Patent Publication Number: US-7213586-B2

Title: Exhaust gas recirculation valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The instant application claims priority to U.S. Provisional Patent Application Ser. No. 60/600,844, filed Aug. 12, 2004, the entire specification of which is expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to exhaust gas recirculation valves, and more particularly to exhaust gas recirculation valve systems that include an anti-stick medium applied to either the valve poppet surface and/or the valve seat surface. 
     BACKGROUND OF THE INVENTION 
     Current Federal and State legislation generally requires control of vehicle exhaust emissions. Oxides of Nitrogen (“NOx”) are one of the exhaust gas emissions that must be controlled. Formation of NOx typically occurs at higher combustion temperatures. A system, generally referred to as the exhaust gas recirculation (“EGR”) system, has been developed to reduce peak combustion temperatures that reduce NOx emissions. An illustrative schematic of this system is generally shown in  FIG. 1 . 
     In this type of system, a portion of the exhaust gas is recirculated back to the intake manifold where it is combined with incoming charged air. When this mixture is compressed and ignited in the cylinder, the result is a lower combustion temperature and a reduction in NOx. The system typically consists of an EGR valve ( 1 ) that controls the flow of exhaust gas to the intake manifold. Conduits ( 2 ), ( 3 ), and ( 4 ) provide the interconnection between the exhaust manifold ( 5 ), EGR valve ( 1 ), and intake manifold ( 6 ). The system shown uses an electrically controlled EGR valve. An engine control unit (“ECU”) ( 7 ) provides a signal that controls the open and/or closing of the valve. As the EGR valve ( 1 ) opens and closes, it will increase or decrease the flow rate of exhaust gas to the intake manifold ( 6 ). It is also typical to have a throttle valve ( 8 ) to control airflow into the intake manifold and, an exhaust gas cooler ( 9 ) to reduce temperature of recirculated exhaust gas. 
     The required EGR flow rate is dependent upon several factors that include the displacement of the engine and the pressure differential between the exhaust and the intake system. EGR valves may be actuated by pneumatic or electric means. Pneumatically actuated valves depend upon the availability of pressure or vacuum on the vehicle and this may be an undesirable requirement. They also require a means of electrically controlling the pneumatic source to allow overall electrical control of the system. An electric vacuum or pressure regulator is use to provide this control. 
     Operating force is another factor used in the selection criteria for the type of actuator used for the EGR valve. Higher flow rates require larger valves with greater area and higher operating forces. Lower pressure differential between the exhaust and intake manifold will require larger valves to achieve the desired flow rate. Components in the exhaust gas can accumulate on the valve components and cause them to stick or restrict movement if sufficient operating force is not available. 
     Referring to  FIG. 2 , a conventional EGR valve typically includes an actuator/valve assembly ( 10 ) and a valve base assembly ( 20 ). The EGR valve is typically mounted by fastening the valve body ( 20 A) of the valve body assembly ( 20 ) to the intake manifold of the engine. A gasket is typically used as a seal to prevent leakage of exhaust gas to the environment. A valve poppet ( 30 ) is installed and retained on a valve stem ( 40 ) by any number of suitable methods, such as but not limited to radial riveting. The poppet valve ( 30 ) can be keyed to the shaft in a manner that will cause it to rotate with the shaft. 
     Still referring to  FIG. 2 , the valve base assembly ( 20 ) typically includes a valve seat ( 50 ) that is secured by suitable methods such as but not limited to press fit and/or staking. The actuator/valve assembly ( 10 ) and the valve body assembly ( 20 ) are combined to form the EGR valve. Fasteners ( 55 ) are used to secure the two assemblies together. Suitable locating features, in the actuator/valve assembly ( 10 ) and valve body assembly ( 20 ), are used to align the valve poppet ( 30 ) and valve seat ( 50 ) such that suitable sealing is provided when the valve poppet ( 30 ) is seated on the valve seat ( 50 ). 
     Referring to  FIGS. 2 and 3 , the EGR valve typically operates in the following manner. The ECU applies an electrical control signal to the actuator/valve assembly ( 10 ) that causes the valve poppet ( 30 ) to lift off of the valve seat ( 50 ). When there is a sufficient pressure differential between the inlet and outlet, the exhaust gas will flow through the EGR valve. The exhaust gas will flow from the inlet ( 60 ), into the chamber ( 70 ), through the valve seat ( 50 ), by the valve poppet ( 30 ), into the cavity ( 80 ), and to outlet ( 90 ). It should be appreciated the EGR system shown employs an EGR cooler that is operable to cool the exhaust gas prior to the exhaust gas reaching the EGR valve. 
