JPH08177557A - Fuel injection quantity control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve the computing accuracy of the engine fuel injection quantity at the time of atmospheric pressure change and transient operation. CONSTITUTION: An engine 1 is provided with a throttle valve opening sensor 17 for detecting the opening of a throttle valve 16, crank rotation angle sensors 5, 6 for detecting engine speed, an intake pressure sensor 3 for detecting the pressure of an engine intake passage 2, and a control circuit 10 for controlling the engine fuel injection quantity. The control circuit 10 computes a filling rate coefficient used to compute the engine intake air quantity on the basis of the prestored relation, using the throttle valve opening and engine speed. The control circuit 10 also computes the engine intake air quantity on the basis of the intake passage pressure and the filling coefficient and sets the engine fuel injection quantity according to the intake air quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection amount control system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, there has been known a fuel injection amount control device for an internal combustion engine which determines the fuel injection amount of the engine based on the engine intake passage pressure and the engine speed. In order to accurately control the engine air-fuel ratio, it is necessary to always set the fuel injection amount to the engine to a value proportional to the intake air amount of the engine. on the other hand,
There is a correlation between the engine intake air amount and the engine intake passage pressure downstream of the throttle valve and the engine speed, and the engine intake air amount can be determined from the intake passage pressure and the engine speed.

Conventionally, when the fuel injection amount is determined based on the intake passage pressure and the engine speed, the intake air weight (G
The intake air amount is calculated as the product of the intake passage pressure and the filling rate coefficient by using the intake filling rate coefficient KTP (KTP = GA / PM) defined as the ratio between A) and the engine intake passage absolute pressure (PM). (GA = PM × KTP). Further, as the filling factor KTP, the intake air weight is measured by changing the operating condition in advance by using an actual engine, and a map is created using the intake passage pressure PM and the engine speed NE under each operating condition. Using the intake passage pressure PM and engine speed NE measured during actual operation, the filling rate coefficient K is calculated from this map.
I try to read out the TP.

An example of this type of fuel injection amount control device is disclosed in Japanese Patent Laid-Open No. 1-285633. In the device of the publication, the intake passage pressure PM and the engine speed NE are detected during engine operation, and the measured intake air in advance under standard conditions (for example, standard atmospheric pressure conditions) is detected from the intake passage pressure and engine speed. The volumetric efficiency (value corresponding to the filling factor coefficient) FEV calculated based on the air amount is obtained, and the fuel amount TP to be injected into the engine is calculated as TP = KINJ × PM × FEV. Here, KINJ is a conversion coefficient between the intake air amount and the fuel amount.

[0005]

However, if the filling rate coefficient is obtained from the engine intake passage pressure PM during operation and the engine speed as described above, a problem may occur. For example, in the device of the above-mentioned Japanese Patent Laid-Open No. 1-285633, the value of the filling rate coefficient under each operating condition is calculated based on the intake air amount measured by changing the intake passage pressure and the engine speed in advance under the standard atmospheric pressure condition. The map is stored as a map of the pressure and the rotation speed, and the filling rate coefficient is read from the map using the values of the intake passage pressure PM and the rotation speed NE actually measured during operation. That is, the filling factor is a value based on the intake passage pressure under the standard atmospheric pressure condition.

However, when the atmospheric pressure actually changes,
The engine intake passage pressure changes accordingly.In such a case, if the intake air amount is calculated using the filling factor coefficient obtained from the map based on the measured intake passage pressure and the rotational speed, the actual intake air amount There is a difference between the amount of air and
There is a problem that the fuel injection amount cannot be controlled accurately and the air-fuel ratio of the engine cannot be maintained at the set air-fuel ratio.

For example, when the atmospheric pressure decreases, the engine intake passage pressure also decreases accordingly. However, as will be described later, if the throttle valve opening and the engine speed are the same, the filling rate itself is under the standard atmospheric pressure condition. It does not change from the value of the filling factor. However, when the filling rate coefficient is calculated based on the intake passage pressure during operation as in the device of the above-mentioned publication, it is calculated when the intake passage pressure becomes lower as the atmospheric pressure decreases. This causes a problem that the filling factor becomes smaller than it actually is.

Strictly speaking, the amount of air taken into the engine is defined by the opening area of the throttle valve (throttle valve opening), the engine speed, the opening / closing timing of the intake valve, the internal EGR amount (the amount of residual burned gas in the cylinder). ) And other conditions. Moreover, the opening / closing timing of the normal intake valve is constant regardless of the engine speed, and the internal EGR amount changes according to the engine speed. Therefore, in actual operation, if the throttle valve opening and the engine speed are determined, the filling rate coefficient is uniformly determined. If these conditions are the same, the filling rate coefficient is the same regardless of changes in atmospheric pressure. Takes the value of.

That is, in actual operation, the filling rate coefficient is uniquely determined by the conditions of the throttle valve opening and the engine speed. Further, the intake passage pressure is determined by the amount of air actually sucked into the engine and the filling rate coefficient, and the filling rate coefficient is not determined by the intake passage pressure and the engine speed. Therefore, when the filling rate coefficient is calculated based on the intake passage pressure and the engine speed as described above, an error occurs in the value of the filling rate coefficient due to fluctuations in atmospheric pressure.

Further, in actual operation, a change in intake passage pressure causes a delay in response to a change in operating condition. For example, since the change in the intake passage pressure is delayed with respect to the change in the operating state during transient operation such as acceleration and deceleration of the engine,
The intake passage pressure shows a value lower than the value corresponding to the operating state during engine acceleration, and conversely shows a value higher than the value corresponding to the operating state during engine deceleration. For this reason, if the fuel injection amount is calculated using the filling factor coefficient obtained based on the intake passage pressure and the rotational speed, the fuel injection amount changes in the engine operating state in the transient operating state such as engine acceleration and deceleration. Therefore, there is a problem that the engine air-fuel ratio cannot be accurately controlled.

In view of the above problems, the present invention provides a fuel injection amount control device for an internal combustion engine, which is capable of performing accurate fuel injection amount control even when the atmospheric pressure changes or during transient operation. Has an aim.

