JP2009221888A - Method for judging combustion condition in internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent misjudgment of deterioration of a combustion condition detection by including the time of after-burning not contributing to torque, in a method for judging the combustion condition in an internal combustion engine detecting ion current generated at each ignition in a combustion chamber of the internal combustion engine and judging the combustion condition based on a period during which detected ion current is not less than a threshold. <P>SOLUTION: In this method for judging the combustion condition, main combustion time from prescribed measurement start point of time until a point of time at which ion current based on main combustion generated at first after ignition gets below threshold including top dead center after ignition, whole elapsed time from the prescribed measurement start point of time until a point of time at which ion current based on the last one of after-burning generated after main combustion gets below the threshold, and combustion retention time adding the main combustion time and time integrating a period during which ion current based on whole after-burning generated after main combustion from measurement start point of time are measured respectively. One of the whole elapsed time and the main combustion time is selected as a criterion for judging the combustion condition based on the combustion retention time and at least one of the main combustion time and the whole elapsed time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion state determination method for an internal combustion engine that detects an ion current generated for each ignition in a combustion chamber of the internal combustion engine and determines a combustion state using the detected ion current.

Conventionally, when the internal combustion engine is started, the fuel injection amount has been increased so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio by starting correction, but the amount of hydrocarbon emissions in the exhaust gas has been increased. In order to comply with the regulations to suppress this, it is necessary to immediately change the air-fuel ratio to around the stoichiometric air-fuel ratio at which the hydrocarbon concentration in the exhaust gas becomes the lowest immediately after the internal combustion engine is started. However, with this setting, when the heavy fuel is put into the fuel tank, the fuel state is deteriorated due to insufficient fuel vaporization during cold start when the O ₂ sensor is not activated. There is. Therefore, a method capable of detecting such deterioration of the combustion state is demanded. As an example of such a method, for example, the following is considered. In other words, the ion current generated for each ignition in the combustion chamber of the internal combustion engine is detected, and the period during which the detected ion current is equal to or greater than the threshold is measured several times as the duration of the combustion state, and the variation rate of this duration is a predetermined value. In the case of the above, it is considered that the combustion state is determined to be deteriorated (see, for example, Patent Document 1).
JP-A-6-42384

  By the way, if the air-fuel ratio is around the stoichiometric air-fuel ratio, there is little afterburning that occurs after the main combustion that occurs first after ignition. In addition, most of the torque used for operation is obtained from the main combustion that occurs first after ignition, and the torque obtained from afterburning is negligibly small. Thus, the duration of the combustion state measured by the method described in Patent Document 1 includes the duration of afterburning. When such a method is adopted, the fluctuation rate of the duration increases due to inclusion in the total duration until afterburning that should not be considered, and it may be erroneously determined that the combustion state has deteriorated.

  The present invention is configured to solve such problems.

  In other words, the combustion state determination method for an internal combustion engine according to the present invention detects an ion current generated for each ignition in the combustion chamber of the internal combustion engine, and determines the combustion state based on a time period during which the detected ion current is equal to or greater than a threshold value. A combustion state determination method, wherein a main combustion time from a predetermined measurement start time including top dead center after ignition to a time when an ion current based on main combustion first generated after ignition falls below a threshold, and the measurement start time And the total elapsed time from the start of measurement to the time when the ion current based on the last one after the main combustion falls below the threshold, and the ion current based on all the post-combustion generated after the main combustion after the main combustion The combustion duration obtained by adding up the period of time and the main combustion time are respectively measured, and at least one of the main combustion time or the total elapsed time and the combustion duration are measured. Based on the between, as criteria for determining the combustion state, and selects one of the total elapsed time or the main combustion period.

  In such a case, it is first determined whether or not the afterburning can be ignored based on at least one of the main combustion time or the total elapsed time and the combustion duration, and the afterburning can be considered negligible. In this case, it is possible to determine the combustion state using the main combustion time instead of the total elapsed time, so by excluding the influence of afterburning that should not be considered, it is erroneously determined that the combustion state has deteriorated. Can be prevented. Furthermore, since the combustion state is determined based on the time rather than the crank angle during the period in which the detected ion current is equal to or greater than the threshold value, the determination accuracy of the combustion state can be ensured regardless of the rotational speed.

  As one of the modes that can prevent erroneous determination due to afterburn more effectively, select the total elapsed time as a criterion for determining the combustion state when the ratio of the combustion duration to the main combustion time exceeds a predetermined value When the ratio of the combustion duration to the main combustion time is less than a predetermined value, the main combustion time is selected as a reference for determining the combustion state. This is because if the afterburning is small, the main combustion time accounts for a large proportion of the combustion duration. Furthermore, since the ratio of the combustion duration to the main combustion time is a dimensionless number, the robustness can be improved by eliminating the influence of other parameters when determining the specific gravity of the afterburning.

