JPS611845A - Control device for internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve exhaust purification performance through realizing optimum air-fuel ratio by providing a calculation unit to output air-fuel ratio control signals based upon exhaust gas constituent concentration sensed by an exhaust detector, and a mixed gas regulator for supplying mixed gas. CONSTITUTION:A pressure detector 51 senses the internal pressure of a cylinder. An exhaust gas detector 52 senses the exhaust gas constituent concentration of an engine. A distinction unit 56 judges if the engine load is within a preset range. In case the distinction unit 56 judges the load out of range, a calculation unit 55 outputs an air-fuel ratio control signal based upon the signals from a pressure detector 51 and a crank angle detector 53. If the distinction unit 56 judges the load within a preset range, then the unit 55 outputs a control signal based upon the signal from the exhaust gas detector 52. A mixed gas regulator 57 controls the mixed gas to be supplied to the engine. These units can realize optimum air-fuel ratio while engine runs under heavy load and a good exhaust purification performance under medium and light load.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a device for controlling the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, and in particular to air-fuel ratio control under high load conditions and air-fuel ratio control based on exhaust purification requirements. The present invention relates to a device that controls the use of the following functions depending on the operating state.

[Prior art]

FIG. 2 is an example diagram of a conventional fuel control device.

In Figure 2, 1 is an air cleaner, 2 is an air flow meter that measures the amount of intake air, 3 is a throttle valve, 4 is an intake manifold, 5 is a cylinder, 6 is a water temperature sensor that detects engine cooling water temperature, and 7 is an engine cooling water temperature sensor. A crank angle sensor detects the rotation angle of the crankshaft, 8 is an exhaust manifold,
9 is an exhaust sensor that detects the concentration of exhaust gas components (for example, oxygen concentration); 10 is a fuel injection valve; 11 is a spark plug; 12
is the control device.

The crank angle sensor 7 is connected, for example, to each crank angle reference position (every 180° for a 4-cylinder engine, 120° for a 6-cylinder engine).
A reference position pulse is output for each unit angle (for example, every 2 degrees), and an i unit angle pulse is output for each unit angle (for example, every 2 degrees).

In the control device 12, the crank angle at that time can be determined by counting the number of unit angle pulses after this reference position pulse is input.

Furthermore, the rotational speed of the engine can be determined by measuring the frequency or period of the unit angular pulse.

In the example shown in FIG. 2, a crank angle sensor is provided within the distributor.

The control device 12 includes, for example, a CPU, RAM, and ROM.

It is composed of a microcomputer consisting of an input/output interface, etc., and includes an intake air amount signal S1 given from the air flow meter 2, a water temperature signal S2 given from the water temperature sensor 6, a crank angle signal S3 given from the crank angle sensor 7, and an exhaust sensor. Exhaust signal S given from 9
4, a battery voltage signal (not shown), a signal from a fully open throttle switch, etc. are input, calculations are performed according to these signals to calculate the amount of fuel to be injected to the engine, and an injection signal S5 is output.

This injection signal S5 causes the fuel injection valve 10 to operate, supplying a predetermined amount of fuel to the engine.

The calculation of the fuel injection amount Ti in the control device 12 is performed, for example, using the following equation (for example, described in Nissan Technical Manual 1979 ECC8L Series Engine).

Tj=TpX(1+Ft+KMR/100)Xβ+Ts
...(1) In the above equation (1), Tp is the basic injection amount. For example, if the intake air amount is Q, the engine rotation speed is N, and the constant is K, then Tp = -Q/N is required.

Further, Ft is a correction coefficient corresponding to the engine cooling water temperature, and for example, the lower the cooling water temperature, the larger the value becomes.

Further, KMR is a correction coefficient during high load, and is read out by table lookup from a value stored in advance in a data table as a value corresponding to the basic injection amount TP and rotational speed N, as shown in Fig. 4, for example. used.

Further, Ts is a correction coefficient based on the battery voltage, and is a coefficient for correcting fluctuations in the voltage that drives the fuel injection valve 10.

Further, β is a correction coefficient according to the exhaust signal S4 from the exhaust sensor 9, and by using this β, the air-fuel ratio of the air-fuel mixture is feedback-controlled to a predetermined value, for example, a value near the stoichiometric air-fuel ratio of 14.8. You can.

However, when food pack control is performed using this exhaust signal S4, the air-fuel ratio of the air-fuel mixture is always controlled to a constant value, so the above corrections due to cooling water temperature and high load are not necessary. It becomes meaningful.

