Abstract:
An expanded-range pintle valve comprising a plurality of stages. Each stage comprises a valve seat and head capable of regulating flow through the valve over its own dynamic range. The valve head of a higher-flow stage includes the valve seat for the next-lower flow stage. The heads and seats for the multiple stages are nested concentrically, the progressively lower-flow stages having progressively smaller diameters. All valve heads except the lowest-flow head have axial and radial bores permitting flow therethrough so that flow may be regulated first by actuating the lowest-flow stage, then by actuating successively higher flow stages. A single pintle shaft connected to a solenoid actuator is adapted to engage each of the valve heads sequentially as the actuator progresses, beginning with the lowest-flow head, thereby extending incrementally the dynamic range of the valve as each stage is successively engaged.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Serial No. 60/183,944, filed Feb. 22, 2000. 
    
    
     TECHNICAL FIELD 
     The present invention relates to pintle-type valves; more particularly, to such valves for variably regulating the flow of fluids and especially gases; and most particularly, to a multiple-stage pintle valve having a greatly expanded range of fluid metering, wherein a low-flow valve is disposed within the valve head of a high-flow valve, the two valves being actuated sequentially by a common pintle shaft and actuator. 
     BACKGROUND OF THE INVENTION 
     Pintle-type valves are used for a wide variety of on/off and metering functions. In general, pintle valves are not well-suited to metering, since flow across the valve seat as a function of pintle and head travel typically is quite non-linear. Many pintle valves go from fully closed to substantially fully open with a relatively short stroke of the actuator, thus making difficult the precise metering of fluid at intermediate degrees of openness. Such valves are said to have a narrow dynamic range. For low total flow applications, relatively small valves typically are used, and for larger total flow applications, larger valves are used. However, a serious problem arises in applications wherein a given pintle valve is required to meter fluid over a wide range of flows. 
     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&#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. 
     Typically, an EGR valve is a pintle-type valve having 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 head fitted to mate with the valve seat; a valve stem or pintle extending from the valve head through a bore 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 stem. The stroke of the solenoid is regulated as by a computer in response to the composition of the intake and exhaust streams to vary the axial position of the valve pintle and valve head with respect to the valve seat to provide a desired flow volume of exhaust gas through the valve. 
     Because of the dynamic range limitations of known pintle-type valves, a wide range of EGR valve sizes is presently required for optimum metering on a wide range of engine sizes. Large engines require large EGR valves, and smaller engines require smaller EGR valves. A large EGR valve on a small engine cannot be controlled with the degree of flow resolution required. If an EGR valve is too small for an engine, then fuel economy and emissions quality can be compromised; if sized too large, then controllability, durability, and performance can be compromised. 
     What is needed is a means for extending the dynamic range of a pintle valve so that a single valve can be used over a wide range of flow requirements, thus reducing manufacturing and replacement part complexity and cost. 
     It is the primary object of the invention to provide an improved pintle valve which extends the precise controllable range of a single valve over a broad range of flow requirements. 
     It is a further object of the invention to save cost and complexity in manufacturing and inventorying a wide variety of sizes of pintle valves. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a pintle valve comprising a plurality of stages. Each stage comprises a valve seat and head capable of regulating flow through the valve over its own dynamic range. The valve head of a higher-flow stage includes the valve seat for the next-lower flow stage. The heads and seats for the multiple stages are nested concentrically, the progressively lower-flow stages having progressively smaller diameters. All valve heads except the lowest-flow head have axial and radial bores permitting flow therethrough so that flow may be regulated first by actuating the lowest-flow stage, then by actuating successively higher flow stages. A single pintle shaft connected to a solenoid actuator is adapted to engage each of the valve heads sequentially as the actuator progresses, beginning with the lowest-flow head, thereby extending incrementally the dynamic range of the valve as each head is successively engaged. 
