AIR-FUEL RATIO CONTROL DEVICE FOR INJECTION CARBURETORS

Abstract: The air-fuel ratio control device for injection carburetors comprises a slow fuel control unit and a main fuel control unit, each of which includes a negative pressure diaphragm (10′, 10″) forming a depression chamber into which negative pressures produced dependently on flow rates of air to be sucked and a fuel injection valve (12a′, 12a″) for opening and closing a fuel injection port (8a′, 8a″). A bypass passage (27) is connected between a main negative pressure passage (25) for introducing negative pressures into the depression chamber of the main fuel control unit and a slow negative pressure passage (26) for introducing negative pressures into the depression chamber of the slow fuel control unit, and an adjusting screw (28) capable of adjusting effective cross sectional area is provided in the bypass passage. This air-fuel ratio control device enables to maintain a constant air-fuel ratio of the mixture during the transition from the slow zone to the main zone and allows engines to exhibit favorable drivability over the entire driving range.

Description: The invention concerns an air-fuel ratio control device for injection carburators comprising a slow fuel control unit and a main fuel control unit for slow and fast engine running conditions each including a negative pressure diaphragm forming a depression chamber for receiving negative pressures produced dependently on flow rates of air to be sucked into a suction bore, and a fuel injection valve for opening and closing a fuel injection port in accordance with displacement of said negative pressure diaphragm a negative pressure passage for introducing negative pressures from a venturi in the suction bore into the depression chamber of the main fuel control unit, a slow negative pressure passage for introducing negative pressure produced at a location downstream said venturi into the depression chamber of the slow fuel control unit. Such an air-fuel ratio control device is known from GB-A-1 021 509, however, this known control device provides no possibility to add the negative pressure produced at a location downstream of a venturi and for introduction into a depression chamber of a slow fuel control unit into the main negative pressure passage so that the air-fuel control device is not capable of maintaining the air-fuel ratio of the mixture at a constant level during the transition from the slow zone to the main zone. Furthermore, from European Patent Application 89 109 196.9 an air-fuel ratio control device for injection carburators is known which is equipped with a slow fuel controller and a main fuel controller, and adjusts fuel injection rate adequately on the basis of negative pressure produced dependently on flow rate of air to be sucked. Fig. 1 is a sectional view illustrating the fundamental structure of the air-fuel ratio control device of the injection carburetor. In this drawing, the reference numeral 1 represents a suction bore of a carburetor having a venturi 2, the reference numeral 3 designates a fuel control unit arranged at a location neighboring the venturi 2 and the reference numeral 4 denotes an air section of regulator arranged at a location also neighboring the venturi 2 but on the side opposite to the fuel control unit 3 with regard to the suction bore 1. The air section of regulator 4 has an air chamber and a depression chamber 5 which is separated from each other by a negative pressure diaphragm 6, and formed in the depression chamber 5 is an opening 5a for communication with the venturi 2. Further, a fuel section of regulator 7 has a fuel injection chamber 8 and a fuel pressure chamber 9 which are separated from each other by a fuel diaphragm 10, and formed in the fuel injection chamber 8 is a fuel injection port 8a in opposite to the opening 5a of the depression chamber 5. The fuel injection chamber 8 is communicated with the fuel pressure chamber 9 through a main jet 11. The reference numeral 12 represents a connecting member inserted through the opening 5a of the depression chamber 5 and the fuel injection port 8a of the fuel injection chamber 8, one end of the connecting member 12 is fixed to the negative pressure diaphragm 10 and the other end of the connecting member 12 is fixed to the fuel diaphragm 10. Formed on the connecting member 12 is a conical valve 12a capable of controlling opening degree of the fuel injection port 8a by opening and closing said port. The reference numeral 13 represents a spring which is arranged in the depression chamber 5 and functions to urge the negative pressure diaphragm 6 upward, i.e., to move the valve 12a in the direction to close the fuel injection port 8a. When a negative pressure corresponding to the flow rate of the air flowing through the venturi 2 is introduced into the depression chamber 5 and the negative pressure diaphragm 6 is displaced toward the depression chamber 5 in the injection carburetor having the structure described above, also the fuel diaphragm 10 is displaced in the same direction (downward) to allow the valve 12a to open the fuel injection port 8a, whereby