JPH0629581B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention detects the property of fuel used in an internal combustion engine such as an automobile, and based on the detection result, particularly corrects the air-fuel ratio at high load. Related to the device.

(Prior Art) Recently, there is a tendency that higher fuel economy and drivability are required for an engine, and from this viewpoint, a microcomputer or the like is applied to more accurately control the air-fuel ratio.

In such control, the characteristics of the fuel may occupy an important position as input information.

A conventional air-fuel ratio control device is, for example, Japanese Patent Laid-Open No. 60-4.
There is one described in Japanese Patent No. 5742. In this device, the oxygen sensor provided in the exhaust pipe detects the air-fuel ratio, and the fuel injection amount is operated based on the detection result to perform feedback control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.

That is, the injection pulse signal (final injection amount) Ti output to the injector is calculated according to the following equation based on the detection results of the air-fuel ratio, the intake air amount, the engine speed, the cooling water temperature, and the like.

Ti = Tp × C ₀ × α × Ts ... where Tp: basic injection amount C ₀ : various correction coefficients α: air-fuel ratio feedback correction coefficient Ts: voltage correction amount In the above equation, various correction coefficients C ₀ are in accordance with the following equations. Is calculated.

C ₀ = 1 + KTRM + KMR + KTW + KAS + KAI + KACC + KH, where KTRM: correction coefficient of mixing ratio KMR: correction coefficient of mixing ratio KTW: water temperature increase correction coefficient KAS: start / start increase correction coefficient KAI: idle increase correction correction coefficient KACC: acceleration decrease Coefficient KH: High water temperature increase correction coefficient Among the above correction values, KMR is used to improve drivability at high load, and at high load where air-fuel ratio feedback control is stopped, this KMR is used to set the theoretical air-fuel ratio. By controlling to a predetermined target air-fuel ratio richer than the fuel ratio, the output is secured and the engine temperature is suppressed.

The above correction values are set on the assumption that standard fuel (eg, regular gasoline) is used as the fuel supplied to the engine.

(Problems to be Solved by the Invention) However, in such a conventional air-fuel ratio control device, the properties of the fuel used by the engine (for example, the level of heaviness)
As a standard, a uniform value corresponding to the standard fuel is used as a standard, and the various correction values as described above are calculated and set on the assumption that the property of the fuel is always constant. Even if the property related to the volatility of the fuel changes accordingly, the air-fuel ratio is not corrected for the property change of the supplied fuel. Therefore, in such a case, there is a difference between the air-fuel ratio calculated on the assumption that standard fuel is used and the actual air-fuel ratio, and it is difficult to achieve accurate air-fuel ratio control.

That is, for example, when heavy gasoline is used, its volatility is poorer than that of regular regular gasoline, and the vaporization component is completed before combustion to dilute the premixed combustion gasoline component. The actual air-fuel ratio becomes leaner than the air-fuel ratio calculated as the reference. In addition, when soft gasoline is used, the actual air-fuel ratio becomes rich, contrary to the above.

Therefore, especially at a high load when the air-fuel ratio feedback control is stopped, even if the output is suppressed and the engine temperature is suppressed by correcting the air-fuel ratio using KMR as described above, It could be insufficient or excessive due to the influence of.

Therefore, the present invention detects the property relating to the volatility of the used fuel, and appropriately corrects the supply air-fuel ratio at the time of high load based on the detection result, so that the actual air-fuel ratio at the time of high load is irrespective of the change in the property of the fuel. The purpose is to further improve the drivability of the engine by making the fuel ratio appropriate.

