JPS6125930A - Control of fuel injection amount of internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the stability of idle revolution by sampling the number of engine revolution in the rate of several times per revolution of an engine and increasing and decreasing the fuel injection amount so as to be proportional to the difference between the weighted average value of the number of engine revolution obtained by a prescribed processing and the number of engine revolution. CONSTITUTION:During engine operation, each output of a crank-angle sensor 28 and a pressure sensor 10 is taken into a control circuit 30, and the fundamental fuel injection pulse width TP is calculated on the basis of the number of engine revolution NE and the suction-pipe pressure PM. On idling when an idle switch 6 is turned ON, the average value NEAVi weighted with the number of engine revolution at this time is calculated. The average value is obtained by weighting the average value of the number of engine revolution in the preceding time with the constant larger than 1 and weighting the number of engine revolution sampling-processed at this time with 1 and averaging the both values. Afterwards, the deviation between the number of engine revolution NE and the average NEAVi is obtained, and a fuel injection valve 16 is controlled by correcting the injection valve width TP by the correction coefficient calculated according to the deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a fuel injection amount of an internal combustion engine, and more particularly to a method of controlling a fuel injection amount of an internal combustion engine for stabilizing idle rotation.

[Conventional technology]

In a general internal combustion engine, the engine speed and engine load (intake pipe pressure or intake air amount per engine revolution) are detected, and the basic fuel injection amount is calculated based on the detected engine speed and engine load. Based on this basic fuel injection amount, the optimum amount of fuel is intermittently injected for each cylinder or group of cylinders, or intermittently injected to all cylinders at once. However, immediately after racing, engine undershoot may occur due to inertia or the like. For this reason, in a conventional internal combustion engine, as shown in Fig. 2 (1)
As shown in , the engine speed at a specific crank angle position for each engine revolution is determined, and the previous engine speed NEi-1 is subtracted from the current engine speed NEi to determine the amount of change Δ in the engine speed.
NF3 is determined and the fuel injection amount TAU is controlled according to the following formula to stabilize the idle.

TAU=TP-FNE ,,,,... (1)
Here, TP is the basic fuel injection amount determined by the engine speed and engine load, and FNE is the correction coefficient determined from FIG. 2 (3).

Therefore, according to this fuel injection amount control method, when the engine speed decreases and the engine speed change amount ΔNE becomes a negative value, the fuel injection amount is increased, and when the engine speed increases, the fuel injection amount increases. The amount of change ΔNB is controlled to be reduced to zero.

[Problem that the invention seeks to solve]

However, in the conventional fuel injection amount control method, the fuel injection amount is increased or decreased according to the amount of change ΔNE in the engine speed.

Therefore, when the engine speed is rapidly decreasing due to undershoot, the amount of fuel is increased, but after the engine speed has already fallen, the amount of change in engine speed ΔNB becomes small, so the amount of fuel is increased. The increase in the amount of fuel is also reduced, which weakens the force that increases engine rotation, causing the engine to stall due to inertia. Further, in the conventional fuel injection amount control method, the engine rotational speed is sampled once per engine rotation. However, since the period of fluctuations in engine rotation due to intake pulsation and the like is shorter than this sampling period, there is a problem in that accurate fluctuations in engine rotation cannot be detected and, on the contrary, hunting increases. In order to solve this problem, it is possible to shorten the sampling period, but simply shortening it will reduce the amount of change ΔNB when there is a large fluctuation at low frequencies, so it is effective when there is a large fluctuation at high frequencies. Hunting cannot be prevented when there are large fluctuations at low frequencies. In the case of group injection or independent injection, injection is performed several times per engine revolution, but as shown in A in Figure 2 (2), 360° CA before injection
Since the injection amount is corrected based on the amount of change ΔNE in between, it cannot be corrected based on the amount of change at the current time, and hunting cannot be sufficiently prevented.

[Means for solving problems]

In order to solve the above problems, the present invention samples the engine speed multiple times per engine revolution, weights the average value of the engine speed obtained last time, and The present invention is characterized in that the average value of the current engine speed is determined by giving less weight to the number, and the fuel injection amount is increased or decreased in proportion to the difference between the engine speed and the average value of the engine speed determined this time. .

