JP2701296B2 - Fuel injection amount control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a fuel injection amount from a fuel injection valve according to a control law set based on a physical model describing the behavior of fuel flowing into a cylinder of an internal combustion engine. The present invention relates to a fuel injection amount control device for an internal combustion engine for controlling the fuel injection amount.

2. Description of the Related Art Conventionally, as one type of a fuel injection amount control device that controls a fuel injection amount from a fuel injection valve so that an air-fuel ratio of a fuel mixture supplied to an internal combustion engine becomes a target air-fuel ratio, for example, As described in Japanese Unexamined Patent Publication No. 59-196930, a correction value for correcting a basic fuel injection amount obtained from the rotation speed of the internal combustion engine and the intake air amount is control input, and the air-fuel ratio detected using the air-fuel ratio sensor is calculated. With the measured value as the control output, identification is performed as that a linear approximation holds between the control input and the control output,
Find a physical model that describes the dynamic behavior of an internal combustion engine,
There is known a control device based on a so-called linear control theory, which is configured to control the fuel injection amount according to a control law designed based on this.

[Problems to be Solved by the Invention] However, the relationship between the control input amount and the control output amount is inherently non-linear, and the dynamic behavior of the internal combustion engine is extremely narrow if the physical model is simply obtained by linear approximation. Conventionally, this type of control device obtains a mathematical model for each of a plurality of operating regions in which linear approximation can be considered to be valid, and performs control for each operating region based on the mathematical model. The rules had to be designed.

Therefore, in this type of control device, the control law used for control must be switched for each operation region of the internal combustion engine in accordance with the physical model, and there is a problem that the control is complicated. There is also a problem that control becomes unstable at a boundary point of each operation region due to switching of a control law.

Accordingly, the applicant of the present application has developed a fuel injection amount control device capable of accurately controlling the fuel injection amount under a wide range of operating conditions of the internal combustion engine without switching the control law as described above (that is, with one control immediately). Designed based on a physical model that describes the behavior of fuel using the amount of fuel attached to the intake pipe wall surface and the amount of fuel vaporized in the intake pipe as state variables according to Japanese Patent Application Nos. 62-189889 and 62-189891. A fuel injection amount control device that calculates the fuel injection amount according to the control law and controls the fuel injection is proposed.

In the proposed device, since the physical model is discretized with the intake cycle of the internal combustion engine as one cycle, the calculated fuel injection amount is injected into the intake system between the intake stroke and the next intake stroke. Should be the amount of fuel to be consumed Further, to calculate the fuel injection amount, it is necessary to know the state variable amounts (that is, the amount of fuel adhering to the intake pipe wall surface and the amount of evaporative fuel in the intake pipe), and these state variable amounts must be directly detected by sensors or the like. Therefore, it is calculated by an arithmetic expression such as an observer set based on the physical model.
For this reason, at least the calculation of the state variable amount must be performed in synchronization with the intake cycle of the internal combustion engine, and in the proposed device, fuel injection is performed for each intake cycle of the internal combustion engine,
The state variable amount is calculated each time the fuel injection is executed.

However, in the proposed device, the fuel cut control for inhibiting the fuel injection during the deceleration operation of the internal combustion engine or the like was not considered, and if the fuel cut control is directly executed by the device, the state changes when the fuel cut control is executed. The quantity is not updated, and when returning to the fuel cut control, the fuel injection is performed by the fuel injection amount calculated based on the state variable amount before the execution of the fuel cut control, and the air-fuel ratio deviates significantly from the target air-fuel ratio. Occurs. In particular, in the device proposed in Japanese Patent Application No. 62-189891, the feedback of the air-fuel ratio is not performed. Therefore, once the air-fuel ratio deviates from the target air-fuel ratio, it takes a long time to recover, and this is a serious problem.

When the fuel cut control is executed, the state variable amount decreases because there is no fuel supply from the fuel injection valve, and eventually becomes 0. Therefore, when the fuel cut control is executed, the state variable amount is reduced. Although it is conceivable to uniformly change the value to 0, the execution time of the fuel cut control is short, and the fuel injection control may return to the normal fuel injection control before each state variable reaches 0. The control accuracy of the air-fuel ratio cannot be ensured under all operating conditions.

Therefore, the present invention provides an apparatus for controlling the fuel injection amount based on the physical model described above with the fuel behavior as a state variable using the amount of fuel attached to the intake pipe wall surface and the amount of evaporated fuel in the intake pipe as described above. When executing fuel cut control,
The purpose was to ensure the control accuracy of the air-fuel ratio when returning from the fuel cut control.

