Patent Publication Number: US-6988488-B2

Title: Fuel pressure relief valve

Description:
This application claims the benefit of U.S. Provisional Application No. 60/462,974, filed Apr. 15, 2003. 
    
    
     BACKGROUND 
     The present invention relates generally to fuel delivery systems, and more particularly to a fuel valve. 
     Several known government standards exist for measuring the amount of evaporative emissions that an automotive vehicle emits during time periods of non-operation. Examples of such government standards are those issued by the Environmental Protection Agency and the California Air Resources Board. In order to measure evaporative emissions, one common test involves operating an automotive vehicle until the vehicle reaches normal operating temperature. The automotive vehicle is then turned off and moved into a sealed chamber. Next, a set of chemical sensors measure the amount and type of emissions released by the vehicle over a time period of several days. During the time period that the emissions are being measured, typical environmental conditions are duplicated, such as the diurnal temperature cycle of rising ambient temperature during the middle of the day and the falling ambient temperature at night. 
     One source of emissions is fuel leakage from the fuel delivery system. Typically, when fuel leaks from the fuel delivery system, the leaked fuel turns to a vapor and is thus sensed by the chemical sensors during evaporative emissions tests. As a result, fuel leakage from the fuel delivery system has a negative impact on automotive manufacturers efforts to satisfy the evaporative emissions standards currently issued and any future standards that might be issued by the Environmental Protection Agency and the California Air Resources Board. 
     Fuel leakage typically occurs because the fuel delivery system remains pressurized after the automotive vehicle is turned off. Maintaining fuel pressure in the fuel delivery system after a vehicle is turned off is a common practice of automotive manufacturers in order to keep the fuel system ready to quickly restart the engine. There are several desirable reasons for keeping the fuel system filled with fuel during periods of non-operation. Those reasons include minimizing emissions during restart and avoiding annoying delays in restarting. However, because the fuel remains pressurized, fuel leaks from various components in the fuel delivery system. One common source of leakage is through the fuel injectors, which are used in most automotive fuel systems. Fuel can also leak by permeation through various joints in the fuel delivery system. 
     Fuel leakage is particularly exacerbated by diurnal temperature cycles. During a typical day, the temperature rises to a peak during the middle of the day. In conjunction with this temperature rise, the pressure in the fuel delivery system also increases, which results in leakage through the fuel injectors and other components. This temperature cycle repeats itself each day, thus resulting in a repeated cycle of fuel leakage and evaporative emissions. 
     Accordingly, a system that maintains fuel in the fuel delivery system after the automotive vehicle is turned off while minimizing fuel pressure buildup is needed in order to minimize evaporative emissions. 
     BRIEF SUMMARY 
     A fuel pressure relief valve is provided to minimize fuel leakage and evaporative emissions during diurnal cycles by preventing pressure buildup as the temperature of the fuel system rises. One version of the fuel pressure relief valve includes an excess flow valve and a back pressure relief valve. (In the art, relief valves and pressure regulators generally have similar functions and thus are considered herein to be alternative terminology.) The excess flow valve seals when fuel flow is generated by the fuel pump during operation of the automotive vehicle. When the automotive vehicle is turned off and the fuel pump is stopped, the excess flow valve unseals after the temperature cools and the fuel pressure drops. Thereafter, during diurnal cycles, a back pressure relief valve prevents pressure buildup by unsealing when the pressure exceeds a release pressure and re-sealing when below that pressure, thereby releasing a small amount of fuel to the fuel tank. One advantage of the fuel pressure relief valve is that it can be employed as an inexpensive passive valve without the need for electronics or a control system. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The invention, including its construction and method of operation, is illustrated diagrammatically in the drawings, in which: 
         FIG. 1  is a schematic of a fuel delivery system with the invented fuel pressure relief valve; 
         FIG. 2  is a schematic of the fuel delivery system of  FIG. 1 ; 
         FIG. 3  is a graph showing a diurnal pressure cycle both with and without the invented fuel pressure relief valve; 
         FIG. 4  is a graph showing fuel pressure versus temperature and the liquid-vapor curves of typical automotive fuels; 
