Abstract:
The present invention relates to an electronic pressure regulator that can be used for gaseous fuel control on internal combustion engines. More particularly, the present invention relates to an electronic pressure regulator that has direct acting electro-mechanical operation with pressure sensor feed back.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Priority is claimed of U.S. Provisional Patent Application Ser. No. 60/457,067, filed on Mar. 24, 2003. 
   U.S. Provisional Patent Application Ser. No. 60/457,067, filed on Mar. 24, 2003, is hereby incorporated by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable 
   REFERENCE TO A “MICROFICHE APPENDIX” 
   Not applicable 
   BACKGROUND 
   1. Field 
   The present invention relates to an electronic pressure regulator that can be used for gaseous fuel-control on internal combustion engines. More particularly, the present invention relates to an electronic pressure regulator that has direct acting electro-mechanical operation with pressure sensor feed back. 
   2. General Background 
   A pressure regulator is a device that maintains a desired pressure quantity at a predetermined value or varies according to a predetermined plan. Most fuel pressure regulators for internal combustion engines have a fixed orifice and work off of a diaphragm. These regulators cannot make accommodations for variations in engine operating conditions in order to provide an optimum fuel to air mixture for gaseous fuel internal combustion engines. 
   Gaseous fuel means a fuel which is in the gaseous state at standard temperature and pressure. Examples of a gaseous fuels used with internal combustion engines are: compressed natural gas (derived from liquid or compressed gas storage state), and propane/butane gas (derived from liquid petroleum gas storage). 
   While certain novel features of this invention shown and described below are pointed out in the annexed claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in any way from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.” 
   BRIEF SUMMARY 
   The apparatus of the present invention solves the problems confronted in the art in a simple and straightforward manner. In one embodiment the present invention allows for dynamically controlling gaseous fuel pressure to provide an optimum gaseous fuel pressure based on selected operating conditions. 
   In one embodiment a butterfly valve responsive to a valve control signal regulates fuel pressure leaving the electronic control pressure regulator and entering the engine. A controller can provide the actuating signal to the butterfly valve in accordance with a pressure control algorithm. 
   In one embodiment, to determine the proper optimal pressure setpoint for engine operation, two modes of engine operation are considered. The first mode is stoichiometric operation, and the second is lean-burn operation. 
   For stoichiometric engine control, the pressure setpoint can primarily be determined by the unwanted exhaust gas emissions after a catalytic conversion process. The pressure setpoint can be manipulated higher or lower to cause slightly richer or leaner engine operation to achieve an optimum trade-off in catalytic conversion efficiency. These changes in pressure setpoint cause very small deviations in the air/fuel ratio setpoint of the engine. These deviations are on the order of 0.1% around the nominal setpoint of the stoichiometric air/fuel ratio for the engine. In a stoichiometric engine, this emissions trade-off and optimization of the catalytic conversion efficiency is an important parameter that influences the selection of the optimum pressure setpoint. This optimization can be performed during normal engine operation using a stoichiometric oxygen sensor, or exhaust gas oxygen (EGO) sensor, with real-time feedback from the sensor causing real-time changes in the instantaneous pressure setpoint of the pressure regulator. This mode of operation and the fuel optimization procedure is essentially the same with or without the use of exhaust gas recirculation (EGR). 
   In the second fundamental mode of engine operation called lean-burn combustion mode, the pressure setpoint of the device may be controlled to cause much larger changes in the air/fuel ratio setpoint of the engine. These changes are on the order of 10.0% or more as opposed to 0.1% for the stochiometric case. The optimal pressure setpoint for this mode of operation is determined by running lean enough to achieve the desired emissions target while still running rich enough to achieve the desired torque target for the engine. Lean operation of the engine is additionally limited by the onset of misfire. Therefore, the optimization of the pressure setpoint is a straight forward calibration since the engine should generally be run at an air/fuel ratio only lean enough to achieve the desired emissions target with a reasonable factor of safety. This can produce the maximum engine torque at the maximum allowable undesirable exhaust emissions point. A wide-range, or universal, exhaust gas oxygen sensor (UEGO) may be used to precisely control this setpoint—although it is not required. 
   Both of the previous pressure optimization algorithms or procedures assume that the engine is required to meet stringent exhaust emissions regulations. However, some engines are not required to meet these types of regulations. For these engines, the pressure setpoint can be manipulated only with engine speed and load information to correct for variations in a variable venturi or fixed venturi carburetion device used downstream of the pressure control device. These variations may be a consistent deviation from the nominally desired air/fuel ratio setpoint caused by engineering design problems with the device itself, or these variations may be random deviations from the nominal setpoint caused by part-to-part production tolerance or wear-out mechanisms over time. 
   In the case of the stoichiometric mode of engine operation, the nominal setpoint of the engine is the stoichiometric air/fuel ratio for the fuel being used, such as natural gas or propane. In the lean-burn mode of engine operation, the nominal setpoint can be determined by reducing in-cylinder and exhaust temperatures to a level that will allow the engine to be durable over time without putting the engine into lean misfire. 
   If the fixed venturi or variable venturi carburetion devices are produced accurately and no other sensors are present on the engine to allow correction for variations in devices over time or due to production tolerance issues, a single static pressure setpoint may be the optimum for the device. This is the simplest and lowest cost use of the pressure control device for engine fuel control. 
   The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein: 
       FIG. 1  is a schematic showing Static Pressure Setpoint Operation; 
       FIG. 2  is a schematic showing Open Loop Operation; 
       FIG. 3  is a schematic showing Closed Loop Operation; 
       FIG. 4  is a schematic showing operation of one embodiment of the pressure control regulator; 
   

