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, said assembly (10) haylng a base (12) with an exhaust gas chamber (18) formed therein, a valve member (36) mounted within the exhaust gas chamber (18) for metering the flow of exhaust gas therethrough, a one-piece bearing (54) having upper and lower bearing members (56,64) for precise positioning of the valve member (36) within the exhaust gas chamber (18), and a valve stem support assembly (88) for mounting the valve stem (38) relative to an actuator (68) which has means for allowing lateral movement between the actuator (68) and the valve member (36), thereby eliminating side-to-side loading and resultant binding of the precisely-positioned valve member (36) within the bearing (54).

Description: The present invention relates to an exhaust gas recirculation (EGR) valve having a valve assembly and actuator as specified in the preamble of claim 1, for example as disclosed in EP-A-0 234 765. 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 towards the seat to reduce recirculation of gas. The seat is incorporated in a base that mounts the valve on an 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, co-axial 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 to develop 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 co-axially with the valve seat. Actuator alignment is very difficult to maintain due to the many components involved. An exhaust gas recirculation valve assembly according to the present invention is characterised by the features specified in the characterising portion of claim 1. In a preferred embodiment of the present invention, an EGR valve for use in controlling the recirculation of exhaust gas in an internal combustion engine is disclosed which also incorporates a novel one-piece bearing for precise positioning of a valve stem therein, as well as a valve stem support assembly for mounting the stem to an actuator according to the present invention. The bearing and the valve stem support assembly are applicable 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 in this preferred embodiment 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 centre, 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 a mounting assembly 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. Additionally, an exhaust gas recirculation valve assembly is provided having a bearing capable of precise positioning of the valve relative to the valve seat. The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 is a sectional view of an exhaust gas recirculation valve assembly embodying the present invention; and Figure 2 is an exploded, perspective view of a portion of the exhaust gas recirculation valve assembly shown in Figure 1. In Figure 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 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 alternative 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-diameter portion 46, which is adjacent to and extends axially from second end 44 a distance less than the first reduced-diameter portion 46 to terminate at shoulder 52 (see Figure 2). 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 co-axial 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 outwards 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 co-axial 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 that 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 that exhaust gas leakage should occur between valve stem 38 and lower bearing portion 56, it is undesirable for the escaping gas to impinge on the upper bearing portion 64, an 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 38. The deflector shield 110 is disposed in an annular groove 112 formed in the surface of valve stem 38 at an axial position along stem 38 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 stem 38 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 co-axial 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-diameter portion 46 of valve stem end 44. Additionally, an axially-extending opening 86, having a diameter greater than that of the first reduced-diameter 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 portion 80 with space extending, in the lateral direction, on either side of the valve end 44, thereby providing room for relative movement between the armature core 76 and the valve assembly 34. This lateral movement facilitates the precise, co-axial 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, whilst allowing for lateral movement of the armature core 76 relative to the valve assembly 34, a valve stem support assembly 88 is provided comprising a lower armature support disc 90 having a central opening 92 which has a diameter corresponding to the diameter of the first reduced-diameter 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 has a diameter corresponding to the diameter of the second reduced-diameter 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 the second reduced-diameter portion 50 of valve stem end 44 to be spun down, into the recess 98, to secure valve assembly 34 to armature core 76. The components of the valve stem support assembly 88 are sized in such a way that lateral movement is allowed between the assembly 88 and the inner wall of hollow central 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 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 thereof, 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, armature core seal 108 is held in position by a 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. As described above, the exhaust gas recirculation valve assembly of the present invention provides a valve support assembly which allows lateral movement of the actuator with respect to the co-axially positioned valve assembly to prevent side-to-side loading and resultant binding of the valve stem within the bearing. Furthermore, a bearing member is disclosed 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.

