Patent Publication Number: US-5020505-A

Title: Exhaust gas recirculation valve assembly

Description:
This is a continuation of application Ser. No. 07/435924 filed on Nov. 13, 1989, now U.S. Pat. No. 4,961,413. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an EGR valve having a valve stem bearing and coupling configuration which eliminates friction and binding caused by side-to-side loading in the bearing area. 
     2. Description of the Relevant Art 
     Typical Exhaust Gas Recirculation (EGR) valves are used to control exhaust gas recirculation in an internal combustion engine. The EGR valve generally comprises a valve, positioned by an actuator to meter the exhaust gas which passes through the valve. The actuator retracts the valve from a seat to increase recirculation of exhaust gas, and advances the valve toward the seat to reduce recirculation of gas. The seat is incorporated in a base that mounts the valve on the engine manifold. 
     Alignment of the valve and the valve seat is critical. Misalignment between the two components will create a path for gas leakage to the engine when not desired, cause exhaust gas flow variability, and result in wear of the valve and seat. To achieve accurate alignment, it is desirable to maintain the valve stem in precise, coaxial alignment with the valve seat through the use of a precision valve stem bearing. However, such precise mounting is difficult to achieve because of the tendency for friction between the bearing and stem, caused by side-to-side loading of the stem by the actuator, to cause binding of the shaft in the bearing. This side-to-side loading is generally a result of misalignment between the valve stem and the actuator which is rigidly attached to the stem and not aligned coaxially with the valve seat. Actuator alignment is very difficult to maintain due to the many components involved. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an EGR valve for use in controlling the recirculation of exhaust gas in an internal combustion engine is disclosed which incorporates a novel bearing for precise positioning of a valve stem therein, and a valve stem support assembly for mounting the stem to an actuator. The bearing and the valve stem support assembly are applicable individually or jointly to an EGR valve to improve the performance thereof. The EGR valve comprises a base having an exhaust chamber formed therein with inlet and outlet openings, and a valve seat surrounding one of the openings. 
     A bearing member comprises a lower bearing portion, a bearing extension projecting outwardly therefrom, and an upper bearing portion supported by the extension in parallel, spaced relationship to the lower portion. Apertures formed in the bearing portions act to support a valve stem extending outwardly from the exhaust chamber. 
     A valve is mounted adjacent the valve seat and has a valve stem which extends out of the base through the openings in the bearing portion. The bearing assures precise alignment of the valve with the valve seat. 
     The end of the valve stem remote from the valve has a stepped area for coupling an actuator thereto. The actuator, which operates the valve relative to the valve seat, is rigidly mounted in a spaced relationship to the base. An armature core, having a hollow center, is disposed for reciprocal motion within the actuator. The armature has a laterally extending web portion formed therein having an axially extending aperture through which the remote end of the valve stem extends, and to which it is mounted. The aperture has a diameter larger than that of the valve stem to allow for lateral movement between the stem and the armature. 
     A valve stem supporting assembly comprising a lower support disc and an upper support disc, mounts the remote end of the valve stem to the armature web portion. The lower disc slides over the end of the stem and rests between a valve stem shoulder, formed between the first stepped portion and the stem, and the lower face of the armature web. The upper disc slides over and is secured to the end of the stem, to rest against the shoulder formed between the second stepped portion and the first, in a face-to-face relationship with the top face of the armature web. As a result, the valve stem is held in engagement with the armature web by the supporting assembly which allows the stem and armature to move laterally with respect to one another but with relative vertical movement restricted due to the action of the upper and lower supporting discs. 
     A valve position sensor is mounted to the top of the actuator housing and has a follower which moves with the armature to determine valve position. A valve return spring is incorporated into the sensor and acts to return the valve to a closed position when the actuator is not in operation. 
     The present invention provides an exhaust gas recirculation valve assembly having a bearing capable of precise positioning of the valve relative to the valve seat. 
     Additionally, a mounting assembly is provided which allows lateral movement between the valve stem and the actuator thereby preventing side-to-side loading and resultant binding of the valve stem within the bearing caused by imperfect alignment of the actuator with the valve stem. 