[Means for Solving the Problems] That is, the configuration of the present invention made to achieve the above object is, as illustrated in FIG. 1, the amount of fuel fw adhering to the wall surface of the intake pipe M1 and the inside of the intake pipe M1. Injecting and supplying fuel from the fuel injection valve M4 every cycle of the internal combustion engine M2 according to a physical model that describes the behavior of fuel flowing into the cylinder M3 every cycle of the internal combustion engine M2 using the evaporated fuel amount fv as a state variable. A fuel injection amount control device for an internal combustion engine that controls a fuel injection amount q to be controlled, comprising: a rotation speed ω of an internal combustion engine M2, an opening / closing state of a throttle valve, a saturated vapor pressure Ps of fuel in an intake pipe M1, and a cylinder.
Operating state detecting means M5 for detecting the amount m of air flowing into M3
Calculating the fuel evaporation amount Vf from the wall surface of the intake pipe M1 based on at least the saturated vapor pressure Ps, dividing the calculation result by the rotation speed ω, and calculating the unit evaporation amount Vfw per cycle of the internal combustion engine.
And a state variable amount based on the unit evaporation amount Vfw and the fuel injection amount q from the fuel injection valve M4 for each cycle of the internal combustion engine M2.
estimating means M7 for estimating fw, fv; and, for each cycle of the internal combustion engine M2, the unit evaporation amount Vfw, the state variable amounts fw, fv, the air amount m detected by the operating state detecting means M5, and the target fuel air. Based on the product λr · m with the ratio λr,
A fuel injection amount calculating means M8 for calculating a fuel injection amount q from the fuel injection valve M4; and the fuel injection amount calculating means for each cycle of the internal combustion engine M2.
A fuel injection execution unit M9 that drives the fuel injection valve M4 according to the calculation result q of M8 to execute fuel injection, and a fuel cut of the internal combustion engine M2 based on the rotational speed ω of the internal combustion engine M2 and the open / close state of the throttle valve. Determining means M10 for determining whether a control condition is satisfied; and fuel cut control means M11 for prohibiting driving of the fuel injection valve M4 by the fuel injection executing means M9 when the determination means M10 makes an affirmative determination. When the fuel cut control condition is not satisfied, the estimation means M7 calculates the state variable amounts fw, fv each time fuel injection is performed, and at a predetermined time synchronized with the fuel injection timing when the fuel cut control condition is satisfied. The gist of the present invention is a fuel injection amount control device for an internal combustion engine, wherein the state variable amounts fw and fv are calculated by setting the fuel injection amount q to 0.

Here, the operating state detecting means M5 detects the rotational speed ω of the internal combustion engine M2, the opening / closing state of the throttle valve, the saturated vapor pressure Ps of the fuel in the intake pipe M1, and the amount m of air flowing into the cylinder M3. For detecting the rotation speed ω of the internal combustion engine M2, a rotation speed sensor conventionally used in a control device of an internal combustion engine can be used.
To detect the open / closed state of the throttle valve, a throttle fully closed switch that is turned on when the throttle valve is fully closed, a throttle opening sensor that generates a signal corresponding to the opening of the throttle valve, or the like can be used. .

Next, it is difficult to directly detect the saturated atmospheric pressure Ps in the intake pipe M1 by a sensor, but the saturated vapor pressure Ps is a function of the temperature T of the fuel adhering to the wall of the intake pipe. Can be represented by the water jacket water temperature or the cylinder head temperature near the intake port. Therefore, the water jacket water temperature or the cylinder head temperature is detected by the temperature sensor, and the detection result T (゜ K) is used as a parameter. The saturated vapor pressure Ps may be obtained by using an arithmetic expression as shown in (1).

Ps = β1 · T ² −β2 · T + β3 (1) (where β1, β2, β3 are constants) Further, the air amount m flowing into the cylinder M3 is, for example, the intake pipe pressure P, the intake temperature Ti, and the internal combustion. (2) m = {βx (ω) · P−βy (ω)} / Ti (2) using the rotation speed ω of the engine M2 as a parameter. P
In addition, the intake air temperature Ti and the intake air temperature sensor may be detected by a known intake pressure sensor and an intake air temperature sensor, and based on the detection result and the detection result by the rotation speed sensor, the above equation (2) may be used. Further, the basic air amount m is obtained from a map using the rotation speed ω of the intake pipe pressure P as a parameter, and the calculation result is corrected based on the intake air temperature to obtain the air amount m. Further, a well-known air flow meter may be provided upstream of the throttle valve to detect the amount of air flowing into the intake pipe M1, and estimate the amount m of air flowing into the cylinder M3 during the intake stroke based on the detection result. .

Next, an example of a basic physical model of the above configuration will be described.

First, the fuel amount fc flowing into the cylinder M3 of the internal combustion engine M2
Is described as the following equation (3) using the fuel injection amount q from the fuel injection valve M4, the amount fw of fuel adhering to the wall surface of the intake pipe M1, and the amount fv of evaporated fuel inside the intake pipe M1. be able to.

fc = α1 · q + α2 · fw + α3 · fv (3) That is, the fuel amount fc is the direct inflow amount α1 · q of the injected fuel from the fuel injection valve M4 and the intake pipe to which the injected fuel adheres.
Since it is considered to be the sum of the indirect inflow amount α2 · fw from M1 and the inflow amount α3 · fv of the evaporated fuel existing inside the intake pipe M1 due to the evaporation of the injected fuel or the wall-adhered fuel, the above equation ( As in 3), the fuel amount fc flowing into the cylinder M3 can be described.

In the above equation (3), since the fuel injection amount q is determined by the control amount of the fuel injection valve M4, if the amount of fuel fw adhering to the wall of the intake pipe M1 and the amount of fuel vapor fv in the intake pipe M1 can be known, The fuel amount fc can be predicted.

Therefore, the amount of deposited fuel fw and the amount of evaporated fuel fv will now be considered.

