JPH05280409A - Control method for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a control method of an internal combustion engine that can reduce the number of sensors to reduce the cost and perform good control without causing control interference. [Configuration] combustion chamber pressure of the engine detects the crank angle position θpmax that maximizes the average value of the crank angle position theta pmax
And the variance σθ pmax of the crank angle position, and the ignition timing is controlled based on the average value θ pmax to obtain the variance σ θ
The air-fuel ratio is controlled based on pmax.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedback control method for an internal combustion engine.

[0002]

2. Description of the Related Art Conventional feedback control methods for internal combustion engines include, for example, MRC (Mixture Ratio Control), ISC (Idle Speed Control) and STC (Spark). Timing Control: Ignition timing control).

First, the MRC (1) detects the oxygen concentration in the exhaust gas by an O ₂ sensor and feedback-controls the air-fuel ratio A / F. From the intake air amount Q, the engine speed N and a constant K, The basic injection time T _p of
Calculate by formula. T _p = K · Q / N (Equation 1) This T _p , the cooling water temperature, whether the engine is cranking or not, and the correction factor COE according to the opening / closing of the throttle valve, etc.
From F, the correction rate α according to the oxygen concentration in the exhaust gas, and the correction time T _s according to the battery voltage, the drive valve opening time T _i of the injector is calculated by the following formula (2). T _i = T _p × COEF × α + T _s (Equation 2) The input of the feedback control in this case is the oxygen concentration in the exhaust gas by the O ₂ sensor, and the output is only the correction rate α, that is, the drive valve opening time T _i. ..

Next, the ISC of
Intended to constant feedback control of the engine speed by changing the air quantity Q _a to bypass the throttle valve, whether the air conditioner is either in operation, depending on the gear position of the transmission is whether neutral, and the battery voltage, etc. The target value of the idling engine speed N corrected and corrected is compared with the actual engine speed N, and the ISC control solenoid is duty-controlled so as to reduce the difference, and feedback control is performed to the target engine speed. In this case, the input is the engine speed N and the output is the control duty 1
Is one.

In the STC, the ignition timing is changed,
The output and knocking are feedback-controlled. Generally, the output comes out when the ignition timing is advanced, but since knocking occurs, the ignition timing is delayed to prevent knocking. In this case, the knocking signal is input and the ignition timing correction signal is output.

[0006]

However, in the conventional feedback control method as described above, one or more inputs (operating variables) are required to perform one control, so that the number of controls increases. There is a problem that the number of sensors for input increases and the cost increases. Also, if you simply control multiple control elements with one input,
There is a fear that good control cannot be performed due to control interference. Further, when controlling one control element, only the control element is controlled, so that there is a fear that the control becomes unstable due to the fluctuation of the input. For example, I
In the SC control, if the engine speed is controlled only by the intake air amount, the fluctuation of the air-fuel ratio causes a large fluctuation of the rotation, and the control becomes unstable.

The present invention has been made to solve the problems of the prior art as described above, and it is possible to reduce the number of sensors to reduce the cost, and to perform good control without causing control interference. It is an object of the present invention to provide a control method of an internal combustion engine capable of performing the above.

[0008]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, in the present invention, the crank angle position θpmax that maximizes the pressure in the combustion chamber of the engine is detected, and a value that represents the average of the crank angle position θpmax and a value that represents the fluctuation of the crank angle position θpmax are set. The ignition timing is controlled on the basis of the value representative of the average, and the air-fuel ratio is controlled on the basis of the value representative of the fluctuation. The average value in the present invention means
It means an average value per predetermined time or a predetermined rotation of the engine, and is a value that does not follow a change in a short cycle of an input, but follows a change in a large level more gently than the change.

[0009]

With the above-described configuration, in the present invention, two control variables (that is, ignition timing and air-fuel ratio) are based on one operating variable (that is, the crank angle position θpmax at which the combustion chamber pressure becomes maximum). Therefore, the number of sensors for detecting operating variables can be reduced. Further, by using the value representing the average and the value representing the fluctuation as the components divided from one operation variable, the control interference is prevented. In addition, good control can be performed by controlling two control variables that are related to each other using a value that represents an average divided from one operation variable and a value that represents variation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic technical idea of the present invention will be described with reference to FIG.
Will be described. In FIG. 1, one operating variable V of the engine is detected, which detected operating variable V is multiplied by _two transfer functions G ₁ and G ₂ in transfer element 1,
One control variable C _{1 of the} engine by _one multiplication value G ₁ · V
And another control variable C ₂ by the other multiplication value G ₂ · V,
Feedback control each.

