that is held secure against a rim  92  at the otherwise open end of the shell side wall by a clinch ring  94 . A circular seal  96  is disposed between the cap and shell to make a sealed joint between them. 
     The radial dimension of shell  14  holds upper pole piece  74  in its axially placed position against ledge  86 . Cap  16  comprises a first pair of electric terminals, only one terminal  100  appearing in FIG. 1, that mate respectively with the terminals on bobbin flange  68 . The cap terminals protrude externally from the cap material where they are bounded by a surround  102  of the cap material to form a connector adapted for mating connection with a wiring harness connector (not shown) for connecting the actuator to an electric control circuit. 
     Cap  16  also comprises a tower  104  providing an internal space for a position sensor that comprises plural electric terminals, only one terminal  106  appearing in the Figure, that protrude into the surround for connecting the sensor with a circuit via the mating wiring harness connector. 
     The construction of valve  10  is such that leakage between passage  36  and air circulation space  80  is prevented. Bearing member through-hole  56  is open to passage  36 , but valve stem  48  has a sufficiently close sliding fit therein to substantially occlude the through-hole and prevent leakage between passage  36  and air circulation space  80  while providing low-friction guidance of the stem along centerline CL. 
     Upper pole piece  74  is a ferromagnetic part that comprises a central, cylindrical-walled, axially-extending hub  110  and a circular radial flange  112  at one end of hub  110 . Hub  110  is disposed co-axially within the upper end of a circular through-hole in bobbin core  66  concentric with centerline CL, and flange  112  is disposed against bobbin flange  68 , thereby axially and radially relating bobbin  64  and upper pole piece  74 . Flange  112  has a clearance slot for bobbin terminals  72 . 
     Lower pole piece  76  is a ferromagnetic part comprising a circular flange  118  that girdles a central hub that has an upper hub portion  114 U extending from flange  118  into the bobbin core through-hole, but stopping short of hub  110  and a lower hub portion  114 L extending in the opposite direction. An annular wave spring  120  is disposed between flange  118  and bobbin flange  70  for maintaining bobbin flange  68  against flange  112  to compensate for differential thermal expansion. 
     As shown in FIG. 2, upper hub portion  114 U comprises a radially outer annular wall  130  and a radially inner annular wall  132  both of which are concentric with centerline CL. In radial cross section, walls  130  and  132  cooperatively define an integral channel  134  in lower pole piece  76 . Channel  134  is annular about, and concentric with, centerline CL, and in radial cross section, has an upwardly open throat. Wall  130  comprises a radially outer face  130 A that has a frustoconical taper about centerline CL and a radially inner face  130 B that is parallel with centerline CL. Wall  132  comprises a radially inner face  132 A that has a frustoconical taper about centerline CL and a radially outer face  132 B that is parallel with centerline CL. This gives channel  134  a cross section that is rectangular in shape. 
     Actuator  60  further comprises a ferromagnetic armature  135  arranged for displacement along centerline CL. Armature displacement is guided in any suitable way, such as by a cylindrical non-ferromagnetic part  126  that axially spans the space between the two pole pieces concentric with centerline CL. Armature  135  cooperates with the stator structure in forming the magnetic circuit of actuator  60 . 
     Armature  135  comprises a circular cylindrical outer wall  138  of suitable radial thickness for the magnetic flux that it conducts. Midway between its opposite ends armature  135  has a transverse wall  140  that serves to provide a point for operative connection of stem  48  to the armature such that motion of the armature along centerline CL is transmitted through stem  48  to position valve head  44  relative to seat element  42 , thereby setting the extent to which valve element  44  allows flow through passage  36 . The nature of the armature/stem connection compensates for any slight non-concentricity between bearing member  50  and part  126  such that force transmitted from the armature to the stem, and vice versa, is essentially exclusively along centerline CL rather than having a radial component that might undesirably affect the transmission of motion from one to the other. Wall  140  also provides a means for transmitting armature motion to the position sensor housed within tower  104 . 
     The lower pole piece hub comprises a circular through-hole that is concentric with centerline CL and that has an internal shoulder  152 . Shoulder  152  enables pole piece  76  to provide a spring seat for one end of a helical coil spring  154  whose other end seats on armature wall  140 . The spring acts on armature  135  and valve element  44  to bias valve head  46  toward seating closed on seat element  42 . 
