JPH01294929A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve exhaust gas emission characteristics and operability, by a method wherein an air-fuel ratio is changed during establishment of a given condition, and based on the change amount, a correction constant by means of which a delay due to an amount of fuel adhered on a wall surface is corrected is computed, and during computation, a running state during the starting of running is maintained. CONSTITUTION:During running of an engine, a fuel amount computing means (c) corrects a target fuel amount, set based on a running state, based on reverse characteristics to transmission characteristics when an injection fuel amount of a fuel feed means (g) is a amount of fuel coming in a cylinder, and computes an actual injection fuel amount. During establishment of a given condition, an air-fuel ratio is changed by means of a correction constant computing means (d), and based on the change amount, a constant by means of which a fuel amount is corrected is computed. In this case, a running state correction means (e) stores a running state during the starting of computation and corrects a running state during computation so as to maintain the running state. From the correction constant and a fuel amount determined according to reverse characteristics, an injection fuel amount is decided by a deciding means (f).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection control device for internal combustion engines such as automobiles. The present invention relates to a device for determining an injection amount.

(Prior art) In general, deviations in the air-fuel ratio from the target air-fuel ratio during engine acceleration/deceleration are mostly caused by quantitative changes in adhering fuel and floating fuel adhering to the intake system manifold and intake boat. The amount of adhering and floating fuel varies greatly depending on the operating conditions of the engine. Further, the amount of adhering and floating fuel does not change stepwise in response to changes in operating conditions, but changes with a certain delay, and the time constant of this delay is also not constant. Furthermore, changes in the amount of adhering and floating fuel vary not only depending on changes in operating conditions, but also depending on the magnitude of the difference between the amount at that point in time and the amount in the equilibrium state (steady state). In other words, the dynamic characteristics of the intake pipe fuel system are such that some of the fuel injected into the intake pipe adheres to the intake pipe wall, or the adhering fuel evaporates and is sucked into the cylinder together with the injected fuel. Therefore, not all of the injected fuel is sucked into the cylinder, and the stoichiometric air-fuel ratio may not be maintained.

Conventional fuel injection control devices for this type of internal combustion engine include:
For example, JP-A-62-2 proposed earlier by the present applicant.
There is one described in Japanese Patent No. 06241. With this device,
A predicted value for predicting the amount of fuel injected from the injector when it flows into the cylinder is calculated based on the throttle valve opening, and the amount of fuel actually injected is corrected based on this predicted value. In other words, the amount of fuel deposited in advance is estimated,
By predicting and controlling the fuel injection amount based on the prediction,
We are trying to improve the transient performance of Eningin by optimizing the amount of fuel injected during transient periods.

In addition, as other devices, Japanese Patent Application Laid-Open No. 62-206247
There is something described in the publication. This device corrects the amount of adhering fuel by varying the amount of fuel injection depending on changes in intake air temperature when the engine enters a transient state, thereby keeping the air-fuel ratio constant during the transient state. ing.

(Problem to be Solved by the Invention) However, in such a conventional fuel injection control device for an internal combustion engine, adhesion fuel is predicted based on information obtained from the throttle valve opening sensor, and the amount of fuel injection is determined. Since the fuel injection amount is corrected based on this information, it ignores the delay when the adhering fuel flows into the cylinder. The incoming fuel is inappropriate and the mixture ratio in the cylinder is wide (misalignment, worsening of exhaust emissions,
This results in deterioration of fuel efficiency and drivability.

In other words, although it is possible to predict the amount of fuel that will flow into the cylinder due to the amount of fuel to be injected next time based on information about the intake system, this does not take into account the delay when the adhering fuel flows into the cylinder. In this case, the delay became noticeable and the above-mentioned problems occurred.

Improvements are desired in these respects.

