JP2022162284A - Internal combustion engine control device - Google Patents

Abstract

To provide an internal combustion engine control device which is less in the cost of an engine system and can accurately estimate a combustion state.SOLUTION: A controller 12 of an internal combustion engine includes a torque fluctuation estimation part 122a which can estimate a combustion state of an engine 1 on the basis of a first cylinder internal pressure P1 acquired in the vicinity of an ignition timing, and a second cylinder internal pressure P2 acquired in the vicinity of a combustion completion timing.SELECTED DRAWING: Figure 2

Description

The present invention relates to an internal combustion engine control system.

In recent years, in vehicles such as automobiles, regulations on fuel consumption (fuel efficiency) and exhaust gas harmful components have been strengthened, and such regulations tend to be further strengthened in the future. Under such circumstances, there is known a technique for estimating the state inside the combustion chamber of the engine and controlling the engine based on the result of the estimation. By appropriately controlling the air-fuel ratio and ignition timing according to the current combustion state, it is possible to improve the thermal efficiency of the engine and reduce the emission of harmful gases.

To estimate the combustion state of an engine, a method of determining the heat release distribution and combustion torque from the results of in-cylinder pressure detection by a pressure sensor is widely applied. Techniques for estimating such a combustion state are disclosed in Patent Documents 1 and 2, for example.

In Patent Document 1, an in-cylinder pressure sensor is provided to detect the cylinder pressure as the in-cylinder pressure, the indicated torque and the pump loss torque are calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor, and the indicated torque and the pump loss torque are calculated. is used to calculate the engine torque of an internal combustion engine.

Patent Document 2 describes a technique of sampling the in-cylinder pressure at a crank angle position of 60° before top dead center and at a crank angle position of 60° after top dead center, and adopting the detected pressure ratio as a combustion state parameter. there is

JP 2017-57803 A JP-A-2002-97996

The method of estimating the combustion state based on the measurement result (in-cylinder pressure) of the in-cylinder pressure sensor described in Patent Document 1 is a predetermined section of the engine cycle, for example, in a section of 360° crank angle centering on the compression top dead center. time-series pressure values are required. Furthermore, in order to estimate the combustion state with sufficient accuracy, it is necessary to sample the pressure at intervals of approximately 1° or less of the crank angle. Therefore, a control device for estimating the combustion state is required to have a large storage capacity and high-speed computing power. A pressure sensor that supports high-speed sampling is also required. There is a problem that the cost of the engine system increases due to these factors.

Further, Patent Document 2 describes that the cylinder pressure is detected at a crank angle position of 60° before the top dead center and at a crank angle position of 60° after the top dead center. It has been found that the combustion state of an internal combustion engine (engine) cannot be accurately estimated based on the internal pressure.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an internal combustion engine control apparatus capable of estimating the combustion state of an internal combustion engine at low cost.

An internal combustion engine control device according to the present invention estimates a combustion state of an internal combustion engine based on a first in-cylinder pressure acquired near ignition timing and a second in-cylinder pressure acquired near combustion end timing. A combustion state estimator is provided.

ADVANTAGE OF THE INVENTION According to this invention, the internal-combustion-engine control apparatus which can estimate the combustion state of an internal-combustion engine at low cost can be provided.
Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the whole structural example of the engine which concerns on the 1st Embodiment of this invention. 1 is a block diagram showing a configuration example of a controller according to a first embodiment of the present invention; FIG. FIG. 5 is a flowchart showing an example of a process of estimating the magnitude of engine torque fluctuation, which is performed by a torque fluctuation estimating section of the controller according to the first embodiment of the present invention; FIG. FIG. 4 is a characteristic diagram showing the correlation between the cycle variation rate of differential pressure and the magnitude of engine torque variation according to the first embodiment of the present invention; 4 is a graph showing an example of in-cylinder pressure detection timing according to the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing an example of an estimation error of torque fluctuation with respect to the difference between the acquisition timing of the first in-cylinder pressure and the ignition timing according to the first embodiment of the present invention; FIG. 5 is a diagram showing a desirable change form of the acquisition timing of the first in-cylinder pressure with respect to the change of the ignition timing according to the first embodiment of the present invention; FIG. 5 is a characteristic diagram showing an example of an estimation error of engine torque fluctuation with respect to a difference between a second in-cylinder pressure acquisition timing and CA90+20° according to the first embodiment of the present invention; FIG. 4 is a characteristic diagram showing the relationship between the combustion timing and the integrated value of the heat release rate according to the first embodiment of the present invention; FIG. 5 is a diagram showing a desirable variation of the second in-cylinder pressure acquisition timing with respect to a change of CA90+20° according to the first embodiment of the present invention; FIG. 2 is a diagram showing an example of control blocks of a controller that performs EGR control according to the first embodiment of the present invention; FIG. FIG. 4 is a diagram showing an example of actuator control based on deviation δCoV in the EGR system according to the first embodiment of the present invention; FIG. 4 is a diagram showing an example in which the controller according to the first embodiment of the present invention controls the amount of ignition energy, gas flow strength, compression ratio, and intake air temperature based on deviation δCoV. FIG. 5 is a diagram showing an example of actuator control based on deviation δCoV in the lean burn system according to the first embodiment of the present invention; FIG. 6 is a block diagram showing a configuration example of a controller according to a second embodiment of the present invention; FIG. FIG. 9 is a characteristic diagram showing the correlation between the reference combustion center of gravity and the ratio between the first and second in-cylinder pressures according to the second embodiment of the present invention; FIG. 9 is a diagram showing an example of correction amounts from the reference combustion center of gravity with respect to changes in volumetric efficiency according to the second embodiment of the present invention; FIG. 9 is a diagram showing an example of a correction amount from a reference combustion center of gravity with respect to changes in engine speed according to the second embodiment of the present invention; 9 is a flowchart showing an example of a procedure for estimating the center of gravity of combustion, which is performed by a center of gravity of combustion estimator of the controller according to the second embodiment of the present invention. FIG. 5 is a diagram showing a general relationship between the optimum combustion center of gravity and the fuel consumption rate of the engine according to the second embodiment of the present invention; FIG. 7 is a diagram showing an example of control blocks of a controller that performs EGR control according to a second embodiment of the present invention; FIG. 8 is a characteristic diagram showing the correlation between the difference between the first in-cylinder pressure and the second in-cylinder pressure and the reference combustion center of gravity according to the second embodiment of the present invention; FIG. 7 is a diagram showing an example of time histories of an ignition signal, a primary voltage and a secondary voltage of an ignition coil, and a secondary current according to a second embodiment of the present invention; FIG. 8 is a characteristic diagram showing the correlation between the maximum value of the primary voltage immediately after the start of discharge, the maximum value of the secondary voltage, and the in-cylinder pressure during discharge according to the second embodiment of the present invention. FIG. 7 is a block diagram showing a configuration example from the ignition coil to the controller when the controller according to the second embodiment of the present invention obtains the in-cylinder pressure based on the secondary voltage of the ignition coil; FIG. 9 is a characteristic diagram showing the correlation between the discharge period and the cylinder internal pressure during discharge according to the second embodiment of the present invention; FIG. 8 is a block diagram showing a configuration example from a crank angle sensor to a controller when the controller according to the second embodiment of the present invention obtains the in-cylinder pressure based on the angular acceleration of the crankshaft;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same function or configuration are denoted by the same reference numerals, thereby omitting redundant description.

