Abstract:
A system for containing leakage along a pintle shaft in a pintle-type gas control valve, such as an exhaust gas recirculation valve for an internal combustion engine or a reformate diverter valve for a fuel cell, comprising a novel seal element and means for sealing the element to the valve&#39;s pintle shaft bearing and to an interrupted pintle shaft. The system comprises two elements: a positive vapor block in the form of an elastomeric boot or folded diaphragm disposed across the pintle interruption, and a pintle shaft bearing disposable in the valve&#39;s body and sealingly secured to the boot or diaphragm. The system may include a coil spring disposed in compression within the boot or diaphragm.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to shaft seals for pintle-type valves; more particularly to seals for solenoid-actuated pintle valves for metering the flow of gases; and most particularly to a gas leakage containment system including an elastomeric boot or folded diaphragm for containing gases leaked from a pintle shaft bore in the valve body, thereby preventing undesirable entry of such gases into the actuator or the atmosphere.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well known to use pintle-type valves to meteringly control the flow of gases from one distributor into another. For example, in the automotive art a variable-flow control valve connecting the exhaust manifold with the intake manifold of an internal combustion engine is used to permit selective recirculation of a portion of an engine&#39;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. In fuel cells, a three-way pintle-type valve may be used to regulate the flow of reformate to either a waste burner or the reaction chamber.  
           [0003]    Typically, a pintle-type gas metering valve has a valve body enclosing a chamber. In an EGR valve, this chamber is 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 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; a spring-retained bearing splash shield; and a solenoid actuator mounted on the exterior of the valve body and having an armature into which the outer end of the valve pintle extends. Typically, a space between the valve body and the valve actuator containing the splash shield is exposed to atmospheric conditions.  
           [0004]    The exhaust gas managed by an EGR valve is moisture-laden, corrosive, and dirty. If this gas is allowed to enter the valve actuator, for example, by leaking along the pintle shaft, then internal corrosion, malfunction, and ultimate failure of the actuator can result. Such failure can lead to emission non-compliance and can incur significant cost to a vehicle manufacturer if a recall is required.  
           [0005]    The gas managed by a fuel cell valve typically is hydrogen, which is very difficult to seal against because of its molecular size and which can be violently explosive in combination with oxygen. Thus, shaft leakage to the atmosphere is highly undesirable.  
           [0006]    In pintle-type gate valves, the shafts may be sealed via well-known packing glands, through which the pintle motion is substantially rotary. Such glands are not practical in metering valves actuated by low-force solenoids in which the pintle motion is entirely axial because adequate packing would create unacceptably large frictional forces on the pintle, requiring very large and expensive actuators.  
           [0007]    In many prior art solenoid-actuated gas control valves in use today, a compromise has been reached wherein leak rates of &lt;0.2 grams/second are accepted, to minimize shaft frictional loading and allow low hysteresis actuation of the valve. However, ever more stringent emission regulations and the advent of fuel cells in the automotive industry make this compromise no longer acceptable. This has increased the industry need for a time-proven, cost-effective actuator and valve which can overcome the historically impossible obstacle of attaining zero leakage from the shaft.  
           [0008]    What is needed is a gas leakage containment system disposed between a pintle-type valve and its actuator which prevents gas and/or moisture from intruding into the actuator and/or escaping to the atmosphere, without impairing efficiency, size, and performance of the valve and actuator. Preferably, such a containment system is simple and inexpensive to fabricate and install.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed to a shaft leakage containment system comprising a novel shaft seal for installation on an interrupted pintle shaft in a pintle-type valve, such as an exhaust gas recirculation valve for an internal combustion engine or a diverter valve for a fuel cell, for preventing leakage of gas and/or moisture along the pintle shaft into the actuator and/or the atmosphere. The system comprises two elements: a positive vapor block in the form of a sealed, impermeable, elastomeric boot or folded diaphragm disposed across the pintle shaft interruption, and means for sealingly securing the boot or diaphragm to the valve body and to the interrupted pintle shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    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:  
         [0011]    [0011]FIG. 1 is an elevational cross-sectional view of a prior art two-way pintle-type metering valve having a continuous pintle shaft extending into the actuator thereof, as may be used as an EGR valve in an internal combustion engine;  
         [0012]    [0012]FIG. 2 is an elevational cross-sectional view of a first embodiment of a sealed gas leakage control system in accordance with the invention, for installation in a pintle shaft valve assembly having an interrupted pintle shaft;  
         [0013]    [0013]FIG. 3 is an elevational cross-sectional view of the system shown in FIG. 2, shown as mounted onto an interrupted pintle shaft;  
         [0014]    [0014]FIG. 4 is an elevational cross-sectional view showing the system shown in FIG. 2 as mounted in FIG. 3 installed in a three-way valve connected to an actuator as may be used as a reformate control valve in a fuel cell;  
         [0015]    [0015]FIG. 5 is a second embodiment of a sealed gas leakage control system; and  
         [0016]    [0016]FIG. 6 is a third embodiment of a sealed gas leakage control system.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    The benefits afforded by the present invention will become more readily apparent by first considering a prior art pintle valve. Referring to FIG. 1, a prior art two-way pintle 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, for example, with the exhaust and intake systems, respectively, of an internal combustion engine (not shown) 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 pintle shaft  22  extends from head  20  through an axial bore  24  in bearing  26  and is captured within armature  28  of solenoid actuator  30 . Bearing  26  is disposed in a port  27  in a wall of valve body  12  and guides shaft  22  in reciprocating motion to open and close the valve when actuator  30  is energized and de-energized, respectively.  
