JPH0750098B2 - Fuel property determination device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion property determination device for an internal combustion engine, and more particularly to a device that gives a fuel heaviness level as an output value of combustion pressure.

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

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

As a conventional fuel supply device, for example, JP-A-60-128958
There is one described in the publication. In this device, the oxygen sensor provided in the exhaust pipe detects the air-fuel ratio, and based on the detection result, the fuel injection amount is operated to perform feedback control so that the air-fuel ratio becomes the target value.

That is, the injection pulse signal (final injection amount) Ti actually 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 × Co × α + Ts ...... However, Tp: basic injection amount Co: various correction coefficients α: air-fuel ratio feedback correction coefficient Ts: voltage correction amount In the above equation, various correction coefficients Co are calculated according to the following equations.

Co = 1 ＋ KTRM ＋ KMR ＋ KTW ＋ KAS ＋ KAI ＋ KACC ＋ KH …… However, KTRM: Mixing ratio correction coefficient KMR: Mixing ratio correction coefficient KTW: Water temperature increase correction coefficient KAS: Start and start increase correction coefficient KAI: Idle increase correction coefficient KACC: Acceleration decrease correction coefficient KH: High water temperature increase correction coefficient Further, at the time of starting, acceleration, and high load, various corrections are added to improve drivability to make the air-fuel ratio richer than the target air-fuel ratio. In addition to this, there is interrupt injection during acceleration,
During rapid acceleration, injection is performed asynchronously with the normal fuel injection control.

On the other hand, during cold start-up and during warm-up, the oxygen sensor is cold and is not activated, so the feedback control is stopped and the air-fuel ratio is set to the rich side to improve startability and engine stability immediately after start. Intended for sex.

The above-mentioned correction values are set on the assumption 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 properties of the fuel used by the engine (for example, heaviness level)
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. Is changed, and even if the heaviness level of the fuel is changed accordingly, the air-fuel ratio correction due to the change in the property of the supplied fuel is not considered. Therefore,
In such a case, a difference occurs between the air-fuel ratio calculated based on the use of standard fuel and the actual air-fuel ratio, and it is 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 component involved in combustion becomes lean. Therefore, the actual air-fuel ratio becomes leaner than the air-fuel ratio calculated using the standard fuel as a reference. As a result, the engine may be operated leaner than the target air-fuel ratio, and the combustion state may deteriorate and the drivability such as starting and the fuel efficiency may deteriorate. When the startability becomes extremely poor, cranking is repeated more than necessary, and so-called battery exhaustion occurs.
Moreover, such a problem becomes remarkable when the poor fuel is used.

As described above, when various calculations are performed on the premise that a uniform fuel such as standard fuel is used as the supplied fuel, some problems occur in terms of control accuracy. That is, in order to aim for more accurate air-fuel ratio control, it is desirable to allow for differences in the properties of fuel used.

For this reason, it is desired to realize a device that can directly detect the fuel property, but at present, a device that detects the fuel property suitable for air-fuel ratio control has not been realized.

(Object of the Invention) Therefore, the present invention detects the combustion pressure of the engine, detects the combustion speed correlated with the fuel property of the fuel used from the detected value, and calculates the combustion speed of the reference fuel from the operating state of the engine. An object of the present invention is to provide a fuel property determination device capable of accurately detecting the property (heaviness level) of fuel by determining the property of the fuel used based on both of these combustion speeds.

(Means for Solving Problems) In order to achieve the above object, the fuel property determination device according to the present invention is
As shown in the basic conceptual diagram of FIG. 1, a pressure detecting means a for detecting the combustion pressure of the engine, a rotational speed detecting means b for detecting the rotational speed of the engine, and a load detecting means c for detecting the load of the engine. A temperature detection means d for detecting the engine temperature, a combustion speed detection means e for calculating the combustion speed of the fuel used based on the output of the pressure detection means a, an engine load,
A calculation means f for calculating the combustion speed of the reference fuel based on the rotation speed and the engine temperature, and a judgment means g for judging the property of the engine use fuel based on the combustion speed of the used fuel and the combustion speed of the reference fuel are provided. ing.

(Operation) In the present invention, the combustion speed of the fuel used is detected from the combustion pressure of the engine, and the combustion speed of the reference fuel is calculated from the operating state of the engine. Then, the property of the fuel used is accurately determined using both of them, which have a close causal relationship with the property of the fuel, as parameters.

