Abstract:
A fuel control device for a combustion engine capable of running on any one of a plurality of fuels has a fuel selection module with a plurality of fuel type settings for selecting a specific fuel type whereupon the fuel control device controls the outlet pressure of the chosen fuel to a desired fuel pressure corresponding to the calorific properties of the chosen fuel. The fuel selection module preferably operates a plurality of fuel flow circuits each designated for a specific fuel type, and each having a biased closed inlet valve and a biased closed outlet valve. Located preferably between each inlet and outlet valve is a pressure regulator designated for the specific fuel type and controlling the outlet fuel pressure. The device preferably includes a fuel metering apparatus and a shutoff valve that communicate with, and control in part, fuel flow through the fuel flow circuits.

Description:
RELATED APPLICATIONS  
       [0001]     Applicants claim priority of Japanese Application No. 2005-123595, filed on Apr. 21, 2005, and Japanese Application No. 2005-152777, filed on May 25, 2005.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a fuel system and more particularly to a fuel control device for a combustion engine.  
       BACKGROUND OF THE INVENTION  
       [0003]     Internal combustion engines can operate on multiple types of gaseous fuels such as petroleum-based propane gas and butane gas. Unfortunately, propane gas and butane gas have different calorific values and therefore must be provided to the engine at specific pre-determined pressures dependent upon the type of gas. Because specific gasses must flow at specific pressures the ability of an engine to run utilizing a variety of different fuels is somewhat moot because an easy and economical means of varying fuel supply pressures to correspond to different gas types is not available.  
       SUMMARY OF THE INVENTION  
       [0004]     A fuel control device for a combustion engine, that is capable of running on any one of a plurality of fuels, has a fuel selection module with a plurality of fuel type settings for selecting a specific fuel type. The fuel control device controls the outlet pressure of a chosen fuel to a fuel pressure that generally corresponds to the calorific properties of the chosen fuel, preferably in a gaseous state. The fuel selection module preferably operates a plurality of fuel flow circuits for each fuel-type setting each having a biased closed inlet valve supported by an inlet valve bank and a biased closed outlet valve supported by an outlet valve bank. Preferably, the fuel selection module includes a single rotating camshaft having a plurality of cams with each cam associated with a specific one of the plurality of fuel flow circuits. Each flow circuit includes a pair of pushrods or followers that are selectively activated by the respective cam to simultaneously open respective inlet and outlet valves. Located preferably between each inlet and outlet valve is a pressure regulator unit or jet designated for the specific fuel type and controlling the outlet fuel flow pressure.  
         [0005]     Located preferably between the pressure regulating units and the inlet valves is a fuel metering apparatus having a shutoff valve for preventing fuel flow after the fuel-type is chosen by an operator but before the engine is started and a flow valve adapted to operate relative to a fuel metering chamber for controlling the amount of fuel flowing through the outlet valve bank. Actuators of the flow and shutoff valves of the fuel metering apparatus are preferably of a diaphragm-type and generally open the valves upon specific pressure signals produced by the starting and/or running engine allowing for a relatively compact fuel metering apparatus design. Preferably, the biased closed flow valve opens upon a sufficient vacuum or decrease in pressure sensed from a venturi region of a mixing passage of a carburetor upstream from a throttle valve. The shutoff valve is preferably biased closed and opens upon a vacuum or decrease in pressure sensed from the mixing passage downstream of the throttle valve.  
         [0006]     In one implementation, the shutoff valve of the fuel metering apparatus and the associated valve actuator preferably operate along a common centerline. Unlike known pressure regulators or fuel metering apparatuses, the fuel flowing through the open shutoff valve of the fuel metering apparatus is not exposed directly to the actuator vacuum and thus is not restricted to a pressure needed to open the valve. The shutoff valve is preferably of a poppet-type having a valve stem that moves along the centerline when an elongated member of the actuator moves along the same centerline and pushes upon the valve stem to move a head of the valve away from a valve seat. The elongated member of the actuator connects to a large diaphragm located between a reference chamber and a vacuum chamber communicating with the mixing passage and a smaller diaphragm near the shutoff valve. The smaller diaphragm generally divides a displacement chamber that communicates with the vacuum pressure of the vacuum chamber and a valve cavity through which the selected fuel type flows downstream of the valve seat. The elongated member of the actuator is displaced linearly toward the valve stem by a force equated from the difference between the vacuum exposed surfaces of the large and smaller diaphragms.  