  According to the combustion state determination method for an internal combustion engine according to the present invention, it is first determined whether or not afterburning can be considered negligible based on at least one of the main combustion time or the total elapsed time and the combustion duration. When the afterburning can be considered negligible, the combustion state can be judged using the main combustion time instead of the total elapsed time, so the combustion state deteriorates by excluding the influence of afterburning that should not be considered. It is possible to prevent erroneous determination as having been made. Furthermore, since the combustion state is determined based on the time rather than the crank angle during the period in which the detected ion current is equal to or greater than the threshold value, the determination accuracy of the combustion state can be ensured regardless of the rotational speed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

An engine 100, which is an internal combustion engine schematically shown in FIG. 1, is a four-cylinder engine for an automobile. A throttle valve 2 that opens and closes in response to an accelerator pedal (not shown) is disposed in an intake system 1 thereof. Is provided with a surge tank 3. A fuel injection valve 5 is further provided in the vicinity of one end of the intake manifold 4 of the intake system 1 communicating with the surge tank 3 and communicating with the cylinder 10 via the intake valve 10a. The electronic control unit 6 controls each cylinder to inject independently. Further, in the exhaust system 20, an O ₂ sensor 21 that is an air-fuel ratio sensor for measuring the oxygen concentration in the exhaust gas is provided upstream of the three-way catalyst 22 disposed in a pipeline leading to a muffler (not shown). Is attached in position. The O ₂ sensor 21 has substantially the same configuration as that known as a normal O ₂ sensor.

The electronic control device 6 is mainly composed of a microcomputer system including a central processing unit 7, a storage device 8, an input interface 9, and an output interface 11. The input interface 9 includes: The intake pressure signal a from the intake pressure sensor 13 for detecting the intake pressure PMTPB in the surge tank 3, the crank angle reference position signal G output from the cam position sensor 14 for detecting the rotation state of the engine 100, and the engine A rotation speed signal b, a vehicle speed signal c from the vehicle speed sensor 15 for detecting the vehicle speed, an LL signal d from the idle switch 16 for detecting the opening / closing state of the throttle valve 2, and a water temperature for detecting the cooling water temperature of the engine water temperature signal e from the sensor 17, a current signal h etc. are input from the O ₂ sensor 21 as described above It is. On the other hand, the output interface 11 outputs a fuel injection signal f to the fuel injection valve 5 and an ignition pulse g to the spark plug 18.

  A bias power source 24 for measuring the ion current I is connected to the spark plug 18, and an ion current measuring circuit 25 is connected between the input interface 9 and the bias power source 24. The bias power source 24 applies a bias voltage for measuring the ion current to the spark plug 18 when the ignition pulse g disappears. The ion current Iion flowing between the electrodes of the spark plug 18 due to the voltage application is measured by the ion current measuring circuit 25. The ionic current measurement circuit 25 has a comparator 25a that is a waveform shaping circuit described later, and is electrically connected to the input interface 9 of the electronic control unit 6, and an ionic current that is an analog signal generated by application of a voltage. The waveform is shaped into a square wave (pulse) and output. As shown in FIG. 2, the comparator 25a compares a predetermined current value Iref having a strength corresponding to a preset threshold value of the ion current Iion with the ion current Iion input via the bias power supply 24, When the current Iion exceeds the predetermined current value Iref, the output signal Iout is output. That is, the output signal Iout becomes a square wave that rises (turns on) when the ion current Iion exceeds the predetermined current value Iref and falls (turns off) when it falls below. The output terminal of the comparator 25a is connected to the central processing unit 7 via the input interface 9 in order to measure the duration of the ion current Iion. As the bias power source 24 and the ion current measuring circuit 25, various devices well known in the art can be applied.

  The electronic control device 6 uses the intake pressure signal a output from the intake pressure sensor 13 and the rotation speed signal b output from the rotation speed sensor 14 as main information, and various correction coefficients determined according to the engine situation. The fuel injection valve opening time, that is, the injector final energization time T is determined by correcting the basic injection time, and the fuel injection valve 5 is controlled by the determined energization time, and fuel corresponding to the engine load is supplied to the fuel injection valve 5. The program for injecting into the intake system 1 is built in.

