JPS62288337A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the drivability and reduce HC in an exhaust gas, by detecting a property of fuel to be used and correcting an air-fuel ratio at deceleration according to the result of detection. CONSTITUTION:A control device 16 receives signals from an air flow meter 7, a throttle valve opening sensor 9, a combustion pressure sensor 10, an oxygen sensor 14, etc. and regulates a fuel injection quantity of a fuel injection valve 4 to control an air-fuel ratio to a target value. At deceleration of an engine, the fuel injection quantity is further corrected according to a property of fuel to be used in addition to the operational condition. The fuel property is obtained as a content of heavy fraction by computing a measured combustion period from an ignition timing and a combustion peak angle and comparing the period with a reference value. Accordingly, the air-fuel ratio at deceleration may be made always optimum irrespective of a change in the fuel property.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Industrial Application Field) The present invention detects the properties of fuel used in internal combustion engines such as automobiles, and based on the detection results, particularly detects air flow during deceleration. The present invention relates to a device for appropriately correcting a fuel ratio.

(Prior Art) In recent years, there has been a trend in which engines are required to have higher fuel economy and drivability, and from this point of view, microcomputers and the like are being applied to more precisely control the air-fuel ratio.

In such control, the characteristics of the fuel may also play an important role as input information.

As a conventional air-fuel ratio control device, for example, Japanese Patent Application Laid-Open No. 60-4
There is one described in Japanese Patent No. 5742. In this device, the air-fuel ratio is detected by an oxygen sensor provided in the exhaust pipe, and based on the detection result, the fuel injection amount is manipulated to perform feedback control so that the air-fuel ratio becomes a target value.

In other words, the injection pulse signal output to the injector (
R final injection amount) Ti is calculated according to the following equation (2) based on the detection results of the air-fuel ratio, intake air amount, engine speed, cooling water temperature, etc.

Ti=TpxCoxα+Ts ・-”■However, Tp:
Basic injection amount Co: Various correction coefficients α; Air-fuel ratio feedback correction coefficient TS: Voltage correction bone In the above formula, the various correction coefficients Co are according to the following formula 〇? Calculated by E.

Co=1 +KTRM+KMR+KTW+KAS+KA
I +KACC+KH・・・・・・■However, KTRM
: Mixing ratio correction coefficient KMR : Mixing ratio correction coefficient KTW : Water temperature increase correction coefficient KAS : Starting and post-start increase correction coefficient KAI?
After idling increase correction coefficient KACC: Acceleration decrease correction coefficient KH: High water temperature increase correction coefficient Also, at startup, acceleration, and under high load, various corrections are made to improve drivability and the air-fuel ratio is lower than the target air-fuel ratio. Make it rich. In addition to this, there is interrupt injection during acceleration,
During sudden acceleration, injection should be performed asynchronously in addition to normal fuel injection control.

Note that each of the above correction values is set on the premise that standard fuel (for example, 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 characteristics of the fuel used in the engine (for example, the level of weight)
The structure was such that the various correction values described above were calculated and set based on the premise that the properties of the fuel were always constant, using a uniform value that corresponded to the standard fuel as a standard, so the properties of the supplied fuel Even in the case where the fuel weight changes and the fuel weighting level changes accordingly, the air-fuel ratio correction due to the change in the properties of the supplied fuel is not taken into account. therefore,
In such a case, a discrepancy occurs between the air-fuel ratio calculated based on the use of standard fuel and the actual air-fuel ratio, making it difficult to achieve accurate air-fuel ratio control.

For example, when heavy gasoline is used, its volatility is lower than that of regular regular gasoline, and the gasoline components involved in combustion are diluted. Therefore, the actual air-fuel ratio is leaner than the air-fuel ratio calculated based on the use of standard fuel. As a result, the engine is operated leaner than the target air-fuel ratio, resulting in poor combustion conditions, and especially immediately after deceleration, a relatively large amount of air remains in the intercommanship hold before deceleration. As a result, the amount of air may be on the verge of being oversupplied, causing the air-fuel ratio to become even leaner, resulting in a sudden decrease in the generated torque. When the generated torque decreases, drivability deteriorates significantly, and a large amount of HC (hydrocarbons) is generated, which adversely affects exhaust emission characteristics. Furthermore, such problems become more noticeable when using inferior fuel.

