Abstract:
A poppet valve wherein centering of the valve stem and head and mating of the valve head to the valve seat are compliantly directed by contact with the valve seat. The poppet valve employs an integral radially-floating valve stem sealing guide or bearing in the valve body, permitting lateral compliant movement of the valve stem as required. The guide also is configured to form a face seal against the valve body, thus permitting the face seal and a valve actuator solenoid to be biased by separate, independent springs, each of which may be optimized for its particular function. Further, the valve head is tiltably and sealably disposed upon the valve stem to permit the valve head to be guided and oriented into the valve seat by contact with the seat itself.

Description:
TECHNICAL FIELD 
     The present invention relates to poppet valves, more particularly, to poppet valves wherein the pintle shaft and the valve head are compliantly centered by contact with the valve seat, and most particularly, to a three-way configuration of such a poppet valve having a single pintle shaft. 
     BACKGROUND OF THE INVENTION 
     Poppet valves are widely used for opening and closing flow paths for gases and liquids, for example, as shift diverter valves in vehicles; for channeling hydrogen into reformers in fuel cells; and as intake, exhaust, and exhaust gas recirculation valves in internal combustion engines. A poppet valve comprises a typically circular valve head mounted transversely on a pintle shaft for axial motion thereof to form or eliminate a flow gap between the valve head and a mating circular valve seat in a valve base. A pintle shaft is also known as a valve shaft or valve stem. 
     Poppet valves can be very demanding in their design and fabrication tolerances. For example, some poppet valves are provided with conical mating surfaces on the valve head and valve seat; however, leak-free sealing over the entire mating surfaces depends on near-perfect circularity and smoothness of both surfaces. In addition, the surfaces must have substantially identical cone angles. The highest quality valves are ground on a precision lathe and then the valve head is lap-ground to its dedicated seat. This is labor-intensive, time-consuming, and expensive. U.S. Pat. No. 4,565,217 discloses a poppet valve having a conical head and a curved seat such that the head and seat can seal along a circular line of contact, thereby obviating the need for matching cone angles. 
     A further requirement for leak-free sealing is concentricity of the head and valve. Typically, concentricity is provided by the precision placement of a valve shaft guide on the co-axis of the valve head and valve seat, as disclosed, for example, in U.S. Pat. Nos. 4,565,217 and 4,907,741. Control of concentricity may be further enhanced by providing a second shaft guide opposite the first, such that the valve head is guided on both sides; see, for example, U.S. Pat. Nos. 4,915,134; 5,211,198; 5,899,232; and Re.33,246. Such precision guiding of a poppet valve shaft can be costly and cumbersome to provide, and expensive to maintain, particularly in poppet valves wherein the diameters of the valve and seat are large relative to the diameter of the shaft or stem. 
     A problem with shaft guides generally is that clearance between the guide and the shaft represents a potential source of leakage from the valve. U.S. Pat. No. 5,467,962, the disclosure of which is incorporated herein by reference (&#39;962), discloses an actuator housing having a linear bearing (valve guide) which is operable both to align the valve stem within the valve base and to define a seal between the base and the housing. The clearance required between the solenoid armature and the armature shell prevents precise alignment thereby of the valve stem in the valve body. Therefore, a small radial clearance is provided between the bearing and the actuator housing, preferably about 0.2 mm, which allows some limited side-to-side or radial movement of the valve and stem, permitting compliant centering of the valve stem and head by contact with the valve seat. This also permits an extremely close tolerance between the valve stem and the bearing, enhancing shaft sealing thereby. A face seal between the bearing member and the actuator housing prevents leakage around the bearing member. Thus, sealing between the bearing and the housing is maintained regardless of radial movement of the bearing in the housing or the position of the valve stem within the bearing. A shortcoming of the disclosed apparatus is that a single coil spring, disposed on axis between the bearing and the solenoid armature, functions both to bias the face seal and to return the armature upon deactivation of the solenoid. The spring must be sufficiently strong to ensure the bearing face seal, but the stronger the spring, the greater the force the solenoid must overcome in closing the valve. In general, a single spring cannot be optimized for both functions. 
     Further, known poppet valves require that the valve head be mounted perfectly orthogonal to the valve stem and that a plane containing the valve seat be perfectly parallel to a plane containing the valve head. Any significant deviation in any one of these relationships can cause the head to mate imperfectly with the seat, which can result in valve leakage. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved poppet valve wherein the centering of the valve stem and head and the mating of the valve head to the seat are directed by, and compliant to, the actual orientation of the valve seat. The poppet valve disclosed herein addresses the indicated shortcomings of known poppet valves in two novel ways. 
