Method of indicating a basic air-fuel ratio condition of an internal combustion engine

#The present invention relates to a method of indicating a basic air-fuel ratio condition of an internal combustion engine which has an air-fuel ratio feedback control system.

#There presently exists an engine equipped with an air-fuel ratio feedback control system which controls an air-fuel ratio of the mixture supplied to the engine in response to an air-fuel ratio correction signal. The air-fuel ratio correction signal is gradually increased or decreased in accordance with an output of an exhaust gas sensor which detects the concentration of a particular component contained in the exhaust gas.

#In such an engine, a basic air-fuel ratio, which is equivalent to an air-fuel ratio of the engine when the air-fuel ratio feedback control operation is stopped, is adjusted by detecting the voltage level or the digital value of the air-fuel ratio correction signal, and by setting a mixture control mechanism, for example a by-pass air adjusting screw of an air-flow sensor, so that the voltage or digital value of the air-fuel ratio correction signal approaches a predetermined value.

#FIG. 1 is a schematic diagram of an internal combustion engine according to an embodiment of the present invention;

#FIG. 2 is a block diagram illustrating one example of a control circuit of FIG. 1;

#FIG. 3 illustrates wave-forms of the air-fuel ratio correction signal in the control circuit of FIG. 2;

#Referring to FIG. 1, which is a schematic diagram of an internal combustion engine having an electronic fuel injection control system as an embodiment according to the present invention, the flow rate of air sucked via an air cleaner 10 is controlled by a throttle valve 11, which is interlocked to an accelerator pedal. The sucked air is introduced into a combustion chamber 14 via a surge tank 12 and an intake valve 13. A fuel injection valve 15 is installed in the intake system in the vicinity of the intake valve 13, and is opened and closed to inject the compressed fuel in response to electric input pulse signals sent via a line 16. A fuel pump 17 compresses the fuel in a fuel tank 18 and sends the fuel to the fuel injection valve 15 via a conduit 19. The exhaust gas, after being burned in the combustion chamber 14, flows via an exhaust valve 20 and an exhaust manifold 21, and is emitted into the open air via a catalitic converter which is not illustrated.

#An air-flow sensor 22 is provided in the intake system between the air cleaner 10 and the throttle valve 11 to detect the flow rate of the sucked air, and sends an output signal to a control circuit 24 via a line 23. A rotational angle sensor 25a (refer to FIG. 2) mounted in a distributor 25 produces a pulse signal every time a crank shaft of the engine rotates by a predetermined angle; this signal is sent to the control circuit 24 via a line 26.

#A throttle position sensor 27 interlocked to the throttle valve 11 sends a signal to the control circuit 24 via a line 28, the signal indicating that the throttle valve 11 is at the idling position. An exhaust gas sensor 29 installed in the exhaust manifold 21 detects the concentration of a particular component, for example, the concentration of oxygen contained in the exhaust gas, and determines whether the air-fuel ratio of the mixture introduced into the combustion chamber 14 is on the rich side or the lean side with respect to the stoichiometric air-fuel ratio, and sends the output signal to the control circuit 24 via a line 30.