JPH0454055B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection control device for an internal combustion engine.

Conventionally, for example, in order to prevent misfires during vehicle deceleration, a minimum fuel injection amount that regulates the lower limit of the fuel injection amount is set in advance to prevent the fuel injection amount from becoming less than the above-mentioned minimum fuel injection amount. However, when decelerating slowly with the brake pedal released, if the fuel injection amount reaches the minimum fuel injection amount, the mixture supplied to the engine cylinder becomes too lean, causing torque fluctuations.
As a result, there is a problem that vehicle drivability deteriorates. On the other hand, if the minimum fuel injection amount is increased in order to solve this problem, the engine idling speed will increase, resulting in a worsening of the fuel consumption rate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel injection control device that increases the minimum fuel injection amount only during deceleration driving of a vehicle where torque fluctuations are likely to occur, thereby ensuring good vehicle drivability without deteriorating fuel consumption rate. .

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, 1 is the engine body, 2 is the cylinder block, 3 is the piston that reciprocates within the cylinder block 2, and 4 is the cylinder block 2.
Cylinder head fixed on top, 5 is piston 3
and a combustion chamber formed between the cylinder head 4, 6 an ignition plug disposed within the combustion chamber 5, 7 an intake port, 8 an intake valve, 9 an exhaust port, and 10 an exhaust valve. The intake port 7 is connected to a common surge tank 12 via a branch pipe 11, while the exhaust port 9 is connected to an exhaust manifold 13. Each branch pipe 11 is provided with a fuel injection valve 15 that is controlled by an output signal from an electronic control unit 14, and from these fuel injection valves 15, a corresponding intake port 7 is provided.
Fuel is injected towards. The surge tank 12 is connected to the atmosphere via an intake pipe 16, an air flow meter 17, and an air cleaner (not shown). A throttle valve 18 is disposed within the intake pipe 16, and the throttle valve 18 is connected to an accelerator pedal provided in the driver's cab of the vehicle. A rotation speed sensor 20 for detecting the rotation speed of the crankshaft is attached to a dist viewer 19 attached to the engine body 1, and this rotation speed sensor 20 is connected to the electronic control unit 14. Further, a brake switch 22 is provided which operates in conjunction with a brake pedal 21 provided in the vehicle cab, and this switch 22 is connected to an input terminal of the electronic control unit 14.
Further, a vehicle speed sensor 23 is connected to an input terminal of the electronic control unit 14.

FIG. 2 shows the electronic control unit 14. Referring to FIG. 2, the electronic control unit 14 is composed of a digital computer, in which a microprocessor (MPU) 30 for performing various calculation processes, a random access memory (RAM) 31, control programs, calculation constants, etc. are stored in advance. A read-only memory (ROM) 32, an input port 33, and an output port 34 are connected to each other via a bidirectional bus 35. Furthermore, the electronic control unit 14
A clock generator 36 is provided therein for generating various clock signals. As shown in FIG. 2, the air flow meter 17 is connected to the buffer 37 and
connected to input port 33 via converter 38;
The rotation speed sensor 20, vehicle speed sensor 23, and brake switch 22 have corresponding buffers 39, 40, and 41.
It is connected to the input port 33 via. The air flow meter 17 generates an output voltage proportional to the amount of intake air, and this voltage is converted into a corresponding binary number by the AD converter 38, and this binary number is input to the MPU 30 via the input port 33 and the bus 35. . The rotational speed sensor 20 and the vehicle speed sensor 23 generate pulses proportional to the engine rotational speed and the vehicle speed, respectively, and these pulses are input to the MPU 30 via an input port 33 and a bus 35. MPU3
Within 0, the engine rotation speed and vehicle speed are calculated based on the output pulse signals of the rotation speed sensor 20 and vehicle speed sensor 23. The brake switch 22 is turned on when the brake pedal 21 is depressed, and the output signal of the brake switch 22 is input to the MPU 30 via an input port 33 and a bus 35.

The output port 34 is provided to output data for operating the fuel injection valve 15, and the binary data is sent to the MPU 3.
0 via bus 35. Each output terminal of the output port 34 is connected to a corresponding input terminal of the down counter 42. This down counter 42 is provided to convert the binary data written from the MPU 30 into the corresponding time length.
starts a down counter of the data sent from the output port 34 in response to a clock signal from the clock generator 36, and when the count value reaches 0, the count is completed and a count completion signal is generated at the output terminal. The reset input terminal R of the S-R flip-flop 43 is connected to the output terminal of the down counter 42, and the set input terminal S of the S-R flip-flop 43 is connected to the clock generator 36. This S-R flip-flop 43 is connected to the clock generator 3.
It is set simultaneously with the start of down counting by the clock signal No. 6, and reset by the count completion signal of the down counter 42 when the down counting is completed. Therefore, the output terminal Q of the S-R flip-flop 43 is at a high level while the down count is being performed. The output terminal Q of the S-R flip-flop 43 is connected to the fuel injection valve 15 via a power amplification circuit 44, and therefore the fuel injection valve 15
is while the down counter is counting down.
It can be seen that it is energized.

