JPH0794809B2 - Air amount detection device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for accurately detecting an intake air amount required as input information for combustion control of an internal combustion engine such as an automobile.

(Prior Art) Generally, in a certain operating condition, the amount of fuel required by the engine has an intake air amount of the engine at that time as one important parameter.

As an air amount detection device for an internal combustion engine, which determines the amount of fuel required by the engine from this kind of conventional intake air amount, for example, "Car Electronics General Technical Data" (edited by Japan Industrial Technology Center, published in October 1981) ) Are listed.

In this device, the air flow rate is extracted from the rotational displacement of the measuring plate of the air flow meter provided in the intake pipe, and converted into an electric signal by the potentiometer. This electric signal is input to the control unit and divided by a predetermined trigger corresponding to the engine speed. The divided electric signal corresponds to the intake air amount for each cylinder, and the fuel supply amount is determined based on the intake air amount so that the target air-fuel ratio is achieved based on the steady state condition.

However, in the intake air flow rate detected by the engine, for example, at the time of sudden acceleration, the intake air flow rate detected by the air flow meter is actually measured by the engine due to the collector volume (manifold pressure filling amount) between the throttle valve and the intake valve. This may cause a so-called overshoot phenomenon, which temporarily becomes a value extremely larger than the required intake air amount. In such a case, the basic injection amount Tp calculated based on the intake air amount will temporarily increase greatly as shown by the solid line in FIG. 10 (B), and the air-fuel ratio will fluctuate and the engine will change. Misfires and disturbances in ignition occur, resulting in deterioration of drivability and exhaust emission characteristics.

Therefore, in order to solve such a problem, for example, JP-A-58
The device described in Japanese Patent No. -173429 has been proposed. In this device, the basic injection amount Tp is provided with a limit value Tpmax as shown in FIG. 7B according to the engine speed N, and the overshoot of the air amount in the portion shown in FIG. 7B is cut by this Tpmax. I am trying.

(Problems to be Solved by the Invention) However, in such a conventional air amount detecting device for an internal combustion engine, a limit value Tpmax uniformly set with respect to N is set.
Therefore, if the limit value Tpmax is too large with respect to Tp, as shown by the solid line in FIG. 10 (B) (actually, to avoid lean misfire, to some extent, Overshoot remains (which is set on the rich side with a margin), and this overshoot causes the air-fuel ratio to greatly change to rich, which causes deterioration of exhaust emission (CO emission, etc.). Further, the above-mentioned overshoot amount is shown as an error with respect to the injection valve air amount (see the broken line portion in FIG. 7B), and this error is greatly affected by the difference in air density. That is, as shown in FIG. 6C, the injection valve air amount is small in the highland where the air density is low.
Since x has a constant value without considering such differences in air density, the error between the injection valve air amount and Tpmax expands, especially in highlands, and a large overshoot remains. , The air-fuel ratio is greatly enriched, and exhaust emission characteristics are significantly deteriorated. Also, Tpma
When x is too small, especially when the intake air temperature is low (air density is high) and the true flow rate is large, the injection valve air amount is limited to a small value by Tpmax as shown by the broken line in FIG. Therefore, there is a problem in that the combustion state deteriorates due to the lean air-fuel ratio, the drivability is deteriorated, and in the worst case, a misfire occurs.

(Object of the Invention) Therefore, the present invention calculates the air density coefficient based on the ratio or difference between the intake air amount and the basic limit value of the air amount when the engine is in the fully open state, and calculates the air density coefficient according to the air density coefficient. By correcting the basic limit value to obtain the maximum limit value, and by preventing the output of the air amount detecting means from exceeding the maximum limit value, overshoot is prevented regardless of changes in intake air temperature, cooling water temperature, and atmospheric pressure. The purpose is to cut properly to improve the detection accuracy of the intake air amount.

(Means for Solving the Problems) In order to achieve the above object, an air amount detecting device for an internal combustion engine according to the present invention has a basic conceptual diagram thereof as shown in FIG. Means a, rotation speed detection means b for detecting the engine speed, full open detection means c for detecting the fully open state of the engine, and basic limit value for calculating the basic limit value of the intake air amount based on the engine speed. A calculating means d, and an air density calculating means e for calculating an air density coefficient for correcting the basic limit value based on the ratio or difference between the output of the intake air amount detecting means a and the basic limit value when the engine is in the fully open state. , The basic limit value is the air density calculating means e
Maximum limit value calculating means f for correcting the maximum air amount limit value according to the output of the above, and maximum value limiting means g for limiting the output of the air amount detecting means a so as not to exceed the maximum air amount limit value. And are equipped with.