[0011] Figure 2 is obtained by further embodying the technical idea of FIG. 1, the signal separator 2 of one operating variable V of the engine is divided into two components V ₁ and V _2, 1-way component V ₁ of One control variable C ₁ of the engine via one transfer element 3 on the basis of
Is feedback-controlled, and another control element C ₂ of the engine is feedback-controlled via another transmission element 4 based on the other component V ₂ .

FIG. 3 is a further embodiment of FIG. 2, in which the operating variable V is passed through a low-pass filter 5 to extract a low-frequency component to make it one component V ₁ , and a high-pass filter 6 is passed to extract a high-frequency component. The two components V ₁ and V ₂ are extracted and used as another component V _2, and two control variables C ₁ and C ₂ are feedback-controlled by the two components V ₁ and V ₂ via the transfer elements 3 and 4, respectively.

FIG. 4 shows another specific example of FIG. 2, in which the operating variable V is divided into a direct current component (one component V ₁ ) by the smoother 7 and an alternating current component (other component V ₂ ) by the high pass filter 6. The DC component may be a value representing the average value V (or the median value) of the operating variable V, and the AC component may be a value representing the variation of the operating variable V. In this case, if n sample values of the operating variable V are V _k (k = 1, 2, ..., N), an average value V ( V indicates an average value of V, the same applies hereinafter)
Is calculated by the following equation (3).

[0014]

[Equation 3]

The median value V _c is calculated by the following equation (4). V _c = (1/2) {(V _k ) _max + (V _k ) _min } (Equation 4) Further, various values representative of fluctuations are defined, for example,
The absolute value error ΔV, the variance σV, the variation rate CV, and the like are included. The above absolute value error ΔV is obtained by the following equation (5).

[0016]

[Equation 5]

The variance σV is obtained by the following equation (6).

[0018]

[Equation 6]

Further, the variation rate CV is obtained by the following equation (7).

[0020]

[Equation 7]

Next, an embodiment embodying the above technical idea will be described with reference to the drawings. FIG. 5 shows an outline of an apparatus for realizing a first embodiment of a control method for an internal combustion engine of the present invention. In the drawing, a crank angle position θ signal is read by a crank angle sensor 10 attached to a crank pulley 9 of an internal combustion engine 8, and the signal is read through a control circuit including a CPU, a ROM, a RAM, etc. via an input interface 11. It is input to 12 and arithmetic processing is performed. As a result, the actuators 15 and 16 are operated via the output interfaces 13 and 14, and various control targets of the engine are feedback-controlled.

FIG. 6 shows the controller of FIG. 5 in more detail. 6, the same parts as those of FIG. 5 are indicated by the same numbers. In the figure, 17 is a water temperature sensor for detecting the temperature of the cooling water,
An O ₂ sensor 18 detects the oxygen concentration in the exhaust gas. 1
Reference numeral 9 is a neutral switch for detecting whether the gear position of the transmission is neutral or parking, 20 is a vehicle speed sensor for detecting the vehicle speed from the rotating shaft of the speedometer cable, and 21 is an air flow meter for detecting the intake air amount Q. To do. The I / O LSI and the peripheral circuit 22 are obtained by combining the input interface 11 and the output interfaces 13 and 14 of FIG. 23
Is an ignition coil, 24 is a distributor,
Reference numeral 25 is a throttle valve, and 26 is a three-way catalyst. 27
Is an injector, 28 is an idle control valve,
Reference numeral 29 is an EGR control valve, which corresponds to the actuators 8 and 9 in FIG. 30 In the idle air adjustment valve, the lift amount change is duty controlled by the idle control valve 28, by changing the air quantity Q _a to bypass the throttle valve 25, the idle rotation is controlled. Reference numeral 31 is an EGR valve, and the lift amount is changed by the EGR control valve 29.
The amount of (exhaust gas recirculation) is controlled. A combustion chamber pressure sensor 32 is provided for each cylinder of the engine 8 and detects the combustion chamber pressure P of each cylinder.

