Abstract:
A two stage exhaust gas recirculation (EGR) valve delivers a wide range of EGR flow while operating with reduced valve actuating forces allowing use of a reduced cost actuator such as a solenoid with smaller sized coil and armature. An attached valve body mounts concentric dual pintle valves including a larger first valve, which engages a valve seat in the valve body to control exhaust gas flow between inlet and outlet openings and a smaller second valve positioned inside the first valve and engaging a second valve seat in the head of the first valve. The second valve controls a low flow passage inside the first valve. The solenoid armature engages only the smaller second valve during a first stage of its stroke so that the smaller valve is opened first and flow control is maintained in a low flow range. Exhaust and intake differential pressures acting on the second valve are overcome by a smaller armature force because of the smaller area of the second valve. In a second stage of its stroke, the armature also engages the first valve, forcing it off its seat and providing a greater amount of exhaust flow. Opening of the larger first valve requires less force than a single pintle valve because the flow from the open smaller valve reduces the pressure differential in the valve body and thus reduces the force opposing opening of the larger valve.

Description:
TECHNICAL FIELD 
     This invention relates to exhaust gas recirculation valves for internal combustion engines and more particularly to solenoid actuated pintle type valves having sequential dual flow stages. 
     BACKGROUND OF THE INVENTION 
     It is known in the art to provide an automotive internal combustion engine with an exhaust gas recirculation (EGR) valve to control a flow of exhaust gases into the engine induction system and limit the formation of nitrogen oxides (NOx) in the engine. Known valve constructions include pintle type valves which have an axially movable valve with a shaped mushroom-like head connected with an axial pintle shaft. The head is seatable upon a valve seat within a valve body and controls flow between inlet and outlet openings on opposite sides of the valve seat. An actuator such as a solenoid actuated armature is provided to controllably drive the valve axially and open the valve in a controlled manner to obtain the amount of EGR required under various engine operating conditions. A valve spring biases the valve in a closing direction to close the valve when the armature is returned to the initial valve closed position. 
     Where a large variation in EGR flow is required, the pintle head and orifice are shaped to provide the required variation in flow. However, a relatively long travel of the armature may be required in such valves. In addition, the solenoid force required to open the valve from the closed position must be large enough to overcome unbalanced pressures in the valve body or seat tube so that a relatively large solenoid coil and armature maybe needed. It is accordingly desired to provide a solenoid or otherwise actuated EGR valve that operates with a lower actuating force while providing a full range of controlled exhaust gas recirculation flow. 
     SUMMARY OF THE INVENTION 
     The presentation invention provides two stage exhaust gas recirculation (EGR) valves that can deliver a wide range of EGR flow while operating with reduced valve actuating forces. A reduced cost actuator, such as a solenoid actuator with smaller sized coil and armature, may thus be used for actuating the valves. An attached valve body mounts dual pintle valves including a larger first valve which engages a valve seat in the valve body to control exhaust gas flow between inlet and outlet openings on axially opposite sides of the valve seat. A smaller second valve is positioned inside the first valve and engages a second valve seat in the head of the first valve. The second valve controls a low flow passage inside the first valve to also control a lower volume of exhaust gas flow between the inlet and outlet openings. 
     The solenoid armature engages only the smaller second valve during a first stage of its stroke so that the smaller valve is opened first and flow control is maintained in a low flow range. Exhaust and intake pressures acting on the second valve require low force to overcome because of the smaller area of the second valve. In a second stage of its stroke, the armature also engages the first valve, forcing it off its seat and providing a greater amount of exhaust flow. Opening of the larger first valve requires less force than single pintle valves because the flow from the open smaller valve reduces the opposing opening of the larger valve. 
     The dual concentric pintle valve design may also be applied to partially or fully balanced valves to provide better control of EGR flow over the full control range of the valve. Additional effective travel of the valve armature may be obtained by underlap of the armature and its magnetic pole so that the smaller valve is opened as the armature force increases to a maximum, leaving the maximum armature force for opening of the larger valve. 