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

2 to 11 are views showing a first embodiment of the present invention, and are examples in which the present discriminating device is applied to a device for controlling an air-fuel ratio of an internal combustion engine.

First, the configuration will be described. In FIG. 2, reference numeral 1 denotes 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 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 in the catalytic converter 6, harmful components (CO, HC, NOx) in the exhaust gas are cleaned by a three-way catalyst and discharged.

Intake air flow rate Qa is an air flow meter (load detection means)
7 and is controlled by the throttle valve 8 in the intake pipe 3. Also, the combustion pressure in the cylinder (hereinafter referred to as the cylinder pressure)
Pa is detected by a pressure sensor (pressure detecting means) 9, and the pressure sensor 9 is composed of a piezoelectric element and is molded as a washer of the ignition plug 10. The pressure sensor 9 detects an in-cylinder pressure Pa acting on the piezoelectric element via the ignition plug 10 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 a crank angle sensor (rotation speed detection means) 11, and the temperature Tw of the cooling water flowing through the water jacket is detected by a water temperature sensor (temperature detection means) 12. Furthermore, the oxygen concentration in the exhaust gas is measured by the oxygen sensor 13
The oxygen sensor 13 outputs its
A material having a characteristic in which Vs suddenly changes is used.

Outputs from the air flow meter 7, the pressure sensor 9, the crank angle sensor 11, and the water temperature sensor 12 are input to the control unit 14, and the control unit 14 determines the fuel property based on the sensor information.
That is, the control unit 14 has a function as a combustion speed detection means, a calculation means and a determination means,
5, ROM16, RAM17, NVM (nonvolatile memory) 18 and I / O
Consists of port 19. CPU15 fetches external data required from I / O port 19 according to the program written in ROM16, RAM17 and NVM18
While exchanging data with and from the engine, it calculates the processing value required for the fuel property determination and the air-fuel ratio control based on the result, and outputs the processed data to the I / O port 19 as necessary. . I / O port 19 has sensor groups 7, 9, 11, 12, 1
The signal from 3 is input, and the injection signal Si is output from the I / O port 19. The ROM 16 stores a calculation program in the CPU 15, and the RAM 17 and the NVM 18 store data used for calculation in the form of a map or the like.

Next, the operation will be described. First, the change in the fuel property and its influence will be described taking gasoline as an example.

Gasoline is composed of several hundreds of hydrocarbons (HC), and is classified into four paraffins, olefins, naphthenes and aromatics according to the ratio of carbon (C) and hydrogen (H) and the bonding mode. To be done. 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 ).
The degree of heavyness of gasoline is typified by T _50. Light (high volatility) T ₅₀ = 80 to 90 ° C, heavy (low volatility) T ₅₀ = 110 to 120 ℃, T on the market
Most of those with a temperature of ₅₀ = 95-100 ° C are in circulation. Therefore, the final injection amount Ti described above is determined by performing various corrections on the assumption that the fuel (that is, regular gasoline) having T ₅₀ = 95 to 100 ° C. is used.

FIG. 3 shows a change in the combustion state when the degree of gasoline is changed as a change in the in-cylinder pressure signal under a predetermined condition (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 drawing indicates an actual combustion period from ignition timing θi to θpmax.

As shown in FIG. 3, in the case of light gasoline, the maximum value Pmax of the in-cylinder pressure signal is large and the fuel progresses quickly, but as the fuel becomes heavier, Pmax decreases and θpmax shifts to the later side. This is the initial stage of combustion (from ignition to θpmax
Up to)), the gasoline component contributing to combustion (hatched portion in Fig. 4) decreases as the fuel becomes heavier. When observing this early combustion light, it is entirely blue, and in light gasoline, only blue is observed,
It disappears immediately after θpmax (that is, combustion has ended).

However, in 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. That is, in heavy gasoline, high-speed combustion (pale white combustion light) and slow combustion (red combustion light) are mixed and burned, and the high-speed combustion (pale white combustion light) contributing to actual combustion is The heavier the fuel, the less. This means that the gasoline component that contributes to combustion becomes leaner as it becomes heavier. In other words, the leaner air-fuel ratio results in a slower combustion speed (Pmax
Is on the delay side).

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

In the present embodiment, in view of the above-described characteristics of the fuel property, the property of the fuel is properly determined by the following program, focusing on the causal relationship with the combustion speed as a parameter.