         [0007]     Because in this implementation the shutoff valve and pressure of the fuel flowing therethrough is independent of the needed operational pressures of the valve actuator and because the elongated member of the actuator moves linearly in the direction of the diaphragm movement, the only relative forces are linear adding to stability of the valve actuation and durability of the diaphragm.  
         [0008]     Moreover, since the vacuum diaphragm is provided externally of the fuel metering chamber associated with the actuator of the flow valve, freedom in layout design can be improved and the size of the vacuum diaphragm can be selected at wi11 without regard to the size of the fuel metering chamber. Therefore, even when the vacuum pressure is small, a relatively large force can be produced, and this expands the range of the control of the shutoff valve. For instance, the shutoff valve can be opened even while the vacuum pressure is relatively small. Whereas, if the vacuum diaphragm of the shutoff valve actuator is provided in the metering chamber of the flow valve actuator, an increase in the size of the vacuum diaphragm necessarily increases the overall size of the fuel metering apparatus.  
         [0009]     Other advantages of the present invention include a fuel control device that facilitates selection of fuel-types, can be mounted to an engine capable of running on any one of a plurality of fuels, and a fuel metering apparatus that is easily adapted to different specifications so as to meet the needs of different engines while utilizing an identical structure. Other advantages include a robust shutoff valve actuator that is generally free of air leakage concerns about the elongated member, and a device that automatically shuts off fuel flow when the engine is stopped thereby conserving fuel, a device that is simple in design and inexpensive enough to warrant use on small engine applications, and in service has a long and useful life. Of course, other advantages may be realized and devices incorporating the present invention may achieve some, all, or none of these advantages. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     These and other objects, features and advantages of the invention will become apparent from the following detailed description of preferred embodiments and best mode, appended claims, and accompanying drawings in which:  
         [0011]      FIG. 1  is a cross section of a fuel control device embodying the present invention having a fuel metering apparatus shown closed and a fuel selection module shown in an all-closed position;  
         [0012]      FIG. 2  is a cross section of a first or upper fuel circuit of the selection module shown closed and taken along line  2 - 2  of  FIG. 1 ;  
         [0013]      FIG. 3  is a cross section of a second or lower fuel circuit of the selection module shown closed and taken along line  3 - 3  of  FIG. 2 ;  
         [0014]      FIG. 4  is a partial cross section of the fuel control device similar in perspective to  FIG. 1  and illustrating the first fuel circuit closed and the second fuel circuit open when the selection module is in a first selected gas position;  
         [0015]      FIG. 5  is a cross section of the first fuel circuit being closed and taken along line  5 - 5  of  FIG. 4 ;  
         [0016]      FIG. 6  is a cross section of the second fuel circuit being open and taken along line  6 - 6  of  FIG. 4 ;  
         [0017]      FIG. 7  is a partial cross section of the fuel control device similar in perspective to  FIG. 1  and illustrating the first fuel circuit of the fuel switching device open and the second fuel circuit closed when the selection module is in a second selected gas position;  
         [0018]      FIG. 8  is a cross section of the first fuel circuit being open and taken along line  8 - 8  of  FIG. 7 ;  
         [0019]      FIG. 9  is a cross section of the second fuel circuit being closed and taken along line  9 - 9  of  FIG. 7 ;  
         [0020]      FIG. 10  is an enlarged cross section of the fuel metering apparatus shown open and similar in perspective to  FIG. 1 ; and  
         [0021]      FIG. 11  is an enlarged cross section of a shutoff valve of the fuel metering apparatus shown open and taken from circle  11  of  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]     As best illustrated in  FIG. 1 , a fuel control device  20  supplies any selected one of a plurality of preferably petroleum-based fuels to a multi-fuel compatible combustion engine. As illustrated, the number of different fuels are preferably two (although more than two may be used) which are preferably butane and propane, which may be stored in a pressurized liquid state and expand into a gaseous state generally when flowing into the device  20  from a propane storage cylinder or source  22  and a butane storage cylinder or source  24 . Although the multiple gaseous fuels are illustrated as propane and butane gas, the present invention is not limited to this example and may be adapted to handle any number or variety of gaseous fuels including but not limited to natural gas.  
         [0023]     The fuel control device  20  is generally modularized, having a centralized fuel selection module  26  located between an inlet valve bank  28  and an interacting outlet valve bank  30 . A fuel metering apparatus  32  is in gaseous communication with and is preferably attached sealably to a side of the fuel selection module  26  spanning between the valve banks  28 ,  30 . Preferably, a control knob  34  projects through a fourth side of the fuel selection module  26  located opposite to the side supporting the metering apparatus  32 .  