(Means for Solving the Problems) In order to achieve the above object, an air-fuel ratio control device for an internal combustion engine according to the present invention detects a property relating to volatility of a used fuel, as shown in a basic conceptual diagram thereof in FIG. Property detecting means a
An operating state detecting means b for detecting a high load operating state of the engine; and an air fuel ratio setting means c for setting the supply air fuel ratio when the engine is in a high load operating state based on the property of the reference fuel. When the property of the used fuel is heavier than the reference fuel, on the rich side of the set supply air-fuel ratio,
The actual supply air-fuel ratio when the engine is in a high load operation state so that when the detected fuel properties are softer than the reference fuel, the air-fuel ratio becomes leaner than the set supply air-fuel ratio. Correction means d for correcting

(Operation) In the present invention, when the property of the used fuel is heavier than the reference fuel, it is set to the rich side than the set supply air-fuel ratio when the property of the used fuel is heavier than the reference fuel, and is set to be softer than the reference fuel in the present invention. The supply air-fuel ratio is corrected to be leaner than the supply air-fuel ratio. Therefore, even if the fuel property relating to the volatility of the used fuel changes, the actual air-fuel ratio at high load becomes appropriate, and the drivability of the engine improves.

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

1 to 13 are views showing a first embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention, in which a combustion speed is detected from an in-cylinder pressure signal, and a property relating to fuel volatility is detected based on the detected value. It shows an example in which is determined.

First, the configuration will be described. In FIG. 2, reference numeral 1 is an engine, intake air is supplied from an air cleaner 2 to each cylinder through an intake pipe 3, and fuel is injected by an injector (operating means) 4 based on an injection signal Si. The waste burned in the cylinder is introduced into the catalytic converter 6 through the exhaust pipe 5, and in the catalytic converter 6, harmful components (CO,
HC, NOx) are cleaned by a three-way catalyst and discharged.

The flow rate Qa of the intake air is detected by the air flow meter 7 and controlled by the throttle valve 8 in the intake amount 3. The opening Cv of the throttle valve 8 is detected by the throttle valve opening sensor 9. Also,
The combustion pressure Pa in the cylinder (hereinafter referred to as cylinder pressure) Pa is detected by a pressure sensor 10, and the pressure sensor 10 is composed of a piezoelectric element and is molded as a washer for an ignition plug 11. The pressure sensor 10 detects an in-cylinder pressure Pa acting on the piezoelectric element via the ignition plug 11 and outputs an analog signal having a voltage value corresponding to the in-cylinder pressure Pa.

The rotation speed N of the engine 1 is detected by the crank angle sensor 12, and the temperature Tw of the cooling water flowing through the water jacket is detected by the water temperature sensor 18. Further, the oxygen concentration in the exhaust gas is detected by the oxygen sensor 14, and the oxygen sensor 14 has a characteristic such that its output Vs suddenly changes depending on the stoichiometric air-fuel ratio.

The air flow meter 7, the throttle valve opening sensor 9, and the crank angle sensor 12 constitute an operating state detecting means 15, and outputs from the operating state detecting means 15, the pressure sensor 10, the water temperature sensor 13 and the oxygen sensor 14 are controlled. Input to unit 16. The control unit 16 has a function as a sex condition determining means together with the pressure sensor 10, and also has a function as an air-fuel ratio detecting means and a correcting means by itself.
It is composed of a ROM 22, a RAM 23, an NVM (nonvolatile memory) 24 and an I / O port 25. CPU21 is ROM22
I / O boat 25 according to the program written in
Get external data that you need more, or RA
While exchanging data with M23 and NVM24, the processing value necessary for air-fuel ratio control based on the determination of the property related to the volatility of the fuel and the result is arithmetically processed, and the processed data is processed as necessary. Output to / O port 25. I
Signals from the sensor groups 7, 9, 10, 12, 13, 14 are input to the / O port 25, and an injection signal Si is output from the I / O port 25. The ROM 22 stores the arithmetic program in the CPU 21, and the RAM 23 and NVM
24 stores the data used for the calculation in the form of a map or the like.

Next, the operation will be described. First, the change in the properties relating to the volatility of the fuel and its influence will be described taking gasoline as an example.