         FIG. 5  is a side cross sectional view of an excess flow valve showing the valve unsealed; 
         FIG. 6  is a side cross sectional view of the excess flow valve of  FIG. 5  showing the valve sealed; 
         FIG. 7  is a side cross sectional view of another excess flow valve with a ball and a spring; 
         FIG. 8  is a side cross sectional view of another excess flow valve with a cylinder sealing member and a spring; 
         FIG. 9  is a side cross sectional view of another excess flow valve with a ball and without a spring; 
         FIG. 10  is a side cross sectional view of another excess flow valve with a cylinder sealing member and magnets; 
         FIG. 11  is a side cross sectional view of one version of the invented fuel pressure relief valve; 
         FIG. 12  is a side cross sectional view of another version of the invented fuel pressure relief valve; 
         FIG. 13  is a side cross sectional view of another version of the invented fuel pressure relief valve; 
         FIG. 14  is a side cross sectional view of a parallel pressure relief valve and the invented fuel pressure relief valve integrated into a single valve assembly; 
         FIG. 15  is a side cross sectional view of a parallel pressure relief valve and the invented fuel pressure relief valve integrated into a single valve assembly; 
         FIG. 16  is a schematic of a parallel pressure relief valve and the invented fuel pressure relief valve integrated into a single valve assembly; and 
         FIG. 17  is a schematic of a parallel pressure relief valve and the invented fuel pressure relief valve integrated into a single valve assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, and particularly to  FIGS. 1 and 2 , a typical fuel delivery system  10  is shown. The fuel delivery system  10  is representative of typical fuel delivery systems used on automotive vehicles and includes a fuel tank  12 , a fuel pump  14 , a pump pressure relief valve  16 , a parallel pressure relief valve  18 , a fuel rail  20 , and a series of fuel injectors  22 . A typical parallel pressure relief valve consists of a 2.5 psi check valve and a 55 psi pressure relief valve. As those skilled in the art will readily appreciate, during operation the fuel pump  14  supplies fuel to the fuel manifold, or fuel rail  20 , through the parallel pressure relief valve  18 . The fuel is then injected into the intake manifold (not shown) of the engine through the fuel injectors  22 . When the automotive vehicle is turned off, the fuel is maintained in a pressurized state in the fuel rail  20  by the parallel pressure relief valve  18 . As described above, the pressurized fuel in the fuel rail  20  can result in undesirable fuel leakage through the fuel injectors  22 , which results in evaporative emissions. 
     As demonstrated in  FIG. 3 , fuel pressure buildup and leakage is exacerbated by diurnal temperature cycles. During operation of the automotive vehicle, the fuel pressure is maintained at about 40 to 80 psi above the intake manifold pressure by the fuel pump  14  and the temperature of the fuel rail  20  typically stays at about 195° F. ( 40 ). Immediately after the automotive vehicle is turned off, the temperature (and thus the fuel rail pressure) increase slightly due to the fact that the cooling systems of the automotive vehicle are no longer running ( 42 ). The temperature of the fuel rail  20  then slowly cools and the pressure in the fuel rail  20  consequently falls along with the temperature decrease ( 44 ). 
     For reference,  FIG. 4  shows the pressure versus temperature characteristics of typical automotive fuels and the resulting liquid-vapor curves. The area above each liquid-vapor curve represents pressure-temperature combinations at which various fuels are in an entirely liquid state. When liquid and vapor coexist, the pressure and temperature of the system are said to lie “on the line,” i.e., are on the liquid-vapor curve. Thus, if there is a vapor space in the system, the pressure is determined by fuel temperature and fuel composition (i.e., the fuel type), assuming a single fuel temperature. 
     During the cool down stage, the volume of the fuel begins to contract. As shown in  FIG. 1 , the contracting fuel in the fuel rail  20  may draw up, or retrieve, additional fuel from either the fuel pump  14  or a fuel line  24  which terminates at the bottom of the fuel tank  12 . On the other hand, if the fuel line  24  terminates above the bottom of the fuel tank  12 , the contracting fuel may draw up fuel vapors into the fuel rail  20  instead. Eventually, the fuel rail temperature reaches a minimum value (typically 65° F.) which usually occurs when the diurnal cycle is at a minimum temperature during the night ( 46 ). At the same time, the fuel rail pressure reaches a corresponding minimum pressure (typically limited to −2.5 psi by the check valve in the parallel pressure relief valve  18 ) ( 46 ). 