<First embodiment>
[Engine configuration example]
First, an example of an engine to which the present invention is applied will be described with reference to FIG.
FIG. 1 is a cross-sectional view showing an example of the overall configuration of an engine 1 according to a first embodiment of the invention.

The engine 1 is an example of a spark ignition four-cycle gasoline engine. A combustion chamber of the engine 1 is formed by an engine head, a cylinder 13 , a piston 14 , an intake valve 15 and an exhaust valve 16 . In the engine 1, the fuel injection valve 18 is provided in the intake port 21, and the injection nozzle of the fuel injection valve 18 penetrates the intake port 21, thereby forming a so-called port injection type internal combustion engine. .

An ignition plug 17b is installed in the engine head, and an ignition coil 17a is installed above the ignition plug 17b. Also, a pressure sensor 10 is installed in the engine head. The pressure sensor 10 detects the in-cylinder pressure in a cylinder 13 (cylinder) by, for example, detecting deformation of a metal diaphragm due to differential pressure with a piezoresistive element.

Combustion air is drawn into the combustion chamber through an air cleaner 19 , a throttle valve 20 and an intake port 21 . Gas after combustion (exhaust gas) discharged from the combustion chamber passes through the exhaust port 24 and the catalytic converter 25 and is discharged to the atmosphere.

The amount of air taken into the combustion chamber is measured by an airflow sensor 22 provided upstream of the throttle valve 20 . The air-fuel ratio of gas (exhaust gas) discharged from the combustion chamber is detected by an air-fuel ratio sensor 27 provided upstream of the catalytic converter 25 .

The exhaust port 24 and the intake port 21 are communicated by an EGR pipe 28, and a part of the exhaust gas flowing through the exhaust port 24 is returned to the inside of the intake port 21, forming a so-called exhaust gas recirculation system (EGR system). ing. The amount of exhaust gas flowing through the EGR pipe 28 is adjusted by an EGR valve 29 .

Furthermore, a timing rotor 26 (signal rotor) is provided on the axial portion of the crankshaft. The crank angle sensor 11 (detecting portion) arranged opposite to the vicinity of the timing rotor 26 (detected portion) detects the rotation of the timing rotor 26 to detect the rotation and phase of the crankshaft, that is, the crank rotation speed (engine rotation speed). ). Detection signals from the pressure sensor 10 , the crank angle sensor 11 , the airflow sensor 22 and the air-fuel ratio sensor 27 are input to the controller 12 .

The controller 12 is an example of a control device for the engine 1, and for example, an ECU (Engine Control Unit) is used. The controller 12 issues commands such as the opening of the throttle valve 20, the opening of the EGR valve 29, the timing and amount of fuel injection by the fuel injection valve 18, and the ignition timing by the spark plug 17b, based on the values detected by various sensors. output to control the engine 1 to a predetermined operating state.

Although only a single cylinder is shown in FIG. 1 to show the configuration of the combustion chamber of the engine 1, the engine according to the embodiment of the present invention may be a multi-cylinder engine composed of a plurality of cylinders. .

[Controller configuration example]
FIG. 2 is a block diagram showing a configuration example of the controller 12 according to the first embodiment of the invention.

The controller 12 includes an input/output unit 121, a control unit 122, and a storage unit 123 electrically connected to each other via a system bus (not shown).
The input/output unit 121 has an input port and an output port (not shown), and performs input and output processing of various signals to each device and each sensor in the vehicle in which the engine 1 is mounted. For example, the input/output unit 121 reads a signal from the pressure sensor 10 and sends the signal to the control unit 122 . In addition, the input/output unit 121 outputs control signals to each device according to commands from the control unit 122 .

Control unit 122 controls the operation of engine 1 . For example, the control unit 122 controls the throttle opening, EGR opening, fuel injection amount, and ignition timing according to the stable combustion state of the engine 1 . The control unit 122 according to the first embodiment includes a torque fluctuation estimation unit 122a and an engine control unit 122b. Torque fluctuation estimator 122a is used as an example of a combustion state estimator.

Torque fluctuation estimator 122 a estimates the magnitude of engine torque fluctuation based on the in-cylinder pressure detected by pressure sensor 10 . The combustion state of the engine 1 estimated in this embodiment is the magnitude of engine torque fluctuation. The combustion state estimator (torque fluctuation estimator 122a) calculates the internal combustion The combustion state of the engine (engine 1) is estimated. Therefore, the combustion state estimator (torque variation estimator 122a) calculates the difference between the first in-cylinder pressure P1 and the second in-cylinder pressure P2 in a plurality of cycles, and based on the variation rate of the difference in a plurality of cycles, The magnitude of the engine torque fluctuation of the internal combustion engine (Engine 1) is estimated.

The engine control section (engine control section 122b) controls the EGR rate or the air-fuel ratio based on the magnitude of the engine torque fluctuation. For example, the engine control unit 122b changes the EGR opening, the throttle opening, and the fuel injection amount of the engine 1 based on the magnitude of the engine torque fluctuation obtained by the torque fluctuation estimating unit 122a. It becomes possible to control the air-fuel ratio. Also, the engine control unit (engine control unit 122b) can control at least one of ignition energy, in-cylinder flow strength, compression ratio, and intake air temperature based on the magnitude of engine torque fluctuation. is.

The storage unit 123 is a volatile memory such as a RAM (Random Access Memory) or a non-volatile memory such as a ROM (Read Only Memory). The storage unit 123 records a control program executed by an arithmetic processing unit (not shown) included in the controller 12 . The function of each block of the control unit 122 is realized by the arithmetic processing unit reading out the control program from the storage unit 123 and executing it. For example, a CPU (Central Processing Unit) or MPU (Micro Processing Unit) is used as an arithmetic processing unit. Note that the controller 12 may have a non-volatile auxiliary storage device such as a semiconductor memory, and the above control program may be stored in the auxiliary storage device.

[Processing for estimating magnitude of engine torque fluctuation]
Next, an example of the process of estimating the magnitude of engine torque fluctuation, which is performed by the controller 12, will be described with reference to FIG.
FIG. 3 is a flowchart showing an example of a process of estimating the magnitude of engine torque fluctuation, which is performed by the torque fluctuation estimator 122a of the controller 12. As shown in FIG.

First, the torque fluctuation estimator 122a initializes the variable S and the variable Q to zero (S1). Then, the torque fluctuation estimator 122a acquires the first in-cylinder pressure P1 (denoted as "in-cylinder pressure P1" in the figure) near the ignition timing detected by the pressure sensor 10 (S2). Subsequently, the torque fluctuation estimator 122a acquires a second in-cylinder pressure P2 (denoted as "in-cylinder pressure P2" in the figure) near the end of combustion detected by the pressure sensor 10 (S3).

Subsequently, torque fluctuation estimator 122a calculates differential pressure dP=P2-P1 between second in-cylinder pressure P2 and first in-cylinder pressure P1 (S4), and adds dP to variable S (S5). Furthermore, the square value of dP is added to the variable Q (S6). The torque fluctuation estimator 122a repeats the process from step S2 to step S6 N times (for example, N=100) set as a predetermined number of cycles, and calculates the integrated value of the pressure difference dP for N cycles as the variable S Ask as Further, the torque fluctuation estimator 122a obtains, as a variable Q, an integrated value of squares of the pressure difference dP for N cycles.

Next, the torque fluctuation estimator 122a obtains the cycle mean value dPmean of the pressure difference dP by dividing the integrated value S of the pressure difference dP by a predetermined number of cycles N (S7).

