GB2111599A

GB2111599A - Compound carburettor

Info

Publication number: GB2111599A
Application number: GB08134350A
Authority: GB
Inventors: Hiroshi Yokoyama; Tokuzi Ishida; Kunio Kikuchi; Kazuaki Zama
Original assignee: Mikuni Corp; Suzuki Motor Corp
Current assignee: Mikuni Corp; Suzuki Motor Corp
Priority date: 1981-11-13
Filing date: 1981-11-13
Publication date: 1983-07-06
Also published as: GB2111599B

Abstract

A compound carburettor for internal combustion engines comprising a primary bore provided with a stationary venturi portion, a secondary bore provided with a piston valve type variable venturi portion and a link mechanism which can forcibly open and close a secondary throttle valve together with a primary throttle valve so as to be able to obtain a smooth transit characteristic and power characteristic over the entire range from the low load to the high load of the engine. The time of beginning to open the secondary throttle valve with the opening of the primary throttle valve can be freely selected. The cross-sectional area ratio of the secondary bore to the primary bore is selected to be not less than 70:30 and the primary bore is so arranged that its center line may occupy a position out of a plane including the center line of the secondary bore and the center line of the piston valve. The piston valve is so arranged as to intersect at right angles with or obliquely downward with the center line of the secondary bore. The downstream side of the primary throttle valve of the primary bore is branched and is connected to the respective cylinders of an engine to be used, and further the downstream side of the venturi of the secondary bore is also branched and is connected to the respective cylinders. Near a inlet valve of the respective cylinders within each branch path of the secondary bore is respectively provided the secondary throttle valve secured to a single secondary throttle shaft. <IMAGE>

Description

SPECIFICATION Compound carburetor a) Field of the Invention: This invention relates to carburetors for internal combustion engines and more particularly to improvements in a compound carburetor.

b) Description of the Prior Art: Generally, in a conventional compound carburetor, for the purpose of its use, the secondary bore diameter is so selected as to be about 2 to 4 mm larger than the primary bore diameter and the venturi is of a stationary type in both primary and secondary bores. Therefore, during the operation, in the course of the transit from the primary side to the secondary side, simultaneously with the opening of the secondary throttle valve, the fuel jetted into the primary bore will decrease and, in the stage in which the flow velocity of air flowing through the secondary venturi part is low, the fuel jetting will be so little that the air-fuel ratio will become lean and the operation will be difficult.At the time of the transit from the primary side to the secondary side, this phenomenon will be further expanded and a temporary addition of the fuel with an accelerator pump or the like will be no longer satisfactory.

Therefore, generally, by operating the secondary throttle valve through a depression chamber controlled by the combined vacuum of the primary venturi part vacuum and secondary venturi part vacuum, its opening is controlled to prevent the temporary reduction of the flow velocity of air.

However, in such method, the generated power was temporarily controlled as a result and, at the same time, there was a fear of causing a transit trouble called a secondary shock.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compound carburetor wherein, in order to eliminate such defects of the conventional system, the secondary venturi part is made variable so as to be able to well satisfy the power requirement, the primary bore diameter is made smaller than in the past, the cross-sectional area ratio of the secondary bore to the primary bore is made larger and the secondary throttle valve as well as the primary throttle valve is forcibly opened and closed by the operation of the accelerator.

According to a preferred formation of the present invention, the cross-sectional area of the secondary venturi part is varied by a piston valve which can be displaced in proportion to the magnitude of the vacuum produced in the venturi part and the time of beginning to open the secondary throttle valve with the opening of the primary throttle valve can be freely adjusted.

Further, the cross-sectional area ratio of the secondary bore to the primary bore is selected to be not less than 70:30. Therefore, not only a smooth power variation characteristic can be obtained even with the quick opening of the throttle valve from the primary bore but also the fuel is efficiently atomized even in the low load range, a uniformed air-fuel mixture can be fed to the engine and an always stabilized fuel combustion is secured.