Therefore, this feedback control using the exhaust signal S4 is performed only when the correction coefficient Ft based on water temperature and the correction coefficient KMR at high load are O.

The relationship between the above-mentioned correction calculations and sensors is shown in FIG. 3.

On the other hand, as an ignition timing control device for an internal combustion engine, there is one as shown in, for example, Japanese Patent Publication No. 59061 of 1982.

In the electronic ignition timing control device as described above, the optimum ignition advance value corresponding to the engine rotational speed N and the basic injection amount Tp as shown in FIG. 5 is stored in advance as a data table, for example, as shown in FIG. It is configured to read a value corresponding to the rotational speed and basic injection amount at that time by table lookup, and control the ignition timing to that value.

[Problem that the invention seeks to solve]

As mentioned above, conventional fuel control devices perform feedback control according to the exhaust sensor signal, but corrections due to high load conditions are determined by the basic injection amount and rotational speed, that is, the intake air amount and rotational speed. The configuration is such that the correction is performed entirely under open-loop control.

Therefore, due to variations in air flow meters, fuel injection valves, etc., changes over time, etc., the air-fuel ratio at high loads may become the optimum air-fuel ratio (
L B T -Leanest Mixture fo
rBest Torque (note that this value is the air-fuel ratio that maximizes the generated torque, and is a different value from the feedback value of the air-fuel ratio based on the exhaust sensor signal) and the torque decreases. or stability may deteriorate.

The present invention aims to solve the problems of the prior art as described above.

[Means for solving problems]

In the frame invention which achieves the above object.

Determines whether the engine load is within a predetermined range, and if it is outside the range, detects the engine cylinder pressure and performs feedback control to set the engine air-fuel ratio to LBT from that value,
In addition, when the load is within the range, the air-fuel ratio is feedback-controlled based on the exhaust sensor signal to the value required for exhaust purification.
The engine is operated at the BT point, and the exhaust gas is effectively purified during medium and low loads.

In addition, in conjunction with the air-fuel ratio control described above, the ignition timing is adjusted to the optimum ignition timing (MB T-...Minimum 5park).
If the feedback control at the LBT point described above is controlled so as to achieve the following (Advance for 5est Torque), the feedback control at the LBT point described above can be made more effective.

Hereinafter, first, the principle for realizing LBT and MBT will be explained.

Fig. 6 is a diagram showing the relationship between crank angle and cylinder pressure, and Fig. 7 is a diagram showing the relationship between air-fuel ratio and generated torque, and the values under the condition that the throttle valve is fully open at a constant rotational speed (for example, 2000 rpm) are shown in Fig. 6. It shows.

As can be seen from Figure 6, the cylinder pressure is at W top dead center (
10° to 20' after T D C), i.e. A T
It is maximum at DC 10° to 20°.

Also, its maximum value changes depending on the air-fuel ratio A/F.
It reaches its maximum when F is around 13.

Furthermore, as can be seen from FIG. 7, the torque generated by the engine also reaches its maximum when the air-fuel ratio is around 13, which is called LBT.

Therefore, by performing feedback control to maximize the cylinder pressure, the air-fuel ratio under high load can always be controlled to the optimum air-fuel ratio LBT.

FIG. 8 is a diagram showing the relationship between the cylinder pressure and the crank angle when the ignition timing is changed, and shows the values under the condition that the throttle valve is fully open at a constant rotational speed (for example, 2000 rpm).

As can be seen from FIG. 8, the cylinder pressure curve changes depending on the ignition timing.

Then, the crank angle O when the cylinder pressure is maximum
The torque is maximized when the ignition timing is controlled so that m is a predetermined angle (for example, 10° to 20°) after top dead center.

The ignition timing at this time is called MBT.

FIG. 9 is a diagram showing the relationship between the cylinder angle θm and the ignition timing at which the cylinder pressure is maximum.

As can be seen from Figure 9, there is a nearly linear correspondence between 0m and the ignition timing, and by controlling the ignition timing,
The value of m can be set to any value.

Therefore, the generated torque can be maximized by controlling the ignition timing so that the value of 0m becomes the value of the point corresponding to MBT (for example, 15 degrees after top dead center).

FIG. 10 is a diagram showing the relationship between ignition timing and generated torque.

As can be seen from FIG. 10, the generated torque is maximized when the ignition timing is controlled to the MBT point (for example, BTDC 20°).

By combining the air-fuel ratio control and the ignition timing control as described above, the characteristics shown in FIG. 11 are obtained as conditions for maximizing the generated torque.