In this way, if the fuel injection amount during deceleration is calculated on the premise that a uniform fuel such as standard fuel is used as the supplied fuel, some problems will occur in terms of control accuracy. In other words, if you are aiming for more accurate air-fuel ratio control during deceleration,
It is desirable to take into account differences in the properties of the fuel used.

(Purpose of the Invention) Therefore, the present invention detects the properties of the fuel used and appropriately corrects the air-fuel ratio during deceleration based on the detection result, thereby adjusting the air-fuel ratio during deceleration regardless of changes in the properties of the fuel. As a suitable one, the purpose is to further improve engine drivability and HC reduction.

(Means for Solving the Problems) In order to achieve the above object, the air-fuel ratio control device for an internal combustion engine according to the present invention has a property detection means for detecting the properties of the fuel used, as shown in FIG. a, an operating state detecting means for detecting the decelerating operating state of the engine; an air-fuel ratio setting means C for setting the supplied air-fuel ratio based on the properties of the reference fuel when the engine is in the decelerating operating state; a correction stage d for correcting the supplied air-fuel ratio during the operating state based on the properties of the fuel used, and controlling the intake air amount or the fuel supply amount so as to achieve the corrected air-fuel ratio; and a correction means. and an operating means C for adjusting the amount of intake air or fuel supplied based on the signal from the controller.

(Function) In the present invention, the properties of the fuel used are detected, and a parameter (
AIR or FUEL) is appropriately corrected. Therefore, regardless of changes in the properties of the fuel used, the air-fuel ratio during deceleration becomes appropriate, improving drivability and reducing HC.

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

Figures 2 to 12 are diagrams showing the first embodiment of the present invention, in which the combustion rate is detected from the in-cylinder pressure signal as a fuel property detection parameter, and the air-fuel ratio control method is used to determine the fuel property based on this detected value. An example of application to a device is shown.

First, the configuration will be explained. In FIG. 2, l 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 exhaust gas burned in the cylinders is introduced into the catalytic converter 6 through the exhaust pipe 5, and the harmful components [C○,
II C1N0x) is purified by a three-way catalyst and discharged.

The intake air flow lQa is detected by an air flow meter 7 and controlled by a throttle valve 8 in the intake pipe 3. The opening Cv of the throttle valve 8 is detected by a throttle valve opening sensor 9. Also,
The combustion pressure (hereinafter referred to as in-cylinder pressure) Pa in the cylinder is detected by a pressure sensor 10, and the pressure sensor IO is constituted by a piezoelectric element and is molded as a washer of the spark plug 11.

The pressure sensor 10 detects the cylinder pressure Pa acting on the piezoelectric element via the spark plug 11, and outputs an analog signal having a voltage value corresponding to the 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 crank angle sensor 12.
is detected by the water temperature sensor 13.

Furthermore, the oxygen concentration in the exhaust gas is detected by an oxygen sensor 14, and the oxygen sensor 14 used is one having a characteristic that its output Vs changes suddenly at the stoichiometric air-fuel ratio.

The air flow meter 7, throttle valve opening sensor 9, and crank angle sensor 12 constitute an operating state detection means 15,
Operating state detection means 15, pressure sensor 10, water temperature sensor 1
The outputs from oxygen sensor 3 and oxygen sensor 14 are input to control unit 16. The control unit 6 has a function as a property detection means together with the pressure sensor 10, and also functions as an air-fuel ratio setting means and a correction means by itself.
(nonvolatile memory) 24 and I10 port 25. The CPU 21 imports necessary external data from the I10 boat 25 according to the program written in the ROM 22, and also imports necessary external data from the RAM 23 and NVM.
While exchanging data with the 110 boat 24, it calculates the processing values necessary for fuel property determination and air-fuel ratio control based on the results, and outputs the processed data to the 110 boat 25 as necessary. . I10 port 25 has sensor group 7
．． The signals from 9.10.13.14 are input, and the injection signal Si is output from the I10 boat 25. The ROM 22 stores calculation programs for the CPU 21, and the RAM 23 and NVM 24 store data used in calculations in the form of a map or the like.

