US2736539A - Carburetor - Google Patents

Description

Feb. 28, 1956 E. o. WlRTH ET AL 2,736,539

CARBURETOR Original Filed Oct. 1'7, 1947 United States Patent CARBURETOR Emil Wirth and Frederik Barfod, .South Bend, Ind., assi gnors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Original application October 17, 1947, Serial No. 780,368, now Patent No. 2,617,397, dated November 11, 1952. Divided and this application November 26, 1951, Serial No. 258,151

Claims. (Cl. 261-34) The present invention relates to .fuel supply systems for internal combustion engines and more particularly to an accelerating pump for use in combination with said systems. This is a division of our application Serial No. 780,368, filed October 17, 1947, now Patent Number 2,617,397, issued November 11, 1952.

One of the principal objects of the present invention is to provide an accelerating pump actuated through the throttle controlled mechanism wherein fuel is discharged gradually and uniformly therefrom irrespective of the rate at which the throttle valve is opened.

Another object is to provide a compact, fluid sealed throttle actuated accelerating pump whch delivers fuel to the main fuel supply conduit not only While the throttle valve is being opened, but also for a time thereafter while the engine is attaining the d sired speed.

7 Still another object is to provide a mechanically actuatcd accelerating pump which delivers fuel to the main supply conduit at a substantially fixed predetermined rate regardless of the rate at which the pump is actuated.

Further objects and advantages will be apparent from the following description of the present invention in its broader aspects and in a specific detailed embodiment thereof. Although the drawings and the detailed description disclose but one specific embodiment of our accelerating pump, it is to be understood that variations may be made without departing from the scope :of the invention.

In the drawings, numeral 10 designates the body of an updraft carburetor, 12 a throttle valve, 14 an air inlet, and 16 a mixture outlet of the induction passage for an internal combustion engine or other fuel consuming device. A controlled supply of liquid fuel is delivered to the induction passage by a metering unit consisting generally of a centrifugal pump 20 adapted to receive fuel from a substantially constant pressure source through conduit 22 and to discharge said fuel at an increased variable pressure through conduit 24, a fuel metering orifice unit 26 and fixed metering orifice 28, and thence to the discharge valve 30 and nozzle '32. An idle cut'oif valve generally shown at 34 may also be included in conduit 24 between metering orifice 26 and the discharge nozzle. The general arrangement of the fuel metering elements comprising the present fuel system is shown and described in detail in our copending application Serial No. 689,712, filed August 10, 1946, now Patent Number 2,443,527, issued June 15, 1948.

The centrifugal pump 20 consists of a fuel chamber 36 and an impeller 38 therein mounted on shaft 40 which is journaled in pump housing 42 and is adapted to be driven by the engine through a cable, shaft or the like connected to the reduced portion 44 of shaft 40. On the intake side of centrifugal pump 20 is a vapor bleed 45 which is preferably connected'by a conduit to the fuel supply tank (not shown) to prevent vapor locking of the centrifugal pump.

The fuel discharged from centrifugal pump 20 is deliv- 2,736,539 Patented Feb. V28, 1956 2 end through conduit 24 to .fuel metering unit 26 mounted on carburetor body 10 adjacent throttle valve 12,. unit is provided wtih a cylindrical valve element or sleeve 46 secured at one end to a flexible sealing diaphragm 48 and adapted to move axially in a cylindrical portion 49 of the metering unit housing 50. Diaphragm 48 is marginally clamped between housing 50 and support 52 formed integrally with throttle body 10 and is reinforced by .a metal stiffening member 56 secured to the back side of said diaphragm bya rivet 58 extending therethrough into the base of cylindrical valve element 46. The metering orifice 60 of said unit is disposed in the forward endof valve element 46 and the effective size thereof is varied, as said valve element reciprocates, by an adjustable tapered screw 62 threaded into the housing 50 in axial alignment with the metering orifice 60. Screw 62 is sccured in its adjusted position by spring 63 reacting between the housing and the knurled head 64 of said screw. The cylindrical valve element 46 and metering orifice 60 are urged axially away from the tapered end of screw 60 by spring 66 reacting between the inner surface of housing 50 and the base'of said valve element. Fuel is .admitted into the central passage of valve element 46 through a plurality of ports 68 formed in the side of said element near the base thereof. The back side of diaphragm assembly 50 abuts against an actuating cam 70 mounted on the end of the throttle shaft 72 and secured thereto by nut '74. During the operation of the engine, the valve element 46 is actuated in unison with the throttle valve which is actuated by a throttle valve lever and linkage mountedon or connected to the free end ofshaft 72.