FIG. 5 is a flow chart showing a program for fuel property discrimination based on the above-mentioned basic principle, and P _{1 to} P _{13 in the} figure show respective steps of the flow. This program is executed once every predetermined time.

The steps of P _{1 to} P ₄ are processing to determine whether or not the engine is in a predetermined operating state. First, at P ₁ , it is determined whether the cooling water temperature Tw is within a predetermined range. If Tw ₁ ≤Tw ≤Tw ₂ , it is determined that the engine temperature is within the predetermined range, and the routine proceeds to P ₂ . Here, it is desirable to set Tw in a range such that Tw = 10 ° C. to 40 ° C. If it is within the predetermined range (N ₁ ≤ N ≤ N ₂ ), it is determined whether the engine speed N is within the predetermined range with P _2.
Intake air quantity Qa proceeds to P _3, it is determined whether or not within a predetermined range. Here, the engine speed N and the intake air amount Qa
Is set to a range that falls within the λ control (air-fuel ratio control) range by the oxygen sensor 13.

When Qa ₁ ≤Qa ≤Qa ₂ , it is determined at P ₄ whether the engine is in a steady state (not in rapid acceleration or rapid deceleration), and in the steady state, the process proceeds to P ₅ . 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.

Stop subsequent processing is determined that not in the predetermined operating condition the engine if the condition is not satisfied even in any one of the steps process is suitable for performing fuel nature discriminating the above P ₁ to P ₄ Do (that is, return).

At P ₅ , the reference combustion rate parameter θ _co {θ _co = func (Qa,
N)} is looked up. This reference burning velocity parameter θ _co represents the burning velocity when using the standard fuel, and by comparing it with the burning velocity of the fuel actually used in the step described later, the difference in burning velocity (for example, (The combustion speed slows down when the quality is improved) is detected.

Then, at P ₆ , the temperature correction coefficient k ₁ {k ₁ = func (Tw)} is set to the sixth value.
Look up from the table map shown. The temperature correction coefficient k ₁ corrects the combustion speed that changes depending on the engine temperature according to the engine temperature Tw even if the fuel property is the same. At the reference temperature Tw _o , k ₁ = 1 and at Tw <Tw _o , k ₁ <1, Tw> Tw _o k
> 1 is set.

Next, at P ₇ , the combustion peak angle (crank angle at which the in-cylinder pressure Pa becomes maximum) θp is detected, and the routine proceeds to P ₈ . The detection of θp will be described in detail later in the program.

Furthermore, in P _8, which is the actual combustion period measured burn time θc from the ignition timing θi and the combustion peak angle θp computed according to the following equation (see Figure 7).

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, θp are predetermined as shown in FIG. 7 (a). The reference crank angle θref at which the [H] level pulse is generated in the reference crank angle signal Sr is used as a reference, and each crank angle is represented by the elapsed crank angle from this θref as shown in FIG.

In P ₉ , the measured fuel period θc ₁ under the reference conditions is set as the temperature correction coefficient.
It is calculated by the product θc ₁ (θc ₁ = k ₁ × θc) of k ₁ and the measured combustion period θc. This θ c ₁ corresponds to the actual burning velocity parameter detected under the reference conditions. Next, at P ₁₀ , the measured combustion period θ c ₁ under the reference conditions and the reference combustion velocity parameter θ _co
The difference Δθ c ₁ with the following is calculated according to the following equation.

Δθc ₁ = θc ₁ −θ _co …… In other words, here, the combustion speed parameter θ _co when the reference fuel is used under the reference conditions and the combustion speed parameter (measured fuel period) θc _{1 of the} fuel actually used The difference with is detected. Since the combustion speed has a certain correlation depending on the property of the fuel, it is possible to properly determine the property of the fuel by accurately detecting the combustion speed.

Furthermore, computed according to the following equation moving average .DELTA..theta.c ₁ ^* of .DELTA..theta.c ₁ at P _11.

However, in the case of m: constant P ₁₂ , the fuel property parameter T _{50 is} calculated based on the value of Δθc ₁ ^*.
Is looked up from the table map having the characteristics shown in FIG. 8, and the value of T ₅₀ is stored in NVM (nonvolatile memory) 18 at P ₁₃ .

