Patent Publication Number: US-6702261-B1

Title: Electronic control diaphragm carburetor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of application Ser. No. 10/294,215, filed Nov. 13, 2002, which is a continuation-in-part application of application Ser. No. 09/917,429 filed Jul. 27, 2001, now U.S. Pat. No. 6,581,916 which applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a diaphragm carburetor suitable for supplying fuel to an engine used as a power source for most handheld gasoline powered products. More particularly, the invention relates to devices and methods for allowing an inexpensive and effective means of electrical control of small engines offering functionality similar to that of auto engines. 
     BACKGROUND 
     Diaphragm carburetors are generally used to supply fuel to two-cycle engines. These carburetors are equipped with a fuel pressure regulator that ensures fuel fed from a fuel pump is regulated at a fixed pressure, and then delivered to an air intake path. The fuel pressure regulator is typically equipped with a constant-pressure fuel chamber that stores fuel sent from the fuel pump. The constant-pressure fuel chamber is generally separated from atmosphere by a diaphragm that adjusts the fuel pressure to a constant pressure. A control valve that is interlocked to the motion of the diaphragm opens and closes a fuel passageway through which fuel flows to the fuel chamber. Fuel from the fuel chamber is delivered to the air intake path via a main fuel path and an idle fuel path. The main fuel path leads to a main nozzle that is open to a venturi in the air intake path. The idle fuel path leads to slow and idle ports that open adjacent to a throttle valve in the air intake path. 
     Conventional diaphragm carburetors are pre-set at an equipment manufacturer&#39;s assembly line to deliver fuel at a predetermined flow rate to an engine the carburetor is coupled to. Manufacturing tolerances in the size and location of fuel paths, and the stiffness of the diaphragms, require that the manufacturer individually adjust each carburetor to achieve a desired flow rate. After these adjustments are made, all fuel path adjustment needles are capped to prevent subsequent tampering. The equipment is then shipped all over the world, and often times the carburetors are never readjusted to accommodate for local environmental conditions, fuel type or engine load. 
     This standardized manufacturing approach can lead to inefficient engine performance. Local environmental conditions, such as temperature and altitude, as well as engine loading and fuel type used can effect engine performance. All of these factors have an effect on the amount of fuel required for an optimal fuel/air ratio. The typical carburetor does not adjust for these variables, and the result is an engine that operates at less than peak performance and has higher exhaust emissions levels. 
     For example, engines operated in cold weather require additional fuel. Cold conditions inhibit fuel vaporization and cold air is denser, requiring additional fuel to achieve the proper fuel/air ratio. At higher altitudes, the air is less dense, and less fuel is required to obtain the proper fuel/air ratio. Typically, carburetors are set for peak performance at full load. However, when engines are run at less than peak power, less fuel is required. Lastly, different regions throughout the country, and the world, have different environmentally driven requirements for the amount of oxygenates that are added to fuel. Currently, engines are adjusted for optimal performance using the most oxygen rich fuels. Thus, when less-oxygenated fuels are used, excess fuel is used. Other conditions, including periods of start-up, warm-up, acceleration and deceleration, may also contribute to engine inefficiencies that could be corrected by varying the fuel flow rate to the engine. 
     Manufacturers have attempted to address this problem by placing a solenoid valve in a fuel passage through which fuel flows to the constant-pressure fuel chamber of the carburetor. The valve can be fully opened or fully closed in response to electronic feedback generated from engine performance indicators. The problem with this device is that the resultant fuel path is either fully open or fully closed with no intermediate positions available. 
     Thus, it would be desirable to provide much finer control of the position of the fuel control valve to enable more accurate control of fuel delivery to the engine without a significant increase in cost or complexity of the device. 
     SUMMARY OF THE INVENTION 
     The proposed device of the present invention tends to facilitate much finer position control of a carburetor fuel flow control valve. This advantageously tends to result in more accurate control of fuel delivery to the engine without a significant increase in cost or complexity of the device. 
