Apparatus for preventing coking in a gas management valve

Abstract

An integral pintle shield and annular scraper for protecting and cleaning the pintle shaft of a pintle valve, such as an exhaust gas recirculation valve for an internal combustion engine, to prevent coking and failure of the valve. The scraper surrounds the shaft, making contact with the shaft surface with sufficient force to dislodge incipient coke deposits but with insufficient force to inhibit the axial motion of the pintle shaft in actuation. The scraper is mounted within a radial shield surrounding the pintle shaft and pintle bushing for preventing exposure of the shaft and bushing to combustion products. The scraper is disposed in such a way that the shaft is scraped in both directions during each actuative cycle of the valve.

Description

TECHNICAL FIELD

[0002] The present invention relates to pintle-type valves; more particularly to axially-operative pintle shaft valves for permitting the controlled admission of exhaust gases into the fuel intake manifold of an internal combustion engine; and most particularly to such a valve having an annular shaft shield and scraper for preventing coking of the portion of the pintle shaft which engages the shaft bearing, thereby preventing coking product from entering the bearing and causing seizure of the shaft.

BACKGROUND OF THE INVENTION

[0003] It is well known in the automotive art to provide a variable valve connecting the exhaust manifold with the intake manifold of an internal combustion engine to permit selective and controlled recirculation of a portion of an engine's exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the burn temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve.

[0004] Typically, an EGR valve has a valve body enclosing a chamber disposed between a first port in the exhaust manifold and a second port in the intake manifold; a valve seat dividing the chamber between the two ports; a valve pintle shaft having a valve head fitted to the valve seat and extending from the valve head through a bearing mounted in a third port in a sidewall of the valve body; and a solenoid actuator mounted on the exterior of the valve body and operationally connected to the outer end of the valve pintle.

[0005] A problem inherent to EGR valve applications is that the managed fluid (exhaust gas) is moisture-laden, corrosive, and dirty with particulates. Especially in diesel engines, the exhaust gas can form coke-like deposits, known generally as coking, on surfaces exposed to these materials including the valve chamber walls and the pintle shaft. The pintle shaft typically passes through a journal bearing disposed in a wall of the valve body which provides radial support and axial guidance to the shaft. To minimize gas leakage along the shaft, the clearance between the bore in the bearing and the pintle shaft typically is made as small as is practical without causing significant drag on the axial actuation of the pintle by the external actuator. If the valve is normally closed, as is typical, a protected and clean portion of the pintle shaft within the bearing bore must become extended into the valve chamber when the pintle is actuated to open the valve and admit exhaust gas into the valve chamber. The clean portion of the pintle shaft may become coked, which coking material will be drawn into the bearing bore when the valve is closed. Thus, a typical EGR valve is undesirably vulnerable to becoming seized and inoperative by coking of the pintle shaft during operation.

[0006] What is needed is a device which may be fitted to an EGR valve that significantly reduces or eliminates coking of the valve shaft without impairing efficiency, size, and performance of the valve and actuator. Preferably, such a device is simple and inexpensive to fabricate and install.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to an integral pintle shield and annular scraper for protecting and cleaning the pintle shaft of a pintle valve, such as an exhaust gas recirculation valve for an internal combustion engine, to prevent coking and failure of the valve. The scraper surrounds the shaft, making contact with the shaft with sufficient force to dislodge incipient coke deposits but with insufficient force to inhibit the axial motion of the pintle shaft in actuation. The scraper is mounted within a radial shield surrounding the pintle shaft and pintle bushing for preventing exposure of the shaft and bushing to combustion products. The scraper is disposed in such a way that the shaft is scraped in both directions during each actuative cycle of the valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0009] FIG. 1 is an elevational cross-sectional view of a prior art EGR valve assembly; and

[0010] FIG. 2 is an elevational cross-sectional view of an improved exhaust gas recirculation valve assembly incorporating anti-coking apparatus in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] The benefits afforded by the present invention will become more readily apparent by first considering a prior art EGR pintle valve assembly. Referring to FIG. 1, a prior art EGR valve assembly 10 includes a valve body 12 having a valve seat 14 separating a first chamber 16 from a second chamber 18, which chambers may communicate with the exhaust and intake systems, respectively, of an internal combustion engine 15 in which the valve is installed, or the reverse. Valve head 20 is disposed adjacent to seat 14 for selectively mating therewith to open or to close communication between chambers 16 and 18. Valve stem, or pintle, 22 extends from head 20 through an axial bore 24 in bearing 26 for conventional actuation by a solenoid actuator (not shown). Bearing 26 is disposed in a bore 27 in a wall of valve body 12 and guides pintle shaft 22 in reciprocating motion to open and close the valve when the solenoid is energized and de-energized, respectively. During operation of the valve, pintle 22 where it enters and exits bearing 26 at the lower end thereof is fully and undesirably vulnerable to coking and fouling by the exhaust gases present in chamber 16.