Gasoline is composed of several hundred kinds of hydrocarbons (HC) and classified into four kinds of paraffin group, olefin group, naphthene group and aromatic group according to the ratio of carbon (C) and hydrogen (H) and the bonding mode. It As a general tendency, the higher the number of C or H, the higher the boiling point and the higher the fractional distillation temperature from crude oil (represented by the 50% distillation temperature T ₅₀ ). Also, the heavy degree of gasoline is represented by _{T 50, T 50} = _80~90 ℃ in those soft (high volatility), _{T 50} = 110 to 120 ° C. at what heavy (less volatile) And
Most of those having T ₅₀ = 95-100 ° C. are in the market. Therefore, the final injection amount Ti is T ₅₀ =
It is determined by making various corrections on the assumption that fuel of 95 to 100 ° C (that is, regular gasoline) is used.

FIG. 3 shows changes in the fuel state when the degree of gasoline is changed as changes in the in-cylinder pressure signal under predetermined conditions (air-fuel ratio, intake air amount, engine temperature and ignition timing are constant). is there. Note that Pmax in the figure is the maximum point of the in-cylinder pressure signal, and θpmax is the crank angle that gives Pmax. Further, t in the figure indicates an actual combustion engine from the ignition timing θi to θpmax.

As shown in FIG. 3, in the case of soft gasoline, the maximum value Pmax of the in-cylinder pressure signal is large and the combustion progresses quickly, but as the fuel becomes heavier, Pmax decreases and θpmax progresses to the later side. This is because the vaporization is completed by the initial stage of combustion (that is, from ignition to θpmax), and the gasoline component (hatched portion in FIG. 4) that undergoes premixed combustion decreases as the fuel becomes heavier. That is,
The heavier the gasoline component that contributes to combustion up to θpmax, which effectively acts as the engine torque, becomes leaner and becomes leaner as the heavier becomes, and the combustion speed becomes slower (Pmax is delayed). It is shown that.

Further, this phenomenon becomes more remarkable as the engine temperature becomes lower, the volatility of heavy gasoline deteriorates, and the air-fuel ratio becomes more diluted.

In the present embodiment, in view of the above characteristics of the fuel property, the property of the fuel is appropriately detected by a program as described later focusing on the causal relationship with the burning velocity as a parameter, and the detection result Based on the above, the air-fuel ratio control under high load is performed more appropriately.

FIG. 5 is a flow chart showing an air-fuel ratio control program written in the ROM 22 at the time of high load, and this program is executed once in synchronization with the engine rotation.

First, the intake air amount Qa is read at P ₁ , and the engine speed N is read at P ₂ . The rotation speed N is the crank angle sensor.
It is calculated by measuring the interval time of the reference signal (signal every 360 °) from 12 or by measuring the number of pulses of the position signal (signal at every 1 °) within a predetermined time. Then P ₃
Then, the basic injection amount Tp {Tp = func (QA, n)} is looked up from a two-dimensional table map having Qa and N as parameters.

_Then, perform the fuel property correction for the mixing ratio correction coefficient P 4 to P _6. That is, in P ₄ , the mixture ratio correction coefficient KM
Look up R {KMR = func (Tp, N)} to obtain P
₅ , the fuel property correction coefficient KMRD {KMRD = func (T
₅₀ ), where T ₅₀ is the fuel property parameter} is looked up from the table map shown in FIG. Correction coefficient K
MRD (coefficients that have already been described are appropriately abbreviated in this way. The same applies hereinafter) is a correction coefficient having the characteristics shown in FIG. 6 depending on the fuel property.
The correction coefficient KMRD increases as the fuel becomes heavier. The program for detecting the fuel property parameter T ₅₀ will be described later with reference to FIG. 7.

Next, at P ₆ , the mixture ratio correction coefficient KMR is corrected according to the following equation.

KMR = KMR '× KMRD ...... However, KMR': _{P 4} in the look-up value P ₇ In the mixing ratio correction coefficient KTRM {KTRM = func (T
p, N)} is looked up, and the water temperature increase correction coefficient KTW is looked up in P ₈ according to the cooling water temperature Tw at that time. Here, the correction coefficient KMR becomes a value larger than 0 in the high speed and high load regions, and becomes 0 in other cases. Also,
The correction coefficient KTRM becomes negative in the low load region of medium speed or lower, and becomes 0 otherwise.