Next, the torque fluctuation estimator 122a obtains the cycle fluctuation rate Cov of dP of the differential pressure dP (S8). The cycle variation rate Cov of dP of the differential pressure dP is obtained by normalizing the cycle standard deviation of the differential pressure dP by the cycle mean value dPmean of the pressure difference dP and expressing it as a percentage, and is obtained by the following equation (1). Also, the coefficient of variation is represented by Cov (Coefficient of variation).

Next, the torque fluctuation estimator 122a calculates the engine torque fluctuation magnitude Cov of IMEP from the cycle fluctuation rate Cov of dP of the differential pressure dP (S9). Here, a method for calculating the magnitude of engine torque fluctuation in step S9 will be described with reference to FIG.

FIG. 4 is a characteristic diagram showing the correlation between the cycle variation rate Cov of dP [%] of differential pressure dP and the magnitude of engine torque variation (Cov of IMEP [%]). This characteristic diagram shows the actual measurement results of the cycle variation rate Cov of dP of the differential pressure dP and the magnitude of the engine torque variation (Cov of IMEP) using a spark ignition engine.

The magnitude of engine torque fluctuation is defined as Cov of IMEP [%], which is the standard deviation of the indicated mean effective pressure (IMEP) over N cycles normalized by the average value of IMEP over N cycles. ing.

According to new findings of the inventors of the present application, between Cov of IMEP, which indicates the magnitude (degree) of engine torque fluctuation, and the cycle variation rate Cov of dP of differential pressure dP, as shown in FIG. It was found that a strong correlation was obtained. Therefore, the inventor of the present application has found that the magnitude of engine torque fluctuation can be estimated from the cycle fluctuation rate Cov of dP of the differential pressure dP.

The storage unit 123 of the controller 12 holds the correlation between the Cov of IMEP and the Cov of dP obtained by calibration in advance as a correlation formula or table data. The torque fluctuation estimation unit 122a refers to the correlation formula or table data from the storage unit 123 and obtains the magnitude Cov of IMEP of the engine torque fluctuation from the Cov of dP.

Then, the torque fluctuation estimator 122a sends the calculated engine torque fluctuation magnitude Cov of IMEP to the engine controller 122b (S10). After a predetermined period of time, the processing of this flowchart is performed again from step S1.

Here, the detection timing of the in-cylinder pressure will be described with reference to FIG.
FIG. 5 is a graph showing an example of in-cylinder pressure detection timing. In each graph shown in FIG. 5, the horizontal axis is the crank angle [deg] and the vertical axis is the in-cylinder pressure [bar].

Graph (1) in FIG. 5 shows an example of conventional in-cylinder pressure detection timing. From the changes in the in-cylinder pressure shown in graph (1), it can be seen that the in-cylinder pressure reaches its maximum when the crank angle is around 360°.

A conventional controller such as that disclosed in Patent Document 1 acquires the cylinder pressure detected by the cylinder pressure sensor at a high sampling rate (for example, at intervals of 1 degree or less of the crank angle), and estimates the combustion state in the combustion chamber. Was. Circle marks added along the graph in the drawing represent the detection timing of the in-cylinder pressure. However, the conventional method in which the controller obtains the cylinder pressure at a high sampling rate not only imposes a computational load on the controller, but also requires a large memory capacity for storing the cylinder pressure obtained by the controller. Therefore, the cost of the engine system increased when the conventional method was adopted.

Note that the conventional controller as disclosed in Patent Document 2 also uses the in-cylinder pressure detected at two points, the crank angle position of 60° before the top dead center and the crank angle position of 60° after the top dead center. Although the combustion state of the engine was grasped, it is different from the acquisition timing of the in-cylinder pressure according to the present embodiment. For this reason, in order to grasp the combustion state with the technique disclosed in Patent Document 2, complicated calculations are required, and the combustion state cannot be accurately estimated at low cost.

[Pressure detection time]
Graph (2) in FIG. 5 shows an example of the detection timing of the in-cylinder pressure according to the present embodiment. The change in the in-cylinder pressure shown in graph (2) is the same as the change in the in-cylinder pressure shown in graph (1). In the figure, the ignition timing indicated by the ignition mark and the combustion period indicated by the thick bar line are newly added.

In the combustion state estimation process performed by the controller 12 according to the first embodiment, the in-cylinder pressure is acquired at two timings in one cycle. The two timings are the timing for acquiring the first in-cylinder pressure P1 in the compression stroke ("P1 pressure acquisition" in the figure) and the timing for acquiring the second in-cylinder pressure P2 in the expansion stroke ("P1 pressure acquisition" in the figure). P2 pressure acquisition"). The timing at which the controller 12 acquires the first in-cylinder pressure P1 is near the ignition timing. Further, the timing at which the controller 12 acquires the second in-cylinder pressure P2 is near the end of combustion. The reason why the acquisition timing of the in-cylinder pressure is defined in this way is that the magnitude of the combustion energy generated by combustion is reflected as the difference in the in-cylinder pressure before and after combustion.

For example, when the acquisition timing of the first in-cylinder pressure P1 is earlier than the ignition timing, the energy for compressing the in-cylinder gas from the pressure acquisition timing to the ignition timing, which is the combustion start timing, is the first in-cylinder pressure P1. and the second in-cylinder pressure P2. Further, for example, when the acquisition timing of the second in-cylinder pressure P2 is later than the combustion end timing, the energy for expanding the in-cylinder gas from the combustion end timing to the pressure acquisition timing is equal to the first in-cylinder pressure P1. This is reflected in the difference in the second in-cylinder pressure P2.

These compression energy and expansion energy are added in excess to the energy generated by combustion, and cause an estimation error in the combustion state estimation process according to the first embodiment. For this reason, in order for the controller 12 to accurately estimate the combustion state, it is preferable to set the acquisition timing of the first in-cylinder pressure P1 as close to the ignition timing as possible, and to set the acquisition timing of the second in-cylinder pressure P2 as close as possible to the combustion end timing. is preferably close to Then, the controller 12 determines the combustion state (ignition timing, etc.) of the engine 1 based on the first in-cylinder pressure P1 and the second in-cylinder pressure P2 acquired at two timings. Therefore, the calculation load of the controller 12 is lightened, and the memory capacity for storing the in-cylinder pressure can be reduced.

FIG. 6 is a characteristic diagram showing an example of the estimation error of the engine torque fluctuation with respect to the difference (ms) between the acquisition timing of the first in-cylinder pressure P1 and the ignition timing. The ignition timing is the timing at which discharge for ignition is started in the ignition plug 17b. In this characteristic diagram, the error [%] between the estimated value and the actual measurement value of the magnitude of the engine torque fluctuation according to the first embodiment with respect to the difference between the acquisition timing of the first in-cylinder pressure P1 and the ignition timing. It shows how changes

As shown in FIG. 6, as the difference between the acquisition timing of the first in-cylinder pressure P1 and the ignition timing increases, the estimation error of the magnitude of the engine torque fluctuation increases. Therefore, a permissible error is set to allow an estimation error of the magnitude of the engine torque fluctuation. In order to make the estimation error of the magnitude of the engine torque fluctuation smaller than the error required for engine control, the difference between the acquisition timing of the first in-cylinder pressure P1 and the ignition timing should be within 1 ms. desirable. Therefore, the combustion state estimator (torque variation estimator 122a) sets the difference between the acquisition timing of the first in-cylinder pressure P1 and the ignition timing of the cylinder within 1 ms.