[0012]

The present invention is an internal combustion engine that is not affected by atmospheric pressure fluctuations, transient operation, etc., by directly calculating the intake charge ratio based on the engine speed and the throttle valve opening. A fuel injection amount control device for an engine is provided. That is, according to the present invention, a throttle valve opening sensor for detecting an opening of a throttle valve provided in an intake passage of an internal combustion engine, and an intake pressure sensor for detecting an intake passage pressure on the downstream side of the throttle valve, A rotation speed sensor for detecting the rotation speed of the engine, a storage means for storing a value of a filling rate coefficient of engine intake air according to a throttle valve opening degree and an engine rotation speed, and a throttle detected by the throttle valve opening sensor A filling rate coefficient calculating means for reading the current value of the engine intake filling rate coefficient from the storage means using the valve opening degree and the engine speed detected by the rotation speed sensor, and the intake filling rate coefficient calculating means. A fuel injection amount calculation means for calculating a fuel injection amount to the internal combustion engine based on a filling factor coefficient obtained by the above and an intake passage pressure detected by the intake pressure sensor; Fuel injection quantity control apparatus of the amount of fuel calculated by the detection means internal combustion engine and a fuel injection means for injecting into the internal combustion engine is provided.

[0013]

The storage means stores the value of the filling rate coefficient corresponding to the throttle valve opening and the engine speed, which is obtained in advance by actual measurement or the like. During operation, the filling rate coefficient calculating means reads the filling rate coefficient according to the current engine operating state from the storage means using the detected values of the throttle valve opening and the engine speed. Since the filling rate coefficient is a value determined by the throttle valve opening and the engine speed, the filling rate coefficient obtained above is a value that is not affected by fluctuations in atmospheric pressure. Further, since the throttle valve opening degree and the engine speed change with respect to the operating state of the engine without causing a response delay, the filling factor coefficient obtained as described above becomes a value that accurately corresponds to the current operating state.

The fuel injection amount calculation means calculates the fuel injection amount to the engine based on the value of the filling factor coefficient which corresponds exactly to the present operating condition obtained as described above, and the fuel injection means calculates the calculated amount. Inject fuel into the engine.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the overall configuration when the present invention is applied to an internal combustion engine for automobiles. In FIG. 1, 1 is an internal combustion engine main body, 2 is an intake passage of the engine 1, 16 is a throttle valve which is arranged in the intake passage 2 and has an opening degree according to an operation amount of an accelerator pedal 21 by a driver, and 17 is a throttle valve 16. A throttle valve opening sensor that generates an output signal according to an operation amount (opening), and a fuel injection valve 7 that injects pressurized fuel into an intake port of each cylinder of the engine 1.

2 (A) and 2 (B) are views for explaining the detection principle of the throttle valve opening sensor 17 of this embodiment. Figure 2
(A) is a diagram showing a throttle valve opening sensor detection unit 17a attached to the end of the rotary shaft 16a (FIG. 1) of the throttle valve 16. In FIG. 2A, the detection unit 17a has a resistance substrate 21 housed in a housing fixed to the intake passage 2, and a conductor such as metal or carbon is provided at the end 16b of the rotating shaft 16a. A brush holder 23 for holding the brush 22 formed from is provided, and the brush 22 slides on the base plate 21 in an arcuate locus along with the rotation of the valve shaft 16a.

Further, on the resistor substrate 21, the resistor 24 and the conductor 25 are arranged so as to match the sliding locus of the brush 22.
And are arranged concentrically, and terminals TE and TB are connected to both ends of the resistor 24, respectively. Further, the conductor 25 has only one end connected to the terminal TA. The brush 22 includes a resistor 24 and a conductor 2 at each sliding position.
5, and the resistor 24 and the conductor 25 are electrically connected to each other via the brush 22 and the brush holder 23.

FIG. 2B is a diagram showing an equivalent circuit of the detecting section 17a. In the figure, the terminal TE of the resistor 24 is grounded, and the terminal TB is connected to the positive electrode of the battery. When the valve shaft 16a rotates with a change in the opening of the throttle valve 16, the brush 22 slides on the resistor 24 and the conductor 25 with this rotation and moves to a position corresponding to the opening of the throttle valve 16. Moving. Therefore, the potential of the terminal TA of the conductor 25 changes according to the position of the brush 22 on the resistor 24, and the terminals TA, T
A voltage corresponding to the opening of the throttle valve 16 is generated between E.

In FIG. 1, 11 is an exhaust manifold for connecting the exhaust ports of the respective cylinders to a common collective exhaust pipe 14, 13
Is an O ₂ sensor that is arranged at the exhaust merging portion of the exhaust manifold 11 and that generates a voltage signal according to the oxygen concentration in the exhaust. Further, reference numeral 12 in FIG. 1 denotes an intake passage pressure detection port provided in a portion of each intake passage 2 on the downstream side of the throttle valve 16. The port 12 is connected to the intake pressure sensor 3 via the pressure guiding pipe 3a. The intake pressure sensor 3 generates a voltage signal corresponding to the pressure (absolute pressure) in the intake passage 2 acting via the pressure guiding pipe 3a.

In FIG. 1, a water jacket 8 of a cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of cooling water. The water temperature sensor 9 generates an electric signal of analog voltage according to the temperature of the cooling water. The output signals of the O ₂ sensor 13, the throttle valve opening sensor 17, the intake pressure sensor 3 and the water temperature sensor 9 described above are input to the A / D converter 101 with a built-in multiplexer of the control circuit 10 described later.

Reference numerals 5 and 6 in FIG. 1 denote crank angle sensors arranged in a distributor (not shown) of the engine 1. The crank angle sensor 5 generates a reference position detection pulse signal every 720 ° when the distributor shaft converts it into a crank angle, and the crank angle sensor 6 similarly detects a crank angle every 30 ° when converted into a crank angle. Generate a pulse signal for. These crank angle sensors 5, 6
Is supplied to the input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

The control circuit 10 is configured as, for example, a microcomputer, and in addition to the A / D converter 101, the input / output interface 102, the CPU 103, the ROM 1
04, RAM 105, backup RAM 106, clock generation circuit 107 and the like. In the present embodiment, the control circuit 10 calculates a basic control amount such as the fuel injection amount of the engine 1 and the ignition timing based on the throttle valve opening and the engine speed, as will be described later, and controls the fuel injection amount and the ignition. Performs basic control of the engine 1 such as timing control.

