Abstract:
An improved electrically operated pilot-type, “instant-on” solenoid assembly for near-instantaneous control over the flow of compressed gas. The assembly may be applied in fuel systems for propulsion in vehicles using gaseous fuel. It includes a housing with inlet and outlet passages connected to a primary chamber where a primary piston is slidably mounted, a secondary chamber having a secondary piston slidably mounted within the chamber, a solenoid to produce translational movement of the pilot piston, and passageways linking the various components. When the solenoid is energized, the pilot piston is moved to permit fluid to flow from the primary to the pilot chamber, producing an increase in the differential pressure in the regions of the primary chamber. The differential pressure then forces the primary piston to move, exposing the outlet to fluid flow from the gas inlet.

Description:
FIELD OF THE INVENTION 
     The invention relates to fuel systems for compressed natural gas fuelled (CNG) vehicles or the like. In particular, the invention relates to a solenoid assembly to control the flow of fuel for a CNG fuelled vehicle or the like. 
     BACKGROUND OF THE INVENTION 
     When compressed natural gas (CNG) is used to fuel vehicles, it is stored in thick walled cylinders at pressures as high as 4500 psig. As there is no fuel pump, an electrical solenoid is used to start and stop the flow of CNG from the cylinders to the engine&#39;s fuelling system. In order to ensure that the vehicle can be quickly re-fuelled, and that it can operate at low cylinder pressures, such solenoids require large orifices. Orifices of 0.150-0.250″ are common. Notably, at 4500 psig, 220 lbs. of force would be required to open a 0.250″ orifice solenoid. Such a force is beyond the capability of reasonably sized 12 Vdc direct acting solenoids. 
     Accordingly, pilot operated solenoids are used. Such solenoids have a direct acting portion (the pilot stage) which opens a small orifice (typically 0.015-0.030″ diameter). That small orifice supplies pressure (flow) to the downstream system. Once the pilot flow has nearly equalized the upstream and downstream pressures, a large (primary) stage opens. The primary stage would have the 0.150″-0.250″ diameter orifice. Both mechanical and pneumatic means are used to couple the pilot and primary stages. Such schemes require large, expensive solenoid coils, generating a significant amount of heat. Further, they are slow to open the primary stage at low cylinder pressures, causing driver complaints (engine won&#39;t accept throttle). 
     Ideally, such solenoids would open instantly (e.g. in less than 250 milliseconds). Further, they would be installed inside the neck of the thick walled cylinder. Such “internal” installation would protect them from physical abuse (both normally and in crashes) and would also protect them from environmental insult (salt spray, stone toss). However, most current solenoids are too large to fit within the neck of common cylinders. (Note: common cylinders neck openings may be as small as 0.840″). 
     Ideally such solenoids would be able to accommodate the two common flow configurations chosen by vehicle designers. One scheme, Configuration 1, has the solenoid&#39;s inlet connected to the gas inside the master cylinder. In that case, the master cylinder is refueled through the solenoid, and its primary piston acts as a back check valve. 
     In Configuration 2 the solenoid is supplied from an external manifold (fuel rail) which is common to all of the on-board storage cylinders. In that case, even though the solenoid would be installed inside one cylinder (e.g. the master cylinder) its inlet would be isolated from the gas in that cylinder. That is, its inlet would be connected to the external fuel rail. In that case, the master cylinder would not be fueled through the solenoid. Most common solenoids cannot accommodate both of these configurations. 
     Most common solenoids use rubber orifice seals, which are prone to manufacturing quality problems and to reliability problems in service. When solenoids are placed inside cylinders, the coil leads can be effected by the gas fill blast (high velocity and as cold as −190° F.). Ideally the coil wires would be shielded from the gas blast and/or routed so that the gas blast misses them. Further, many common solenoids place the primary sealing surface such that the fill-gas impinges directly onto the elastomer face. This condition reduces both the life expectancy and the reliability of those solenoids. 
     SUMMARY OF THE INVENTION 
     This invention provides an electrically operated, pilot-type, “instant-on” solenoid addressing all of the issues mentioned above. The advantages of this invention include but are not limited to the following: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 OPERATION: 
                 instant on (e.g. less than 250 m-sec) 
               
