Exhaust gas recirculation valve assembly

Abstract: An exhaust gas recirculation valve assembly (10) for controlling the recirculation of exhaust gas in an internal combustion engine having a base (12) with an exhaust gas chamber (18) formed therein, a valve assembly having a valve member (34) mounted within the exhaust gas chamber (18) for metering the flow of exhaust gas therethrough, and a valve stem (38) extending out of the chamber (18) through an opening (30) therein, a one piece bearing (54) having upper, intermediate, and lower bearing members (55,59,60) for precise positioning of the valve member (34) within the exhaust gas chamber (18), and a valve stem support assembly (80,88) for mounting the valve stem (38) relative to an actuator (68). The intermediate and upper bearing portions (59,60) operate to deflect exhaust gas escaping from the exhaust gas chamber (18) and travelling along the valve stem (38) of the valve member (34), from impinging on the actuator (68).

Description: The present invention relates to an exhaust gas recirculation valve assembly. Typical exhaust gas recirculation (EGR) valves are used to control exhaust gas recirculated to the intake side of 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 towards the seat to reduce recirculation of gas. The seat is incorporated in a base that mounts the valve on the engine manifold. Precise alignment of the valve relative to the valve seat is desirable since misalignment of the two components may create a path for gas leakage to the engine, causing exhaust gas flow variability and resulting in wear of the valve and seat. 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. Such a bearing should, in addition to providing the desired alignment, operate to prevent exhaust gas escaping from within the EGR valve around the interface with the valve stem and to minimize impingement of any escaping exhaust gas on the valve stem actuator. Contact of the actuator with the moisture laden exhaust gas may result in conditions affecting the optimal performance of the EGR valve. EP-A-0,428,274 discloses an exhaust gas recirculation valve assembly including the features in the pre-characterising portion of claim 1. The present invention seeks to provide an improved exhaust gas recirculation assembly. According to the present invention, there is provided an exhaust gas recirculation assembly as specified in claim 1. An EGR valve for use in controlling the recirculation of exhaust gas in an internal combustion engine is provided which incorporates a three-tiered bearing for precise positioning of a valve stem therein and effective deflection of escaping exhaust gas from impingement on the valve actuator. The EGR valve may comprise 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 is provided which comprises a lower bearing portion, a bearing extension or web projecting outwardly therefrom and intermediate and upper bearing portions interconnected by the web in parallel, spaced relationship to the lower portion. Apertures formed in the bearing portions act to guide a valve stem extending outwardly from the exhaust chamber. The intermediate and upper bearing portions, in addition to providing support for the valve stem, may act to deflect escaping exhaust gas which may flow upwardly along the pintle shaft carrying moisture towards the valve actuator, which is described below. A valve is mounted adjacent the valve seat and has a valve stem which extends out of the base through the opening in the lower bearing portion and the intermediate and upper portions. The bearing can assure precise alignment of the valve with the valve seat and minimise misalignment of the valve relative to the 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 preferably rigidly mounted in a spaced relationship to the base. An armature core, having a hollow centre, may be disposed for reciprocal motion within the actuator. The armature may have 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 may have a diameter larger than that of the valve stem to allow for lateral movement between the stem and the armature web. Advantageously, there is provided a valve stem support assembly comprising a lower support disc and an upper support disc mounting the remote end of the valve stem to the armature web. The lower disc preferably 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 preferably 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 can be held in engagement with the armature web by the supporting assembly which can allow 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 may be mounted to the top of the actuator housing and may have a follower which moves with the armature to determine valve position. A valve return spring can be incorporated into the sensor and to return the valve to a closed position when the actuator is not in operation. The present invention can provide an exhaust gas recirculation valve assembly having a bearing capable of precise positioning of the valve relative to the valve seat and of diverting moisture laden exhaust gas from impinging on the valve actuator. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is an elevational view, in part cross-section, of an embodiment of exhaust gas recirculation valve assembly; and Figure 2 is an exploded perspective view of a portion of the exhaust gas recirculation valve assembly of Figure 1. In Figure 1 there is shown an exhaust gas recirculation valve assembly 10 for use in controlling the recirculation of exhaust gas in an internal combustion engine. The assembly 10 comprises a base 12, shown in detail in Figure 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 around inlet opening 20. A bearing recess 26 is formed in base 12, generally in alignment with valve seat 24. In order that valve seat 24 and the bearing recess 26 are accurately aligned with respect to each other, it is preferred that the base 12 be constructed as a single piece, powder metal part with the outlet opening 22, the valve seat 24, and the bearing recess 26 formed in the same powder metal tooling. Such a construction technique generally eliminates misalignment between the valve seat 24 and the bearing recess 26 which would occur if these elements 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 extending outwardly from cover 28. 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 by 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 by 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 55 having an aperture 56 extending therethrough in coaxial alignment with valve seat 24, which is configured to guide valve stem 38 in a sliding relationship therewith. Disposed about the outer perimeter of lower bearing portion 55 are positioning means such as flange 57 which engage bearing recess 26 to position bearing 54 in precise alignment with valve seat 24. Projecting outwardly from lower bearing portion 55 through opening 30 in cover assembly 27 is web 58 which supports intermediate and upper bearing portions 59 and 60, respectively, in parallel spaced relationship to lower bearing portion 55. Intermediate bearing portion 59 and upper bearing portion 60 have apertures 61 and 62, respectively, extending therethrough in coaxial alignment with valve seat 24 and lower bearing aperture 56 to guide valve stem 38 in a sliding relationship therewith. The spacing of the bearing portions 55, 59 and 60 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 bearing apertures 56, 61 and 62. This process allows very precise aperture positioning and a high degree of accuracy with respect to locating the bearing positioning flange 57 because the entire part is formed at the same time and in the same tool. Leakage of exhaust gas out of exhaust chamber 18 between the valve stem 38 and the lower bearing portion 55 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. In the event of exhaust gas leakage between valve stem 38 and lower bearing portion 55, it is undesirable for the escaping gas to impinge on the actuator 68. Moisture carried by the exhaust gas may freeze during cold weather operation, interfering with proper actuator and, consequently, EGR valve functioning. Intermediate bearing portion 59 operates as an exhaust gas deflector to redirect the flow of any escaping exhaust gas travelling along valve stem 42. 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 80, having upper and lower surfaces 82 and 84 respectively, extends laterally across hollow central portion 78. Web 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 Figure 1, valve stem end 44 extends through opening 86 in web 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 precise 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 substantially 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 80. In a similar fashion, an upper armature support disc 94 has a central opening 96 which substantially 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 such as spring washer 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 chosen to be of a size which allows lateral movement 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. 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 a 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 Figure 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. The exhaust gas recirculation valve assembly described above can provide a bearing member which allows precise alignment of the valve with the valve seat, thereby minimizing leakage past the valve member and assuring accurate metering of exhaust gas recirculation. The bearing member is configured to minimize impingement of any escaping exhaust gas on the valve actuator by disrupting gas flow along the surface of valve stem 38, thereby directing the gas away from actuator 68.