From the crank angle position θ signal from the crank angle sensor 10 and the combustion chamber pressure P signal from the combustion chamber pressure sensor 32, a waveform of the combustion chamber pressure P with respect to the crank angle position θ is obtained as shown in FIG. 7, for example. .. From this P-θ curve, the crank angle position θpmax when the combustion chamber pressure P reaches the maximum value _Pmax can be obtained. This θpmax is set as the operation variable V. Then, by sampling n θpmax for each cycle, (θpmax) _k (k = 1, 2, ..., N) is obtained. In accordance with this (? Pmax) _k from the above equation (3), the average value theta pmax of? Pmax is determined by the following equation (8).

[0024]

[Equation 8]

The above average value θ pmax is defined as one component V ₁ of the operating variable V. Further, according to the equation (6), the dispersion σθpmax can be obtained by the following equation (9).

[0026]

[Equation 9]

The above-mentioned variance σθpmax is used as another component V ₂ of the operating variable V. In FIG. 7, the position of θpmax changes depending on whether the ignition timing is early or late. Ignition timing is controlled so that the engine operates at maximum torque, that is, the best fuel economy (this is MBT control: Minimun advance for Best Torqu
(It is called e) and the P-θ curve becomes like A ₁ , and θpmax at the time of MBT control has a different value depending on the model of the engine, but the specific model does not depend on the operating conditions. The value is almost constant (14 ° ATDC: about 14 ° after top dead center).
Therefore, if the engine is in MBT control, θpmax should be
The engine can be MBT controlled by setting the value of as the target value (θpmax) _r and adjusting the ignition timing so that the measured actual θpmax matches the target value (θpmax) _r . In FIG. 7, a waveform A ₂ shows a case where the ignition timing is too advanced and a waveform A ₃ shows a case where the ignition timing is too late with respect to the waveform A ₁ during MBT control.

Further, as shown in FIG. 8, when the air-fuel ratio A / F is changed, the stability of combustion changes, and when the air-fuel ratio A / F becomes leaner than the stoichiometric air-fuel ratio (A / F) _th , the combustion The stability gradually decreases, and when it becomes leaner than a certain value, the stability sharply deteriorates and becomes unstable. In addition, the variance σθpmax of the crank angle position where the pressure in the combustion chamber is maximum is also the air-fuel ratio A
When / F becomes leaner, the value gradually increases, and when it becomes leaner than a certain value, the stability of combustion rapidly deteriorates and the value of the dispersion σθpmax also rapidly increases. Therefore, the variance σ becomes the limit air-fuel ratio A / F at which combustion does not become unstable.
If θpmax is set as the target value (σθpmax) _r and the air-fuel ratio A / F is fed back so that the measured dispersion σθpmax matches this target value (σθpmax) _r , the combustion will be performed within the stable combustion range. You can make the fuel ratio lean as much as possible,
Fuel economy can be improved.

Next, the operation will be described with reference to the flowchart of FIG. Using the crank angle position θ signal from the crank angle sensor 10 and the combustion chamber pressure P signal from the combustion chamber pressure sensor 32, the crank angle position θpmax at which the combustion chamber pressure becomes maximum is measured (step 50 in FIG. 9). .. Next, n sample values (θpmax) _k (k = 1, 2, ..., N)
Each time the latest value is read, the oldest value is discarded and stored while updating (step 51), and the average value is calculated according to the equation (8).
The dispersion σθpmax is calculated in accordance with the equation (9) (θ52) (step 52). Next, the target value (θpmax) _r of the crank angle that maximizes the pressure in the combustion chamber is set from the operating state of the engine at that time (step 53). Then, by comparing the θ pmax and _{(θpmax) r, θ pmax- (} θpmax) r
<0, that is, if θ pmax is advanced, the ignition timing is delayed according to the value of the difference, and θ pmax> ( θ pmax) _r , that is,
If θ pmax is delayed, the ignition timing is advanced according to the value of the difference (step 54). As a result, the actual value θpmax is always matched with the target value (θpmax) _r , and feedback control is performed so that the engine is always in MBT control. Further, in accordance with the operating state of the engine at that time, a target value (σθpmax) _r of the crank angle position that maximizes the fuel chamber pressure is set (step 55), and the actual value σθpmax and the target value (σθpma
x) _r are compared, and when σθpmax- (σθpmax) _r <0, the air-fuel ratio A / F is made lean according to the difference, and σθpmax-
When (σθpmax) _r > 0, the air-fuel ratio A / F is changed according to the difference.
Are enriched (step 56). The engine is thus run as lean as possible within a stable combustion range.