  In addition, the electronic control unit 6 includes a point in time at which the ion current Iion based on the main combustion generated for the first time after ignition falls below a threshold from a predetermined measurement start time including top dead center after ignition for a predetermined time from ignition. The main combustion time atdc up to the time point, the total elapsed time atdcmax from the measurement start time point to the time point when the ion current Iion based on the last one after the main combustion is below the threshold, and the main combustion time point from the measurement start time point The total duration time atdcmax or the main combustion time atdc is measured by adding up the period in which the ion current Iion based on all of the afterburning that occurs later is equal to or greater than the threshold and the main combustion time atdc. Is selected as the combustion determination time atcombl3, and the combustion state is selected based on the selected combustion determination time atcombl3. Constant burning state determination program also incorporates.

  Here, the measurement of the main combustion time atdc, the total elapsed time atdcmax, and the combustion duration time atdcint starts when the output signal Iout from the comparator 25a exceeds the predetermined current value Iref corresponding to the threshold value. (Turned on), and using the fact that it falls when it falls below the predetermined current value Iref corresponding to the threshold value.

  The selection of the combustion determination time atcombl3 is performed based on the ratio R1 of the combustion duration time atdcint to the main combustion time atdc. When the main combustion occupies a large proportion, this ratio R1 becomes small. Specifically, the main combustion time atdc is selected as the combustion determination time atcomb3 because the afterburning can be ignored if the ratio R1 is less than 2.5. On the other hand, if this ratio R1 exceeds a predetermined value, which is 2.5 in this embodiment, afterburning cannot be ignored, the total elapsed time atdcmax is selected as the combustion determination time atcombl3. Then, by determining whether or not the selected combustion determination time atcombl3 is longer than the combustion state deterioration determination threshold value L, it is determined whether or not the combustion state has deteriorated. The combustion state deterioration determination threshold value L is set to a value sufficiently longer than the average main combustion time atdc when the air-fuel ratio is close to the theoretical air-fuel ratio.

  Next, the flow of control by the combustion state determination program will be described below with reference to FIG. 3 which is a flowchart.

  In step S1, main combustion time atdc, total elapsed time atdcmax, and combustion duration time atdcint are measured. Then, the process proceeds to step S2.

  In step S2, the ratio R1 of the combustion duration time atdcint to the main combustion time atdc is obtained. Then, the process proceeds to step S3.

  In step S3, it is determined whether or not the ratio R1 exceeds a predetermined value, which is 2.5 in this embodiment. When the ratio of the combustion duration time atdcint to the main combustion time atdc exceeds 2.5, the process proceeds to step S4. Otherwise, the process proceeds to step S5.

  In step S4, the total elapsed time atdcmax is set as the combustion determination time atcombl3, and the process proceeds to step S6.

  In step S5, the main combustion time atdc is set as the combustion determination time atcombl3, and the process proceeds to step S6.

  In step S6, it is determined whether or not the combustion determination time atcombl3 exceeds the combustion state deterioration determination threshold value L. When the combustion determination time atcombl3 exceeds the combustion state deterioration determination threshold L, the process proceeds to step S7. Otherwise, the process proceeds to step S8.

  In step S7, it is determined that the combustion state has deteriorated.

  In step S8, it is determined that the combustion state is good.

  That is, in such a configuration, when the air-fuel ratio is close to the stoichiometric air-fuel ratio or richer, it is difficult for afterburning to occur. Therefore, as shown in FIG. The portion excluding the combustion time atdc does not exceed 1.5 times the main combustion time. That is, since it is determined in step S3 that the ratio R1 of the combustion duration time atdcint to the main combustion time atdc does not exceed 2.5, the main combustion time atdc is selected as the combustion determination time atcombl3 in step S5, and then in step S6. Process. Since the main combustion time atdc is sufficiently shorter than the combustion state deterioration determination threshold value L as described above, the process for determining that the combustion state is good is performed in step S8, and the combustion state determination program is terminated. That is, the processes of steps S1, S2, S3, S5, S6, and S8 are sequentially performed. At this time, since the main combustion time atdc is sufficiently shorter than the combustion state deterioration determination threshold value L as described above, the combustion state determination program is terminated without increasing the fuel injection amount. On the other hand, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, afterburning is likely to occur, and the combustion duration atdcint exceeds 2.5 times the main combustion time atdc as shown in FIG. There is. In such a case, after the determination in step S3, the process proceeds to step S4, where the total elapsed time atdcmax is selected as the combustion determination time atcombl3, and then the process of step S6 is performed. If the total elapsed time atdcmax exceeds the combustion state deterioration determination threshold value L, a process for determining that the combustion state has deteriorated is performed in step S7. That is, the processes of steps S1, S2, S3, S4, S6, and S7 are sequentially performed.