     In an exemplary embodiment of the present invention, a magnet and wire coil assembly are coupled to a metering diaphragm of the carburetor&#39;s fuel pressure regulator. The diaphragm, as with conventional diaphragm carburetors, contacts a lever that is connected to an inlet needle of a fuel control valve positioned in a passageway through which fuel flows to a constant pressure fuel chamber. Movement of the diaphragm controls the size of the opening of the control valve and, thus, fuel flow through the passageway to the constant-pressure fuel chamber. Preferably, the magnet is attached to the metering diaphragm and extends outside a bottom cover of the carburetor into the center of a wire coil that is attached to or is an integral part of the bottom cover. 
     Application of an electric current to the coil turns the coil into an electromagnet. By controlling the direction and amount of current through the wire coil, the direction and degree to which the magnet travels can be controlled. Movement of the magnet, in turn, pushes or pulls the metering diaphragm inward and outward relative to the fuel chamber. In operation, the current flow through the coil is preferably modulated to provide either an inward bias or an outward bias on the diaphragm. An inward bias will cause the inlet needle to open further than normal and result in a greater amount of fuel being delivered to the engine. An outward bias Will prevent the inlet needle from opening as far as normal and will result in less fuel being delivered to the engine. Thus, by controlling the current through the wire coil, one can control the amount of fuel flow through the carburetor and to the engine. 
     Electronic feedback generated from engine performance can be used to control the current input to the wire coil. In this way the engine will self-adjust so that the optimal fuel/air ratio will be achieved. This will result in lower exhaust emissions and improved engine performance. 
    
    
     Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cut-away front view of a prior art carburetor having a fuel supply and control circuit. 
     FIG. 2 is a cut-away front view of a carburetor having a fuel supply and control circuit constructed in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to FIG. 1, a prior art carburetor having a fuel supply and control circuit is shown. The carburetor  1  includes a body  2  with an air intake path  5  that extends horizontally, and covers  3  and  4  mounted on the top and bottom of the body  2 . The intake path  5  has a venturi  6  and a throttle valve  7  mounted upstream of the venturi  6 . 
     A fuel pump diaphragm  9  of a fuel pump  8  is sandwiched between the body  2  of the carburetor  1  and the top cover  3 . Fuel in a fuel tank (not shown) passes from a fuel pipe  10  through an inlet valve  11 , an inlet chamber  12 , a pump chamber  13 , an outlet valve  14 , and an outlet chamber  15 , and is fed, via a fuel path  17  to a metering or constant-pressure fuel chamber  20  of a fuel pressure regulator  18 . A pulse pressure generated in an engine crankcase is introduced into a pulse chamber  16  which opposes a pump chamber  13  (both of which sandwich the fuel pump diaphragm  9 ), which causes the fuel to be sucked into the pump chamber  13 , from which it is dispensed, all of which is generally known in the art. 
     A metering diaphragm  19  of a fuel pressure regulator  18  is sandwiched between the body  2  and the bottom cover  4  of the carburetor  1 , and divides the fuel chamber  20  above from an air chamber  21  below. A lever  23 , which is housed in the fuel chamber  20  and supported in free rotation by a pin  22 , is biased by a spring  24  so one end  23   a  of the lever  23  contacts the center of the metering diaphragm  19 . At the other end  23   b , the lever  23  supports an inlet needle  25  of a fuel control valve  33  that opens and closes the fuel path  17 . When the pressure drops in the fuel chamber  20  as fuel is fed from the chamber  20  into the air intake  5 , the metering diaphragm  19  is biased upward, biasing the inlet needle  25  downward or away from the control valve  33  to open the control valve  33  and allow fuel to flow through the fuel path  17  into the fuel chamber  20 . When the pressure rises in the fuel chamber  20  due to the flow of fuel into the chamber  20 , the metering diaphragm  19  is biased downward, biasing the inlet needle  25  upward or toward the control valve  33  to close the control valve  33 . In this manner, the fuel chamber  20  is always kept at a constant pressure. 
