Electronically-Controlled Fuel Injection System

The present invention relates to an electronically-controlled fuel injection system which is chiefly applied to vehicular engines.

Heretofore, there has been known a system of this type comprising a synchronous counter which receives main injection time data corresponding to an amount of fuel to be injected synchronously to engine revolutions, and an asynchronous counter which receives increment injection time data corresponding to an amount of fuel to be injected at a selected time interval asynchronously to the engine revolutions, wherein the synchronous counter is operated for a period of time equal to the main injection time data upon receiving a synchronous signal which is generated synchronously to the engine revolutions, while the asynchronous counter is operated for a period of time equal to the increment injection time data upon receiving an asynchronous signal which is generated at the selected time interval, so as to open a fuel injection valve by the operations of the respective counters. In this case, when during the operation of one of the two counters, for example, the operation of the synchronous counter, the asynchronous signal is generated to operate the asynchronous counter, both the counters operate overlapping in time, and an actual increment injection period of time is shortened by the overlapping time. A system wherein, in order to solve this drawback, the fuel injection valve is opened longer in correspondence with the overlapping time has been known from the official gazette of Japanese Patent Application Publication No. 17939/1985.

Meanwhile, during the operation of each counter, a pulse as shown in FIG. 4 is output from the counter, and the fuel injection valve is opened by this pulse. However, when a battery voltage lowers, the rise of the pulse lags as indicated by a phantom line, and the opening period of time of the fuel injection valve shortens as compared with the operating period of time of the counter. In this regard, there has been known a measure wherein the counter is supplied with injection time data obtained in such a way that a correction time .DELTA.T dependent upon the battery voltage is added to a desired injection time T, whereby the lag of the rise of the pulse is compensated by operating the counter superfluously for .DELTA.T, and the opening time of the fuel injection valve is controlled so as to equalize to T. For the situation as in the above prior art where, when the synchronous counter and the asynchronous counter have operated in overlapping fashion, the fuel injection valve is opened longer for the overlapping period of time. Then, letting T.sub.1 denote the desired main injection time and T.sub.2 denote the desired increment injection time, a pulse of a duration as shown in FIG. 5 obtained by simply adding the operating time T.sub.1 +.DELTA.T of the synchronous counter and that T.sub.2 +.DELTA.T of the asynchronous counter is impressed on the fuel injection valve. As a result, the opening time of the fuel injection valve actually contributing to fuel feed becomes T.sub.1 +T.sub.2 +.DELTA.T, and the fuel is injected excessively in correspondence with .DELTA.T.

The present invention has for its object to solve such a problem, and to provide a system which can inject fuel accurately without excess or deficiency.

The present invention for accomplishing the object is characterized by providing timers which add a predetermined period of time after the ends of operations of a synchronous counter and an asynchronous counter, and delay means operating when, during the operation of one of the two counters, a synchronous signal or an asynchronous signal for operating the other counter has been generated, to delay in input of the signal to the other counter until the timekeeping of the timer ends.

Assuming that the asynchronous signal have been generated during the operation of the synchronous counter, this signal is input to the asynchronous counter at the point of time at which the timekeeping of the predetermined time t by the timer ends after the end of the operation of the synchronous counter. Eventually, a fuel injection valve is supplied with a pulse from the asynchronous counter after the output of the synchronous counter has fallen into a low level owing to the end of the operation thereof, as illustrated in FIG. 3. Accordingly, when the main injection time data is set at T.sub.1 +.DELTA.T and the increment injection time data is set at T.sub.2 +.DELTA.T as stated above, the total opening time of the fuel injection valve actually contributing to fuel feed becomes the desired T.sub.1 +T.sub.2, and the fuel is not injected excessively in correspondence with .DELTA.T as in the prior art.

FIG. 1 is a general block diagram of an embodiment of a system according to the present invention;

FIG. 2 is a block diagram of the essential portions of the embodiment;

FIG. 3 is a diagram showing pulses which are impressed on a fuel injection valve;

FIG. 4 is a diagram showing the waveform of a pulse which is output from each counter; and

FIG. 5 is a diagram showing a pulse in a prior art which is impressed on a fuel injection valve.