FIG. 7 is a diagram showing a desirable change form of the acquisition timing of the first in-cylinder pressure P1 with respect to changes in ignition timing. In FIG. 7, the dotted line indicates that the ignition timing and the acquisition timing of the first in-cylinder pressure P1 are the same. Also, the solid line indicates that the difference between the ignition timing and the acquisition timing of the first in-cylinder pressure P1 is 1 ms. That is, the range sandwiched between the two solid lines is the desirable acquisition timing of the first in-cylinder pressure P1. Therefore, the combustion state estimator (torque variation estimator 122a) changes the acquisition timing of the first in-cylinder pressure P1 in accordance with the ignition timing of the cylinder.

FIG. 8 shows the difference (°) between the acquisition timing of the second in-cylinder pressure P2 and the timing retarded by 20° from the 90% combustion timing CA90 (hereinafter abbreviated as “CA90+20°”). It is a characteristic diagram showing an example of. This characteristic diagram shows how the error [%] between the estimated magnitude of the engine torque fluctuation and the measured value changes with respect to the difference between the acquisition timing of the second in-cylinder pressure P2 and CA90+20°. shown. Therefore, the combustion state estimator (torque variation estimator 122a) changes the acquisition timing of the second in-cylinder pressure P2 in accordance with the 90% combustion timing CA90 of the cylinder.

As shown in FIG. 8, the estimation error of the magnitude of the engine torque fluctuation increases as the difference between the acquisition timing of the second in-cylinder pressure P2 and CA90+20° increases. Therefore, a permissible error is set to allow an estimation error of the magnitude of the engine torque fluctuation. In order to make the estimation error of the magnitude of the engine torque fluctuation smaller than the error required for engine control, the difference between the acquisition timing of the second in-cylinder pressure P2 and CA90+20° should be within 10°. desirable.

FIG. 9 is a characteristic diagram showing the relationship between the combustion timing and the integrated value of the heat release rate.
The 90% combustion timing CA90 shown in the figure is defined as the crank angle (°) at which the integrated value of the heat release rate is 90% when the integrated value of the heat release rate at the end of combustion is 100%. Similarly, the 50% combustion timing CA50 is defined as the crank angle at which the integrated value of the heat release rate is 50%. The combustion timing CA50 is also called a reference combustion center of gravity CA50ref.

As the burn rate changes from cycle to cycle, the 90% burn timing also changes from cycle to cycle. Therefore, the 90% combustion timing CA90 according to the first embodiment shown in FIG. 9 indicates the 90% combustion timing averaged over a predetermined number of cycles (eg, 100 cycles).

FIG. 10 is a diagram showing a desirable change form of the acquisition timing of the second in-cylinder pressure P2 with respect to a change of CA90+20°. The dotted line in FIG. 10 indicates that CA90+20° and the second in-cylinder pressure P2 are acquired at the same time. Also, the solid line indicates that the difference between CA90+20° and the acquisition timing of the second in-cylinder pressure P2 is 10°. That is, the range sandwiched between the two solid lines is the desired acquisition timing of the second in-cylinder pressure P2. Therefore, the combustion state estimator (torque fluctuation estimator 122a) determines the acquisition timing of the second in-cylinder pressure P2 and the 20° retardation timing (90% combustion timing CA90+20°) of the 90% combustion timing CA90 of the cylinder. The difference shall be within 10°.

In general, the 90% combustion timing CA90 varies depending on engine operating state parameters such as engine speed, load, air-fuel ratio, EGR rate, ignition timing, and cooling water temperature. The storage unit 123 of the controller 12 stores the 90% combustion timing CA90 with respect to the engine operating state parameter, which is obtained in advance by calibration, as map data. The torque fluctuation estimator 122a can obtain the 90% combustion timing CA90 by referring to the map data based on the current engine operating state parameters.

[EGR system]
Next, an example of engine control by the engine control section 122b will be described.
For example, in the EGR system that configures the engine 1 , the controller 12 needs to appropriately control the EGR rate in order to increase the thermal efficiency of the engine 1 . In general, a higher EGR rate at part load reduces pumping losses and increases thermal efficiency. In addition, since the combustion temperature is lowered by increasing the EGR rate, it is possible to reduce cooling loss and NOx emissions. Furthermore, it is possible to suppress knocking and reduce exhaust loss by increasing the EGR rate at high load.

On the other hand, if the EGR rate becomes excessively high, the ignitability of the air-fuel mixture becomes low, and the flame propagation becomes low, which increases the possibility of misfiring. Therefore, it is important for increasing the thermal efficiency of the engine 1 that the controller 12 increases the EGR rate as much as possible within a range in which misfire does not occur or a misfire is permissible.

If there is a misfiring cycle in the operation of the engine 1, the engine torque fluctuation will increase. Therefore, by estimating the magnitude of the engine torque fluctuation and changing the EGR rate based on the magnitude of the engine torque fluctuation, the controller 12 can improve the thermal efficiency of the engine while suppressing misfires.

FIG. 11 is a diagram showing an example of control blocks of the controller 12 that performs EGR control.
Based on the output of the pressure sensor 10 of the engine 1, the torque variation estimator 122a estimates the current engine torque variation Cov of IMEP.

A deviation calculation unit 122c of the engine control unit 122b calculates a deviation δCoV by subtracting the target engine torque fluctuation magnitude (target CoV) from the current engine torque fluctuation magnitude Cov of IMEP. The target CoV is a value read from the ROM of the storage unit 123 by the engine control unit 122b.

An operation amount calculation section 122d included in the engine control section 122b calculates an operation amount for the actuator of the engine 1 based on the deviation δCoV. The actuator is, for example, a device provided in the engine 1 for adjusting the opening degrees of the throttle valve 20 and the EGR valve 29 and adjusting the ignition timing of the spark plug 17b. The manipulated variable calculator 122d is configured by, for example, a PID controller. The operation amount calculation unit 122d obtains the operation amount of the actuator of the engine 1 so that the current engine torque fluctuation magnitude Cov of IMEP and the target engine torque fluctuation magnitude (target CoV) are close to each other. Then, the engine control unit 122b sends the actuator operation amount of the engine 1 to the engine 1 to control the operating state of the engine 1. FIG.

(Example of actuator control in EGR system)
FIG. 12 is a diagram showing an example of actuator control based on the deviation δCoV in the EGR system. The horizontal axis represents the deviation δCoV [%], and the vertical axis represents the state of the actuator and the like.

When the EGR system controller 12 controls the actuator based on the deviation δCoV, the magnitude of the engine torque fluctuation is suppressed as the deviation δCoV increases, for example. Therefore, the controller 12 performs control so that the opening degree of the EGR valve 29 (dotted line) and the opening degree of the throttle valve 20 (solid line) are decreased. Since this control reduces the EGR rate, the ignition delay time is shortened and the combustion speed is increased. Therefore, the controller 12 performs control so that the ignition timing advance amount (chain line) is decreased in order to set the combustion at an appropriate timing (best fuel consumption timing).

Under the control of the controller 12, when the magnitude of the engine torque fluctuation is equal to or greater than a predetermined value, the EGR rate is set low so as to suppress the torque cycle fluctuation. As a result, the combustion of the engine 1 is controlled to stabilize. Further, when the magnitude of the engine torque fluctuation is smaller than a predetermined value, the controller 12 sets the EGR rate high, so that the thermal efficiency of the engine 1 can be increased.

Further, the amount of ignition energy supplied to the spark plug 17b, the strength of the gas flow in the cylinder, the compression ratio, and the intake air temperature can be adjusted, and the controller 12 controls these adjustment amounts based on the deviation δCoV. is also conceivable.