               
                   
                 SIZE: 
                 less than 0.840″ in diameter 
               
               
                   
                 FLOW PATH: 
                 adaptable to Configuration 1 or 2 
               
               
                   
                 POWER: 
                 low power continuous duty 12 Vdc coil 
               
               
                   
                 ORIFICE SEALS: 
                 hard elastomer (e.g. Teflon[PW1], vespel) 
               
               
                   
                 SEAL LOCATION: 
                 not impinged by fill gas 
               
               
                   
                 WIRE SHIELDING: 
                 coil wires routed inside solenoid 
               
               
                   
                   
               
             
          
         
       
     
     This invention is also simple in design and does not require expensive tooling. 
     In its first form, the invention operates from the gas inside the master cylinder and acts as a re-fuelling check valve. In a second embodiment, the invention is slightly modified to be installed inside a cylinder, while operating from an external fuel rail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described by way of example and with reference to the drawings in which: 
     FIG. 1 is a general cross-sectional view of the first embodiment of the invention; 
     FIG. 2 is another detailed cross-sectional view of the first embodiment of the invention; 
     FIG. 3 is a further detailed cross-sectional view of the first embodiment of the invention; 
     FIG. 4 is a detailed cross-sectional view of the second embodiment of the present invention; and 
     FIG. 5 is a detailed cross-sectional view of the third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Configuration 1 
     This invention has a primary and a pilot piston, preferably placed in line with each other. According to one embodiment of the invention, the primary piston has a tight fit to its bore, such that the annular clearance area is preferably equivalent to an orifice of diameter about 0.022″. The direct acting pilot opens a pathway for the fluid to the outlet with an effective flow area of typically about 0.030″ diameter. The pilot piston connects the “backside” of the primary piston to the outlet port (e.g. low pressure). As a result, as soon as the pilot opens, a large differential pressure appears across the primary piston, forcing it open regardless of inlet pressure. As the 2 pistons are pneumatically coupled, the only coil force needed is that required to open the pilot piston (0.795 lbs for a 0.015″ orifice at 4500 psig). Thus, a low power continuous duty coil can be used, for example, a 12 V dc coil. In fact, the long, thin solenoid design provides a very low power density (watts/square inches), ensuring that the solenoid will run cool. 
     Referring to FIG. 1, the solenoid assembly according to the present invention receives gas from the master cylinder through a series of channels (possibly radially drilled holes)  24  in body  20  (typically about 4-6 holes). If the solenoid is off, as shown, spring  50  acts to move primary piston  30  downwards to its closed (no flow) position. Raised lands on that piston seat against the primary seal  40 , providing a gas tight seal. In the off state, spring  90  also acts to move pilot piston  70  downwards to its closed (no flow) position. The pilot seal  80  contained within the pilot piston seals against a raised sealing in body  20 , preventing gas flow through the pilot orifice channel  22   b.  Note that in the off state, the input-output differential pressure acts to help close both pistons. 
     If the coil windings  140  are energized, pilot piston  70  (made of ferromagnetic material, e.g. magnetic steel) opens. When the pilot piston  70  is open the back side of primary piston  30  is connected to the outlet channel  11  via the following path: a channel  22   e,  pilot orifice channel  22   b,  channel  22 C, channel  22   a,  connector channel  46 , channel  17 , channel  18 . The resulting differential pressure across the primary piston  30  forces it to its open position. Channel  22   c  is sealed via a permanent ball-and-cup type of plug  60 . The assembly is connected to a cylinder valve (not part of this invention)) at the end of adapter  10 , most typically via threads. A magnetic pole piece  120 , a tubular ferromagnetic (e.g. magnetic steel) coil cover  130 , and a flux washer  110  complete the coil&#39;s flux path. 