As described above, according to this embodiment, the engine can perform lean limit control and MBT control at the same time. However, performing both controls at the same time is more effective than performing both of them independently. Is shown in FIG. That is, in FIG. 10, the air-fuel ratio A / F is controlled while controlling the ignition timing to be the MBT control rather than making the air-fuel ratio A / F lean by fixing the ignition timing as shown by the dotted line.
By making the fuel leaner, it is possible to make it leaner while maintaining stable combustion.

Although the detected combustion chamber pressure P and crank angle position θ are directly input to the control circuit (control unit) 12 in the above embodiment, the control unit is divided into a measurement unit and a control unit (calculation speed, In some cases, it may be advantageous to separate into three systems because of the capability.) When the measuring unit inputs P and θ, it outputs a signal corresponding to the crank angle position θpmax where the combustion chamber pressure becomes maximum. In this case, the control unit controls the ignition timing according to the low frequency component of the output, and controls the air-fuel ratio A / F according to the high frequency component.

When the air-fuel ratio A / F is too lean and misfire occurs, the dispersion σθpmax becomes large and θpmax of the misfire cycle becomes almost 0 ° (ATDC). When the misfire occurs as described above, the variance σθpmax becomes large. Therefore, even in normal control, the air-fuel ratio A / F is controlled to be rich when the value of the variance σθpmax exceeds the target value (σθpmax) _r. However, if misfire continues, the drivability and exhaust characteristics will deteriorate significantly, so it is necessary to prevent misfire as quickly as possible. Therefore, even if the value of the variance σθpmax does not exceed the target value (σθpmax) _r , when θpmax = 0 ° is observed, the air-fuel ratio A / F is immediately enriched by the configuration. It is possible to prevent misfires and prevent poor drivability and deterioration of exhaust characteristics. This method is effective as a means for compensating for the time delay and insensitivity, which are the drawbacks of statistical processing.

Next, a second embodiment will be described. The first
In the P-θ waveform (FIG. 7) shown in the above embodiment, when knocking occurs in the engine, a waveform of a specific high frequency (about 7 kHz) appears. Accordingly, the combustion chamber pressure P signals through a band-pass filter centered on the order of 7 kHz, to extract knock waveform to obtain the maximum amplitude P _N of the high frequency of each cycle (1 waveform P-theta), reference this P _N is If the value (P _N ) _max or more, it is determined that knocking has occurred, the ignition timing is delayed, and knocking can be prevented. In this case,
Average value of crank angle position that maximizes combustion chamber pressure θ pm
It is preferable to give priority to the ignition timing control for preventing knocking, over the MBT control for controlling the ignition timing so that ax always matches the target value (θpmax) _r .

Next, the operation will be described with reference to the flowcharts of FIGS. 11 and 12. Similar to the first embodiment, θpmax
Is measured (step 60), and n samples (θpmax) _k
(K = 1, 2, ..., N) is stored (step 61). Then, according to the equations (8) and (9), the average value θ pm
Ax and variance σθpmax are calculated (step 62). Also,
The maximum amplitude P _N of the high frequency signal obtained through the band pass filter is measured (step 63). In order to determine whether or not there is a misfire in each cycle, it is compared whether | θpmax | is smaller than a preset reference value (θpmax) _min (step 64), and | θpmax | ≤ (θpmax) If it is _min , it is determined that the engine is misfiring, and the air-fuel ratio A / F is made rich (step 65) to prevent misfiring. The above (θpmax) _min is a constant determined by the error of the measurement system,
It may be a value close to 0 ° ATDC and a value at which θpmax becomes a misfire. Further, the allowable maximum amplitude (P _N ) _max of knocking vibration is set according to the operating state of the engine (step 66), and the actually measured maximum amplitude P _N is set as this reference value (P _N ) _max . Compare (step 67), P _N >
If ( _PN ) _max , it is determined that knocking has occurred, and the ignition timing is delayed (step 68) to prevent knocking. Next, as in the case of the first embodiment described above, the target value (θpmax) _{r of the} crank angle position that maximizes the pressure in the combustion chamber is set according to the operating state of the engine at that time (step 69), and θ pmax is The ignition timing is controlled (steps 71 and 72) depending on whether it is larger or smaller than (θpmax) _r (step 70), and the engine is set to MBT control. further,
Similar to the first embodiment, the dispersion target value (θpmax) _r is set (step 73), and the air-fuel ratio A / F is adjusted according to whether σθpmax is larger or smaller than (σθpmax) _r (step 74). Then, (steps 75 and 76), the air-fuel ratio A / F is controlled to lean so that the combustion state of the engine becomes unstable on the lean side. The ignition timing and the air-fuel ratio A /
It is checked whether or not the control output of F is within the permissible range predetermined by the operating state (step 77). If the control output is outside the permissible range, the control output is corrected to be within the permissible range. And output (step 78).