     After the fuel rail temperature drops to the minimum temperature during the night, the temperature begins to increase again during the diurnal cycle of daytime warming. As the temperature of the fuel rail  20  increases, the pressure in the fuel rail  20  increases ( 48 ) until the temperature and pressure reach a maximum (typically 105° F.) which usually occurs in the middle of the day ( 50 ). In conventional fuel delivery systems, the pressure increase that occurs during the diurnal cycle causes fuel to leak through the fuel injectors  22 , thereby contributing to evaporative emissions. This cycle is repeated each day until the automotive vehicle is restarted. 
     However, fuel leakage and evaporative emissions can be minimized by adding a fuel pressure relief valve  26  to the fuel delivery system  10 . The fuel pressure relief valve  26  includes an excess flow valve  28  and a back pressure relief valve  32 . In  FIGS. 1 and 2 , the fuel pressure relief valve  26  is shown with the excess flow valve  28  connected to an input  36  that is in open communication with the fuel pump  14  and the fuel rail  20 . The back pressure relief valve  32  is then connected to the excess flow valve  28  in series, with the output  38  of the back pressure relief valve  32  being connected to a fuel line  39  that extends back to the fuel tank  12 . In order to avoid leakage through the joints of the fuel pressure relief valve  26  by permeation, and in order to minimize the costs of the valve  26 , the fuel pressure relief valve  26  is preferably located in the fuel tank  12  of the automotive vehicle. The fuel pressure relief valve  26  may be used in numerous fuel systems, including return fuel systems (“RFS”), mechanical returnless fuel systems (“MRFS”), and electronic returnless fuel systems (“ERFS”), although ERFS systems are illustrated herein. 
     Generally speaking, back pressure relief valves, sometimes referred to as back pressure regulators, open at pressures above a particular setting and seal for pressures below the setting. Back pressure relief valves have some flow sensitivity but typically regulate to a constant pressure regardless of flow characteristics. Often, back pressure relief valves are constructed with an elastomeric diaphragm so that a large surface area exists against which the controlled pressure may act. In contrast, pressure relief valves are typically of a more simple construction than back pressure relief valves. Pressure relief valves usually consist of a ball or poppet lifted off of a seat. Thus, pressure relief valves are more sensitive to flow characteristics. For this reason, once a pressure relief valve is unsealed, it can stay off the seat until the flow rate is low. To minimize this flow sensitivity, an orifice is often placed in series with the pressure relief valve. However, these valves often have large hysteresis. This means that they unseal at the set pressure but reseal at a pressure at least a few psi below the set pressure. Unless special care is taken to eliminate this hysteresis, the valve will not be suitable for some tasks. 
     Although the fuel pressure relief valve  26  may be embodied by several different structures, one possible version is shown in  FIGS. 1 and 2 . In this version, the excess flow valve  28  includes a spring  29  that biases a ball  30  away from a seat  31 . Preferably, the excess flow valve  28  seals against the seat  31  when the fuel flow exceeds about 5 cc/sec and remains sealed until the input pressure drops below about 2 psi. The back pressure relief valve  32  includes a spring  33  that biases a ball  34  towards a seat  35 . Preferably, the back pressure relief valve  32  remains sealed when the input pressure is less than about 3 psi and unseals when the input pressure exceeds about 3 psi. 
     Thus, it can now be seen that the fuel pressure relief valve  26  minimizes fuel pressure buildup and resulting fuel leakage and evaporative emissions when the automotive vehicle is not operating. When the automotive vehicle is turned on and the fuel pump  14  begins to supply fuel to the fuel rail  20 , the excess flow valve  28  will experience a flow greater than the preferred 5 cc/sec shut-off flow. The excess flow valve  28  will then seal and stay sealed while the automotive vehicle operates. Therefore, throughout operation of the vehicle, the fuel flow to the back pressure relief valve  32  will be prevented by the excess flow valve  28 . 
     When the automotive vehicle is turned off and the fuel pump  14  stops, the parallel pressure relief valve  18  maintains pressure in the fuel rail  20 . As the fuel rail  20  cools and the pressure of the fuel drops, the excess flow valve  28  unseals when the pressure drops below the preferred 2 psi release pressure. The excess flow valve  28  then remains unsealed throughout the remaining time that the automotive vehicle is not operating. As shown in  FIG. 2 , now when the ambient temperature increases during the next diurnal cycle, fuel will be released through the back pressure relief valve  32  whenever the fuel rail pressure exceeds the preferred 3 psi release pressure. Thus, as shown in  FIG. 3 , the fuel rail pressure remains at a lower pressure throughout subsequent diurnal cycles (limited to about 3 psi by the back pressure relief valve  32 ) ( 47 ), while at the same time keeping the fuel rail  20  mostly filled with liquid fuel. 