The down counter 108 of the control circuit 10,
The flip-flop 109 and the drive circuit 110 are for controlling the fuel injection valve 7. That is, in the routine described below, when the fuel injection amount (injection time) TAU is calculated, the injection time TAU is reduced by the down counter 108.
And the flip-flop 109 is set. As a result, the drive circuit 110 causes the fuel injection valve 7
Start urging. On the other hand, when the down counter 108 counts a clock signal (not shown) and the output terminal finally becomes the “1” level, the flip-flop 109
Is reset and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized for the above-described fuel injection time TAU, and the amount of fuel corresponding to the time TAU is supplied to the combustion chamber of the engine 1.

The input / output interface 102 of the control circuit 10 is connected to the ignition circuit 112 and controls the ignition timing of the engine 1. That is, the control circuit 10
Is the crank angle sensor 6 on the input / output interface 102.
After inputting the reference crank angle pulse signal of 1, the ignition signal is output to the ignition circuit 112 every time the crankshaft reaches a predetermined rotation angle, and spark is generated in the ignition plug (not shown) of each cylinder. The optimal ignition timing of the engine 1 is stored in the ROM 104 of the control circuit 10 as a function of operating conditions such as load (intake passage pressure) and rotational speed, and the optimal ignition timing is determined according to the operating conditions. .

The engine rotational speed (rotational speed) data is calculated based on the pulse interval of the crank angle sensor 6 by interruption at every predetermined crank angle (for example, every 30 °), and is stored in the RAM.
It is stored in a predetermined area 105. That is, the RAM 105
The latest rotation speed data is always stored in. Next, calculation of the fuel injection amount of the engine of this embodiment will be described.

In this embodiment, the fuel injection amount (injection time of each fuel injection valve) TAU is calculated from the following equation based on the throttle valve opening and the engine speed. TAU = KINJ × PMFWD × KTP × α × FAFC + FMW (1) Here, PMFWD is predicted from the actual intake passage pressure measured by the intake pressure sensor 3, and when any cylinder of the engine next closes. The predicted value of the intake passage pressure of is shown. PMFW
The method of calculating D will be described in detail later.

KTP is a filling factor coefficient determined from the throttle valve opening and the engine speed, and PMFWD × KT.
P represents the intake air weight per engine revolution. As described above, the filling factor KTP is the opening area of the throttle valve 16 (throttle valve opening) and the engine speed, the opening / closing timing of the intake valve, the internal EGR amount (the amount of residual burned gas in the cylinder).
It is determined by the conditions such as. Further, the opening / closing timing of the intake valve is constant regardless of the engine speed, and the internal EGR
The quantity changes depending on the engine speed. Therefore, the filling rate coefficient KTP is a function of the throttle valve opening and the engine speed, and has the same value under the same throttle valve opening and engine speed conditions regardless of changes in atmospheric pressure. In this embodiment, the throttle valve opening and the engine speed are changed in advance using an actual engine to measure the intake passage pressure and the intake air weight, and the filling factor coefficient under each throttle valve opening and engine speed conditions. (Ratio of intake air weight per engine revolution to intake passage pressure) is calculated and stored in the ROM 104 of the control circuit 10 as a map of the format shown in FIG. 3 using the throttle valve opening TA and the engine speed NE. are doing.

The filling rate coefficient KTP is determined from the map of FIG. 3 using the actual throttle valve opening TA detected by the throttle valve opening sensor 17 and the engine speed NE.
Since this filling factor coefficient KTP is a value determined only by the throttle valve opening and the engine speed, the KTP obtained above is used without any correction when calculating the intake air amount under different atmospheric pressure conditions. be able to.

In the equation (1), KINJ is a conversion constant for converting the engine intake air amount (PMFWD × KTP) into the basic fuel injection amount. The basic fuel injection amount (PMFWD × KTP × KINJ) is the fuel injection amount required to make the engine air-fuel ratio the stoichiometric air-fuel ratio. Furthermore, α
Is a correction coefficient determined from the warm-up state of the engine and other operating states. FAFC is an air-fuel ratio correction coefficient after learning correction, and is calculated based on the exhaust air-fuel ratio detected by the O ₂ sensor 13 in order to accurately maintain the engine air-fuel ratio at the theoretical air-fuel ratio. FMW is a correction coefficient for correcting the fuel injection amount in consideration of the fuel adhering to the wall surface. FAFC, FMW
The details will be described later.

As can be seen from the above equation (1), the fuel injection amount TAU of the engine in this embodiment is based on the filling rate coefficient KTP calculated from the throttle valve opening and the engine speed and the intake passage pressure PMFWD. Based on the calculated engine intake air amount, first, the basic fuel injection amount (PMFWD × KTP
XKINJ), and this basic fuel injection amount is calculated by correcting the basic fuel injection amount according to the engine operating state (α), the actual air-fuel ratio (FAFC), and the wall surface adhered fuel amount (FMW).

Next, the intake passage pressure PMFWD of the present embodiment.
The prediction method will be described. As described above, in the present embodiment, the intake air amount is calculated as the product of the filling rate coefficient KTP determined from the throttle valve opening TA and the engine speed NE and the intake passage pressure. However, when the throttle valve opening TA or the engine speed NE changes, the filling factor coefficient KTP is immediately calculated after the change, but the actual intake passage pressure changes TA and NE. On the other hand, since it changes with a certain delay time, the value does not immediately correspond to the changed KTP. Therefore, when the intake air amount is calculated as the product of the intake passage pressure actually measured and KTP calculated from TA and NE during transient operation such as acceleration and deceleration of the engine, the calculated amount is the air amount actually sucked into the engine. There will be an error between the intake air amount and
In some cases, it may not be possible to accurately control the fuel injection amount.