     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 through a solenoid actuated two-stage concentric pintle EGR valve in accordance with the invention; 
     FIG. 2 is a schematic view illustrating various initial positions of the valve armature relative to an associated magnetic pole; 
     FIG. 3 is a graph comparing armature magnetic force versus valve travel for the initial armature positions shown in FIG. 2; 
     FIG. 4 is a fragmentary cross-sectional view similar to FIG. 1 but illustrating a modified valve providing partial pressure balancing; and 
     FIG. 5 is a view similar to FIG. 4 but showing a further modified valve providing full pressure balancing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 of the drawings in detail, numeral  10  generally indicates a two-stage exhaust gas recirculation (EGR) valve in accordance with the invention. Valve  10  includes an upper housing  12  enclosing a magnetic coil  14  surrounding an armature  16  reciprocable on an axis  17  within a non-magnetic sleeve  18 . The sleeve  18  extends into a recess  19  in a primary pole piece  20  extending outwardly under the coil  14  and forming a lower wall of the housing  12 . While the armature  16  may be of any suitable shape, it is preferably cylindrical and, in the present instance, includes a small protrusion  22  on its primary lower surface  23  extending axially downward for a purpose to be subsequently described. The housing also includes a secondary pole piece  24  extending across upper portions of the coil  14 . A position sensor  26  may be mounted on the top of the housing having a spring-loaded drive arm  28  engaging the top of the armature to sense its position for control purposes. 
     Centrally positioned on the lower side of the primary pole piece  20  is a circular recess  30  in which is received a flanged upper portion  32  of a thin wall drawn metallic seat tube or valve body generally indicated by numeral  34 . The valve body  34  is generally cylindrical although the upper portion  32  is enlarged and includes a stepped portion defining an annular abutment  36 . A floating bushing  38  is received in the upper portion  32  and seats against the abutment  36 . A wave spring  40  between the pole piece  20  and the bushing  38  holds the floating bushing downward against the abutment  36 . Below the abutment  36 , the valve body  34  is generally cylindrical, having an inwardly extending valve seat  42  intermediate its ends and an end cap and bushing  44  crimped into its open lower end. 
     The lower portion of the valve body  34  defines internally a valve chamber  46  divided by the valve seat into a lower inlet portion  48  and an upper outlet portion  50 . An inlet opening  52  communicates with the inlet portion to receive exhaust gas from the exhaust system, not shown, of an associated engine. An outlet opening  54  communicates with the outlet portion to deliver recirculated exhaust gas to the intake system, not shown, of the associated engine. 
     Within the valve chamber  46 , first and second pintle valves  56 ,  58 , respectively, are mounted for reciprocation on the axis  17 . The first valve  56  includes a head  60  adapted to seat against the valve seat  42 . The head connects with a hollow pintle shaft  62  that extends up through a close clearance opening in the floating bushing  38  into a lower portion of the sleeve  18  within the primary pole piece recess  19 . An upper end of the shaft  62  is spaced a predetermined distance below the axially adjacent primary lower surface  23  of the armature  16  for a purpose to be subsequently described. A retainer cap  66  is crimped onto the upper end of the valve shaft  62  and retains a biasing spring  68  extending between the cap  66  and the floating bushing  38  for biasing the first pintle valve in a closing direction toward the valve seat  42 . 
     The second pintle valve  58  is concentrically mounted within the first pintle valve  56  which internally defines a second valve seat  70  at the lower end of the valve head  60 . The valve seat  70  communicates with an axially extending low flow passage  72  that extends upward within the valve shaft  62  to an outlet opening  74 . 
     The second pintle valve  58  includes a relatively smaller valve head  76  that is seatable against the second valve seat  70  in the first pintle valve  56 . Valve  58  further includes a pintle shaft  78  that extends axially up through low flow passage  72  in the first valve and upward into close supporting clearance with a reduced diameter portion  80  of the hollow interior of the first pintle shaft  62 . Shaft  78  extends upward into contact with the downward protrusion  22  of the armature. 
     Below the second valve head  76 , a lower pintle shaft  82  extends downward into a guide opening  84  in the bushing and end cap  44 . Shaft  84  engages a second biasing spring  86  which is adjustable by a set screw  88  located at the bottom end of the end cap  44  and closing the lower end of the guide opening  84 . 