In this way, the fuel property parameter of the used fuel at that time is appropriately obtained by comparing the difference in the combustion speed depending on the property of the used fuel with the combustion speed of the standard fuel. Therefore, it is possible to provide a fuel property determination device suitable for the conventionally desired air-fuel ratio control.

FIG. 9 is a flow chart showing a program for detecting the combustion peak angle θp, and this processing corresponds to P ₇ of the step described in FIG. This program is executed once every 2 ° in crank angle.

First, it is determined whether the current crank angle (piston position) theta corresponds to the compression top dead center TDC at P _21, theta = analog signal representing the cylinder pressure Pa in P ₂₂ when the TDC A / proceeds to P ₂₃ after storing as D conversion cylinder pressure converted value ADo. On the other hand, θ ≠
When the TDC, the process proceeds to P ₂₃ to jump the P _22. P In ₂₃ crank angle θ is TDC excess value shown in Figure 10 whether or not (TDC + alpha DEG) or more, that the engine 1 is judged as to whether or not the rotation or alpha DEG beyond TDC. Here, α = 2 ° to 4 ° is set. Since the peak of the in-cylinder pressure Pa due to combustion (hereinafter referred to as the combustion peak) appears after TDC, a dead zone of α ° is set and the in-cylinder pressure Pa at TDC is mistakenly used as the combustion peak value. This is to avoid it.

When θ <TDC + α °, that is, θ is before top dead center (BTDC)
Or if TDC ≦ θ <TDC + α, the current routine is ended. On the other hand, when θ ≧ TDC + α °, the processing for detecting the combustion peak angle after P ₂₄ is executed. First, the crank angle θ is determined whether or not exceeds the combustion peak angle determination limit θe at P _24. θe is a crank angle at which it can be assumed that combustion in the cylinder has been completed, and is set to a predetermined value exceeding TDC (see FIG. 10). The combustion peak is assumed to be between TDC and θe. For example, F ₁ shown in FIG.
The F ₂ point corresponds to this (curve X represents when combustion conditions are different). Therefore, the A / D conversion process of the cylinder pressure Pa for obtaining the combustion peak is performed up to θe.

When θ ≤ θe in P ₂₄ , the θ counter that counts θ in P ₂₅ is incremented, and in P ₂₆ the cylinder pressure Pa at this time is A / D.
The in-cylinder pressure conversion value AD ₁ is converted and stored. Next, at P ₂₇ , the difference value ΔP between the in-cylinder pressure conversion values AD ₁ and AD ₀ is calculated and P
Proceed to ₂₈ . If the in-cylinder pressure Pa is increasing, the difference value ΔP is
If it is positive or decreasing, it will be a negative value. In addition, it becomes a very small value near the combustion peak time. At P ₂₈ , the absolute value | ΔP | of the difference value ΔP is compared with the reference value ΔP ₀ . The reference value ΔP ₀ is a value for determining whether or not the change in the in-cylinder pressure Pa has become substantially flat. When | ΔP | ≦ ΔP ₀ , it is judged that the change in the in-cylinder pressure Pa is substantially flat, and the count value of the θ counter is stored as the combustion peak angle θp in P ₂₉ , and in-cylinder pressure conversion of this routine is performed in P _30. The value AD _{1 is set} to AD ₀ and the routine ends. On the other hand, when | ΔP |> ΔP ₀ , it is determined that the position is not flat, and the process proceeds to P ₃₀ .

Here, the condition of | ΔP | ≦ ΔP ₀ is satisfied when the in-cylinder pressure Pa is maximum, minimum, maximum, or minimum. The determination of such a state is not limited to the example of the present embodiment, and may be performed using, for example, the differential value of the in-cylinder pressure Pa. The manner in which the in-cylinder pressure Pa actually changes under the condition of | ΔP | ≦ ΔP ₀ is summarized in the examples of FIGS. 11 (a) to 11 (c). FIG. 11 (a) shows the most general Pa change curve. In this example, the crank angle satisfying the condition of | ΔP | ≦ ΔP ₀ after TDC is θp, and the combustion peak angle can be easily obtained. Figures 11 (b) and 11 (c) are for low loads.
After TDC, Pa will be flat in two places. 11th
In the case of Fig. (B), the cylinder pressure Pa _{1 at} θp becomes smaller than the value Pa _{TDC at TDC} , and the local minimum value P in the middle
a ₂ appears. However, Pa ₂ appears at this time, so Pa ₁
Becomes a maximum value, and θp can be identified. On the other hand, the eleventh
In the case of Fig. (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.