     First, the valve employs an integral valve stem sealing guide or bearing configured to also form a face seal, similar to the sealing guide in the actuator discussed supra. In the present invention, however, the bearing is disposed in the valve base rather than in the actuator, permitting the face seal and the actuator solenoid to be biased by separate, independent springs, each of which may thus be optimized for its particular function. 
     Second, the valve head is not rigidly mounted to the valve stem but rather is tiltably and sealably disposed thereupon to permit the valve head to be guided and oriented into the valve seat by contact with the seat itself. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features, and advantages of the invention, as well as presently preferred embodiments thereof, will become more apparent from a reading of the following description, in connection with the accompanying drawings in which: 
     FIG. 1 is an elevational cross-sectional view of a prior art poppet valve; 
     FIG. 2 is an elevational cross-sectional view of a twoway poppet valve and actuator in accordance with the present invention; 
     FIG. 3 is a detailed view of the compliant mechanism in the poppet valve shown in in FIG. 2; 
     FIG. 4 is an elevational cross-sectional view of a first embodiment of a three-way poppet valve in accordance with the present invention; 
     FIG. 5 is a detailed view like that shown in FIG. 3 with reference to the valve shown in FIG. 4; 
     FIG. 6 is a view like that shown in FIG. 4, showing a second embodiment of a three-way poppet valve in accordance with the invention; 
     FIGS. 7 a ,  7   b , and  7   c  are detailed cross-sectional views showing three different embodiments of valve seat and valve head sealing surface combinations; and 
     FIG. 8 is a cross-sectional view of an alternative embodiment of a compliant mechanism similar to that shown in FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a prior art two-way poppet valve  10  for use as an exhaust gas recirculation (EGR) valve for an engine  12 , substantially as disclosed in the incorporated &#39;962 reference, includes four principal subassemblies: a valve base assembly  14 , a valve assembly  16 , an actuator assembly  18 , and a valve position sensor  20 . 
     Actuator assembly  18  includes solenoid armature  22  which is responsive conventionally to a magnetic field exertable by electromagnet coil  24  to axially drive valve stem  26  supporting valve head  28  to open or close a gap between valve head  28  and valve seat  30 , thereby regulating flow of gas between engine exhaust passage  32  and engine intake passage  34 . 
     A valve stem bearing or guide  36  is received in stepped extension  38  of actuator housing  40 . Guide  36  is not fixed in radial position but is free to float, to a limited extent, utilizing clearance  42  to allow radial movement of the valve stem  26  occurring as a result of factors such as actuator variabilities, machining imperfections, or operation-caused wear. The side-to-side, or radial, movement facilitated by the floating bearing allows the interface between the axial bearing bore  44  and valve stem  26  to be of an extremely close tolerance, virtually eliminating gas leakage along valve stem  26  into actuator assembly  18 . 
     In addition to the sealing interface established between the valve stem  26  and bearing  36 , a face seal is defined between the lower surface  46  of bearing member  36  and an upper surface  48  of housing extension  38 . A biasing force is exerted on the upper surface  50  of bearing  36  by a spring  52  inserted and operable between bearing member  36  and solenoid armature  22 . Spring  52  thus biases armature  22  and valve assembly  14  toward the closed position and also exerts axial force on bearing member  36  to ensure the face seal of lower surface  48  against housing extension  38 . 
     Referring to FIG. 2, a two-way poppet valve  60  in accordance with the invention is provided with a valve base assembly  62 , a valve assembly  64 , an actuator assembly  66 , and a valve position sensor  68 . 
     Valve base assembly  62  comprises first and second chambers  70 , 72  which may be intake or exhaust chambers, respectively, as shown in FIG. 1 or the reverse. Between chambers  70 , 72  is port  74  which is preferably circular in plan view (not shown). Port  74  is provided with a valve seat  76  at an edge thereof, which seat may be conical as shown in FIGS. 7 a  and  7   c  or curved as shown in FIG. 7 b , for sealingly receiving a matable valve head  78  having a reciprocally curved or conical sealing periphery  79  as shown in FIGS. 7 a  and  7   b , respectively, or both valve head and seat may be provided with mating conical surfaces as shown in FIG. 7 c . Preferably, curved or radiused mating surfaces on valve seats and valve heads are spherical sections. 