  That is, when the combustion state determination method according to the present embodiment is employed, when the ratio of afterburning is small, the main combustion time atdc is selected as the combustion determination time atcombl3, and the combustion state is determined based on the combustion determination time atcombl3. By doing so, it is possible to eliminate the influence of afterburning that has a small contribution to the generation of torque, and to prevent erroneous determination that the combustion state has deteriorated. Furthermore, since the combustion state is determined based on the time rather than the crank angle during the period in which the detected ion current Iion is equal to or greater than the threshold value, the determination accuracy of the combustion state can be ensured regardless of the rotational speed.

  If the ratio R1 of the combustion duration time atdcint to the main combustion time atdc exceeds a predetermined value 2.5, the total elapsed time atdcmax is selected as the combustion determination time atcombl3. Otherwise, the main combustion time atdc is determined as the combustion determination. Since the combustion state is determined based on this combustion determination time atcombl3, when the main combustion time atdc occupies a large proportion of the combustion duration atdcint, which is 40% or more in this embodiment, the afterburning Can be ignored, and the air-fuel ratio can be determined based on the main combustion time atdc by main combustion. Accordingly, it is possible to prevent erroneous determination caused by afterburn more effectively. Furthermore, since the ratio of the combustion duration time atdcint to the main combustion time atdc is a dimensionless number, the robustness can be improved by eliminating the influence of other parameters when determining the specific gravity of the afterburning.

  The present invention is not limited to the embodiment described above.

  For example, in the combustion state determination program of the above-described embodiment, after measuring the main combustion time atdc, the total elapsed time atdcmax, and the combustion duration time atdcint in step S1, the ratio of the combustion duration time atdcint to the main combustion time atdc in step S3. Before determining whether or not R1 exceeds a predetermined value, it is determined whether or not the main combustion time atdc is 0 and whether or not the ion current Iion contains a lot of noise. When it is determined that the combustion time atdc is less than a predetermined value or the ion current Iion includes a lot of noise, it is determined that the combustion state has deteriorated and control is performed to increase the fuel injection amount by a predetermined amount. It is even better to select the total elapsed time as the combustion determination time atcombl3. Here, whether or not the ion current Iion includes a lot of noise is determined based on the number of times the rising or falling of the output signal Iout is input from the comparator 25a, for example, when this number exceeds a predetermined value. A mode in which it is determined that the ion current Iion contains a lot of noise may be used.

Further, in the above-described combustion state determination program, instead of comparing the combustion determination time atcombl3 with the combustion state deterioration determination threshold value L, an average A _av and n ignition deviation ΔA for the latest n times of the combustion determination time atcombl3 are obtained, and n A mode in which it is determined whether or not the fluctuation rate Af, which is a ratio of the ignition deviation ΔA to the average A _av , exceeds a predetermined value LL, and it is determined that the combustion state has deteriorated when the fluctuation rate Af exceeds the predetermined value LL. May be adopted. Note that the n ignition difference ΔA is obtained by the following equation (3).

ΔA = (| A ₁ −A _av | + | A ₂ −A _av | +... + | A _n −A _av |) / n (3)
Furthermore, after each ignition, a has the combustion determination time last n times the mean A _av and n ignition fraction with a deviation on the basis of .DELTA.A n times emphasized fluctuation B _n further on the basis of the n times emphasized fluctuation B _n emphasized variation of atcombl3 A mode may be adopted in which BB _n is obtained and it is determined that the combustion state has deteriorated when the enhancement variation annealing BB _n exceeds a predetermined value LL. Here, the n-time emphasis variation B _n and the emphasis variation annealing BB _n are obtained by the following equations (4) and (5), respectively.

_{B n = {ΔA / A av} a} × b (4)
_{BB n = B n-1 +} (B n -B n-1) × c (5)
Here, a, b, and c are predetermined parameters. B _n−1 is the ratio of the (n−1) ignition component deviation Astd to the average Aave of the most recent (n−1) combustion determination times atcombl3.

  Further, instead of the control by the combustion state determination program in the above-described embodiment, a mode in which the control device 6 performs the control by the combustion state determination program as described below is also conceivable. In this aspect, if the ratio R2 of the total elapsed time atdcmax to the combustion duration atdcint is greater than 2, the combustion is interrupted in the time zone that exceeds half of the total elapsed time, so that afterburning is considered negligible. The main combustion time atdc is selected as the combustion determination time atcombl4, and if not, the total elapsed time atdcmax is selected as the combustion determination time atcombl4, and the combustion state is determined based on the combustion determination time atcombl4. .