In FIG. 11, the X mark is the LMBT point, that is, the point where both LBT and MBT are realized.

As can be seen from the above explanation, in order to operate the internal combustion engine at the LMBT point, the pressure inside the cylinder of the engine is detected, and based on that value, the air-fuel ratio of the engine is feedback-controlled to the LBT. The crank angle at which the pressure is maximum may be detected, and the ignition timing may be feedback-controlled so that the crank angle is set at a predetermined angle after top dead center.

The predetermined crank angle θm for achieving the above MBT point is a value determined depending on the engine's rod ratio, and is a value unique to that engine, and is generally 10° to 20° after top dead center.
For example, the value is 15 degrees after top dead center.

The connecting rod ratio is the ratio between the length of the connecting rod and the radius of rotation of the crankshaft (172 of the stroke), and when the length of the connecting rod is L and the radius of rotation of the crankshaft is r, Rod ratio λ=L
/ r.

Next, FIG. 1 is a block diagram showing the functions of the present invention.

First, in FIG. 1(A), reference numeral 51 denotes pressure detection means for detecting the pressure inside the cylinder, for example, the pressure sensor 13 shown in FIG. 12 described later.

Further, the exhaust gas detection means 52 detects the engine exhaust gas component concentration (
For example, the exhaust sensor 9 in FIG. 2 is used to detect the oxygen concentration.

Further, 53 is a crank angle detection means for detecting the crank angle, and is, for example, the crank angle sensor 7 shown in FIG. 2 above.

Further, 54 is a load detection means for detecting the load of the engine, and is, for example, the air flow meter 2 shown in FIG. 2 described above.

Next, the first determining means 56 is a means for determining whether or not the engine load is within a predetermined range. For example, from the values stored in the data table as shown in FIG. If the value corresponding to the rotational speed N is 0, it is determined to be within the range (medium-low load range), and if it is not 0, it is determined to be outside the range (high load range).

In addition, when the determining means 56 determines that it is outside the range, the calculating means 55 determines that the inside of the cylinder at the first predetermined crank angle within one ignition cycle is detected based on the signals from the pressure detecting means 51 and the crank angle detecting means 53. A control signal that detects the pressure Pmbt and the cylinder internal pressure Pt at a second predetermined crank angle, calculates the ratio Pmbt/Pt between the two, and controls the air-fuel ratio so that the ratio P+nbt/Pt is maximized. Output.

Furthermore, when the determining means 56 determines that the exhaust gas is within the range, the calculating means 55 outputs a control signal based on the signal from the exhaust detecting means 52. This control signal is for feedback control, for example, so that the air-fuel ratio is set to a value near the stoichiometric air-fuel ratio of 14.8.

The above-mentioned determining means 56 and calculating means 55 can be constituted by, for example, a microcomputer.

Next, the air-fuel mixture metering means 57 controls the air-fuel mixture to be supplied to the engine in accordance with the control signal given from the arithmetic means 55 described above.

This air-fuel mixture adjusting means 57 includes, for example, the fuel injection valve 10 shown in FIG.
No. 2326) can be used.

Next, in FIG. 1(B), when the discriminating means 56 determines that it is outside the range, the calculating means 58 calculates, based on the signals from the pressure detecting means 5 and the crank angle detecting means 53, that the The maximum value Pi of the cylinder internal pressure and the cylinder internal pressure Pt at a predetermined crank angle are detected, and the ratio between the two is Pi/P.
t is calculated, and a control signal is output to control the air-fuel ratio so as to maximize the ratio Pi/Pt.

Further, when the determining means 56 determines that the exhaust gas is within the range, the calculating means 58 outputs a control signal based on the signal from the exhaust detecting means 52. The other parts are the same as in (A) above.

Next, in FIG. 1(C), when the determining means 56 determines that the range is out of range, the calculating means 59 calculates the indicated value within one ignition cycle based on the signals from the pressure detecting means 5I and the crank angle detecting means 53. Calculate the average effective pressure Pi, detect the cylinder internal pressure Pt at a predetermined crank angle, and calculate the ratio Pj/P of both.
t is calculated, and a control signal is output for controlling the air-fuel ratio so as to maximize the ratio Pi/'Pt.

Further, when the determining means 56 determines that the exhaust gas is within the range, the calculating means 58 outputs a control signal based on the signal from the exhaust detecting means 52. The other parts are the same as in (A) above.