Next, the effect will be explained, but first, changes in fuel properties and their effects will be explained using gasoline as an example.

Gasoline is composed of more than several hundred types of hydrocarbons (HC), and depending on the ratio and bonding style of carbon (C) and hydrogen (H), there are four types: paraffinic, olefinic, naphthenic, and aromatic. are categorized. As a general tendency, the higher the number of C and H, the higher the boiling point and the higher the fractionation temperature from crude oil (represented by 50% distillation temperature T). Also, the heavy degree of gasoline is T. It is represented by T, which is light (highly volatile). =80-90℃, T for heavy M (low volatility). =110~120℃
And there are T, in the market. = 95 to 100°C is the most widely distributed. Therefore, the final injection amount T
i is T. It is determined by making various corrections on the premise that fuel (ie, regular gasoline) with a temperature of 95 to 100° C. is used.

Figure 3 shows changes in the fuel condition when the degree of gasoline heaviness changes as changes in the in-cylinder pressure signal under specified conditions (when the air-fuel ratio, intake air amount, engine temperature, and ignition timing are constant). be. Note that Pmax in the figure is the maximum point of the cylinder pressure signal, and θpmax is the crank angle that provides Pmax. In addition, t in the figure shows the ignition timing θi to θpm.
The actual combustion period 11JI up to ax is shown.

As shown in Fig. 3, in the case of light gasoline, the maximum value Pmax of the in-cylinder pressure signal is large and combustion proceeds quickly;
As the fuel becomes heavier, Pmax decreases and θpmax
shifts to the later side. This is because the gasoline component (hatched area in FIG. 4) that contributes to combustion in the initial stage of combustion (from ignition to θpn+ax) decreases as the fuel becomes heavier. When this initial combustion light is observed, it is entirely blue, and in the case of light gasoline, only the blue color is observed, and it disappears after θpmaxvi (that is, the combustion has finished). However, with heavy gasoline, blue combustion light is observed up to θpmax, but the light is weaker than in the case of light gasoline, and red combustion light is observed immediately after θpmax. In other words, heavy gasoline burns as a mixture of fast combustion (bluish-white combustion light) and slow combustion (red combustion light), and the fast combustion (bluish-white combustion light) that contributes to actual combustion is The heavier the fuel, the less it becomes.

This means that the heavier the gasoline, the more diluted the components that contribute to combustion.In other words, as the gasoline becomes heavier, the air-fuel ratio becomes leaner and the combustion speed becomes slower (
(Pmax is on the delayed side).

Furthermore, this phenomenon becomes more noticeable as the engine temperature decreases, as the volatility of heavy gasoline deteriorates and the air-fuel ratio becomes leaner.

In this embodiment, in view of the above-mentioned characteristics of fuel properties, the properties of the fuel are appropriately detected by a program as described later, focusing particularly on the causal relationship using the burning rate as a parameter, and the detected results are Based on this, air-fuel ratio control during deceleration is performed more appropriately.

FIG. 5 is a flowchart showing a program for air-fuel ratio control during acceleration written in the ROM 22, and this program is executed once in synchronization with engine rotation.

First, the intake air 11Qa is read at P, and the engine rotational speed N is read at P2. The rotation speed N is calculated by measuring the interval time of the reference signal (signal every 360 degrees) from the crank angle sensor 10, or by measuring the number of pulses within a predetermined time of the position signal (signal every 1"). .Then,
Basic injection 11Tp (Tp=func (Q
Look up a, N)).

In P4, the mixture ratio correction coefficient KMR (KMR=func(T
p, N)), and use Ps to calculate the mixture ratio correction coefficient K.
Look up TRM (KTRM=func (Tp, N)). The mixture ratio correction coefficient KMR1KTRM is an increase correction for high loads and high rotations, and the correction coefficient KMR (coefficients that have already been explained will be abbreviated as appropriate. The same applies hereinafter) is for high speed and high load ranges. In this case, the value will be larger than O, and in other cases, it will be 0. Further, the correction coefficient KTRM is negative in the low load range below medium speed, and is 0 otherwise.

