Patent GB-859777-A (GB)
Title: Carburetor
Inventor: FISH JOHN ROBERT
IPC: F02M1/00
Filed: 1957-05-20
Abstract: 859,777. Carburetters. FISH CARBURETOR CORPORATION. May 20, 1957, No. 15930/57. Class 7(3). A downdraught carburetter comprises a throttle member adapted to have its position determined by control by an operator independently of suction in the air passage, one or more nozzles entering the air passage adjacent the throttle valve and subject in operation and at idling settings of the throttle member to at least a substantial portion of the full intake manifold vacuum, a fuel supply chamber having an upper opening communicating with a source of at least substantially atmospheric pressure and means to furnish fuel from the chamber to the nozzles the means comprising a continuously and gradually variable restrictor valve controlling a restriction to the flow of fuel through the means the restrictor valve being connected to the throttle member for movement therewith and being arranged gradually to reduce the restriction to fuel flow with gradually increasing power settings of the throttle member and gradually to increase the restriction with gradually decreasing power settings of the throttle member. Under idling conditions with the throttle 4 horizontal or nearly horizontal and substantially closing the main air passage air enters the upper vaporizing ports 21 as seen in Fig. 6 and carries fuel with it in passing on through the lower vaporizing ports 55 into the intake manifold. The position of the arm 11 with respect to the groove 22 is adjustable by changing the idling position of the throttle shaft conveniently by adjustments to the idling adjustment stay screw 48. Separate adjustments are provided for altering the position of the throttle on the throttle shaft. The amount of air passing the throttle through the low speed air by-pass passages 63<SP>1</SP> and 63<SP>11</SP> is also adjustable and knob 61 and valve screw 62 are provided for this purpose. Fuel during idling is freely admitted through ports 17 and 18 from the float reservoir into the fuel supply chamber under the atmospheric or nearly atmospheric pressure which is maintained in the fuel supply chamber and fuel reservoir through channel 38 from the intake portion 2 of the main air passage. It is stated that it is an important feature of the carburetter that the pressure differential which causes the fuel to flow from the supply chamber into the air stream is very much greater than in prior aril carburetters. Under constant power or steady state conditions the size of the groove 22 at the arm 11 is controlling for lower power settings while for higher power settings the maximum fuel supply rate may be limited by the adjustable screw-controlled valve 23 or by the size of the groove 22 or by the size of the passage 41. In the preferred arrangement the groove 22 is made larger than the passage 41 and the size of the passage 41 limits the maximum fuel supply rate. Screw 23 may be adjusted to limit the maximum rate by imposing additional restriction at this screw. All of the ports 21 and 55 on respective opposite sides of the throttle shaft come into fuel supplying operation when the throttle is opened beyond about three-quarters throttle position. Upon rapid movement of the throttle link 9 in an accelerating direction important changes take place. The arm 11 moves toward the wider and deeper end of groove 22 thereby providing less restriction to the flow of fuel into the throttle shaft for vaporizing into the air stream, feather valve 19 closes to seal port 18, and the pressure within the fuel supply chamber 12 ahead of arm 11 increases. The increase in pressure forces fuel into the upper portion 58 of the fuel supply chamber and fuel is thus ejected from nozzle 59 into the air stream. Since the rear compartment of the fuel supply chamber 12 behind arm 11 is in communication with the float reservoir through the relatively large open port 17 the fuel pressure behind the arm 11 remains nearly at atmospheric pressure and the net effect is that fuel is forced into the passage 41 and passage 20 of the arm at more than atmospheric pressure. During forward accelerating motion of arm 11 some fuel will be forced back through the small aperture 27 into the float reservoir but aperture 27 is sufficiently small to pass ordinarily only a relatively small amount of fuel during the relatively brief period of acceleration. The aperture 27 therefore serves as a by-pass which provides a desired amount of accelerating fuel. During forward movement of the arm 11 in the fuel supply chamber the short by-pass channel 44 formed from the forward face 45 of the arm 11 and communicating with the groove 22 immediately behind the opening 41 performs a useful function in supplying fuel from the forward compartment to the groove 22 whereby opening 41 receives fuel through the groove 22 from both directions under the increased pressure in the forward chamber during accelerating periods. Channel 44 provides another and different function during rapid accelerating motion of the arm 11 in preventing the build up of pressure in the groove 22 in the portion of the groove toward which the arm is moving by by-passing the fuel. The channel 44 serves to increase the amount of fuel supplied through the channel 20 to ports 21 and 55 during rapid accelerating movement of the arm and to overcome any tendency to supply increased fuel through the passage 20 upon rapid decelerating movement of the arm. As the throttle is opened toward full throttle position the streamlined form of the throttle element 4 causes the throat of the air passage more nearly to approach Venturi form. The action of the ports 21 in supplying gasoline to the air stream changes at approximately three-quarter throttle position from the admission of air into the hollow throttle shaft to the ejection of fuel into the air stream. Thus at full throttle position with the throttle member 4 substantially vertical approximately equal streams of fuel will issue from the ports 55 and 21 on opposite sides of the throttle shaft. When the throttle is at other than full throttle position at least the larger portion of fuel will be introduced through the ports 55 into the air stream below the throttle. Turbulence in the area below the throttle is sufficient to cause thorough dispersion of the fuel particles into the air stream and the action of the throttle is accordingly such as to provide improved fuel mixing under all conditions it being understood that the spray produced by air passing into ports 21 and mixed with fuel out of ports 55 during idling conditions provides good dispersion and that the six sprays of fuel emerging from the throttle in fully open position similarly provides even distribution of the fuel throughout the air stream. If other than even distribution of fuel is desired the ports 21 and 55 may be of different sizes. The groove 22 is preferably proportioned to be small throughout approximately one quarter of the full arm movement distance at the low speed end of the groove and gradually to increase in size toward its full throttle end. The first one-quarter of throttle motion accordingly changes the fuel supply rate primarily as a result of motion of the throttle member with respect to the by-pass passages 631, 63<SP>11</SP>. Thereafter the gradually increasing size of the groove 22 meters the gradually increasing fuel rate.