         [0018]    Bearing  26  is provided with a circumferential flange  32  having an axial face  34  for sealing against axial outer surface  36  of valve body  12  to prevent leakage of gases therebetween. A cup-shaped bearing splash shield  38  has an inward-extending flange  40  with a central aperture for passage of shaft  22 , preferably without contact therebetween, and a cylindrical skirt  44  extending axially to shield a substantial portion of bearing  26  from external contaminants. Shield  38  is open in a downwards direction to permit venting to the atmosphere of gases which may leak along bore  24  during operation of the valve. Actuator  30  is connected to valve body  12  via a plurality of bolts  46  extending through a plurality of standoffs  48 . A coil spring  50  surrounding pintle shaft  22  is disposed within shield  38 , being compressed between actuator  30  and a second surface  52  on flange  32  for urging flange  32  to seal against surface  36  under all operating conditions. Spring  50  also serves to urge shield  38  against surface  49  of primary polepiece  51  of actuator  30  to inhibit dust intrusion into the actuator.  
         [0019]    A second spring  54  disposed in compression within actuator  30  between armature  28  and polepiece  51  keeps valve  10  in the normally-closed position shown in FIG. 1 when the solenoid is de-energized, pintle shaft  22  thus being under tension. When the valve is opened, by energizing of the actuator, pintle shaft  22  is subjected to compressive force, an important consideration in providing an interrupted pintle shaft and gas leakage containment system in accordance with the invention.  
         [0020]    It will be readily seen that the surface of pintle shaft  22  is continuous from head  20  all the way into the center of armature  28 , providing a direct and continuous pathway for moisture and/or gases to leak from chamber  18  in valve body  12  along pintle shaft  22  into the interior of actuator  30 . This feature represents an important shortcoming of prior art valve assembly  10  which is overcome by the present invention.  
         [0021]    Prior art leakage control efforts have been directed to stopping leakage along bore  24 , principally by making the diametral clearance between the diameter of bore  24  and pintle shaft  22  as small as possible without inhibiting the smooth sliding action of the pintle in the bore. In arriving at the present invention, the inventors recognize that such leakage cannot ever be completely eliminated as long as there exists an unbroken pathway and a pressure drop along bore  24 . Therefore, the present invention is directed to means for breaking the pathway and containing leakage which inevitably must occur along bore  24  until the pressure drop between chamber  18  and the outer end of bore  24  is zero. A further disadvantage of prior art valve assemblies having a continuous pintle shaft is that all valve elements intended to be coaxially aligned must be manufactured and assembled to very tight tolerances to avoid introduction of unwanted radial forces on pintle shaft  22  resulting from misalignment. Such forces place parasitic and detrimental loads on the actuator.  
         [0022]    Referring to FIG. 2, a first embodiment  53  of a containment system in accordance with the invention is shown, including a bearing  26 ′ having an axial bore  24 ′ for guiding and radially supporting a pintle shaft (not shown) in reciprocating motion through bearing  26 ′, as described below. Bearing  26 ′ is provided with a circumferential flange  32 ′ having a first axial face  34 ′ for sealing against an axial outer surface of a valve body to prevent leakage of gases therebetween, bearing  26 ′ being disposable in a bore in a valve body as described below, similar to the manner in which prior art bearing  26  is disposed in valve body  12 . Bearing  26 ′ is provided with means, such as an equatorial groove  35  in flange  32 ′ for retaining the skirt  55  of a cup-shaped elastomeric boot  56  radially compressed into and retained in groove  35  by a clamp  58 . Preferably, clamp  58  comprises a continuous cylindrical metal ring which is permanently compressed into groove  35  as by swaging or, preferably, by magneforming. Thus, skirt  55  is impermeably sealed against bearing  26 ′. Boot  56  further comprises a necked portion  60  having an axial opening  62  for receiving a pintle shaft as described below. Preferably, captured within boot  56  is a formed supporting ring  64  for receiving a coil spring  50 ′ disposed in compression between ring  64  and flange  32 ′.  