     Other objects and features of the invention will become apparent by reference to the following description and to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an exhaust gas recirculation valve assembly embodying the present invention; and 
     FIG. 2 is an exploded, perspective view of a portion of the exhaust gas recirculation valve assembly of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 there is shown an exhaust gas recirculation valve assembly, designated generally as 10, useful for controlling the recirculation of exhaust gas in an internal combustion engine. The assembly 10 comprises a base 12, shown in detail in FIG. 2, having upper and lower surfaces, 14 and 16 respectively. An exhaust chamber 18 is formed in base 12, with an inlet opening 20 and an outlet opening 22 disposed therein. A valve seat 24 surrounds exhaust opening 22, although, in an alternate embodiment the valve seat may be placed about inlet opening 20. A bearing recess 26 and bearing alignment surface 26a are formed in base 12, generally in alignment with valve seat 24. In order that valve seat 24, the bearing recess 26, and the alignment surface 26a are accurately aligned with respect to each other, it is preferred that the base 12 be constructed as a one piece, powder metal part with the outlet opening 22, the valve seat 24, the bearing recess 26, and the bearing alignment surface 26a formed in the same powder metal tooling. Such a construction technique eliminates misalignment between the valve seat 24, the bearing recess 26, and the bearing alignment surface 26a which would occur if these features were machined in separate operations. 
     A cover assembly 27, comprising cover 28 and gasket 29 closes exhaust chamber 18. The cover assembly 27 has an opening 30 extending therethrough, in general alignment with valve seat 24, and one or more support spacers 32 extends outwardly therefrom. The spacers provide support for an actuator 68, described in further detail below. 
     A valve assembly 34 is disposed within base 12. The valve assembly 34 comprises a valve member 36 mounted adjacent valve seat 24, and a valve stem 38 having a first end 40 from which valve member 36 extends, a central portion 42, extending outwardly from exhaust chamber 18 through opening 30 in cover assembly 27, and a second end 44 for engagement with actuator 68. Second end 44 is stepped, with a first, reduced diameter portion 46 extending axially from second end 44 to terminate at shoulder 48, and a second reduced diameter portion 50, having a diameter less than that of the first reduced portion 46, which is adjacent to and extends axially from second end 44 a distance less than the first reduced portion to terminate at shoulder 52. 
     A one piece bearing 54 aligns valve member 36 with valve seat 24. The bearing 54 comprises a lower bearing portion 56 having an aperture 58 extending therethrough, in coaxial alignment with valve seat 24, which is configured to support valve stem 38 in a sliding relationship therewith. Disposed about the outer perimeter of lower bearing portion 56 are positioning means such as flange 60 which engage bearing recess 26 and bearing alignment surface 26a to position bearing 54 in precise alignment with valve seat 24. When installed in base 12, lower bearing portion 56 is substantially positioned below and is retained axially by cover assembly 27. 
     Projecting axially outwardly from lower bearing portion 56 through opening 30 in cover assembly 27 is bearing extension 62. Extension 62 supports an upper bearing portion 64 in parallel, spaced relationship to lower bearing portion 56. Upper bearing portion 64 has an aperture 66 extending therethrough in coaxial alignment with valve seat 24 and lower bearing aperture 58 to support valve stem 38 in a sliding relationship therewith. The spacing of the bearing portions 56 and 64 is such that a minimum amount of axial misalignment of the valve assembly 34, relative to valve seat 24 occurs. In a preferred embodiment, the bearing 54 is constructed in a powder metal process with a pin in the powder pressing machine used to produce both bearing apertures 58 and 66. This process allows very precise aperture positioning and a high degree of accuracy with respect to locating the bearing positioning flange 60 because the entire part is formed at the same time and in the same tool. 
     Leakage of exhaust gas between the valve stem 38 and the lower bearing portion 56 is undesirable due to the release of untreated exhaust gas to the atmosphere and also because of the detrimental effect soot and other contaminants have on the performance and durability of the bearing 54 and actuator 68. To minimize egress of exhaust gas, a bearing seal 57 is disposed within exhaust chamber 18 below lower bearing portion 56. The bearing seal 57 is configured to engage a seal mounting recess 59 formed in land 61 which extends outwardly from the lower surface of lower bearing portion 56. 
     In the event exhaust gas leakage between valve stem 38 and lower bearing portion 56, it is undesirable for the escaping gas to impinge on the upper bearing portion 64, the armature core seal 108, described below, or to enter actuator 68. Moisture carried by the exhaust gas will freeze during cold weather operation, interfering with proper EGR valve functioning. Exhaust gas deflector shield 110 is utilized to redirect the flow of the exhaust gas along valve stem 42. The deflector shield 110 is disposed in an annular groove 112 formed in the surface of valve stem 42 at an axial position along stem 42 which will place the shield 110 between the upper and lower bearing portions 64 and 56 respectively. The deflector shield is a disc-like member formed of a flexible metal, such as spring steel, having an opening through which valve assembly 34 passes. 