     Referring now to FIGS. 1 and 2, the assembly is preferably attached to a cylinder valve (not part of this invention) by adapter  10 , typically using threads  12  to secure the connection. O-Ring  14   a,  acting against O-ring gland  13  and a companion gland in the cylinder valve seals the adapter from external leaks. Any gas flow from the solenoid passes outwards from outlet channel  11  and on into the cylinder valve. In this version, threads  15  in adapter  10  mate with threads  23  in body  20 , rigidly securing them together. O-ring  14   b,  acting against glands  16  and  23   a,  seals adapter  10  to body  20 . Channel  18  connects the outlet channel  11  to channel  17 . A shoulder on adapter  10  engages a companion shoulder  25  in body  20 , providing a positive stop as  10  and  20  are threaded together. Shoulders  19  and  25   a  provide sealing surfaces for primary seal  40 . 
     Channel  22   a  intersects annular groove  26  in body  20 . This ensures that the “venting gas” from  22   a  will always connect with the connector channel  46  in seal  40  (see FIG.  1 ), regardless of how the adapter  10  and body  20  may index as they are tightened. Body  20  preferably contains a 3-step bore ( 21   a - b - c ) for primary piston  30 . Gas from the master cylinder enters bore area  21   a  through inlet  24  in body  20  (typically about 4-6 equally spaced holes). The annular area between bore  21   a  and piston outside diameter  31  is sized to be non-restrictive to flow compared to the downstream through the pilot chamber. Bore section  21   b  is sized to provide a small clearance with piston outside diameter  32 . This small clearance, clearance (typically 0.005″) minimizes the possibility of debris migrating into the tight clearance between bore  21   c  (known as the back section of the primary chamber) and piston outside diameter  32 . The clearance between  21   c  and  32  is small (less than about 0.001″), so that the equivalent flow area through the annular gap will be less than approximately 0.025″. For example, if  21   c= 0.249″ and  32 =0.250″, the annular gap would be equivalent to a 0.022″ orifice, which would be thoroughly vented by a 0.035″ pilot orifice channel  22   b.    
     Preferably, a spring pocket  33  in piston  30  acts to hold the primary return spring  50 . The steps in the bore  21   a - 21   b - 21   c  are preferably selected so that the larger piston diameter  31  seats against the end of bore  21   b  (a positive stop) before the spring pocket end of the piston hits the end of bore  21   c.  Bore area  21   c  is connected to the pilot piston bore  28   a  via channel  22   e,  the latter otherwise known as the primary channel (see FIG.  1 ). When the solenoid is off, the pilot piston seal  80  (FIG. 1) seats preferably against a conventional conical seat  28   b,  preventing leakage to the outlet. When the coil is energized, pilot piston  70  and seal  80  move to their open position, allowing flow from pilot bore  28   a  into pilot orifice channel  22   b.  This vented gas then passes sequentially from channel  22   b  to channel  22 C to channel  22   a  to connector channel  46  to channel  17  to channel  18  and into outlet channel  11 . This pilot chamber vent path ( 22   e - 28   a - 22   b - 22   c - 22   a - 46 - 17 - 18 - 11 ) causes the outlet pressure to exist at backside of primary piston  30 . Since piston  30  has the inlet-outlet pressure differential across its length, that differential pressure forces primary piston  30  to its open position. Channel  22   b  is sealed from potential leakage by preferably a ball and cup plug  60 , which is permanently installed in socket  22   d.  Potential leakage passes seal  40  is prevented preferably by the circumferential clamping action of the edge of body  20  at  45  (see FIG.  3 ). 
     For the solenoid, the coil  140  is preferably wound on core tube  100 . The coils termination wires are preferably routed through channel  29   a  in body  20 . The wires enter  29   a  at an expanded opening  29   b  and exit at the expanded exit area  29   c.  Channel  29   a  is preferably placed midway between the inlet  24  so that the gas blast during refilling cannot impinge on the wires near  29   c.  The entry point  29   b  is further protected from gas blast by the bottom edge  132  (see FIG. 3) of coil cover  130 . Threads  27   a  in body  20  mate with threads  102  (FIG. 3) to hold the core tube. O-ring gland  27   b  and O-ring  27   c  seal body  20  to core tube  100 . Shoulder  27   d  provides a positive stop for  100  as it is threaded into  20 . 
