JPH0477142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fuel injection control method for an internal combustion engine.

Prior Art In an independent injection internal combustion engine in which fuel is injected independently and sequentially into each cylinder, fuel is normally injected during the intake stroke because good responsiveness can be obtained. In this case, the fuel injection amount is calculated in advance before starting fuel injection, and based on the calculated fuel injection amount, fuel injection is started, for example, at the top dead center of the intake stroke. When the fuel injection operation is started at a predetermined crank angle, for example at the top dead center of the intake stroke as described above, the fuel injection end timing changes depending on the engine speed and fuel injection amount, and the engine speed is high. When the fuel injection amount is large, the fuel injection operation continues even after the intake valve is closed. However, in order to obtain good response, it is preferable that all the injected fuel is supplied into the engine cylinders regardless of the engine operating state, so that the fuel injection action is completed well before the intake valve closes. Must. Therefore, if the fuel injection start timing is fixed at a predetermined crank angle as described above, depending on the operating conditions, it may not be possible to supply all the injected fuel into the engine cylinders, thus improving responsiveness. The problem is that it cannot be obtained.

As a countermeasure to this problem, Japanese Patent Laid-Open No. 148636/1983 discloses a fuel injection control method as shown in FIG.

Referring to FIG. 5, arrow A indicates the opening period of the intake valve, and the injection end crank angle B of the fuel injector is fixed in advance to a constant value that is earlier than the intake valve closing crank angle C by θ. There is. If the crank angle from top dead center TDC to fuel injection end crank angle B is φ and the engine speed N _rpn , then the fuel injection time τ _1nsec based on top dead center TDC is τ ₁ = 60000・φ/
It is expressed as (360・N).

When the fuel injection time is τ ₂ , the fuel injection start time τ ₃ is expressed as τ ₁ −τ ₂ .

In this control method, at top dead center TDC, τ ₁ ,
τ ₂ and τ ₃ are calculated, and when τ ₃ elapses from top dead center TDC, fuel injection from the fuel injection valve starts, and when the fuel injection time τ ₂ elapses and the crank angle reaches B, fuel injection ends. so that the fuel injection is always ended at the injection end crack angle B.

By the way, in this fuel injection control method, τ ₁ ,
The reference time for calculating τ ₂ and τ ₃ is the top dead center TDC, but considering the case where the fuel injection time τ ₂ becomes longer, it is necessary to advance the reference time as much as possible. For example, if the fuel injection time τ ₂ becomes longer and the fuel injection time start time becomes earlier than the top dead center TDC, the reference time must be earlier than the top dead center TDC.

However, if the time point (reference time) at which the fuel injection time τ ₂ is calculated is advanced in this way, if the fuel injection time τ ₂ is short, the time point at which the fuel injection time τ ₂ is calculated will be the fuel injection start time. Therefore, when the engine is in transient operation, a problem arises in that it is not possible to accurately inject the amount of fuel corresponding to the engine operating state.

Purpose of the Invention An object of the present invention is to provide a fuel injection control method for an internal combustion engine so as to ensure good responsiveness at all times and to accurately inject fuel in an amount corresponding to the engine operating state. It is in.

Configuration of the Invention The configuration of the present invention provides a fuel injection control method for an internal combustion engine in which fuel injection times are sequentially determined at predetermined timings and fuel is injected independently for each cylinder based on the fuel injection times. The fuel injection start timing for the next cylinder to be injected is set immediately after the start of fuel injection in the cylinder currently being injected so that the fuel injection in the cylinder to be injected is completed at the target crank angle during the intake stroke of the next cylinder to be injected. It is determined based on the fuel injection time determined during fuel injection, and is determined based on the fuel injection time determined during fuel injection immediately after the start of fuel injection of the cylinder currently being injected. The reason is that the fuel injection completion time is determined.