In the present embodiment, in order to solve the above problem, the intake air amount is not calculated based on the current intake passage pressure detected by the intake pressure sensor 3 but based on the current intake passage pressure. Next, the intake passage pressure at the time when the intake valve of either cylinder is closed is predicted, and the intake air amount is calculated using this predicted value. In other words, when the intake passage pressure changes with time while the intake valve is open, the intake passage pressure reached during closing of the intake valve is not the actual intake air pressure, not the intake passage pressure during the change. It is believed to best reflect the amount. Therefore, by calculating the intake air amount using the intake passage pressure PMFWD when the intake valve is closed, it is possible to accurately control the fuel injection amount even during the transient operation.

In the present embodiment, PMFWD is calculated using the intake passage pressure PMTA in the steady operation determined from the throttle valve opening TA and the engine speed NE. As described above, when the throttle valve opening TA and the engine speed NE are determined, the filling rate coefficient KTP is determined, and as a result, the intake passage pressure should be uniquely determined. In this embodiment, the intake passage pressure that is uniquely determined from the throttle valve opening TA and the engine speed NE is called PMTA.

In this embodiment, standard atmospheric pressure conditions (for example, 1a) are used.
tm), the intake passage pressure in a steady operation state (a state in which the throttle valve opening TA and the engine speed NE are maintained constant) is actually measured using an actual engine under the condition of FIG. It is stored in the ROM 104 of the control circuit 10 in the form of a map using TA and NE in the format shown in FIG. That is, the intake passage pressure during the engine steady operation is set to PMT.
What is used as A is the measured value of the intake passage pressure when the throttle valve opening and the engine speed are maintained constant (a state in which a sufficient time has passed after the change of TA and NE). This is because it is considered to be the value.

In the actual operation, since the response delay occurs in the change of the intake passage pressure as described above, the intake passage pressure immediately changes after the change of TA and NE.
Does not become a value (PMTA) corresponding to, and reaches PMTA after a lapse of a certain delay time. By the way, the intake passage pressure (PMT during steady operation read from the above map)
A) changes immediately if the throttle valve opening TA or the engine speed NE changes, but the actual intake passage pressure is T
Even if A and NE change, the changed PMTA does not immediately occur, but changes with a certain delay time.

FIG. 4 shows the PMT due to changes in TA, NE, etc.
Actual intake passage pressure P when A changes stepwise
It is a figure explaining the change of M. As shown in FIG. 4, PM
After TA changes, PM changes relatively slowly and reaches the changed PMTA after a certain period of time. This PM behavior can be approximated to a change in PMTA by a first-order lag response system.

By approximating the actual change of PM with respect to the change of TA and NE (change of PMTA) by the first-order lag response system, the current intake passage pressure PMCRT shown in FIG.
Using a first-order lag response model, it can be expressed using the following equation from the past intake passage pressure change history and the current PMTA value. PMCRT = PMCRT _i-1 + (PMTA-PMCRT
_i-1 ) × (1 / N) where PMCRT is the current intake passage pressure, PMCRT
_i-1 is the intake passage pressure before the time Δt from the present, and PMTA is the intake passage pressure in the steady state determined from the current throttle valve opening TA and the engine speed NE.

N is a weighting coefficient, which is expressed as N = T / Δt using the time constant T of the first-order lag response and Δt. The time constant T is a value determined by the throttle valve opening TA and the engine speed NE, and can be obtained as a function of TA and NE by an experiment using an actual engine in advance. In this embodiment, PMTA uses the value obtained under the standard atmospheric pressure condition. However, when the atmospheric pressure decreases at high altitudes, the calculated PMCRT value differs from the actual intake passage pressure. However, in order to calculate the engine intake air amount using the filling factor, it is necessary to use the actual intake passage pressure. Therefore, in the present embodiment, the value PMTA 'obtained by correcting PMTA using the atmospheric pressure correction coefficient KPA.
Using (PMTA ′ = PMTA × KPA), PMCRT is calculated from the above equation. That is, PMCRT = PMCRT _i-1 + (PMTA'-PMCRT _i-1 ) × (1 / N) (2) Note that the atmospheric pressure correction coefficient KPA is the current atmospheric pressure PA and the standard atmospheric pressure (1 atm). Is calculated as the ratio of. That is, KPA = PA / 1 atm. Also, the current atmospheric pressure P
A is just before the engine starts (the ignition switch is OFF
Is turned on), the value of the intake passage pressure detected by the intake passage pressure sensor 3 in the absence of intake air flow is used as an initial value of PA, and a predetermined operating condition is satisfied during engine operation. Each time, it is obtained by successively updating the value of PA based on the result of comparison between PMTA 'and the intake passage pressure actually detected by the intake passage pressure sensor 3. Also,
An atmospheric pressure sensor is installed to measure the atmospheric pressure separately.
May be detected.

In this embodiment, PMCRT =
The calculation of the above formula (2) is started using the initial value of PMTA ', and thereafter the calculation of the above formula (2) is repeated at every engine operating time Δt to obtain the result of the sequential calculation from the engine start. The current intake passage pressure PMCRT is calculated.
By the way, the PMCRT calculated above is the value of the current intake passage pressure, but the amount of air actually taken into the engine is best reflected by the intake passage pressure when the intake valve of each cylinder is closed. Is the value of. Therefore, in order to accurately calculate the fuel injection amount, it is necessary to calculate the intake air amount using the intake passage pressure when the intake valve is closed. On the other hand, as shown in FIG. 4, the current intake passage pressure PMCRT is calculated by approximating the response of the intake passage pressure by a first-order delay response system, so if PMTA 'is constant, the same first-order delay response model is used. It is possible to predict the intake passage pressure at a time point earlier than the present time (PMCRT calculation time point) by further repeating the sequential calculation of the equation (2) using the above.