Claims: An exhaust gas recirculation valve assembly (10) comprising: a base (12) having an exhaust chamber (18) through which exhaust gas passes, a valve assembly (34) having a valve member (36) mounted within said exhaust chamber (18) and a valve stem (38) extending out of said chamber (38), said valve stem (38) including a central portion (42) extending axially outwards of said exhaust chamber (18), said valve stem being coupled to an actuator (68) by a stepped end (44) to operate said valve member (36) into and out of engagement with a valve seat (24) in said exhaust chamber (18), said stepped end (44) having a first reduced-diameter portion (46) extending axially from said stepped end (44) to terminate at a lower shoulder portion (48), said actuator (68) being maintained in a fixed relationship to said base (12) and comprising an armature (76) disposed within said actuator (68) for reciprocal motion therein, said armature (76) having an axially-extending hollow central portion (78) in substantially co-axial alignment with said valve seat (24), and a central web portion (80), having upper and lower surfaces (82,84), extending laterally across said hollow central portion (78); characterised in that said valve stem (38) includes a second reduced-diameter portion (50), of a diameter less than the diameter of said first reduced-diameter portion (46), adjacent to and extending axially from said stepped end (44) a distance less than said first reduced-diameter portion (46) to terminate at an upper shoulder portion (52); said central web portion (80) has an axial thickness less than said first reduced-diameter portion (46) of said valve stem (38) and an axially-extending opening (86) formed therein, having a diameter greater than the diameter of the first reduced-diameter portion (46) of said valve stem (38), through which said valve stem (38) extends; and a valve stem support assembly (88) comprising a lower armature support disc (90), having a central opening (92) therein which has a diameter corresponding to the diameter of the first reduced-diameter portion (46) of said valve stem (38) for sliding engagement over said second end (44) of said valve stem (38) so as to rest between said lower shoulder portion (48) and said lower surface (84) of said web portion (80) in a supporting relationship therewith, an upper armature support disc (94) having a central opening (96) therein which has a diameter corresponding to the diameter of said second reduced-diameter portion (50) of said valve stem (38), for sliding engagement over said second end (44) of said valve stem (38), to engage said upper shoulder portion (52), and to be fixable thereon, so as to lie in face-to-face engagement with said upper surface (82) of said web portion (80) to sandwich said web portion (80) between said upper armature support disc (94) and said lower armature support disc (90), thereby mounting said armature (76) to said valve stem (38), said valve stem support assembly (88) having an external diameter which is less than the internal diameter of said hollow central portion (78) of said armature (76) allowing lateral movement of said valve stem (38) within said central web portion opening (86), whilst minimizing axial movement between said valve stem (38) and said armature (76), to prevent misalignment between said armature (76) and said valve seat (24), thereby preventing any such misalignment from affecting the reciprocal operation of said valve stem (38) relative to said valve seat (24). An exhaust gas recirculation valve assembly (10) according to claim 1, characterised in that said exhaust chamber (18) has a one-piece bearing member (54) comprising a lower bearing portion (56) having an opening (58) extending therethrough which is co-axially aligned with said valve seat (24) and is configured to support said valve stem (38) in a sliding relationship therewith, bearing positioning means (60) extending from said lower bearing portion (56) to engage corresponding positioning means (26,26a) to maintain said bearing member (54) in alignment with said valve seat (24), an extension (62) projecting outwards from said lower bearing portion (56) through an opening (30) in a cover (28), and an upper bearing portion (64) extending from said extension (62) in parallel, spaced relationship to said lower bearing portion (56), and having an opening (66) extending therethrough which is co-axially aligned with said valve seat (24) and which is configured to support said valve stem (38) in said sliding relationship therewith, said bearing member (54) being configured to minimize axial misalignment of said valve member (36) relative to said valve seat (24). An exhaust gas recirculation valve assembly (10) according to claim 1 or 2, characterised in that the assembly (10) includes an armature-biasing means comprising a curved spring washer (100) disposed between said lower armature support disc (90) and said lower surface (84) of said central web portion (80) to bias said armature (76) against said upper armature support disc (94) and to minimize vertical movement between said valve assembly (34) and said armature (76). An exhaust gas recirculation valve assembly (10) according to any one of claims 1, 2 or 3, characterised in that there is a valve position sensor (102) mounted to said actuator (68) which has a follower (104) which extends into said hollow portion (78) of said armature (76) for engagement with said upper armature support disc (94), said follower (104) being biased against said upper armature support disc (94) to move said armature (76) and said valve assembly (34) axially towards said base (12). An exhaust gas recirculation valve assembly (10) according to any one of claims 2, 3 or 4, characterised in that said base (12) is a one-piece, powder metal casting in which said valve seat (24), and said bearing positioning means (26,26a) are all formed at the same time in the same powder metal tooling. An exhaust gas recirculation valve assembly (10) according to any one of the preceding claims, characterised in that said bearing member (54) is a one-piece, powder metal casting.

Inventors: BRAUN, CHARLES WILSON, GREY, THADDEUS JOSEPH, PALMER, DWIGHT ORMAN
Applicants: GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: F02M25
IPC codes: F16K31, F02M25