     During refueling of the gas source, all gas flow patterns are reversed. Gas enters at outlet channel  11 , impinges on primary piston  30 , forcing it open, The gas then turns and exits through inlet  24  into the cylinder. Notably, the filling gas does not impinge on the primary seal  40 . Thus, the refueling process does not reduce its life expectancy. 
     Referring to FIG. 3, the outside diameter  71  of pilot piston  70  rides in the central bore  101  of core tube  100 . Due to the low production volumes that are expected for this product, core tube  100  is typically made of brass. A reasonable radial clearance is used (e.g., 0.005″) to minimize the air gap while limiting manufacturing expense. A pocket  72  receives the pilot seal  80 , which may be secured by a number of known means. The outside diameter  81  of seal  80  is chosen so as be a slight press fit into pocket  72 . A typical securing method would use a {fraction (1/16)}″ SAE spring pin passed through  70  and  80  at the vertical center of  80  (not shown). The sealing face  82  would be flat and free of burrs or radial scratches so that it forms a good seal against the horizontal face of  28   b.  A spring pocket  73  provides a location for pilot piston return spring  90 . 
     A gland  103  in core tube  100  acts with o-ring  27   b  to seal the core  100  to  20 . The flat bottom edge  104  both completes the o-ring gland and serves as the positive stop when core tube  100  is threaded into  20 . Face  104  terminates at outsider diameter  106 , which is chosen so as to leave room to route the coil leads past and into entry area  29   b.  Otherwise, the outside of the  100  is at outside diameter  107 , which is the diameter upon which the coil is wound. A flux washer  110 , magnetic steel is installed from the top of  100  and seated against the bottom of outside diameter  107 , seating firmly at  105 . The inside diameter  111  of flux washer  100  is chosen so as to be a slight press fit onto  107 . The outside diameter  112  is chosen to provide a snug fit with the inside diameter of coil cover  130 . A pocket  114  is provided in  110  so that the coil termination leads  146  may be routed before cover  130  is installed. This pocket is necessary since the location of coil leads  146  may not match up exactly with the location of the entry area  29   b.  In such case, leads  146  are routed circumferentially in pocket  114  to entry area  29   b.    
     Again, to minimize cost, the coil is preferably wound directly onto core tube  100 . A plastic insulator  143  is installed over bore  107  and seated against the upper face of flux washer  110 . A second similar plastic insulator  142  is installed at the top end of bore  107 . A pole piece  120 , typically magnetic steel, is threaded into  100  until its shoulder  125  provides a positive stop. Insulator  142  is then moved upwards to seat against  120 . A layer of insulating tape  144  is wrapped over outer diameter  107  and magnet wire  141  is then applied. A nominal design would have 10 layers of 28 awg copper magnet wire, comprising 1030 turns and 11 ohms of resistance. Magnet wire  141  would then be attached to plastic insulated copper wire  146 . 
     Pole piece  120  has 2 holes  128  to provide for tightening. Slot  127  provides for an E-type snap ring (not shown) to be installed. Alternatively, both a wave washer and a snap ring could be used. The outside diameter  126  of the pole piece is selected so as to provide a snug fit with cover  130 . Coil cover  130  is a ferromagnetic tube typically made of magnetic steel. After cutting the tube to length, one end of the tubing is rolled over, forming lip  131 . The E-type snap ring then engages lip  131  to clamp the coil cover in place. 
     Configuration 2 