     Turning now to  FIGS. 5–10 , various types of excess flow valves that may be used in the fuel pressure relief valve  26  are shown.  FIG. 5  shows an excess flow valve  50  in an open position, in which the sealing member is a vane  52 . The excess flow valve  50  also includes a spring  54  that biases the vane  52  away from the seat  56 . In  FIG. 5  a small amount of flow is shown passing from the input  58  to the output  60  of the valve  50  without closing the valve  50 . In  FIG. 6 , the same valve  50  is shown with the vane  52  sealed against the seat  56  as a result of the flow exceeding the shut-off flow rate. 
     In  FIG. 7 , another excess flow valve  64  is shown. In this version of the excess flow valve  64 , a spring  66  biases a ball  68  away from the seat  70 . A filter member  72  with a stop portion  73  is installed in the input  74 . The stop portion  23  thereby retains the ball  68  within the valve  64 . Thus, when the flow from the input  74  exceeds the shut-off flow rate, the ball  68  seals against the seat  70  and prevents flow through the output  76 . 
     In  FIG. 8 , another excess flow valve  80  is shown which is similar to the version in  FIG. 7 . Thus, in this version, the input  82 , output  84 , spring  86  and seat  87  are similar to those shown in  FIG. 7 . However, in this version, the sealing member is a cylinder-shaped member  88 , and the cylinder-shaped member  88  is retained with a roll pin  90 . 
     In  FIG. 9 , another excess flow valve  94  is shown with an input  96  and an output  98 . In this version, no spring is used to bias the ball  100  away from the seat  102 . Instead, a spacer  104  traps the ball  100  between the spacer  104  and the seat  102 . When the flow from the input  96  exceeds the shut-off flow rate, the ball  100  is pushed up against the seat  102 . Then, when the pressure drops below the release pressure, the ball  102  falls away from the seat  102  as shown. 
     In  FIG. 10 , another excess flow valve  106  is shown. In this version, attracting magnets  108 ,  110  are used to unseal the valve  106 . The adjustable stationary magnet  108  is mounted in an endplug  112 . The endplug  112  is sealed with the body  114  to prevent leakage with o-rings  115  and a cover  116 . The position of the stationary magnet  108  may then be adjusted with an adjusting screw  118 . The moveable piston  120  includes a magnet  110 , which is attracted towards the stationary magnet  108 . An o-ring  122  is also included at the output  124  to seal the piston  120  in the closed position (as shown). Thus, in operation, fuel flows through the input  126  and creates a pressure differential across the piston  120  as the fuel flows to the output  124 . When the pressure differential becomes high enough, the piston  120  moves towards the output  124  and restricts additional flow between the input  126  and the output  124 . However, when the pressure equalizes between the input  126  and the output  124 , the magnets  108 ,  110  pull the piston  120  away from the output  124 , thus unsealing the valve  106 . 
     Turning now to  FIG. 11 , a version of the fuel pressure relief valve  130  is shown, which may be more cost effective to manufacture since parts of the excess flow valve  28  and the back pressure relief valve  32  have been combined. In this version, the body  132  of the valve  130  is made from acetal and includes an input  132  and an output  134 . A single ball  136  is used in the fuel pressure relief valve  130  and acts like a joined sealing member. A spring  138  is installed between the ball  136  and the output  134 . The ball  136  is then trapped between two seats formed from viton o-rings  140 ,  142 . Cylindrical acetal spacers  144  are pressed into the input  132  to position the o-rings  140 ,  142 . 
     The function of the fuel pressure relief valve  136  in  FIG. 11  is now apparent. When the fuel flow at the input  132  exceeds the shut-off flow rate, the ball  136  is pressed against the o-ring  140  adjacent the output  134  thereby sealing the valve  130 . In this position, the valve  130  acts like the excess flow valves  28  previously described. When the pressure drops below a release pressure, the ball  136  is pushed away from the output o-ring  140  by the spring  138  and is pushed against the o-ring  142  adjacent the input  132 . When the ball  136  is pressed against the input o-ring  142 , the ball  136  again seals the valve  130 . In this position, the valve  130  acts like the back pressure relief valve  32  previously described. Thus, when the pressure at the input  132  exceeds the release pressure, the ball  136  moves away from the input o-ring  142  and lets a small amount of fuel pass through the valve  130  to the output  134 . 