fuel is ejected into the suction bore 1 and pressure drops in the fuel injection chamber 8 accordingly. When pressure differential between the negative pressure in the depression chamber 5 and atmospheric pressure is balanced with the fuel pressure differential between both the sides of the main jet 11, the pressure applied to the negative pressure diaphragm 6 is balanced with the pressure applied to the fuel diaphragm 10 and air-fuel ratio is maintained constant in this condition. When resilience of the spring 13 is so selected as to be equal to the total weight of the assembly consisting of both the diaphragms 6 and 10 and the connecting member 12 in order to obtain high responsibility of the injection carburetor of this type, however, a negative pressure is not produced substantially at the starting time of an engine as shown in Fig. 2A since air flows through the venturi at a low rate at that time. Accordingly, variation of fuel flow rate is slower than variation of air flow rate, thereby producing a deviation of x from a target value as illustrated in Fig. 2B. Therefore, the injection carburetor of this type has a defect that a long time is required until an air-fuel ratio of the mixture attains to a target value corresponding to an opening degree of the throttle valve after it is opened widely in the main zone as shown in Fig. 2C. Fig. 3 illustrates a carburetor so adapted as to control air-fuel ratio of the mixture in a broad range by combining two air-fuel ratio control devices having the fundamental structure illustrated in Fig. 1 as a slow fuel control unit 14 mainly for controlling the slow zone and a main fuel control unit 15 chiefly for controlling the main zone. In Fig. 3, the members and parts of the slow fuel control unit 14 which are similar to those illustrated in Fig. 1 are represented by the same numerals but with a prime, and the members and parts of the main fuel control unit 15 similar to those shown in Fig. 1 are designated with the same numerals but with double primes. The reference numeral 16 represents an air valve arranged openably and closably downstream the venturi 2 in the suction bore 1, the reference numeral 17 designates a stopper for holding the air valve 16 at the minimum opening degree thereof, the reference numeral 18 denotes a negative pressure actuator which is connected to the air valve 16, and functions to open and close the air valve 16 in conjunction with variation of the negative pressure produced downstream the air valve 16, the reference numeral 19 represents a throttle valve arranged downstream the air valve 16, the reference numeral 20 designates a fuel tank and the reference numeral 21 denotes a fuel pump. The discharge side of the fuel pump 21 is communicated with the fuel pressure chamber 9″ of the main fuel control unit 15 and the fuel injection chamber 8″ thereof is communicated with the fuel pressure chamber 9′ of the slow fuel control unit 14. The negative pressure chamber of the slow fuel control unit 14 is communicated with the suction bore 1 at a location downstream the air valve 16, whereas the negative pressure chamber of the main fuel control unit 15 is communicated with the venturi 2. The fuel injection port 8a′ of the slow fuel control unit 14 and the fuel injection port 8a″ of the main fuel control unit 15 are communicated with a fuel passage 22 which is open to the suction bore 1 at a location downstream the throttle valve 19. The carburetor described above has already been proposed by the applicant and functions as follows. In the slow zone of the engine where the throttle valve is opened at a small degree, a low negative pressure is produced downstream the air valve 16 and the negative pressure actuator does not operate. Accordingly, the air valve 16 is held at the position shown in Fig. 3 and only the slow fuel control unit 14 is set in the operating condition. The slow fuel control unit 14 functions in the same manner as the fuel control unit described with reference to Fig. 1, and the fuel ejected through the fuel injection port 8a′ is discharged into the suction bore 1 through the fuel passage 22. When the throttle valve 19 is opened to a predetermined degree from the condition described above, the negative pressure actuator operates to displace the air valve 16 to the fully open position thereof. During this transient process, the negative pressure acting on the depression chamber of the slow fuel control unit 14 is gradually reduced and the negative pressure acting on the depression chamber of the main fuel control unit 15 is gradually increased, whereby the fuel injection port 8a″ of the main fuel control unit 15 begins to eject the fuel. The fuel ejected from the fuel injection port 8a″ is discharged into the suction bore 1 through the fuel passage 22 and operating condition of the engine shifts to the main zone. However, since both the slow fuel control unit 14 and the main fuel control unit 15 have the defect described with reference to the carburetor illustrated in Fig. 1, the air-fuel ratio controlled by both the fuel control units are disturbed as shown in Fig. 4 during the transition from the