Abstract:
An electronically controlled fuel injection system mounting an oxygen content detector in the exhaust system of the engine comprises at least two kinds of fuel injection valve, one of which has a different injection opening from the other, whereby an optimum air-fuel ratio for reducing harmful components in the exhaust gas from the engine is obtained.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improved and electronically controlled fuel injection system having an oxygen content detector mounted in the exhaust system thereof to control the fuel injection in accordance with the oxygen content in the exhaust system, thereby reducing the harmful components in the exhaust gas. 
     Generally the amount of oxygen in the exhaust gas varies with air-fuel ratio as shown in FIG. 1. Conventional oxygen content detectors generate in response thereto an electromotive force as shown in FIG. 2 having a peculiar point at the air-fuel ratio of about 14.8 which corresponds to the starting point of oxygen (O 2 ) content in the curve of FIG. 1. Conventional oxygen content detectors are formed of a metal oxide, such as Zirconium dioxide and Titanium dioxide, and generate an electromotive force when heated. A difference of oxygen content is produced between one side of the detector and the other by the movement of oxygen ions. 
     In a conventional fuel injection system mounting such oxygen content detector, the air-fuel ratio is controlled at no other value than the theoretical one of 14.8, since the electromotive force of the detector changes abruptly at the point of about 14.8 as seen from FIG. 2, making detection of the point easy. The detector supplies the control signal generated therein to a computer, which operates to modify the injection pulse so that the air-fuel ratio always keeps a value of about 14.8 by increasing the fuel when the ratio is above 14.8 and decreasing it when below 14.8. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of this invention, the air-fuel ratio, can be varied from the theoretical value of 14.8. This is accomplished by utilizing two groups of fuel injection valves having different sized injection openings. A conventional oxygen detector which produces a easy to detect signal is mounted in one exhaust line which connects to one group of valves so that the overall air-fuel ratio can be varied from the theoretical 14.8 value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a graph representing the relation between air-fuel ratio and two typical components in the exhaust gas. 
     FIG. 2 shows a graph representing the relation between air-fuel ratio and electromotive force generated in the oxygen content detector. 
     FIG. 3 shows a schematic plan view of the electronically controlled fuel injection system of the present invention. 
     FIGS. 4a and 4b show graphs representing the relation between air-fuel ratio and diameter ratio of the injection openings of the fuel injection valves of the present invention. 
     FIG. 5 shows a block diagram of the computer of the present invention. 
     FIG. 6 shows an electric diagram of main part of the computer of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 3, numeral 1 designates a fuel tank, 2 a fuel pump, 3 a pressure regulator which is connected with the tank and pump by fuel pipes 4, regulating the pressure of fuel constant. Numeral 5 designates a 6-cylinder internal combustion engine, whose exhaust pipes 6 are divided into two groups 6a and 6b near the exhaust port of the engine 5 and open to the atmosphere through a silencer 7. Numerals 8a and 8b designate fuel injection valves divided into two groups corresponding to the exhaust pipes 6a and 6b. In this embodiment, one group of the injection valves consists of one valve 8a and the other group of the injection valves consists of 5 valves 8b. Numeral 9 designates electromagnetic coils mounted in the fuel injection valves 8a and 8b for operating those valves. Numeral 21 designates an injection opening of the fuel injection valve 8b through which the fuel is injected into the engine 5 when the valve is energized to open. The injection openings 21 of the fuel injection valves 8b have smaller diameter than that of the injection opening of the fuel injection valve 8a in this embodiment. As the result, the fuel injection valves 8b each inject less fuel than valve 8a, since the injection valves 8a and 8b open for exactly the same time period. For example, when the diameter of the injection opening 21 of the fuel injection valves 8b is 0.77 times that of the diameter of valve 8a and when the air-fuel ratio of the fuel injected from the fuel injection valve 8a is kept at 14.8, the air-fuel ratio of the fuel injected from the valves 8b becomes 19.15 and the total average air-fuel ratio becomes 18.5 which is a suitable value for the engine to reduce the harmful components in the exhaust gas. The ratio of the diameters of the injection openings 21 can be set at various values from 0.7 to 1.3 for obtaining various total air-fuel ratios. Further the ratio can be controlled at various values in response to engine parameters such as vacuum pressure in the intake pipe 12. When the diameter of the injection opening of the fuel injection valve 8a is D1 and that of the valves 8b is D2, the total air-fuel ratio varies as shown in FIG. 4a according to the ratio D1/D2. Likewise, the total air-fuel ratio also varies as the air-fuel ratio of the fuel injection valves 8b varies as shown in the FIG. 4b. Numeral 10 designates above-explained oxygen content detector mounted in the exhaust pipe 6a. Numeral 11 designates a conventional computer, 12 an intake pipe, 13 a revolution detector connected to a crank shaft of the engine 5 to close two times per one crank shaft revolution. Numeral 14 designates a driving circuit for energizing the fuel injection valves 8a and 8b via resistors 15. Numeral 16 designates a throttle valve for controlling the output power of the engine 5, 17 an air cleaner, 18 an air-flow meter mounted at an upstream part of the throttle valve 16 and having a plate 19 which turns according to the air amount passing therethrough to produce an electric signal across a variable resistor 23. 