That is, after calculating PMCRT, the same PM
If the calculation of equation (2) is performed once using the value of TA ′,
The intake passage pressure after Δt from the present is calculated, and (2)
If the calculation of the formula is repeated twice, the intake passage pressure after 2 × Δt has elapsed can be calculated. In other words, now (at the time of PMCRT calculation)
From the next time until the intake valve of one of the cylinders is closed is L, the calculated value of PMCRT is used as an initial value, and the current PMTA 'is used to calculate the expression (2) as L / Δ.
By repeating t times, it is possible to predict the intake passage pressure PMVLV (see FIG. 4) when the intake valve of any of the cylinders is closed next. That is, PMCRT _{i + 1} = PMCRT + (PMTA'-PMCRT) x (1 / N) PMCRT _{i + 2} = PMCRT _{i + 1} + (PMTA'-PMCRT _{i + 1} ) x (1 / N) ... (Repeat P times, but P = L / Δt) ………… PMVLV = PMCRT _{i + P} = PMCRT _{i + P-1} + (PMTA′-PMCRT _{i + P-1} ) × (1 / N) …… ( 3) The applicant of the present application has already proposed a method of predicting the intake passage pressure when the intake valve is closed in Japanese Patent Laid-Open No. 63-2154848.

FIG. 6 shows a flowchart of the PMCRT and PMVLV calculation routine. This routine is
Control circuit 10 for every fixed time (every 8 ms in this embodiment)
Is executed. When the routine starts in FIG. 6, in step 601, the output of the throttle valve opening sensor 17 is AD-converted and taken in as throttle valve opening data TA. Next, in step 603, RAM1
The latest rotational speed data NE stored in 05 is read, and in step 605, the throttle valve opening TA and the engine rotational speed NE are used to store the intake passage pressure PMTA in a steady state under standard atmospheric pressure in the ROM 104. It is read out from the map shown in FIG.

In step 607, the PMTA calculated above is corrected based on the current atmospheric pressure, and the atmospheric pressure corrected value PMTA 'is calculated as PMTA' = PMTA × KPA. The atmospheric pressure correction coefficient KPA is calculated as KPA = current atmospheric pressure / standard atmospheric pressure at regular time intervals in a routine (not shown) that is separately executed. Step 60
In 9, the time constant T of the first-order lag in the above equation (2) is calculated based on the intake passage pressure PMTA and the engine speed NE calculated above. In this embodiment,
The time constant T is created in advance as a map using TA and NE in the same format as in FIGS. 3 and 5, and is stored in the ROM 104. At step 609, the time constant is calculated using TA and NE from this map. T is read out.

Further, in step 611, the weighting coefficient N in the above equation (2) is N = T / Δt using this time constant.
Is calculated as In this case, Δt corresponds to the execution interval of this routine, and Δt = 8 ms in this embodiment. Next, in step 613, the PMT calculated above is calculated.
A ', N, and PMCRT value P at the time of previous routine execution
The current intake passage pressure PMCRT is calculated from the equation (2) using MCRT _i−1 .

Next, at step 615, the number of repetitions P of the equation (3) for calculating PMVLV is calculated. Here, P becomes equal to an integer value of a value obtained by dividing the time L from the present time until the intake valve of any cylinder is closed next by the execution interval Δt of this routine. In step 615, the time L until the intake valve is closed in any of the cylinders is calculated from the current crank rotation angle detected by the crank angle sensor and the engine speed NE, and divided by Δt = 8 ms. The number of repeated calculations P is calculated by.

In step 617, the iterative calculation of the equation (3) is executed the number of times calculated above,
PMVLV is calculated. Also, in step 619,
The calculated values of PMCRT and PMVLV are stored in the RAM 10
The data is stored in the predetermined area 5 and this routine ends. By executing this routine, PMCRT and PMVLV are calculated every 8 ms based on the throttle valve opening TA and the engine speed NE during engine operation, and the latest values are stored in the RAM 105.

By the way, the current intake passage pressure PMCRT and the intake passage pressure PMVLV at the time of closing the intake valve obtained by the routine of FIG. 6 are independent of the intake passage pressure measured by the intake pressure sensor 3 and the throttle valve opening degree TA. And the engine speed NE are values obtained by sequential calculation. For this reason,
The values of PMCRT and PMVLV may have an error due to sequential calculation.

Therefore, in this embodiment, the value P obtained by calibrating the intake passage pressure PMVLV obtained when the intake valve is closed as described above using the current intake passage pressure detected by the intake pressure sensor 3 is used.
The amount of intake air will be calculated using MFWD. That is, PMFWD = PMI + (PMVLV-PMCRT) (4) where PMI is the smoothed value of the intake passage pressure PM detected by the intake pressure sensor 3. Since the intake passage pressure fluctuates due to the pulsation of intake air, the intake pressure sensor 3 is used in this embodiment.
The output of is cut by the CR filter for a minute fluctuation component of about 3 ms or less, and the weighted coefficient is further set to 8 using the value after this filtering, and the following weighted average calculation (meaning calculation) is performed to obtain PMFWD. It is used as the intake passage pressure PMI used to calculate

PMI = (7 × PMI _i-1 + PM) / 8 (5) where PMI is the intake passage pressure used for PMFWD calculation, PMI _i-1 is the PMI value at the previous weighted average, PM
Is the output of the intake pressure sensor 3 after filtering. In this embodiment, the value of PM after filtering is AD-converted every 2 ms and fetched by a routine (not shown) that is separately executed, and P
The weighted average is performed every time M is taken in (that is, every 2 ms), and the calculated intake passage pressure PMI is stored in a predetermined area of the RAM 105. That is, in the RAM 105,
The latest PMI value is stored every 2 ms.

FIG. 7 is a flowchart showing the PMFWD calculation routine. This routine is executed by the control circuit 10 at regular intervals (every 8 ms in this embodiment).
When the routine starts in FIG. 7, step 7
At 01, the value of the weighted average value PMI of PM stored in the predetermined area of the RAM 105 is read out, and at step 703, PMVLV, PM calculated by the routine of FIG. 7 described above.
The CRT value is read out from a predetermined area of the RAM 105.

Next, at step 705, the value of PMFWD is calculated by using the above equation (4), at step 707, the calculated value of PMFWD is stored in the predetermined area of the RAM 105, and this routine ends. In this embodiment,
PMFWD calculated as described above as shown in equation (1)
Using the value of, the basic fuel injection amount is KINJ x PMFW
Calculated as D × KTP.

