JPH01104933A - Fuel injection quantity control for internal combustion engine - Google Patents

Abstract

PURPOSE:To carry out the proper asynchronous injection by varying the injection starting time according to the engine revolution speed in the execution of the fuel injection in the case when the difference between the digital value of the intake pipe pressure at this time which is obtained for each prescribed crank angle and the value in the preceding time exceeds a prescribed value. CONSTITUTION:When the asynchronous injection is executed during acceleration, etc., a control circuit 44 executes the A/D conversion of the intake pipe pressure detected by a pressure sensor 6 for each prescribed crank angle. The asynchronous injection angle for the obtained engine revolution speed is obtained from the output of a revolution angle sensor 48, and when the asynchronous injection angle accords with the crank angle at this time, the digital value of the intake pipe pressure obtained in the preceding time is subtracted from the digital value of the intake pipe pressure obtained at this time, and the difference is obtained. Then, it is judged if the difference exceeds a prescribed value or not, and acceleration state is judged. When the acceleration state is judged, the asynchronous fuel injection time is calculated, and the asynchronous fuel injection is started by a fuel injection valve 24.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection amount control method for an internal combustion engine, and particularly relates to a synchronous injection in which fuel is injected at a predetermined crank angle related to the intake stroke, and a synchronous injection during acceleration. The present invention relates to a fuel injection amount control method for an internal combustion engine that performs asynchronous injection in which fuel is injected independently.

[Conventional technology]

Conventionally, a fuel injection valve is provided for each cylinder so that it protrudes into the intake manifold, and a microcomputer processes signals input from various sensors to determine the engine operating state, and injects the amount of fuel according to the operating state. A method of injecting fuel is known.

In this fuel injection method, synchronous injection in which fuel is injected simultaneously to all cylinders or to each specific cylinder at every predetermined crank angle related to the intake stroke, and asynchronous injection in which fuel is injected during acceleration regardless of synchronous injection are performed. There is. In internal combustion engines, where the basic fuel injection time is determined by intake pipe pressure and engine rotation speed, a pressure sensor is installed inside the intake pipe, and the pressure sensor output is processed with a filter with a time constant that can remove engine pulsation components. The filter output is digitally converted, and the difference ΔPM is obtained by subtracting the previously obtained digital value PMO of the intake pipe pressure from the digital value PM of the intake pipe pressure obtained this time.
When the acceleration exceeds a predetermined acceleration determination level, it is determined that the engine is in an acceleration state, and fuel is injected (asynchronous injection) at this point (FIG. 3 of Japanese Patent Application Laid-Open No. 59-90728).

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, since the digital value of the intake pipe pressure is taken in at predetermined intervals, as shown in FIG.
As shown in the figure, at a certain engine rotation speed, digital values can be captured without being affected by engine pulsation, but as the engine rotation speed increases, the period of engine pulsation becomes shorter, so the peaks and troughs of the pulsation are The digital value will be imported with
As shown by the two-dot chain line in FIG. 10 (2), depending on the engine rotational speed, the pulsation component greatly influences the intake pipe pressure, and the difference ΔPM in the digital value of the intake pipe pressure fluctuates due to the pulsation component, leading to erroneous determination of the acceleration state. Problems arise in that asynchronous fuel injection is performed even in a steady operating state, or that asynchronous fuel injection is performed at an unnecessary timing during acceleration. In order to solve this problem, a predetermined crank angle (180° in the case of 4 cylinders)
It is conceivable to take in the digital value of the intake pipe pressure for each CA). By doing this, the phase of the engine pulsation and the acquisition of the digital value will match, so even if the engine rotation speed changes, the pulsation will not occur, as shown by the dashed line in Fig. 10 (2). The acceleration state can be determined without being influenced by the components.

However, while the flight time of fuel is approximately constant regardless of the engine rotation speed, as the engine rotation speed increases, the time required to rotate the crank at a given crank angle becomes shorter.
As shown in FIG. 10 (1), as the engine speed increases, the timing of asynchronous injection is delayed and the injected fuel is no longer sucked into the cylinder, resulting in a lean spike at the beginning of acceleration.

The present invention has been made to solve the above-mentioned problems, and provides a fuel injection amount control method for an internal combustion engine that can start asynchronous fuel injection at an optimal timing in consideration of the flight time of the injected fuel. The purpose is to

[Means for solving problems]

In order to achieve the above object, the present invention obtains a digital value of intake pipe pressure at each predetermined crank angle, subtracts the previously obtained digital value from the currently obtained digital value to obtain a difference, and the difference is determined by the presently obtained digital value. In a fuel injection amount control method for an internal combustion engine in which fuel is injected when the fuel exceeds a predetermined value determined by a function of a digital value, the timing at which the fuel injection is started is changed according to the engine rotation speed. Features.