   DETAILED DESCRIPTION 
   Detailed descriptions of one or more preferred embodiments are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in any appropriate system, structure or manner. 
   The operation of one embodiment of pressure regulator  10  will first be described.  FIG. 4  is a operation schematic showing one embodiment of the pressure regulator  10 . One object is to have outlet fuel pressure  350  equal to pressure setpoint  360 . Determination of pressure setpoint  360  is described below for three modes of operation, static, open loop, and closed loop operation. It is noted that pressure setpoint  360  can be dynamic and change from sampling increment to sampling increment. Outlet fuel pressure  350  is controlled by valve  300 . 
   Valve  300 , which can be a butterfly valve, is used to regulate fuel inlet pressure  340  to fuel outlet pressure  350 . Fuel, at fuel outlet pressure  350 , is routed to engine  90 . Regulation is performed by incrementally opening and closing valve  300 . 
   Valve  300  is incrementally opened or closed by actuator  310 . The position of valve  300  is determined by position sensor  320 . Actuator  310  is controlled by position controller  390 . Pressure control algorithm  380  provides commands to position controller  390 , which sends signals to actuator  310 , which incrementally opens or closes valve  300 . 
   Outlet fuel pressure  350  is measured by pressure sensor  330  and compared to pressure setpoint  360 . The difference between these two measurements is used to calculate pressure error  370 . Pressure error  370  is inputted to pressure control algorithm  380 . Pressure control algorithm  380  is then used to provide a command to position control  390 , which actuates actuator  310  and either incrementally opens or incrementally closes valve  300 . If outlet pressure  350  is lower than pressure setpoint  360 , valve  300  is incrementally opened. If higher, valve  300  is incrementally closed. The process is continued until outlet pressure  350  is within acceptable error limits to pressure setpoint  360  and/or pressure setpoint  360  is changed to a new setpoint. 
   Three modes of operation are described below: 
   A. Static Pressure Set Point Operation 
     FIG. 1  is a schematic showing Static Pressure Setpoint Operation. In static pressure setpoint operation no additional sensors or inputs are needed to operate pressure regulator  10 . A static pressure setpoint  30  is set by the user. This pressure is usually set as the nominal manufacturer&#39;s recommended supply pressure for a fixed venturi or variable venturi carburetor. 
   The operation of pressure regulator  10  is as described above in the discussion of  FIG. 4 . Pressure setpoint  360  is set to static pressure setpoint  30 . In this embodiment pressure setpoint  360  should not change over time (i.e., be static), unless reset by the user. 
   Pressure regulator  10  is set to static pressure setpoint  30 . Fuel  50  enters pressure regulator  10  at fuel inlet pressure  340  and leaves at fuel outlet pressure  350 . Fuel  50  at fuel outlet pressure  350  is then combined with air  60  at carburetor  70 . Air/fuel mixture  80  leaves carburetor  70 , enters engine  90 , and is combusted. Exhaust  100  then exits engine  90 . 
   B. Open Loop Operation 
     FIG. 2  is a schematic showing Open Loop Operation. In an open loop configuration various inputs are used to determine pressure setpoint  40 . One or more of the following inputs are used to operate in this mode: 
   MAP—Manifold Absolute Pressure  140   
   RPM—revolutions per minute of engine (engine speed)  150   
   MAT—Manifold Air Temperature  160   
   ECT—Engine Coolant Temperature  170   
   Baro—Barometric Pressure  180   
   MAF—Engine Mass Air Flow  190   
   TP—Throttle position  200   
   TIP—Throttle Inlet Pressure  210   
   The operation of pressure regulator  10  is as described above in the discussion of  FIG. 4 . Pressure setpoint  40  is set by an algorithm based on one or more of the inputs  140  through  210  plugged into calibration tables/equations  120 . 