(Object of the Invention) Therefore, the present invention changes the air-fuel ratio when a predetermined condition is satisfied during engine operation, and calculates a correction constant for correcting the delay due to the amount of fuel adhering to the wall based on the amount of change.
Maintaining the operating state at the time of starting the calculation of the correction constant during the calculation, and determining the fuel injection amount so that the amount of fuel flowing into the cylinder matches the target fuel amount set according to the operating state. This eliminates the delay in the fuel transmission system due to the amount of fuel adhering to the wall, stabilizes the operating condition during correction constant calculation, improves the accuracy of fuel amount correction, and improves engine stability.
The purpose is to improve exhaust emission characteristics, drivability and fuel efficiency.

(Means for Solving the Problems) In order to achieve the above object, the fuel injection control device for an internal combustion engine according to the present invention has an operating state detection means for detecting the operating state of the engine, as a basic conceptual diagram thereof is shown in FIG. a, a target fuel amount setting means for calculating a target air-fuel ratio based on the operating state of the engine and setting a target fuel amount to achieve the target air-fuel ratio; and a target fuel amount setting means for injecting the target fuel amount from the fuel supply means g. When the amount of fuel injected into the cylinder of the engine becomes the amount of fuel flowing into the cylinder of the engine, a fuel amount calculating means based on the inverse characteristic corrects the amount of fuel based on the inverse characteristic of the transmission characteristic and calculates the amount of fuel actually injected from the fuel supply means g. C, a correction constant calculation means d for calculating a correction constant for changing the air-fuel ratio and correcting the fuel amount based on the amount of change when a predetermined condition is satisfied during engine operation; The operating state at the start of the calculation is stored, and during the calculation of the correction constant, the output of the operating state correction means e that corrects the operating state so as to maintain the operating state, and the fuel amount calculation means C based on the inverse characteristic. and injection amount determining means f for determining the amount of fuel to be injected into the engine based on the output of the correction constant calculating means d, and fuel supply means g for supplying fuel to the engine based on the output of the injection amount determining means f.
It is equipped with.

(Function) In the present invention, when a predetermined condition is satisfied during engine operation, a correction constant is calculated to correct the amount of fuel adhering to the wall surface based on the amount of change by changing the air-fuel ratio, and the correction constant is calculated. The operating state at the start is maintained during calculation. and,
The fuel injection amount is determined so that the amount of fuel flowing into the cylinder matches a target fuel amount set according to the operating state. Therefore, the delay of the fuel transmission system in the amount of fuel adhering to the wall is removed, and the accuracy of correcting the fuel amount is improved by stabilizing the operating condition during correction constant calculation, maintaining engine stability. The air-fuel ratio becomes appropriate, improving stability, exhaust emission characteristics, drivability, and fuel efficiency.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 7 are diagrams showing one embodiment of the present invention, and the present invention is an example applied to a four-cylinder engine.

First, the configuration will be explained. 1 is a four-cylinder engine (engine), intake air is supplied to each cylinder through an intake pipe 2 by each branch of an intake manifold 3, and fuel is supplied to each cylinder by an injector (fuel supply means) provided in each cylinder based on an injection signal Si. ) 4a to 4b.

Each cylinder is equipped with spark plugs 5a to 5d, and high-pressure pulses Pi from an igniter 6 are supplied to the spark plugs 5 via a distributor. spark plug 5
a to 5d, the igniter 6 and the distributor constitute an ignition means 8 that ignites the air-fuel mixture, and the ignition means 8 generates a high-voltage pulse Pi based on the ignition signal Sp to cause discharge. Then, the air-fuel mixture in the cylinder is high-pressure pulse Pi
ignites and explodes due to the discharge of
Co, HC, NOx) are purified by a three-way catalyst and discharged.