     Valve base assembly  62  further comprises an opening  80  substantially coaxial with port  74  for receiving a valve stem bearing  82  functionally similar to bearing  36  in FIG.  1 . Opening  80  is greater in diameter than bearing  82 , preferably by about 0.2 mm, such that bearing  82  may float side-to-side, or radially, in opening  80 . Axial bore  84  in bearing  82  is sealingly receivable of valve stem  26 , which is captured and operated by actuator assembly  66  substantially as disclosed in the &#39;962 reference. Opening  80  is stepped to provide a planar shoulder  86 , functionally corresponding to upper surface  48 , and bearing  82  is provided with a flange having a lower surface  88  corresponding to lower surface  46 . Lower surface  88  is urged against planar shoulder  86  to form a face seal by biasing spring  90 . Spring  90  is centered and retained by retainer  92  which is captured between valve base  62  and housing  94  of actuator assembly  66 . Thus, the valve stem bearing may be spring-sealed to whatever force is desired without regard to the action of the actuator, in distinction from the prior art valve  10 . The action of solenoid armature  22  is modulated by a separate spring  67  disposed within the actuator assembly and independent of seal spring  90 . 
     Referring to FIG. 3, valve assembly  64  includes a compliant mechanism  65  for allowing limited angular departure of the plane including valve head  78  from orthogonality to the axis  96  of valve stem  26  to accommodate any small departures from orthogonality of the plane containing the valve seat  76  and from the approximate valve head centering provided by solenoid armature  22 . 
     Specifically, stem  26  is provided with a smaller diameter portion  98  and a larger diameter portion  100 , the transition zone  102  therebetween defining a surface for sealing against a preferably conical central opening  104  in valve head  78 . The transition zone must include a curved portion such that zone  102  and opening  104  sealingly mate in a continuous line contact therebetween. Preferably, the curved portion is spherical so that the line contact is circular at any angle of tilt of the valve head with respect to the valve stem. 
     Valve head  78  is urged against transition zone  102  by compression spring  106  which is captured by spring retainer  108 , itself being captured axially on stem  26  by insertion of neck  110  into circumferential groove  112 . 
     Opening  104  is further provided with a flange  114  which is flared outwards from stem portion  98  at a predetermined angle  116 , preferably about 5° or less, corresponding to the maximum angle of tilt allowable for the plane of valve head  78  from stem axis  96 . 
     An embodiment  101  of an angularly compliant valve head mechanism alternative to mechanism  65  is shown in FIG.  8 . Stem  26  is provided with a ball end  103 , and the upper surface  105  of valve head  78  is provided with a matable spherical socket  107  to form a conventional ball-and-socket joint with ball end  103 . An annular stop  109  on ball end  103  limits the permissible angle of tilt  116 . Of course, central opening  104  and flange  114  are omitted from this embodiment. 
     In operation to move from a valve-open state to a valve-closed state, actuator assembly  66  drives valve stem  26  axially to engage valve head  78  with valve seat  76 . The stroke of solenoid armature  22  is limited by formation of a circular line of contact between head  78  and seat  76 . Such line of contact may lie in a plane not quite orthogonal to the axis  96  of stem  26 , and may not be quite concentric with axis  96 . The herein-disclosed compliant mechanism permits the valve seat to direct the valve head concentrically into itself at the urging of the valve stem, via the radial compliance of the stem bearing  82  in opening  80  and the angular compliance of valve head  78  on valve stem  26 . 
     Other valve configurations are possible. For example, referring to FIGS. 4 and 6, a three-way poppet valve  118  may be useful in alternating two flow paths into a common flow path, or providing rationed flows into or out of a common flow path. Valve  118  is similar to two-way valve  60  but with a second valve comprising a third chamber  120  defining a second independent chamber in communication with chamber  72  via a second port  122  provided with a second valve seat  124  similar to seat  76 , chamber  72  thereby being commonly accessible to both first chamber  70  and third chamber  120 . Valve assembly  64  is extended to comprise a second compliant head mechanism  126  substantially identical to mechanism  65  just described (or to mechanism  101 ) but in inverse orientation such that when the first valve is fully closed, the second valve is fully open, as shown in FIG.  4 . Valve seats  76  and  124  may both face into chamber  72 , and compliant mechanisms  65  and  126  may both be disposed substantially in chamber  72 , as shown in FIG. 4; or valve seats  76  and  124  may face into chambers  70  and  120 , respectively, and compliant mechanisms  65  and  126  may be disposed substantially in chambers  70  and  120 , respectively, as shown in FIG.  6 . 
     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.