By the way, the discrimination is possible if the differential processing of Pa is performed, but it is slightly accurate. However, it is in the case of extremely low load that Pa decreases uniformly after TDC, and in this case θp
Is stopped and the operation state (engine speed N and load Qa) is determined.

Thus, if θ is in the range of TDC + α ° ~ θe,
The combustion peak angle θp can be accurately detected by the above A / D conversion method.

On the other hand, when θ ≧ θe in P ₂₄ , it is judged that the combustion in the cylinder is sufficiently completed, and the average value of θp in the past several times is calculated in P ₃₁ to improve the reliability of the θp data. This routine ends.

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

As described above, in the present embodiment, attention is paid to the correlation between the fuel property and the combustion speed, and the combustion speed of the used fuel is accurately detected to properly determine the property of the used fuel.
Therefore, according to this embodiment, a device that can directly detect the fuel property can be realized, and if this is applied to the air-fuel ratio control device,
It is possible to solve the problem of control deviation due to the difference in fuel properties pointed out in the conventional problems.

For example, when heavy gasoline is used, the amount of gasoline that actually contributes to combustion is smaller than that of the standard fuel, and the mixing ratio is practically lean. On the other hand, according to the present device, since the heavy-duty level of the used fuel is appropriately discriminated and the deviation from the target air-fuel ratio is appropriately corrected according to the degree of heaviness, the heavy-duty fuel is used as described above. When quality gasoline is used, the condition that the amount of gasoline that contributes to combustion is small is corrected. That is, at this time, the total amount of fuel injection is corrected so as to increase. Therefore, the state where the mixture ratio is lean is effectively avoided, and the original effect of the air-fuel ratio control can be achieved. As a result, the deterioration of the combustion state can be prevented, the drivability, the fuel efficiency, and the exhaust emission characteristics can be remarkably improved, and the air-fuel ratio can be optimized even when the poor fuel is used.

Further, in this embodiment, no special sensor or member is required, and conventional components can be used as they are, so that it is not necessary to modify the hardware surface of the device. That is, since it is possible to provide the device only by supporting software, it is possible to avoid the device from becoming complicated and costly.

Although the first embodiment described above calculates the combustion peak angle θp in order to detect the combustion speed parameter, the combustion speed parameter may be detected by another method.
This will be shown in Examples.

12 to 14 are views showing a second embodiment of the present invention, and in this embodiment, the value of the in-cylinder pressure at a predetermined crank angle after TDC is used as a combustion speed parameter.

The hardware configuration of this embodiment is the same as that of the first embodiment, so the hardware configuration diagram is omitted. The program of this embodiment is executed for each unit crank angle (for example, 1 °) after TDC.

In the program of FIG. 12, step P ₄₁ is a process of determining whether or not the engine is under a predetermined condition.
This corresponds to the step processing of P _{1 to} P _{4 in} the embodiment. If it is not under the predetermined condition, the subsequent processing is stopped (returned) as in the first embodiment.

Engine when in a predetermined condition to determine whether the crank angle after TDC at P ₄₂ theta is equal to a predetermined determination crank angle theta _0. That is, in this step, the timing for detecting the in-cylinder pressure P for obtaining the combustion speed parameter is set, and when θ = θ ₀ , the process proceeds to the steps of P _{43 and} subsequent steps. Here, the discriminating crank angle θ ₀ is a predetermined crank angle after TDC, and is preset to a value equal to the crank angle θpmax (this θpmax is a known value by actual measurement, etc.) that gives Pmax of light gasoline in FIG. 1, for example. Has been done. Therefore,
In the present embodiment, θ ₀ is set to θpmax of light gasoline, but it may be set to any value as long as a significant difference in the in-cylinder pressure (combustion pressure) due to the fuel property appears.

It should be noted that, if not under the predetermined condition, the subsequent processing is stopped (return).

Next, at P ₄₃ , the analog signal representing the in-cylinder pressure P when the crank angle θ is θ = θ ₀ is A / D converted to the in-cylinder pressure conversion value Pθ.
₀ proceeds to P ₄₄ after storing as. At P ₄₄ , the basic injection amount Tp is calculated from the two-dimensional table map with θa and N as parameters.
To look up. Then, in P ₄₅ , the in-cylinder pressure conversion value P ₁ normalized by the load at that time is calculated according to the following equation.