         [0024]     A support body  36  of the inlet valve bank  28  carries a propane inlet port  38  that generally communicates with and preferably threads to the propane storage cylinder  22  via suitable tubular or pipe fittings. A propane inlet passage  40  in the support body  36  communicates between the inlet port  38  and an intake manifold  42  generally defined between the support body  36  of the inlet valve bank  28  and a centralized main body  44  of the fuel selection module  26 . Similarly, a butane inlet passage  46  extends through the support body  36  and intermittently communicates between the intake manifold  42  and preferably a butane conditioning module  48  that receives butane fuel from the butane storage cylinder  24  at an inlet port  50  of the module  26 , is heated as the butane flows through a heating element  52  and pressure controlled at a butane gas pressure regulator  54  of the module  26  typically known in the art. Preferably, the inlet port  50  is threaded for receipt of external butane cylinder fittings and is carried by a heater cover  56  that when removed from the conditioning module  48  exposes the heating element  52  for repair and/or replacement. One skilled in the art would now know that the butane conditioning module  48  can be remotely located away from the fuel switching and pressure regulating device  20  or may not be required at all if butane fuel is not one of the plurality of fuels controlled by device  20 .  
         [0025]     As best illustrated in  FIGS. 1-4 , a blind bore  58  in the main body  44  of the fuel selection module  26  receives a camshaft  60  that rotates about axis  62  and projects outward to a distal end terminating at the control knob  34 . Preferably, the camshaft  60  is held axially in the blind bore  58  by a retaining pin  64  fixed to the main body  44  and projecting into a circumferential, continuous groove  66  in the camshaft  60 . As illustrated, the camshaft  60  carries two preferably recessed cams described as a butane cam  68  ( FIG. 2 ) and a propane cam  70  ( FIG. 3 ) for opening and closing respective flow circuits  72 ,  74  each having a biased closed inlet valve  76  and a generally redundant and biased closed outlet valve  78 . The axial cross section of the butane cam  68  is preferably generally S-shaped (see  FIG. 2 ) and the axial cross section of the propane cam  70  is generally a mirror image or Z-shaped (see  FIG. 3 ). Both shapes are substantially symmetric about the axis  62 . Alternatively, one skilled in the art would now know that the cams  68 ,  70  could be more than two, thus controlling more than two flow circuits. Furthermore, one skilled in the art would now know that the cams need not be radially recessed but can, for example, be lobes that project radially outward from the shaft  60 , and the cross sections could both be S-shaped or otherwise contoured or shaped, for instance restricting rotation of knob  34  in the counter-clockwise direction or vise-versa.  
         [0026]     As best illustrated in  FIGS. 2-4 , each flow circuit  72 ,  74  has an inlet push rod  80  associated with the inlet valve  76  and an outlet push rod  82  associated with the outlet valve  78 . The push rods  80 ,  82  are preferably opposed diametrically to one another with respect to axis  62  and are supported axially slidably in respective inlet and outlet through-bores  84 ,  86  in the main body  44  of the fuel selection module  26 . The inlet though-bores  84  extend and communicate between the blind bore  58  and the intake manifold  42  defined preferably by the main body  44  and a body  36  of the inlet valve bank  28 . Similarly, the outlet through-bore  86  associated with the butane flow circuit  72  extends and communicates between the blind bore  58  and a butane cavity  88  defined between the main body  44  of the fuel selection module  26  and a support body  90  of the outlet valve bank  30 . The outlet through-bore  86  associated with the propane flow circuit  74  extends and communicates between the blind bore  57  and a propane cavity  92  defined between the main body  44  of the fuel selection module  26  and the support body  90  of the outlet valve bank  30 .  
         [0027]     The inlet and outlet push rods  80 ,  82  preferably reciprocate along a common centerline  94  concentric to the through-bores  84 ,  86  and substantially perpendicular to axis  62 . Each rod  80 ,  82  of each flow circuit  72 ,  74  when open (see  FIGS. 4 and 6 - 8 ) is biased against the butane and propane cams  68 ,  70  at rounded radial inward ends  99 ,  101  by respective compression springs  96 ,  98  coiled about the opposite radially outward ends  100 ,  102  of the respective push rods  80 ,  82 . Preferably, the spring  96  associated with the inlet push rod  80  is compressed axially between a circumferentially extending and radially projecting collar  104  of push rod  80  and the body  36  of the inlet valve bank  28 . The outward end  100 , the spring  96  and the collar  104  are generally located in the intake manifold  42 . Similarly, the spring  98  associated with the outlet push rod  82  is compressed axially with respect to centerline  94  between a circumferentially extending and radially projecting collar  106  of push rod  82  and the body  90  of the outlet valve bank  30 . The outward ends  102 , the springs  98  and the collars  106  are generally located in the respective cavities  88 ,  92 .  