     One embodiment of the computer 11 will be explained below. Referring to FIG. 5, numeral 20 designates a discriminating circuit connected with the oxygen content detector 10 for comparing actual air-fuel ratio with a set value which is brought thereinto from a setting circuit 40. Numeral 30 designates an integrating circuit connected with the discriminating circuit 20, the output of which varies in response to the output of the discriminating circuit 20. Numeral 22 designates an injection control circuit of usual type which is conventional and described in printed publications such as Japanese provisional publication No. 47-9757. The circuit 22 determines the duration of the injection pulse in accordance with the output signal of the circuit 30 and voltage level signal coming from the air-flow meter 18 in response to the signal applied from the revolution detector 13. The injection pulse produced in the injection control circuit 22 is applied to the fuel injection valves 8a and 8b of the engine 5 through the driving circuit 14 and resistors 15. Referring to FIG. 6, the main circuit of above-described embodiment will be explained. Numerals 40a and 40b designate resistors for fixing the set value in response to the temperature of the exhaust gas, 20a an input transistor to point A of which the signal from the oxygen content detector 10 is applied. 20b a voltage comparator, 20c a Zener diode, 20d, 20e and 20f resistors, 20g a transistor, 20h and 20i emitter resistors, 20j and 20k input resistors for the voltage comparator 20b, 20l a bias resistor, 20m, 20n, 20o and 20p resistors for setting voltage level of point E, 20q and 20r transistors, 20s and 20t base resistors. This circuit makes the voltage at point D higher than that at point E when the output of the voltage comparator 20 b is in a low level and the voltage relation between point D and E reverses when the output is in a high level. 
     Numeral 30a is an operational amplifier, 30b a capacitor which forms an integrator with the amplifier 30a, 30c and 30d input resistors, 30e a bias resistor. When the signal of the oxygen content detector 10 is in the range b in FIG. 2, making the output level higher, the voltage comparator 20b compares the voltage at point B which is corresponding to the signal from the detector 10 with the set voltage at point C to produce low level output signal. Then the transistor 20q becomes conductive to make the voltage level at point D higher than that of point E. Therefore the operational amplifier 30a produces at its output point F such an output voltage signal that has negative inclination to decrease gradually. Next, when the signal of the oxygen content detector 10 is in the range of C in FIG. 2, making the level lower, the voltage comparator 20b produces high level output signal. Then the transistor 20r becomes conductive to make the voltage level at point D lower than that of point E. Therefore the operational amplifier 30a produces such an output voltage signal that has positive inclination to increase gradually. This output voltage signal is applied to the injection control circuit 22 to make the circuit operate in such a way that the injection pulse duration is rendered longer when the voltage signal from the amplifier 30a is higher and is rendered shorter when the voltage signal is lower, thereby controlling the air-fuel ratio of the injection valve 8a  at about theoretical value 14.8. At this time, the air-fuel ratio of the fuel injection valves 8b becomes at about 19.15 making the total air-fuel ratio fix at about 18.5 in the above-described embodiment. 
     While a preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that modifications can be made without departing from the principles and spirit of the present invention, the scope of which is defined in the appended claims.