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. The armature is guided within a sleeve and includes a damping ring disposed to act between the armature and the sleeve to damp motion of the armature within the sleeve.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to electric-actuated automotive emission control valves, and more particularly to exhaust gas recirculation (EGR) valves for internal combustion engines that power automotive vehicles. 
     BACKGROUND OF THE INVENTION 
     A solenoid is a known electric actuator for an EGR valve. 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 toward a position that causes the valve member to close the passageway. 
     In a linear solenoid valve, displacement of the armature, and also of the valve member when the valve member is displaced in exact correspondence with the armature, should theoretically bear a relationship of direct proportionality to the electric current in the solenoid coil. In other words, a graph plot of armature displacement versus electric current for such a valve should start at the origin of the graph and extend from the origin at a constant slope. 
     A known linear solenoid EGR valve comprises a stator having an upper stator part that is disposed at an upper end of the coil and a lower stator part at the lower end of the coil. These two parts have respective cylindrical walls, one tapered and the other non-tapered, 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 in a substantially linear relationship of armature displacement to coil current. 
     Where flow through the valve is proportional to armature displacement, the functional relationship of flow to electric coil current is also substantially linear. 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, and such linearity facilitates implementation of the control strategy in a particular engine. 
     For various reasons, such as smaller engines, and use of multiple EGR valves on an engine, certain automotive vehicle manufacturers are seeking to reduce the size of EGR valves, but without sacrificing desired control accuracy. 
     The present invention arises as a consequence of the inventor&#39;s observations about such smaller valves. In particular, the inventor has observed that because such a valve has a smaller mass, its less massive internal mechanism is more likely to be affected by external perturbations that the valve experiences when in use. Examples of such perturbations include: pulsations in the fluid whose flow is being controlled; mechanical vibrations arising from operation of the vehicle and running of the engine that powers the vehicle; and instabilities in control strategies for a valve. 
     Such perturbations may be significant enough to impart disturbances to the valve mechanism in ways that are contrary to intended control strategy. Accordingly, improvements in the solenoid that would attenuate, and ideally eliminate, such effects are believed desirable, and it toward that end that the present invention is directed. 
     SUMMARY OF THE PRESENT INVENTION 
     It is therefore an object of this invention to provide such improvements, particularly in linear solenoid actuators of EGR valves. 
     One general aspect of the invention 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. The armature is guided within a sleeve. A damping ring is disposed to act between the armature and the sleeve to damp motion of the armature within the sleeve. 
     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 an elevation view, substantially in cross section, of an exemplary embodiment of the present invention comprising an electric EGR valve have a solenoid as the actuator. 
     FIG. 2 is an enlarged view of a portion of FIG.  1 . 
     FIG. 3 is a full plan view of one part of the valve shown by itself and looking in the direction of arrows  3 — 3  in FIG.  2 . 
     FIG. 4 is a view like FIG. 4 showing another embodiment of the one part. 
     FIG. 5 is a fragmentary cross section view of a still further embodiment. 
    
    
     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 of a base  22  with a spacer  25  between them. Fasteners (not shown) secure the shell to the base. Base  22  is adapted to mount on a component of an internal combustion engine 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. 
     An annular valve seat element  42  comprising a through-hole is disposed in passage  36  with its outer perimeter sealed to the passage wall. A one-piece valve member  44  comprises a valve head  46  and a valve stem  48  that extends 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 having a circular flange  52  for seating in a counter-bore at one end of a hole that lies on centerline CL. Member serves to guide valve motion along centerline CL by having a close fit with stem  48 . 
     Stem  48  extends, diametrically reduced, beyond the upper end of bearing member  50  where a spring locator member  54  is fit to it to provide a seat for one axial end of a helical coil spring  56 . 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. The opposite axial end of spring  56  seats on an internal shoulder of a lower pole piece  76 . 
     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. The portion of shell  14  between pole pieces  74 ,  76  complete the stator structure exterior of the coil and bobbin. 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  between the cap and shell makes a sealed joint between them. 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 Fig., 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. Valve stem  48  has a sufficiently close sliding fit within bearing member  50  to 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 ferromagnetic and comprises a circular annular ring  118  that girdles and is fit to a central tapered hub  114  that extends from ring  118  into the bobbin core through-hole, but stopping short of hub  110 . An annular wave spring  120  is disposed between ring  118  and bobbin flange  70  for maintaining bobbin flange  68  against flange  112  to compensate for differential thermal expansion. 
     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, or sleeve,  126  that is fit coaxially within hub  110 . 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 . Spring  56  biases a tip end of spring locator member  54  against one side of wall  140  while the plunger of the position sensor housed within tower  104  is biased against the opposite side of wall  140 . 
     FIG. 1 shows the closed position of valve  10  wherein a pre-load force is being applied by spring  56  to force 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. 
     In accordance with principles of the invention, damping is intentionally introduced into actuator  60  to damp armature displacement along centerline CL. A first embodiment is disclosed in FIGS. 2 and 3, and it should be understood that the scale of FIG. 1 does not permit this embodiment to appear conveniently in that Fig. although it is in fact present. The first embodiment comprises a split ring  170  that is fit to a circumferential groove  172  in armature  135 . FIG. 4 shows a second embodiment of split ring. The outer edge of each is essentially circular. The difference between them resides essentially in the shape of the inner edge. The thickness is uniform. Each ring is capable of being circumferentially expanded to fit over the end of armature  135  and be moved along the armature toward groove  172 . Once registration with the groove has been achieved, the ring is released and its inherent elasticity circumferentially contracts it, lodging its inner margin in the groove. The outer margin of the split ring then protrudes outward beyond the outside diameter of the armature. 
     The ring of FIG. 3 has an essentially circular inner edge that is free of lands. Self-centering of the ring of FIG. 4 on the armature is achieved by providing its inner edge with three lands  174  essentially equiangularly spaced. The outer edge of each ring defines a diameter that is less than the inside diameter of sleeve  126  by some amount. Depending on specific design, the outside diameter of ring  170  in its free condition may be slightly greater than the inside diameter of the sleeve, in which case, the outer edge will exert an outwardly directed force against the wall of the sleeve, creating friction. Damping of armature motion due to such friction will be additional to any pneumatic damping created by the presence of ring  170  in the clearance space between the armature and sleeve. A suitable material for split ring  170  is a synthetic material, such as polytetrafluroethylene (PTFE). 
     FIG. 5 shows still another example where ring  170  is a cup having an inner margin lodging in groove  172 . The outer margin forms a curved lip  176  that exhibits a wiping type action against the sleeve wall. 
     The total amount of damping is a function of various factors additional to the inclusion of any of the various embodiments of rings  170 . The invention allows armature damping to range from predominantly friction damping to predominantly pneumatic damping depending on design details. The extent to which a split ring exerts radial force on the sleeve is a major factor in friction damping. The extent to which air is trapped in various spaces whose volumes change as the armature moves is a major factor in pneumatic damping. By making armature wall  140  imperforate, air cannot pass through the armature, only around the armature, in the space between the armature and sleeve, to the extent that air can pass through that space. 
     Armature mass, radial magnetic force, and rate of spring  56  also influence damping. Characteristics of the valve mechanism, such as valve head size and the amount of force-balancing, are also factors. 
     The particular embodiments that have been illustrated in the drawings have a single split ring. In those embodiments, the outer cylindrical surface of armature wall  138  preferably has lubricity to minimize friction with the inner wall of sleeve  126 . Other embodiments not specifically illustrated comprise two split rings that are spaced axially apart along centerline CL. The cooperation of the two split rings with the wall of sleeve  126  provide armature guidance. 
     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.