(Operation) In the present invention, the air density coefficient is calculated based on the ratio or difference between the intake air amount and the basic limit value of the air amount when the engine is fully open, and the basic limit value is calculated according to the air density coefficient. Is corrected and the maximum limit value is calculated. Then, the output of the air amount detecting means is limited so as not to exceed the maximum limit value. Therefore, the overshoot is appropriately cut regardless of changes in the intake air temperature, the cooling water temperature, and the atmospheric pressure, and the accuracy of detecting the intake air amount is improved.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 9 are diagrams showing an embodiment of an air amount detecting device for an internal combustion engine according to the present invention, and this embodiment is an example in which the present invention is applied to a fuel supply control device. First, the configuration will be described.
FIG. 2 is a diagram showing the overall configuration of this device. In FIG. 2, reference numeral 1 denotes an engine, intake air passes from an air cleaner 2 to an intake pipe 3, and fuel is injected from an injector 4 based on an injection signal Si. Then, the exhaust gas burned in the cylinder is introduced into the catalytic converter 6 through the exhaust pipe 5,
Hazardous components (CO, HC, NO in exhaust gas in the catalytic converter 6)
x) is cleaned by a three-way catalyst and discharged.

The flow rate Qa of the intake air is detected by a hot wire type air flow meter (intake amount detecting means) 7 and controlled by a throttle valve 8 in the intake pipe 3. The type of the air flow meter 7 may be a hot film type, and any type that measures the flow rate of intake air may be used. Therefore,
A flap type may be used, but the negative pressure sensor is excluded.

The opening TVO of the throttle 8 is a throttle opening sensor (opening detection means) 9
The rotation speed N of the engine 1 is detected by a crank angle sensor (rotation speed detecting means) 10. In addition, the temperature Tw of the cooling water flowing through the water jacket is measured by the water temperature sensor.
The oxygen concentration in the exhaust gas is detected by the oxygen sensor 12. Oxygen sensor 12 outputs at stoichiometric air-fuel ratio
A material having a characteristic in which Vs suddenly changes is used. further,
The idle state of the engine 1 is detected by the idle switch 13.

The air flow meter 7, the throttle valve opening sensor 9, the crank angle sensor 10 and the water temperature sensor 11 constitute an operating state detecting means 14, and the outputs from the operating state detecting means 14, the oxygen sensor 12 and the idle switch 13 are controlled. Input to unit 20.

The control unit 20 has a function as a fully open detection means, a basic limit value calculation means, an air density calculation means, a maximum limit value calculation means and a maximum value limit means, a CPU 21, a ROM 21,
It consists of RAM23 and I / O port 24. CPU21 is ROM
I / O port 24 according to the program written in 22
RAM2 to capture external data that is needed by
While exchanging data with the 3 and the like, the processing value necessary for the air amount detection and the combustion control is arithmetically processed, and the processed data is output to the I / O port 24 as necessary. I / O port 24
The signals from the sensor groups 7, 14, and 12 are input to the I / O port 24, and the injection signal Si is output from the I / O port 24. ROM22
Stores the calculation program in CPU21, RAM23
Stores data used for calculation in the form of a map or the like.

Next, the operation will be described.

FIG. 3 is a flowchart showing a program for calculating the AvTp maximum limit value Tpmax.
It is executed once every ms. First, the start switch in the P ₁
ON / OFF is discriminated, and if ON, the air density coefficient Aden is determined from the table map shown in FIG. 4 based on the temperature Tw of the cooling water at P ₂ .
Look up st to finish the process. When the start switch is OFF, the AvTp limit value table value (basic limit value) Ttpmax is looked up from the table map shown in FIG. 5 based on the engine speed N at P ₃ , and the throttle valve opening TVO at P ₄ Full throttle determination throttle valve opening WOTTVO # or more (TVO ≧ WOTTVO #)
Determines whether, TVO ≧ WOTTVO # engine speed N in P ₅ when the it is determined whether or not the predetermined value (e.g. 1000 rpm) or more. When N ≧ 1000 rpm, N is the learning condition upper limit GTP in P ₆
It is determined whether MN # or more (N ≧ GTPMN #), N <GTPMN
When it is #, it is determined that the rewriting condition is satisfied, and in P ₇ , the current flat A / F correction pulse width TrTp is multiplied by the AvTp limit value table value Ttpmax and the previous Adenst (Ttpmax
X Adenst). Where Ttpmax and TrTp above
Will be explained with the program shown in FIG. 7 described later. TrTp
≧ Ttpmax × when Adenst rewrites the Adenst according to the following equation by P _8, when the TrTp <Ttpmax × Adenst rewritten Adenst according to the following equation at P _9. Where Adenst is WOT (wid
e open throtle: The ratio of Tp and Ttpmax at full speed.

