Patent Publication Number: US-6655657-B2

Title: Coking-resistant bearing

Description:
TECHNICAL FIELD 
     This invention relates to automotive vehicle engine valves, and in particular to a bearing disposed within an exhaust gas recirculation (EGR) valve. 
     BACKGROUND OF THE INVENTION 
     It is known in the art relating to automotive vehicle engines to provide selective recirculation of engine exhaust gases into the intake manifold in order to control exhaust emissions. To this end, an exhaust gas recirculation (EGR) valve may be provided which includes a valve assembly connectable with associated intake and exhaust manifolds or systems of the engine to meter the flow of exhaust gas from the intake to the exhaust. 
     EGR valves typically include a valve assembly operable to close or open a passage between the intake and exhaust manifolds. The valve assembly includes a valve member (or pintle) having a head connected with a shaft supported by a bearing for reciprocating motion within a valve body. An actuator assembly is operably connected with the valve assembly and includes a solenoid coil and an armature connectable with the valve member. The solenoid coil actuates the armature to open the EGR valve, which, in turn, is closed by a spring when the coil is deenergized. 
     To minimize leakage of exhaust gas into the valve assembly and/or the solenoid actuator, the diametral clearance between the valve shaft and its bearing is very tight, in the range of ±0.03 mm or less. The need to minimize gas leakage is balanced against the need to minimize hysteresis (and thus enhance actuator performance) which requires the diametral clearance between the valve shaft and its supporting bearing to be as large as possible (i.e. large enough to permit only an acceptable amount of exhaust gas leakage, less than 0.5 g/s, while limiting moisture intrusion). 
     In operation, the valve shaft is selectively exposed to exhaust gas as it operates to selectively admit exhaust gas into the valve assembly. Because exhaust gas (particularly diesel exhaust gas) has a high moisture content and is laden with particulates, the valve shaft may become coked, and the coking drawn into the bearing when the valve is closed. The accumulation of contaminants on the surfaces of the valve shaft and bearing may cause the shaft to seize in the bearing. 
     It is therefore desirable to provide a bearing having coking-resistant features that may be retrofit to any valve assembly, and in particular to EGR valves. 
     SUMMARY OF THE INVENTION 
     The present invention provides a coking-resistant bearing for use in an engine valve including a valve body defining an internal passage for the passage of exhaust gas through the valve and a valve member movable in the valve body for controlling exhaust gas flow through the passage, the valve member includes a shaft supported for reciprocating motion within the bearing. 
     The coking-resistant bearing includes an engagement surface having an end portion adjacent to the internal passage defined by the valve body. The end portion of the engagement surface includes at least one groove disposed therein sufficient to create an air pocket that resists fluid intrusion into said bearing. The groove may also include a scraping edge formed along the bearing surface such that the scraping edge of the groove gently scrapes against the valve shaft as it reciprocates along the engagement surface to remove contaminants from the shaft without interfering with shaft actuation. 
     To further inhibit the formation of coking contaminants within the bearing, a highly lubricious insert may be provided within the engagement surface of the bearing adjacent its end portion. The insert may be used within a bearing with or without an end portion including a groove. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a cross-sectional view of an EGR valve including a shaft bearing according to the invention; 
     FIG. 2 is a pictorial cross-sectional view of the shaft bearing in the embodiment of FIG. 1; and 
     FIG. 3 is a view similar to FIG. 1 showing an alternative embodiment of shaft bearing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, numeral  10  generally indicates an EGR valve suitable for diesel applications. Valve  10  includes a valve assembly  12  coupled to a solenoid actuator  14 . The valve assembly  12  includes a valve body  16  having a generally cylindrical form and defining an internal passage  18  for the passage of exhaust gas through the valve  10 . The valve body  16  further includes a mounting portion  20  that connects the valve assembly  12  to the solenoid actuator  14 . Mounting portion  20  also carries a shaft bearing  22  formed according to the invention. 
     Valve assembly  12  further includes a valve member  24  including a shaft  26  supported by the bearing  22  for reciprocating motion along an axis  28  on which the cylindrical valve body  16  is aligned. Below the bearing  22 , the shaft supports dual valve heads  30 ,  32  which seat against spaced seats in the valve body  16 . 
     The shaft bearing  22  is mounted so as to permit slight lateral motion within the valve body  16  to allow alignment of the bearing with the valve seats along the axis  28 . Bearing  22  is provided with a relatively long, high aspect ratio bearing surface  34  which extends the full length of the bearing for engaging and guiding the valve shaft  26 . 
     As seen in FIG. 2, the lower end portion  35  of the bearing includes a plurality of longitudinally extending circumferentially spaced grooves or flutes  36 . The flutes provide a reduction in the solid engagement length of the bearing but without diminishing support for the shaft over the bearing length. Capillary volume between the bearing surface and the shaft is increased in correspondence with the flute volume, thereby diminishing the potential intrusion and accumulation of sooty fluids from the exhaust gases passing through the valve. The flutes  36  generate standing insulating air pockets which resist fluid intrusion. In addition the flutes facilitate free expulsion of debris and act in a scraping capacity to help maintain the shaft clean. This action thus contributes appreciably to the reduction of hysteresis during valve operation which may be caused by deposits accumulating between the bearing surface and the valve shaft. Lower edge surfaces  38  of the bearing surface  34  and upper edge surfaces  40  at the upper ends of the flutes provide scraping edges which tend to remove any buildup of sooty deposits from the bearing and cause them to pass out through the bottom of the flutes or prevent their being formed above the lower edge of the bearing surface  34 . 
     Referring now to FIG. 3 there is shown an alternative embodiment of shaft bearing  42  which is similar to bearing  22  as is best shown in FIG.  2  and wherein like numerals indicate like features. Bearing  42  differs in the addition to the upper portion of the bearing of a self conforming lubricious metal polymer sleeve  44  which lowers the coefficient of friction in the bearing and improves actuator efficiency by inhibiting the adhesion of resin forming particulate particles such as soot. To the extent that sooty particles do work their way up the bearing surface to the sleeve  44 , any sooty particles which become trapped within the bearing surface will become embedded in the conforming polymer sleeve and thus be disinclined to adhere to the valve shaft and cause any impairment of its free movement. 
     The improved embodiments of a shaft bearing for an EGR valve as described provide an extended bearing life by reducing the collection of soot particles and varnish-like materials on the valve shaft and bearing surfaces as well as providing means for reducing the effect of any contaminants which do find their way into the bearing surface area. The result is an increased operating life for the associated EGR valve without the development of substances which interfere with motion of the shaft and the resulting operation of the EGR valve. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.