An electronic control fuel injection device is well known in the art as disclosed, for example, in Japanese patent Laid-Open No. 56632/1982 published on Apr. 5, 1982 in the title of "Method of fuel control".
The electronic control fuel injection device to which the present invention is applied will be explained referring to FIG. 1.
In FIG. 1, the flow rate of the air sucked from an air cleaner 1 is controlled by a throttle valve 4 which is disposed in a throttle body 2 and operates in the interlocking arrangement with an acceleration pedal 3 operated by a driver of a car. Then, the air is supplied to a combustion chamber 9 of an internal combustion engine 8 through a surge tank 5, an intake branch pipe 6 and an intake valve 7. The fuel-air mixture burnt in the combustion chamber 9 is discharged into the atmosphere through an exhaust valve 10 and an exhaust branch pipe 11. A fuel injection valve 14 is disposed in the intake branch pipe 6 in such a manner as to correspond to the combustion chamber 9, but one fuel injection valve may be disposed upstream of the throttle valve 4.
An electronic control unit 15 comprises a microprocessor as an operation unit, read-only memories (ROMs), random-access memories (RAMs) and an input/output device (I/O port). The electronic control unit 15 receives input signals from a throttle sensor 16 for detecting the full open state of the throttle valve 4, a water temperature sensor 18 fitted to a water jacket 17 which is used for cooling the engine, a heat wire type air flow meter 19 for measuring the intake air quantity, an intake air temperature sensor 20 for detecting the intake air temperature, a rotating angle sensor 23 for detecting the rotating angle of a distributor 33, which controls the ignition timing of the engine, coupled to a crank shaft in order to detect the rotating angle of the crank shaft coupled to a piston 21 through a connecting rod 22, an ignition switch 24 and a starter switch 25.
The rotating angle sensor 23 includes a position sensor 26 which generates one pulse whenever the crank shaft rotates twice and an angle sensor 27 which generates a pulse whenever the crank shaft (not shown) rotates by a predetermined angle such as 30.degree., for example.
The fuel is pressure-fed by a fuel pump 31 to the fuel injection valve 14 from a fuel tank 30 through a fuel passage 29. The electronic control unit 15 calculates a fuel injection quantity and a fuel injection timing on the basis of various input signals, sends a fuel injection pulse to the fuel injection valve 14, calculates the ignition timing and sends a current to the ignition coil 32. A primary current of the ignition coil 32 is sent to the distributor 33 and then to an ignition plug.
FIG. 2 is a block diagram showing the construction of the electronic control unit 15. The outputs of the water temperature sensor 18, the air flow sensor 19, the intake air temperature sensor 20 and the throttle sensor 16 are sent to an A/D converter 34 and are converted to digital signals. A revolution sensor 35 includes a gate which is opened and closed by the pulses from the angle sensor 27 of the rotating angle sensor 23 and a counter which counts the clock pulses sent thereto from a clock pulse generator 36 through this gate, and a value inversely proportional to the number of revolution N is generated as the output of the counter.
The outputs of the ignition switch 24, the starter switch 25 and the position sensor 26 of the rotating angle sensor 23 are temporarily stored in a latch circuit 37. The microprocessor 40 is connected to ROM 42, RAM 43 and other blocks 34, 35, 37 through a bus line 41 and calculates the fuel injection quantity on the basis of a predetermined program. The value corresponding to this fuel injection quantity is stored in a fuel injection control circuit 44, and when this stored value is in agreement with the clock pulse, the output pulse is generated and is sent to the fuel injection valve 14 through a driving circuit 45.
Correction of acceleration and deceleration of a car is controlled by increasing and decreasing the fuel by receiving the output from the throttle sensor 16 and processing it in the microprocessor 40.
In the fuel injection device of the kind explained above, when the starter switch signal is turned on and cranking is effected as shown in the chart (a) of FIG. 3, the injection start signal is generated as shown in the chart (b) and the injection pulses are applied to the fuel injection valve as shown in the chart (c).
Here, the injection pulses ar divided into T.sub.ON and T.sub.OFF between the injection start signals, and T.sub.ON is changed by the temperature of cooling water.
However, there exists the problem that the fuel does not evaporates suitably because large quantities of fuel is supplied at one time only for the T.sub.ON period so that the fuel-air mixture density inside the fuel chamber is not optimized, and start ability is not very good. This problem becomes all the more remarkable with a lower temperature.
For solving the problem explained above, "Method of fuel control of gasoline injection engine at the time of start" was invented as shown in Japanese patent publication No. 45650/1974 published on Dec. 5, 1984. This prior art discloses that injection pulses are generated continuously between preceding and succeeding injection start signals.
However, there exists the problem that the fuel is consumed excessively more than the necessary fuel for the engine because the fuel is injected successively without judging necessary quantity of the fuel.