    
    
     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 pintle valve in closed position; 
     FIG. 2 is an elevational cross-sectional view of a first embodiment of an extended-range multiple-stage pintle valve in accordance with the invention, showing a two-stage valve with both stages closed; 
     FIG. 3 is a view like that shown in FIG. 2, showing the valve with the first stage open; 
     FIG. 4 is a view like that shown in FIGS. 2 and 3, showing the valve with both stages open; 
     FIG. 5 is a graph showing flow delivery curves as a function of actuator stroke for each of the individual stages and for the combined stages of the valve shown in FIGS. 2-4; 
     FIG. 6 is a cross-sectional view showing the embodiment of FIG. 2 installed for use as an EGR valve between the intake and exhaust manifolds of an internal combustion engine; and 
     FIG. 7 is a cross-sectional view of a second embodiment of an expanded-range multiple-stage pintle valve in accordance with the invention, showing a three-stage valve with the three stages closed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The benefits afforded by the present invention will become more readily apparent by first considering a prior art single-stage pintle valve. 
     Referring to FIG. 1, a prior art pintle valve  10  includes a valve body  12  having a valve seat  14  disposed in a first bore  15  between a first chamber  16  and a second chamber  18 . In use as, for example, an EGR valve, chambers  16  and  18  may communicate with the exhaust and intake systems, respectively, of an internal combustion engine (not shown in FIG. 1) 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 a second bore  24  in body  12 , coaxial with first bore  15 , and typically is actuated reciprocally by an external solenoid actuator (not shown) attached to pintle  22  to open and close the valve. 
     Referring to FIGS. 2-6, a two-stage pintle valve  26  having first and second stages  27 , 29 , respectively, in accordance with the invention includes a valve body  12  having a secondary valve seat  14 ′ in a first bore  15  separating first and second chambers  16 , 18 , and a second bore  24  for receiving a pintle as described below connected for reciprocal actuation to a conventional solenoid actuator (not shown). As will be seen below, the two-stage valve is operated first with its primary stage alone and then in combination with its secondary stage; the secondary stage cannot be operated without the primary stage. However, the presentation of components is facilitated by presenting herewith the secondary stage before the primary stage. 
     Coaxially disposed within chamber  18  is a secondary valve head  28 ′ having a secondary mating surface  30 ′ opposable to secondary seat  14 ′ for secondary regulation of fluid flow between chambers  16  and  18  across secondary seat  14 ′. 
     Secondary valve head  20 ′ is adapted as follows to contain and form part of a primary valve stage therein. Secondary head  20 ′ is provided with a central chamber  32  in communication with chamber  16  via a bore comprising a primary valve seat  14  and with chamber  18  via one or more radial bores  34 . Chamber  32  further is stepped to form an annular shoulder  36  for receiving a shaft stop washer  38  having an axially-extending cylindrical flange  40 . An optional spring stop washer  42 , also flanged, is included in the preferred embodiment. Head  20 ′ is provided with a cylindrical flange  37  surrounding shoulder  36 , which flange is rolled or crimped inwards during valve assembly, as shown in FIG. 2, to centrally position and immovably retain washers  38 , 42  within head  20 ′. 
     A well  44  in body  12  is receivable of one end of a partially-compressed coil spring  46 , the opposite end being received by spring stop washer  42 . A valve pintle  48  is axially and slidably disposed through second bore  24 , spring  46 , spring stop washer  42 , shaft stop washer  38 , and chamber  32 , and terminates in a primary valve head  20  having a primary mating surface  30  opposable to primary seat  14  for primary regulation of fluid flow between chambers  16  and  18  across primary seat  14  and via radial bores  34  in secondary head  20 ′. Primary head  20  is provided with an axial shoulder  50  having a diameter greater than the diameter of pintle  48  and flange  40 . The distance between shoulder  50  and flange  40  governs the extent of removal of surface  30  from seat  14  and therefore the total open area of the primary valve. 
     For optimal performance, shaft stop washer  38  preferably is formed of a lubricious material, for example, brass, to minimize friction with pintle  48 . Washer  38  may act as a bearing or guide for pintle  48  and therefore has a close diametrical tolerance to the pintle. Spring stop washer  42 , which guides the action of the spring and prevents contact of the spring with the pintle, may be formed of the same or different material as washer  38 . Preferably, the bore of washer  42  is slightly larger than the bore of washer  38 . 