As described above, the filling rate coefficient KTP is a value determined only by the throttle valve opening and the engine speed, and is not affected even when the atmospheric pressure condition or the like changes. Further, the throttle valve opening and the engine speed change even during a transient operation such as acceleration and deceleration of the engine without causing a response delay with respect to a change in the operating state. Therefore, in the present embodiment, the filling factor coefficient is determined by the throttle valve opening and the engine speed, so that the engine intake air amount can be accurately determined even when the atmospheric pressure condition changes or during transient operation. It is possible to set the basic fuel injection amount corresponding to.

Next, the correction amount FMW of the wall surface adhered fuel amount in the calculation of the fuel injection amount of this embodiment will be described. In the present embodiment, the fuel injection amount TAU is calculated by the above equation (1). That is, TAU = KINJ × PMFWD × KTP × α × FAFC + FMW (1) where FMW is a correction amount of TAU based on the amount of fuel adhering to the wall surface. Part of the fuel injected from the fuel injection valve during engine operation directly flows into the combustion chamber, and part of the fuel once adheres to the intake port wall surface, then vaporizes or flows along the wall surface and flows into the combustion chamber. . The amount of fuel adhering to the wall surface varies depending on the operating condition of the engine. For example, if the fuel injection amount is large, the amount of fuel adhering to the wall surface increases, and if the intake passage pressure rises, the vaporization amount of the wall surface adhering fuel decreases, so the amount of adhering fuel held on the wall surface also increases. In the present embodiment, the fuel injection amount is the intake passage pressure (to be exact, the above-mentioned PMFWD).
Therefore, the amount of fuel adhering to the wall surface changes according to the intake passage pressure.

Here, when the operating condition of the engine is kept constant and PMFWD does not change, the amount of fuel newly adhering to the wall surface and the amount of fuel leaving the wall surface due to vaporization or flow are in balance. The amount of fuel adhering to the wall surface is kept constant. However, if the engine operating state changes abruptly, this balance may be lost, so that a difference may occur between the amount of fuel injected from the fuel injection valve and the amount of fuel actually supplied to the combustion chamber. For example, when the intake passage pressure (PMFWD) suddenly increases, the fuel injection amount is also increased accordingly, but the fuel amount attached to and retained on the wall surface also increases in accordance with PMFWD. Part of the increase in the injection amount is consumed to increase the amount of fuel adhering to the wall surface, and the amount of fuel actually supplied to the combustion chamber becomes temporarily less than the amount of increase in the fuel injection amount. . Therefore, when the amount of fuel is increased during acceleration or the like, the amount of fuel actually supplied to the combustion chamber becomes insufficient, which causes a problem that the acceleration performance of the engine deteriorates.

Further, when the fuel injection amount is reduced during deceleration of the engine, the amount of fuel adhering to the wall surface is reduced, and this reduced amount flows into the engine combustion chamber and is actually supplied to the combustion chamber. The amount of fuel to be supplied becomes larger than the fuel injection amount, and during deceleration, the air-fuel ratio becomes too rich and the exhaust properties deteriorate. In this embodiment, the above problem is solved by correcting the fuel injection amount TAU according to the change in the amount of fuel adhering to the wall surface by the method described below.

As described above, in this embodiment, the amount of fuel adhered to and retained on the wall surface of the intake port is determined by the engine intake pressure (PMFW).
It changes according to the value of D). Therefore, in the present embodiment, an experiment was conducted in advance using an actual engine, the value of the wall surface adhered fuel amount QMW with respect to each PMFWD value was measured, and the relationship between PMFWD and QMW was stored in the ROM 104 in the form of a numerical table. is there.

The control circuit 10 uses a numerical table from the value of PMFWD by a routine (not shown) executed at constant crank rotation angles (for example, every 720 °) and uses the numerical table to attach the wall surface corresponding to the present value of PMFWD. The fuel amount QMW is read out, the amount of change DQMW from the value of QMW QMW _i−1 read at the time of the previous routine execution is calculated, and the wall surface adhered fuel correction amount FMW is calculated using this DQMW by the following formula.

FMW = DQMW × β Here, β is a conversion coefficient of DQMW into the fuel injection amount (time), and takes a positive value determined according to the intake air temperature, the engine warm-up state, and the like. For example, when the PMFWD sharply increases, the fuel injection amount is also increased accordingly, but the wall surface adhered fuel amount also increases in accordance with the PMFWD, and a part of the injected fuel is consumed to increase the wall surface adhered fuel amount. Therefore, the amount of fuel actually supplied to the combustion chamber does not increase by an amount according to PMFWD. Therefore, the amount of fuel supplied to the combustion chamber is P
In order to increase the amount in accordance with the increase in MFWD, it is necessary to further increase the fuel supply amount.

In the present embodiment, in such a case, the fuel injection amount is corrected by increasing the fuel injection amount by the amount FMW corresponding to the change amount DQMW of the wall surface adhered fuel amount, so that the fuel amount supplied to the combustion chamber is PMFWD. The amount is increased appropriately according to That is, when DQMW is positive, the amount of fuel adhering to the wall surface increases by DQMW from the time when the previous routine is executed, so that the fuel actually supplied to the combustion chamber is insufficient by an amount corresponding to DQMW from an appropriate value. become. Also,
When DQMW is negative, the amount of fuel adhering to the wall surface decreases by DQMW from the time when the previous routine is executed, so that the amount of fuel corresponding to the decrease in the amount of fuel adhering to the wall surface leaves the wall surface and flows into the combustion chamber. Therefore, the amount of fuel actually flowing into the combustion chamber becomes excessive by an amount corresponding to DQMW. Therefore, by correcting the fuel injection amount TAU with the FMW calculated as described above, it becomes possible to appropriately maintain the amount of fuel supplied to the combustion chamber even during a transition in which the PMFWD changes.

If the PMFWD continues to be constant after the operating state changes, the amount of fuel newly adhering to the wall surface and the amount of fuel desorbing from the wall surface gradually balance, and the change in the amount of fuel adhering to the wall surface approaches zero. Therefore, in this embodiment, PMFWD
When there is no change (that is, when the value of DQMW becomes 0), the wall surface adhesion correction amount FMW is gradually reduced, and after a certain period of time, FMW = 0.