First, the amount of fuel fw adhering to the wall of the intake pipe M1 decreases by a part of α2 in each intake cycle due to inflow into the cylinder M3 during the intake stroke, and also decreases due to evaporation into the intake pipe M1. It increases due to the attachment of a part α4 of the fuel injection amount q injected from the fuel injection valve M4 in synchronization with the cycle. Further, the amount of fuel evaporation from the wall of the intake pipe M1 for each intake stroke can be expressed as α5 · Vf / ω. Therefore, the amount fw of fuel adhering to the wall of the intake pipe M1 can be described as shown in the following equation (4).

fw (k + 1) = (1−α2) · fw (k) + α4 · q
(K) −α5 · Vf (k) / ω (k) (4) (where k is the intake cycle) On the other hand, the amount of fuel vapor fv in the intake pipe M1 flows into the cylinder M3 during the intake stroke. As a result, a part α3 of the fuel injection amount q is increased by evaporating a part of the fuel injection amount q, and further increased by fuel evaporation of the adhering fuel, in addition to the reduction of the part α3 in each intake cycle. Therefore, the fuel vapor amount fv in the intake pipe M1
Can be described as shown in the following equation (5).

fv (k + 1) = (1−α3) · fv (k) + α6 · q
(K) + α5 · Vf (k) / ω (k) (5) Next, the fuel amount fc drawn into the cylinder M3 of the internal combustion engine M2.
(K) can be described as the following equation (6) from the fuel-air ratio λ (k) of the fuel mixture supplied to the internal combustion engine M2 and the air amount m (k) flowing into the cylinder M3.

fc (k) = λ (k) · m (k) (6)
Therefore, if the coefficients α1 to α6 in the above equations are determined by a system identification method, as shown in the following equations (7) and (8), the intake system represented by a discrete system using the intake cycle of the internal combustion engine M2 as a sampling cycle. A state equation (7) and an output equation (8) using the amount of fuel adhering to the pipe wall surface and the amount of steam fuel as state variables can be obtained, and a physical model representing fuel behavior in the internal combustion engine is determined.

The unit evaporation amount calculating means M6 calculates Vf /
For calculating ω, the saturated vapor pressure in the intake pipe M1
Using Ps as one parameter, the evaporation amount Vf of the fuel attached to the wall of the intake pipe M1 is calculated, and the calculation result is divided by the rotation speed ω of the internal combustion engine M2 to obtain a unit evaporation amount Vfw (that is, Vf / ω).
Is calculated. First, the fuel evaporation amount Vf from the intake pipe M1 wall surface is
To be precise, the saturated vapor pressure Ps detected by the operating state detecting means M5
And the intake pipe pressure P, and the fuel evaporation amount Vf varies greatly depending on the saturated vapor pressure Ps, so that the fuel evaporation amount Vf can be approximately determined only from the saturated vapor pressure Ps. For this reason, the unit evaporation amount calculating means M6 calculates the fuel evaporation amount Vf using a map or an arithmetic expression using only the intake pipe pressure P and the saturated vapor pressure Ps or only the saturated vapor pressure Ps as parameters. May be divided by the rotation speed ω.

Next, the estimating means M7 and the fuel injection amount calculating means M8 are set based on the physical models of the above equations (7) and (8).

First, the estimating means M7 is for estimating the adhering fuel amount fw and the evaporative fuel amount fv, but these values cannot be directly detected using a sensor like the rotational speed ω, but first, like the air amount m. Since indirect detection is not possible using an arithmetic expression or the like that uses the detection result of the sensor as a parameter, the estimation is performed using this estimation means M7. As the estimating means M7, for example, a minimum dimension observer (Minimal Order Observer), an identical dimension observer (Identity Observer), a finite settling observer (D
ead Beat Observer), Linear Function Observer (Linear Fu)
nction Observer or Adaptive Obse
Well-known design methods such as those described in Katsuhisa Furuta et al., “Basic System Theory” (1973), Corona Corporation, or Katsuhisa Furuta et al., “Mechanical System Control” (1984), Ohmsha, etc. Thus, it can be realized by configuring as an observer based on the above equations (7) and (8), or by calculating the state variable using the above equation (7) as it is.

Further, the fuel injection amount calculation means M8 controls the fuel-air ratio of the fuel-air mixture supplied to the internal combustion engine M2 to the target fuel-air ratio λr.
The product of the unit evaporation amount Vfw, the attached fuel amount fw, the evaporated fuel amount fv, and the air amount m detected by the operating state detecting means M5 and the target fuel-air ratio λ (that is, the target fuel amount flowing into the cylinder M3) λrm ,
Is used to calculate the fuel injection amount q from the fuel injection valve M4 based on the above formula. Based on the physical model of the above formulas (7) and (8), a calculation formula is set by a well-known design method, and the calculation formula is calculated. The fuel injection amount q may be calculated by adding a value obtained by multiplying each of the above values by a predetermined coefficient.