[0012] Referring to FIG. 2, improved EGR valve assembly 10′ is similar to prior art assembly 10, including a valve body 12′, valve seat 14′, first chamber 16′, second chamber 18′, and may communicate with the exhaust and intake systems of an internal combustion engine 15 in which the valve is installed. Valve pintle 22′ extends from head 20′ through an axial bore 24′ in bearing 26′ for conventional actuation by a solenoid actuator (not shown). Bearing 26′ is press-fit into a bore 27′ in a wall of valve body 12′ and guides pintle 22′ in reciprocating motion to open and close the valve when the solenoid is energized and de-energized.

[0013] Surrounding bearing 26′ is a cup-shaped bearing shield 28 having an inward-extending flange 30 with a central aperture 32 for passage of pintle 22′, preferably with minimal contact therebetween, and an outward-extending flange 34. Bore 27′ and bearing 26′ are radially sized to snugly capture shield 28 therebetween when bearing 26′ is fully entered into bore 27′. Further, bearing flange 36 simultaneously captures shield flange 34 against abutment 38 in valve body 12′. Pintle 22′ is thus shielded beyond aperture 32 from materials in chamber 16′, except for materials which may enter the shielded space via aperture 32.

[0014] Within shield 28, and preferably secured to the inner wall of flange 30 and inner wall 40 of shield 28 as by adhesives or other retaining means, is a pintle scraper 42 surrounding pintle 22′. Scraper 42 is a cylindrical, annular element sized to fit closely to pintle 22′, without impeding significantly the reciprocal action thereof, to remove incipient coking deposits from the surface 44 of pintle 22′ as the pintle is actuated by the solenoid actuator. The adhesion of scraper 42 to flange 30 and wall 40 prevents leakage of exhaust gases around scraper 42. Further, unlike radial wire brushes, scraper 42 is not readily permeable by gases and particulates in the axial direction. Scraper 42 may be formed of various materials, for example, woven metal mesh, stainless steel “wool”, polymer fiber such as Teflon, ceramic or glass fiber, sintered ceramics, and similar packing-type materials. Common to all such materials is a long, tortuous path for gases and particulates to permeate through the scraper.

[0015] The combination of shield 28 and scraper 42 provides superior protection against entry of particulates into bore 24′ of bearing 26′, and against coking of surface 44 of pintle 22′.

[0016] The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above teachings. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 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.

Claims

1. An anti-coking apparatus for a valve pintle disposed for axial reciprocation in a linear bearing in a valve body of an exhaust gas recirculation valve, comprising: a) shield means surrounding said bearing and extending between said valve pintle and said valve body; and b) scraper means disposed within said shield means and surrounding said valve pintle for removing deposits therefrom and preventing particulates from reaching said bearing.

2. An apparatus in accordance with claim 1 wherein said shield means is a formed element having an inwardly extending flange for closely surrounding said pintle and an outwardly extending flange for retention against said valve body.

3. An apparatus in accordance with claim 2 wherein a portion of said element is captured between said bearing and said valve body.

4. An apparatus in accordance with claim 1 wherein said scraper means is a cylindrical, annular element.

5. An apparatus in accordance with claim 4 wherein said scraper means is attached to said shield.

6. An apparatus in accordance with claim 4 wherein said element is formed of a material selected from the group consisting of woven metal mesh, stainless steel “wool”, polymer fiber such as Teflon, ceramic fiber, glass fiber, sintered ceramics, and combinations thereof.

7. An apparatus in accordance with claim 4 wherein shield containing said scraper extend into a region of said valve containing exhaust gas.

8. An exhaust gas recirculation valve for an internal combustion engine, comprising: a) a valve body; b) a valve pintle disposed for axial reciprocation in a linear bearing in said valve body; c) shield means surrounding said bearing and extending between said valve pintle and said valve body; and d) scraper means disposed within said shield means and surrounding said valve pintle for removing deposits therefrom and preventing particulates from reaching said bearing.

9. An internal combustion engine, comprising an exhaust gas recirculation valve, including a valve body, a valve pintle disposed for axial reciprocation in a linear bearing in said valve body, shield means surrounding said bearing and extending between said valve pintle and said valve body, and scraper means disposed within said shield means and surrounding said valve pintle for removing deposits therefrom and preventing particulates from reaching said bearing.