         [0028]     Pressure regulating units or jets  95 ,  97  permit a desired fuel supply pressure to be achieved and provided into respective cavities  88 ,  92  from a common distribution chamber  93  in the main body  44 . The pressure regulating units  95 ,  97  are preferable fuel jets press fitted or fixed into bores defined by the main body  44 . The butane and propane jets  95 ,  97  preferably are manufactured with equal outer diameters but have varying inner diameters dependent upon the type of gaseous fuel they will flow. As best shown in  FIGS. 1 and 10 , the distribution chamber  93  receives the flow of gaseous fuel from the metering apparatus  32 , which meters fuel flow and in-part controls fuel pressure regardless of fuel type. The metering apparatus  32  communicates with and receives fuel flow from the upstream intake manifold  42 . Because the gaseous fuel pressure at the inlet side of the butane and propane jets  95 ,  97  is known and held substantially constant by the metering apparatus  32 , the inner diameters of the respective jets  95 ,  97  are sized to obtain the desired fuel pressures at a given flow rate for the respective gases at an outlet passage  120  of the fuel control device  20  in the outlet valve bank  30 . Although fuel jets are an efficient and economical way to control fuel pressure, one skilled in the art would now know that other types of pressure regulating units can be exchanged with the fuel jets including, for example, more complex units typically incorporating biasing springs and/or resilient diaphragms.  
         [0029]     The biased closed inlet valves  76  of the butane and propane flow circuits  72 ,  74  are preferably poppet valves and have peripheral housings or sleeves  108  (see  FIGS. 4 and 7 ) that press fit or thread into outlets of the respective butane and propane inlet passages  46 ,  40 . A valve stem  110  of each valve carries an enlarged head  112  at a leading end and an enlarged abutment or heel  114  at the opposite trailing end along the centerline  94 . A semi-conical compression spring  116  is located concentrically about the associated centerline  94  and compressed axially between an annular surface carried by the sleeve  108  and the enlarged abutment  114  for biasing the valve head  112  sealably against an annular valve seat  130  carried by the sleeve  108  and substantially facing upstream into the passages  46 ,  40 . The spring  116  and abutment  114  of valve stem  110  are generally exposed in the intake manifold  42 .  
         [0030]     Similarly, the biased closed outlet valves  78  of the butane and propane flow circuits  72 ,  74  are preferably poppet valves and have peripheral housings or sleeves  118  that press fit or thread into inlet ports of the common outlet passage  120  of the outlet valve bank  30  in the support body  90 . As best shown in  FIGS. 2-3  and  5 - 6 , a valve stem  122  of each outlet valve  78  carries an enlarged head  124  at one end and an enlarged abutment or heel  126  at the opposite end. A semi-conical compression spring  128  is located concentrically about the associated centerline  94  and compressed axially between an annular surface carried by the sleeve  118  and the enlarged abutment  126  for biasing the valve head  124  sealably against an annular valve seat  130  carried by the sleeve  118  and substantially facing downstream into the outlet passage  120  (see  FIG. 7 ). The spring  128  and abutment  126  of valve stem  122  or respective butane and propane flow circuits  72 ,  74  are generally exposed in respective butane and propane cavities  88 ,  92 . The enlarged abutments  114 ,  126  of the respective inlet and outlet valves  76 ,  78  co-axially confront the radially outward ends  100 ,  102  of the inlet and outlet push rods  80 ,  82 .  
         [0031]     As best illustrated in  FIG. 1 , the intake manifold  42  communicates with an inlet channel  140  in a support body  138  of the metering apparatus  32 . The distribution chamber  93  receives gaseous fuel at a prescribed pressure and generally regardless of fuel type from an outlet channel  144  in the support body  138 .  
         [0032]     As best illustrated in  FIGS. 1 and 10 , the support body  138  includes a base portion  146  that also includes a cover  148 , a middle plate  150 , and a cap  152 . The middle plate  150  is sealably carried between the cover  148  and the base portion  146 , and the base portion  146  is disposed between the middle plate  150  and the cap  152 . The base portion  146  supports an upstream, diaphragm-operated, shutoff valve  154  of the metering apparatus  32  orientated operatively between the inlet channel  140  and a mid channel  156  in the base portion  146  and supports a downstream, diaphragm-operated, flow valve  158  biased closed and orientated operatively between the mid channel  156  and the outlet channel  144 .  
