US2361334A - Mixture control - Google Patents

Description

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S. M. UDALE MIXTURE CONTROL Filed Nov. 17, 1941 Oct. 24, 1944.

INVENT OR.

Patented Oct. 24, 1944 UNITEDv STATES APATENT OFFICE MIXTURE CONTROL stanley M. Udala, Detroit, Mich., assigner to George M. Holley and Earl Holley Application November 1.7, 1941, Serial No. 419,373 3 Claims. A(Cl. 261-39) This application is a continuation in part of my co-pending application Serial No. 224,959, filed August 15, 1938, for Mixture control which issued December 2, 1941, as Patent No. 2,264,347.

The objectof this invention is to improve the operation of an airplane carburetor so that the mixture ratio is maintained at the correct figure in spite of changes in:

(a) Temperature of the air in the air entrance to the carburetor;

(b) Pressure of the air in the air entrance leading to the carburetor, commonly known as altitude;

(c) Changes in the air flow at any given throttle position, otherwise known as changes in load.

.The specific form of carburetor to which this invention relates is one in which two streamlined throttles form variable Venturi passages, one on ,each side of a streamlined partition with which they both engage. In the throat of the variable venturi thus formed fuel is discharged from a' sage. Thedischarge of this fuel 'is controlled byl a needle valve moved by a cam. The two throttles charger pressure is used in the air entrance, then to the pressure in the air entrance.

The air flowing past the needle valve |9 passes -into a passage 23 into which also discharges the air flowing past the needle valve I4. AThere' 'is a second chamber 24 in which is located a third needle 25 which controls a third opening 28 which also admits air to the passage 23 from the air pressure equalizing ring Ii. The passage 23 thus communicates with the chamber 30 which communicates with the restricted passage 3| which is in communication with a fuel needle chamber 32'which surroundsJ the movable needle 33, which and the cam operating the needle valve are all geared together so that as the throttles open, the needle opens the fuel passage.

Description In the air entrance I of the carburetor is located an air pressure equalizing ring Il. Immediately below is located a thermostatic needle I2. This needle contains a core |3 which has a relatively high co-efiicient of expansion (a plastic material similar to hard rubber is suitable). By this means, the needle point I4 moves to the left when the temperature increases and to the right when` the temperature decreases. 'I'his needle controls the flow of air through the small passage which is connected through a passage I6 to a chamber I1 which is in free communication with the air pressure equalizing ring The upper wall of the chamber I'I consists of a flexible diaphragm I8 which carries a needle valve I9. This diaphragm 'forms the lower wall of the chamber 20, the upper wall of which is formed by a stamped w-all 2|. A spring 22 is provided between the cover 2|,and the flexible diaphragm I8. The chamber is evacuated so that the diaphragm I8 and spring 22 c`arry the fuel atmospheric pressure. The movement of the needle I9 thus responds to changes) in the atmospherlc pressure in the air entrance or, if supercontrols the fuel flow through a fuel orifice 34 which is located at the right handend ofthe fuel passage 35, which passage communicates with the upper portion of the fuel diaphragm chamber 36.

This diaphragm-chamber 36 is bounded on the left by a flexible diaphragm 31 which forms the right hand wall of the air chamber 30. The dlaphragm 38 forms the left hand wall of the chamber ||I| which is in communication with the chamber 30 through a passage 94. The diaphragm chamber 35 and its two diaphragms 31 and 38 operate the two fuel needle shut-off valves 39, 39 through the usual fuel needle valvemechanism. 'I'hese fuel needle valves control the flow of fuel from a high pressure fuel passage 4|.

The needle valve 25 is carried by the diaphragm 5| which forms the left hand wall of'the ch'alnber 9| and the right hand wall of the. chamber 90. Springs 64 and |00 in chambers 90 and 9| oppose eaeh other so that the needle 25 moves in response to pressure differences between the chambers and 9|. An adjustment 65 regulates the pressure exerted by the spring 54. 53 is the left hand wall of the chamber 90 and the right hand wallof the chamber 9| is 'numbered 52. The chamber 9| communicates through the -pipe 59 with the back of. the throttle 49 which moves a lever 8| which engages with a needle4 valve 33, which controls the metering orifice 34. The spring 84 keeps the lever 8|,` or rather the roller 82 carried by the lever 8|, in contact with the cam 53. The lever 8| is mounted on the fulcrum 03. By this'means; when the cam is rotated, the-throttles 4I and 40 are opened and the needle is opened.