The pressure PM in the intake pipe 2 is detected by an intake pipe pressure sensor 10, and the flow rate of intake air is controlled by a throttle valve 11. The opening TH of the throttle valve 11 is detected by a throttle opening sensor 12, and the crank angle of the four-cylinder engine I is detected by a crank angle sensor 13 built into the distributor. The crank angle sensor 13 is set at a predetermined position of the engine before compression top dead center (TDC) of each cylinder at every explosion interval (180° for a 4-cylinder engine, 120° for a 6-cylinder engine), for example, at 70° BTDC.
] Outputs the reference signal Ca that becomes a level pulse, and also outputs [H
] Outputs a unit signal CI that becomes a level pulse. Note that the engine rotation speed N can be determined by counting the pulses of the signal CI. The temperature TW of the cooling water flowing through the water jacket is detected by the water temperature sensor 14,
The intake air temperature TA is detected by the intake air temperature sensor 15. Further, the oxygen sensor 16 detects 4 degrees 0□ of oxygen in the exhaust gas, and the vehicle speed VSP is detected by the vehicle speed sensor 17. Furthermore, ON10FF of the air conditioner is detected by the air conditioner switch 18, and the operating state of the starter motor is detected by the starter switch 19.

Further, a control unit 30, which will be described later, is supplied with a predetermined voltage from the battery 20 via a key switch (not shown), and is also supplied with a voltage VB supplied to the injector.

The above-mentioned intake pipe pressure sensor 10 and throttle opening sensor 12
, the crank angle sensor 13 and the intake air temperature sensor 15 constitute an operating state detecting means 21, and the operating state detecting means 2
1. Water temperature sensor 14, oxygen sensor 16, vehicle speed sensor 17
, the outputs from the air conditioner switch 18 and the starter switch 19 are input to the control unit 30. The control unit 30 has functions as a target fuel amount setting means, a fuel amount calculation means based on inverse characteristics, a correction constant calculation means, and an injection amount determination means.
2, a RAM 33, a bank amplifier RAM 34, an A/D converter 35, and an I10 port 36, which are connected to each other by a common bus 37. The A/D converter 35 converts PM, etc. input as an analog signal into a digital signal, and outputs the signal to the CPU 31, RAM 33, or bank amplifier R at a predetermined time according to instructions from the CPU 31.
Output to AM34. The CPU 31 imports necessary external data according to the program written in the ROM 32, and also imports necessary external data from the RAM 33 and backup RAM 3.
The I10 boat 36 performs arithmetic processing on processing values necessary for fuel injection control while exchanging data with the I10 boat 36 as necessary. Signals from various sensors are input to the I10 boat 36, and an injection signal Si and an ignition signal Sp are output from the I10 boat 36. The ROM 32 stores calculation programs and data used in the calculations in the CPU 31, and the RAM 33 temporarily stores data used in the calculations in the form of a map or the like. Further, the backup RAM 34 is made of, for example, a non-volatile memory, and retains its stored contents even after the four-cylinder engine is stopped.

Next, the operation will be explained, but first, the basic principle of the present invention will be described.

As shown by the solid line in Fig. 3 (A), when the injection amount QF injected from the injector is changed from Q to Q2 without performing wall adhesion amount correction, the amount of fuel that actually flows into the cylinder QFC slowly changes from Ql to Q2 as shown by the solid line in FIG. Therefore, when the intake air amount QAC is the same, the mixture ratio MR in the cylinder is the same (C
), it changes slowly from MRI to MRB2. If the QF of the injection amount is corrected as shown in the broken line in Figure (A) by executing the path of the transfer characteristic from QF to QFC, the actual QFC will be as shown in the broken line in Figure (B). As shown, the mixture ratio changes from Ql to Q2, and the mixture ratio MR in the cylinder becomes as shown by the broken line in FIG.

Specifically, the wall surface adhesion amount is corrected as follows.

In a 4-stroke engine, the crankshaft rotates once every two revolutions.
Since the combustion stroke is completed, the injection 11QF and the combustion amount QFC flowing into each cylinder for each of the injectors 4a to 4d are calculated as a first-order lag system as shown in the following equation (2) with a period of two crank revolutions depending on the engine rotation speed. ...■ However, α, β: Constants or shown by the following formula ■.