The fuel delivered through metering orifice 60 passes through one or more fixed metering orifices 28 disposed in the main fuel line 24 and thence through the orifice J of idle cut-off unit 34. The flow of fuel through orifice 80 is controlled by a tapered valve 82 mounted in a rec'iprocable piston 84 which is actuated by a pinion 86 so disposed in said unit that it engages a rack formed in the surface of the piston 34. The pinion is rotated by a manually actuated lever 88 which may be operated from some remote place by a linkage secured to the end of said lever. pered valve 82 is completely withdrawn from orifice 80 and thus has no effect on the operation of the fuel supply system; however, when the engine is stopped, said taper-ed valve is manually seated over orifice 80 to prevent the :fuel from leaking into the engine 'induction system while the engine is not running.

The fuel passes from orifice 80 through main fuel conduit 24" to chamber 90 of the discharge valve assembly and thence through conduit 92 to discharge nozzle 32. The discharge valve 30 is regulated by a flexible diaphragm 94 marginally clamped between a boss on carburetor body 10 and housing 96 of the discharge valve assembly. A second fuel chamber 98, which is separated from chamber 90 by diaphragm 94, is connected by conduit 100 with the intake side of centrifugal pump 20 and maintains at all times the same pressure as that of the fuel delivered to pump 20 from the source of supply, said latter pressure preferably being of a substantially constant value. The fuel, on leaving chamber 90, flows into conduit 92 and passes into chamber 102 of nozzle 32 and there forms an emulsion with air supplied through conduit 104 from the air inlet 14 of the carburetor, the air being discharged into said chamber through a plurality of ports 106 disposed in the side of the conduit. The annular groove 108 between the air and fuel conduits is the outlet port of the nozzle and is so calibrated that it forms a critical flow orifice which is adapted to prevent any substantial amount of engine suction from being transmitted from the intake manifold to chamber 102. By this arrange- During the operation of the engine, the ta- I ment, engine suction is prevented from influencing the operation of valve 30, which would otherwise be atfected if the fuel in conduit 92 were subjected to any substantial variations in pressure. A venturi 110 is disposed in the induction passage adjacent the critical flow nozzle for the purpose of obtaining an even distribution of the fuel in the air flowing through the induction passage and for obtaining satisfactory air flow lines in said passage.

An accelerating pump generally shown at 120 is mounted on carburetor body 1% adjacent the throttle valve 12 and is actuated by the throttle actuating mechanism through throttle shaft 72 and cam 70 mounted on the end thereof. A pump chamber 121 is formed by a pair of spaced diaphragrns 122 and 124 separated from one another by a spacer element 126, the thickness of which determines the size of the pump chamber. in the central portion of diaphragm 124 and clamped thereto is a cylindrical element 132 which is adapted to reciprocate in a recess in the top portion of housing 134 of the pump and is urged downwardly, as shown on the drawings, by a spring 136 reacting between a stiffening member 138 on -Although only a single conduit is employed for both the fuel inlet and outlet of said pump, it may be desirable in some adaptations to use separate conduits having check valves disposed therein. In the operation of the engine when the throttle valve is closed, spring 144 urges cylindrical element 142, together with diaphagm 122, downwardly against a depressed portion inthe periphery of cam 70, thus enlarging chamber 121 and causing fuel to flow from conduit 24 through conduit 150 and restriction 152 into said chamber. During this time, diaphragm 124 is prevented from following diaphragm 122 by spacer element 126. The under side of the diaphragm is provided with a stiffening member 154 which engages and seats on the spacer element while the throttle valve is closed and diaphragm 122 is in its lowermost position. As the throttle valve is opened, fuel is discharged through conduit 150 and restriction 152 into main fuel conduit 24. How- .ever, should the throttle valve be opened at a rate greater than that at which the fuel can be fully discharged through restriction 152, diaphragm 124 is forced upwardly in opposition to spring 136, compressing said spring while maintaining chamber 121 of substantially the same capacity as that assumed when the throttle valve is closed. As the throttle valve is held in open position, the pressure of spring 136 on diaphragm 124 gradually forces the fuel from chamber 121 through conduit 150 and restriction 152, thus providing a gradual and sustained enrichment in the fuel-air mixture as the engine attains a desired speed. When the fuel has been discharged, the diaphragm 124 and stiffening member 154 again seat on spacer element 126.

In the operation of the present fuel metering system, liquid fuel is supplied to the centrifugal pump 20 through inlet conduit 22 and is discharged by said pump through main fuel conduit 24 to fuel metering unit 26. The fuel then passes through variable metering orifice 60 into conduit 24' through metering orifice 28, idle cut-off orifice 80, conduit 24 and thence into chamber 90 of the fuel discharge valve. As the speed of the engine increases, the speed of the impeller likewise increases, causing the pressure of the fuel in conduit 24 to become greater and consequently causing the. differential across metering orifices 60 and 28 to become greater. The pressure in conduit 24 anterior to the metering unit is at all 4 times greater than the impeller inlet pressure by an amount directly proportional to the square of the impeller speed and therefore is proportional to the square of the engine speed. The pressure in conduit 24" and chamber 90 during operation is always less than the pressure in conduit 24 anterior to the metering unit by an amount equal to the increase in pressure obtained by impeller 38. The difference in the two pressures constitutes the total effective metering head across metering orifices 28 and 60. Since the quantity of fuel which will flow through a given size metering orifice will vary in proportion to the square root of the differential between the pressures of the unmetered fuel and the metered fuel on opposite sides of the metering orifice, and since this difference varies with the square of engine speed, the quantity of fuel flowing through orifices 28 and 60 for a given setting of valve element 46 I will vary directly as the engine speed.