     The fuel from the fuel chamber  20  enters a nozzle chamber  27  via a main fuel path  26 . The fuel is fed from the nozzle chamber  27  to the air intake path  5  through a main nozzle  28  that opens into the venturi  6  of the air intake path  5 . The fuel from the fuel chamber  20  also enters a port chamber  30  via an idle fuel path  29 . Depending on the position of the throttle valve  7 , the fuel is fed from the port chamber  30  into the air intake path  5  through an idle port  31  or part throttle ports  32  adjacent to the throttle valve  7 . 
     Turning to FIG. 2, a preferred embodiment of a carburetor  100  having a fuel supply and control circuit constructed in accordance with the present invention is shown. As with a conventional carburetor  1  described above, the carburetor  100  of the present invention includes a body  102  with an air intake path  105  that extends horizontally, and covers  103  and  104  mounted on the top and bottom of the body  102 . The intake path  105  has a venturi  106  and a throttle valve  107  mounted upstream of the venturi  106 . 
     A fuel pump diaphragm  109  of a fuel pump  108  is sandwiched between the body  102  of the carburetor  100  and the top cover  103 . Fuel in a fuel tank (not shown) passes from a fuel pipe  110  through an inlet valve  111 , an inlet chamber  112 , a pump chamber  113 , an outlet valve  114 , and an outlet chamber  115 , and is fed, via a fuel path  117  to a metering or constant-pressure fuel chamber  120  of a fuel pressure regulator  118 . A pulse pressure generated in an engine crankcase is introduced into a pulse chamber  116  which opposes the pump chamber  113  (both of which sandwich the fuel pump diaphragm  109 ), which causes the fuel to be sucked into the pump chamber  113 . 
     A metering diaphragm  119  of a fuel pressure regulator  118  is sandwiched between the body  102  and the bottom cover  104  of the carburetor  100 , and divides the fuel chamber  120  above from an air chamber  121  below. A lever  123 , which is housed in the fuel chamber  120  and supported in free rotation by a pin  122 , is biased by a spring  124  so one end  123   a  of the lever  123  contacts the center of the metering diaphragm  119 . The other end  123   b  of the lever  123  supports an inlet needle  125  of a control valve  133  that opens and closes the fuel path  117 . When the pressure drops in the fuel chamber  120  as fuel is fed from the fuel chamber  120  into the air intake path  105 , the metering diaphragm  119  is biased upward, biasing the inlet needle  125  downward or away from the control valve  133  to open the control valve  133  and allow fuel to flow through the fuel path  117  to the fuel chamber  120 . When the pressure rises in the fuel chamber  120 , the metering diaphragm  119  is biased downward, biasing the inlet needle  125  upward or toward the control valve  133  to close the control valve  133 . In this manner, the fuel chamber  120  is always kept at a constant pressure. 
     The fuel from the fuel chamber  120  enters a nozzle chamber  127  via a main fuel path  126 . The fuel is fed from the nozzle chamber  127  to the air intake path  105  through a main nozzle  128  that opens into the venturi  106  of the air intake path  105 . The fuel from the fuel chamber  120  also enters a port chamber  130  via an idle fuel path  129 . Depending on the position of the throttle valve  107 , the fuel is fed from the port chamber  130  into the air intake path  105  through an idle port  131  or part throttle ports  132  adjacent to the throttle valve  107 . 
     However, to accommodate variations in local environmental conditions, fuel type or engine load, the carburetor  100  of the present invention includes a supplement fuel flow control device comprising a magnet and coil assembly  140  coupled to the metering diaphragm  119 . The magnet  141 , which is preferably a permanent magnet, attaches to the metering diaphragm  119 . The magnet  141  extends from the diaphragm  119  out of the pressure regulator  118  through the bottom cover  104  and through the center of a wire coil  142  that is attached to the bottom cover  104  of the carburetor  100 . Alternatively, the wire coil  142  may be formed as an integral part of the bottom cover  104 . 