     The above design can be adjusted to accommodate the Configuration 2 form described in the Background Section. That is, in this second embodiment, the gas inlet is external, and the master cylinder is not re-filled through the solenoid and the solenoid does not act as a check valve during refueling (see FIG.  4 ). In this case, the gas inlet and outlet must occur through a single connection. To accomplish this, a side inlet, center outlet configuration is chosen, with o-ring seals separating the inlet and outlet. Specifically, adapter  10  is replaced with adapter  210 . Adapter  210  has an annular groove  234   a,  which receives the gas inlet form a port in the side of the cylinder valve&#39;s single port. O-ring  234   c  acts to seal body  210  so that the inlet and outlet ports are kept isolated. Groove  234   a  is intersected by several channels  234   b,  which route the inlet gas to the primary piston cavity  221   a.  There would typically be about 5 equally spaced holes  234   b.    
     The primary orifice seal function of seal  40  would be replaced by seal  240 , which is preferably moved into the primary piston. An appropriate sealing face  210   a  would be machined onto  210 , against which  240  would seal. Primary piston  30  would be replaced by piston  230 , which is modified to hold seal  240 . The seal could be held in place by a variety of known means, with the {fraction (1/16)}″ SAE spring pin being the most common choice (not shown). Body  220  replaces body  20 , which has only a few differences. In order to accommodate the seal moving into the piston, the outside diameter  231  is slightly larger than outside diameter  31  was. The annular gap between  221   a  and  231  is similarly chosen to be non-restrictive to flow. As before, bore  221   b  is chosen so as to minimize the chance of debris migrating into the tight tolerance area of  221   c - 232 . Diameters  221   c  and  232  would be the same as  21   c  and  32 . A new seal  245  would assume the feature where seal  40  seals the vent gas path. Seal  245  is essentially a narrower version of seal  40 . A channel  246  in seal  245  communicates the venting gas from  222   a  to channel  217  in body  210 . Due to the size of diameter  221   a,  the wire exit point  29   c  must move upwards, becoming  229   c.  Similarly, to accommodate the size of  221   a,  channel  22   a  becomes channel  222   a,  which is positioned at an angle to ensure acceptable wall thickness. The gas outlet channel  11  becomes  211 . Otherwise the solenoid for Configuration 2 would be the same as for Configuration 1 in these embodiments. 
     Piston-ring Embodiments 
     FIG. 5 depicts alternative embodiments of the coil and primary piston parts of this invention. The coil style shown is applicable to cylinders with larger thread neck sizes (for example 2″ threads). The alternative primary piston style shown is applicable to any use of this invention and is more tolerant of dirt and extreme temperatures. 
     The solenoid valve as shown in FIG. 5 is substantially the same a shown in FIGS. 1,  2  and  3 . However, it will be appreciated that the embodiments shown here are equally applicable to the format shown in FIG.  4 . However, a 3-step bore may not necessary in this case due to the way the differential pressure is created; a 2-step bore is sufficient. 
     As shown, the primary piston  330  slides within a central bore  321   b  of body  320 . Gas from the cylinder enters bore area  321   b  and if primary piston  330  is open, passes to outlet channel  11  in body  10 . If primary piston  330  is closed, as shown, gas flow is prevented by primary piston  330  seating against seal  40 . 
     Primary piston  330  has an outer diameter  331  which slides in bore area  321   b.  These two parts would typically have a relatively large clearance to better tolerate dirt and temperature extremes. The  331  portion of the piston would also have a piston ring gland  331   a,  which would receive a piston ring  331   b.  Ring  331   b  could be of either metallic or plastic construction. In the intended application, the ring may only stroke and pressure cycle 50,000 times in its useful life. Thus wear and strength properties are not major issues. Suitable rings are commercially available or can be readily manufactured. Ring  331   b  would be sized to match bore  321   b,  and would have a small gap in the ring when installed on the piston. The gap would be sized to create the flow restriction needed for the solenoid to open quickly at any input pressure. For example, if the bore ( 321   b ) was 0.375″ and the piston ( 331   a ) was 0.368″, a 16° angular gap between the ring ends would have a flow area equivalent to a 0.015″ orifice. Ring gap, ring thickness, ring material (yield strength), and the piston-bore clearance would be chosen to ensure that the ring would not extrude into the clearance gap during opening (e.g. during the brief time when a large differential pressure exists across the ring faces). By adjusting the piston to bore clearance, the invention&#39;s tolerance to contamination and to differing coefficients of expansion can be enhanced. 