In addition, the indicated average effective pressure Pi is the cylinder internal pressure for each crank angle, P, and the crank angle is a predetermined angle (for example, 2 degrees).
When the amount of change in the stroke volume at each change is Δ■ and the stroke volume is V, it is determined by Pi=Σ(PXΔV)/v.

In (A) above, when the load of the engine is outside the predetermined range, that is, when the load is high, the first predetermined crank angle (for example, AT
The cylinder pressure Pmbt at a second predetermined crank angle (for example, TDC) is
In (B), the air-fuel ratio is controlled according to the value normalized by the maximum cylinder pressure Pm at a predetermined crank angle (for example, TDC). The air-fuel ratio is controlled, and in (C) 1
The indicated mean effective pressure Pi is set at a predetermined crank angle (for example, TDC
), the air-fuel ratio is controlled according to the value normalized by the cylinder pressure Pt at
It becomes possible to control to the BT point.

Further, when the engine load is within a predetermined range, the air-fuel ratio is feedback-controlled in accordance with the signal from the exhaust detection means, so that the exhaust purification performance can also be satisfied.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on Examples.

FIG. 12 is a diagram showing an embodiment of the present invention.

In FIG. 12, 13 is a pressure sensor that detects the pressure inside the cylinder.

This pressure sensor 13 is used in place of the washer of the spark plug 11, and extracts changes in cylinder pressure as an electrical signal.

The control device 15 is composed of, for example, a microcomputer, and includes an intake air amount signal S1 given from the air flow meter 2, a water temperature signal S2 given from the water temperature sensor 6, a crank angle signal S3 given from the crank angle sensor 7, The exhaust signal S4 given from the exhaust sensor 9 and the pressure signal 86 given from the pressure sensor 13 are input, and predetermined calculations are performed to generate the injection signal S5 and the ignition signal S7.
and thereby output the fuel injection valve 10 and the ignition device 1.
6.

Note that the ignition device 16 generates a high voltage when the ignition signal S7 is given from the control device 15, and transmits it to the spark plug 11.
For example, a device consisting of a power transistor switching circuit and an ignition coil can be used.

In addition, the same symbols as in FIG. 2 indicate the same parts.

Next, FIG. 13 is an example diagram of the pressure sensor 13, (
A) shows a front view, and (B) shows a sectional view.

In FIG. 13, 13A is a ring-shaped piezoelectric element; 1.
3B is a ring-shaped negative electrode, and 13C is a positive electrode.

Further, FIG. 14 is a diagram showing how the pressure sensor 13 is mounted, and is mounted to the cylinder head 14 by being tightened by the spark plug 11.

Next, calculations within the control device 15 will be explained.

FIG. 15 is a block diagram showing an embodiment of the control system of the present invention.

In FIG. 15, air flow meter 2, water temperature sensor 6
, the exhaust sensor 9 and the pressure sensor 13, and the voltage signal of the battery 17 are applied to a multiplexer 18 in the control device 15.

Further, the signal from the crank angle sensor 7 is applied to a latch circuit 19, and depending on the output of the latch circuit 19, the multiplexer 18 is switched to selectively send each of the above signals to the AD converter 20.

Each signal converted into a digital signal by the AD converter 20 and the signal from the crank angle sensor 7 are sent to the CPU 21.
Calculations as shown in the flowchart described later are performed, and the injection signal (corresponding to the above-mentioned control signal) calculated as a result of the calculation is power-amplified in the output circuit 23 and then sent to the fuel injection valve 10. Further, the ignition timing control signal calculated as the calculation result is converted into an ignition signal by the output circuit 24, and then sent to the ignition device N16.

Note that 22 is a memory, which is comprised of a RAM that temporarily stores data during calculations, and a ROM that stores calculation procedures and various data (KMR data table, etc.) in advance.

Next, the contents of the calculation will be explained in detail.

FIG. 16 is a flowchart showing an example of calculations within the control device 15.

First, in FIG. 16(A), at Pl, the rotational speed N of the engine is read from the signal of the crank angle sensor.

Next, in P2, the intake air amount Q is read from the signal of the air flow meter.

Next, in P3, -Q/N is calculated for the basic injection amount Tp=.

Next, in P4, the ignition advance value ADV is looked up in a data table as shown in FIG. 5, according to the above determined N and Tp.

Next, at P5, a high load correction value KMR is determined from the data table as shown in FIG.
table lookup.

Next, in P6, the cylinder internal pressure P at that time is measured from the signal of the pressure sensor and stored.

Next, at Pl, the crank angle at that time is compression top dead center (T
DC).