ΔQFC(k)=βxx(k)+αxΔQF(k)
x (k+1)= (1-β)xx (k)+(1-α
)

Here, the above Z-1 is a delay operator for two revolutions of the crank, and ΔQF and ΔQFC are the initial points of QF and QFC (
For example, it is the amount of change from x (steady value before change), and
k) is the amount of change in the amount of combustion adhering to the wall. Also, the constant α,
β is predetermined as a property of the engine, and usually takes a different value depending on the engine temperature, rotation speed, intake air amount, etc. Therefore, in the present invention, these α and β are calculated by a microcomputer and used as correction constants, which will be described in detail later.

The above correction calculation is performed by realizing the path (Z) of the transfer characteristic H(Z) from QF to QFC as shown in the following equation (2), and is represented by a block diagram as shown in FIG. 4. QF
R is the target fuel amount.

α-(α-β)Z-1 As a result, the transfer characteristic W(Z) from QFR to QFC is expressed by the following formula ∆QFR∆QF ∆QFR -G (Z) ・H(Z)=1 ...・■Δ
QFC=ΔQFR.

The problem here is the realization of G (Z), which can be realized by the following equation (2).

・・・・・・■ However, y (k): Internal state at time 0th
The correction method shown in the formula cannot realize W(Z)-1 if α and β change because the internal state y (k) does not correspond to the same physical quantity as the original wall surface adhesion amount x (k). A situation arises. To prevent this, it is recommended to use the correction method shown in the following equation.

(This page, hereafter in the margin) ...■ Here, v (k) is a quantity corresponding to the same physical quantity as x (k), and indicates a change in the amount of wall surface adhesion. It goes without saying that these correction calculations are performed for each injector (for each cylinder). Further, the injection amount QF (k) is expressed by the following equation 〇, and QFR(k) is expressed by the following equation ◯.

QF (K)=ΔQF (k)+QFO・・・・・・■
However, QFO indicates the initial value of the above QF.

QFR(k)=ΔQFR(k)+QFRO・・・・・・
■ Figures 5 to 7 are flowcharts showing fuel injection control programs based on the above basic principle, and in the figures, P1 to P2,
pH~PIS and Pill~P'J3 indicate each step of each flow.

FIG. 5 is a flowchart showing a program for calculating the air IQAC flowing into the cylinder, and this program is interrupted at predetermined time intervals sufficient to represent the behavior of the intake air amount. First, the A/D converter 35 reads the throttle opening signal TH1, intake pipe pressure PM, and intake air temperature TA at Pl, and calculates the air IQAc flowing into the cylinder at P2, and the process ends. Here, a method for calculating the air IQAc flowing into the cylinder is described in, for example, Japanese Unexamined Patent Publication No. 62-206241, and detailed explanation will be omitted here.

FIG. 6 is a flowchart showing a program that calculates the fuel injection pulse width Ti, and this program is executed every predetermined period (for example, every 180
Executed once. ,) First, read the air IQAc flowing into the cylinder calculated by the program shown in Figure 5 using pH, and then calculate the target mixture ratio M according to the engine operating state using pH.
Read RR.

Then, in PI3, air 1QAc and target mixture ratio MRR
The target fuel amount QFR is calculated based on the following equation (3).

It goes without saying that the target mixture ratio MRR may take different values in the steady state and transient state of the engine.