     In assembly with an engine, housing  12  is mounted upon an outer surface of an engine component, such as a cylinder head or manifold, and the seat tube or valve body  34  extends downward into an opening within the engine component, not shown. The lower inlet portion  48  of the valve chamber communicates through opening  52  with a passage, not shown, in the exhaust system of the engine and the upper outlet portion  50  of the valve chamber communicates through an outlet opening  54  with a passage not shown in the induction system of the engine. 
     In operation, when only a small amount of exhaust gas recirculation is required, the coil  14  is energized at a low level, causing the armature  16  to move downward a small amount. The downward motion forces protrusion  22  of the armature against the shaft  62  of the second pintle valve  58 , forcing it downward against biasing spring  86 . This opens the low flow passage  78  to flow from the inlet portion  48  of the valve chamber, past the second valve head  76  and through the low flow passage  72  to outlet opening  74 . There, the exhaust gas passes out into the outlet portion  50  of the valve chamber and out through outlet opening  54  into the engine induction system, not shown. 
     This initial downward movement of armature  16  requires a relatively low force to open the second pintle valve  58  because the small size of the valve head  76  limits the force of differential exhaust and inlet pressures acting on the head  76 . If the need for EGR flow remains low, the energy of the magnetic coil  14  is controlled at a low level to obtain the desired amount of exhaust gas flow by movement only of the second pintle valve  58  toward and away from its seat  70  located in the head of the first pintle valve. 
     When a greater flow of recirculated exhaust gas is required, the magnetic energy of the coil is increased, causing the armature  16  to move further downward until its primary lower surface  23  engages the retainer cap  66  at the upper end of the first pintle valve shaft  62 . Further downward motion of the armature forces the first pintle valve  56  downward, moving the head  60  off its seat and opening the first valve to greater flow past the valve seat  42  from the lower portion  48  to the upper portion  52  of the valve chamber. 
     Because opening of the smaller second pintle valve precedes opening of the larger first pintle valve in every case, a flow of exhaust gases through the low flow passage  72  reduces the pressure differential between the inlet and outlet portions of the valve chamber  46  prior to opening of the first pintle valve  56 . The reduced pressure differential results in a reduced requirement for magnetic energy to open the first pintle valve and thus the size of the magnetic coil  14  and armature  16  required for actuating the concentric dual pintle valves of the invention is reduced as compared to a single pintle valve which must be opened against a larger pressure differential between inlet and outlet portions of a valve chamber. The design accordingly allows reduction of the size of the solenoid members of the EGR valve  10 , resulting in a more compact construction and a reduction in cost. At the same time, better control is provided of EGR flow through the valve by the dual stage operation of the second and first pintle valves. 
     Referring now to FIG. 2, numerals  90 ,  92  and  94  illustrate various initial positions for the primary lower surface  23  of the armature  16  in the valve closed position relative to the adjacent upper edge  95  of the pole piece  20  of the valve. FIG. 3 presents a graph which compares force exerted by the armature against travel of the armature under the conditions indicated in FIG.  2  and illustrated by corresponding curves  90 ,  92  and  94 . It will be seen that in position  90 , the armature extends within and therefore overlaps the pole piece  20  a small amount in the initial position of the armature. In this condition, the curve  90  of FIG. 3 shows a relatively constant relation of force versus travel of the valve with the amount of force decreasing as the amount of valve travel increases. However, the maximum force, which might be applied by the armature, is less than that which is available from the design of the solenoid components. 
     Position  92  as shown in FIG. 2 has the main lower surface  23  of the armature  16  aligned with the upper edge of the pole piece  20 . The corresponding curve  92  of FIG. 3 illustrates that the initial motion of the armature occurs at the point of the maximum magnetic force, dropping off rapidly in a relatively constant curve of force versus travel similar to that of curve  90 . For an ordinary single pintle EGR valve, this would be the most desirable position for setting of the armature since the maximum magnetic force would be applied at the point of opening of the valve, where maximum force is required to overcome the differential pressure between the exhaust and intake systems acting across the valve head. 
     However, an alternative positioning of the armature  16  relative to the pole  20  in an underlapped condition is illustrated in FIG. 2 by numeral  94 . In this condition, the primary lower surface  23  of the armature is positioned axially outward from the upper edge of the pole piece  20  so that initial motion of the armature occurs with less than the maximum available force. 