Next, the air-fuel ratio feedback control of the engine of this embodiment will be described. In the present embodiment, the air-fuel ratio correction coefficient FAF is calculated based on the output of the O ₂ sensor 13 provided in the exhaust manifold 11, and the air-fuel ratio correction coefficient FAF is used to correct the fuel injection amount TAU, whereby the intake pressure sensor The engine air-fuel ratio is accurately maintained at the stoichiometric air-fuel ratio regardless of the error of the throttle valve opening sensor 17 and the throttle valve opening sensor 17.

Further, as will be described later, the air-fuel ratio correction coefficient FA
F is learned and corrected during engine operation, and is used in the form of FAFC in the above equation (1), TAU = KINJ × PMFWD × KTP × α × FAFC + FMW (1). Where FAF
C = FAF × KG, where KG represents a learning correction coefficient.
This learning correction will be described later.

8 and 9 are flow charts showing a routine for calculating the air-fuel ratio correction coefficient FAF in this embodiment. This routine is executed by the control circuit 10 at regular intervals (every 4 ms in this embodiment). In the routines of FIGS. 8 and 9, the output V ₁ of the O ₂ sensor 13 is compared with the comparison voltage V _R1 (the theoretical air-fuel ratio equivalent voltage), and the current exhaust air-fuel ratio is richer than the theoretical air-fuel ratio (V ₁ > V _R1 ), The air-fuel ratio correction coefficient FAF is decreased, and when lean (V ₁ ≦ V _R1 ), the FAF is increased. As a result, the engine air-fuel ratio is accurately corrected to near the stoichiometric air-fuel ratio even if there is some error in the intake pressure sensor and the throttle valve opening sensor. The flowcharts of FIGS. 8 and 9 will be briefly described below. In step 801, a feedback control execution condition (for example, activation of the O ₂ sensor, completion of engine warm-up, etc.) is established. It is determined whether or not there is a step 802 only when the condition is satisfied.
The following FAF calculation is performed. Steps 802 to 81
Reference numeral 5 indicates the determination of the air-fuel ratio.

Flag F shown in steps 809 and 815
1 indicates that the engine air-fuel ratio is rich (F1 = 1) or lean (F1).
Is an air-fuel ratio flag indicating whether or not F1 = 0 to F1.
= 1 (lean to rich) is switched to the O ₂ sensor 13
Continues for a predetermined time (TDR) or longer and the rich signal (V ₁ >
V _R1 ) is output, F1 = 1 to F1 = 0
The switching from (rich to lean) is continued by the O ₂ sensor 13 for a predetermined time (TDL) or more and the lean signal ((V ₁ ≦ V
_R1 ) is output. CDLY is a counter for determining the air-fuel ratio flag switching timing.

In steps 816 to 822 in FIG. 9, the FAF is increased or decreased according to the value of the flag F1 set as described above. That is, in the case of F1 = 0 (lean), the FAF is increased in a skip manner by a relatively large value RSR immediately after changing (reversing) from F1 = 1 to F1 = 0 (rich to lean) (step 818). ), Then F
A relatively small value KI for each routine execution while 1 = 0
The FAF is gradually increased by R (step 821).
Further, in the case of F1 = 1 (rich), FAF is first decreased by a relatively large value RSL immediately after reversing from F1 = 0 to F1 = 1 (lean to rich) (step 81
9) After that, while F1 = 1, the FAF is gradually decreased by a relatively small value KIL each time the routine is executed (step 822). Further, after the FAF value calculated as described above is guarded (steps 823 to 826) so as not to exceed the minimum value (FAF = 0.8 in this embodiment) and the maximum value (FAF = 1.2), It is stored in a predetermined area of the RAM 105.

FIG. 10 shows changes in the air-fuel ratio (A / F) (FIG. 10 (A)) when the control shown in FIGS.
Counters CDLY (same (B)), F1 (same (C)), FAF
The same (D) changes are shown. As shown in FIG. 10 (D), the FAF value fluctuates around the value corresponding to the stoichiometric air-fuel ratio. In an ideal state where there is no error in the intake pressure sensor, the throttle valve opening sensor, and other fuel system elements, the air-fuel ratio correction coefficient FAF fluctuates around 1.0. In this case, FAF = 1.0 corresponds to the theoretical air-fuel ratio. FAF equivalent to the theoretical air-fuel ratio when there are errors due to inter-individual variations in sensors and fuel system elements and aging
Becomes a value outside 1.0, and the FAF fluctuates around the value outside 1.0.

However, since the FAF is limited to the maximum value and the minimum value (steps 823 to 826 in FIG. 9), if the FAF is controlled around a value outside 1.0, There is a problem that the range of change is limited by the maximum value or the minimum value and the control range of the air-fuel ratio becomes narrow. For example, if the FAF is controlled around 1.1,
On the lean air-fuel ratio side, FAF can change only from 1.1 to the maximum value of 1.2, and the control range on the lean air-fuel ratio side becomes narrow.

In this embodiment, this problem is solved by calculating the fuel injection amount TAU by using the value FAFC obtained by learning and correcting the air-fuel ratio correction coefficient FAF by using the correction coefficient KG in the above equation (1). There is. The FAF learning correction of the present embodiment will be described below. In this embodiment, when the FAF theoretical air-fuel ratio equivalent value calculated by the routines of FIGS. 8 and 9 deviates from 1.0, the value of the learning correction coefficient KG is increased or decreased so that the FAF theoretical air-fuel ratio equivalent value is always The control range of the FAF is prevented from becoming narrow by making it close to 1.0. For example, in the above example, when there is a secular change such that the FAF theoretical air-fuel ratio equivalent value becomes 1.1, the learning correction coefficient KG is increased until KG = 1.1. FA
Since FC = FAF × KG, this reduces the theoretical air-fuel ratio equivalent value of FAF to 1.0.
Since the value of FC itself is maintained at 1.1, there is no change in the air-fuel ratio control.