Embodiment Referring to FIG. 1, 1 is the engine body, 2 is the piston, 3 is the combustion chamber, 4 is the spark plug, 5 is the intake valve, and 6 is the engine body.
7 indicates an intake port, 7 indicates an exhaust valve, and 8 indicates an exhaust port, and the intake port 6 is connected to a surge tank 10 via a branch pipe 9. The surge tank 10 is connected to an air cleaner (not shown) via an intake duct 11 and an air flow meter 12, and a throttle valve 13 connected to an accelerator pedal is disposed within the intake duct 11. A fuel injection valve 14 is installed in each branch pipe 9, and this fuel injection valve 14
Fuel is injected from the intake port 6 into the corresponding intake port 6. Each fuel injection valve 14 is controlled by an electronic control unit 3
0, and the fuel injection valve 14 is controlled by the output signal of the electronic control unit 30.

The electronic control unit 30 consists of a digital computer, which is interconnected by a bidirectional bus 31 and includes a ROM (read-on memory) 32, a RAM (random access memory) 33, and a CPU (microprocessor) each having a known function. Setusa) 3
4, an input port 35 and an output port 36. Output port 36 is connected to drive circuits 37, 38, 3
It is connected to the corresponding fuel injection valve 14 via 9 and 40. The air flow meter 12 generates an output voltage proportional to the amount of intake air, and the air flow meter 12 is connected to the input port 35 via the AD converter 41. On the other hand, a water temperature sensor 14 is attached to the engine body 1 and generates an output voltage proportional to the engine cooling water temperature in response to the engine cooling water temperature.
Connected to 5. Furthermore, a distributor 15 is attached to the engine body 1, and the distributor 15 is equipped with a TDC sensor 16 that detects the intake top dead center of any one cylinder, and a TDC sensor 16 that detects the intake top dead center of any one cylinder. A crank angle sensor 17 that generates pulses is attached. these
TDC sensor 16 and crank angle sensor 17 are connected to input port 35. Further, an exhaust manifold 18 is connected to the exhaust port 8 , and an oxygen concentration detector 19 is inserted into the exhaust manifold 18 . The output voltage of the oxygen concentration detector 19 changes depending on whether excess oxygen exists in the exhaust gas, that is, whether the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is greater than the theoretical air-fuel ratio. . This oxygen concentration detector 19 is connected to the input port 35 via a comparator 43.

Next, the fuel injection control method according to the present invention will be explained with reference to FIGS. 2 to 4. First of all, referring to FIG. 4, section _T1 indicates the intake stroke of a certain cylinder, and section _T2 indicates the intake stroke of the cylinder in which fuel injection is to be performed next. Also, in Figure 4, M
indicates the timing of calculating the basic fuel injection amount, and it can be seen from FIG. 4 that the calculation of the basic fuel injection amount is performed at approximately constant time intervals. A base routine for calculating this basic fuel injection amount is shown in FIG. 2, and this base routine will first be explained.

Referring to FIG. 2, first, in step 50, the intake air amount Q and engine speed NE are calculated from the output signals of the air flow meter 12 and crank angle sensor 17, and then in step 51, the intake air amount Q per engine rotation is calculated. /Calculate NE. Next, in step 52, a basic fuel injection pulse width T is calculated from the calculated intake air amount Q/NE and a constant determined by the characteristics of the fuel injection valve used. Next, in step 53, the output signal of the water temperature sensor 14 is taken in, and in step 54, a fuel increase coefficient _K1 corresponding to the engine cooling water temperature is calculated. Next, in step 55, the correction coefficient _K2 calculated in the air-fuel ratio feedback routine (not shown) is read from the output signal of the oxygen concentration detector 19, and in step 56, the increase coefficient _K1 and the correction coefficient are read.
The final correction coefficient K for the basic fuel injection pulse width T is determined from _K2 . Next, in step 57, the invalid injection time t of the fuel injection valve 14 is determined, and the base routine is ended.