     FIG. 1 shows the closed position of valve  10  wherein spring  154  is pre-loaded, forcing valve head  46  to seat on seat element  42 , closing passage  36  to flow between ports  38  and  40 . As electric current begins to increasingly flow through coil  62 , the magnetic circuit exerts increasing force urging armature  135  in the downward direction as viewed in FIG.  1 . Once the force is large enough to overcome the bias of the pre-load force of spring  154 , armature  135  begins to move downward, similarly moving valve element  44  and opening valve  10  to allow flow through passage  36  between the two ports. The extent to which the valve is allowed to open is controlled by the electric current in coil  62 , and by tracking the extent of valve motion, the position sensor can provide a feedback signal representing valve position, and hence the extent of valve opening. The actual control strategy for the valve is determined as part of the overall engine control strategy embodied by an associated electronic engine control. One or more through-holes  142  that extend through wall  140  provide for the equalization of air pressure at opposite axial ends of the armature. 
     In accordance with principles of the invention, the lower end portion of armature wall  138  cooperatively associates with channel  134 . The juxtaposed faces  130 B,  132 B of the two walls  130 ,  132  are spaced apart sufficiently to allow armature wall  138  to be disposed between them. With actuator  60  not electrically energized, wall  138  just slightly enters channel  134 . As actuator  60  is increasingly energized to increasingly displace armature  135  downward and open the valve, wall  138  increasingly enters channel  134 . Part  126  extends into channel  134  to assure magnetic separation of the radially outer face of wall  138  from face  130 B, and the radial thickness of wall  138  is small enough to assure that its radially inner face does not short out against face  132 B. 
     The shapes of walls  130 ,  132  determine the pattern of magnetic flux passing across the interface between wall  138  and pole piece  76  and hence functionally relates the magnetic force acting on armature  135  to the electric current in coil  62 . At least one of the walls  130 ,  132  that has a radial thickness that changes as a function of its location along centerline CL. In the particular embodiment shown in FIGS. 1 and 2, both walls have linear tapers that cause the radial thickness of each wall to progressively decrease along centerline CL in the direction of upper pole piece  74 . This makes the pole piece bi-conical. In radial cross section, each wall appears as the mirror image of the other. Linear taper is imparted to wall  130  by making face  130 A frustoconical to centerline CL while face  130 B is parallel to centerline CL. Linear taper is imparted to wall  132  by making face  132 A frustoconical to centerline CL while face  130 B is parallel to centerline CL. 
     By providing one pole piece with two walls for conducting magnetic flux to inner and outer faces of the armature wall concurrent with the ability to shape each wall independent of the other, it is believed that solenoid and valve designers will have the ability to create many different force vs. displacement characteristics in solenoids and valves. Some examples that are considered possible are shown by the traces in the graph plot of FIG.  6 . 
     Each trace plots armature force as a function of armature displacement for a constant current in coil  62 . Zero armature displacement represents the closed position of the valve. Positive armature displacements open the valve while negative armature displacements are plotted for reference. The legend accompanying the plot correlates each trace with a particular pole piece. Trace A is a characteristic for a solenoid having a lower pole piece like the one that has been described in FIGS.  1  and  2 . Trace B is a characteristic for a solenoid having a lower pole piece like the one shown in FIG.  3 . Trace C is a characteristic for a solenoid having a lower pole piece like the one shown in FIG.  4 . Trace D is a characteristic for a solenoid having a lower pole piece like the one shown in FIG.  5 . 
     In each FIGS. 3,  4 , and  5 , the same reference numerals as in FIGS. 1 and 2 mark the same walls and faces. 
     The pole piece of FIG. 3 differs from that of FIG. 2 in that walls  130 ,  132  are narrower, i.e. more sharply tapered, and the extension of face  132 A to shoulder  152  is tapered. 
     The pole piece of FIG. 4 has a wall  130  like that of FIG. 2 but its wall  132  is shorter. The extension of face  132 A to shoulder  152  is tapered. 
     In the pole piece of FIG. 5, wall  132  is provided by a separate ferromagnetic part  160  that is fit to the part containing wall  130 . 
     Trace E represents a characteristic for a solenoid having a pole piece like that of FIG. 3, but with an even sharper taper. Trace F represents a characteristic for a solenoid having a pole piece like that of FIG. 4, but with an even shorter inner wall. Trace G represents a characteristic for a solenoid having a pole piece like that of FIG. 5, but with a smaller thickness. Trace H represents a baseline reference where the valve solenoid comprises a lower pole piece having a single tapered wall. 
     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.