Next, at P ₉ , the fuel property correction coefficient KTWD {KTWD =
func (T ₅₀ )} is looked up, and at P ₁₀ , the water temperature increase correction coefficient KTW is corrected according to the following equation. Correction coefficient K
The TW is for stabilizing the combustion when the engine temperature is low, and the required amount thereof largely changes depending on the volatility of the fuel. Therefore, it is preferable to make the correction according to the fuel property as described above.

KTW = KTW '+ KTWD ...... However, KTW': calculates the lookup value P ₁₁ in starting and after-start increment correction coefficient KAS at _{P 8.} The correction coefficient KAS is for improving the guidance and improving the engine stability immediately after the start, and the correction amount is determined according to the cooling water temperature Tw and the elapsed time after the start. Next, at P ₁₂ , the post-idle amount increase correction coefficient KAI is calculated. The correction coefficient KAI is for smooth starting and acceleration during warm-up, and the throttle switch is turned from ON to OFF.
Immediately after that, the correction amount is determined according to the cooling water temperature Tw and the elapsed time after the start, and becomes 0 at a constant rate with the elapse of time.
Decrease until. _Moreover, to calculate the acceleration decrease correction coefficient KACC in _{P 13.}

The above-mentioned start-up and post-start-up increase correction coefficient KAS, post-idle increase increase correction coefficient KAI, and acceleration decrease correction coefficient KACC are well known as those described in the related art document, and therefore,
Detailed description is omitted here.

_Then, determine the high water temperature increase correction coefficient KH at each step of the P 14 _{to P 17.} Here, the steps of P _{14 to} P ₁₆ are processes for determining whether or not the engine is under a high load condition at high water temperature. First, in P ₁₄ , it is determined whether or not the throttle valve switch is ON, and when it is OFF, P ₁₅
And the mixing ratio correction coefficient KMR '(this KMR' is the above-mentioned P ₄
It is determined whether or not the value looked up in step 1) is greater than 0. Then, the cooling water temperature Tw at P _16, it is determined whether or not 100 ° C. or more, to look up the high water temperature increase correction coefficient KH proceeds to P ₁₇ If 100 ° C. or higher. That is,
Since knocking easily occurs under high load conditions at high water temperature, it is necessary to make the air-fuel ratio rich to suppress knocking.In addition, after hot start, gasoline vapor is generated in the fuel pipe and the air-fuel ratio May temporarily become lean, so it is desirable to perform appropriate correction to prevent such knocking occurrence and temporary lean state.

Then, the process proceeds to P _20, and calculates an air-fuel ratio feedback correction coefficient alpha. The air-fuel ratio feedback correction coefficient α corrects the deviation between the basic air-fuel ratio and the stoichiometric air-fuel ratio (λ = 1), but since it has little relation to the present invention, its detailed description is omitted. Note that the feedback control is not performed at the time of starting or high load, and α is clamped to 1 as in the conventional case.

Then, the process proceeds to P _21, the aforementioned, the final injection amount Ti is calculated according to the equation, the Ti and stored in I / O register P _22, the fuel injection signal Si having a pulse width corresponding to the Ti at a predetermined crank angle Is output to the injector 4.

On the other hand, if the condition is not satisfied even in any one of the steps treatment of the aforementioned P ₁₄ to P _16, it is determined that the engine is not in the high temperature and under a high load, high temperature and high load KH = 0 at P ₁₉ without performing the increase correction processing of
Proceed to _{P 20} as.