     Application of an electric current to the wire coil  142  turns the coil  142  into an electromagnet. By controlling the direction and amount of current through the wire coil  142 , the direction and degree to which the magnet  141  travels can be controlled. Movement of the magnet  141 , in turn, pushes or pulls the metering diaphragm  119  inward and outward relative to the fuel chamber  120 . In operation, the current flow through the coil  142  is preferably modulated to provide either an inward bias or an outward bias on the diaphragm  119 . An inward bias will cause the inlet needle  125  to open further than normal and result in a greater amount of fuel being delivered to the engine. An outward bias will prevent the inlet needle  125  from opening as far normal and will result in less fuel being delivered to the engine. In this way, the amount of fuel entering metering chamber  120 , and ultimately reaching the engine, can be varied. 
     The magnet and wire coil assembly  140  can be used to override the normal pressure activated movement of metering diaphragm  119 . For example, the magnet and wire coil assembly  140  can be activated in cold conditions to apply an inward bias to the metering diaphragm  119  to increase fuel flow to the air intake path  105  to achieve the proper fuel/air ratio. At higher altitudes, the magnet and wire coil assembly  140  can be activated to apply an outward bias to the metering diaphragm  119  to decrease fuel flow to the air intake path  105  to achieve the proper fuel/air ratio. When engines are run at less than peak power, the magnet and wire coil assembly  140  can be activated to apply an outward bias to the metering diaphragm  119  to decrease fuel flow to the air intake path  105  to achieve the proper fuel/air ratio. However, if there is no electrical current running through the wire coil, then the metering diaphragm  119  will maintain a constant pressure within metering chamber  120 , just as the pressure regulator diaphragm  19  maintains a constant fuel pressure in fuel chamber  20  in a conventional carburetor  1  discussed above. 
     In a preferred embodiment, the control valve  133  can be controlled from fully open to fully closed and all intermediate positions there between. The primary limitation on the position of the control valve  133  is the degree to which the current through the wire coil  142  can be controlled. The fuel flow control device  140  is easily adaptable to operate with an engine&#39;s control system and utilize the engine&#39;s response to a control input as a sensor. Electronic feedback generated from engine performance is then used to control the current input to the wire coil  142 . In operation, a control system will typically input a pre-programmed mixture change as the engine is running and then analyze the engine&#39;s response. For example, in a “skip fire” control system, fuel is shut off for one revolution every 100 revolutions. By interpreting the engine&#39;s rpm change during the “fuel off ” cycle the control system can determine if the engine is running richer or leaner than optimum and adjust the current to the wire coil  142  to adjust the fuel flow accordingly. In this way the engine will self-adjust so that the optimal fuel/air ratio will be achieved. 
     In another preferred embodiment, the diaphragm carburetor  100  is operated in conjunction with a two-stroke engine. Alternatively, the carburetor  100  may be operated in conjunction with a four-stroke engine. 
     In an alternative embodiment, the coil and magnet assembly  140  may be used as a sensor in the system of the present invention. As a permanent magnet  141 , any motion of the magnet  141  within the coil  142  will generate an electric current. Motion of the magnet can be induced either by the normal pressure actuated inward deflection of the metering diaphragm  119  on each fuel intake stroke, or by the vibration of the magnet  141  and diaphragm  119  during engine operation. In either case, the electric current induced in the coil  142  can be sensed and used as a signal to determine the speed of the engine. An engine controller (not shown) may use the signal to control the speed of the engine. 
     Although the teachings of this invention have been illustrated with specific examples and embodiments to enable one skilled in the art to make and use the invention, it is equally apparent that many more embodiments, applications and advantages are possible without deviating from the inventive concepts disclosed, described, and claimed herein. The invention, therefore, should only be restricted in accordance with the spirit of the claims appended hereto or their legal equivalent, and it is not to be restricted by the specification, drawings, or the description of the preferred embodiment.