The control amount calculating means M8 detects the amount of fuel flowing into the cylinder of the internal combustion engine M2 so that the fuel-air ratio does not greatly deviate from the target fuel-air ratio due to disturbance. The deviation from the fuel amount λrm is sequentially added,
A control amount calculating means expanded to a so-called servo system (Servo System), in which a value obtained by multiplying the detection result by a coefficient is added to the calculation result of the fuel injection amount q to obtain a fuel injection amount q used for control. You may. In this case, it is necessary to detect the amount of fuel that has flowed into the cylinder of the internal combustion engine M2. For this purpose, the fuel-air ratio λ of the fuel mixture supplied to the internal combustion engine M2 is detected using a known air-fuel ratio sensor. Then, the fuel λm may be obtained by multiplying the detection result by the air amount m detected by the operating state detecting means M5.

Next, the judgment means M10 and the fuel cut control means M11 perform the fuel injection when the fuel cut control condition that the internal combustion engine M2 is in the deceleration operation in which the throttle is fully closed and the rotational speed ω is equal to or higher than a predetermined value is satisfied. This is for performing a well-known fuel cut control that prohibits fuel injection from the valve M4, and the determination means M10 determines whether or not an execution condition of the fuel cut control is satisfied, and when the fuel cut control condition is satisfied, Then, the fuel cut control means M11 prohibits the operation of the fuel injection execution means M9 and stops the fuel injection from the fuel injection valve M4.

[Operation] In the fuel injection amount control device of the present invention configured as described above, when the determining means M10 determines that the internal combustion engine M2 fuel cut control condition is satisfied, the fuel cut control means M11 operates to execute fuel injection. The driving of the fuel injection valve M4 by the means M9 is prohibited, and the fuel cut control is executed. Estimation means
M7 normally calculates the state variable amounts fw and fv using the injected fuel amount q as one parameter after executing the fuel injection by the fuel injection executing unit M9, but when executing the fuel cut control, the fuel injection executing unit M9 (I.e., fuel injection) is not executed, and the state variable quantities fw and fv are estimated by setting the fuel injection amount q to 0 at a timing synchronized with the fuel injection timing.

For this reason, in the present invention, the state variable amounts fw and fv are also sequentially updated even during execution of the fuel cut control, and the fuel injection amount q at the time of returning from the fuel cut control is changed to the state variable amounts fw and fv corresponding to the actual values. The control accuracy of the air-fuel ratio at the time of returning from the fuel cut control can be ensured.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

First, FIG. 2 is a schematic configuration diagram showing the configuration of an internal combustion engine 2 and peripheral devices to which the present invention is applied.

In the figure, reference numeral 4 denotes an intake pipe for sucking air through an air cleaner 6. The intake pipe 4 has a throttle valve 8 for controlling the amount of intake air and a throttle opening sensor for detecting the opening of the throttle valve. 9, a surge tank 10 for suppressing pulsation of intake air, an intake pressure sensor 12 for detecting a pressure (intake pipe pressure) P inside the surge tank 10, and an intake temperature sensor 14 for detecting an intake temperature Ti.

On the other hand, reference numeral 16 denotes an exhaust pipe provided with a three-way catalytic converter 18 for purifying exhaust gas.

The internal combustion engine 2 includes a throttle opening sensor 9, an intake pressure sensor 12, and an intake air temperature sensor 14 as sensors for detecting the operating state of the internal combustion engine 2, and a rotational speed of the internal combustion engine 2 based on the rotation of the distributor 20. A rotation speed sensor 22 for detecting ω, a crank angle sensor 24 for detecting the timing of fuel injection from the rotation of the distributor 20 to the internal combustion engine 2, and a cooling water temperature T attached to a water jacket of the internal combustion engine 2. A water temperature sensor 26 for detection is provided. Distributor
Numeral 20 is for applying a high voltage from the igniter 28 to the ignition plug 29 at a predetermined ignition timing.

A detection signal from each of the above sensors is output to an electronic control circuit 30 configured as a logical operation circuit centered on a microcomputer, and drives the fuel injection valve 32 to control the fuel injection amount from the fuel injection valve 32. Used to do.

That is, the electronic control circuit 30 performs an arithmetic process for controlling the fuel injection amount according to a preset control program.
CPU 40, a ROM 42 in which control programs and initial data necessary for executing arithmetic processing by the CPU 40 are recorded in advance,
A RAM 44 for temporarily reading and writing data used to execute arithmetic processing at 40, an input port 46 for inputting a detection signal from each of the above sensors, and a fuel injection valve 32 according to the arithmetic result at the CPU 40. And an output port 48 for outputting a drive signal to the cylinder 2a of the internal combustion engine 2.
The fuel injection amount q from the fuel injection valve 32 is controlled such that the fuel / air ratio λ of the fuel mixture flowing into the fuel tank reaches a preset target fuel / air ratio λr.

Next, the basics of a control system used for this fuel injection control will be described based on a block diagram shown in FIG.
FIG. 3 is a diagram showing a control system, and does not show a hardware configuration, but is actually realized as a discrete system by executing a series of programs shown in the flowchart of FIG. Further, the control system of the present embodiment is designed based on the physical model shown in the above-described equations (7) and (8).