In this device, the fuel injection amount is appropriately corrected based on the characteristic detection information of the used fuel during the high load operation in which the air-fuel ratio feedback control is not performed. For example, when heavy gasoline is used, the gasoline component that actually contributes to combustion is smaller than the standard fuel, and the mixing ratio is practically lean. Since the level is properly discriminated and the deviation from the target air-fuel ratio is appropriately corrected according to the degree of heavyness, in this case, the total amount of fuel injection is corrected so as to increase. Therefore, as described above, when heavy gasoline is used, the gasoline component that contributes to combustion is reduced, the state where the mixture ratio becomes lean is avoided, and the original execution of air-fuel ratio control can be achieved. As a result, the air-fuel ratio at the time of high-load operation is corrected to an appropriate value corresponding to the property of the fuel used at that time, and it is possible to achieve the initially planned output improvement and engine temperature suppression.

FIG. 7 shows the parameter T ₅₀ of the property relating to the volatility of the fuel.
It is a flow chart showing a program for detecting, and this program is executed once every predetermined time.

Each step of the P ₃₁ to P ₃₄ is a process for determining whether the engine is in the predetermined operating condition. First, it is determined whether or not the cooling water temperature Tw at P ₃₁ is within a predetermined range, Tw
Engine temperature when the ₁ ≦ Tw ≦ Tw ₂ proceeds to _{P 32} it is determined that the predetermined range. Here, Tw is Tw = 10 ° C
It is desirable to set the range to 40 ° C. P ₃₂
It is determined whether or not the engine speed N is within a predetermined range. If it is within a predetermined range (N ₁ ≦ N ≦ N ₂ ), the routine proceeds to P ₃₃ , where it is determined whether the intake air amount Qa is within the predetermined range. Determine whether. The engine speed N and the intake air amount Qa are set in a range that is within the λ control (air-fuel ratio control) range by the oxygen sensor 14.

When Qa ₁ ≦ Qa ≦ Qa ₂ , it is determined at P ₃₄ whether or not the engine is in a steady state (a sudden acceleration, a state other than sudden acceleration), and when it is a steady state, the routine proceeds to P ₃₅ . Whether or not the engine is in a steady state is determined by the amount of change in the engine speed N and the intake air amount Qa within a predetermined time.

If any one of the above-mentioned steps P _{31 to} P ₃₄ does not satisfy the condition, it is determined that the engine is not in a predetermined operating state suitable for the fuel property determination, and the subsequent processing is performed. Stop (ie return).

Basic burn rate parameters .theta.c the P ₃₅ In Qa and N from a two-dimensional table maps to parameter ₀ {θc ₀ = func
Look up (Qa, N)}. This reference combustion speed parameter θ c ₀ represents the combustion speed when the reference fuel is used under the reference conditions, and by comparing it with the combustion speed of the fuel actually used in the step described later, the difference in the combustion speed (for example, , The combustion speed becomes slower when the fuel becomes heavier) is detected.

Then, at P ₃₆ , the temperature correction coefficient k ₁ {k ₁ = func (T
w)} is looked up from the table map shown in FIG. The temperature correction coefficient k ₁ corrects a combustion speed parameter that changes depending on the engine temperature even in the same fuel property according to the engine temperature Tw.
For w ₀ , k ₁ = 1; for Tw <Tw ₀ , k ₁ <1, T
For w> Tw ₀ , k ₁ > 1 is set.

_Then, to detect the θp combustion peak angle _{P 37} (crank angle cylinder pressure pa is the _maximum), the process proceeds to _{p 38.} Note that θ
The detection of p will be described in detail later in the program.

Which is the actual combustion engine measured combustion engine θc from the P ₃₈ in the ignition timing θi and the combustion peak angle θp computed according to the following equation. (See FIG. 9).

θc = θp−θi ... where θi: crank angle corresponding to ignition timing θp: crank angle at which cylinder pressure Pa becomes maximum (combustion peak angle) θi and θp are predetermined reference crank signals as shown in FIG. 9. With reference to the reference crank angle θref at which the [H] level pulse is generated in Sr, as shown in FIG.
It is expressed by the elapsed crank angle from.