Next, at P, the water temperature increase correction coefficient KTW is looked up according to the cooling water temperature TW at that time, and at P7, the fuel property correction coefficient KTWD (
KTWD=func (Ts.) However, T. : Look up fuel property parameters).

Note that the fuel property parameter T. Regarding the detection of
This will be explained in detail in the program shown in the figure below.

At P, the current correction coefficient KTW is corrected according to the following equation (2).

KTW=KTW' +KTWD...■ However, KTW': Calculate the starting and post-starting increase correction coefficient KAS using the value P looked up at P. Correction coefficient K
AS is intended to improve startability and engine stability immediately after starting, and its correction amount is determined according to the cooling water temperature TW and the elapsed time after starting.

Then Pl. Calculate the post-idle increase correction coefficient KAI. The correction coefficient KAI is for smooth starting and acceleration during warm-up, and is used when the throttle switch is turned from ON to OFF.
Immediately after reaching F, the correction amount is determined according to the cooling water temperature TW and the elapsed time after starting, and decreases at a constant rate until it reaches 0 as time passes. Furthermore, an accelerated weight loss correction coefficient KACC is calculated using the pH.

The above starting and post-start increase correction coefficient F3 [K A S, post-idle increase correction coefficient KAI, and acceleration reduction correction coefficient K
Since ACC is well known as described in conventional known literature, a detailed explanation is omitted here. Then the pH
At z, it is determined whether or not the engine is decelerating, and if the engine is decelerating, the process advances to PI3. It is determined whether or not the engine is decelerating by checking whether the rate of change of the intake air iiiQa is larger than a predetermined value on the deceleration side. Further, instead of the intake air lQa, the throttle valve opening T■0 or the basic injection amount 'rp may be used to determine whether the engine is decelerating (TVO or Tp is less than a predetermined value). Here, the degree of deceleration is determined as e-deceleration in which the throttle valve opening degree TVO is almost returned to its original value, and deceleration in which the throttle valve opening degree TVO is returned from fully open to approximately half is not determined as deceleration.

At P13, flag FDEC is set (FDEC=l). The flag FDEC is set during deceleration, and indicates that the throttle valve is returned rapidly to indicate that the vehicle is decelerating, or that the throttle valve opening T
This shows that even if VO remains constant, it is still in a state immediately after deceleration.

Next, fuel property correction is performed for the deceleration correction coefficient at PI4 to pz. That is, at P14, look up the deceleration air-fuel ratio correction coefficient KDEC (KDEC=func (N)1), and at P15, look up the fuel property correction coefficient KDECD
Look up (K D E CD =func (TS6) ). Further, at Pl6, the deceleration correction coefficient KDEC is corrected according to the following equation (2).

KDEC=KDEC' xKDECD ・・・・・・
■However, KDEC': Value PI looked up in Pl4? Then, the current basic injection amount during deceleration (that is, the moving average value of the basic injection 1tTp) TpD is calculated according to the following formula 0, and the process proceeds to pH+.

・・・・・・■ However, TpD': Basic injection amount at previous deceleration 'rpDO value (However, the first TpD at the start of deceleration is the value of Tp at that time) Tp: Basic injection amount Like this Since Tp changes by the moving average 1/KDEC, TpD'>'l' during and immediately after deceleration.
It is p.

Next, at Pl8, the basic injection amounts TpD and P during deceleration are determined.

Compare the basic injection ITp' calculated in , and find that TpD〉Tp
', TpD is adopted as the basic injection ITp (Tp=
TI) D) and proceed to pz+. On the other hand, when TpD≦Tp', it is determined that the correction of the air-fuel ratio during deceleration has been completed, and P2
Reset the flag FDEC at ° (FDEC=O) and press P.
Proceed to Z+.

In PZ, an air-fuel ratio feedback correction coefficient α is calculated. The air-fuel ratio feedback correction coefficient α is used to correct the deviation between the basic air-fuel ratio and the stoichiometric air-fuel ratio (λ = 1), but since it is well known as well as those described in conventional publicly known documents, it will not be described in detail here. Omit explanation. Next, in P2□, the final injection amount Ti is calculated according to the following equation 〇.