FIG. 13 is a diagram showing an example in which the controller 12 controls the amount of ignition energy, strength of gas flow, compression ratio, and intake air temperature based on the deviation δCoV. The horizontal axis of FIG. 13 represents the deviation .delta.CoV [%], and the vertical axis represents the ignition energy and the like.

In general, the higher the ignition energy amount, the gas flow strength in the cylinder, the compression ratio, and the intake air temperature, the more the ignition or flame propagation is promoted and the torque fluctuation is suppressed. Therefore, as shown in FIG. 13, it is desirable for the controller 12 to perform control so that the values of these items increase as the deviation .delta.CoV increases.

For example, the amount of ignition energy can be adjusted by the controller 12 controlling the amount of current supplied to the spark plug 17b. In addition, the strength of the gas flow in the cylinder can be adjusted by the controller 12 controlling the flow velocity of the air in the intake port 21 . Also, the compression ratio can be adjusted by the controller 12 controlling the position of the top dead center of the piston 14 . Also, the intake air temperature can be adjusted by the controller 12 controlling on/off of a heater provided in the intake port 21 .

For these controls, the controller 12 may control any one of the gas flow strength, the compression ratio, and the intake air temperature independently, or may control some of them in combination. In addition to these controls, the controller 12 may combine control of the EGR valve opening degree, throttle valve opening degree, or ignition advance amount described above.

[Lean burn system]
Furthermore, in the lean burn system that constitutes the engine 1 as well, it is necessary to appropriately control the air-fuel ratio in order to increase the thermal efficiency of the engine 1 . Generally, a higher air/fuel ratio at part load reduces pumping losses and increases thermal efficiency. In addition, since the combustion temperature is lowered by increasing the air-fuel ratio, it is possible to reduce cooling loss and NOx emissions. On the other hand, if the air-fuel ratio becomes excessively high, the ignitability of the air-fuel mixture becomes low and the flame propagation becomes low, which increases the possibility of misfiring. Therefore, it is important for increasing the thermal efficiency of the engine 1 that the controller 12 performs control to increase the air-fuel ratio as much as possible within a range in which misfire does not occur or a misfire is permissible.

(Example of actuator control in a lean burn system)
FIG. 14 is a diagram showing an example of actuator control based on the deviation δCoV in a lean burn system. The horizontal axis of FIG. 14 represents the deviation .delta.CoV [%], and the vertical axis represents the state of the actuator and the like.

The controller 12 in the lean burn system controls the actuators based on the deviation δCoV. For example, the controller 12 controls the actuator so that the opening degree (solid line) of the throttle valve 20 decreases as the deviation δCoV increases in order to suppress torque cycle fluctuations. This control lowers the air-fuel ratio, shortening the ignition delay time and increasing the combustion speed. Therefore, the controller 12 controls the actuator so that the ignition timing advance amount (one-dot chain line) is decreased in order to set the combustion at an appropriate timing (best fuel consumption timing).

With this control, when the magnitude of engine torque fluctuation is equal to or greater than a predetermined value, the air-fuel ratio is set low so as to suppress the torque cycle fluctuation. By setting the air-fuel ratio to be low, the combustion of the engine 1 is controlled to be stabilized. Further, when the magnitude of the engine torque fluctuation is smaller than the predetermined value, the air-fuel ratio is set high, so the thermal efficiency can be enhanced.

Also, the control of the amount of ignition energy, the strength of gas flow in the cylinder, the compression ratio, and the intake air temperature shown in FIG. It is possible.

<Second embodiment>
[Estimation of the combustion center of gravity]
Next, a second embodiment of the present invention, in which the combustion center of gravity CA50 is estimated based on the first in-cylinder pressure P1 acquired near the ignition timing and the second in-cylinder pressure P2 acquired near the combustion end timing. will be described.

As shown in FIG. 9, the combustion center of gravity CA50 is defined as the crank angle at which the integral value of the heat release rate is 50% when the integral value of the heat release rate at the end of combustion is 100%. Also, the combustion center of gravity changes for each cycle due to cycle fluctuations in the combustion speed, but the combustion center of gravity CA50 according to the second embodiment indicates the combustion center of gravity averaged over a predetermined number of cycles (eg, 100 cycles).

FIG. 15 is a block diagram showing a configuration example of the controller 12A according to the second embodiment.

The controller 12A includes an input/output unit 121, a control unit 124, and a storage unit 123 electrically connected to each other via a system bus (not shown).
Since the input/output unit 121 and the storage unit 123 are the same as the input/output unit 121 and the storage unit 123 of the controller 12 in the first embodiment, detailed description thereof will be omitted.

Control unit 124 controls the operation of engine 1 . For example, the control unit 124 controls the throttle opening, EGR opening, fuel injection amount, and ignition timing according to the stable combustion state of the engine 1 . The control unit 124 according to the second embodiment includes a combustion center-of-gravity estimation unit 124a and an engine control unit 124b.

The combustion center of gravity estimator 124 a estimates the combustion center of gravity CA50 based on the in-cylinder pressure detected by the pressure sensor 10 . The combustion state of the engine 1 estimated in this embodiment is the combustion center of gravity CA50.
The engine control section (engine control section 122b) controls the ignition timing based on the ratio between the first in-cylinder pressure P1 and the second in-cylinder pressure P2. For example, the engine control unit 124b controls the ignition timing and the like of the engine 1 based on the combustion center of gravity CA50 obtained by the combustion center of gravity estimation unit 124a.

[Principle of estimating the combustion center of gravity]
Next, the principle of estimating the combustion center of gravity will be described with reference to FIGS. 16 to 18. FIG.

FIG. 16 is a characteristic diagram showing the correlation between the reference combustion center of gravity CA50ref (°) and the ratio between the first in-cylinder pressure P1 and the second in-cylinder pressure P2. This characteristic diagram represents the results of actual measurements of the pressure ratio P2/P1 and the reference combustion center of gravity CA50ref using a spark ignition engine. The combustion center-of-gravity estimator 124a obtains the first in-cylinder pressure P1 near the ignition timing and the second in-cylinder pressure P2 near the combustion end timing using the pressure sensor 10 . FIG. 16 shows the measurement results of the volumetric efficiency of the engine 1, the pressure ratio P2/P1 with the engine rotation speed constant, and the reference combustion center of gravity CA50ref. Here, the volumetric efficiency is defined as reference volumetric efficiency ηref, and the rotational speed is defined as reference rotational speed Nref.

According to new findings of the inventors of the present application, the ratio between the reference combustion center of gravity CA50ref, the first cylinder pressure P1 acquired near the ignition timing, and the second cylinder pressure P2 acquired near the combustion end timing It was found that a strong correlation was obtained between P2/P1 as shown in FIG. Therefore, the inventor of the present application has found that the reference combustion center of gravity CA50ref can be estimated from the pressure ratio P2/P1.

Further, according to new findings of the inventors of the present application, when the volumetric efficiency is different from the reference volumetric efficiency ηref and the engine rotation speed is different from the reference rotation speed Nref, the combustion center-of-gravity estimator 124a determines the reference volumetric efficiency ηref and the reference rotation speed Nref, it is possible to estimate the combustion center of gravity CA50 at the current rotation speed and volumetric efficiency.

FIG. 17 is a diagram showing an example of the correction amount ΔCA50_1 (°) from the reference combustion center of gravity CA50ref with respect to changes in volumetric efficiency (%).
FIG. 18 is a diagram showing an example of the correction amount ΔCA50_2 (°) from the reference combustion center of gravity CA50ref with respect to changes in the engine speed (1/min).
Based on these correction amounts ΔCA50_1 and ΔCA50_2, the combustion center of gravity CA50 at the current rotational speed and volumetric efficiency is obtained by the following equation (2).