     Components in the exhaust gas can accumulate on the valve components and cause them to stick or restrict movement if sufficient operating force is not available. By way of a non-limiting example, during normal operation of diesel engines, especially those employing cooled EGR systems, the EGR valve poppet often becomes stuck to the valve seat in the closed position, due to excessive build up of various exhaust gas components, which renders the valve inoperable. 
     More specifically, certain EGR systems that run with cooled exhaust gas (e.g., cooled or cold side EGR systems) may have a tendency to produce a moist vapor like (e.g., lacquer) material, until the engine warms up, which builds up on the valve poppet ( 30 ) and valve seat ( 50 ) as exhaust gas flows past them, as previously described. This material could combine with a powdery (e.g., soot) type of contamination that is present in the exhaust gas at elevated exhaust gas temperatures (e.g., greater than 140° C.). When the EGR valve is commanded to the closed position, the lacquer, soot or a combination of the two, starts to harden and causes a “bond” to be formed between the valve seat and poppet. This often happens after then engine is shut down for a time duration of about 20 minutes or greater. When the engine is started again, and the EGR valve is commanded to open, the “bond” that has formed prevents the EGR valve from opening when there is insufficient force and or torque available from the EGR valve to overcome the bonded sticking force. 
     Accordingly, there exists a need for new and improved EGR valve systems that are able to avoid sticking and/or bonding of the various surfaces of the components thereof, especially the valve poppet and valve seat surfaces. 
     SUMMARY OF THE INVENTION 
     In accordance with the general, teachings of the present invention, new and improved EGR valve systems are provided. 
     The EGR valve systems of the present invention preferably include an anti-stick medium that is applied to either a surface of a valve poppet and/or a surface of a valve seat of the EGR valve system. By “anti-stick medium,” as that phrase is used herein, it is meant any material that will resist and/or prevent the accumulation of lacquer, soot, lacquer-like, or soot-like material on either the surface of the valve poppet and/or the surface of the valve seat of the EGR valve system. By “lacquer,” “soot,” “lacquer-like,” or “soot-like” material, as those terms and/or phrases are used herein, it is meant any solid (e.g., particulate), fluid (e.g., liquids, gases, or the like) and/or condensable material that is capable of sticking, bonding, or otherwise adhering, either permanently and/or non-permanently, to either the surface of the valve poppet and/or the surface of the valve seat of the EGR valve system. 
     In accordance with a first embodiment of the present invention, a mechanical system is provided, comprising: (1) a first member; (2) a second member, wherein the first member is selectively operable to contact the second member; and (3) an anti-stick medium disposed on an external surface of either the first or second members, wherein the anti-stick medium is operable to substantially prevent material contained in a fluid from adhering to the external surface of either the first or second members, wherein the anti-stick medium is comprised of a material selected from the group consisting of boron nitride, thin dense chrome plating, perfluoralkoxy, and combination thereof. 
     In accordance with a second embodiment of the present invention, a mechanical system is provided, comprising: (1) a first member; (2) a second member, wherein the first member is selectively operable to contact the second member; and (3) an anti-stick medium disposed on an external surface of either the first or second members, wherein if the first and second members become at least partially stuck to one another, at least a portion of the anti-stick medium is operable to breakaway from itself so as to permit the first and second members to become unstuck from one another. 
     In accordance with a third embodiment of the present invention, an exhaust gas recirculation valve system is provided, comprising: (1) a valve member; (2) a valve seat member, wherein the valve member is selectively operable to contact the valve seat member; and (3) an anti-stick medium disposed on a surface of either the valve member and/or the valve seat member, wherein the anti-stick medium is comprised of a material selected from the group consisting of boron nitride, thin dense chrome plating, perfluoralkoxy, and combination thereof. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of a conventional EGR valve system, in accordance with the prior art; 
         FIG. 2  is a partial sectional view of a conventional EGR valve design, in accordance with the prior art; 
         FIG. 3  is a partial sectional view of a valve poppet and valve seat, in the closed position, of a conventional EGR valve design, in accordance with the prior art; 
         FIG. 4  is a partial sectional view of an EGR valve system, wherein an anti-stick medium has been applied to the valve poppet surface and the valve seat surface, in accordance with a first embodiment of the present invention; 
         FIG. 5  is a perspective view of a valve poppet having a boron nitride-based anti-stick medium applied to a surface thereof, in accordance with a first alternative embodiment of the present invention; 
         FIG. 6  is a perspective view of a valve poppet having a thin dense chrome plating anti-stick medium applied to a surface thereof, in accordance with a second alternative embodiment of the present invention; 
         FIG. 7  is a perspective view of a valve seat having a thin dense chrome plating anti-stick medium applied to a surface thereof, in accordance with a third alternative embodiment of the present invention; 
         FIG. 8  is a sectional view of a valve system having an anti-stick medium applied to various surfaces thereof, in accordance with a fourth alternative embodiment of the present invention; 
         FIG. 9  is a sectional view of a turbocharger system having an anti-stick medium applied to various surfaces thereof, in accordance with a fifth alternative embodiment of the present invention; 
         FIG. 10  is a sectional view of a gasoline engine solenoid EGR valve system having an anti-stick medium applied to various surfaces thereof, in accordance with a sixth alternative embodiment of the present invention; and 
         FIG. 11  is a graphical view comparing the performance characteristics of EGR valve systems with and without anti-stick mediums applied to various surfaces thereof, in accordance with a seventh alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     In accordance with the general teachings of the present invention, an anti-stick medium is applied to an external surface of a member that contacts, regardless of orientation, action, or purpose, another member. The intended function of the anti-stick medium is to prevent the adherence, accumulation, bonding, and/or sticking of any contaminants (e.g., lacquer) or other undesirable materials contained or entrained in a fluid (e.g., exhaust gas) on the surfaces that have been coated with the anti-stick medium. 