'ri='rpx (1+KTRM+KMR+KTW+
KAS+KA I +KACC) ×cx+Ts-old-
■However, KTRM: Mixing ratio correction coefficient KMR: Mixing ratio correction coefficient KTW: Water temperature increase correction coefficient KAS: Start and post-start increase correction coefficient KAI:
Post-idle increase correction coefficient Maki KACC: Acceleration: IJi amount correction coefficient P2. The final injection fft'r't is stored in the I10 register, and an injection signal Si having a fuel injection pulse width corresponding to this Ti is output to the injector 4 at a predetermined crank angle.

On the other hand, if it is determined at P1□ that the engine is not decelerating, it is determined at P24 whether or not the engine is accelerating. That is, this determination is made in the same way as in step PL2.Qa (or TV
O or Tp (However, this 'rp is the value calculated by P3)
) is greater than or equal to a predetermined value. When it is determined that the vehicle is not accelerating, it is determined by the Push button whether the flag FDEC is set (FDEC=1) or not. FDEC=
If it is 1, it is determined that the air-fuel ratio is in the midline during deceleration immediately after deceleration.
Proceed to P.14.

Also, when it is determined that the acceleration is being performed at P24, or when P24 determines that the
When it is determined in step 5 that FDEC≠1, it is determined that the engine is not decelerating or immediately after decelerating, and the subsequent steps are jumped to proceed to P21.

In this way, the fuel injection amount during deceleration is appropriately corrected based on the detected information on the properties of the fuel used.

For example, when heavy gasoline is used, the amount of gasoline that actually contributes to combustion is smaller than that of standard fuel, and the mixture ratio is effectively lean. On the other hand, according to this device, the level of heavy fuel used is appropriately determined and the deviation from the target air-fuel ratio is appropriately corrected according to the degree of heavy fuel. When quality gasoline is used, the situation in which the amount of gasoline that contributes to combustion is small is corrected. That is, at this time, the total amount of fuel injection amount is corrected to increase. Therefore, a situation in which the mixture ratio becomes lean is effectively avoided, and the original effectiveness of the air-fuel ratio control can be achieved. As a result, during deceleration, the air-fuel ratio at the time of deceleration is corrected to an appropriate value corresponding to the properties of the fuel used at that time. It is possible to appropriately avoid the increase in torque, prevent the torque from becoming low, and significantly improve drivability and reduce Fr c.

FIG. 6 is a flowchart showing a program for detecting the fuel property parameter TSO, and this program is executed once every predetermined time.

Step P3+-Pxa is a process for determining whether the engine is in a predetermined operating state. First, the Pill determines whether the cooling water temperature Tw is within a predetermined range, and then
When I≦Tw≦Twt, it is determined that the engine temperature is within a predetermined range, and the process proceeds to P3t. Here, Tw is TW=10℃
It is desirable to set the temperature within a range of ~40°C.

Pzz determines whether the engine speed N is within a predetermined range, and if it is within a predetermined range (N I ≦N≦N2), P
Proceeding to step 3j, it is determined whether the intake air amount Qa is within a predetermined range.

The engine speed N and intake air amount Qa are determined by the oxygen sensor 14.
It is set to a range that falls within the λ control (air-fuel ratio control) range.

When Qa, ≦Qa≦Qa, it is determined in P'14 whether or not the engine is in a steady state (state B of neither sudden acceleration nor sudden deceleration), and if it is in a steady state, the process proceeds to P35.

A determination as to whether the engine is in a steady state is made based on the amount of change in the engine rotational speed N or the intake air lQa within a predetermined period of time.

If any one of the above-mentioned step processes from PHI to P34 does not satisfy any of the conditions, it is determined that the engine is not in a predetermined operating state suitable for fuel quality determination, and subsequent processes are canceled. (i.e. return).

For pus, the basic combustion rate parameter θc is obtained from a two-dimensional table map with Qa and N as parameters.

Look-amplify (θco-4unc (Qa, N)).