[Effect]

According to the present invention, the digital value of the intake pipe pressure is determined at every predetermined crank angle, and the difference ΔPM is determined by subtracting the previously determined digital value PM'0 from the currently determined digital value PM. This difference ΔPM is compared with a predetermined value f (PM) determined by the function of the digital value PM obtained this time, and when the difference ΔPM exceeds the predetermined value f (PM), it is determined that the acceleration state is occurring and the asynchronous fuel is activated. Injected. Here, if the difference ΔPM changes due to the influence of the engine pulsation component, the predetermined value f(P
Since M ) is determined as a function of the digital value of the intake pipe pressure, the predetermined value f (PM) is changed so that the engine pulsation component does not affect the erroneous determination of acceleration detection. Therefore,
If the difference ΔPM becomes large due to the influence of the engine pulsation component, the predetermined value f
(PM) also increases, and the difference Δ is due to the influence of engine pulsation components.
If PM becomes smaller, the predetermined value f (PM) also becomes smaller, and since the predetermined value f (PM) is changed according to the intake pipe pressure, the difference ΔPM of the digital values becomes the predetermined value f (
PM), it is possible to judge the acceleration state without being influenced by the engine pulsation component.

Furthermore, the asynchronous fuel injection start timing is changed depending on the engine rotation speed. Here, if the fuel injection start timing is made earlier as the engine speed increases, asynchronous fuel injection can be executed at the optimal timing, thereby preventing lean spikes and improving acceleration response. can.

[Effects of the Invention] As explained above, according to the present invention, since the start timing of asynchronous fuel injection is changed according to the engine rotation speed,
Asynchronous fuel injection can be performed at optimal timing, thereby preventing lean spikes and improving acceleration response.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 schematically shows a 4-cylinder 4-samo engine equipped with a fuel injection amount control device to which the present invention is applicable.

This engine is controlled by a 1-chip 8-bit microcomputer 44, and a throttle valve 8 is arranged downstream of an air cleaner (not shown), and a surge tank 12 is arranged downstream of the throttle valve 8. It is provided. A semiconductor pressure sensor 6 is attached to this surge tank 12 . The output end of this pressure sensor 6 has a small time constant (for example, 1-10 m5ec) for removing the pulsating component of the intake pipe pressure and a high-response CR.
It is connected to a filter (FIG. 3) composed of filters and the like. This time constant is determined through experiments to a value that can remove some pulsation components without impairing acceleration response. Note that this filter may be built into the pressure sensor. Further, a bypass passage 14 is provided so as to bypass the throttle valve 8 and communicate the upstream side of the throttle valve with the surge tank 12 on the downstream side of the throttle valve.

An I5C (idle speed control) valve 16B whose opening degree is adjusted by a pulse motor 16Δ having a four-pole stator is attached to this bypass path 14. The surge tank 12 is connected to the intake manifold 18
and communicates with the combustion chamber of the engine 20 via an intake port 22.

A fuel injection valve 24 is attached to each cylinder so as to protrude into the intake manifold IB.

The combustion chamber of the engine 20 is communicated via an exhaust port 26 and an exhaust manifold 28 to a catalyst device (not shown) filled with a three-way catalyst. An 02 sensor 30 is attached to the exhaust manifold 28 and outputs a signal that is inverted from the stoichiometric air-fuel ratio. A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate through the engine block 32 and protrude into the water jacket. This cooling water temperature sensor 34
detects the engine cooling water temperature and outputs a water temperature signal, which represents the engine temperature. Note that the engine oil temperature may be detected to represent the engine temperature.

A spark plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and protrude into the combustion chamber. This spark plug 38 is connected to a microcomputer 44 via a distributor 40 and an igniter 42. This distributor 40
Inside, there is a cylinder discrimination sensor 4, each consisting of a signal loaf fixed to the distributor shaft and a pickup fixed to the dis) IJ computer housing.
6 and a rotation angle sensor 48 are attached.

The cylinder discrimination sensor 46 outputs a cylinder discrimination signal consisting of a pulse train generated every 720° CA, for example, and the rotation angle sensor 48 outputs an engine rotation speed signal consisting of a pulse train generated every 30° CA, for example.