     Turning now to  FIG. 12 , another version of the fuel pressure relief valve  150  is shown. Like the version shown in  FIG. 12 , this version may be more cost effective since certain parts have been combined or eliminated. In this version, the body is made from two portions  152 ,  154  that are welded together with sonic welding. The first portion  152  includes the input  156 , and the second portion  154  includes the output  158 . A single o-ring  160  is trapped between the two portions  152 ,  154  of the body, thereby acting like joined seats. A poppet  162  with two joined vane surfaces  164 ,  166  is also trapped by the o-ring  160 , which is positioned between the two vane surfaces  164 ,  166 . A spring  168  is then installed between the poppet  162  and the output  158 . 
     The function of the fuel pressure relief valve  150  in  FIG. 12  is now apparent. When the fuel flow at the input  156  exceeds the shut-off flow rate, the poppet vane  162  adjacent the input  156  is pressed against the o-ring  160 , thereby sealing the valve  150 . In this position, the valve  150  acts like the excess flow valve  28  previously described. When the pressure drops below a release pressure, the poppet  162  is pushed away from the o-ring  160  by the spring  168 , and the poppet vane  164  adjacent the output  158  is pushed against the o-ring  160 . When the output poppet vane  164  is pressed against the o-ring  160 , the poppet  162  again seals the valve  150 . In this position, the valve  150  acts like the back pressure relief valve  32  previously described. Thus, when the pressure at the input  156  exceeds the release pressure, the output poppet vane  164  moves away from the o-ring  160  and lets a small amount of fuel pass through the valve  150  to the output  158 . 
     Turning now to  FIG. 13 , another version of the fuel pressure relief valve  180  is shown. Like the versions shown in  FIGS. 11 and 12 , this version may be more cost effective since certain parts have been combined or eliminated. In this version, the body is made from two portions  182 ,  184 . The first portion  182  includes the input  186  and an inner bore  188 . The second portion  184  includes the output  190  and an outer bore  192  sized to fit within the inner bore  188  of the first portion  182 . The first and second portions  182 ,  184  are affixed to each other through a press fit, welding, gluing or the like. A single ball  194  is used in the fuel pressure relief valve  180  and acts like a joined sealing member. The ball  194  is preferably made of viton. A spring  196  is installed between the ball  194  and the output  190 . The ball  194  is trapped between one seat  198  formed in the first portion  182  and another seat  200  formed in the second portion  184 . 
     The function of the fuel pressure relief valve  180  in  FIG. 13  is now apparent. When the fuel flow at the input  186  exceeds the shut-off flow rate, the ball  194  is pressed against the output seat  200  in the second portion  184  thereby sealing the valve  180 . In this position, the valve  180  acts like the excess flow valves  28  previously described. When the pressure drops below a release pressure, the ball  194  is pushed away from the seat  200  by the spring  196  and is pushed against the input seat  198  in the first portion  182 . When the ball  194  is pressed against the seat  198 , the ball  194  again seals the valve  180 . In this position, the valve  180  acts like the back pressure relief valve  32  previously described. Thus, when the pressure at the input  186  exceeds the release pressure, the ball  194  moves away from the input seat  198  and lets a small amount of fuel pass through the valve  180  to the output  190 . 
     Turning now to  FIGS. 14–17 , various versions of a single valve assembly are shown with the fuel pressure relief valve  26  integrated with the parallel pressure relief valve  18 . In  FIG. 14 , the integrated valve assembly  170  is shown with a parallel pressure relief valve  18  on the left side of the valve assembly  170  and the fuel pressure relief valve  26  on the right side of the valve assembly  170 . (The integrated valve assembly  174  shown in  FIG. 16  is similar to this version). In this version, the fuel pressure relief valve  26  is connected to the pump  14  on one end and the fuel rail  20  on the other end. Thus, the excess flow valve  28  closes when the automotive vehicle is turned off and the pump  14  de-energizes. In  FIG. 15 , an integrated valve assembly  172  is shown using the fuel pressure relief valve  180  shown in  FIG. 13  and described above. In  FIG. 17 , the integrated valve assembly  176  is shown with the fuel pressure relief valve  26  connected between the fuel rail  20  and the return fuel line  39 . Thus, in this version the excess fuel valve  28  closes when the automotive vehicle is turned on and the pump  14  is energized. ( FIG. 17  represents the same system schematic as shown in  FIGS. 1 and 2 .) 
     While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.