[For production]

By calculating the weighted average value of the engine speed as described above, even if the engine speed fluctuates rapidly, the average value (if the engine speed fluctuates slowly, this average value changes approximately according to fluctuations in engine speed.

Therefore, the difference between the engine speed and the weighted average value of the engine speed found this time is a value proportional to the amplitude of the fluctuation in the engine speed just before the fuel injection timing, and An increased or decreased amount of fuel will be injected depending on the amplitude of the fluctuation.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain the effect that the idle rotation can always be stabilized regardless of whether the frequency of fluctuations in the engine speed is high or low.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 3 is a schematic diagram of an internal combustion engine equipped with a fuel injection control device according to an embodiment of the present invention. An intake temperature sensor 2 is installed downstream of an air cleaner (not shown) to detect the temperature of intake air and output an intake temperature signal. A throttle valve 4 is arranged downstream of the intake air temperature sensor, and is linked to the throttle valve 4 and turns on when the throttle valve is in the idle position (fully closed) to output an idle signal and when the throttle valve opens. An idle switch 6 that turns off is attached. A surge tank 8 is provided downstream of the throttle valve 4, and a pressure sensor 10 is attached to the surge tank 8 to detect the intake pipe pressure downstream of the throttle valve and output an intake pipe pressure signal. The surge tank 8 is communicated with a combustion chamber 14 of the engine via an intake manifold 12. A fuel injection valve 16 is attached to the intake manifold 12 for each cylinder. The combustion chamber 14 of the engine is communicated via an exhaust manifold with a catalytic converter (not shown) filled with a three-way catalyst. Further, a water temperature sensor 20 is attached to the engine block to detect the engine cooling water temperature and output a water temperature signal. A tip of a spark plug 22 projects into the combustion chamber 14 of the engine, and a distributor 24 is connected to the spark plug 22. The distributor 24 includes a cylinder discrimination sensor 26 and a crank angle sensor 2, each of which includes a pickup fixed to the distributor housing and a signal loaf fixed to the distributor shaft.
8 is provided.

The cylinder discrimination sensor 26 detects, for example, every intake top dead center of the first cylinder (
The crank angle sensor 28 outputs a crank angle signal to the control circuit 30, for example, every 3σCA). Further, the distributor 24 is connected to the igniter 32. Note that 34 is an O sensor that detects the residual acidity in the exhaust gas and outputs an air-fuel ratio signal.

As shown in FIG. 4, the control circuit 30 includes a central processing unit (C
PU) 36, read-only memory (ROM) 38, random access memory (RAM) 40, backup RAM (BU-RAM) 42, input/output port (Ilo) 44
, an analog/digital converter (ADC) 46, and buses such as a data bus and a control bus that connect these. A cylinder discrimination signal, a crank angle signal, an air-fuel ratio signal, and an idle signal output from the idle switch 6 are input to the l1044, and a fuel injection signal and a fuel injection signal that control the opening/closing time of the fuel injection valve 16 via a drive circuit are input. An ignition signal that controls the on/off time of the igniter 32 is output. Further, an intake pipe pressure signal, an intake air temperature signal, and a water temperature signal are input to the ADC 46 and converted into digital signals.

The above crank angle signal is passed through a waveform shaping circuit to l104.
4, and a digital signal representing the engine speed is formed from this crank angle signal. The cylinder discrimination signal is input to l1044 and converted into a digital signal in the same manner as above. This cylinder discrimination signal, together with the crank angle signal, serves as an interrupt request signal for basic fuel injection pulse width calculation.
It is used to form fuel injection start signals, cylinder discrimination signals, etc.

The idle signal from the idle switch 6 is
is sent to a predetermined bit position and temporarily stored.

In addition, a well-known fuel injection control circuit including a presettable counter, a register, etc. is provided in the l1044, and forms a fuel injection signal having the pulse width from binary data regarding the injection pulse width sent from the CPU 36. Then, this fuel injection signal is input to the fuel injection valve 16 to energize the injection valve. As a result, an amount of fuel corresponding to the pulse width of the fuel injection signal is injected in synchronization with the crank angle.