This and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of an embodiment of a compound carburetor according to the present invention; Fig. 2 is a vertically sectioned view of an essential part of the carburetor shown in Fig. 1; Fig. 3 is an elevational view of a link mechanism part for operation a primary throttle valve and secondary throttle valve; Fig. 4 is a plan view showing another embodiment of the compound carburetor according to the present invention; Fig. 5 is a partly vertically sectioned view showing still another embodiment of the compound carburetor according to the present invention; and Fig. 6 is a vertically sectioned view showing still further embodiment of the compound carburetor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, with reference to Figs. 1 and 2, the reference numeral 1 indicates a primary bore having a stationary venturi portion 1 a, 2 indicates a primary main nozzle, 3 indicates a primary main well, 4 indicates a primary main jet, 5 indicates a primary slow running fuel system, 6 indicates a primary throttle valve, 7 indicates a secondary bore, 8 indicates a piston valve fitted slidably in the direction intersecting at right angles with the center line of the secondary bore 7 and forming a variable venturi part, 9 indicates a diaphragm secured on the inner peripheral edge to the piston valve 8 and sectioning an atmospheric chamber 10 and a vacuum chamber 11 communicating with the venturi part of the secondary bore 7, 12 indicates a spring biasing the piston valve 8 rightward, 1 3 indicates a jet needle secured to the piston valve 8, 14 indicates a secondary main well, 1 5 indicates a secondary main jet, 16 indicates a float chamber, 1 7 indicates a float, 1 8 indicates a secondary throttle valve and 1 9 indicates a secondary slow running fuel system set as required. In this case, the primary bore diameter is selected to be 14 to 20 mm and the cross-sectional area ratio of the secondary bore 7 to the primary bore 1 is selected to be 80:20.In Fig. 3, the reference numeral 20 indicates an operating lever pivoted to the carburetor body and connected to an accelerator pedal not illustrated through a cable 21, 22 indicates an opening adjusting screw retreatably screwed to the operating lever 20, 23 indicates a spring biasing the operating lever 20 counterclockwise, 24 indicates a stopper for limiting the clockwise rotation of the operating lever 20, 25 indicates an interlocking lever pivoted to the carburetor body coaxially with the operating lever 20, 26 indicates a spring biasing the interlocking lever 25 counterclockwise, 27 indicates a stopper adjustably screwed to the carburetor body and determining the idle opening of the primary throttle valve 6, 28 indicates a primary throttle lever secured to the primary throttle valve 6 and engageable with the stopper 27 at one end, 29 indicates a connecting rod for connecting the parimary throttle lever 28 to the operating lever 20, 30 indicates a stopper adjustably screwed to the carburetor body and determining the fully closed position of the secondary throttle valve 18, .31 indicates a secondary throttle lever secured to the secondary throttle valve 1 8 and engageable with the stopper 30 at one end and 32 indicates a connecting rod for connecting the secondary throttle lever 31 to the interlocking lever 25.

As the carburetor according to the present invention is formed as mentioned above, while the engine is operating, if the accelerator pedal not illustrated is trodden, the operating lever 20 will be rotated clockwise and the primary throttle lever 28 will be first rotated counterclockwise to increase the opening of the primary throttle valve 6. Therefore, the vacuum around the venturi part 1 a will gradually increase and a more proper airfuel mixture will be fed to the engine.Thus, when the tip of the opening adjusting screw 22 engages with the bent part 25a of the interlocking lever 25, thereafter the interlocking lever 25 will be rotated clockwise integrally with the operating lever 20 to gradually open the secondary throttle valve 1 8. In this case, if the opening area of the secondary venturi part is properly selected in advance, with the increase of the opening of the secondary throttle valve 1 8, the opening area of the secondary venturi part will also gradually increase and a proper mixture will be additionally fed to the engine. This additional feed of the proper mixture will be made so smoothly without having any bad influence on the primary bore that the transit from the primary bore to the secondary bore will be made very smoothly as a result.After the necessary increase of the engine power is thus attained, if the accelerator pedal is released, the operating lever 20 and interlocking lever 25 will be returned to the initial positions repectively by the springs 23 and 26, the primary throttle lever 28 and secondary throttle lever 31 will engage respectively with the stoppers 27 and 30 and the primary throttle valve 6 and secondary throttle valve 1 8 will be returned respectively to the illustrated positions. By the way, when the bent part 20a of the operating lever 20 enages with the stopper 24, the primary throttle valve 6 and secondary throttle valve 1 8 will respectively reach the fully opened positions.

As evident from the above explanation, the time of beginning to open the secondary throttle valve 1 8 with the opening of the primary throttle valve 6 can be properly selected by adjusting the adjusting screw 22 and therefore this type of carburetor having a required power characteristic can be easily provided.Further, as the primary bore diameter is smaller than in the conventional type and therefore the cross-sectional area of the primary venturi part 1 a is also comparatively smaller, the flow velocity of air flowing through the primary bore will be higher than in the conventional type, therefore no fuel will flow intermittently or along the inside surface of the bore when it is jetted, the atomized fuel and air will be able to be uniformly mixed, the mixture will be well distributed to the respective cylinders, a stabilized combustion will be obtained by a lean air-fuel ratio, the drivability will be smooth and the fuel consumption will improve. Further, a slow running fuel system cooperating with the secondary throttle valve 1 8 can be provided as illustrated in the secondary bore to further improve the constant performance.By the way, the cross-sectional area ratio of the secondary bore 7 to the primary bore 1 is selected to be 80:20 in the embodiment but is confirmed by experiments to be not less than 70:30 to obtain results desirable in practice. Generally, in the compound carburetor, such a cross-sectional area ratio of the secondary bore to the primary bore cannot be adopted. According to the present invention, however, such large cross-sectional area ratio as, for example, 70:30 can be selected because the secondary venturi is variable, whereby a delay of jet of the fuel at the time of beginning to open the secondary throttle valve does not occur and therefore a good pulverization characteristic and distribution characteristic will be able to be obtained.