   Pressure regulator  10  is set to pressure setpoint  40 . Fuel  50  enters pressure regulator  10  at fuel inlet pressure  340  and leaves at fuel outlet pressure  350 . Fuel  50  at fuel outlet pressure  350  is then combined with air  60  at carburetor  70 . Air/fuel mixture  80  leaves carburetor  70 , enters engine  90 , and is combusted. Exhaust  100  then exits engine  90 . 
   One or more of the inputs  140  through  210  are then measured at various points on the engine  90  or outside of the engine such as exhaust  100 . Pressure setpoint  40  is then reset by an algorithm based on one or more of the inputs  140  through  210  plugged into calibration tables/equations  120 . The functions/operations of calibration tables/equations  120  would be understood by one of ordinary skill in the art related to engine calibration and control based on the specified input parameters. 
   This procedure is continued throughout the operation of engine  90 . 
   C. Closed Loop Operation With EGO/UEGO feedback 
     FIG. 3  is a schematic showing Closed Loop Operation. In a closed loop configuration various inputs are used to determine first pressure setpoint  45 . One or more of the following inputs are used to operate in this mode: 
   MAP—Manifold Absolute Pressure  140   
   RPM—revolutions per minute of engine (engine speed)  150   
   MAT—Manifold Air Temperature  160   
   ECT—Engine Coolant Temperature  170   
   Baro—Barometric Pressure  180   
   MAF—Mass Air Flow  190   
   TP—Throttle position  200   
   TIP—Throttle Inlet Pressure  210   
   Pressure setpoint  40  is calculated as a combination of the initial pressure setpoint  45  and correction pressure  46 . Correction pressure  46  is calculated by on one or more of the inputs: 
   EGO —Exhaust Gas Oxygen Sensor  220   
   UEGO—Universal Exhaust Gas Oxygen Sensor  230 . 
   The operation of pressure regulator  10  is as described above in the discussion of  FIG. 4 . First pressure setpoint  45  is set by an algorithm based on one or more of the inputs  140  through  210  plugged into calibration tables/equations  120 . The functions/operations of calibration tables/equations  120  would be understood by one of ordinary skill in the art related to engine calibration and control based on the specified input parameters. 
   Correction pressure  46  is calculated based on the difference between one or more of the inputs  220  and  230  and a desired Phi or A/F ration  430 . This difference is the Phi or A/F error  421  and is the input to a proportional, integral, derivative (PID) controller  410 . The inputs  220  and  230  can also be combined at point  420  with a desired Phi or A/F ratio  430 . Pressure setpoint  40  is calculated as the combination of first pressure setpoint  45  and correction pressure  46 . In its simplest form, an error driven PID is well known to those of ordinary skill in the art of engine controls. 
   Pressure regulator  10  is set to pressure setpoint  40 . Fuel  50  enters pressure regulator  10  at fuel inlet pressure  340  and leaves at fuel outlet pressure  350 . Fuel  50  at outlet fuel pressure  350  is then combined with air  60  at carburetor  70 . Air/fuel mixture  80  leaves carburetor  70 , enters engine  90 , and is combusted. Exhaust  100  then exits engine  90 . 
   One or more of the inputs  140  through  230  are then measured. First pressure setpoint  45  is then reset by an algorithm based on one or more of the inputs  140  through  210  plugged into calibration tables/equations  120 . Correction pressure  46  is then reset based on one or more inputs  220  and  230 , differenced can also be combined at point  420  with a desired Phi or A/F ratio  430 . Pressure setpoint  40  is then recalculated as the combination of reset first pressure setpoint  45  and recalculated correction pressure  46 . 
   This procedure is continued throughout the operation of engine  90 . 
   The following is a list of reference numerals: 
   