Next, the operation of the fuel injection control device according to the present invention will be explained with reference to FIG. Referring to FIG. 3, first, in step 50, the fuel injection time τ is calculated from the output signal of the air flow meter 17 and the output signal of the rotational speed sensor 20. Next, in step 51, it is determined whether the current vehicle speed V is slower than the vehicle speed _V0 in the previous processing cycle, that is, whether or not the vehicle is currently decelerating. If the vehicle is not decelerating, the process proceeds to step 52, where the fuel is Constant minimum fuel injection time τ _nio with injection time τ stored in advance
It is determined whether or not it is larger than L. step 52
If it is determined that τ is larger than τ _nio L, the process proceeds to step 53, where fuel injection processing (fuel is injected from the fuel injection valve 15 for a fuel injection time τ), while in step 52, when τ If _it is determined that τ _nio L is not larger than
Proceed to 53. On the other hand, when it is determined in step 51 that the vehicle is decelerating, the process proceeds to step 55, where it is determined whether or not the brake switch 22 is on, that is, whether or not the brake pedal 21 is depressed. is on, proceed to step 52. On the other hand, if it is determined in step 55 that the brake switch 22 is not on, that is, if the brake pedal 21 is released, the process proceeds to step 56, where it is determined whether the vehicle speed V is greater than a pre-stored constant vehicle speed H. It is determined. If it is determined in step 56 that the vehicle speed V is not greater than the vehicle speed H, then in step 57 the vehicle speed V is set to a pre-stored constant vehicle speed L (however, L
It is determined whether or not it is smaller than <H). In step 56, it is determined that V>H, or in step 56,
When it is determined in step 57 that V<L, the process proceeds to step 52, and when it is determined in step 57 that V<L is not satisfied, the process proceeds to step 58. Therefore step 58
It is during deceleration driving that the brake pedal 2
1 is open, and the vehicle speed V is L<V<H.
is within the range of In step 58, it is determined whether the fuel injection time τ is longer than a pre-stored constant minimum fuel injection time τ _nio H (where τ _nio H>τ _nio L). In step 58, τ>τ _nio
If it is determined to be H, proceed to step 53,
On the other hand, if it is determined in step 58 that τ>τ _nio H, then τ _nio H is set in τ in step 59, and the process then proceeds to step 53.

FIG. 4 shows the vehicle speed V and the minimum fuel injection time τ _nio . Note that H and L of τ _nio in FIG. 4 correspond to τ _nio H and τ _nio L in FIG. 3, respectively, and H and L of V in FIG. 4 correspond to H and L in FIG. 3. As shown in FIG. 4, when the vehicle speed V decreases with time T, that is, when the brake pedal 21 is depressed during deceleration driving, the minimum fuel injection time τ _nio is maintained at τ _nio L, as shown by the solid line. be done. In this way, when the brake pedal 21 is depressed, the rotation of the engine is restrained by the braking force based on the depression action of the brake pedal 21, so torque fluctuations are suppressed, and in this way, even if the fuel injection amount is small, the engine Drivability does not deteriorate. On the other hand, when the brake pedal 21 is released when the vehicle is decelerating, the fuel injection time τ increases to the minimum fuel injection time τ _{nio H as shown by the broken line in FIG. 4 when the vehicle speed V is in the range L<V<} H. It will be done. Therefore, when the vehicle speed V gradually decreases, the fuel injection amount is increased, so that even if the brake pedal 21 is released, torque fluctuations are suppressed, thus ensuring good vehicle drivability. can.

As described above, according to the present invention, the reference minimum fuel injection time τ _nio L can be set to a low value, so the idling speed does not increase, thus maintaining a good fuel consumption rate. can do. In addition, the minimum fuel injection time is low τ _nio L
If it is fixed at , when the vehicle decelerates, the fuel injection time becomes τ _nio L and the air-fuel mixture becomes too lean, and if the brake pedal is not depressed at this time, the engine speed decreases, and in other words, the vehicle speed decreases. Vehicle speed V is L<V
When the torque falls within the range <H, torque fluctuations tend to occur. According to the present invention, in such a case, the minimum fuel injection time is increased to τ _nio H, so that torque fluctuations are suppressed and good vehicle drivability can be ensured. Furthermore, during deceleration of the vehicle, even if the vehicle speed V drops to a range of L<V<H, torque fluctuations are suppressed as long as the brake pedal is depressed. Therefore, in this case, the minimum fuel injection time is set to a low value τ _nio L to improve the fuel consumption rate.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an internal combustion engine according to the present invention;
Fig. 2 is a circuit diagram of the electronic control unit shown in Fig. 1, Fig. 3 is a flowchart for explaining the operation of the fuel injection control device, and Fig. 4 is a diagram showing the vehicle speed V and the minimum fuel injection time τ _nio . be. 7...Intake port, 8...Intake valve, 12...Surge tank, 14...Electronic control unit, 15...
...Fuel injection valve, 17...Air flow meter, 18
... Throttle valve, 21 ... Brake pedal, 2
2...brake switch, 23...vehicle speed sensor.

Claims (1)

[Claims] 1. In a fuel injection control device that presets a minimum fuel injection amount that regulates the lower limit of the fuel injection amount and prevents the fuel injection amount from becoming less than the minimum fuel injection amount, a vehicle speed sensor that detects vehicle speed;
The vehicle is equipped with an electronic control unit that calculates the vehicle speed from the output signal of the vehicle speed sensor, and a brake switch that detects the depression of the brake pedal, when the brake pedal is in a released state and the vehicle speed is within a predetermined speed range. A fuel injection control device for an internal combustion engine, wherein the minimum fuel injection amount is increased to a predetermined setting value.