United States Patent Shiobara et al. [4 1 June 13, 1972 [54] CARBURETOR OF VARIABLE-AREA 3,342,463 9/1967 Date et ...26l/44 R VENTURI TYPE 3,444,848 5/1969 Lawrence..... ...26l/44 R 3,503,594 3/1970 Goto ..26l/63 [72] Inventors: Masqii Shiobara, Chigasakr City; Genii Watanabe, Tokyo, both of Japan FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Nissan Motor Company, Limited, 119,187 9/1918 Great Britain ..26l/44 R Kanagawa-ku, Yokohama City, Japan Primary Etaminer-Tim R. Miles [22] Flled: 1970 Attorney-McCarthy, Depaoli & OBrien 21 Appl. No.: 96,141

[57] ABSTRACT 52 U.S. Cl. ..26l/44 R, 261/63 A carburetor of variable-area venturi yp for an internal 511 Int. Cl ..F02m 3/08 combusiio" engineaddPted reduce the amount 01 [58] Field oiSearch ..261/44R 63 50A hydmcarbms exhaus gases emmed engine during idle operation of the automotive. The carburetor in- [56] References Ched eludes additional passages by-passing the carburetor throttle valve and means to adjust an air-fuel ratio and amount of a UNITED STATES PATENTS fuel mixture to be supplied to the engine during the idle operation. 3,210,055 10/1965 Kingsley ..261/44 R 3,243,167 3/1966 Winkler ..26l/44 R 2 Claims, 2 Drawing Figures l l I l 1 m K 1 l i I l i I F0 1 r l \1 :1 ,6 m 4 L PATENTEDJUH 13 I972 SHEET 1 OF 2 INVENTORS MASAJI S'H/OBARA BY GEWJI WATA/VABE' git ,WMBML PATENTEUJUII 13 m2 3, 569 424 SHEET 20F 2 CONTACT POINT OF A SUCTION PISTON VOLUME OF SUCTION AIR INVENTOR s MASAJI SHIOBARA BY G ENJI WA TANA BE QM zww A ORNEYS CARBURETOR OF VARIABLE-AREA VENTURI TYPE This invention relates to a carburetor of the variable-area venturi type for an automotive internal combustion engine, and more particularly to an improvement in a carburetor of such type and adapted to supply the engine with a fuel mixture of a selected air-fuel ratio by changing the effective sectional area at the venturi in accordance with the variation in the vacuum existing downstream of the venturi of the carburetor.

In a conventional carburetor of the variable-area venturi type, a throttle valve is substantially closed during idle operation or under a light engine-load condition so that there exists little or no suction around the venturi. This causes the effective sectional area at the venturi to decrease, thereby increasing the velocity of air flowing therethrough. Under this condition, an excess liquid fuel is drawn fromthe fuel jet, and the fuel mixture to be supplied to the engine becomes too rich, with the result that the engine discharges a large quantity of unburned gases containing noxious hydrocarbons into the atmosphere.

The air-fuel ratio of the air-fuel mixture for the idling operation is controlled, in the conventional carburetor of the variable-area venturi type, by changing the position of the fuel jet relative to the jet needle. Such position of the nozzle critically dictates the air-fuel ratios during engine operating conditions other than idling so that it is extremely difficult to supply the engine with a fuel mixture of an optimum air-fuel ratio during the idle operation without scarificing the air-fuel ratios optimum for other operating conditions.

The present invention therefore contemplates to eliminate this and other drawbacks that are inherent in the carburetor of the variable-area venturi type and it is an object of this invention to provide an improved carburetor adapted to control the air-fuel ratio of the fuel mixture to be supplied to the engine during the idle operation in an economical and simplified manner thereby to preclude the emission of the unburned hydrocarbons from the engine without substantial sacrifice to the air-fuel ratios during other operating conditions of the engine.

In the accompanying drawings:

FIG. 1 is a schematic sectional view of a carburetor of the variable-area venturi type incorporating the improvements according to the invention; and

FIG. 2 is a graph illustrating a typical example of the relationship between the volume of suction air and the air-fuel ratio of the air-fuel mixture, which is attained in the embodiment shown in FIG. 1.