Adenst = Old Adenst + DADENA # ...... However, DADENA #: Learning coefficient rewriting amount plus Adenst = Old Adenst + DADENS # ...... However, DADENS #: Learning coefficient rewriting amount minus Next, at steps P _{10 to} P ₁₃ , Adenst is the air density upper limit value. ADEMX # and air density lower limit value ADEMN # limit (AD
EMX # ≤ Adenst ≤ ADEN #). That is, at P ₁₀ , Adenst
Is equal to or greater than ADEMX #, and when Adenst <ADEMX #, limit Adenst to ADEMX # with P ₁₁ (Adenst ← ADEMX
#). Adenst ≧ ADEMX # Adenst in P ₁₂ when of ADEMN #
If it is smaller than A, if Adenst ≥ ADEMN #, then P
Limit Adenst to ADEMN # with ₁₃ (Adenst ← ADEMN #)
proceeds to P ₁₄ when ENST <of ADEMN # was determined to be within the limits. On the other hand, when at P ₄ TVO <of WOTTVO #, at P ₅ N <1000 r
Adens when pm or when P ₆ and N <GTPMN #
Judge that the condition to calculate t is not satisfied and P
Proceed to ₁₄ . In P ₁₄ , AvTp maximum limit value Ttpma
The x is calculated and the processing this time is ended.

Tpmax = Tpmax × Kqho × Adenst + YUTORI # ...... However, Kqho: α-N The correction amount looked up from the table map shown by the solid line in Fig. 6 based on the flow rate Qho. Note that α
The -N flow rate Qho is for obtaining the air flow rate from the throttle valve opening TVO and the rotation speed N, and is already known.

In the formula, YUTORI # is a margin, and the maximum limit value has a certain margin. Becomes useless.

FIG. 7 shows the pulse width (average injection amount) AvTp equivalent to the injection valve flow rate.
It is a flowchart showing a program for calculating, and this program is executed once every 10 ms, for example. First,
Loading the output of the air flow meter 7 by P ₂₁ obtains the intake air quantity Q _2. This is due to table lookup, for example. Next, at P ₂₂ , the unsmoothed basic pulse width Tpo is calculated according to the following equation.

Next, at P ₂₃ , Tpo is weighted and averaged to calculate the basic pulse width Tp. Thereby, the pulsation based on the output of the air flow meter 7 is smoothed. In P ₂₄ , flat A according to the following formula
/ F Calculate corrected basic pulse width TrTp.

TrTp = Tp × Kflat In the equation, Kflat is a flat A / F correction coefficient, which is obtained by interpolation calculation from the map assigned by the rotation speed N and the α−N flow rate Qho.

Then, at P ₂₅ , compare TrTp with the maximum limit value Tpmax calculated by the program shown in Fig. 3. If TrTp> Tpmax, TrTp at P ₂₆
Limit p to Tpmax and proceed to P _{27. If} TrTp ≤ Tpmax, P
Jump ₂₆ and proceed to P ₂₇ . In P ₂₇ obtains the delay corrected pulse width Thstp as alpha-N precorrection pulse width. This is obtained as the amount of change for every 10 ms of the value Thstp that is looked up from the table with interpolation calculation based on the α-N flow rate Qho. However, if the amount of change is less than or equal to the correction determination level, Th
When stp = 0 and the amount of change is negative (deceleration), the amount of change is multiplied by a predetermined deceleration correction rate. Thstp is a term for correcting the injection amount with good response in advance of changes in the throttle valve 8. Next, at P ₂₈ , the smooth injection amount AvTp (corresponding to the smooth intake amount) is calculated according to the following equation.

AvTp = TrTp x Fload + AvTp _-1 x (1-Fload) + Thstp ...
However, AvTp _-1 : In the previous AvTp formula, Fload is a weighted average coefficient, and Fload = Tf
given by load + K2D (deceleration only). Since Tfload is a function of only the intake volume, it is obtained from a map from the flow rate area AA determined by the throttle valve 8 and (rotation speed x exhaust amount) NMV. Therefore, the first and second terms of the equation
The term is the weighted average value of the flat A / F corrected basic pulse width TrTp calculated based on the pulsation corrected value of the output of the air flow meter 7 using Fload, in other words TrT.
It corresponds to the part where the temporary delay of p is calculated (by software). Further, the third term of the equation is a portion for pre-correction by the throttle valve opening TVO, and this portion is disclosed for the first time in this embodiment.