As shown in FIG. 3, in the control system of the present embodiment, first, the intake pipe pressure P detected by the intake pressure sensor 12 and the water temperature sensor
The cooling water temperature T detected at 26 is input to the first calculation unit P1. Then, in the first calculation unit P1, the input cooling water temperature T is converted into the saturated vapor pressure Ps of the fuel in the intake pipe 4 by using the calculation formula such as the above-mentioned formula (1), and further converted. From the saturated vapor pressure Ps and the intake pipe pressure P, the evaporation amount Vf of the fuel attached to the wall surface of the intake pipe 4 is calculated. Further, the converted evaporation amount Vf is input to the division unit P2, and the rotation speed sensor
It is divided by the rotational speed ω of the internal combustion engine 2 detected using Then, the division result Vf / ω (that is, the above-described unit evaporation amount Vfw) is input to the coefficient f4 multiplication unit P3, and is multiplied by a preset coefficient f4.

On the other hand, the intake pipe pressure P detected by the intake pressure sensor 12 and the rotational speed ω detected by the rotational speed sensor 22 are also input to the second arithmetic unit P4 together with the intake temperature Ti detected by the intake temperature sensor 14. The second calculation unit P4 calculates the amount m of air flowing into the cylinder 2a from the rotation speed ω of the internal combustion engine 2, the intake pipe pressure P, and the intake air temperature Ti using an arithmetic expression such as the expression (2). The calculation result is the multiplication unit P5
Is output to Then, in the multiplication unit P5, the second operation unit P4
And the target fuel-air ratio λr set in advance
Is calculated, whereby the fuel amount (target fuel amount) λrm that should flow into the cylinder 2a is calculated. Then, the target fuel amount λrm calculated by the multiplier P5 is input to the coefficient f3 multiplier P6, and is multiplied by a preset coefficient f3.

On the other hand, the division result Vf / ω of the division unit P2 is
Also output to 7. The state variable estimating unit P7 calculates the division result Vf / ω of the dividing unit P2 and the fuel injection amount q from the fuel injection valve 32 by using a preset arithmetic expression (Equation (7) in the present embodiment). From the previously estimated fuel amount w adhering to the wall surface of the intake pipe 4 and the fuel vapor amount v in the intake pipe 4, the state variable quantities of the physical model represented by the above-mentioned equations (7) and (8),
That is, it is for estimating the attached fuel amount fw and the evaporated fuel amount fv, and the estimation results w and v are added to the coefficient f1 multiplication unit P8.
And the coefficient f2 multiplication unit P9 multiplies the coefficients by f1 and f2, respectively.

The multiplication results from the multiplication units P8 and P9 are added together with the multiplication results in the other multiplication units P3 and P6 in the addition units P10 to P12, whereby the fuel injection amount q from the fuel injection valve 32 is determined. .

Next, a method of designing the control system shown in FIG. 3 will be described. Incidentally, as a design method of this kind of control system, for example,
Katsuhisa Furuta, “Digital Control of Real System”, System and Control, Vol.28, ωo.12 (1984).

As described above, the control system according to the present embodiment is designed based on the physical model shown in the above-described equations (7) and (8).
Since the physical model is nonlinear, the physical model is first linearly approximated.

In the above equations (7) and (8), Equations (7) and (8) are Can be represented by

here, When becomes steady, Then, the above equations (19) and (20) become the following equations (19) ′, (2
0) '.

From the above equations (19), (19) 'and (20), (20)', Next, in the above equations (21) and (22), Then, the equations (21) and (22) are as shown in the following equations (26) and (27).

In these (26) and (27), if X (k) → 0, then Y (k) = 0, Becomes Therefore, the optimum regulator of the above equation (26) may be designed. That is, by preaching the discrete Riccati equation,
The optimal control is obtained as in the following equation (28).

The equation (28) becomes the following equation (29) from the equations (23) and (24).

Therefore, in the above equations (19) 'and (20)', But Equation (29) is determined if Can be asked for.

In the case of the present embodiment, the above equation (30) is obtained by using the above-described equations (10) to (1).
From equation (8), the following equation (31) is obtained. (That is, fwr, fvr, qr) are obtained as in the following equations (32) to (34), respectively.

Therefore, from the above equation (29), f1 to f4 are constants, and Thus, the control system shown in FIG. 3 can be designed.

Note that the above equation (35) is an arithmetic expression in the above-described fuel injection amount calculation means M8 for obtaining the fuel injection amount.

Next, the state variable estimating unit P7 calculates the amount of fuel fw adhering to the wall of the intake pipe 4 and the amount of fuel vaporized in the intake pipe 4 in the above equation (35).
Since fv cannot be measured directly, it is for estimating its value. This type of estimating apparatus is usually configured as an observer designed by the Gopinas design method or the like. However, in this embodiment, since the air-fuel ratio λ of the fuel mixture actually supplied to the internal combustion engine 2 cannot be measured, Normal observers cannot be used. However, since the fuel behavior in the internal combustion engine 2 can be described by the above equation (7), the fuel amount fw adhering to the wall of the intake pipe 4 can be obtained by using the equation (7) as it is.
And the fuel vapor amount fv in the intake pipe 4 can be obtained.

