US2399077A - Power limiting carburetor - Google Patents

Description

April 2 3, 1946. s UDALE I r 2,399,077

POWER LIMITING CARBURETOR Fil ed May 10, 1940 I 39 INVENTOR.

Patented Apr. 23, 1946 UNITED STATE S v PATENT v OFFICE POWER LIMITING CARBURETOR Stanley M. Udale, Detroit, Mich, asslgnor to George M. Holley and Earl Holley Application May 10, 1940, Serial No. 334,328 Claims. (Cl. 261-50) The object of this invention is to open the fuel nozzle manually and to open the throttle automatically and by this means, assuming a constant pressure for the fuel, a definite quantity of fuel will be admitted when the fuel needle is wide open.

This means that only a definite amount of power can be developed, assuming that the air flow is wide as possible, then asthe plane continues to ascend it will be necessary to automatically close the fuel to maintain the mixture constant when the throttle is wide open at high altitudes. Hence the automatic mixture control must first open the throttle and dilute the mixture with air, and then close the fuel valve with the throttle wide open, so that th mixture ratio may be maintained at the cruising lean ratio at high altitudes.

Figure 1 shows diagrammatically the applicant's invention based in part on the disclosure in patent to Lundgaard 1,333,986.

Figure 2 shows a sectional plan'view taken on plane 2-2 of Figure 1 looking down.

In the drawing, i0 is the air entrance, ii is a venturi in the air entrance, l2 are the orifices communicating with the annular chamber i3 which surrounds the venturi, it is the chamber containing the aneroid barometric elements it, which control the lever 58 pivoted at a fulcrum l'l eccentrically mounted in a bearing 18 controlled by a lever i9; This eccentric support which is provided for the pivots ll permits an adjustment to be made in fiight. The barometric elements l5 contain an inherent spring in the material of which they are made, or a spring is added, or they contain air. Th lever 16 is connected by the link 15 with the. link 16 which has a fulcrum at 20 and carries a pin 25.

The annular chamber l3 communicates with the chamber 2| which is closed on its right hand side by the diaphragm 22. This diaphragm is connected by the link 23 with the lever 24 pivoted on the pin 25 carried by the lever 16. The lower end of the lever 24 is pivotally connected with'the link 26 connected to a diaphragm 21 which forms the right hand wall of a chamber 28, which chamber communicates through the pipe 29 with the throat of the fuel venturi 30 located downstream from a fuel entrance 34 connected with a source of fuel under constant pressure.

A similar fuel chamber 3! is formed with a similar diaphragm 11 which is connected bya similar link 33 with the-lever-24 at the same pivot to which link 26 is attached. The pressure in the chamber 3| corresponds to the pressure in the fuel entrance 34. The diaphragms I1 and 210i chambers 8| and 28 are of equal size.

The upper end of the lever 24 is connected by means of the link 35 with thevalve 36 which controls the servo mechanism 31. This servo mechanism comprises a piston 18 and operates a roller- 38 which engages with the cam surface 39 of the bell crank lever 5i mounted on the throttle shaft so which shaft moves the throttle 4!, shown in broken lines. The source of working fluid for the servo motor is not shown as this servo motor is not applicant's invention and serve motors are now in universal use on airplanes and their function and their details of construction are well known. I