If NO at Pl, go to PIO immediately.

If YES (7) at P'7, go to P8, measure and store the cylinder internal pressure Pt at TDC.

Next, in P9, the above measured Pt is set as the initial value of the maximum value Pm of the cylinder internal pressure.

Further, the crank angle θ at this time is set to 0.

Next, in PLO, it is determined whether the current cylinder internal pressure Pn is greater than the maximum value Pm of the cylinder internal pressures up to the previous time.

If Plo is No, go to Pl2 immediately.

If YES in PlO, go to pH and store the current cylinder internal pressure Pn as a new maximum value Pi.

Further, the crank angle at that time, that is, the crank angle θm corresponding to the maximum value is set to n.

Next, at Pl2, the crank angle at that time is ATDC15
”, and if YES, ATDC at Pl3.
Measure and store the cylinder pressure Pmbt at 15°.

The ATDC 15° at Pl2 is a value determined by the engine's continuous rod ratio as described above, and is the crank angle at which the cylinder internal pressure is thought to reach its maximum value.

Next, at Pl4, it is determined whether the crank angle is greater than ATDC90'.

If YES in P14, the section in which the maximum value of the cylinder pressure occurs in the explosion cycle has ended, so the process goes to P15 in FIG. 16(B).

If No at Pl4, return to Pl again and repeat the above procedure.

Next, in FIG. 16(B), at Pl5, the ratio between the maximum value Pmbt and the cylinder pressure Pt at TDC is calculated and stored.

Note that the entire calculation in the flowchart of FIG. 16 is repeated once for each ignition cycle, and the subscript of (Pmbt/Pt)n of Pl5. indicates that it is the value in the current calculation.

Next, in Pl6, the KMR read in the above P5 is
Determine whether or not.

If KMR=O, this indicates that the load is in a medium to low load range within a predetermined range, so air-fuel ratio control is performed based on the signal from the exhaust sensor.

First, the output of the exhaust sensor is read at Pl7.

Next, at Pl8, the air-fuel ratio at that time is determined from the output of the exhaust sensor. In this method, for example, the output of the exhaust sensor is compared with a predetermined reference value, and if the output is greater than the reference value, the air-fuel mixture is rich (the air-fuel ratio is smaller than the target), and if it is smaller, the air-fuel mixture is lean (the air-fuel ratio is lower than the target). is larger than the target).

If Pl is rich at 8, go to Pl9 and set the air-fuel ratio correction coefficient α to α=α−Δα.

If it is lean at Pl8, go to P2O and set the air-fuel ratio correction coefficient α to α=α+Δα.

In other words, if the air-fuel ratio is richer than the target value (for example, the stoichiometric air-fuel ratio), the air-fuel ratio correction coefficient is subtracted by Δα to make it lean, and conversely, if it is lean, it is subtracted by Δα to make it rich. I'll add it up.

On the other hand, if Pl6 is NO, L13T control is performed from the load force 1 at that time (a force indicating that the load force is in a high load range outside the predetermined range).

First, in P21, the value calculated in the current ignition cycle in P15 is compared with the value of (Pmbt/Pt)n-x, that is, the value calculated in the previous ignition cycle. In P21, if the value in the current calculation is larger, the process goes to P22 and it is determined whether the rich flag is 21 or not.

The rich flag is 1 when the air-fuel ratio is rich, that is, rich, and is O when the air-fuel ratio is lean, that is, thin.

If YES in P22, the process goes to P24 and the air-fuel ratio correction coefficient α is set to α=α+Δα.

That is, in a state where the air-fuel ratio is enriched, Pm
If the value of bt/Pt is increasing, the air-fuel ratio is further changed toward richer.

If No at P22, go to P23 and set α to α=α−Δ
Let it be α.

In other words, when the air-fuel ratio is lean, P mbt
/Pt, is increasing, the air-fuel ratio is controlled to be leaner.

On the other hand, if the answer is NO in P21, the process goes to P25, and it is determined whether the rich flag is 1 or not.

If YES in P25, the process goes to P26, where the rich flag is set to 0, and then, in P27, α=α−Δα is set.

In other words, when enriching the air-fuel ratio, Pmbt/P
If t is decreasing, it is necessary to lean the air-fuel ratio, so after setting the rich flag to O in P26,
7, α is decreased by a constant amount Δα.

In the case of No in P25, the process goes to P28 and the rich flag is set to 1, and then α=α+Δα is set in P29.