This reference combustion rate parameter θco represents the combustion rate when using standard fuel, and by comparing it with the combustion rate of the fuel actually used in the step described later, differences in combustion rate (for example, if the fuel is heavy (the combustion rate slows down when the combustion rate decreases) is detected.

Next, in PI3, the temperature correction coefficient kl (k, =func
(TV)) is looked up from the table map shown in FIG. The temperature correction coefficient is used to correct the combustion rate, which changes depending on the engine temperature even if the fuel properties are the same, according to the engine temperature Tw, and at the reference temperature TW0, + = 1.
Tw<Two,<l.

Tw>'l'w0 and k>1 is set.

Next, the combustion peak angle (crank angle at which the in-cylinder pressure pa becomes maximum) θp is detected at pst, and the process proceeds to P3a.

Note that the detection of θp will be described in detail in the program described later.

Furthermore, in Pill, ignition timing θi and combustion peak angle θp
From this, the measured combustion period θC, which is the actual combustion period, is calculated according to the following equation (see FIG. 8).

θC=θp-θi ・・・・・・■ However, θi: Crank angle corresponding to the ignition time θp: Crank angle at which the cylinder pressure Pa becomes maximum (combustion peak angle) θi and θp are as shown in Figure 8 (a) As shown in the figure, the reference crank angle θref at which a (H) level pulse is generated in the predetermined reference crank angle signal S is used as a reference, and as shown in FIG. .

In Pff9, the product θC1 (θc,
=, XθC). This θC1 corresponds to the actual combustion rate parameter detected under reference conditions. Next, at P4°, the difference Δθc1 between the measured combustion period θC under the reference condition and the reference combustion rate parameter θc0 is calculated according to the following equation (2).

ΔθC, = θC1 - θCo ・・・・・・■ In other words, here, the combustion rate parameter θco when using standard fuel under standard conditions and the combustion rate parameter of the fuel actually used (measured combustion period) The difference from θc1 is detected. Since the combustion rate has a certain correlation depending on the properties of the fuel, if the combustion rate is detected accurately, it becomes possible to accurately determine the properties of the fuel.

Furthermore, in P41, the moving average θC9' of ΔθC is calculated using the following formula
Calculate according to

□(Current Δθc+)...■ However, m: For constant Pd2, fuel property parameter T, based on the value of ΔθC3'. is looked up from a table map having the characteristics shown in FIG. 9, and P4'J is used to find this T. The value of is stored in NVM (non-volatile memory) 24.

In this way, by comparing the difference in combustion rate due to the properties of the fuel used with the combustion rate of the standard fuel, the fuel property parameters of the fuel used at that time can be appropriately determined.

FIG. 10 is a flowchart showing a program for detecting the fuel peak angle θp, and this process is performed in step P3? of the step described in FIG. 6 above. corresponds to This program is executed once every 2 degrees of crank angle.

First, PSI determines whether the current crank angle (piston position) θ corresponds to compression top dead center TDC, and θ=
In the case of TDC, in P5□, the analog signal representing the cylinder pressure Pa is A/D converted and stored as the cylinder pressure conversion value A Do , and then the process proceeds to P53. On the other hand, when θ≠TDC, Psi is jumped and P3. Proceed to.

PSI determines whether the crank angle θ is greater than or equal to the TDC excess value (TDC+α°) shown in FIG. 11, that is, whether the engine 1 has rotated by more than α° exceeding TDC. Here, α is set to 2° to 4°. This is because the peak of the cylinder pressure pa due to combustion (hereinafter referred to as the combustion peak) appears after TDC, so a rest zone of α° is set and the cylinder pressure Pa at TDC is mistakenly adopted as the combustion peak value. This is to avoid

When θ<TDC+α°, that is, θ is before top dead center (BT
DC) or TDC≦θ<TDC+α°, the current routine ends. On the other hand, when θ≧TDC+α°, processing for detecting combustion peak angles after ps4 is executed. First, at ps4, it is determined whether the crank angle θ exceeds the combustion peak angle determination limit value θe. 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. 11).

The combustion peak is assumed to be between TDC and θθ, and corresponds to, for example, points Fl and F2 shown in FIG. 11 (curve X represents different combustion states). Therefore, the A/D conversion process of the in-cylinder pressure pa for determining the combustion peak is performed up to θθ.