     By way of a non-limiting example, an EGR valve system is provided, wherein an anti-stick medium is applied to the EGR valve components such as, but not limited to: (a) the valve (e.g., a poppet); (b) the valve seat; or (c) the valve and valve seat together. The present invention is particularly suitable for use with cooled or cold side EGR valve systems. However, it should be appreciated that the present invention can also be practiced with heated or hot side EGR valve systems, as well as any other type of valve system wherein accumulation of contaminants or other material on the components thereof is not desired. 
     In accordance with a preferred embodiment of the present invention, an anti-stick medium is applied to the EGR valve components such as, but not limited to: (a) the valve (e.g., poppet); (b) the valve seat; or (c) the valve and valve seat together. By way of a non-limiting example, the anti-stick medium of the present invention can be applied to all or substantially the entire exposed surfaces of the valve and/or valve seat, but can also be applied in a discontinuous pattern as well (e.g., dots, circles, ovals, stripes, chevrons, squares, rectangles, or the like). In accordance with a preferred embodiment, the anti-stick medium is preferably applied to the areas corresponding to the mating surfaces of the valve, valve seat, and combinations thereof, as well as areas adjacent thereto. The exact pattern and/or depth of the medium layer will vary, in part, depending on choice of medium type, application requirements, and/or cost considerations. 
     The anti-stick medium of the present invention can comprise, without limitation, compositions containing boron nitride, thin dense chrome plating, perfluoralkoxy (PFA), and combination thereof. The anti-stick medium of the present invention preferably impedes, hinders or otherwise prevents the sticking, bonding, adherence, or adhesion of the exhaust gas components to the EGR valve components, especially the valve poppet surface and/or the valve seat surface. In accordance with a preferred embodiment of the present invention, the anti-stick medium can be applied as an aerosol, grease, paint, coating, plating, and combinations thereof. 
     The thin dense chrome plating is readily commercially available from Electro-Coatings, Inc. (Berkeley, Calif.) under the trade name ELECTRALLOY. The nickel boron nitride coating is readily commercially available from Endura Coatings, Inc. (Warren, Mich.) under the trade name ENDURA 225. The aerosol-based boron nitride spray is readily commercially available from GE Advanced Ceramics, Inc. (Cleveland, Ohio). The boron nitride grease is readily commercially available from Lubrication Technology, Inc. (Jackson, Ohio) under the trade name CHRISTO-LUBE MCG 132 BN. The water-based boron nitride coating is readily commercially available from GE Advanced Ceramics, Inc. (Cleveland, Ohio). Additionally, ethanol-based boron nitride coating may be used in the practice of the present invention. The ethanol-based boron nitride coating is readily commercially available from Wacker Ceramics, Inc. (Munich, Germany) under the trade name EKAMOLD. The PFA is readily commercially available from the Huni Company (Friedrichshafen, Germany) under the trade name PROCO-PFA. 
     The preferred method of application of the anti-stick medium to the EGR valve components can be, but is not limited to: (a) spraying; (b) dipping; (c) brushing; (d) plating; (e) primer coating with top coating; (f) electrochemical deposition; and/or (g) autocatalytic plating w/submicron sized lubricant particle dispersion. The application can be done on the separate components in a stand-alone setting or, alternatively, can be done once the components are assembled together, either completely or partially. The anti-stick medium can either be allowed to air dry, or alternatively, can be cured with the application of heat, depending on the material chosen and in accordance with the manufacturer&#39;s suggestions. 
     The EGR valve components also may be made from a lower grade of steel due to the anti-stick medium&#39;s anti-corrosion properties, which gives the potential for product cost savings. 