Referring to FIG. 1, numeral 1 designates an engine, and numeral 2 a control circuit which is constructed of a microcomputer. A fuel injection valve 5, which is disposed upstream of a throttle valve 4 in the suction passage 3 of the engine 1, is controlled to open and close by the control circuit 2.

The control circuit 2 includes therein an input circuit 10 which receives signals from sensors such as a crank angle sensor 6, a throttle opening degree sensor 7, a suction-pipe absolute pressure sensor 8 and a coolant temperature sensor 9; a central processing unit ("CPU") 11; a memory 12, and a driver circuit 13 for the fuel injection valve 5. The CPU 11 calculates a main injection time T.sub.1 which corresponds to an amount of fuel to be injected synchronously to engine revolutions, for example, an amount of fuel conforming to an amount of suction air, an increment injection time T.sub.2 which corresponds to an amount of fuel to be injected at a predetermined time interval asynchronously to the engine revolutions, for example, an amount of fuel for an accelerating increment, and a compensation time .DELTA.T which depends upon a battery voltage and which serves to compensate the lag of the rise of a pulse, so as to generate main injection time data with .DELTA.T added to T.sub.1 and increment injection time data with .DELTA.T added to T.sub.2.

As shown in FIG. 2, the driver circuit 13 comprises a synchronous counter 14 to which the main injection time data is input, and an asynchronous counter 15 to which the increment injection time data is input. Each of the counters 14 and 15 is so constructed as to be loaded with the corresponding injection time data through a data bus 16 upon receiving a high level signal at its L terminal, to be triggered upon receiving a high level signal at its S terminal and then operate for a period of time equal to the injection time data, and to output a pulse of high level to its 0 terminal during the operation. The output sides of both the counters 14 and 15 are connected through an OR circuit 17 to an output terminal 18 which leads to the fuel injection valve 5, so that the injection valve 5 is opened whenever either of the two counters 14 and 15 operates. In the drawing, numeral 19 indicates an input terminal for a synchronous signal A which is generated synchronously to the engine revolutions on the basis of the signal from the crank angle sensor 6, while numeral 20 indicates an input terminal for an asynchronous signal B which is generated at the predetermined time interval asynchronously to the engine revolutions. The synchronous signal A and the asynchronous signal B are directly applied from the input terminals 19 and 20 to the L terminal of the synchronous counter 14 and that of the asynchronous counter 15, respectively. Timers 21.sub.1 and 21.sub.2 which add a predetermined period of time t, for example, 1 msec after the ends of the operations of the counters 14 and 15 and produce signals of high level, are connected to the output sides of the counters 14 and 15, respectively. Further, a first D-type flip-flop 22.sub.1 and a first AND circuit 23.sub.1 are interposed between the input terminal 19 and the S terminal of the synchronous counter 14, while a second D-type flip-flop 22.sub.2 and a second AND circuit 23.sub.2 are interposed between the input terminal 20 and the S terminal of the asynchronous counter 15. In addition, there are disposed a first NOR circuit 24.sub.1 which receives as its inputs the output of the asynchronous counter 15 and that of the second timer 21.sub.2 located on the output side thereof, and a second NOR circuit 24.sub.2 which receives as its inputs the output of the synchronous counter 14 and that of the first timer 21.sub.1 located on the output side thereof. Thus, the first AND circuit 23.sub.1 is supplied with the output of the Q terminal of the first D-type flip-flop 22.sub.1 and the output of the first NOR circuit 24.sub.1, while the second AND circuit 23.sub.2 is supplied with the output of the Q terminal of the second D-type flip-flop 22.sub.2 and the output of the second NOR circuit 24.sub.2. Each of the D-type flip-flops 22.sub.1 and 22.sub.2 is so constructed that, in response to the rise of an input signal to a C terminal, a signal of high level is delivered to the Q terminal, this signal continuing until the output of the corresponding counter 14 or 15 subsequently entering an R terminal falls.