When θ≦θe on PS4, count θ with pss θ
The counter is incremented, and the current cylinder pressure Pa is A/D converted by PSII to the cylinder pressure conversion charger A D.
Find + and memorize it. Next, PS? Then, the difference value ΔP between the converted cylinder pressure values ADI and AD is determined, and the process proceeds to PSa. The difference value ΔP will be a positive value if the cylinder pressure Pa is increasing, and will be a negative value if it is decreasing.

Moreover, the value becomes very small near the combustion peak time. P
At sa, the absolute value 1ΔP1 of the difference value ΔP is compared with the reference value ΔP0. The reference value ΔP0 is a value for determining whether the change in the cylinder pressure Pa has become substantially flat. lΔPI≦
When ΔP, it is determined that the change in the cylinder pressure Pa is substantially flat, and at PS9, the counter I-value of the θ counter is stored as the combustion peak angle θp, and P. Then, the routine ends with the cylinder pressure conversion value ΔD and A Do of this routine.

On the other hand, when )API>ΔP0, it is determined that the surface is not flat and the process proceeds to P6°.

Here, the condition 1ΔI)l≦ΔPa is satisfied when the cylinder pressure Pa is at its maximum, minimum, maximum, or minimum.

Note that the determination of such a state is not limited to the example of the present embodiment 91, and may be performed using, for example, the differential value of the cylinder pressure Pa.

The manner in which the actual cylinder pressure Pa changes under the condition of 1ΔP1≦ΔP0 can be summarized in the examples shown in FIGS. 12(a) to 12(C).

FIG. 12(a) shows the most common Pa change curve. In this example, 1ΔP1≦ΔP after TDC
The crank angle that satisfies the condition of 0 is θp, and the combustion peak angle can be easily determined. Figure 12(b)
, (C) are both under low load and Pa is 2 after TDC.
A situation where the area becomes flat occurs. In the case of Fig. 12(b), the cylinder pressure Pa at θp becomes smaller than the value Pa at TDC, and at the same time, the minimum value Pa
2 appears. However, in this case, Pa2 appears, so P
a, becomes the local maximum value, and θp can be identified. on the other hand,
In the case of Fig. 12(c), the minimum value does not appear and the flat part P
paz corresponding to the combustion peak angle θp appears after a:l (pa, <pa,). This is a case where the combustion pressure is very low, and it is actually difficult to detect θp using the A/D conversion method.

Incidentally, it is possible to distinguish by performing differential processing of Pa, but
A little more accurate. However, it is only at extremely low loads that Pa uniformly decreases after TDC, and in this case, the detection of θp is stopped and the operating state (engine speed N
and load Qa).

In this way, if θ is within the range of TDC+α° to θe, the combustion peak angle θp can be accurately detected by the above-mentioned A/D conversion method.

On the other hand, when θ≧θe in P54, it is determined that the combustion in the cylinder has been sufficiently completed, and in p6+, the average value of θp over the past several times is calculated, increasing the reliability of θp data, and calculating the current value. End the routine.

Note that detection of the combustion peak angle is not limited to the method using a piezoelectric element such as an in-cylinder pressure sensor. For example, the detection of the combustion peak angle can also be performed by detecting the light inside the combustion chamber through a glass window and an optical fiber, and identifying this detected light. It's okay.

In this way, in this embodiment, attention is paid to the correlation between the fuel properties and the combustion rate, and by accurately detecting the combustion rate of the used fuel, the properties of the used fuel are appropriately determined.

Then, the accurately detected fuel property parameter T. is applied to the fuel injection amount during deceleration, it is possible to eliminate the problem of deviations in air-fuel ratio control during deceleration due to differences in fuel properties, which were pointed out in the conventional problems.

FIG. 13 is a diagram showing a second embodiment of the present invention. In explaining this embodiment, the steps that perform the same processing as in the first embodiment are given the same numbers and the explanation thereof will be omitted, and the steps that perform the same processing as in the first embodiment will be omitted. The step numbers are marked with circles and the contents are explained.