         [0033]     As best illustrated in  FIGS. 10 and 11 , the shutoff valve  154  is preferably a poppet valve actuated by a vacuum pressure from an operating combustion engine, and similar in design to the inlet and outlet valves  76 ,  78 . The shutoff valve  154  is preferably an insert  160  fitted into an outlet end or counter bore of the inlet channel  140  through a first side  162  of the base portion  146 . Preferably, the insert  160  includes a cylindrical spring retainer  164  and a valve seat  174  press-fit to the retainer  164 . The valve seat  174  and retainer  164  surround or encircle a valve stem  166 . The valve stem  166  extends axially and carries an enlarged head  168  at a leading end and an enlarged abutment or heel  170  at a trailing opposite end. A semi-conical or frustum-shaped compression spring  172  is located concentrically about the valve stem  166  and compressed axially with respect to the centerline between an annular ledge preferably carried by the spring retainer  164  and a spring clip  165  engaged to the heel  170  for biasing the valve head  168  sealably against the valve seat  174 . One skilled in the art would now know that other alternatives exist to hold an insert  160  carrying a valve seat  174  firmly to the base portion  146  of the support body. For instance, the insert  160  could be engaged threadably to the base portion  146  or if orientation and machining techniques permit, the annular seat  174  could be machined directly to the base portion  146 .  
         [0034]     The heel  170  of the shutoff valve  154  communicates with a chamber  176  that communicates directly downstream with the mid channel  156  and is generally defined between a gas side of a resiliently flexible diaphragm  178  sealed along a periphery to the middle plate  150  of the support body  138 , and the first side  162  of the base portion  146  of the body  138 . A displacement chamber  180  is defined between an opposite vacuum side of the diaphragm  178  and the middle plate  150 .  
         [0035]     An actuator  182  of the shutoff valve  154  opens the shutoff valve  154  preferably upon receiving a sufficient vacuum pressure from a starting or running combustion engine. The actuator  182  preferably has reciprocating rod or member  184  located and supported slidably in a bore  186  in the supplemental portion  150 . A first end of the member  184  is generally located in the middle plate  180  and is attached to a central portion of the diaphragm  178 . The rod  84  is connected at its other end to a resilient diaphragm  190  that defines a vacuum or pressure chamber  188  on one side and a reference chamber  192  on the other side. The reference chamber may communicate with the atmosphere through a vent  193 . Because the actuator  182  must produce a sufficient axial force to open the shutoff valve  154  against the resilient compressive force of spring  172 , the diameter or size of diaphragm  190  preferably is substantially larger than that of the diaphragm  178 .  
         [0036]     A peripheral edge  194  of the diaphragm  190  is sealed continuously between the middle plate  150  and the cover  148 . A compression return spring  196  is disposed in the pressure chamber  194  for compression between the middle plate  150  and a reinforcement plate  198  generally carried by the diaphragm  190 . The cover  148  further has an inward projecting stop that opposes or confronts the diaphragm  190  in the reference chamber  192  to define the maximum displacement of the diaphragm  190  under the biasing force of the return spring  196 .  
         [0037]     Preferably, the middle plate  150  supports a barbed nipple  200  that generally communicates with a fuel-and-air mixing passage  202  of a carburetor downstream of a throttle valve  204  (see  FIG. 1 ) and a vacuum channel  206  in the supplemental portion  150  that tees-off to communicate with both the displacement chamber  180  and the pressure chamber  188  (see  FIG. 10 ). One skilled in the art would now know that alternatively to the carburetor, the nozzle  200  and thus vacuum chamber  184  could communicate with an intake manifold of the engine, or a crankcase of a two-stroke engine.  
         [0038]     For two-stroke engine applications which produce positive pressure pulses or blow-back from the engine, a check valve  208  ( FIG. 10 ) preferably is located at the inlet of the vacuum channel  206  and preferably is supported by the middle plate  150  adjacent to the nozzle  200 . The check valve  208  opens when the pressure in the displacement chamber  180  and pressure chamber  188  are greater than in the nipple  200 , and closes when this condition does not exist or a positive pressure impulse is received from the two-stroke engine. For four-stroke engine applications, the check valve  208  can be omitted since such engines provide a stable negative pressure signal.  