As shown in FIG. 3, the microcomputer 44 includes a microprocessing unit (MPU) 60, a read-only memory (ROM) 62, and a random access memory.
Memory (RAM) 64, backup RAM (BU-R)
AM) 66, an output capotro 8, an input port door 0, an output port door 2, 74, 76, and a bus 75 such as a data bus or a control bus that connects these. The input/output capotro 8 has analog-digital (A
/D) The converter 78 and the multiplexer 80 are connected in sequence. The pressure sensor 6 is connected to the multiplexer 80 via a filter 7 and a buffer 82 which are composed of a resistor R and a capacitor C, and the cooling water temperature sensor 34 is also connected via a buffer 84 . The MPU 60 controls the multiplexer 80 and the A/D converter 78 to sequentially convert the pressure sensor 6 output and the coolant temperature sensor 34 output input via the filter 7 into digital signals and store them in the RAM 64. Therefore, multiplexer 80
, the A/D converter 78, the MPU 60, and the like act as sampling means for sampling the pressure sensor output at predetermined time intervals. The input port door 0 is connected to the 02 sensor 30 via a comparator 88 and a buffer 86, and also to the cylinder discrimination sensor 46 and rotation angle sensor 48 via a waveform shaping circuit 90. The output port door 2 is connected to the igniter 42 via a drive circuit 92, the output port door 4 is connected to the fuel injection valve 24 via a drive circuit 94 with a down counter, and the output port door 6 is connected to the fuel injection valve 24 via a drive circuit 96. It is connected to the pulse motor 16A of the ISC valve. Note that 98 is a clock and 99 is a counter. The ROM 62 stores in advance a control routine program, etc., which will be explained below.

FIG. 1 shows a routine for determining the asynchronous fuel injection start timing of this embodiment. This routine is executed at every predetermined crank angle (for example, every 30° CA). First, in step 140, the current crank angle CCRNK is detected by counting the pulses of the engine rotational speed signal based on the cylinder discrimination signal. Next step 142
Now, the engine rotation speed NE is calculated from the pulse interval of the engine rotation speed signal. In step 144, FIG.
), the asynchronous injection angle CINJ for the current engine speed NE is calculated.

The non-synchronized injection angle CINJ is set at 60° CA ATDC (after top dead center) below 1000 rpm, and is advanced as the engine rotation speed increases to 30° CA ATDC.
60°CA BTDC (before top dead center) at 00rpm or more
It is determined that it will become.

Note that the asynchronous injection angle CI N J may be changed stepwise as described above, or may be changed continuously as shown in FIG. 4(2). In the next step 146, it is determined whether a predetermined crank angle (for example, 180° CA) has elapsed since the previous process, and if so, step 148
Asynchronous injection processing is performed at

FIG. 5 shows details of the asynchronous injection process in step 148. First, in step 100, the intake pipe pressure is
After starting A/D conversion and executing other processing such as starting A/D conversion of other signals in the next step 102, step 1
In step 04, it is determined whether the A/D conversion of the intake pipe pressure has been completed by determining whether or not the A/D conversion end signal is manually input from the A/D converter 78. Since step 148 is executed at every predetermined crank angle, A/
D conversion is also performed at every predetermined crank angle (for example, 180° CA). When it is determined that the A/D conversion has been completed, the current crank angle CCRN is determined in step 105.
It is determined whether or not K and the asynchronous injection angle CINJ match, and if they match, in step 106, the digital value PMO of the intake pipe pressure obtained last time is subtracted from the digital value PM of the intake pipe pressure obtained this time. Then, the difference ΔPM between the digital values of intake pipe pressure is determined. In the next step 108, it is determined whether or not the vehicle is in an acceleration state by determining whether the difference ΔPM between the digital values exceeds a predetermined value αPM. However, α is a constant.

When it is determined that the acceleration state is ΔPM>αPM, the asynchronous fuel injection time TAUASY is calculated in accordance with the following formula in step 110.

T A U A S Y = (Ao + Bo
・ΔPM) ・C・・・[1] However, Ao SBo is a constant, and C is a magnification determined as shown in FIG. This magnification C is determined to increase as the engine rotation speed increases.

Note that the magnification C may be constant.

Then, in step 112, an asynchronous fuel injection start process is executed.