         [0023]    Referring to FIG. 3, containment system  53  is disposed in axial bore  27 ′ in a valve body  12  such that axial face  34 ′ of flange  32 ′ is sealingly mated against valve surface  36 . Preferably, the diameter of bore  27 ′ is slightly greater than the diameter of bearing portion  29  disposed in bore  27 ′ such that a cylindrical gap  66  is formed therebetween. Gap  66  permits bearing  26 ′ to be radially compliant to accommodate small axial misalignments of valve components, thereby relaxing the manufacturing and assembly tolerances thereof. A modified pintle shaft  22 ′ is axially disposed in bore  24 ′ and axial opening  62  and terminates outside boot  56  in a flat-headed flange  68  having a planar underside  70  against which necked portion  60  of boot  56  is sealingly urged by ring  64  and compressed spring  50 ′. Thus, any gas or moisture leakage along bore  24 ′ from chamber  18  in valve body  12  is captured within boot  56  and cannot escape.  
         [0024]    In operation, pintle shaft  22 ′ is axially and reversibly reciprocated by an actuator (not shown but described below) through bore  24 ′ in bearing  26 ′ in opposition to bias spring  50 ′. As spring  50 ′ is further compressed, elastomeric boot  56  is similarly and reversibly compressed by flange  68 , the sidewalls  59  resiliently being reversibly collapsed.  
         [0025]    Referring to FIG. 4, a three-way metering diverter valve assembly  72  includes a three-way diverter valve  74 , leakage containment system  53 , and a modified solenoid actuator  30 ′. Valve body  12 ′ includes a central chamber  18 ′ containing valve head  20 ′ in disposed to matingly seal against either first seat  76  leading to first port  78  or second seat  80  leading via second port  82  to a second chamber  84 . Compressed spring  50 ′ biases head  20 ′ toward closure against second seat  80 .  
         [0026]    Modified actuator  30 ′ includes a stub pintle shaft  22 ″ disposed axially within armature  28  and engaged against the upper surface  86  of flange  68  for actuating pintle shaft  22 ′ against bias spring  50 ′ to vary the position of head  20 ′ within chamber  18 ′ thereby meteringly varying the volumes of gas flow across seats  76  and  80 . Because valve head  20 ′ is urged towards the closed valve position by spring  50 ′, armature  28  and stub shaft  22 ″ act on pintle shaft  22 ′ only under compression. Because flat-headed flange  68  presents a relatively broad contact surface for stub shaft  22 ″, the axial alignment of actuator  30 ′ with valve  74  is significantly relaxed over the tight tolerance required in prior art valve  10 .  
         [0027]    As seen clearly in FIG. 4, shaft leakage along bore  24 ′ is entirely contained within containment system  53  and can escape to neither armature  30 ′ or the ambient atmosphere outside system  53 . In operation, gas and/or moisture can leak along bore  24 ′ in response to a pressure difference between opposite ends of bore  24 ′ until sufficient pressure builds up within boot  56  to stop further leakage. Thus, boot  56  is required to be able to withstand the range of operating pressures to be encountered within valve  74 , plus a small margin to allow for compression of the volume of boot  56  during actuation of the valve. Accordingly, boot  56  may be formed of any of various well-known durable elastomers and may, for example, be fiber-reinforced for high-pressure applications.  
         [0028]    The boot portion of a containment system in accordance with the invention may take various forms within the scope of the invention.  
         [0029]    Referring to FIG. 5, a second embodiment  86  of a containment system includes a generally cylindrical boot  56 ′ disposed within spring  50 ′ which is compressedly retained between upper and lower retaining rings  88  disposed in annular slots in boot  56 ′. Boot  56 ′ is thus sealingly urged by spring  50 ′ against both pintle flange underside  70  and bearing flange  32 ′, obviating the need for groove  35  and clamp  58  as in system  53 .  
         [0030]    Referring to FIG. 6, a third embodiment  90  of a containment system includes a folded diaphragm or bellows  56 ″ as the containment element, captured between upper and lower retaining rings  88 ′. Diaphragm  56 ″ may be formed of a polymer which may be an elastomer, or of folded metal, for example, titanium, in known fashion.  
         [0031]    A functional element common to all the embodiments shown in that each is capable of maintaining a sealed space below flange  68  while being deformed by the action of pintle shaft  22 ′ without creating significant frictional or other loads on actuator  30 ′. This is an important consideration in providing a sealing system which is retrofittable to existing designs and which requires no increase in actuator size or power over present actuators.  
         [0032]    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.