In other words, when the air-fuel ratio is lean, Pmbt/P
When t is decreasing, it is necessary to enrich the air-fuel ratio, so after setting the rich flag to 1, control is performed to increase α by Δα.

Next, at P2O, using the air-fuel ratio correction coefficient α calculated as described above, the fuel injection amount Ti2TP·α+Ts is calculated and output.

Note that Tp uses the value obtained in P3 above, and Ts is calculated from the battery voltage read separately.

Next, in P31, it is determined whether the crank angle Om at which the cylinder internal pressure determined based on the pH reaches the maximum value Pm is greater than 15°.

This value of 15° is a value for realizing the above-mentioned MBT, and is a value determined by the continuous culm ratio of the engine in the range of <ATDCIO° to 20°.

In this embodiment, the angle is set to 15 degrees as an example.

If NO in P31, this indicates that the crank angle at which the cylinder pressure is maximum is smaller than ATDC15°, that is, the ignition advance angle is ahead of MBT, so go to P32 and change ΔA from the ignition advance angle ADV. The value obtained by subtracting is the new ignition advance angle.

If YES in P31, this indicates that the crank angle θm at which the cylinder pressure is maximum is greater than ATDC15', that is, the ignition advance angle is behind MBT, so go to P33 and set ΔA to ADV. The value added is the new ignition advance angle ADV.

As mentioned above, in the calculation shown in Fig. 16, when the load is in the medium to low load range within a predetermined range, the air-fuel ratio is controlled to a predetermined value according to the signal from the exhaust sensor, and when the load is outside the predetermined range, the air-fuel ratio is controlled to a predetermined value. When in the load range, the air-fuel ratio is controlled so that the value obtained by normalizing the value Pmbt at the crank angle at which the cylinder pressure reaches its maximum value by the cylinder pressure Pt at compression top dead center becomes the maximum value. .

In addition, the ignition timing is controlled so that the crank angle at which the cylinder pressure is maximum is a predetermined angle after top dead center.

By controlling as described above, it is possible to control the air-fuel ratio to a predetermined air-fuel ratio suitable for exhaust gas purification in a medium-low load range, and to control the air-fuel ratio to LBT in a high-load range. The ignition timing can also be controlled by MBT6.
Therefore, by the above control, the LMB shown in FIG.
It can be controlled to match the T point.

In the above control, if the ignition timing is not controlled, the portions of θm=0 in P4 and P9 in FIG.
It is sufficient to delete o, Pit, pzo to P33.

Next, FIG. 17 is a flowchart showing a second embodiment of the calculation according to the present invention.

First, in FIG. 17(A), the steps from PL to Pl4 are the same as those from Pl to Pl4 in FIG. 16.

However, the difference is that Pl2 and Pl3 are deleted.

Next, at P34 in FIG. 17(B), the maximum value PIIl determined at the pH and the cylinder internal pressure P at TDC are determined.
The ratio with t is calculated and stored.

Further, in P35, the magnitude of the value calculated for the current ignition cycle and the value calculated for the previous ignition cycle is compared with (Pll/Pt)nt, that is, the value calculated for the previous ignition cycle.

The calculations from P16 to P33 thereafter are the same as those in FIG. 16 above.

As mentioned above, in the calculation shown in Fig. 17, when the load is in the medium and low load range within a predetermined range, the air-fuel ratio is controlled to a predetermined value according to the signal from the exhaust sensor, and when the load is outside the predetermined range, the air-fuel ratio is controlled to a predetermined value. When in the load range, find the actual maximum value of the cylinder internal pressure and use that value as the cylinder internal pressure P at compression top dead center.
The air-fuel ratio is controlled so that the value normalized by t becomes the maximum.

In addition, the ignition timing is controlled so that the crank angle at which the cylinder pressure is maximum is a predetermined angle after top dead center.

In the above control, if ignition timing is not controlled, Om=0 portions of P4 and P9 in FIG.
It is sufficient to delete the part of θm=n, P30 to P33.

Next, FIG. 18 is a flowchart of an embodiment showing the third calculation of the present invention.

First, in FIG. 18(A), the steps from P1 to pH are the same as in FIG. 16 above.

However, the difference is that P36 and P37 are inserted between P6 and Pl.

That is, in P36, the amount of change ΔV in the stroke volume every time the crank angle changes by a predetermined angle (for example, 2 degrees) is calculated.

Next, in P37, the indicated mean effective pressure Pi is calculated.