An idle stop I3 prevents the complete closure of the throttle 4i. I

A fuel orifice 42 is controlled by a movable needle valve 43 which engages with the camsurface 44 of the bell crank lever 46 and is held in contact therewith by means of the compression spring 45. Another bell crank lever 4'! is mounted on a pin 48 on a bracket 49. A rod 50 is connected with any suitable manual control for opening and closing the fuel valve 43.- When the rod 50 is pushed up to permit the fuelv valve to open, it pushes the rod 52 against the bell crank lever 5i and compresses the spring 53 and also opens the throttle ti slightly, but in such a way that the mixture remains on the rich side but not so rich as to stall the engine. at th same time th lever 41 carries the adjustable stop 54 to the right, permitting the cam surface 44 also to move to the right under the influence of the compression spring. The rod 52 moves relatively less than the needle 53 so that the mixture is rich. As the fuel flows through the venturi 30 and the air fiows through the venturi l I, pressure differentials are set up in the throats of the two venturis. The depression in the fuel venturi 3D is established in the chamber 28 and the depression in the air venlever 24 is moved clockwise slightly by the lack of balance due to the relatively excessive flow of fuel through the venturi 30 as compared with the flow of air through the venturi II. The effect of the depression due to velocity in these two venturis acting on the three diaphragms 22, 21 and l1 disturbs the equilibrium ofthe lever 24 and moves the valve 38 to the right, causing the servo piston i8 also to move to the right, carrying, the roller 38 against the cam surface 39 of the lever, so as to open the throttle H to lean out the mixture' until the desired cruising lean mixture is obtained.

Obviously as the plane ascends into the air, an altitude is reached at which the throttle 4| becomes wide open and the fuel flowing through the venturi 30 continues to be at its definite maximum flow, so that thereafter the mixture would become progressively richer. To prevent this, the roller 38 then engages with the cam surface 55 of the lever 56 pivoted at 51' on the air entrance. When the lever 55 is thu rotated anti-clockwise it engages with the roller on the end of the rod 58, by which means the rod 58 is forced down and engages with the bell crank lever 46 and the cam surface 44 presses against the head of the needle .43 and thus reduces the size of the orifice 42 compressing the spring. 45 and restricting the fuel flow until equilibrium between the two venturis is once more established.

The air entrance 59 leads to a passage 60 which discharges through an opening 6| together with the fuel issuing from the orifice 42. The fuel thus discharges under substantially atmospheric pressure at all throttle positions, as the air entrance 59 is connected to the air entrance ill of the carburetor by a pipe 14. The fuel issuing through 42 thus discharges under atmospheric pressure and thus the maximum flow is constant regardless of the position of the throttle 4|. For this reason the maximum amount of fuel flowing through the venturi 30 is a constant amount determined by a stop 52 which limits the clockwise movement of the bell crank lever 46 and therefore determines the maximum opening of the The movement of the pin 25 in response to variations in altitude is necessary to correct for a the change in air density. So long as air density remains at sea level density, the flow through the venturi l3 and the venturi 30 increases and decreases at the same rate for variations in fuel flow and air flow, thereby maintaining a constant mixture ratio. If we assume the air denorifice 42. This stop 52 therefore acts as an adjustable power control.

To adjust for idle a stop 13; limits the closing of the throttle 4|. The stop 13' in conjunction with. the adjustable stop 54 on the lever 4l-determines the minimum ripening of the orifice 42 and the minimum opening of the throttle 4|.

It is desirable to increase the richness of the mixture at wide open throttle at maximum speed,

especially when running in conjunction with air cooled engines. To get this extra fuel the invention of M. E. Chandler, Patent 2,125,886, is incorporated with this invention as follows:

The passage 64 leads from the.chamber 3lto the chamber 55. A passage 55 leads from the chamber 28 to a chamber 61. A diaphragm 68 is located between the two chambers 65' and 61, and is connected to a needle 69 and is supported by a spring 10 located in the cover II which encloses the chamber 61. The fuel discharging past the needle 59 is delivered to the air flowing up through the passage 50. 4 Hence this fuel discharges into a chamber connected with the air entrance 59, connected with the air entrance I. The fuel therefore discharges against the atmospheric pressure. Assuming that the pressure in the fuel entrance 34 is constant, and this will be true within a range of plus or minus two per cent, any pressure differential between the venturi 30 and the fuel entrance 34 will give a definite increment to the mixture ratio determined by the taper of the needle 69 and the stillness of the spring 10.