         [0039]     As best illustrated in  FIGS. 1 and 10 , the flow valve  158  of the metering apparatus  32  located downstream of and communicating with the shutoff valve  154  via the mid channel  156  is preferably actuated or opened by a diaphragm-type actuator  210  and biased closed by a compression spring  212 . An elongated lever or arm  214  of the flow valve  158  connects pivotally to a pin  216  fixed to the base portion  146  of the support body  138 . When the valve  158  is biased closed, a valve head  218  fixed to one end of the lever  214  releasably seats against an annular valve seat  220  carried by a cylindrical, flanged, ring  222  press fitted into a counter bore of the mid channel  156  (see  FIG. 10 ). An opposite end  224  of the lever  214  is located substantially diametrically opposite the valve head  218  with respect to the center pin  216  and is biased away from an external side  226  of the base portion  146  by the biasing force of the spring  212  compressed axially between the end  224  and the external side  226 . Preferably, the external side  226  of the body portion  146  generally faces in an opposite direction with respect to the face or side  162  of the body portion  146 .  
         [0040]     The spring  212 , the lever  214 , the pin  216  and the valve head  218  are located in a control or fuel metering chamber  228  of the actuator  210  communicating between the mid channel  156  and the outlet channel  144  of the metering apparatus  32 . The metering chamber  228  is generally defined between the external side  226  of the base portion  146  and a gaseous side of a resiliently flexible diaphragm  230 . A reference or atmospheric chamber  232  of the actuator  210  is defined generally between an opposite or dry side of the metering diaphragm  230  and the cap  152 . A breathing hole  236  in the cap  152  communicates the reference chamber  232  with the outside environment and a peripheral edge  238  of the metering diaphragm  230  is compressed sealably between the base portion  146  and the cap  152 .  
         [0041]     The metering diaphragm  230  of the flow valve actuator  210  carries a centrally positioned projection  240  located in the metering chamber  228  that confronts and is preferably spaced from the end  224  of the lever  214  when the flow valve  158  is closed and the actuator  210  is in a rest position (see  FIG. 1 ). When the control chamber  228  is communicated with a vacuum pressure preferably from a venturi region  242  of the carburetor, operation of the actuator  210  is initiated and the diaphragm  230  flexes toward the lever  214  against the biasing force of a return spring  244  located in the reference chamber  232  and engaged under tension between the lid structure  234  and the dry side of the diaphragm  230 . Continued flexing of the diaphragm  230  upon sufficient vacuum pressure in the control chamber  228  causes the projection  240  to push upon the end  224  of lever  214  against the compressive force of the spring  212  to open the flow valve  158  (see  FIG. 10 ).  
         [0042]     As a fuel flow adjustment feature, the cap  152  of the fuel metering device  32  preferably carries a threaded cylindrical member or screw  246 . An external end of the screw  246  has a diametrically extending slot or recess  248  for receipt of a screwdriver or tool. An opposite end of the screw  246  is located in the reference chamber and has a surface  250  that engages the return spring  244 . During adjustment, rotation of the screw  246  toward the diaphragm  230  relieves a portion of the tensile force produced by the return spring  244 , thus less vacuum is required in the metering chamber  228  to open the flow valve  158 . Movement of the screw  246  away from the diaphragm  230  increases the spring force on the diaphragm  230  so a greater magnitude pressure signal is required to open the valve  158 .  
         [0043]     As best illustrated in  FIGS. 1-3 , when the combustion engine is shutdown, the operator rotates knob  34  to place the fuel selection module  26  in an all-closed position  252  so that gaseous fuel does not leak through the carburetor and engine. When in the all-closed position  252 , the inlet and outlet push rods  80 ,  82  of the butane flow circuit  72  fully project into the blind bore  58  by the biasing force of the respective springs  96 ,  98 , and are preferably radially spaced with respect to axis  62  from the cam  68  and spaced axially with respect to centerline  94  or from the respective heels  114 ,  126  of the inlet and outlet valves  76 ,  78  of the butane flow circuit  72 . Axial spacing of the rods  80 ,  82  from the heels  114 ,  126  permits the biasing force of the valve springs  116 ,  128  to seat the respective valve heads  112 ,  124  sealably against the valve seats  130 . Similar to the butane flow circuit  72 , the inlet and outlet pushrods  80 ,  82  of the propane flow circuit  74  are axially spaced from the respective heels  114 ,  126  of the inlet and outlet valves  76 ,  78 . Unlike the butane flow circuit  72 , the inlet and outlet pushrods  80 ,  82  of the propane flow circuit  74  are not radially spaced from the propane cam  70  of the camshaft  60 . Instead, the pushrods  80 ,  82  are slightly biased against the propane cam  70  in respective and diametrically opposed intermediate recesses  254 ,  256  carried by the propane cam  70 . Placement of the propane pushrods  80 ,  82  into the respective recesses  254 ,  256  provides a positive indication to the operator that the fuel selection module  26  is in the all-closed position  252 .  