The effect of adding Thstp of the third term is shown in FIG. In Fig. 8, when accelerating at a certain timing, the basic pulse width Tp
o and Tp change, and the waveform obtained by correcting Tpo and Tp changes as the flat correction basic pulse width TrTp as shown in FIG.
On the other hand, the α-N flow rate Qho changes stepwise according to the opening degree of the throttle valve 8 as shown in FIG. 7D, and the delay correction pulse width Thstp is calculated based on this opening change amount.
On the other hand, the smooth injection amount AvTp is given by the first-order delay of TrTp, and Th
In the case of the conventional phase control without stp, the change is shown by the alternate long and short dash line in the figure and the response is lacking. At this time, the income negative pressure is shown by a broken line and is substantially equal to the air flow rate of the injection valve portion (injector 4 portion), but this cannot follow the change in the opening degree of the throttle valve 8 without delay. Further, the intake volume also affects the amount of fuel adhered to the wall surface of the intake pipe 3.

On the other hand, AvTp of the present embodiment has a very responsiveness because the correction term Thstp is added as a pre-correction of α-N (pre-correction of 10 ms), as shown by the solid line in the figure. It matches the change in the air flow rate. An example of a highland is also shown.

Thus, by the ratio of Tp at the time of WOT and the reference value Ttpmax of Tpmax stored in advance (corresponding to the air density coefficient Adenst)
Tpmax is learned and corrected to find Tpmax, and Tp is limited so as not to exceed Tpmax. Therefore, FIG. 9 (A)
As shown by the solid line in the figure, even when AvTp at low intake air temperature is large, the limit level of Tpmax becomes appropriate according to AvTp, and overshoot is appropriately cut. Also,
Figure 9 (A) broken line or Figure 8 (F) even at high altitude
Optimal limit level Tpmax according to AvTp as shown in
Is set, the overshoot can be appropriately cut. In this embodiment, by performing the phase control (that is, the calculation of TrTp) using the signal limited by Tpmax, it is possible to improve the calculation accuracy of AvTp as the injection valve air amount, and FIG. ), The flatness of the air-fuel ratio can be sufficiently enhanced. As a result, drivability and exhaust gas purification performance can be significantly improved.

The maximum air amount limit in the claims is the intake air amount.
Basic pulse width expressed by Qa as injection pulse width Needless to say, the concept also includes
Even in this embodiment, Tpmax for limiting Tp is used as the maximum air amount limit value in the claims.

(Effect) According to the present invention, the air density coefficient is calculated based on the ratio or difference between the intake air amount and the basic limit value of the air amount when the engine is in the fully open state, and the basic density is calculated according to the air density coefficient. The limit value is corrected to obtain the maximum limit value, and the output of the air amount detecting means is set so as not to exceed the maximum limit value. Therefore, overshoot is prevented regardless of changes in intake air temperature, cooling water temperature, and atmospheric pressure. It can be cut appropriately and the detection accuracy of the air amount can be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 9 are diagrams showing an embodiment of an air amount detecting device for an internal combustion engine according to the present invention, and FIG. 2 is an overall configuration diagram thereof, and FIG. Is a flowchart showing a program for calculating the AvTp maximum limit value Tpmax, FIG. 4 is the Adenst table map, FIG. 5 is the Ttpmax table map, FIG. 6 is the Kqho table map, and FIG. Injection valve flow equivalent pulse width AvTp
FIG. 8 is a flow chart showing a program for calculating, FIG. 8 is a timing chart for explaining its operation, FIG. 9 is a timing chart for explaining its effect, and FIG.
The drawing is a timing chart for explaining the problems of the conventional air amount detecting apparatus for an internal combustion engine. 1 ... Engine, 7 ... Air flow meter (intake air amount detection means), 10 ... Crank angle sensor (rotation speed detection means), 20 ... Control unit (fully open detection means, basic limit position calculation means, air density calculation means) , Maximum limit value calculation means,
Maximum limit means).

Claims (1)

[Claims] Claims: 1. A) intake air amount detection means for detecting the intake air amount of the engine; b) rotation speed detection means for detecting the rotation speed of the engine; and c) full opening detection means for detecting the fully opened state of the engine. d) a basic limit value calculating means for calculating a basic limit value of the intake air amount based on the engine speed, and e) a ratio or a difference between the output of the intake air amount detecting means and the basic limit value when the engine is in a fully open state. Air density calculating means for calculating an air density coefficient for correcting the basic limit value on the basis of: f) maximum limit for calculating the maximum air amount limit value by correcting the basic limit value according to the output of the air density calculating means An air amount detecting device for an internal combustion engine, comprising: a value calculating means; and g) maximum value limiting means for limiting the output of the air amount detecting means so as not to exceed the air amount maximum limit value.