     FIG. 5 also depicts the use of a more conventional coil construction method. As shown, a plastic overmolded coil, with strain relieved wire exit is used. Instead of a cylindrical coil cover, a lower cost C-shaped “yoke” is used for the flux return path. While this approach is less costly, it requires slightly more space and is therefore applicable to larger gas cylinder thread sizes. 
     The coil  440  consists of magnet wire  441  would on a spool shaped bobbin  442 . The assembly is overmolded  443  with plastic to provide environmental tolerance. A bulge  444  in the overmolding houses the wire terminations  445  which joins the coil&#39;s magnet wire to the leads  446 . In order to protect the wires from the gas blast during filling, the leads  446  would be retained to the body  320  by a suitable cable clamp (not shown). That is, they would be held to the body midway between the radial fill/discharge holes. The core tube  420  would be shorter than the core tube  100  from FIG. 1, as the wire routing and part  110  have been eliminated. A shoulder  404  in core tube  400  would be sized based on strength requirements. Pole piece  420  would be somewhat smaller and would be sized to engage a companion hole in flux yoke  430 . As shown, pole  420  has a gland to receive an external E-ring (snap ring) to retain the yoke  430 . Yoke  430  serves as the flux return path and is made from a suitable magnetic steel or stainless steel. Pilot piston  370 , which acts against return spring  390 , is shorter so as to match the length of core tube  400 . 
     The operation of the solenoid the same as previously described. If coil  440  is energized, pilot piston  370  overcomes spring  390  and moves upward to its open position. Gas in chambers  321   b  and  321   c  is evacuated to the downstream section (e.g. low pressure) via connecting passages  322   e - 322   b - 322   c - 322   a - 46 - 17 - 18 - 11 , also known as the pilot chamber vent path. As the area of the piston ring gap is much smaller than the effective flow area through the pilot chamber vent path, the evacuated pressure cannot be fully replaced. Thus, a large differential pressure exists across ring  331   b,  forcing piston  331  upward to its open position. 
     It should be obvious to a person in the art that a 3-step bore is not necessary for the primary chamber due to the way the differential pressure is created; a 2-step bore would be sufficient but a 3-step will also work. 
     In FIGS. 1 to  5 , connector channel  46  is shown drilled through orifice seal  40 . In another embodiment of this invention, connector channel  22   a  can be positioned by bypass orifice seal  40  so as to avoid contact with the hard elastomer orifice seal, and connector channel  46  would not be needed. 
     In all forms (FIGS. 1 through 5) the pilot and primary pistons ( 370 ,  330 ) are pneumatically coupled. As a result, the position of the primary piston  330  varies with inlet pressure, outlet pressure and flow rate, even though the solenoid is continuously energized. At higher flow rates the primary piston  330  will be held in its fully opened position. At lower flow rates, the primary piston  330  will tend to move to a point between open and shut, acting as a constant pressure drop device. Under no flow conditions, the primary piston will move to its closed position and stay there until flow is again demanded by the downstream system. For example, if the load from spring  350  was 1.1 lbs. when piston  330  is fully-open, and diameter  321   b  was 0.375″, the input output differential pressure would be 9.95 psi. This characteristic is quite acceptable to a gaseous fuel injection system. 
     Although the above description discusses compressed natural gas for vehicular use, it is obvious to the person versed in the art that the invention is equally useful for the flow control of any pressurized gas. 
     It will be appreciated that the above description relates to the preferred embodiment by way of example only. Many variations on the invention will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described.