FIG. 3 shows an interrupt routine for controlling fuel injection operations. As will be described later, at the pre-calculated fuel injection time start timing and fuel injection end timing, an interrupt is performed and an injection interrupt routine shown in FIG. 3 is executed. At this time, it is first determined in step 60 whether or not it is time to end the fuel injection, and if it is the time to end the fuel injection, the process proceeds to step 61 and the fuel injection action from the fuel injection valve 14 is stopped. On the other hand, if it is not the fuel injection end time, the process advances to step 62 to start fuel injection from the fuel injection valve 14.
Fuel injection starts from. How the timing to start this fuel injection is determined will be described later. Referring to FIG. 4, the timing of the fuel injection start process is shown by S, and when the fuel injection start process is completed, the fuel injection action from the fuel injection valve 14 is started as shown by I in FIG. Next, in step 63, the latest basic fuel injection pulse width T, final correction coefficient K, and invalid injection time t calculated in the base routine immediately before the fuel injection start process are read, and then in step 64, the fuel injection time τ is calculated. Next, in step 65, the fuel injection end time is calculated from the fuel injection time τ, and this fuel injection end time is set. This fuel injection end time is set, for example, by setting a numerical value corresponding to the time until the fuel injection end time in a down counter. When the count value of the down counter reaches zero, an interrupt is performed as described above and the step is started. 61, the fuel injection action is stopped. Next, in step 66, the next fuel injection start timing is calculated as follows. That is, in order for all the fuel injected from the fuel injection valve 14 to be supplied into the combustion chamber 3, fuel injection must be stopped well before the intake valve 5 closes. The target crank angle at which this fuel injection should be stopped is predetermined, and therefore, in step 66, the fuel injection time τ determined in step 64 is adjusted so that the entire fuel injection action is completed by the time the target crank angle is reached. The next fuel injection start time is calculated. Next, in step 67, the fuel injection start timing is set for the cylinder to which fuel is to be injected next. The target crank angle determines the approximate timing at which fuel injection should be stopped, and the accurate fuel injection end timing is calculated from data such as the latest basic fuel injection pulse width T. In this way, since the latest data for calculating the fuel injection time τ is used, it is possible to inject an amount of fuel that corresponds to the operating state. Calculation of fuel injection time τ, fuel injection end time, and next fuel injection start time is as shown in F in Figure 4.
Therefore, it can be seen that these calculations are performed immediately after the start of fuel injection and during fuel injection.

As described above, in the present invention, in order to stop the fuel injection operation well before the intake valve closes, the next fuel injection start timing is set during the previous fuel injection operation. When the fuel injection action starts, the fuel injection is performed based on the fuel injection amount calculated based on the latest data, not the fuel injection amount calculated last time, so the fuel injection is performed based on the fuel injection amount calculated based on the latest data. fuel injection control can be performed.

Effects of the Invention The fuel injection start timing is controlled according to the operating condition of the engine so that all the fuel injected from the fuel injection valve is supplied into the engine combustion chamber, thereby ensuring good responsiveness of the engine to the fuel injection action. Furthermore, since the amount of fuel corresponding to the engine operating condition can be injected with high precision, an air-fuel mixture with an optimal air-fuel ratio is supplied into the combustion chamber, thus achieving stable combustion. Fuel consumption rate can be improved and exhaust emissions can be reduced.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of the internal combustion engine, Figure 2 is a flowchart for calculating the basic fuel injection amount, etc.
FIG. 3 is a flowchart for performing fuel injection control according to the present invention, FIG. 4 is a timing chart for fuel injection control according to the present invention, and FIG. 5 is a diagram for explaining a conventional fuel injection control method. . 3... Combustion chamber, 5... Intake valve, 6... Intake port, 14... Fuel injection valve, 30... Electronic control unit.

Claims (1)

[Claims] 1 Sequentially determine the fuel injection time at a predetermined timing,
In the fuel injection control method for an internal combustion engine, in which fuel is injected independently for each cylinder based on the fuel injection time, the fuel injection of the next cylinder to be injected is performed in the intake process of the next cylinder to be injected. The fuel injection start timing of the next cylinder to be injected is determined based on the fuel injection time determined immediately after the start of fuel injection of the currently injected cylinder and during fuel injection so that the fuel injection is completed at a target crank angle of The fuel for an internal combustion engine is determined based on the fuel injection time determined immediately after the start of fuel injection in the currently injected cylinder and during the fuel injection, and determines the fuel injection completion timing for the currently injected cylinder. Injection control method.