This indicated average effective pressure Pi is the value obtained by dividing the work done by the combustion gas on the piston during one cycle by the stroke volume, and the cylinder pressure at each crank angle is P, and the crank angle changes by a unit angle (for example, 2 degrees). Assuming that the change in stroke volume each time is Δ■, and the stroke volume is V, then Pi=Σ(pxΔ
V)/V.

Also, P in: P in-, +ΔV' P n
Approximate calculations can also be made using the formula.

In addition, in the above formula, Pin is Pi in this calculation.
, Pin-4 is the value of Pi in the previous calculation (2 degrees ago in terms of crank angle), and Pn is the value of P in the current calculation.

Next, after calculating from Pl to pH, in P38 it is determined whether the crank angle at that time is the exhaust top dead center.

If No in P38, this indicates that the combustion cycle has not yet ended, so the process returns to P1 and repeats the above procedure again.

If YES in P38, one combustion cycle has been completed, so the process goes to P39 in FIG. 18(B).

In P39, the ratio between the indicated average effective pressure Pi and the cylinder internal pressure Pt at TDC is calculated and stored.

In P2O, the value calculated for the current ignition cycle is compared with the value calculated for the previous ignition cycle. The subsequent calculations of P16 to P33 are performed in the 16th
This is the same as the case shown in the figure.

As mentioned above, in the calculation shown in Fig. 18, when the load is in a medium to low load range within a predetermined range, the air-fuel ratio is controlled to a predetermined value according to the signal from the exhaust sensor, and when the load is outside the predetermined range, the air-fuel ratio is controlled to a predetermined value. When in the load range, the indicated mean effective pressure Pi is converted to the cylinder internal pressure Pt at compression top dead center, which represents the engine load.
Since the air-fuel ratio is controlled to be corrected so that the normalized value becomes the maximum, it is possible to accurately realize the four optimum air-fuel ratios LBT.

Furthermore, since the ignition timing is feedback-controlled so that the crank angle θm at which the cylinder pressure is maximum is at a predetermined position after top dead center, the ignition timing can always be controlled to the MBT point.

In the above control, if the ignition timing is not controlled, the portion θm=Q of P4 and P9 in FIG.
All you have to do is delete the θm20 part, P30 to P33.6 In the example shown in Fig. 12, only one cylinder is shown, but in the case of a multi-cylinder engine, each cylinder should be It is possible to correct and control the fuel injection amount for each cylinder according to the signal from the pressure sensor.

Further, although a pressure sensor is attached to each cylinder to measure the cylinder pressure, it is also possible to correct fuel injection by performing the same injection in all cylinders.

It is also possible to provide a pressure sensor in only one of several cylinders and correct the same injection amount for all cylinders based on the output of the pressure sensor.

Further, in the explanation so far, only the case where a fuel injection valve is used as the air-fuel mixture metering device has been explained, but it is possible to perform similar control even when a carburetor is used.

〔Effect of the invention〕

As explained above, in the present invention, when the load is in a medium to low load range within a predetermined range, the air-fuel ratio is controlled to a predetermined value according to the signal from the exhaust sensor, and when the load is in a high load range outside the predetermined range, the air-fuel ratio is controlled to a predetermined value. In some cases, the pressure inside the cylinder is detected using a pressure sensor, the maximum value of the cylinder pressure, the indicated average effective pressure, etc. are determined from that value, and these values are calculated as the cylinder pressure at a predetermined crank angle such as compression top dead center. The air-fuel ratio is configured to be feedback-controlled so that the normalized value is maximized, so even if there are variations in parts or changes over time, the optimal air-fuel ratio LBT can always be achieved at high loads. Not only can the highest torque be obtained, but also good exhaust purification performance can be achieved at medium to low loads.