Next, at Pl4, the target fuel amount QFR is corrected based on the inverse characteristic of the transmission characteristic when the fuel amount QF injected from the injectors 4a to 4d becomes the fuel amount QFC flowing into the cylinder, and the fuel actually injected from the injectors is corrected. Calculate the quantity QF. Here, the fuel amount QF is determined depending on the structure of the engine, the shape of the injectors 43 to 4d, the pressure of fuel applied to the injectors 4a to 4d, and the like. In PIS, the fuel injection pulse width Ti that realizes the fuel amount QF actually injected from the injectors 4a to 4d is determined from the injector characteristics, battery voltage VB, fuel pressure, etc., and this Ti is stored in the output register of the I10 port 36 and is injected at a predetermined value. The fuel injection pulse width corresponding to this Ti at the crank angle of is set as the injection signal Si.
is output to the injectors 4a to 4d, and the current process ends. Further, the conversion from QF to Ti is a conversion based on the flow rate characteristics of the injector, and the basic form is the following formula [phase].

T i =TE+TS・・・・・・0 However, k, , k2, N, , f,: constant (kt, k
(2 is determined by the injector shape, fuel pressure, etc.) Here, the target mixture ratio MRR may be different between a steady state and a transient state of the engine.

FIG. 7 is a flowchart showing a program for calculating correction constants α and β. This program intentionally adjusts the air-fuel ratio (A/F) of one cylinder for a predetermined period when a predetermined condition is satisfied during engine operation. The system changes the A/F to an arbitrary value and calculates it based on the A/F change and the amount of injected fuel, and maintains the operating state at the start of the calculation even during the calculation.

In FIG. 7, correction constants α and β are calculated in step P 31 “” P 31, and the operating state at the start of the calculation is maintained in steps P41 to P46. First, P3. ~P
The thirteenth step process will be explained. In P31, the air-fuel ratio (A/F) of any one cylinder of the engine is intentionally changed stepwise to the rich or lean side as shown in Fig. 8 when the engine is running at a predetermined steady state, and piz is used to control the change. The calculated values are read as FA (a) and FA (n), and a correction constant is calculated from the change in F/A of that cylinder using Pil+. Now, FA is 1/(A/F) during steady rotation.
(a), target 1/(A/F) when intentionally swung
When FA(b) is FA(n), and FA(n) is 1/(A/F) of the actual measurement at the Nth cycle when A/F is changed, the correction constants α and β are calculated according to the following formulas ○, ■, and ■. calculate.

α−□ ・・・・・・O Here, the variable i represents the i-th engine cycle from the time when the A/F was intentionally changed, and this arbitrary cylinder was changed to rich or more. When this cylinder and other cylinders are turned to the opposite side, that is, when turned to rich, the cylinder is turned to lean.
By swinging rich when running lean, the stability of the engine will be maintained. P 41 ”” P 46
First, in P41, when starting the calculation of the correction constant, the current engine operating state (for example, steady low rotation) is read, and then in P4
□ to store this as a predetermined condition. Then, Pa
While calculating the correction constant in ff, the current operating state is always read in Paa, and if there is no difference between the operating state at the start of the calculation in p4s, it returns to Pa2, and on the other hand, when a difference occurs, In step P46, an operation is performed, for example, by changing the throttle valve to keep the operating state of the engine always in the state at the start of the calculation. Then, steps P43 to Pab are repeatedly executed until the calculation of the correction constant is completed.

In this way, the correction constant calculation is performed by intentionally changing the A/F of one cylinder to an arbitrary value for a predetermined period while keeping the engine running, and then calculating the A/F change at that time and the injection amount. Correction constants α and β are calculated from the fuel amount. Therefore, in order to keep the engine operating condition constant during calculation, the correction constant α,
β has good accuracy and can be easily determined.