P ₁ = Pθ ₀ / Tp ...... Here, the in-cylinder pressure conversion value Pθ ₀ that changes depending on the state of the engine load (for example, intake air amount) is a normalized parameter (Pθ ₀ / Tp) in which the influence of the load is excluded. Is being processed. The normalized in-cylinder pressure converted value P ₁ represents the magnitude of the in-cylinder pressure based on the fuel used actually used at that time, the reference cylinder pressure converted value for the standard fuel used later in P ₄₆ By comparing with P ₀ , the combustion speed parameter dp / dθ based on the difference in the in-cylinder pressure conversion value (however, dθ is constant and dθ is omitted) is detected.

At P ₄₆ , the reference cylinder pressure conversion value P ₀ {P ₀ = func (N)} is looked up from the table map. This reference cylinder pressure conversion value P ₀ is the standard fuel (that is, regular gasoline (T
₅₀ = 95.5 ° C.) is a value obtained by dividing the in-cylinder pressure conversion value Pθ ₀ when the basic injection amount Tp is used, and varies slightly depending on the engine speed N.

Then, in P ₄₇ , the temperature correction coefficient k ₂ {k ₂ = func (Tw)} is set to the first value.
3 Look up from the table map shown in Fig. The temperature correction coefficient k ₂ corrects the in-cylinder pressure conversion value that changes depending on the engine temperature according to the engine temperature Tw even with the same fuel property, and corresponds to the temperature correction coefficient k ₁ of the first embodiment.

At P ₄₈ , the combustion speed parameter ΔP ₁ based on the difference between the in-cylinder pressure conversion values is calculated according to the following equation.

ΔP ₁ = k ₂ · P ₁ −P ₀ ……, where P _{1 is the in-} cylinder pressure conversion value P _{0 is the} reference in-cylinder pressure conversion value In this way, the magnitude of the in-cylinder pressure conversion value has a certain correlation depending on the fuel properties. (As the fuel becomes heavier, the value of Pθ ₀ becomes smaller). Therefore, if the in-cylinder pressure conversion value is accurately detected, the property of the fuel can be appropriately determined.

Furthermore, it calculates the moving average [Delta] P ₁ ^* for [Delta] P ₁ according to the following equation at P _49.

However, m: a fuel property parameter T ₅₀ based on the values of the constants P ₅₀ [Delta] P ₁ ^* lookup from a table map having the characteristics shown in FIG. 14, the value of the T ₅₀ in P ₅₁ NVM ( Non-volatile memory) 18.

The above steps of P ₄₉ , P ₅₀ , and P ₅₁ are the same as those in P ₁₁ of the first embodiment.
It corresponds to the processing of each step of P ₁₂ and P ₁₃ .

In this way, by comparing the in-cylinder pressure conversion value due to the property of the fuel used with the in-cylinder pressure conversion value of the standard fuel as a reference,
Similar to the first embodiment, the fuel property parameter of the used fuel can be appropriately obtained. In addition to the effects of the first embodiment, this embodiment requires a routine for detecting the combustion peak angle θp shown in FIG. 9, so it is necessary to process this routine every 2 ° of crank angle. Disappear. Therefore, the time required for the fuel property determination program is short, and the opening time (off time) of the program can be made sufficiently long. As a result, the processing of other programs such as ignition timing and air-fuel ratio control can be frequently executed during that time, and there is an advantage that the control accuracy of them can be improved.

Further, by not performing the processing for every 2 ° of crank angle, the fuel property determination processing up to the high rotation speed region is enabled.

FIG. 15 is a diagram showing a third embodiment of the present invention, which is the same as the second embodiment except that a step for detecting the in-cylinder pressure conversion value even when θ = TDC is added. is there. In the description of the present embodiment, steps for performing the same processing as those in the second embodiment are given the same numbers and their explanations are omitted, and different steps are given step numbers surrounded by a circle to explain the contents. .

In the program of FIG. 15, after passing through P ₄₁ , it is determined at P ₆₁ whether or not the current crank angle θ corresponds to the compression top dead center TDC, and when θ = TDC, the cylinder pressure P is set at P _62. After changing the analog signal to A / D and storing it as the in-cylinder pressure conversion value P _TDC , P ₄₂
Proceed to. On the other hand, when θ ≠ TDC, jump P ₆₂ and proceed to P ₄₂ .