In the program shown in Figure 13, when the engine is decelerating at PI2, is the flag FDEC reset at P'FI?
FDEC=O) or not. In other words, P? I determines whether or not the engine has entered deceleration for the first time.

If it is the first time the deceleration has started (FDEC=0), ptz
The value of basic injection ff1Tp at this time is stored in the memory as T p o, and when FDEC≠0, it is P?
Jump to 4. P? 2 resets the counter Tc (Tc=O)L, counts the elapsed time after deceleration.

After passing through PI3, fuel property correction is performed regarding the deceleration correction coefficient in P74 to P7&. This P'? Steps I to Plh correspond to steps P+a to PI6 in the first embodiment. In other words, in PI4, the deceleration air-fuel ratio correction coefficient KDEC(
Look up KDEC=func (N)), P7
S is the fuel property correction coefficient KDEC:D (KDECD =
func (Tso) ). Here, the air-fuel ratio correction coefficient KDEC during deceleration is K in the first embodiment.
Although the same symbol as DEC is used, the meaning is different as will be described later in Pill. Furthermore, the deceleration correction coefficient KDEC is corrected using the PVA according to the following equation (2).

KDEC=KDEC' xKDECD ・・・・・・
■However, KDEC': The value looked up in P74. Next, the counter Tc is incremented in P77, and P'l
11, basic injection during deceleration fttTpD according to the following formula [phase]
Calculate.

TpD=Tpo By correcting this, it is possible to achieve the same effect as in the first embodiment.

In each of the above embodiments, the fuel property detection method is to detect the combustion rate as shown in FIGS. 6 to 12,
Although an embodiment has been shown in which the fuel property parameter T5o is calculated based on this detected value, the present invention is not limited thereto. It goes without saying that a method of determining based on the response delay of the air-fuel ratio or a method of determining based on the response delay of a parameter correlated to the generated torque (or indicated mean effective pressure) under accelerated driving conditions may also be adopted.

(Effects) According to the present invention, the properties of the fuel used are detected, and the parameters (A I R or FUEL) that determine the air-fuel ratio during deceleration are appropriately corrected based on the detection results. Regardless of changes in properties, the air-fuel ratio during deceleration can always be optimized, and both drivability and HC reduction can be improved.

[Brief explanation of the drawing]

Figure 1 is a basic conceptual diagram of the present invention, Figures 2 to 12 are books? Fig. 2 is a diagram showing the first embodiment of the invention, Fig. 2 is an overall configuration diagram thereof, and Fig. 3 is a diagram showing a change in the combustion state when the heavy degree of gasoline is changed by a crank angle signal and an in-cylinder pressure signal. Figure 4 is a diagram showing the proportion of gasoline components depending on its weight, Figure 5 is a flowchart showing the air-fuel ratio control program during deceleration, and Figure 6 is a diagram showing the fuel property determination. Flow chart showing the program, Figure 7 is a table map of the temperature correction coefficient, Figure 8 (a) is a diagram showing the reference crank angle signal, and Figure 8 (b) is the relationship with the reference crank angle signal. Fig. 9 is a table map of the fuel property parameter T5°, Fig. 10 is a flowchart showing the program for detecting the combustion peak angle, and Fig. 11 shows the change in the cylinder pressure. 12(a) to 12(c) are diagrams showing general changes in cylinder pressure, respectively, to explain the effect thereof, and FIG. 13 is a diagram showing a second embodiment of the present invention, showing the air pressure during deceleration. 3 is a flowchart showing a fuel ratio control program. 1...Engine, 4...Injector (operating means), 15...
... Operating state detection means, 16... Control unit (property detection means, air-fuel ratio setting means, correction means).

Claims (1)

[Scope of Claims] a) property detection means for detecting the properties of the fuel used; b) operating state detection means for detecting the deceleration operating state of the engine; and c) supply air-fuel ratio when the engine is in the deceleration operating state. d) an air-fuel ratio setting means for setting the air-fuel ratio based on the properties of the reference fuel; An internal combustion engine comprising: a correction means for controlling the amount of intake air or the amount of fuel supplied; and e) an operation means for controlling the amount of intake air or fuel supplied based on a signal from the correction means. Air-fuel ratio control device.