         [0044]     Also with the engine not running, the vacuum pressure required to open the shutoff valve  154  and the flow valve  158  of the fuel metering apparatus  32  is not present, hence, the valves  154 ,  158  are biased closed by respective springs  172 ,  212 . Primarily, closure of shutoff valve  154 , and to a lesser degree closure of flow valve  158 , act as a backup to further assure gaseous fuel does not leak into the engine during engine shutdown conditions.  
         [0045]     As best illustrated in  FIGS. 4-6 , when operating the engine with propane gas, the operator first rotates the knob  34  of the camshaft  60  by about ninety rotational degrees in a clockwise direction. This places the fuel selection module  26  in a propane flow position  258  prior to starting the engine. When rotating toward the propane flow position  258 , the general Z-shape of the propane cam  70  causes the inlet and outlet pushrods  80 ,  82  of the propane flow circuit  74  to ride radially against the propane cam  70  and out of the respective intermediate recesses  254 ,  256 . Continued rotation in the clockwise direction moves the pushrods  80 ,  82  linearly and radially outward against the biasing force of the respective springs  96 ,  98 , and when the pushrods  80 ,  82  abut the valve heels  114 ,  116 , then also against the biasing force of the respective inlet and outlet valve springs  116 ,  128 . The camshaft  60  rotates until the pushrods  80 ,  82  slip into diametrically opposed recesses  260 ,  262  opened radially outward in the propane cam  70 . Placement of the propane pushrods  80 ,  82  into the respective recesses  260 ,  262  provides a positive indication to the operator that the fuel selection module  26  is in the propane flow position  258 .  
         [0046]     When rotated into the propane flow position  258 , the butane cam  68  of the camshaft  60  has simultaneously rotated with the propane cam  70 , however, the S-shape of the butane cam  68  maintains a radial and circumferential space between the corresponding inlet and outlet pushrods  80 ,  82  thus the respective inlet and outlet valves  76 ,  78  of the butane flow circuit  72  remain spring-biased closed as previously described. Moreover, because the engine is not yet started, the fuel metering apparatus  32 , located between the intake manifold  42  and the outlet passage  120 , remains closed and propane does not yet flow through the fuel control device  20  (see  FIG. 1 ).  
         [0047]     When the combustion engine is started, the vacuum chamber  188  and the displacement chamber  180  of the shutoff valve actuator  182  receive a vacuum signal via the vacuum channel  206  and preferably from the mixing passage  202  of the carburetor downstream from the throttle valve  204 . A force generally equal to the vacuum pressure times the difference between the exposed areas of the diaphragm  190  and the diaphragm  178  overcomes the biasing force of the actuator spring  196  and moves the diaphragm  190  toward the middle plate  150  (see  FIG. 10 ). Because the member  184  is connected between the diaphragms  178  and  190 , the diaphragm  190  also displaces the member  184  and the diaphragm  178  until the member  184  or diaphragm  178  engages the heel  170  and opens the shutoff valve  154  against the combined biasing force of the valve spring  172  and the actuator spring  196 .  
         [0048]     With the shutoff valve  154  open, propane gas flows through the propane inlet passage  40  from the propane cylinder  22 , past the open propane inlet valve  74 , through the intake manifold  42 , the inlet channel  140  of the fuel metering apparatus  32 , past the open shutoff valve  154  and generally to the mid channel  156 . As the shutoff valve actuator  182  receives the vacuum pressure from downstream of the throttle valve  204 , the flow valve actuator  210  of the fuel metering apparatus  32  receives a substantially smaller vacuum pressure from the venturi region  242  of the mixing passage  202  upstream of the substantially or nearly closed throttle valve  204  and during engine starting. This smaller vacuum pressure during engine start is transmitted through the outlet passage  120  of the outlet valve bank  30 , then through the open propane outlet valve  78 , through the propane cavity  92 , the propane jet  97 , the distribution chamber  93 , and then through the outlet channel  144  of the fuel metering apparatus  32  that communicates directly with the metering chamber  228  of the flow valve actuator  210 . The vacuum pressure from the carburetor venturi region  242  creates a force acting on the diaphragm  230  and tending to flex the diaphragm toward the lever  214 .  