In the above explained embodiment, the secondary fuel path is arranged on the central upper side of the primary venturi part 1 a but, if the primary bore 1 is so arranged that its center line may be in a position out of a plane including the center line of the secondary bore 7 and the center line of the piston valve 8 as shown in Fig. 4 the secondary fuel path will be able to be moved to a position not obstructing the primary bore 1 and further the primary nozzle and secondary nozzle will be able to be arranged on the same level higher than the fuel surface of the float chamber.

Further, as shown in Fig. 5, the piston valve 8 can be arranged as directed downward so that its center line may obliquely intersect with the center line of the secondary bore 7. With such arrangement, the operation of the piston valve will be smooth and the fuel will be able to be better jetted.

In Fig. 6 is shown another further embodiment of the present invention. According to this embodiment, the downstream side of the primary throttle valve 6 of the primary bore 1 is branched in response to the number of the cylinders of the engine to be used and is connected to the respective cylinders 33. The downstream side of the venturi of the secondary bore 7 is also branched and is connected to the respective cylinders. Further, the secondary throttle valve 18 is provided near the cylinder 33, that is, a suction valve 34 within each branch path 7a of the secondary bore 7. Each secondary throttle valve 1 8 is secured to a single secondary throttle shaft 1 8a passed through each branch path 7a of the secondary bore 7 in the direction intersecting at right angles with the center line of said branch path 7a. In this case, the secondary slow running fuel system 19 not illustrated is provided near each secondary throttle valve 18. The primary throttle shaft and secondary throttle shaft 1 8a are operatively connected through the same link mechanism as illustrated in Fig. 3.

As the operation of the embodiment shown in Fig. 6 is the same as those of the embodiments shown in Figs. 2 and 3, the explanation is omitted.

Claims

1. A compound carburetor for internal combustion engines comprising a primary bore provided therein with a stationary venturi and a primary throttle valve, and a secondary bore adjacent to said primary bore and provided therein with a piston valve type variable venturi and a secondary throttle valve.

2. A compound carburetor according to claim 1 wherein said carburetor further comprises a link mechanism arranged adjacently to either of said primary bore and secondary bore and formed so as to be abled to forcibly open and close said secondary throttle valve together with the primary throttle valve and to adjust the time of beginning to open the secondary throttle valve with the opening of the primary throttle valve.

3. A compound carburetor according to claim 2 wherein said link mechanism comprises an operating lever rotatably supported adjacently to said primary bore, an opening adjusting screw screwed on said operating lever, an interlocking lever rotatably supported coaxially with said operating lever and engageable with said opening adjusting screw, a primary throttle lever secured to said primary throttle valve, a connecting rod connected at one end to said operating lever and at the other end to said primary throttle lever, a secondary throttle lever secured to said secondary throttle valve and a connecting rod connected at one end to said interlocking lever and at the other end to said secondary throttle lever.

4. A compound carburetor according to claim 3 wherein said carburetor further comprises a spring connected to said operating lever and biasing said operating lever to close said primary throttle valve, a stopper screw arranged engageably with said primary throttle lever and able to adjust the closing position of said primary throttle valve, a spring connected to said interlocking lever and biasing said interlocking lever to close said secondary throttle valve and a stopper screw arranged engageably with said secondary throttle lever and able to adjust the closing position of said secondary throttle valve.

5. A compound carburetor according to claim 1 or 2 wherein the cross-sectional area ratio of said secondary bore to said primary bore is at least 70:30.

6. A compound carburetor according to claim 1 or 2 wherein said primary bore is so arranged that its center line is in a position out of a plane including the center line of said primary bore and the center line of the piston valve to form said variable venturi portion.

7. A compound carburetor according to claim 1 or 2 wherein the piston valve to form said variable venturi portion is arranged as directed downward so that its center line obliquely intersects with the center line of said secondary bore.

8. A compound carburetor according to claim 1 wherein the downstream side of said primary throttle valve of said primary bore is branched in response to the number of cyliners of an engine to be used, the downstream side of said variable venturi of said secondary bore is also branched in response to said number of the cyliners and said secondary throttle valves movable integrally with each other are provided respectively adjacent to a suction valve of said respective cylinders within the respective branch paths.

9. A compound carburetor according to claim 8 wherein said carburetor further includes a link mechanism capable of operating to open said secondary throttle valve when said primary throttle valve has been opened in predetermined opening position.

10. A compound carburetor substantially as hereinbefore described with reference to the accompanying drawings.