FIG. 7 shows the details of step 112. In step 120, the injector boat connected to the fuel injection valve (injector) is turned on and the fuel injection valve is opened, and then in step 122, the injector boat connected to the fuel injection valve (injector) is turned on and the fuel injection valve is opened. The closing time of the fuel injection valve is calculated by adding the fuel injection time TAUASY. Then, in step 124, the fuel injection valve closing time is set in the conveyor register. As a result, at the time set in the conveyor register, the fuel injection valve is closed and the asynchronous fuel injection is terminated. Here, since the flight time of the fuel is constant, by advancing the fuel injection start timing as the engine rotational speed increases as described above, the fuel is injected at an appropriate timing and the acceleration response is improved.

Next, another example of the asynchronous processing in step 148 will be explained with reference to FIG. Note that in FIG. 8, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and explanations thereof will be omitted. When it is determined in step 108 that the acceleration state is present, in step 114 the previously calculated difference ΔPMO is subtracted from the currently calculated difference ΔPM to calculate the rate of change Δ'' PM of the difference. In step 116, the rate of change Δ' PM is calculated. It is determined whether acceleration is in the initial stage by determining whether or not exceeds a predetermined value β.Here, the function that satisfies the digital value of the intake pipe pressure during acceleration is approximately a cubic function, and this cubic Since the second-order differential value (Δ" PM) becomes a positive value in the downwardly convex portion of the function, it is possible to determine whether acceleration is in the initial stage by determining Δ2 PM>β. When it is determined in step 116 that it is the beginning of acceleration, the asynchronous fuel injection time TAUASY is calculated in step 118 according to the following equation.

TAUASY= (A, +B+ ・Δ' PM)
・C...(2) However, A, , B, are constants, and C is the same magnification as above.

Then, in step 112, asynchronous fuel injection start processing is performed in the same manner as described above.

Digital value P of intake pipe pressure when controlled as above
Figure 9 shows the changes in M, ΔPM, and Δ'' PM.As mentioned above, since asynchronous fuel injection is executed when ΔPM>αPM and Δ''PM>β, Asynchronous fuel injection is performed, and the effect is that rich spikes in the latter stages of acceleration, which are caused by the filter output being behind the actual intake pipe pressure due to filter processing, can be prevented.

In the above, an example has been described in which the asynchronous fuel injection start time is changed according to the engine rotation speed by A/D conversion at every predetermined crank angle (for example, 180" CA).
As shown in Fig. 1 and Fig. 12, the asynchronous fuel injection start timing may be changed by A/D converting each crank angle CINJ, which changes depending on the engine speed, and determining the asynchronous condition. good. Note that Figure 12 is the first
This shows details of step 148 in FIG.
In the figures and FIG. 12, parts corresponding to those in FIGS. 1 and 4 are given the same reference numerals, and explanations thereof will be omitted.

In the above embodiment, an example was explained in which the digital value of the intake pipe pressure is obtained by performing A/D conversion at every predetermined crank angle. The digital value of the intake pipe pressure may be determined for each predetermined crank angle by taking in the digital value for each angle.

In addition, the asynchronous fuel injection time is the digital value P of the intake pipe pressure.
With M as a parameter (A2 + 82 P M)・
It may be defined as C.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a routine for changing the asynchronous fuel injection start timing according to an embodiment of the present invention, FIG. 2 is a schematic diagram of an internal combustion engine equipped with a fuel injection amount control device to which the present invention is applicable, and FIG. is a block diagram showing details of the control circuit in FIG. 2, FIGS. 4 (1) and (2) are diagrams showing examples of asynchronous injection angles, and FIG. 5 is a flow chart showing details of step 14.8.
FIG. 6 is a diagram showing the magnification C, FIG. 7 is a flowchart showing details of step 112, FIG. 8 is a flowchart showing another example of the asynchronous fuel injection time calculation routine, and FIG. 9 is a diagram showing the intake pipe pressure, Δ
PM, Δ” Line diagram showing changes in PM, Figure 10 (1) is a diagram explaining injection delay, Figure 10 (2) is a diagram explaining the influence of pulsation, Figures 11 and 12 is a flowchart showing another routine for changing the asynchronous fuel injection start timing. 6... Pressure sensor, 24... Fuel injection valve.

Claims (1)

[Claims] (1) Calculate the digital value of intake pipe pressure at each predetermined crank angle, subtract the previously calculated digital value from the currently calculated digital value to determine the difference, and determine the difference as a function of the currently calculated digital value. A fuel injection amount control method for an internal combustion engine in which fuel injection amount is injected when the fuel exceeds a predetermined value, characterized in that the timing at which the fuel injection is started is varied according to the engine rotation speed. Volume control method.