slow zone to the main zone, or the transition from the slow zone to the main zone is not performed smoothly. In order to correct these defects, i.e., to match actual air-fuel ratios with target values from the beginning of the main zone, there has been proposed a carburetor wherein the negative pressure diaphragms 6 and 6″ are so designed as to operate with higher responsibility to air flow rate by selecting resilience of the spring 13 so as to be smaller than the total weight of the diaphragm assembly 6, 10, 12 in Fig. 1 and resilience of the spring 13″ so as to be smaller than the total weight of the diaphragm assembly 6″, 10″, 12″ in Fig. 3, or arranging, in the air chamber of the air section of regulator 4, a compensating spring 23 urging the negative pressure diaphragm 6 toward the depression chamber 5, and providing an adjusting screw permitting adjustment of resilience of the adjusting spring 23 as illustrated in Fig. 5. This proposal makes it possible to match fuel flow rates to be controlled nearly with target values from the beginning of the main zone and to control air-fuel ratios of the mixture nearly at target values from the beginning of the main zone as illustrated in Fig. 6B. When the fuel control units are composed as described above, however, the forces for urging the negative pressure diaphragms 6 and 6″ toward the depression chambers 5 and 5″ are too strong, and the fuel injection ports 8a and 8a″ are kept in the open condition thereof even while the engine is rested, thereby producing defects that the mixture is made overrich by the fuel discharged from the main fuel control unit 15 even in the slow zone and that the fuel is ejected through the fuel injection ports 8a and 8a″ before the engine starts rotating at the restart time by the fuel pump 21 which starts operating upon the ON operation by the engine key. A primary object of the present invention is to provide an air-fuel ratio control device for injection carburetors which is capable maintaining of air-fuel ratio of the mixture at a constant level during transition from the slow zone to the main zone. Another object of the present invention is to provide an air-fuel ratio control device for injection carburetors which is capable of securely preventing unnecessary fuel from being discharged into the suction bore at the rest time or restart time of an engine. A further object of the present invention is to provide an air-fuel ratio control device for injection carburetors which has very excellent responsibility over the entire operating range of an engine. According to the present invention it is thus provided that the negative pressure for introducing into the depression chamber of the slow fuel control unit is produced downstream an air valve arranged in the suction bore, a bypass passage connected between said main negative pressure passage and said slow negative pressure passage is provided, and an adjusting means is provided, arranged in said bypass passage and capable of adjusting ratios of the negative pressure to be introduced from said slow negative pressure passage into said main negative pressure passage. The air-fuel ratio control device according to the present invention allows the negative pressure produced downstream the air valve to be added at a predetermined ratio into the main negative pressure passage through the bypass passage so that a total of the negative pressure in the venturi and the added negative pressure if introduced into the depression chamber of the main fuel control unit in the slow zone, and opens the fuel injection valve to start discharging the fuel when the total negative pressure exceeds a predetermined level, whereby the air-fuel control device is capable of maintaining air-fuel ratio of the mixture at a constant level during the transition from the slow zone to the main zone. In a preferred formation of the present invention, provided in the main fuel control unit is a resilient means which functions to generate a force acting to close the fuel injection valve which is stronger than the force acting to open the fuel injection valve until the negative pressure to be introduced into the depression chamber of the main fuel control unit exceed the predetermined level. This means prevents the fuel from being leaked while the engine is rested or at the initial stage of the slow zone. These and other objects as well as the features and the advantages of the present invention will become apparent from the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings. In the drawings: Fig. 1 is a sectional view illustrating the fundamental structure of the conventional air-fuel ratio control device for injection carburetors; Fig. 2A, Fig. 2B and Fig. 2C are graphs illustrating various characteristics of the air-fuel ratio control device shown in Fig. 1; Fig. 3 is a sectional view illustrating overall structure of the injection carburetor; Fig. 4 shows characteristic curves illustrating relationship between air flow rate and air-fuel ratio during transition from the slow zone to the main zone in the carburetor shown in Fig. 3; Fig. 5 is a schematic sectional view