That is, first, in the equation (7), q (k) can be known on the electronic control circuit 30 side as a control amount, and Vf (k) represents the saturated vapor pressure Ps from the cooling water temperature T detected by the water temperature sensor 26. And can be detected from this value and the intake pipe pressure P detected by the intake pressure sensor 12, and furthermore, ω (k)
Can be detected by the rotation speed sensor 22,
The second and third terms on the right side can be calculated. Then, δw (k) = fw (k) −w (k) (36) δv (k) = fv (k) −v (k) (37) Becomes In the above equation (38), 1−α2 <1, 1−α3 <
(38) is stable because it is 1, δw (k), δv (k)
→ 0, ie w (k) → fw (k), v (k) → v
(K). Therefore, if appropriate initial values are given as fw (k) and fv (k), fw (k) and fv (k) can be estimated by the above equation (7).

Therefore, in the present embodiment, the state variable estimating unit P7 is configured to estimate the amount fw of fuel adhering to the wall surface of the intake pipe 4 and the amount fv of fuel vapor evaporated in the intake pipe 4 using the above equation (7). ing. Note that fw (k) {w, fv (k)}
Even if v, w (k) and v (k) are fw (k),
Since it follows fv (k), (That is, the fuel injection amount q (k)) can be calculated without any problem.

Next, the fuel injection control executed by the electronic control circuit 30 is changed to the fourth.
The description will be made based on the flowchart shown in FIG. In the following description, the quantity handled in the current processing is represented by a subscript (k).

The fuel injection control 30 is started when the operation of the internal combustion engine 2 starts, and is repeatedly executed during the operation of the internal combustion engine 2.

When the process is started, first execute step 100,
Initially, the attached fuel amount wo, the evaporated fuel amount vo, and the fuel injection amount q are set. Then, in step 110, the intake pipe pressure P (k), the intake air temperature Ti (k), the rotational speed ω (k) of the internal combustion engine 2, and the cooling water temperature T (k) are obtained based on the output signals from the sensors. Then, the process proceeds to step 120.

In step 120, a target fuel-air ratio λr corresponding to the load on the internal combustion engine 2 is calculated based on the intake pipe pressure P (k) obtained in step 110 and the rotational speed ω (k) of the internal combustion engine 2. In this step 120, normally, the target fuel-air ratio λ is set so that the excess air ratio of the fuel mixture becomes 1 (ie, the stoichiometric air-fuel ratio).
When the internal combustion engine 2 is operated under a high load, the target fuel-air ratio λr is set to a rich side in order to increase the output of the internal combustion engine by increasing the fuel more than usual. At times, the target fuel-air ratio λr is set to the lean side in order to improve the fuel efficiency by reducing the fuel more than usual.

When the target fuel-air ratio λr (k) is set in step 120, the process proceeds to step 130, in which the intake pipe pressure P (k) and intake temperature Ti (k) obtained in step 120 and the internal combustion engine 2 Based on the rotation speed ω (k), the cylinder 2a is calculated using an arithmetic expression or a data map as shown in the above-mentioned expression (2).
Computing unit P4 for calculating the amount of air m (k) flowing into the air
Is executed.

In the following step 140, the evaporation amount Vf of the fuel adhering to the wall of the intake pipe 2a is obtained based on the cooling water temperature T (k) and the intake pipe pressure P (k) obtained in the above step 110, and the obtained value is used as the internal combustion engine 2 Divided by the rotation speed ω (k) of
(K) (= Vf (k) / ω (k))
And the processing as the division unit P2 is executed.

The following step 150 is based on the unit evaporation amount Vfw (k) from the intake pipe wall surface obtained in the above step 140, the previous fuel injection amount q, the previously-obtained attached fuel amount wo and the previously-evaporated fuel amount vo. 7) The following equation (39) set based on the equation Is used to determine the amount of deposited fuel w (k) and the amount of evaporated fuel v
A process as a state variable estimating unit P7 for estimating (k) is executed.

When the attached fuel amount w (k) is calculated in step 150 in this way, the process proceeds to step 160, where the value w (k) is calculated.
It is determined whether or not (k) is a negative value that cannot be realized. If w (k) is a negative value, step 170 is performed.
Then, the value of the attached fuel amount w (k) is changed to 0.

Then, in the subsequent step 180, the following equation (40) Vfw (k) = １− (1−α2) · wo + α4 ·, based on the adhering fuel amount wo and the fuel injection amount q (k) used in the previous calculation of the fuel injection amount. q
(K) The unit evaporation amount Vfw (k) is calculated again using｝ / α5 (40). This equation (40) is the amount of fuel deposited on the left side in equation (4).
Assuming that fw (k + 1) is 0, the unit evaporation amount Vfw (that is, Vf / ω)
This is an arithmetic expression modified for calculation.

In the following step 190, the above equation (5) is calculated based on the calculated unit evaporation amount Vfw (k), the evaporated fuel amount vo and the fuel injection amount q (k) used in the previous calculation of the fuel injection amount. To calculate the fuel vapor amount v (k) again.

Here, the processing of steps 180 and 190 is a processing for setting the unit evaporation amount Vfw and the evaporated fuel amount fv to accurate values when the amount of fuel fw adhering to the intake pipe wall becomes zero. That is, first, at step 140, the intake pipe pressure P,
Based on the cooling water temperature T and the rotation speed ω, the unit evaporation amount Vfw is calculated assuming that the fuel has sufficiently adhered to the intake pipe wall surface. Therefore, the adhering fuel amount w calculated in step 150 as described above is negative. If the value becomes a value and all the fuel attached to the intake pipe evaporates by the next intake stroke, the value becomes too large. Therefore, in such a case, the fuel vapor amount Vfw is calculated again assuming that the amount of fuel adhering during the next intake stroke becomes 0 using the above equation (40), and further, the fuel vapor amount Vfw is calculated based on the calculation result. v is calculated again.