Next, the operation of the above embodiment will be described. When the synchronous signal A is generated, it is input to the L terminal of the synchronous counter 14, and the main injection time data is loaded in the counter 14. Simultaneously, owing to the input of the synchronous signal A to the C terminal of the first D-type flip-flop 22.sub.1, the output of the Q terminal thereof becomes the high level. In this case, also the output of the first NOR circuit 24.sub.1 is at the high level ordinarily, so that a signal at the high level is input immediately from the first AND circuit 23.sub.1 to the S terminal of the synchronous counter 14, in other words, the synchronous signal A is input to the S terminal without a lag. The counter 14 operates for a period of time T.sub.1 +.DELTA.T and delivers a pulse of high level as shown in FIG. 3, and the lag of the rise of the pulse from a low level is compensated by the increase of a pulse width corresponding to T, whereby the fuel injection valve 5 is opened for the desired main injection time T.sub.1.

In addition, when the asynchronous signal B is generated during the operation of the synchronous counter 14, it is input to the L terminal of the asynchronous counter 15, and the increment injection time data is loaded in the asynchronous counter 15. Here, since the output of the synchronous counter 14 is at the high level, the output of the second NOR circuit 24.sub.2 becomes the low level. Thus, even when the input of the asynchronous signal B to the C terminal of the second D-type flip-flop 22.sub.2 brings the output of the Q terminal thereof to the high level, the output of the second AND circuit 23.sub.2 remains at the low level, and the asynchronous counter 15 is not operated. Even after the operation of the synchronous counter 14 has ended, the output of the first timer 21.sub.1 is at the high level during the timekeeping of the first timer 21.sub.1. Therefore, the output of the second NOR circuit 24.sub.2 becomes the low level to prevent the asynchronous counter 15 from operating, and the output level of the synchronous counter 14 drops rapidly to the low level, so that the fuel injection valve 5 is closed. When the predetermined period of time t has lapsed since the end of the operation of the synchronous counter 14, the timekeeping of the first timer 21.sub.1 ends. Then, the output of the second NOR circuit 24.sub.2 becomes the high level, and the signal of high level is input from the second AND circuit 23.sub.2 to the S terminal of the asynchronous counter 15. In other words, the input of the asynchronous signal B to the asynchronous counter 15 is delayed until the end of the timekeeping of the first timer 21.sub.1 by delay means composed of the second D-type flip-flop 22.sub.2, the second AND circuit 23.sub.2 and the second NOR circuit 24.sub.2. Thereafter, the asynchronous counter 15 operates for a period of time T.sub.2 +.DELTA.T and produces a pulse at the high level. On this occasion, the output of the counter 15 rises from the low level, and the lag of the rise is compensated without excess or deficiency by the increase of a pulse width corresponding to .DELTA.T, whereby the fuel injection valve 5 is opened for the desired increment time T.sub.2.

In a case where the synchronous signal A is generated during the operation of the asynchronous counter 15, the input thereof to the synchronous counter 14 is delayed until the timekeeping of the second timer 21.sub.2 ends upon the lapse of the predetermined period of time t since the end of the operation of the asynchronous counter 15, by delay means composed of the first D-type flip-flop 22.sub.1, the first AND circuit 23.sub.1 and the first NOR circuit 24.sub.1. Accordingly, the fuel injection valve 5 is opened for the period of time T.sub.2, it is thereafter closed once, and it is opened accurately for the period of time T.sub.1. In a case where the timers 21.sub.1, 21.sub.2 are off-delay type timers which produce signals of high level even during the operations of the respective counters 14, 15, the outputs of these timers 21.sub.1, 21.sub.2 may be input to the respective AND circuits 23.sub.1, 23.sub.2 through NOT circuits.

As described above, according to the present invention, even during the operation of one of a synchronous counter and an asynchronous counter, a signal for operating the other is generated, the other counter is not operated unless a predetermined period of time lapses after the end of the operation of one counter. This brings forth the effect that, even when each counter is operated superfluously in correspondence with a correction time for compensating for the lag in the rise of a pulse, a fuel injection valve can be always opened accurately without excess or deficiency, without unnecessarily prolonging the opening time of the fuel injection valve as in the prior art in which the operating periods of time of both the counters are simply added so as to continue the opening of the fuel injection valve.