Next, referring to FIG. 1, the pulse width T A' of the fuel injection signal
A routine for calculating U will be explained. First, step 1
At step 00, the engine speed performance and intake pipe pressure PM are taken in, and at step 102, a basic fuel injection pulse width TP is calculated based on the engine speed NB and intake pipe pressure PM. In the next step 104, it is determined whether the engine is idling by determining whether the idle switch is on based on the idle signal. If the idle switch is on, it is determined in step 106 whether a time corresponding to the sampling period (for example, 1 to 32 mesc) has elapsed, and if an affirmative determination is made in step 106, the engine speed is determined based on the following formula. A weighted average value NEAVi is calculated.

=NEAVt-1+(NEiNEAVi-1)/'K
... ... (1) However, NEAVi is the weighted average value of the current engine speed, NEAVi, -1 is the weighted average value of the previous engine speed, NEi is the engine speed sampled this time, K is a constant greater than 2.

As can be understood from the above equation (1), the current average engine speed NBAVi is determined by adding a weight of -1 to the previous engine speed average NEAVi-1 for the engine sampled this time. The weighting is averaged by assigning a weight of 1 to the rotational speed NEi.

Note that the sampling period of the engine rotational speed is preferably a time equal to or less than the period of synchronization of fluctuations in the engine rotational speed, since weighting accurately determines fluctuations in the engine rotational speed using an average value.

In the next step 110, the weighted average value 88 people Vi of the current engine speed calculated in step 108 is subtracted from the engine speed NK taken in step 100 to obtain the deviation ΔNB. The correction coefficient FNE is calculated by the interpolation method from the map shown in FIG. This correction coefficient FNB becomes 1 when the deviation ΔNFi is 0, becomes a positive value less than 1 when the deviation ΔNE is positive, that is, when the engine speed is greater than the average value NEAVi, and becomes a positive value less than 1 when the deviation ΔNE is negative. When f, that is, the engine speed NE is smaller than the average value NEAVi, it becomes a positive value exceeding 1. Then, in step 114, the basic fuel injection pulse width TP is multiplied by the correction coefficient FNB to calculate the fuel injection pulse width TAU. The fuel injection pulse width TAU determined in this way is used in an injection routine (not shown) that injects fuel for each cylinder, for each group, or for all cylinders simultaneously.

Engine rotation speed NB and average value NE A Vi when the fuel injection pulse width is determined as described above and the fuel injection amount of the 6-cylinder engine group injection is controlled.

FIG. 6 shows changes in fuel injection pulse width TAU.

In the above, an example was explained in which the present invention is applied to an engine in which the basic fuel injection pulse width is determined based on the engine speed and the intake pipe pressure. It can also be applied to engines for which the basic fuel injection pulse width is determined. Furthermore, although the example in which the engine speed is sampled at predetermined intervals has been described above, it is also possible to sample the engine speed at predetermined crank angles (for example, 30'CA) and obtain a weighted average value. ,').

Furthermore, since the weighted average value changes approximately according to the fluctuation of the engine speed when the engine speed fluctuates at a low frequency, the weighted average value is calculated based on the following transfer function G (s). Alternatively, a value obtained by processing the engine speed with a characteristic that reduces attenuation of low frequency components of the engine speed and increases attenuation of high frequency components may be used as the weighted average value.

G (s) =□ ・・・・・・・・・・・・・・・
(2) 1-)-T8 However, T is the time constant of the first-order lag, and S is the complex frequency.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a fuel injection pulse width calculation routine according to an embodiment of the present invention, and FIG. 2 (1), (2), (
3) is a diagram for explaining the conventional fuel injection amount control method, FIG. 3 is a schematic diagram of an engine equipped with a fuel injection device to which the present invention is applied, and FIG. 4 is a diagram showing the control circuit of FIG. A block diagram showing details, Figure 5 is a diagram showing a map of correction coefficients,
FIG. 6 is a diagram showing changes in engine speed, fuel injection pulse width, etc. in this embodiment. 6... Idle switch, 10... Pressure sensor, 1
6...Fuel injection valve.

Claims (1)

[Claims] (1) The engine speed is sampled multiple times per engine revolution, and the average value of the engine speed obtained last time is weighted heavily, and the engine speed sampled this time is weighted lightly. 1. A fuel injection amount control method for an internal combustion engine, characterized in that the average value of the engine rotation speed is determined, and the fuel injection amount is increased or decreased in proportion to the difference between the engine rotation speed and the currently determined average value of the engine rotation speed.