Next, when it is determined in step 160 that the attached fuel amount w (k) is not a negative value, or in step 160, it is determined that the attached fuel amount w (k) is a negative value.
When a series of processing from 170 to 190 is executed,
Step 200 is executed to determine whether or not the fuel cut control (F / C) execution condition such that the rotation speed of the internal combustion engine 2 is equal to or higher than a predetermined speed and the throttle valve 8 is fully closed is satisfied. Is performed as the determination means M10.

If it is determined in step 220 that the fuel cut control execution condition is not satisfied, the process proceeds to step 210, where the target fuel-air ratio λr (k) set in step 120 is set.
Is multiplied by the air amount m (k) obtained in step 130 to calculate a target fuel amount λrm (k) to be supplied into the cylinder 2a. Then, using the aforementioned equation (35), the attached fuel amount w (k) and the evaporated fuel amount v (k) set in step 150 or 170 and 190 are obtained in step 200. Target fuel amount λrm (k) and step 140
Alternatively, the processing as the above-described fuel injection amount calculating means M8 for calculating the fuel injection amount q (k) based on the unit evaporation amount Vfw (k) obtained in step 180 is executed. And the following steps
At 230, at the fuel injection timing determined based on the detection signal from the crank angle sensor 24,
The processing as the above-described fuel injection execution means M9, in which the fuel injection valve 32 is opened and fuel injection is actually performed for a time corresponding to the fuel injection amount q (k) calculated at 0, is executed.

On the other hand, if it is determined in step 200 that the fuel cut control execution condition of the internal combustion engine is currently satisfied, step 24 is executed.
After shifting to 0 and setting the fuel injection amount q to 0, the process shifts to step 250 and waits for the detection signal from the crank angle sensor 24 to be input.

And whether the fuel injection is executed in the above step 230,
Alternatively, if it is determined in step 250 that the detection signal from the crank angle sensor 24 for determining the fuel injection timing has been input, the process proceeds to step 260, in which
0, or the values of the attached fuel amount w (k) and the evaporated fuel amount v (k) set in steps 170 and 190 are used to estimate the attached fuel amount w and the evaporated fuel amount v in the next process. Reference values wo of the attached fuel amount and the evaporated fuel amount,
vo is set, and the process returns to step 110 again.

As described above, in the fuel injection control device according to the present embodiment, since the control law is set based on the physical model describing the behavior of the fuel in the internal combustion engine 2, the intake pipe temperature of the internal combustion engine 2, that is, the internal combustion engine 2 The behavior of the fuel that changes depending on the warm-up state can be nonlinearly compensated by Vfw (that is, Vf / ω), and the fuel injection amount can be controlled by a single control law. Therefore, complicated control such as changing the control law according to the operating state of the internal combustion engine becomes unnecessary, and the control system can be simplified.

Further, in the present embodiment, when the execution condition of the fuel cut control is satisfied, the fuel injection execution process of step 230 is not performed, and
In step 240, the fuel injection amount q is set to 0, and the process of step 110 is executed again when the detection signal is input from the crank angle sensor 24 for determining the fuel injection timing. Therefore, even when the fuel cut control is executed, the processing of steps 150 to 190 is executed in synchronization with the actual fuel injection timing. The fuel vapor amount fv is sequentially updated, and the fuel injection amount q calculated in step 220 at the time of returning from the fuel cut control can be set to a value corresponding to the operating state of the internal combustion engine.

That is, for example, if the processing after step 110 is executed only when the fuel injection is executed in step 230, the fuel injection is not executed when the fuel cut control is executed, and the fuel injection amount when the fuel cut control is returned is reduced. The air-fuel ratio is calculated based on the adhering fuel amount fw and the evaporative fuel amount fv calculated before the execution of the fuel cut control, and the air-fuel ratio greatly deviates from the target air-fuel ratio as shown by a dotted line in FIG. ,
Even during execution of fuel cut control, the amount of deposited fuel fw and the amount of evaporated fuel
Since fv is updated and the value becomes an accurate value corresponding to the operation state of the internal combustion engine 2, the fuel injection amount at the time of returning from the fuel cut control can be set to a value corresponding to the state of the internal combustion engine. As shown by the solid line in FIG. 5, the air-fuel ratio at the time of return from the fuel cut control becomes the target air-fuel ratio, and the control accuracy of the air-fuel ratio can be improved.

Further, in the present embodiment, when the attached fuel amount w (k) calculated in step 150 becomes a negative value which is not practically possible, the value w (k) is reduced by the processing in steps 160 and 170. 0, and in steps 180 and 190, the unit evaporation amount Vfw (k) and the evaporation fuel amount v
(K) is set to be calculated again. Therefore, in the present embodiment, the unit evaporation amount Vfw (k) calculated in step 140 is larger than the actual amount when the internal combustion engine 2 rotates at a high load and at a high speed where all the fuel attached to the intake pipe wall surface evaporates. As a result, the fuel injection amount q does not become a value that does not correspond to the operation state of the internal combustion engine 2, and the fuel injection amount q can always be calculated with high accuracy corresponding to the operation state of the internal combustion engine. The control accuracy of the fuel ratio can be improved.