Further, the combustion center of gravity estimator 124a calculates the correction amount of the reference combustion center of gravity CA50ref from each reference value for not only the volumetric efficiency and the rotation speed, but also for the EGR rate, the air-fuel ratio, the ignition timing, the cooling water temperature, and the like. By calculating and correcting the reference combustion center of gravity CA50ref, the combustion center of gravity CA50 can be estimated with higher accuracy.

Next, a process of estimating the combustion center of gravity CA50 performed by the controller 12A will be described with reference to FIG.
FIG. 19 is a flowchart showing an example of a procedure for estimating the center of gravity of combustion, which is performed by the center of gravity of combustion estimator 124a of the controller 12A.

First, the combustion center-of-gravity estimator 124a initializes a variable R to zero (S21). Next, the combustion center-of-gravity estimator 124a acquires the first in-cylinder pressure P1 near the ignition timing detected by the pressure sensor 10 (S22). Subsequently, the combustion center-of-gravity estimator 124a acquires the second in-cylinder pressure P2 near the end of combustion detected by the pressure sensor 10 (S23).

Next, the combustion center-of-gravity estimator 124a obtains a ratio PR=P2/P1 between the second in-cylinder pressure P2 and the first in-cylinder pressure P1 (S24), and adds the ratio PR to the variable R (S25). The combustion center-of-gravity estimator 124a repeats steps S22 to S25 a predetermined number of cycles N times (for example, N=100), so that R is an integrated value of the pressure ratio PR for N cycles.

After the N cycles have passed, the combustion center of gravity estimator 124a obtains the cycle mean value PRmean of the pressure ratio PR by dividing the integrated value R of PR by the predetermined number of cycles N (S26).

Next, the combustion center of gravity estimator 124a calculates a reference combustion center of gravity CA50ref from the average value PRmean of the pressure ratio PR (S27). The storage unit 123 of the controller 12A holds the correlation between the pressure ratio PR obtained by calibration in advance and the reference combustion center of gravity CA50ref as a correlation formula or table data. The combustion center of gravity estimator 124a calculates the reference combustion center of gravity CA50ref from the average value PRmean of the pressure ratio PR by referring to this correlation formula or table data.

Subsequently, the combustion center of gravity estimator 124a calculates the combustion center of gravity CA50 from the reference combustion center of gravity CA50ref and the correction value ΔCA50 for the combustion center of gravity. In the storage unit 123 of the controller 12A, the correlation between the volumetric efficiency and the correction value of the center of gravity of combustion, the correlation between the rotation speed and the correction value of the center of gravity of combustion, and the like, obtained by calibration in advance, are stored as correlation formulas or table data. . The combustion center of gravity estimator 124a obtains the sum of the correction values ΔCA50 of the combustion center of gravity by referring to this correlation formula or table data, and adds them to the reference combustion center of gravity CA50ref to obtain the combustion center of gravity CA50 (S28).

Finally, the combustion center of gravity estimator 124a sends the found combustion center of gravity CA50 to the engine control unit 124b (S29).

[Engine control]
Next, an example of engine control by the engine control section 124b will be described.
In order to increase the thermal efficiency of the engine, it is necessary to set the combustion center of gravity appropriately.
FIG. 20 is a diagram showing a general relationship between the optimum combustion center of gravity CA50 and the fuel consumption rate of the engine.

In general, when the center of gravity of combustion advances from the proper timing, the compression work of the piston increases and thermal efficiency decreases. Further, if the combustion center of gravity is retarded from the appropriate timing (target), exhaust energy increases and thermal efficiency decreases.

Normally, in an engine, the ignition timing is set in advance for each load and rotation speed so that the center of gravity of combustion is at the optimum timing. However, it is conceivable that the center of gravity of combustion shifts from the optimum timing due to changes in environmental conditions, temporal changes in engine component characteristics, and the like. Therefore, the engine control unit 124b controls the ignition timing to set the center of gravity of combustion to a predetermined optimum timing. High thermal efficiency can be maintained.

FIG. 21 shows an example of a control block of the controller 12A that performs EGR control.
The combustion center-of-gravity estimator 124a estimates the current combustion center-of-gravity CA50 based on the output (in-cylinder pressure) of the pressure sensor 10 provided in the engine 1 .

A deviation calculation unit 124c included in the engine control unit 124b obtains a deviation δCA50 between the current center of gravity CA50 of combustion and a target center of gravity CA50 (described as "target CA50" in the figure).
An ignition timing calculation unit 124d included in the engine control unit 124b calculates the ignition timing of the engine 1 based on the deviation δCA50. The ignition timing calculator 124d is composed of, for example, a PID controller, and obtains the ignition timing of the engine 1 so that the current center of gravity of combustion approaches the target center of gravity of combustion. Then, the engine control section 124b sends the ignition timing obtained by the ignition timing calculation section 124d to the engine 1, and the engine 1 is operated at the new ignition timing.

Although the method for estimating the combustion center of gravity CA50 has been described in the present embodiment, the present invention is not limited to the combustion center of gravity CA50. The combustion state estimator can estimate the combustion phase based on the ratio between the first in-cylinder pressure P1 and the second in-cylinder pressure P2. For example, the combustion phase such as the 10% combustion timing CA10 and the 90% combustion timing CA90 is calculated by the combustion state estimating unit as the first in-cylinder pressure P1 acquired near the ignition timing and the first cylinder pressure P1 acquired near the combustion end timing. It can be estimated using the ratio P2/P1 to the second in-cylinder pressure P2.

Also, the pressure ratio is not limited to P2/P1, and the pressure ratio may be P1/P2. Further, the combustion phase can be estimated by a similar method using the pressure difference ΔP=P2−P1 or ΔP=P1−P2 instead of the pressure ratio. An example where the pressure difference ΔP=P2−P1 will be described with reference to FIG.

FIG. 22 is a characteristic diagram showing the correlation between the difference between the first in-cylinder pressure P1 and the second in-cylinder pressure P2 and the reference combustion center of gravity CA50ref (°). This characteristic diagram shows the results of actual measurements of the pressure difference P2-P1 and the reference combustion center of gravity CA50ref using a spark ignition engine. Again, the first in-cylinder pressure P1 is acquired by the pressure sensor 10 near the ignition timing, and the second in-cylinder pressure P2 is acquired near the combustion end timing. FIG. 22 shows the results of measuring the pressure difference P2−P1 and the reference combustion center of gravity CA50ref with the volumetric efficiency of the engine 1 and the engine speed kept constant. Here, the volumetric efficiency is defined as reference volumetric efficiency ηref, and the rotational speed is defined as reference rotational speed Nref.

According to new findings of the inventors of the present application, the pressures of the reference combustion center of gravity CA50ref, the first cylinder pressure P1 acquired near the ignition timing, and the second cylinder pressure P2 acquired near the combustion end timing It was found that there is a strong correlation between the difference P2-P1 as shown in FIG. Therefore, the inventor of the present application has found that the reference combustion center of gravity CA50ref can be estimated from the pressure difference P2-P1.

Further, according to new findings of the inventors of the present application, when the volumetric efficiency is different from the reference volumetric efficiency ηref and the engine rotation speed is different from the reference rotation speed Nref, the combustion center-of-gravity estimator 124a determines the reference volumetric efficiency ηref and the reference rotation speed Nref, it is possible to estimate the combustion center of gravity CA50 at the current rotation speed and volumetric efficiency.