Referring now to FIG. 1, a carburetor of the variable-area venturi type incorporating the improvements according to the invention is generally indicated by reference numeral 10. As shown, the carburetor includes as customary a main air passage 12 leading from the open air, a main upstream mixture passage 14 communicating with the main air passage 12, a main downstream mixture passage 16 leading to an intake manifold (not shown) of the engine, a throttle valve 18 adapted to control the flow of an air-fuel mixture to be supplied to the engine via the mixture passages 14 and 16, and a venturi 20 including a flow regulating means 22 and a constriction or bridge 24. The carburetor 10 also includes a fuel jet 26 for supplying a liquid fuel into the mixture passage 14. A

liquid fuel supply passage 28 terminates in the fuel jet 26 at the venturi 20 of the carburetor 10. The fuel supply passage 28 communicates through a passage 30 with a float chamber (not shown). The flow regulating means 22 comprises a casing 32 and a movable suction piston 34 of known construction. A

jet needle 36 extends from the bottom wall of the suction piston 34 and is inserted through the fuel jet 26 into the fuel supply passage 28. The jet needle 36 is tapered toward its tip for continuously changing the amount of fuel to be admitted into the venturi 20 as the suction piston 34 and accordingly the jet needle 36 move upwardly and downwardly in response to the fluctuations in the intake manifold to thereby vary the effective venturi area into which the liquid fuel is drawn from the fuel jet 26.

During the idle operation, as shown in FIG. 1, the throttle valve 18 is substantially kept closed so that the atmospheric pressure obtains upstream of the throttle valve 18, causing the suction piston 34 to approach the constriction or bridge 24 to limit the flow of air through the venturi 20. In this instance, the velocity of air flowing through the effective sectional area of the venturi 20 increases with the result that the excess liquid fuel is caused to be drawn from the fuel supply passage 28 into the main upstream mixture passage 14. Thus, the fuel mixture is enriched and the amount of unburned or partially burned fuel mixture content of the engine exhaust emission is increased during the idle operation due to the incomplete combustion.

In order to supply the engine with the fuel mixture of an optimum air-fuel ratio during the idle operation, this invention proposes to provide on the carburetor an auxiliary air passage 38 which has its inlet port 40 open to the main air passage 12, an auxiliary primary mixture passage 42 having its inlet port 44 open to the main upstream mixture passage 14 and communicating with the auxiliary air passage 38 at a junction 46 as shown, and an auxiliary secondary mixture passage 48 leading from the junction 46 and having its outlet port 50 open to the main downstream mixture passage 16 or, where desired, to the intake manifold of the engine. The passages 38, 42 and 48 thus meet each other at the junction 46 where the air drawn from the main air passage 12 through the auxiliary air passage 38 is mixed with the fuel mixture delivered from the main upstream mixture passage 14 and the resultant air-fuel mixture is passed over to the main downstream mixture passage 16 through the auxiliary secondary mixture passage 48.

For regulating the flow of air through the passage 38 and the flow of fuel mixture through the passage 48, a flow control unit, generally represented by numeral 52, is interposed between the passages 38 and 48. v

The flow control unit 52 comprises a casing 54 and an air flow adjusting means 56 to control the flow of the air passing through the passage 38, and a fuel mixture flow adjusting means 58 to control the flow of the fuel mixture passing through the passage 48. These adjusting means 56 and 58 are herein shown as adjustable screws by way of example.

The flow control unit 52 is thus adapted to control both the air-fuel ratio and the amount of the fuel mixture to be supplied to the engine during the idle operation. The air flow adjusting screw 56 controls the amount of air supplied to the junction 46 where the air delivered from the main air passage 12 is mixed with the fuel mixture delivered from the main upstream mixture passage 14 into a relatively lean fuel mixture. The fuel mixture produced at the junction 46 is metered by the screw 58 and admitted into the intake manifold of the engine through the port 50 and the main downstream mixture passage 16.

When, in operation, the throttle valve 18 is substantially closed during the idle operation or under a light engine-load condition, a high vacuum develops downstream of the throttle valve 18 so as to cause a pressure difference across the throttle valve 18. This causes the air in the main air passage 12 to pass through the port 40 and the passage 38 to the junction 46. Since, on the other hand, an atmospheric pressure obtains upstream of the throttle valve 18, the suction piston 34 approaches the constriction 24, decreasing the effective sec tional area at the venturi 20. The air is passed through the venturi 20 into the mixture passage 14, so that the liquid fuel is drawn from the fuel supply passage 28 into the mixture passage 14 and mixed with the air therein.