illustrating another conventional example obtained by improving the air-fuel ratio control device shown in Fig. 1; Fig. 6A, Fig. 6B and Fig. 6C are graphs illustrating various characteristics of the air-fuel ratio control device shown in Fig. 5; Fig. 7 is a sectional view illustrating the main members of an embodiment of the air-fuel ratio control device according to the present invention; Fig. 8A and Fig. 8B are characteristic curves illustrating variations of air-fuel ratio in the embodiment of the air-fuel ratio control device according to the present invention; and Fig. 9 is a curve visualizing variation characteristic of the negative pressure produced downstream the air valve. Now, the embodiment of the present invention will be described with reference to Fig. 7. In this drawing wherein the slow fuel control unit is omitted, the members and the parts which are substantially the same as those shown in Fig. 3 are represented by the same reference numerals. The reference numeral 25 represents a main negative pressure passage which is open to the venturi 2, has a jet 25a and serves for introducing a negative pressure P 1 of the venturi into the depression chamber of the main fuel control unit 15, the reference numeral 26 designates a slow negative pressure passage which is open at a location downstream the air valve 16 and serves for introducing a negative pressure P 2 produced downstream the air valve 16 into the depression chamber of the slow fuel control unit 14, the reference numeral 27 denotes a bypass passage communicated at one end thereof with the slow negative pressure passage 26 and at the other end thereof with the main negative pressure passage 25 at a location dowstream the jet 25a, the reference numeral 28 represents an adjusting screw which is adjustably provided in the bypass passage 27 and capable of adjusting a ratio of the negative pressure P 2 downstream the air valve 16 to be added into the main negative pressure passage 25, and the reference numeral 29 designates a spring which is arranged in the air chamber 5″ of the main fuel control unit 15 and functions to urge the negative pressure diaphragm 6″ toward the depression chamber. Let us now assume that a reference symbol w 1 represents weight of the diaphragm assembly of the main fuel control unit 15, a reference symbol w 2 designates resilience of the spring 13″, a reference symbol w 3 denotes resilience of the spring 29, and a reference symbol w 4 represents a force which is generated by the total negative pressure P 3 of the negative pressures P 1 and P 2 produced in the slow zone during operation of the engine, and acts to raise the diaphragm assembly. Resilience of the spring 13″ and that of the spring 29 are selected so as to satisfy the following relation (1) in the rest condition of the engine and the following condition (2) when the force w 4 exceeds a predetermined value: w 3 < w 1 + w 2 w 3 + w 4 > w 1 + w 2 In this embodiment, the air-fuel ratio control device illustrated in Fig. 3 is used as the slow fuel control unit 14. Now, functions of the air-fuel control device preferred as the embodiment will be described below: While the engine is rested, the negative pressures P 1 and P 2 are not produced, whereby the fuel injection valves 12a′ and 12a″ are held in the closed positions thereof to prevent the fuel from being leaked into the fuel passage 22. While the engine is operating in the slow zone after it is started, a very low negative pressure is produced in the venturi 2, whereas the negative pressure P 2 at a certain level is produced downstream the air valve 16. This negative pressure P 2 is introduced through the slow negative pressure passage 26 into the depression chamber of the slow fuel control unit 14. Accordingly, the fuel is ejected from the fuel injection port 8a′ in a quantity corresponding to the level of the negative pressure P 2 in the slow fuel control unit 14 as already described with reference to Fig. 3, whereby the mixture at the air-fuel ratio suited for operation in the slow zone (target value) is fed to the engine as indicated by the solid line in Fig. 8B. On the other hand, the negative pressure P 2 is added, at the predetermined ratio set by the adjusting screw 28, through the bypass passage 27 into the main negative pressure passage 25, and a total negative pressure P 3 of the added pressure and the very low pressure P 2 in the venturi 2 is introduced into the depression chamber of the main fuel control unit 15. At the initial stage of the slow zone, however the fuel injection port 8a″ is closed by the valve 12a″ since the raising force w 4 generated by the total negative pressure P 3 is small and the force w 1 + w 2 acting to close the fuel injection valve 12a″ is larger than the force w 3 acting to open the fuel injection valve 12a″. The negative pressure P 3 increases as air is sucked at higher rates into the suction bore 1. (See Fig. 9) When the total negative pressure P 3 exceeds a predetermined level in the depression chamber of the main fuel control unit 15 to establish the above-mentioned relation (2), the negative pressure diaphragm 6″ is displaced toward