<Example of finding cylinder internal pressure using discharge voltage>
The controllers 12 and 12A according to the above-described embodiments have shown an example in which the pressure sensor 10 is used to detect the in-cylinder pressure, but it is also possible to obtain the in-cylinder pressure using a method other than the pressure sensor 10.

For example, the controller 12 can obtain the in-cylinder pressure from the discharge voltage of the ignition coil 17a. Therefore, the combustion state estimator (pressure calculator 31a) is based on the voltage value of the ignition coil (ignition coil 17a), the current value of the ignition coil (ignition coil 17a), or the discharge time of the ignition coil (ignition coil 17a). , the first in-cylinder pressure P1 and the second in-cylinder pressure P2 can be obtained.

FIG. 23 is a diagram showing an example of time histories of the ignition signal, the primary voltage and secondary voltage of the ignition coil 17a, and the secondary current. An ignition signal is generated from the controller 12 to the ignition coil 17a. Then, the voltage on the primary side (primary voltage), the voltage on the secondary side (secondary voltage), and the current on the secondary side (secondary current) of the ignition coil 17a change with time. The discharge period is defined as the period from when the ignition signal transitions from high level to low level, when the secondary current starts to change, until the secondary current returns to its original value.

FIG. 24 is a characteristic diagram showing the correlation between the maximum value V1max of the primary voltage immediately after the start of discharge, the maximum value V2max of the secondary voltage, and the in-cylinder pressure during discharge. FIG. 24 shows changes in the ignition signal, the primary voltage and secondary voltage of the ignition coil 17a, and the secondary current.

When the ignition signal transitions from high level to low level, a large potential difference is generated on the secondary side of the ignition coil 17a, and discharge is started at the ignition plug 17b. The maximum value V2max (kV) of the secondary voltage immediately after the start of discharge has a high correlation with the in-cylinder pressure during discharge, as shown in FIG. Therefore, by measuring the maximum value V2max of the secondary voltage, the in-cylinder pressure during discharge can be obtained.

In addition, immediately after the discharge of the spark plug 17b, a back electromotive force is generated on the primary side of the ignition coil 17a, and the maximum value V1max (V) of the primary voltage immediately after the start of discharge also increases as shown in FIG. A high correlation with internal pressure appears. Therefore, the controller 12 can also obtain the in-cylinder pressure during discharge by measuring the maximum value V1max of the primary voltage of the ignition coil 17a.

FIG. 25 is a block diagram showing a configuration example from the ignition coil 17a to the controller 12 when the controller 12 obtains the in-cylinder pressure based on the secondary voltage of the ignition coil 17a.

The internal combustion engine (engine 1) has an ignition coil (ignition coil 17a) and a voltage peak value holding unit that detects the voltage of the ignition coil (ignition coil 17a) and holds the peak value of the voltage of the ignition coil (ignition coil 17a). (Peak hold circuit 30). Then, the combustion state estimator (pressure calculator 31a) calculates the first in-cylinder pressure P1 and the second in-cylinder pressure P2 based on the peak values.

The secondary voltage of the ignition coil 17a is sent to the peak hold circuit 30. The peak hold circuit 30 holds the peak value of the secondary voltage measured within a predetermined time. It is detected as the maximum value V2max of the next voltage. The peak hold circuit 30 may be provided in a circuit that supplies an ignition signal to the ignition coil 17a.

The peak hold circuit 30 sends the maximum value V2max of the secondary voltage to the controller 12 . A pressure calculation unit 31a in the controller 12 obtains the cylinder pressure at the time of discharge using a correlation equation between the secondary voltage maximum value V2max and the cylinder pressure obtained by calibration in advance, or table data.

Further, the pressure calculation unit 31a performs the process of obtaining the in-cylinder pressure from the primary voltage of the ignition coil 17a in the same manner as the process of obtaining the in-cylinder pressure from the secondary voltage. That is, the maximum value V1max of the primary voltage of the ignition coil 17a is detected by the peak hold circuit 30 and sent to the controller 12. FIG. A pressure calculation unit 31a provided in the controller 12 obtains the cylinder pressure during discharge using a correlation equation between the primary voltage maximum value V1max and the cylinder pressure obtained by calibration in advance, or table data.

When the in-cylinder pressure detection by the ignition coil 17a is applied to the method of estimating the combustion state according to the present embodiment, the pressure calculation unit 31a first calculates the secondary voltage maximum value V2max or the primary voltage maximum value associated with the discharge of the ignition timing. A first in-cylinder pressure P1 is obtained based on V1max. In the vicinity of the combustion end timing, the controller 12 sends an ignition signal to the ignition coil 17a to cause the ignition coil 17a to discharge. The second discharge is performed at the timing for obtaining the second in-cylinder pressure P2, but the ignition does not occur at this timing. The pressure calculator 31a obtains the second in-cylinder pressure P2 based on the secondary voltage maximum value V2max or the primary voltage maximum value V1max of the ignition coil 17a during discharge.

When the pressure calculation unit 31a obtains the in-cylinder pressure based on the voltage of the ignition coil 17a, the ignition coil 17a needs to be charged and discharged. Therefore, it is necessary to detect the in-cylinder pressure at a certain interval (for example, 4 ms) or more. . However, in the combustion state detection method according to the present embodiment, the pressure calculator 31a may detect the in-cylinder pressure near the ignition timing and near the combustion end timing. Normally, the interval between the ignition timing and the combustion end timing is longer than the charging/discharging time of the ignition coil 17a. Therefore, it is preferable to apply a method of detecting the in-cylinder pressure based on the voltage of the ignition coil 17a in the method of estimating the combustion state according to the present embodiment.

When the pressure calculator 31a detects the in-cylinder pressure based on the voltage of the ignition coil 17a in this way, the pressure sensor 10 becomes unnecessary, and the cost of the engine system can be reduced. Moreover, there is no need for a space for mounting the pressure sensor 10 on the engine, and there is an advantage that the degree of freedom in designing the engine, such as the shape of the cooling water passage and the combustion chamber, is increased.

(Example of finding the cylinder pressure using the discharge period)
The in-cylinder pressure can be obtained by using not only the maximum voltage of the ignition coil 17a but also the discharge period. In general, the discharge period of the ignition coil 17a becomes shorter as the cylinder internal pressure becomes higher. FIG. 26 shows that the period from the start of discharge until the secondary current of the ignition coil 17a becomes equal to or less than a predetermined value is the discharge period.

FIG. 26 is a characteristic diagram showing the correlation between the discharge period and the in-cylinder pressure during discharge. This characteristic diagram shows the result of actual measurement of the discharge period [ms] and the cylinder internal pressure during discharge using a spark ignition engine.

According to new findings of the inventors of the present application, it was found that a strong correlation as shown in FIG. 26 can be obtained between the discharge period and the in-cylinder pressure during discharge. The pressure calculator 31a can obtain the in-cylinder pressure using the correlation between the in-cylinder pressure and the discharge period of the ignition coil 17a. Therefore, the combustion center of gravity CA50 can be estimated based on the first in-cylinder pressure P1 obtained in the vicinity of the ignition timing from the discharge period and the second in-cylinder pressure P2 obtained in the vicinity of the combustion end timing. Become.