In P ₃₉ , the measured combustion engine θc ₁ under the reference condition is calculated by multiplying the temperature correction coefficient k1 by the measured combustion engine θc by the product θc ₁ (θc ₁ =
It is calculated by k ₁ × θc). This θc ₁ corresponds to the actual burning velocity parameter detected under the reference condition. Next, at P ₄₀ , the difference Δθc ₁ between the measured combustion engine θc ₁ and the reference combustion speed parameter θc ₁ under the reference condition is calculated according to the following equation.

Δθc ₁ = θc ₁ −θc ₀ ...... That is, here, the combustion speed parameter θc ₀ when the reference fuel is used under the reference conditions and the combustion speed parameter (measurement combustion engine) θc _{1 of the} fuel actually used The difference with is detected. Since the burning rate has a certain correlation with the property relating to the volatility of the fuel, it is possible to properly determine the property relating to the volatility of the fuel by accurately detecting the burning rate.

_Furthermore, computed according to the following equation moving average .DELTA..theta.c ₁ ^* of .DELTA..theta.c ₁ at _{P 41.}

However, in the case of m: constant P ₄₂ , the fuel property parameter T ₅₀ is looked up from the table map having the characteristics shown in FIG. 10 based on the value of Δθc ₁ ^* , and the value of T ₅₀ is N in P _43.
Store in VM24.

In this way, by comparing the difference in the burning speed depending on the property of the used fuel with the burning speed of the reference fuel, the fuel property parameter relating to the volatility of the used fuel at that time can be appropriately obtained.

FIG. 11 is a flowchart showing a program for detecting the combustion peak angle θp, and this processing corresponds to P ₃₇ of the step described in FIG. This program is executed once every 2 ° in crank angle.

First, at P ₅₁ , it is determined whether the current crank angle (piston position) θ corresponds to the compression top dead center TDC, and θ
When TDC, the analog signal representing the in-cylinder pressure Pa is A / D converted at P ₅₂ , stored as the in-cylinder pressure conversion value AD ₀ , and then the process proceeds to P ₅₃ . On the other hand, when θ ≠ TDC, P ₅₂ is jumped to P ₅₃ . At _P53 , the crank angle θ is
It is determined whether or not it is equal to or greater than the TDC excess value (TDC + α °) shown in FIG. 12, that is, whether or not the engine 1 has rotated over αDC by more than TDC. Here, α is set to 2 ° to 4 °. This is because the peak of the in-cylinder pressure Pa (combustion peak angle θp) due to combustion appears after TDC, so α °
This is for avoiding erroneously adopting the in-cylinder pressure Pa at TDC as the combustion peak value by providing the dead zone.

When θ <TDC + α °, that is, θ is before top dead center (BT
DC) or when TDC ≦ θ <TDC + α °, this routine ends. On the other hand, when θ ≧ TDC + α °, the process of detecting the combustion peak angle after P ₅₄ is executed. First, the crank angle θ is determined whether it exceeds the combustion peak angle determination limit θe at P _54. θe is a crank angle at which it can be assumed that combustion in the cylinder has been sufficiently completed, and is set to a predetermined value exceeding TDC (see FIG. 12). It is assumed that the combustion peak angle is between TDC and θe, and for example, points F ₁ and F ₂ shown in FIG. 12 correspond to this (curve X represents when the combustion state is different).
Therefore, A of the in-cylinder pressure Pa for obtaining the combustion peak
The / D conversion processing is performed up to θe.