     
       
             
           
             
             
           
             
             
           
         
             
                 
             
             
               LIST FOR REFERENCE NUMERALS 
             
           
        
         
             
               (Reference 
                 
             
             
               Numeral No.) 
               (Description) 
             
             
                 
             
           
        
         
             
               10 
               Pressure Regulator 
             
             
               20 
               Static Pressure 
             
             
               30 
               Pressure Setpoint Static 
             
             
               40 
               Pressure Setpoint 
             
             
               45 
               First Pressure Setpoint 
             
             
               46 
               Corrected Pressure 
             
             
               50 
               Fuel 
             
             
               60 
               Air 
             
             
               70 
               Carburetor 
             
             
               80 
               Air/Fuel Mixture 
             
             
               90 
               Engine 
             
             
               100 
               Exhaust 
             
             
               110 
               Calibration Lookup Table Static 
             
             
               120 
               Calibration Lookup Table and/or flow estimation 
             
             
                 
               equations 
             
             
               130 
               Input 
             
             
               140 
               MAP - - Manifold Absolute Pressure 
             
             
               150 
               RPM - - revolutions per minute of engine 
             
             
                 
               speed) 
             
             
               160 
               MAT - - Manifold Air Temperature 
             
             
               170 
               ECT - - Engine Coolant Temperature 
             
             
               180 
               Baro - - Barometric Pressure 
             
             
               190 
               MAF - - Engine Mass Air Flow 
             
             
               200 
               TP - - Throttle position 
             
             
               210 
               TIP - - Throttle Inlet Pressure 
             
             
               220 
               EGO - - Exhaust Gas Oxygen Sensor 
             
             
               230 
               UEGO - - Universal Exhaust Gas Oxygen Sensor 
             
             
               300 
               valve 
             
             
               310 
               actuator 
             
             
               320 
               position sensor 
             
             
               330 
               pressure sensor 
             
             
               340 
               inlet fuel pressure 
             
             
               350 
               outlet fuel pressure 
             
             
               360 
               pressure setpoint 
             
             
               370 
               error in pressure 
             
             
               380 
               pressure control algorithm 
             
             
               390 
               position controller 
             
             
               410 
               Proportional, Integral, Derivative Controller 
             
             
                 
             
           
        
       
     
   
   All measurements disclosed herein are at standard temperature and pressure, at sea level on Earth, unless indicated otherwise. All materials used or intended to be used in a human being are biocompatible, unless indicated otherwise. 
   It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention set forth in the appended claims. The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.