Temperature compensated fluid flow metering carburetor and method

In a carburetor having a mixing passage, a fuel supply chamber, fuel duct means to conduct fuel from the chamber to the mixing passage, and a fuel metering system associated with said fuel duct means including variable restriction means for varying the effective flow cross-sectional area of said fuel duct means to modulate the mass flow rate of fuel to said mixing passage, said variable restriction means comprising support means and fuel metering means defining said flow cross-sectional area and respectively having first and second different linear coefficients of expansion such that differential expansion and contraction of said support and fuel metering means relative to one another in response to fuel temperature changes varies the flow-controlling cross-sectional area of said fuel duct means inversely relative to such temperature changes to thereby modulate temperature-dependent fuel density changes to reduce resultant mass fuel flow rate variations, said fuel metering means being disposed in flow controlling relation with said fuel duct means and having mounting means supported in fixed relation by and to said support means and a valve member, said mounting means being disposed at one end of said valve member and said fuel metering means comprising an extension of said valve member extending longitudinally of said valve member away from said one end of said valve member and terminating in a free end slidable in said support means, said valve member being unrestrained from said free end to one end thereof, said valve member free end having a free edge movable in a fuel passageway of said fuel duct means to define therewith said flow controlling cross-sectional area such that the differential expansion and contraction of said valve member relative to said support means in response to fuel temperature changes causes movement of the free end of said valve member in a direction to effect the variation in flow controlling cross-sectional area of said fuel duct means, said movement of said valve member being in a direction transverse to the direction of fuel flow in said fuel passageway in the zone of said flow controlling cross-sectional area, said free end and free edge being configured relative to said valve member movement direction and to said fuel passageway to create turbulent flow of the fuel flowing past said flow-controlling cross-sectional zone whereby the effect of temperature-induced viscosity changes in said fuel is essentially nullified and essentially only temperature-induced changes in fuel density are compensated by said differential expansion and contraction variation of said flow-controlling cross-sectional area, the improvement in combination therewith wherein said valve member comprises a needle slidable in a bore of said support means and having a stem protruding therefrom defining said free end and edge of said fluid metering means, and also comprises a bi-metal strip fixed at one operative end by said mounting means to said support means and another operative end spaced longitudinally of said strip remote from said one strip end and operably coupled to said needle to generate at least the principal differential expansion and contraction of said flow restriction means relative to said support means to cause the variation of said flow-controlling cross-sectional area.

A method of controlling the air-to-fuel ratio (A/F) in the operation a carburetor having a body with a liquid fuel metering system associated with liquid fuel duct means in the body including variable flow restriction means for varying the effective flow cross-sectional area of the duct means to modulate the flow rate of liquid fuel into a ambient air and liquid fuel mixing passage of the carburetor body, the variable flow restriction means comprising fixed support means on the body containing the fuel duct means and an operably associated temperature responsive movable fuel metering actuating means including valve means directly immersed in the liquid in the duct means and operably disposed in liquid fuel flow controlling relation with the duct means, the variable flow restriction actuating means also including a temperature responding element having a valve coupling portion operably connected to the valve means and a mounting portion secured in fixed relation to the body support means and spaced remotely from the valve coupling portion of the actuating means element such that differential expansion and contraction of the actuating means element relative to said support means in response to temperature changes in the element causes bodily movement of the valve means in a direction effective to vary the flow-controlling cross-sectional area of the fuel duct means inversely relative to temperature changes in the element, said method comprising the control step of:

• (1) mounting the temperature responding element on the carburetor body in a location exposed to ambient exterior air temperature surrounding the carburetor and generally remote from and out of direct contact with the liquid fuel flow in the carburetor body such that the temperature of the element tracks that of ambient atmosphere surrounding the element whereby the element is directly responsive to temperature changes in such surrounding ambient atmosphere,
• (2) determining a first range of ambient air temperatures in which the carburetor is normally to be operated and establishing within the first range a desired predetermined first ambient air temperature set point value for peak lean out of A/F produced by operation of the carburetor in the first temperature range,
• (3) positionally setting the valve means and associated element relative to the carburetor body to produce the peak lean out of A/F at this predetermined set point temperature, and
• (4) structurally preventing the movement of the temperature responding element to thereby prevent bodily movement of the valve means when the temperature of the ambient air surrounding the carburetor is in the first range in which the carburetor is normally operable and varies in such first range above the predetermined first ambient temperature set point whereby in operation of the carburetor the A/F output of the carburetor is made progressively richer both when ambient air temperatures progressively decreases below and progressively increases above the predetermined first set point temperature.