As described above, in this embodiment, the amount of fuel adhering to the wall surface is corrected by realizing the path of the fuel transfer characteristic in which the fuel injected from the injector flows into the cylinder. In addition, when the engine 1 is in a predetermined operating state, the air-fuel ratio of one cylinder is varied for a predetermined period, and the correction constants α and β are determined based on the amount of change, and the operating state during the calculation is the operating state at the start of the calculation. Therefore, the delay in flowing into the cylinder due to the amount of fuel adhering to the wall surface is corrected with high precision according to the operating state of the engine, and the correction of the fuel amount becomes even more accurate. Therefore, the amount of fuel flowing into the cylinder becomes appropriate, the mixture ratio within the cylinder is maintained at an optimum state, and exhaust emissions, fuel efficiency, and drivability are improved. By the way, since the air amount QAC changes during transient operation, it is necessary to appropriately set the mixture ratio in the cylinder to improve exhaust emissions.
According to the present invention, the amount of fuel QFC corresponding to 1 QAC of air actually enters the cylinder, so that the mixture ratio in the cylinder can always be kept appropriate. Furthermore, the target mixture ratio M during the transient period
By appropriately determining RR, it is possible to achieve an in-cylinder mixture ratio that corresponds to the operating state of the engine, and it is also possible to further improve drivability and fuel efficiency.

Although this embodiment shows an example in which the calculation of the air amount QAC and the calculation of the fuel injection pulse width Ti are performed using separate programs, the invention is of course not limited to this, and for example, as shown in FIG. The operation of the microcomputer shown in FIG. 5.6 may be performed only by the 180'' CA routine (steps that perform the same processing are given the same numbers). However, step P51 in FIG. Calculating the amount of air flowing into the cylinder is the same as step P2 in Fig. 5, but since it is only calculated every 180° CA,
The calculation formula will be different. Examples of this include those described in JP-A-60-169647 and JP-A-62-206246.

Further, in this embodiment, the intake pipe internal pressure PM is used to obtain the intake air amount, but it goes without saying that a mode that measures the air flow rate in the intake pipe, such as an air flow meter, may also be used.

(Effects) According to the present invention, when a predetermined condition is satisfied during engine operation, the air-fuel ratio is changed, and a correction constant for correcting the delay due to the amount of fuel adhering to the wall is calculated based on the amount of change. During the calculation, the operating state at the start of the calculation is maintained, so the fuel injection amount can be determined so that the fuel amount matches the target fuel amount set according to the operating state.
The delay in the fuel transmission system due to the amount of fuel adhering to the wall surface can be corrected with high precision according to the operating condition. As a result, engine stability, exhaust emission characteristics, drivability, and fuel efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 9 are diagrams showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. is a diagram for explaining its basic principle, Fig. 4 is its block diagram, Fig. 5 is a flowchart showing a program that calculates the amount of air flowing into the cylinder, and Fig. 6 calculates the fuel injection pulse width. FIG. 7 is a flowchart showing a program to calculate the correction constant, FIG. 8 is a diagram to explain the correction constant, and FIG. 9 shows a program to calculate the fuel injection pulse width. It is a flowchart. ■・・・・・・4 cylinder engine (engine), 4a~4
d... Injector (fuel supply means) 21...
... Operating state detection means, 30 ... Control unit (target fuel setting means, fuel amount calculation means, correction constant calculation means, injection amount determination means).

Claims (1)

[Scope of Claims] a) Operating state detection means for detecting the operating state of the engine; b) Calculating a target air-fuel ratio based on the operating state of the engine and setting a target fuel amount to achieve the target air-fuel ratio. c) correcting the target fuel amount based on an inverse characteristic of the transmission characteristic when the amount of fuel injected from the fuel supply means becomes the amount of fuel flowing into the cylinder of the engine, and d) when a predetermined condition is satisfied during operation of the engine, the air-fuel ratio is changed and the amount of fuel is injected from the fuel supply means based on the amount of change; a correction constant calculation means for calculating a correction constant for correcting the amount; an operating state correction means for correcting the state; f) an injection amount determining means for determining the amount of fuel to be injected into the engine based on the output of the fuel amount calculation means based on inverse characteristics and the output of the correction constant calculation means; and g) injection amount. A fuel injection control device for an internal combustion engine, comprising: fuel supply means for supplying fuel to the engine based on the output of the determination means.