When θ ≦ θe at P ₅₄ , θ is counted at P ₅₅ θ
The counter is incremented, and the in-cylinder pressure Pa at this time is A / D converted at P ₅₆ to obtain the in-cylinder pressure conversion charger AD ₁ , which is stored. Next, at P ₅₇ , the difference value ΔP between the in-cylinder pressure conversion values AD ₁ and AD ₀ is obtained, and the routine proceeds to P ₅₈ . The difference value ΔP has a positive value if the in-cylinder pressure Pa is in the increasing direction and a negative value if the in-cylinder pressure Pa is in the decreasing direction. In addition, it becomes a very small value near the combustion peak time. At P ₅₈ , the absolute value of the difference value ΔP | ΔP |
It is compared with the reference value ΔP ₀ of. The reference value ΔP ₀ is the cylinder pressure Pa
This is a value for determining whether or not the change in is substantially flat. When | ΔP | ≦ ΔP ₀ , it is determined that the change in the in-cylinder pressure Pa is substantially flat, and at P ₅₉ , the count value of the θ counter is stored as the combustion peak angle θp, and P
_{At 60} , the in-cylinder pressure change value AD ₁ of this routine is set to AD ₀ , and the routine ends. On the other hand, when | ΔP |> ΔP ₀ , it is determined that the condition is not flat, and the process proceeds to P ₆₀ .

Here, it is the cylinder pressure P that satisfies the condition of | ΔP | ≦ ΔP _0.
It is the maximum, minimum, maximum, or minimum of a. The determination of such a state is not limited to the example of the present embodiment, and may be performed by using, for example, the differential value of the in-cylinder pressure Pa.

The manner of actual changes in the in-cylinder pressure Pa with respect to the condition | ΔP | ≦ ΔP ₀ is summarized in the examples of FIGS. 13 (a) to 13 (c). First
FIG. 13 (a) shows the most general Pa change curve. In this example, the crank angle that satisfies the condition of | ΔP | ≦ ΔP ₀ after TDC is θp, and the combustion peak angle can be easily obtained. 13 (b) and 13 (c) both show a case where the load is low and Pa becomes flat in two places after TDC. In the case of FIG. 13 (b), the in-cylinder pressure Pa _{1 at} θp becomes smaller than the value Pa _{TDC at TDC} , and the minimum value Pa ₂ appears in the middle thereof.
However, at this time, since Pa ₂ appears, Pa ₂ has a maximum value, and θp can be identified. On the other hand, in the case of FIG. 13 (c), the minimum value does not appear, and Pa ₁ corresponding to the combustion peak angle θp appears behind the flat portion Pa ₃ (Pa
₁ <Pa ₃ ). This is when the combustion pressure is very low, and it is actually difficult to detect θp by the A / D conversion method. Although it is possible to make a distinction by performing a Pa differential processing, the accuracy is somewhat low. However, in this way Pa is TD
It is in the case of an extremely low load that it uniformly decreases after C. In this case, the detection of θp is stopped and the judgment is made based on the operating state (engine speed N and load Qa).

As described above, when θ is in the range of TDC + α ° to Qe, the combustion peak angle θp can be accurately detected by the A / D conversion method described above.

On the other hand, when θ ≧ θe in P ₅₄ , it is determined that the combustion in the cylinder is sufficiently completed, the average value of θp in the past several times is calculated in P ₆₁ , and the reliability of θp data is improved. This routine ends.

The detection of the combustion peak angle is not limited to that using a piezoelectric element such as an in-cylinder pressure sensor. For example, the light in the combustion chamber may be detected through a glass window and an optical fiber, and the detected light may be identified. You may

As described above, in this embodiment, paying attention to the relationship between the property relating to the volatility of the fuel and the burning speed, and accurately detecting the burning speed of the used fuel, the property of the used fuel is properly determined. . Since the accurately detected fuel property parameter T ₅₀ is applied to the fuel injection amount control under high load, there is a problem that the air-fuel ratio control shifts under high load due to the difference in fuel property pointed out as a conventional problem. It can be resolved.

FIG. 14 is a diagram showing a second embodiment of the present invention. In this embodiment, the present invention is applied when the throttle is under a high load, which is closer to full opening than in the first embodiment.

In the description of the present embodiment, steps for performing the same processes as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted, and different steps will be designated by step numbers enclosed by a circle to explain the contents thereof. .

In the program of FIG. 14, after passing P ₄ , the basic injection amount Tp is compared with a predetermined value Tp ₀ at P ₇₁ , and if Tp ₀ ≦ Tp, the routine proceeds to P ₇₂ . At P ₇₂ , the engine speed N is compared with a predetermined value N _0, and if N ₀ ≦ N, the process proceeds to P ₅ . on the other hand,
If P ₇₁ and P ₇₂ are smaller than the predetermined value, P
Jump to ₇ .