Then, after passing through P ₄₄ , the in-cylinder pressure conversion value P at θ = θ ₀ at P ₆₃
The difference between θ ₀ and the in-cylinder pressure conversion value P _TDC when θ = TDC is ΔPθ ₀
Is calculated according to the following equation.

ΔPθ ₀ = _{Pθ 0} -P _TDC ...... That is, in this example Δ in place of Pshita ₀ in the second embodiment
Pθ ₀ is used. Further, the normalized in-cylinder pressure converted value ΔPθ calculated according to the following equation by the load as in step P ₄₅ of the second embodiment in P _64, criteria in P ₆₅ cylinder pressure converted value ΔP ₀ {ΔP ₀ = func ( N)} is looked up from the table map.

ΔPθ = ΔPθ ₀ / Tp ...... Further, as in step P ₄₈ of the second embodiment in P ₆₆ through P ₄₇ burn rate parameters [Delta] P ₁ calculates according to the following equation.

ΔP ₁ = k ₂ · ΔP θ-ΔP _{0 (} where k ₂ : temperature correction coefficient) The subsequent processing is the same as in the second embodiment. As described above, in the present embodiment, the in-cylinder pressure conversion value Pθ ₀ is not directly processed, but the difference ΔPθ between the in-cylinder conversion value P _TDC when θ = TDC.
Since the subsequent processing is performed using, it is possible to more clearly detect the change in the cylinder pressure due to the difference in the fuel property,
This leads to improved accuracy. Therefore, in this embodiment, in addition to the effect of the second embodiment, a more accurate fuel property parameter can be detected.

(Effect) According to the present invention, the combustion speed of the used fuel is detected from the combustion pressure of the engine, the fuel speed of the reference fuel is calculated from the operating state of the engine, and the property of the used fuel is determined based on these combustion speeds. Since the determination is made, it is possible to provide the fuel property determination device that can accurately determine the fuel property at low cost.

As a result, if the present device is applied to the air-fuel ratio control of the internal combustion engine, the air-fuel ratio can be accurately corrected and the air-fuel ratio control can be effectively performed.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 11 are diagrams showing a first embodiment of the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. FIG. 4 is a diagram showing the relationship between the crank angle signal and the in-cylinder pressure signal showing the change in the combustion state when there is a change, FIG. 4 is a diagram showing the proportion of gasoline components depending on the degree of heavyness, and FIG. FIG. 6 is a flowchart showing the program, FIG. 6 is a table map of the temperature correction coefficient k ₁ , FIG. 7 (a) is a diagram showing the reference crank angle signal, and FIG. 7 (b) is a relationship with the reference crank angle signal. Fig. 8 shows a change in the in-cylinder pressure, Fig. 8 is a table map of the fuel property parameter T ₅₀ , Fig. 9 is a flow chart showing a program for detecting the combustion peak angle, and Fig. 10 is a change in the in-cylinder pressure. FIGS. 11 (a) to 11 (c) explain the operation. FIGS. 12 to 14 are views showing a general change in the in-cylinder pressure, respectively, and FIGS. 12 to 14 are views showing a second embodiment of the present invention. FIG. 12 is a flow chart showing a program for determining the fuel property, and FIG. Is a table map of the temperature correction coefficient k ₂ , FIG. 14 is a table map of the fuel property parameter T ₅₀ , and FIG. 15 is a flowchart showing a program of the fuel property determination showing the third embodiment of the present invention. 1 ... Engine, 7 ... Air flow meter (load detection means), 9 ... Pressure sensor (pressure detection means), 11 ... Crank angle sensor (rotation speed detection means), 12 ... Water temperature sensor (temperature detection means) , 14 ... Control unit (combustion speed detection means, calculation means, discrimination means).

Claims (1)

[Claims] 1. A) pressure detection means for detecting engine combustion pressure, b) rotation speed detection means for detecting engine speed, c) load detection means for detecting engine load, and d) engine. Temperature detecting means for detecting the temperature; e) combustion speed detecting means for calculating the combustion speed of the fuel used based on the output of the pressure detecting means; and f) combustion of the reference fuel based on the engine load, engine speed and engine temperature. A fuel property discriminating device comprising: a computing unit for computing a velocity; and g) a discriminating unit for discriminating the property of the fuel used by the engine based on the burning velocity of the used fuel and the burning velocity of the reference fuel.