     Referring to  FIGS. 4–7 , there are shown various views wherein an anti-stick medium  100  has been applied to the surface of both the valve (e.g., poppet)  130  and the valve seat  150  (e.g.,  FIG. 4 ) of an EGR valve system  200 , in accordance with a first embodiment of the present invention, the valve  300 ,  400 , respectively, only with various anti-stick mediums, such as boron nitride-based materials  302  or thin dense chrome plating  402 , respectively, (e.g.,  FIGS. 5–6 ), in accordance with first and second alternative embodiments of the present invention, or the valve seat  500  only with various anti-stick mediums, such as thin dense chrome plating  502  (e.g.,  FIG. 7 ), in accordance with a third alternative embodiment of the present invention. 
     It should be appreciated that the anti-stick mediums of the present invention can be applied to any type of contacting member, sealing member, and/or the like, in any number of applications other than for use with EGR valve systems. That is, the anti-stick mediums can be applied to any type of surface of any type of member that is intended to contact another member, especially where the problem of sticking between the members exists or can develop over time. For example, instead of the members contacting one another to provide a sealing function, the members can be rotationally engaged to one another, slidingly engaged to one another, and/or the like. 
     With respect to valve systems, the anti-stick medium of the present invention can be applied to various surfaces of butterfly valves, rotary discs, vanes, balls, drums, and/or other systems and/or components thereof. 
     Referring to  FIG. 8 , there is shown a valve system  600  including a valve stem  602  having an outer diameter  604  and a valve stem bushing  606  having an inner diameter  608  enveloping the outer diameter  604  of the valve stem  602 , in accordance with a fourth alternative embodiment of the present invention. By way of a non-limiting example, the anti-stick medium  610  of the present invention can be disposed on either the outer diameter  604  and/or the inner diameter  608 . The anti-stick medium  610  can be comprised of any of the materials previously described, e.g., boron nitride, thin dense chrome plating, perfluoralkoxy (PFA), and combination thereof. 
     Referring to  FIG. 9 , there is shown a turbocharger system  700  including a shaft member  702  having an outer diameter  704  engaged with a bearing member  706  having an inner diameter  708  enveloping the outer diameter  704  of the shaft member  702 , in accordance with a fifth alternative embodiment of the present invention. By way of a non-limiting example, the anti-stick medium  710  of the present invention can be disposed on either the outer diameter  704  and/or the inner diameter  708 . The anti-stick medium  710  can be comprised of any of the materials previously described, e.g., boron nitride, thin dense chrome plating, perfluoralkoxy (PFA), and combination thereof. 
     Referring to  FIG. 10 , there is shown a gasoline engine solenoid EGR valve system  800  including a valve stem member  802  having an outer diameter  804  engaged with a valve stem bushing member  806  having an inner diameter  808  enveloping the outer diameter  804  of the valve stem member  802 , and also engaged to a valve seat member  810  having an external surface  812 , in accordance with a sixth alternative embodiment of the present invention. By way of a non-limiting example, the anti-stick medium  814  of the present invention can be disposed on the outer diameter  804 , the inner diameter  808 , and/or the external surface  812 . The anti-stick medium  810  can be comprised of any of the materials previously described, e.g., boron nitride, thin dense chrome plating, perfluoralkoxy (PFA), and combination thereof. It should be appreciated that the anti-stick medium of the present invention can be used in vehicles employing diesel engines or gasoline engines, as well as hybrid vehicles employing one of these types of engine designs. 
     Referring to  FIG. 11 , there is shown a graphical comparison of the performance characteristics of EGR valve systems with and without anti-stick mediums applied to various surfaces thereof, in accordance with a seventh alternative embodiment of the present invention. As  FIG. 11  illustrates, those EGR valve systems that did not include an anti-stick medium disposed on the valve poppet, valve seat, or combination thereof, failed after a relatively short operational duration as compared to those EGR valve systems there were provided with an anti-stick medium in accordance with the general teachings of the present. 
     In accordance with another aspect of the present invention, if contaminants, such as exhaust gas components, actually do stick to the anti-stick medium of the present invention, it will greatly reduce the breakaway force required by one member to free it from the second member, i.e., should they become stuck to one another. For example, the breakaway force required by an actuator will be reduced to within the actuator&#39;s normal operating force range, thus allowing the two members to be pulled apart, thus allowing the valve to return to its normal intended functional characteristics. 
     Without being bound to a particular theory of the operation of the present invention, it is believed that the sacrificial nature of the anti-stick medium may be responsible for this breakaway feature. By way of a non-limiting example, the mechanical system&#39;s motion, whether it be linear (i.e., up and down), rotary, sheering and/or the like, can possibly remove small layers of the anti-stick medium when stuck together due, in part, to the relatively weaker bonds in the anti-stick medium as compared to the bonds between the contaminants themselves, e.g., the exhaust gas lacquer material. In this manner, the anti-stick medium can fracture, flake, chip, or otherwise break apart, from itself or from an adjacent anti-stick medium, thus freeing the previously stuck together members to resume their normal motion and function. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.