Therefore, there are excellent effects such as eliminating the possibility of insufficient torque or deterioration of exhaust purification performance.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the functions of the present invention, Fig. 2 is an example of a conventional fuel control device, Fig. 3 is a diagram of the relationship between the calculation contents and sensors in the device shown in Fig. 2, and Fig. 4 is Characteristic diagram of high load correction coefficient, Figure 5 is ignition advance angle characteristic diagram, Figure 6 is characteristic diagram of crank angle and cylinder pressure, Figure 7 is characteristic diagram of air fuel ratio and torque, Figure 8 is ignition advance characteristic diagram. A characteristic diagram of the cylinder pressure and crank angle when the timing is changed. Figure 9 is a characteristic diagram of the crank angle and ignition timing at which the cylinder internal pressure is maximum. Figure 10 is a characteristic diagram of the ignition timing and output torque. Fig. 11 is a torque characteristic diagram depending on the air-fuel ratio and ignition timing, Fig. 12 is an example of the present invention, Fig. 13 is an example of the pressure sensor used in the present invention, and Fig. 14 is the pressure FIG. 15 is a block diagram showing an embodiment of the control system of the present invention, and FIGS. 16 to 18 are flow charts showing the calculations of the present invention. Explanation of symbols 1... Air cleaner 2... Air flow meter 3... Throttle valve 4... Intake manifold 5... Cylinder 6... Water temperature sensor 7...
・Crank angle sensor 8...Exhaust manifold 9...
・Exhaust sensor 10...Fuel injection valve 11...
Spark plug 12...Control device 13...Pressure sensor 13A...Piezoelectric element 13B...Negative electrode 13G...Positive electrode 14...Cylinder head 15...Pa control device engineering 6...Ignition Device 1
7...Battery 18...Multiplexer 19.
...Latch circuit 20...AD converter 21...
・CPU22...Memory 23.24...
・Output circuit 51...Pressure detection means 52...Exhaust detection means 53...Crank angle detection means

Claims (1)

[Claims] 1. Pressure detection means for detecting cylinder internal pressure, crank angle detection means for detecting crank angle, exhaust detection means for detecting engine exhaust gas component concentration, and engine load. A load detection means, a determination means for determining whether or not the engine load is within a predetermined range, and signals from each of the above means are input, and when the engine load is outside the predetermined range, the pressure detection means and the crank angle are input. From the signal with the detection means, the cylinder pressure Pmbt and the second cylinder pressure at the first predetermined crank angle within one ignition cycle are determined.
detect the cylinder pressure Pt at a predetermined crank angle,
Calculate the ratio Pmbt/Pt of both, and calculate the ratio Pmbt/P
Outputs a control signal to control the air-fuel ratio so as to maximize t, and when the engine load is within a predetermined range, outputs a control signal to control the air-fuel ratio based on the detection result of the exhaust detection means. A control device for an internal combustion engine, comprising a calculation means and an air-fuel mixture adjusting means for supplying an air-fuel mixture to the engine according to the above control signal. 2. The calculation means uses a value in the range of 10° to 20° after compression top dead center as the first predetermined crank angle, and uses compression top dead center as the second predetermined crank angle. A control device for an internal combustion engine according to claim 1, characterized in that: 3. The determination means determines whether the load at that time is within a predetermined range from values stored in a data table in advance according to values corresponding to the intake air amount and rotation speed of the engine. A control device for an internal combustion engine according to claim 1, characterized in that the control device for an internal combustion engine is characterized in that: 4. Pressure detection means for detecting cylinder internal pressure; crank angle detection means for detecting crank angle; exhaust detection means for detecting engine exhaust gas component concentration; load detection means for detecting engine load; A discriminating means for determining whether or not the load of the engine is within a predetermined range, and signals from each of the above means are input, and if the load of the engine is outside the predetermined range, a signal from the pressure detecting means and crank angle detecting means is input. The maximum value Pm of cylinder pressure within one ignition cycle and the cylinder pressure Pt at a predetermined crank angle are detected, the ratio Pm/Pt of the two is calculated, and the ratio Pm/Pt is maximized. a calculation means for outputting a control signal for controlling the air-fuel ratio, and for outputting a control signal for controlling the air-fuel ratio based on the detection result of the exhaust detection means when the engine load is within a predetermined range; A control device for an internal combustion engine, comprising an air-fuel mixture adjusting means for supplying an air-fuel mixture to the engine according to a signal. 5. Pressure detection means for detecting the cylinder internal pressure, crank angle detection means for detecting the crank angle, exhaust detection means for detecting the exhaust gas component concentration of the engine, load detection means for detecting the load of the engine, A discriminating means for determining whether or not the load of the engine is within a predetermined range, and signals from each of the above means are input, and if the load of the engine is outside the predetermined range, a signal from the pressure detecting means and crank angle detecting means is input. The indicated average effective pressure Pi within one ignition cycle is calculated, the cylinder pressure Pt at a predetermined crank angle is detected, the ratio Pi/Pt of both is calculated, and the ratio Pi/Pt is maximized. a calculation means for outputting a control signal for controlling the air-fuel ratio, and for outputting a control signal for controlling the air-fuel ratio based on the detection result of the exhaust detection means when the engine load is within a predetermined range; A control device for an internal combustion engine, comprising an air-fuel mixture adjusting means for supplying an air-fuel mixture to the engine according to a signal.