_Moreover, to calculate the final injection amount Ti in accordance with the following equation by _{P 73} when going through the _{P 20.} This P ₇₃ corresponds to the formula of P ₂₁ of the first embodiment with the high water temperature increase correction coefficient KH omitted.

Ti = Tp × (1 + KTRM + KMR + KTW + KAS + KACC) × α + TS ... In the present embodiment, attention is paid to the fact that the correction of the high water temperature increase correction coefficient KH is not necessary when the KMR control near full opening can be executed with high accuracy. The high water temperature increase correction coefficient KH is not corrected. Therefore, in the present embodiment, it is possible to reduce the matching man-hours by limiting the region while improving the fuel efficiency and the torque particularly near the fully opened position.

In each of the above-described embodiments, as a fuel property detection method, a mode in which the combustion speed is detected as shown in FIGS. 7 to 13 and the parameter T ₅₀ of the property relating to the volatility of the fuel is calculated based on the detected value is used. Although shown, the present invention is not limited to this, for example, a mode of detecting combustion light with an optical fiber sensor or a mode of determining from a response delay of the air-fuel ratio under accelerated operating conditions or an accelerated operating condition. It goes without saying that a mode or the like in which the determination is made from the response delay of the parameter correlated with the generated torque (or the indicated mean effective pressure) below may be adopted.

(Effect) According to the present invention, the property relating to the volatility of the used fuel is detected, and the parameter (AIR or FUEL) that determines the air-fuel ratio at the time of high load is appropriately corrected based on the detection result. The air-fuel ratio at the time of high load can always be optimized regardless of the change in fuel properties, and the drivability of the engine can be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 13 are diagrams showing a first embodiment of the present invention, FIG. 2 is an overall configuration diagram, and FIG. FIG. 4 is a diagram showing the change in the combustion state when there is a change in the relationship between the crank angle signal and the in-cylinder pressure signal, FIG. FIG. 6 is a flow chart showing a program for air-fuel ratio control, FIG. 6 is a table map of the fuel property correction coefficient KTSD, FIG. 7 is a flow chart showing a program for judging the property relating to fuel volatility, and FIG. 8 is its temperature correction coefficient k _1. Table map of the
FIG. 9 (a) is a diagram showing the reference crank angle signal,
FIG. 11B is a diagram showing a change in the in-cylinder pressure in relation to the reference crank angle signal, FIG. 10 is a table map of the property parameter T ₅₀ relating to the volatility of the fuel, and FIG. 11 is detecting the combustion peak angle. Flowchart showing the program to
FIG. 12 is a diagram showing changes in the in-cylinder pressure, and FIG. 13 (a)-
(C) is a diagram showing a general variation of in-cylinder pressure for explaining the action, and FIG. 14 is a flow chart showing a program for air-fuel ratio control at the time of high load showing a second embodiment of the present invention. is there. 1 ... Engine, 4 ... Injector, 15 ... Operating state detecting means, 16 ... Control unit (property detecting means, air-fuel ratio setting means, correcting means).

Claims (1)

[Claims] Claims: 1. a) a property detecting means for detecting a property relating to the volatility of the fuel used; b) an operating condition detecting means for detecting a high load operating condition of the engine; and c) when the engine is in a high load operating condition. Air-fuel ratio setting means for setting the supply air-fuel ratio of the fuel on the basis of the property of the reference fuel, and d) when the detected property of the used fuel is heavier than the reference fuel, it is richer than the set supply air-fuel ratio. When the detected fuel used is softer than the reference fuel, the air-fuel ratio on the lean side of the set air-fuel ratio becomes the actual supply when the engine is under high load operation. An air-fuel ratio control device for an internal combustion engine, comprising: a correction unit that corrects an air-fuel ratio.