     Referring to FIG. 3, and line  94  therein, the force versus travel of the underlapped arrangement of FIG. 2 is illustrated. As may be seen, the armature force at initial valve opening is lower but increases to the maximum amount at the peak of the curve, after which it moves downwardly in a relatively constant ratio of force versus travel. It is this latter arrangement which is suggested as preferable for a concentric dual pintle valve of the type shown in FIG.  1 . With this arrangement, the primary lower surface  23  of the armature  16  would be aligned with the upper edge of the primary pole piece  20  at the point where the lower surface  23  engages the upper end of stem  62  of the larger first pintle valve or the retainer cap  66  mounted thereon. Thus, initial opening of the smaller valve will be accomplished with a reduced armature force. This is acceptable because of the lower forces acting on the smaller valve which allow armature actuation with less than the maximum available armature force. Then, when the smaller valve is fully opened, the armature engages the larger first pintle valve at the point where the armature force is at a maximum and thus opens the larger valve at the armature&#39;s maximum force point. As the armature continues downward, the magnetic force developed is reduced, however it is sufficient to fully open the valve against the biasing spring and allow control of the valve opening to proceed along the curve  94  with a predetermined calibration of valve position versus force developed. 
     Use of the curve  94  and the underlapped position of the armature as suggested, requires a dual calibration of the curve for control of armature position and valve opening by the control program providing electric energy to the coil  14 . The first calibration is of the left-hand portion of the curve from the initial opening of the smaller valve to the maximum magnetic energy point at the top of the curve. The second calibration extends from the top of the curve downward to the right along the relatively constant portion of line  94  as shown if FIG.  3 . With these dual calibrations, the position of the armature can be located by a corresponding control program responding to the sensor drive arm  28  so that proper operation of the EGR valve can be maintained under all circumstances. 
     Referring now to FIGS. 4 and 5, there are shown alternative embodiments of the valve body portions of EGR valves generally indicated by numerals  96  and  98  respectively. Both valves utilize some of the components from valve  10  of FIG. 1 so that like numerals indicate like parts. In FIG.  4 ,valve  96  differs in modification of the first pintle valve  100  to include a balance piston  102  received within a cylinder  104  in a modified floating bushing  106 . The piston  102  has a close clearance in the cylinder  104  and defines a balance chamber  108  which communicates with ambient pressure through clearance  110  between the shaft  112  of valve  100  and a through opening  114  of the bushing  106 . 
     In operation, ambient pressure in chamber  108  approximates exhaust pressure in the lower portion  48  of the valve chamber  46  and thus reduces the pressure differential acting on the first pintle valve  100  so that opening of this valve can be accomplished with less magnetic force than without the balancing piston arrangement. 
     In FIG. 5, valve  98  includes a first pintle valve  116  with a balance piston  102  in cylinder  104  of floating bushing  106  like the corresponding components of the embodiment of FIG.  4 . However, the balance chamber  108  is sealed against exposure to ambient pressure by a shaft seal  118 . Instead, when the second pintle valve  58  is open, the balance chamber  108  communicates with the valve chamber lower inlet portion  48  to balance pressures on the first pintle valve  116  and allow it to be opened with a smaller magnetic force than would be needed for an unbalanced valve. The communication of balance chambers  108  is through balance ports  120  in the first pintle shaft  122 , then through increased clearance  124  between the upper portion of the second pintle shaft  78  and a through opening  126  in the first pintle shaft  122  through which the stem  78  extends, and finally through the low flow passage  72  which in turn connects with exhaust pressure in the inlet portion  48  of the valve chamber when the second pintle valve  58  is open. 
     The specific construction of various components of the illustrated embodiments of the invention is intended to be exemplary and not limiting as to the invention. Thus, the drawn seat tube or valve body could be replaced by a casting or other suitable structure. Similarly the pintles, bushing, end cap and components of the solenoid actuator may be replaced with suitable alternative constructions. Also, other forms of actuators, such as stepping motors or pressure devices, could be used instead of a solenoid armature and such known alternative devices should be considered within the scope of the claims. 
     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.