the depression chamber against the force w 1 + w 2 acting to close the fuel injection valve 12 a″and the valve 12a″ is opened, whereby the fuel is ejected through a fuel discharge passage 22 into the suction bore 1. Air-fuel ratio of the mixture which is low at the beginning is gradually enhanced as indicated by the curves a in Fig. 8A and Fig. 8B, and reaches a target valve. As opening degree of the throttle valve 19 is increased, the slow zone is switched to the main zone in a condition where the air-fuel ratio is maintained at the target value, and the condition is kept also in the main zone. (See Fig. 8A and Fig. 8B ) Further, at restart time after the engine is stopped, the above-mentioned relation (1) is satisfied and the fuel injection valve 12a″ is kept at the closed condition thereof before the engine starts rotation even in the condition where the engine key is turned ON and the fuel pump 21 is operating. As is understood from the foregoing description, the embodiment of the present invention prevents unnecessary fuel from being discharged at rest time of engine or initial stage of the slow zone since the force w 1 + w 2 acting to close the fuel injection valve 12a″ is stronger than the force w 3 acting to close the valve 12a″ at the engine rest time or initial stage of the slow zone before the total negative pressure P 3 in the depression chamber of the main fuel control unit 15, exceeds a predetermined level, assures stable operation of the fuel injection valve 12a″ at opening start time thereof, and is capable of maintaining air-fuel ratio of the mixture at a constant level with the main fuel control unit 15 during transition from the slow zone to the main zone as well as in the main zone by adding a predetermined ratio of the negative pressure produced dependently on air flow rate into the depression chamber of the main fuel control unit 15 at the stage of the slow zone. Further, the embodiment of the present invention does not allow mechanical operation delay since opening and closing of the fuel injection valve 12a″ are controlled by variation of the negative pressure. Furthermore, it is possible, needless to say, to use the known piston valve as the air valve 16 though the embodiment uses a leaf valve. In addition, though the embodiment is so constructed as the strengthen the closing force for the fuel injection valve 12a″ by the resilience of the spring 13″, it is possible to select such a structure as the strengthen the closing force for the fuel injection valve 12a″ weakening the resilience of the spring 28 with the spring 13″ omitted.

Claims: An air-fuel ratio control device for injection carburators comprising a slow fuel control unit (14) and a main fuel control unit (15) for slow and fast engine running conditions each including a negative pressure diaphragm (10′, 10″) forming a depression chamber (5) for receiving negative pressures (P 2 ) produced dependently on flow rates of air to be sucked into a suction bore (1), and a fuel injection valve (12a′, 12a″) for opening and closing a fuel injection port (8a′, 8a″) in accordance with displacement of said negative pressure diaphragm (10′, 10″), a negative pressure passage (25) for introducing negative pressures (P 2 ) from a venturi (2) in the suction bore (1) into the depression chamber (5) of the main fuel control unit (15), a slow negative pressure passage (26) for introducing negative pressure produced at a location downstream said venturi (2) into the depression chamber (5) of the slow fuel control unit (14), characterized in that the negative pressure for introducing into the depression chamber (5) of the slow fuel control unit (14) is produced downstream an air valve (16) arranged in the suction bore (1), a bypass passage (27) connected between said main negative pressure passage (25) and said slow negative pressure passage (26) is provided, and an adjusting means (28) is provided, arranged in said bypass passage (27) and capable of adjusting ratios of the negative pressure to be introduced from said slow negative pressure passage (26) into said main negative pressure passage (25). The device of claim 1, wherein said adjusting means (28) is designed as an adjusting screw fitted in said bypass passage (27) and capable of effecting a cross sectional area of said bypass passage (27). The device of claim 1, wherein said air valve (16) is a leaf valve. The device of claim 1, wherein said air valve (16) is a piston valve. The device according to anyone of the claims 1 to 4, further comprising a resilient means (13″, 29) functioning in such a manner that a force acting to close the fuel injection valve (12a′, 12a″) of the main fuel control unit (15) is stronger than a force acting to open said valve until the negative pressure to be introduced into the depression chamber (5) of said main fuel control unit (15) exceeds a predetermined level while operating condition of the engine is in slow zone.

Inventors: SEKIYA, MITSURU MIKUNI KOGYO KABUSHIKI KAISHA, TAKENAKA, SHINTARO MIKUNI KOGYO KABUSHIKI KAISHA
Applicants: MIKUNI KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: F02M69
IPC codes: F02M69