         [0049]     With sufficient vacuum, the diaphragm  230  moves until the projection  240  of the diaphragm pushes against the end  224  of the lever  214  and against the added compressive force of valve spring  212  and generally minus any force produced by the propane pressure against the confronting valve head  218 . Movement of the end  224  of the lever  214  moves the head  218  away from the valve seat  220  opening the flow valve  158  until a sufficient increase in pressure in the metering chamber  228  causes the valve to close. When open as in  FIG. 10 , the propane gas flows through the metering chamber  228 , the outlet channel  144  and the distribution chamber  93 . From chamber  93  and as illustrated in  FIG. 4 , the propane gas flows through the propane jet  97  sized to cause a prescribed pressure drop placing the propane gas at a desired pressure for running the engine specifically on propane. The propane gas at the prescribed pressure flows past the open propane outlet valve  78 , through the outlet passage  120  and into the venturi region  242  of the carburetor.  
         [0050]     After the engine has started, and the throttle valve  204  moves toward a wide open throttle position, the vacuum at the venturi region  242  increases causing preferably a greater deflection of the diaphragm  230  and preferably at a greater frequency. This causes the head  218  of the flow valve  158  to move further from the valve seat  220  and generally more often thus increasing propane gas flow to coincide with the increase in quantity of air flow resulting in a substantially consistent fuel-to-air mixture ratio supplied to the running engine.  
         [0051]     As best illustrated in  FIGS. 7-9 , when operating the engine with butane gas, the operator first rotates the knob  34  of the camshaft  60  by about ninety rotational degrees in a counter-clockwise direction. This places the fuel selection module  26  in a butane flow position  264  prior to starting the engine. When rotating toward the butane flow position  264 , the general S-shape of the butane cam  68  causes the inlet and outlet pushrods  80 ,  82  of the butane flow circuit  72  to ride radially against the rotating butane cam  68  and the pushrods  80 ,  82  of the propane flow circuit  74  to ride out of the respective intermediate recesses  254 ,  256 . Continued rotation in the counter-clockwise direction moves the pushrods  80 ,  82  of the butane flow circuit  72  linearly and radially outward against the biasing force of the respective rod springs  96 ,  98  and when the pushrods  80 ,  82  abut the valve heels  114 ,  116 , then also against the biasing force of the respective inlet and outlet valve springs  116 ,  128  of the butane flow circuit  72  (see  FIG. 8 ). The camshaft  60  rotates until the pushrods  80 ,  82  slip into diametrically opposed butane recesses  266 ,  268  opened radially outward in the butane cam  68 . Placement of the butane pushrods  80 ,  82  into the respective recesses  266 ,  268  provides a positive indication to the operator that the fuel selection module  26  is in the butane flow position  264 .  
         [0052]     When rotated into the butane flow position  264 , the propane cam  70  of the camshaft  60  has simultaneously rotated with the butane cam  68 , however, the Z-shape of the propane cam  70  creates a radial space between the inlet and outlet pushrods  80 ,  82  thus the respective inlet and outlet valves  76 ,  78  of the propane flow circuit  74  remain spring-biased closed as previously described (see  FIG. 9 ). Moreover, because the engine is not yet started, the fuel metering apparatus  32 , located between the intake manifold  42  and the outlet passage  120 , remains closed and butane does not yet flow through the fuel control device  20  (see  FIG. 1 ).  
         [0053]     Starting of the engine with butane gas is similar to starting the engine with propane gas, and operation of the fuel metering device  32  is generally the same. However, the inlet passage  46  is preferably fitted with the butane pressure regulator  54  so that when the butane fuel is gradually consumed from the butane cylinder  24  the decrease in butane pressure in the commonly marketed and relatively small cylinder is not transmitted through the fuel metering apparatus  32 . Instead, the pressure regulator  32  supplies fuel at a relatively consistent pressure regardless of any considerable pressure decrease in the cylinder  24 . The butane gas preferably is further pressure regulated by the butane jet  95  before it is supplied to the carburetor mixing passage  202 .  
         [0054]     When the operator shuts down the engine and the intake vacuum pressure decreases with the sudden decrease in engine speed or power, the resilient biasing force of springs  172  and  196  acting upon the large-diameter diaphragm  190  of the shutoff valve actuator  182  overcomes the force produced by vacuum pressure in the pressure chamber  188  and the shutoff valve  154  closes. With shutoff valve  154  closed, the supply of gaseous fuel flowing to the engine is stopped.  
         [0055]     While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. For instance, the fuel selection module  26  and fuel flow circuits  72 ,  74  can be replaced with solenoid valves requiring an electric power and an electric/electronic control unit. Furthermore, if the fuel is stored in gaseous form air can be premixed with the fuel thus alleviating the need for a conventional carburetor. It is not intended herein to mention all the possible equivalent forms, modifications or ramifications of the invention. It is understood that terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention as defined by the following claims.