A spring 53 is available for maintaining the cam surface 39 in contact with the roller 38 and a similar spring supports the lever 55 which carries the cam surface 55 with which the roller 38 ultimately engages.

sity becomes one-half that of the atmosphere at sea level, then the effect of any given velocity is one-half, that is to say, the suction in the chamber 2! is one-half what it would be at sea level. The suction in the chamber 28 would also be one-half the suction at Sea level. The density of the fuel will not change and therefore the velocity through the venturi 30 would be 1 5 of the velocity at sea level for equilibrium. Therefore, the weight of fuel would be and the weight of air would only be 50%, so that the mixture ratio would be 40% richer, and to correct this the pin 25 moves up at altitude so that the leverage of the fuel flow increases and the leverage due to air flow decreases, and therefore a greater volume of low density air flow is necessary to balance a given fuel flow when the air ventu'ri, and means responsive to the depression in the fuel venturi, said means being adapted to act in opposition to eachother for the control of said servomotor valve, operating means con-' nected to' the servomotor adapted to open the throttle and means whereby after the air throt' tle is wide open, the continued motion of the servomotor is adapted to close the fuel valve, manual means for permitting the fuel valve to open, a one-way connection from the manual control means to the throttle valve wherebyl when the fuel valve is permitted to open the throttle valve is opened a limited amount to provide the necessary rich mixture for acceleration.

2. In a carburetor, a source of fuel supply under pressure, a fuel passage leading therefrom, a restriction therein creating a pressure difference proportional to the square of the velocity of the fuel, a fuel outlet, fuel throttling means therein, an air passage, a restriction therein creating a pressure difference proportional to the square of the velocity of the air, a throttle in the air passage, mechanism responsive to the simultaneous effect of the relative pressure difference created by the fuel fiow as compared with the similar pressure difference created by the air flow, the effect of excessive airflow tending to automatically close the throttle and the effect of excessive fuel fiow being adapted to automatically open the throttle in the air passage after the fuel restricting means is opened, whereby the air flow is'increased and the two devices responsive to the said pressure difference are balanced, and additional means responsive to the fuel flow for moving the fuel restricting means to a more restricted posistriction therein creating a' pressure difference proportional to the square of the velocity of the fuel flow being adapted to automatically open the throttle in the air passage after the fuel restricting means is opened, whereby the air flow is increased and the two devices responsive to the said pressure differences are balanced, and means responsive to the air density for changing the mechanical advantage of the air flow responsive elements over the fuel flow responsive elements whereby the pressure difference due to the fuel flow is more effective at high altitude so as to oppose a greater pressure difference due toair flow for a given fuel flow and thereby maintain the mixture ratio constant at altitude.

4. A carburetor having an air entrance, a venturi therein, a throttle valve, a mixture outlet, 9, fuel nozzle having a discharge orifice therein, a valve controlling said fuel orifice, a fuel passage leading to said orifice, a venturi therein, a servomotor, a valve control therefor, means responsive to the difference between the respective depresa. fuel outlet passage sions in the fuel venturi and in the air venturi for controlling the valve of said servomotor, said servomotor being adapted to first open the throttle valve, said servomotor being adapted after the throttle valve is fully open to move the fuel valve to a fuel flow restricting position, manual control means for limiting the opening movement of the fuel valve, and a stop for limiting tho-opening movement of the fuel valve,

5. In a fuel-air mixture ratio control device, a fuel entrance, a restricted fuel passage therein, leading therefrom, a fuel throttle valve therein, a fuel throttle lever therefor, an air entrance, an air venturi therein, an

air outlet, air throttling means located in said outlet, means responsive to the pressure difference created by said restriction in said fuel passage, additional means responsive to a similar pressure difierence created by said air venturi, a mechanical connection between the two pressure responsive means adapted to bring into opposition with each other the two resultant forces produced by the two pairs of pressures, means responsive to the unbalance between said two opposing forces throttle in response to adapted to open said air an increase in fuel flow, means responsive to the opening of said air throttle to its wide-open position to close said fuel throttle valve independently of said fuel throttle lever.

ST M. UDiiLE.

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