Next, the FAF learning correction of the present embodiment will be described. In this embodiment, the FAF skip processing (steps 818, 81) is performed when the engine is in the steady operation state.
9) The FAF value immediately before the previous skip processing (for example, FIG. 10 (D))
Value indicated by FAFR) and FA immediately before this skip processing
An arithmetic mean value FAFAV with the value of F (for example, the value indicated by FAFL in FIG. 10D) is calculated (FAFAV = (FAF
R + FAFL) / 2), this FAFAV is approximately FA
The following operation is performed assuming that it is the theoretical air-fuel ratio equivalent value of F.

That is, when FAFAV is equal to or larger than a predetermined value (eg, 1.02) larger than 1.0, the learning correction coefficient KG is a constant value (eg, 0.002) from the current value.
If FAFAV is equal to or smaller than a predetermined value (for example, 0.98) smaller than 1.0, the learning correction coefficient KG is decreased by a constant value (for example, 0.002) from the current value. FAFAV is between these values (1.02> F
If AFAV> 0.98), the value of KG is maintained as it is.

When the learning correction coefficient KG is increased, the theoretical air-fuel ratio equivalent value of FAF is decreased by executing the routines shown in FIGS. Further, when KG decreases, the FAF theoretical air-fuel ratio equivalent value increases. Therefore, by performing the above-described learning correction for each FAF skip processing, the theoretical air-fuel ratio equivalent value (FAFAV) of FAF is within a predetermined range (for example, 0.
98 to 1.02) and the control range of the FAF is prevented from being narrowed. In this embodiment, the value of the learning correction coefficient KG is the backup RAM 106 of the control circuit 10.
The value of FAF is maintained within a predetermined range from the time of engine start-up because it is stored in a predetermined area of and is saved even when the engine is stopped.

FIG. 11 shows a fuel injection amount TAU calculation routine of this embodiment. This routine is performed by the control circuit 10 for a fixed time or a fixed crank rotation angle (for example, 360 degrees).
It is executed every time. When the routine starts in FIG. 11, in step 1101, the output TA of the throttle valve opening sensor is AD converted and read, and the RAM 1 is read.
The latest rotation speed data NE stored in the predetermined area 05 is read. Further, in step 1103, the above TA, N
The value of the filling factor KTP is read from the map (FIG. 3) stored in the ROM 104 using the value of E.

Next, at step 1105, the intake passage pressure PMFWD at the time of the next intake valve closing, which is calculated by the routines of FIGS. 6 and 7, is read from a predetermined area of the RAM 105. Further, the value of the air-fuel ratio correction coefficient FAF calculated by the routine of step 1107, FIG. 8 and FIG.
5, the value of the learning correction coefficient KG of FAF is read from the backup RAM 106, respectively, and step 110
In 9, the corrected air-fuel ratio correction coefficient FAFC is calculated from FAF and KG as FAFC = FAF × KG. Further, in step 1111, the wall surface adhered fuel correction amount FMW calculated by a routine (not shown) is read, and in step 1113, the fuel injection amount TAU of the engine is calculated based on the above equation (1).

After the fuel injection amount TAU is calculated as described above, TAU is set in the down counter 108 in step 1115, and this routine ends. In the above embodiment, the filling rate coefficient KTP is obtained based on the throttle valve opening TA and the engine speed NE. However, as described above, the filling rate coefficient strictly depends on the opening area of the throttle valve. Change. Therefore, the opening area of the throttle valve may be calculated from the throttle valve opening TA, and the filling rate coefficient KTP may be calculated based on the opening area and the engine speed.

[0074]

According to the present invention, the filling rate coefficient is not determined based on the engine speed and the engine intake passage pressure as in the prior art, but is based on the engine speed and the throttle valve opening. By determining the rate coefficient, the filling rate coefficient can be set accurately even when the atmospheric pressure changes or during transient operation of the engine, so that the engine air-fuel ratio can be accurately controlled. Has the effect that is possible.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of an internal combustion engine to which the present invention is applied.

FIG. 2 is a diagram showing a structure of a throttle valve opening sensor.

FIG. 3 is a diagram illustrating a format of a numerical map of a filling rate coefficient using an engine speed and a throttle valve opening.

FIG. 4 is a timing diagram illustrating a method of calculating intake passage pressure based on a throttle valve opening.

5 is a diagram illustrating a format of a numerical map used in the routine of FIG.

FIG. 6 is a flowchart illustrating an intake passage pressure calculation routine.

FIG. 7 is a flowchart illustrating an intake passage pressure calculation routine.

FIG. 8 is a flowchart illustrating an air-fuel ratio correction coefficient calculation routine.

FIG. 9 is a flowchart illustrating an air-fuel ratio correction coefficient calculation routine.

FIG. 10 is a timing diagram that supplementarily describes the flowcharts of FIGS. 8 and 9.

FIG. 11 is a flowchart illustrating a fuel injection amount calculation routine.

[Explanation of symbols]

 1 ... Internal combustion engine body 2 ... Intake passage 3 ... Intake pressure sensor 5, 6 ... Crank rotation angle sensor 10 ... Control circuit 16 ... Throttle valve 17 ... Throttle valve opening sensor

Claims (1)

[Claims] 1. A throttle valve opening sensor for detecting an opening of a throttle valve provided in an intake passage of an internal combustion engine; an intake pressure sensor for detecting an intake passage pressure downstream of the throttle valve; A rotation speed sensor for detecting a rotation speed, a storage means for storing a value of a filling rate coefficient of engine intake air according to a throttle valve opening degree and an engine rotation speed, and a throttle valve opening degree detected by the throttle valve opening sensor And the engine rotation speed detected by the rotation speed sensor, the filling rate coefficient calculating means for reading the current value of the engine intake filling rate coefficient from the storage means, and the intake filling rate coefficient calculating means A fuel injection amount calculating means for calculating a fuel injection amount to the internal combustion engine based on a filling rate coefficient and an intake passage pressure detected by the intake pressure sensor; A fuel injection amount control device for an internal combustion engine, comprising: a fuel injection unit that injects the amount of fuel calculated by the above into the internal combustion engine.