     In operation, starting from a fully closed position as shown in FIG. 2, actuation of the solenoid actuator retracts pintle  48 , causing primary surface  30  on primary head  20  to be withdrawn axially from primary seat  14 , thereby permitting primary flow between chambers  16  and  18  through bores  34 . Spring  46  keeps the secondary stage closed during operation of the first stage. Shoulder  50  approaches flange  40  as the primary stage valve opens. When shoulder  50  engages flange  40 , as shown in FIG. 3, the primary valve is fully open. The metering range of the solenoid stroke for the primary stage is thus between fully closed and the engagement of the shoulder and flange. This distance may be varied by varying the axial length of flange  40  as desired for a particular application. In general, there is no benefit to making this distance greater than is required for the pressure drop across seat  14  to become substantially zero, beyond which point no further variable flow metering by the primary stage is possible, flow being governed by the total fixed cross-sectional area of bores  34 . 
     Because washer  38  is captured within secondary head  20 ′, continued axial retraction of pintle  48 , overcoming the spring force of spring  46 , causes secondary surface  30 ′ on secondary head  20 ′ to be withdrawn axially from secondary seat  14 ′, thereby permitting secondary flow between chambers  16  and  18  across seat  14 ′ in addition to the primary flow through bores  34 . Head  20 ′ may be withdrawn as far as may be desired for a particular application; as shown in FIG. 4, head  20 ′ may be withdrawn until flange  37  engages surface  52  of body  12 , spring  46  being compressed into well  44 . 
     Typical sigmoid flow curves for the primary and secondary stages as a function of pintle travel are shown as curves  54  and  56 , respectively, in FIG.  5 . The distance between shoulder  50  and flange  40  being approximately 2.5 mm, the secondary valve begins to open with pintle travel beyond that point. Thus the primary and secondary flows shown in curves  54  and  56  are added together as a total flow, shown in curve  58  which is an extension of primary curve  54 . 
     The advantage conferred by a two-stage pintle valve in accordance with the invention is shown clearly in FIG. 5. A prior art single-stage valve, such as valve  10  in FIG. 1, is capable of metering flow only over a limited flow range, such as is indicated to by curve  54  or curve  56 , depending upon the actual size of the valve. However, by placing a smaller valve within the metering head of a larger valve and operating both valves sequentially with a single pintle and actuator, as shown in FIGS. 2-4, an expanded metering range is obtained which is greater than can be obtained with any comparable single-stage valve. 
     Stage multiples larger than two-stage are possible. A three-stage pintle valve  57  in accordance with the invention is shown in FIG. 7, in which a tertiary stage  59  surrounds the primary and secondary stages  27 , 29  shown in FIGS. 2-4. The tertiary stage  59  is essentially a larger version of the secondary stage disclosed in the two-stage embodiment. A valve body  12  is provided with a first bore  15 ′ containing a tertiary seat  14 ″. A tertiary mating surface  30 ″ on tertiary metering head  20 ″ is opposable to seat  14 ″. The tertiary stage comprises elements analogous to those in the secondary stage: axial bores  34 ′, shaft stop washer  38 ′, spring stop washer  42 ′, flange  40 ′, spring  46 ′, shoulder  36 ′, chamber  32 ′, as well as secondary seat  14 ′. Chamber  32 ′ contains all the elements of the two-stage valve shown in FIGS. 2-4. Pintle  48 ′ is configured as shown in FIG. 7 to accommodate springs  46  and  46 ′ and to permit the pintle to operate primary head  20 , secondary head  20 ′, and tertiary head  20 ″ sequentially, in an operating sequence which is an obvious extension of the sequence discussed supra regarding the two-stage valve. 
     The invention is especially useful in the field of automotive engines, in which it may be desirable to recirculate a portion of the exhaust gases into the intake manifold to reduce the burn temperature of the mix and thus reduce formation of nitrogen and sulfur oxides. The invention permits use of an improved, single size, multiple-stage EGR valve on a wide range of engines, each usage being optimized for a specific engine displacement. FIG. 6 shows such a valve installed in an internal combustion engine between port  60  in an exhaust manifold  62  and port  64  in an intake manifold  66  to permit exhaust gas recirculation therebetween. 
     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.