[0035]

As described above, according to the present invention, the crank angle position θpmax at which the pressure in the combustion chamber is maximized is obtained, the ignition timing is controlled based on the value representing the average of the θpmax, and θpmax of By configuring the air-fuel ratio based on the value that represents the fluctuation, the engine can be controlled to the leanest air-fuel ratio within the stability limit of combustion with maximum torque, and fuel consumption and exhaust performance can be improved. The effect is that both can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a basic technical idea of the present invention.

FIG. 2 is a block diagram illustrating a technical idea embodying FIG.

FIG. 3 is a block diagram illustrating a technical idea that is a more specific version of FIG. 2;

FIG. 4 is a block diagram for explaining another technical idea in which FIG. 2 is further embodied.

FIG. 5 is a configuration diagram showing an apparatus for realizing a first embodiment of a method for controlling an internal combustion engine of the present invention.

6 is a block diagram showing the control device of FIG. 5 in detail.

FIG. 7 is a characteristic diagram showing a waveform of a pressure in a combustion chamber with respect to a crank angle position.

FIG. 8 is a characteristic diagram showing the relationship between the combustion stability with respect to the air-fuel ratio and the dispersion of the crank angle position where the pressure in the combustion chamber is maximum.

FIG. 9 is a flowchart showing the contents of calculation in the first embodiment.

FIG. 10 is a characteristic diagram showing an ignition timing and a stable region of combustion with respect to an air-fuel ratio.

FIG. 11 is a flowchart showing a part of the contents of calculation in the second embodiment.

FIG. 12 is a flowchart showing a part of the rest of the calculation contents of the second embodiment.

[Explanation of symbols]

5 ... Low-pass filter 6 ... High-pass filter 7 ... Smoother 8 ... Internal combustion engine 10 ... Crank angle sensor 12 ... Control circuit 22 ... I / O LSI and peripheral circuits 25 ... Throttle valve 27 ... Injector 28 ... Idle control valve 29 ... EGR control valve 30 ... idle air adjusting valve 31 ... EGR valve 32 ... combustion chamber pressure sensor C _1, C ₂ ... control variables A / F ... air P ... combustion chamber pressure Q _a ... bypass air quantity V ... operating variables V _1, V ₂ … Component of operating variable θ… Crank angle position θpmax… Crank angle position where combustion chamber pressure becomes maximum θ pmax… Average value of θpmax σ θpmax… Variance

Claims (3)

[Claims] 1. A crank angle position θpmax at which the pressure in the combustion chamber of the engine is maximum is detected, and a value representative of the average of the crank angle position and a value representative of the fluctuation of the crank angle position are obtained, and the average is obtained. Is controlled on the basis of a value representative of the above, and the air-fuel ratio is controlled on the basis of a value representative of the above fluctuation. 2. The ignition timing is controlled so that the engine attains the maximum torque, and the air-fuel ratio is controlled to a limit at which the fuel state of the engine becomes unstable on the lean side of the air-fuel ratio. 1. The control method for an internal combustion engine according to 1. 3. The control method for an internal combustion engine according to claim 1, wherein when the crank angle position θpmax≈0 is detected, the air-fuel ratio is made rich.