(Example of finding the cylinder pressure using the angular acceleration of the crankshaft)
Further, the combustion state estimator (pressure calculator 31b) can obtain the first in-cylinder pressure P1 and the second in-cylinder pressure P2 based on the angular acceleration of the crankshaft.
The angular acceleration of the crankshaft is expressed by the following equation (3). ω is the crank rotational speed, J is the moment of inertia, _Te is the combustion torque, and _TL is the load torque. Note that the load torque T _L is estimated based on the rotation speed of the engine 1 .

Also, the combustion torque _Te is expressed by the following equation (4), which is a function of the in-cylinder pressure Pc and the crank angle θ.

The controller 12 can obtain the in-cylinder pressure Pc at the crank angle θ by substituting the angular acceleration dω/dt of the crankshaft at the crank angle θ into the equation (3) and solving the simultaneous equation with the equation (4). .

FIG. 27 is a block diagram showing a configuration example from the crank angle sensor 11 to the controller 12 when the controller 12 obtains the in-cylinder pressure based on the angular acceleration of the crankshaft.

The internal combustion engine (engine 1) includes an angular acceleration calculator (angular acceleration calculator 32) that calculates the angular acceleration of the crankshaft.
Further, the combustion state estimating section (pressure calculating section 31b) calculates the first in-cylinder pressure P1 and the second in-cylinder pressure P2 based on the angular acceleration of the crankshaft.

The crank angle θ detected by the crank angle sensor 11 is sent to the angular acceleration calculator 32 . The angular acceleration calculator 32 calculates the angular acceleration dω/dt of the crankshaft using the crank angle θ. Then, the angular acceleration calculator 32 sends the angular acceleration dω/dt of the crankshaft and the crank angle θ to the controller 12 . The pressure calculation unit 31b in the controller 12 obtains the in-cylinder pressure by solving the simultaneous equations (3) and (4).

When the in-cylinder pressure detection based on the angular acceleration of the crankshaft is applied to the method of estimating the combustion state according to the present embodiment, the angular acceleration calculator 32 uses the crank angle sensor 11 near the ignition timing and the combustion end timing. to detect the angular acceleration dω/dt of the crankshaft. Then, the pressure calculation unit 31b solves the simultaneous equations of the equations (3) and (4) using the angular acceleration dω/dt to obtain the first in-cylinder pressure P1 near the ignition timing and the second pressure P1 near the combustion end timing. A second in-cylinder pressure P2 is obtained.

When the in-cylinder pressure Pc is detected based on the angular acceleration of the crankshaft in this way, the pressure sensor 10 becomes unnecessary, and the cost of the engine system can be reduced.

The controller 12 according to the first and second embodiments described above can accurately estimate the combustion state (torque fluctuation, combustion phase) using the in-cylinder pressure. In the first and second embodiments, it is possible to accurately estimate the combustion state by using two cylinder pressures obtained near the ignition timing and the combustion end timing per cycle for estimating the combustion state. can. In addition, since calculation is performed using two points of in-cylinder pressure, the required memory and required computation load can be reduced.

In addition, since high-speed pressure sampling is not required, the controller 12 can detect the cylinder pressure using existing engine devices such as the ignition coil 17a and the crank angle sensor 11 without using the cylinder pressure sensor. . With these, it is possible to keep the system cost required for combustion state estimation low.

<Others>
The present invention is not limited to the above-described embodiments, and of course, various other applications and modifications can be made without departing from the gist of the present invention described in the claims.
For example, each of the above-described embodiments describes the configuration of the controller 12 in detail and specifically in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the components described. Also, it is possible to replace part of the configuration of one embodiment with the constituent elements of another embodiment. It is also possible to add components of other embodiments to the configuration of one embodiment. Moreover, it is also possible to add, replace, or delete other components for a part of the configuration of each embodiment.
Further, each configuration, function, processing unit, etc. of the controller 12 may be realized by hardware, for example, by designing a part or all of them using an integrated circuit. As hardware, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or the like may be used.
Further, the control lines and information lines indicate those considered necessary for explanation, and not all control lines and information lines are necessarily indicated on the product. In practice, it may be considered that almost all configurations are interconnected.
In addition, in the flowcharts shown in FIGS. 3 and 19, a plurality of processes may be executed in parallel or the order of processes may be changed as long as the processing results are not affected.

DESCRIPTION OF SYMBOLS 1... Engine 10... Pressure sensor 12... Controller 17a... Ignition coil 17b... Spark plug 30... Peak hold circuit 31a... Pressure calculation part 31b... Pressure calculation part 32... Angular acceleration calculation part 121... Input/output unit 122 control unit 122a torque fluctuation estimation unit 122b engine control unit 122c deviation calculation unit 122d operation amount calculation unit 123 storage unit

Claims (14)

A combustion state estimator for estimating a combustion state of the internal combustion engine based on a first in-cylinder pressure acquired near ignition timing and a second in-cylinder pressure acquired near combustion end timing Internal combustion engine control Device. The combustion state estimating unit calculates a difference between the first in-cylinder pressure and the second in-cylinder pressure in a plurality of cycles, and calculates torque fluctuation of the internal combustion engine based on a variation rate of the difference in the plurality of cycles. 2. The internal combustion engine control system of claim 1, wherein the magnitude is estimated. The internal combustion engine control device according to claim 2, further comprising an engine control section that controls an EGR rate or an air-fuel ratio based on the magnitude of the torque fluctuation. 3. The internal combustion engine control device according to claim 2, further comprising an engine control section that controls at least one of ignition energy, in-cylinder flow strength, compression ratio, and intake air temperature based on the magnitude of the torque fluctuation. 2. The internal combustion engine control device according to claim 1, wherein the combustion state estimator changes the acquisition timing of the first in-cylinder pressure in accordance with the ignition timing of the cylinder. The internal combustion engine control device according to claim 5, wherein the combustion state estimator sets the difference between the acquisition timing of the first in-cylinder pressure and the ignition timing of the cylinder within 1 ms. 2. The internal combustion engine control device according to claim 1, wherein the combustion state estimator changes the acquisition timing of the second in-cylinder pressure in accordance with the 90% combustion timing of the cylinder. 8. The internal combustion engine control device according to claim 7, wherein the combustion state estimating unit sets a difference between the acquisition timing of the second in-cylinder pressure and the 20° retardation timing of the 90% combustion timing of the cylinder within 10°. . The internal combustion engine control device according to claim 1, wherein the combustion state estimator estimates a combustion phase based on a ratio between the first in-cylinder pressure and the second in-cylinder pressure. The internal combustion engine control device according to claim 9, further comprising an engine control section that controls ignition timing based on the ratio between the first in-cylinder pressure and the second in-cylinder pressure. 2. The combustion state estimator obtains the first cylinder pressure and the second cylinder pressure based on a voltage value of the ignition coil, a current value of the ignition coil, or a discharge time of the ignition coil. The internal combustion engine control device according to . The internal combustion engine includes an ignition coil,
A voltage peak value holding unit that detects the voltage of the ignition coil and holds the peak value of the voltage of the ignition coil,
The internal combustion engine control device according to claim 1, wherein the combustion state estimator calculates the first in-cylinder pressure and the second in-cylinder pressure based on the peak value. The internal combustion engine control device according to claim 1, wherein the combustion state estimator obtains the first in-cylinder pressure and the second in-cylinder pressure based on the angular acceleration of the crankshaft. The internal combustion engine includes an angular acceleration calculator that calculates an angular acceleration of the crankshaft,
The internal combustion engine control device according to claim 1, wherein the combustion state estimator calculates the first in-cylinder pressure and the second in-cylinder pressure based on the angular acceleration of the crankshaft.

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