Claims: An exhaust gas recirculation valve assembly comprising a base (12) including an exhaust gas chamber (18) through which in use exhaust gas can pass; a pintle valve (34) including a valve member (36) disposed within the exhaust gas chamber and movable relative to a valve seat (24) disposed in the gas chamber so as to regulate the flow of exhaust gas through the base, and a valve stem (38) attached to the valve member and extending outwardly of the chamber through an opening (26) therein; an actuator (68) maintained in a substantially fixed relationship relative to the base and coupled to the valve stem so as in use to move the pintle valve reciprocably relative to the valve seat; a one-piece bearing member (54) including lower and upper bearing portions (55,60) supported in substantially parallel spaced relationship relative to one another by a web (58) extending between the bearing portions, the bearing portions including substantially coaxially aligned apertures (56,62) extending therethrough for guiding the pintle valve in a sliding relationship therewith, the lower bearing portion (55) in use being operable to close the opening (26) in the base and being configured to cooperate with the base so as substantially to align the bearing apertures and the pintle valve with the valve seat; characterised by an intermediate bearing portion (59) supported between and in substantially parallel spaced relationship relative to the lower and upper bearing portions by the web and including an aperture (61) therein substantially aligned with the apertures in the lower and upper bearing portions, the intermediate bearing portion (59) being operable to deflect exhaust gas travelling along the valve stem from impinging on the valve actuator. An exhaust gas recirculation valve assembly according to claim 1, wherein the intermediate and upper bearing portions (59,60) are operable to deflect exhaust gas escaping from the chamber at the interface of the pintle valve and the lower bearing portion aperture and travelling along the valve stem from impinging on the valve actuator.

Inventors: LOCKWOOD MARK STEPHEN, LOCKWOOD, MARK STEPHEN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1992
Main classification: F02M25
IPC codes: F02M25