     Actuator 68 is disposed at the second end 44 of valve assembly 34 to operate valve member 36 into and out of engagement with valve seat 24, thereby allowing exhaust gas to flow out of exhaust chamber 18. Actuator 68 comprises a housing 70 fixedly supported in spaced relationship to base 12 by spacers 32 and support screws 33. A coil assembly 72 is mounted within housing 70 with a non-magnetic armature sleeve 74 disposed in a hollow cylindrical central portion thereof. An armature core 76 is mounted within sleeve 74 for reciprocal motion relative to sleeve 74, coil assembly 72, and housing 70. Armature core 76 has an axially extending, hollow central portion 78 in coaxial alignment with valve seat 24, and into which valve stem 38 extends. A central web portion 80, having upper and lower surfaces 82 and 84 respectively, extends laterally across hollow central portion 78. Web portion 80 has a thickness, in the axial direction which is less than the axial length of the first reduced portion 46 of valve stem end 44. Additionally, an axially extending opening 86, having a diameter greater than that of the first reduced portion 46 of valve stem end 44, is formed in web 80. As shown in FIG. 1, valve stem end 44 extends through opening 86 in web portion 80 with space extending, in the lateral direction, on either side of the valve end 44, thereby providing room for relative movement between armature core 76 and valve assembly 34. This lateral movement facilitates the precise, coaxial alignment of the valve stem 38, relative to valve seat 24, by the bearing 54. Binding of the stem 38 may occur without provision for such movement since perfect alignment of the valve assembly 34 and the actuator 68 is difficult to maintain due to the many components involved in positioning the armature core 76. 
     To provide accurate movement in the axial direction, while allowing for lateral movement of the armature core 76 relative to the valve assembly 34, a valve stem support assembly is provided comprising a lower armature support disc 90 having a central opening 92 which corresponds to the diameter of the first reduced portion 46 of valve stem end 44. The support disc is placed over the end 44 of valve stem 38 where it rests against shoulder 48 in a supporting relationship to the lower surface 84 of central web portion 80. In a similar fashion, an upper armature support disc 94 has a central opening 96 which corresponds to the diameter of the second reduced portion 50 of valve stem end 44. The upper armature support disc 94 rests against shoulder 52 of valve stem end 44 in a face-to-face relationship with the upper surface 82 of central web portion 80. A recess 98 formed in the upper surface of upper support disc 94 allows the end of second reduced portion 50 of valve stem end 44 to be spun down, into the recess to secure valve assembly 34 to armature core 76. In order to minimize any vertical movement of the armature core 76 relative to valve assembly 34, armature biasing means comprising curved spring 100 may be disposed between lower support disc 90 and the lower surface 84 of web 80. 
     The components of the valve stem support assembly 88 are sized in such a way that lateral movement is allowed between the assembly and the inner wall of hollow portion 78 of armature core 76. As a result, during operation, armature core 76 is capable of lateral movement relative to valve stem end 44 due to the space provided within opening 86, as described above. 
     In order to minimize any axial movement of the armature core 76 relative to valve assembly 34 which may be caused by tolerance variations between the valve stem 38, the armature core 76, and the valve stem support assembly 88, armature biasing means such as spring washer 100 may be disposed between one of the armature support discs 90, 94 and the armature web 80. The spring washer 100 is preferably disposed between lower support disc 90 and armature web lower surface 82 so that armature 76 moves against a solid disc 94 when opening valve 36 thereby maximizing response time and durability. 
     Vent passages 106 extend axially through web portion 80. The passages prevent a pressure or vacuum condition from occurring on either side of the armature core 76 during reciprocal movement, which would affect response time of the EGR valve. 
     To prevent ingress of dirt and other contaminants which may affect the operation of actuator 68, armature core seal 108 closes the central opening in coil assembly 72 in which armature core 76 is disposed. Armature core seal 108 has an opening formed therein through which valve assembly 34 passes. Additionally, core seal 108 is held in position by compression spring 109 which extends between the seal and the cover assembly 27, as shown in FIG. 1. 
     A valve position sensor 102 is mounted to the top of housing 70 and has a follower 104 which is axially aligned with, and extends into the hollow portion 78 of armature core 76 to engage the upper support disc 94. Follower 104 is biased against the armature core 76 by a return spring (not shown) which acts to move the armature and valve assembly axially to seat valve member 36 within valve seat 24 when the actuator is not in operation. 
     As described above, the exhaust gas recirculation valve assembly of the present invention provides a bearing member which allows precise alignment of the valve with the valve seat thereby preventing leakage past the valve member and assuring accurate metering of exhaust gas recirculation. 
     Furthermore, a valve support assembly is disclosed which allows lateral movement of the actuator with respect to the coaxially positioned valve assembly to prevent side-to-side loading and resultant binding of the valve stem within the bearing. 
     While one embodiment of the invention has been described in detail above in relation to an exhaust gas recirculation valve assembly, it would be apparent to those skilled in the art that the disclosed embodiment may be modified. Therefore the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.