[Effects of the Invention] As described above, in the fuel injection amount control device for an internal combustion engine according to the present invention, the physical behavior in which the fuel behavior in each cycle of the internal combustion engine is described by using the state variables of the attached fuel amount and the evaporated fuel amount. 1 of the internal combustion engine according to the control law set based on the model
In controlling the fuel injection amount to be injected and supplied for each cycle, the state variable amount required for the control is estimated at the time of fuel injection, and the injected fuel amount at that time is estimated as one parameter. The fuel injection amount is estimated to be 0 at a timing synchronized with the injection timing. Therefore, according to the present invention, the state variable amount is updated every cycle of the internal combustion engine not only at the time of executing the fuel injection but also at the time of executing the fuel cut control. In addition, the control can be performed based on the state variable amount (estimated value) corresponding to the actual attached fuel amount and the evaporated fuel amount, and the control accuracy of the air-fuel ratio at the time of returning from the fuel cut control can be ensured.

Further, in the present invention, each calculation part for controlling the fuel injection amount, such as the estimating means and the fuel injection amount calculating means, performs calculation such as estimation of the state variable amount and calculation of the fuel injection amount for each cycle of the internal combustion engine. It is configured to perform an operation. For this reason, for example, the estimation of the state variable amount, the calculation of the fuel injection amount, and the like can be performed with higher accuracy than when, for example, a control law is set according to a physical model describing the fuel behavior of the internal combustion engine at regular intervals. The control accuracy of the air-fuel ratio can be improved.
That is, as the physical model used for controlling the fuel injection amount, in addition to the physical model discretized along the intake cycle of the internal combustion engine as in the present invention, a physical model discretized at regular intervals is used. However, since the fuel behavior in the internal combustion engine is synchronized with the intake cycle of the internal combustion engine, control for estimating the state variable amount, calculating the fuel injection amount, etc. according to the physical model describing the fuel behavior per unit time When the rule is determined, the calculation timing and the behavior of the internal combustion engine are not synchronized, and thus an error occurs in the estimated state variable amount and the fuel injection amount calculated based on the state variable amount.
However, in the present invention, since various calculations are performed for each cycle of the internal combustion engine, it is possible to prevent an error from occurring in the calculation results and improve control accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a schematic configuration diagram showing an internal combustion engine and peripheral devices of the embodiment, FIG.
FIG. 4 is a block diagram showing the basic configuration of the control system of the embodiment, FIG. 4 is a flowchart showing the fuel injection control of the embodiment, and FIG. 5 is a time chart showing the change of the air-fuel ratio when executing the fuel cut control. M1, 4 ... intake pipe, M2, 2 ... internal combustion engine M3, 2a ... cylinder, M4, 32 ... fuel injection valve M5 ... operating state detecting means M6 ... unit evaporation amount calculating means M7 ... estimating means , M8 ... fuel injection amount calculation means M9 ... fuel injection execution means, M10 ... determination means M11 ... fuel cut control means 12 ... intake pressure sensor, 14 ... intake temperature sensor 20 ... rotational speed sensor, 26 …… Water temperature sensor 30 …… Electronic control circuit

Claims (1)

(57) [Claims] 1. A physical model that describes the behavior of fuel flowing into a cylinder for each cycle of an internal combustion engine using the amount of fuel adhering to an intake pipe wall surface and the amount of evaporated fuel in the intake pipe as state variables. A fuel injection amount control device for an internal combustion engine, which controls a fuel injection amount supplied from a fuel injection valve for each cycle of the internal combustion engine, comprising: a rotation speed of the internal combustion engine, an opening / closing state of a throttle valve, and a fuel injection amount in an intake pipe. Operating state detecting means for detecting the saturated vapor pressure and the amount of air flowing into the cylinder; calculating an amount of fuel evaporation from the intake pipe wall based on at least the saturated vapor pressure; and dividing the calculation result by the rotational speed. A unit evaporation amount calculating means for calculating a unit evaporation amount per one cycle of the internal combustion engine, and the state variable based on the unit evaporation amount and the fuel injection amount from the fuel injection valve for each cycle of the internal combustion engine. And a fuel injection valve for each cycle of the internal combustion engine based on the unit evaporation amount, the state variable amount, and the product of the air amount detected by the operating state detection unit and the target fuel-air ratio. Fuel injection amount calculating means for calculating a fuel injection amount from the fuel injection means, and a fuel injection executing means for driving a fuel injection valve in accordance with the calculation result of the fuel injection amount calculating means for each cycle of the internal combustion engine to execute fuel injection Determining means for determining whether or not fuel cut control conditions for the internal combustion engine are satisfied based on the rotational speed of the internal combustion engine and the open / closed state of the throttle valve; Fuel cut control means for prohibiting the fuel injection valve from being driven by the injection execution means.The estimating means calculates a state variable amount every time fuel injection is performed when the fuel cut control condition is not satisfied, A fuel injection amount control device for an internal combustion engine, wherein a fuel injection amount is set to 0 and a state variable amount is calculated at a predetermined timing synchronized with the fuel injection timing when a cut control condition is satisfied.