An increased flow of fuel produces a temporary rise in the pressure of chamber 93 and thus forces diaphragm 94 and valve portion 34) thereof away from the inlet end of fuel conduit 92, thereby permitting a greater flow of fuel into the discharge nozzle.

As the throttle valve is opened, cam 70 permits the cylindrical valve element 46 to move away from tapered screw 62, thus increasing the effective size of orifice 60, screw 62 preferably being so contoured that the effective size of orifice 60 varies in approximately straight-line relationship with absolute manifold pressure as the throttle valve is opened or closed. Also, as the throttle valve is opened, cam 70 urges diaphragm 122 toward diaphragm 124, thus forcing additional fuel into conduit 24' and causing a further, though temporary, rise in pressure in chamber 99 and consequently a greater flow of fuel through the discharge nozzle. This produces a temporary enrichment in the fuel-air mixture delivered to the engine. Rapid or successive operation of the present accelerating pump does not produce excessive enrichment of the fuelair mixture since the pump is not in effect positively actuated, but rather is yieldably urged by spring 136 to discharge fuel when the throttle valve is opened. It is seen that by the present construction a sustained increased flow of fuel is obtained by the enlargement of the effective size of the metering orifice when the throttle valve is opened, together with a temporary further increase for enrichment of the fuel-air mixture while the engine is attaining the desired speed.

Although only one embodiment of the invention has been illustrated and described, various changes in the arrangement of elements may be made to suit requirements.

We claim:

1. A mechanically actuated accelerating pump for a fuel system comprising a single pump chamber for supplying an increased fiow of fuel to said system; a movable wall forming one side of said chamber and being adapted to be positively moved inwardly in respect to said chamber; a cylindrical element secured to said wall; a second movable wall forming another side of said chamber; a cylindrical element secured to said second wall adapted to slidably receive said first mentioned element; a spring for urging said' elements apart; and a resilient means for urging said second wall inwardly in respect to said chamber.

2. A mechanically actuated accelerating pump for a fuel system having a main fuel conduit comprising a single pump chamber for supplying an increased flow of fuel to said system; a movable wall forming one side of said chamber and being adapted to be positively moved inwardly in respect to said chamber; a cylindrical element secured to said wall; a second movable wall forming another side of said chamber; a cylindrical element secured to said second Wall adapted to slidably receive said first mentioned element; a spring for urging said elements apart; a resilient means for urging said second wall inwardly; and a conduit connecting said chamber with said main fuel conduit.

3. A mechanically actuated accelerating pump for a fuel system having a main fuel conduit comprising a single pump chamber for supplying an increased flow of fuel to said system; a diaphragm forming one side of said chamber and being adapted to be positively moved inwardly in respect to said chamber; a cylindrical element secured to said diaphragm; a second diaphragm forming another wall of said chamber; a cylindrical element secured to said second diaphragm adapted to slidably receive said first mentioned element; a spring for urging said elements apart; a spring for urging said second wall inwardly; and a conduit having a restriction therein for connecting said chamber with said main fuel conduit.

4. In a carburetor having a fuel supply means and an induction passage with a throttle valve therein: a single pump chamber for supplying an increased flow of fuel to said system; a diaphragm forming a wall of said chamber; a means operated by the valve for moving said wall inwardly in respect to said chamber; a cylindrical element secured to said diaphragm; a second diaphragm forming another wall of said chamber; a cylindrical element secured to said second diaphragm adapted to slidably receive said first mentioned element; a spring for urging said elements apart; a spring for urging said second wall inwardly; and passageways connecting said chamber 6 with said fuel supply means and with said induction passage.

5. In a carburetor having a fuel supply means and an induction passage with a throttle valve therein: a single pump chamber for supplying an increased flow of fuel to said system; a diaphragm forming a wall of said chamber; a means operated by the valve for positively moving said wall inwardly in respect to said chamber; a cylindrical element secured to said diaphragm; a second diaphragm forming another wall of said chamber; a cylindrical element secured to said second diaphragm adapted to slidably receive said first mentioned element; a spring for urging said elements apart; a spring for urging said second wall inwardly; and a conduit connecting said chamber with said fuel supply means and another conduit connecting said chamber with said induction passage.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,536 Prentiss Apr. 10, 1934 2,092,685 Viel Sept. 7, 1937 2,141,594 Cole Dec. 27, 1938 2,186,480 Ensign Jan. 9, 1940 2,212,946 Mock et al. Aug. 27, 1940 2,277,930 Mock et al. Mar. 31, 1942 2,400,035 Weber May 7, 1946

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