It is important in this instance that the throttle valve 18 be completely or substantially fully closed so as to cause the fuel mixture to pass completely through the passage 48 in an optimum volume and at an optimum mixture ratio into the intake manifold of the engine during the idle operation for thereby eliminating the emission of the noxious unburned hydrocarbons.

During the idle operation, as previously mentioned, the flow rate of the fuel mixture through the venturi 20 is so low that,

when the flow rate of the air'through the passage 38 is increased by turning the screw 56, the flow of air passing through the venturi 20 further decreases and accordingly the suction piston 34 further approaches the constriction 24. At this instant, an excess liquid fuel is drawn from the fuel supply passage 28 into the main upstream mixture passage 14, whereby the fuel mixture is excessively enriched as shown by the curve A in FIG. 2.

To avoid such a difficulty, a stop 60 may be mounted on the constriction 24. The stop 60 is adapted to limit the movement of the suction piston 34 whereby the air is permitted to pass through the venturi 20 at a limited, constant rate once the suction piston 34 has abutted against the stop 60 for thereby maintaining the air-fuel ratio at a constant level as shown by broken line B in FIG. 2. The air-fuel ratio of the air-fuel mixture is thus adjusted by turning the screw 56 after the suction piston 34 has abutted against the constriction 24 so as to eventually eliminate the emission of the unburned hydrocarbons.

When the throttle valve 18 is moved toward open position during a high speed operation or under a heavy engine-load condition, the subatmospheric pressure prevailing downstream of the venturi 20 causes the suction piston 34 to move away from the constriction 24, thereby increasing the flow of air and fuel through the venturi 20. Thus, the engine is supplied with the fuel mixture of an optimum volume and an optimum mixture ratio during the high speed operation. Since, in this instance, the pressure difference between the main air passage 12 or the main upstream mixture passage 14 and the main downstream mixture passage 16 decreases as the open area of the throttle valve 18 increases, the amount of fuel mixture passing through the passage 48 decreases and accordingly exerts no significant influence on the performance efficiency of the engine during the high speed operation.

This will be accounted for by the fact that the hydrocarbon content which is about 7 percent where the conventional carburetor is used can be reduced to about 0.2 percent during the idle operation where the carburetor incorporating the improvement according to the present invention is used, and that the hydrocarbon content is reduced from 0.5 to 0.2 percent when the vehicle is driven at the speed of 60 km/h.

It will be appreciated from the foregoing that the air-fuel ratio is adjusted in an economical and simplified manner by output of the engine when the vehicle is driven at high speeds or under heavy engine-load condition.

What is claimed is:

1. In a carburetor for an automotive internal combustion engine having a main air passage, a throttle valve, a venturi intervening between said main air passage and said throttle valve and including a constriction and a flow regulating means to continuously reduce the effective sectional area at the venturi as said throttle valve closes, a main upstream mixture passage intervening between said venturi and said throttle valve, a main downstream mixture passage positioned downstream of said throttle valve and leading to an intake manifold of said engine, and a fuel jet opening into said venturi and communicating with a fuel supply passage, the improvement comprising an auxiliary air passage leading from said main air passage, an auxiliary primary mixture passage leading from said upstream mixture passage, said auxiliary passages meeting each other at a junction whereby air drawn from said main air passage through said auxiliary air passage is mixed with a fuel mixture drawn from said upstream mixture passage through said auxiliary primary mixture passage, an auxiliary secondary mixture passage leading from said junction to said intake manifold through said main downstream mixture passage for supplying said fuel mixture to the engine, and a flow control means interposed between said auxiliary air passage and said auxiliary secondary mixture passage and including an air flow adjusting means provided in said auxiliary air passage to control the rate of air passing through said auxiliary airpassage for determining an air fuel ratio of said fuel mixture and a fuel mixture adjusting means provided in said auxiliary secondary mixture passage for controlling the rate of said fuel mixture passing therethrough,

2. The improvement according to claim 1, wherein said constriction has mounted thereon a stop to limit movement of said flow regulating means toward said constriction to permit air to pass through said venturi at a limited, constant rate for thereby preventing the supply of an excess liquid fuel from said jet during the idle operation.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 669 424 Dated June 13 1972 Inventor(s) Shiobara et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet the following should be added:

[30] Foreign Application Priority Data December 9, 1969 Japan.......................44/985l7 Signed and Sealed this Nineteenth Day of October 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Palenls and Trademark