Although the low speed operation is no part of -this invention, it isl shown on the drawing in order to complete the description. The slot 1l 4 in the needle 33 communicates with the cham ber 32 and opening 19 when the throttle isclosed.

2'V I I 2,881,384

responsiveness of the diaphragm independently of throttle position.

Thus airis admitted to the fuel outlets 41 and thus the suction on.the orice 34' is reduced by the venting that occurs when air flows through and along thepassage 10 to the fuel outlet 41. In addition to theventing that occurs during idle when the needle 33 moves to the left and permits air to ilow through 10 toA the outlet 41, there is at all times a flow of air through the vent 80 into the outlet 41. The opening 40 indicates that there is a series of holes 41 and there.

fore the passage 40 extends below and above the plane of the drawing, extending across the whole width of the carburetor.

zand connected to said nozzle, a fuel supply valve and an air chamber associated with said wall, said wall, valve and air chamber being adapted to control the head on the fuel nozzle, a restricted passage connecting the air-chamber with the throat of the variable venturi, a second passage The suction back of the throttles 48 and 40 isv the suction existing in the throat of the variable venturi because there is a free communication through the openings 54 and 54 between the The result is that the pipe 59 imposes the Venturi suction in the chamber 9|. a

In the variable Venturi carburetor, at part throttle position, excessive suction occurs in the throat of the venturi which causes a'n excessive l flow of fuel for thel reason that air expands freely.

In order to cancel this effect the needle valve responds to any excessive pressure differential between the pressure in the throat of the venturi vand the pressure existing in the air entrance.

'I'he diaphragm 6| moves to the right under the influence of this pressure diierential compressing the spring |00 which normally balances the spring 64, the balance beingadjusted by the adjustable spring seat 65 which is threaded into the cover 63, the other cover 62 communicating through the passage 59 withf the back of the venturi 49.

By this means, when the suction in the throat of the venturi becomes excessive, the needle 25 closes and the ow of atmospheric air past. 25 .is restrlctedand to that extent the mixture becomes leaner than it otherwise would become.l 0n the other hand, if the engine slows down under a heavy load, that is to say, if the propeller is adjusted to have a large pitch, which is the position of a propeller to give maximum economy, then the suction in the venturi is not great, and

the needle 25 moves to the left, atmospheric pressure is admitted to the passage 23 and a slight enrichment of the mixture results. This is commonly known as the load control.

In order to adjust for load control independently of altitude and of temperature control, the

opposed springs E4 and |00 are provided and the adjustment screw permits the adjustment of the 'Venturi throat and the back of the throttles.

, connecting the air chamber with the air entrance,

two' restricted entrances to said' passage, the rst one controlled by a pressure responsivev valve adapted to respond to the pressure of the fair in the airentrance, the-second entrance controlled by a pressure responsive valve. a movable wall connected to said valve, means to apply to one side of said wall the pressure in the air entrance and to the other the llow pressure of the air in the throat of said variable venturi said valve' being adapted to close with a 'decrease of pressure in said throat.

2. A device as set forth in claim 1 in which y there is. also a third restricted entrance to said passage, a temperature responsive valve, means for moving said valve towards itsclosing position in response to an increase in temperature,

,said means being so located as to respond to the average temperature of the lair in the air4 entrance independently of the temperature of the walls of the air entrance.

3. In an airplane carburetor an air entrance, V a throttle valve therein adapted to form a vari-I able Venturi passage in the air entrance, a fuel nozzlev discharging into the throat of said venturi, a fuel supply chamber having a flexible .wall and connected to saldi-nozzle, a fuel supply valve and an air chamber associated with said wall, said wall, valve and air chamber being adapted to control the head on the fuel nozzle, a restricted passage connecting the air chamber with the throat of the variable venturi, asecond passage connecting the air chamber with the air entrance, two restricted entrances to said passage, the first one controlled by a pressure responsive valve adapted to respond to the pressure of the air in the air entrance, the second entrance controlled by a pressure responsive valve, a moveable wall connected to said valve, opposed springs supporting said wall, means for adjusting one of said springs independently of throttle position, means to apply to one side of said wall the'pressure in the air entrance and to the fother the low prespressure in the throat of said venturi falls.

STANLEY M. UDALE.

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