  A schematic procedure of control by this combustion state determination program will be described with reference to FIG. 5 which is a flowchart.

  In step S11, the main combustion time atdc, the total elapsed time atdcmax, and the combustion duration time atdcint are measured. Then, the process proceeds to step S12.

  In step S12, a ratio R2 of the total elapsed time atdcmax to the combustion duration time atdcint is obtained, and the process proceeds to step S13.

  In step S13, it is determined whether or not the ratio R2 exceeds a predetermined value, which is 2 in this aspect. When the ratio R2 exceeds 2, the process proceeds to step S14. Otherwise, the process proceeds to step S15.

  In step S14, the main combustion time atdc is set to the combustion determination time atcombl4, and the process proceeds to step S16.

  In step S15, the total elapsed time atdcmax is set as the combustion determination time atcombl4, and the process proceeds to step S16.

  In step S16, it is determined whether or not the combustion determination time atcombl4 exceeds the combustion state deterioration determination threshold value L. When the combustion determination time atcombl4 exceeds the combustion state deterioration determination threshold L, the process proceeds to step S17. Otherwise, the process proceeds to step S18.

  In step S17, it is determined that the combustion state has deteriorated.

  In step S18, it is determined that the combustion state is good.

  The combustion state deterioration determination threshold value L is set to a value sufficiently longer than the main combustion time atdc when the air-fuel ratio is close to the theoretical air-fuel ratio.

  That is, even in this mode, when the afterburning is so small that it can be ignored, it is considered that only the main combustion has occurred, and the combustion state is determined, so that the influence of the afterburning that contributes to the generation of torque is small. It can exclude and it can prevent misjudging that the combustion state deteriorated. Furthermore, since the ratio R2 of the total elapsed time atdcmax to the combustion duration time atdcint is a dimensionless number, the robustness can be improved by eliminating the influence of other parameters when determining the specific gravity of the afterburning.

  In addition, instead of the control by the combustion state determination program in the above-described embodiment, a mode in which the control device 6 performs the control by the combustion state determination program as described below is also conceivable. In this aspect, when the non-combustion time Tn, which is the difference between the total elapsed time atdcmax and the combustion duration time atdcint, exceeds a predetermined value La, the time period in which the combustion is interrupted after the end of the main combustion is long, and after the end of the main combustion The detected afterburning is regarded as negligible, and the main combustion time atdc is selected as the combustion determination time atcombl2, and if not, the total elapsed time atdcmax is selected as the combustion determination time atcombl2, and this combustion determination time atcombl2 is set. Based on this, the combustion state is determined. The predetermined value La is a time limit for determining that the non-burning time Tn is long enough to determine that the afterburning is so small that it can be ignored, and is determined experimentally in advance.

  A schematic procedure of control by this combustion state determination program will be described with reference to FIG. 6 which is a flowchart.

  In step S21, the main combustion time atdc, the total elapsed time atdcmax, and the combustion duration time atdcint are measured. Then, the process proceeds to step S22.

  In step S22, the non-burning time Tn is obtained. Then, the process proceeds to step S23.

  In step S23, it is determined whether or not the non-burning time Tn exceeds a predetermined value La. When the non-burning time Tn exceeds the predetermined value La, the process proceeds to step S24. Otherwise, the process proceeds to step S25.

  In step S24, the main combustion time atdc is set to the combustion determination time atcombl2, and the process proceeds to step S26.

  In step S25, the total elapsed time atdcmax is set as the combustion determination time atcombl2, and the process proceeds to step S26.

  In step S26, it is determined whether or not the combustion determination time atcombl2 exceeds the combustion state deterioration determination threshold value L. When the combustion determination time atcombl2 exceeds the combustion state deterioration determination threshold L, the process proceeds to step S27. Otherwise, the process proceeds to step S28.

  In step S27, it is determined that the combustion state has deteriorated.

  In step S28, it is determined that the combustion state is good.

  The combustion state deterioration determination threshold value L is set to a value sufficiently longer than the main combustion time atdc when the air-fuel ratio is close to the theoretical air-fuel ratio.

  That is, even in this mode, when the afterburning is so small that it can be ignored, it is considered that only the main combustion has occurred, and the combustion state is determined, so that the influence of the afterburning that contributes to the generation of torque is small. It can exclude and it can prevent misjudging that the combustion state deteriorated.

  Then, instead of the control by the combustion state determination program in the above-described embodiment, a mode in which the control device 6 performs the control by the combustion state determination program as described below is also conceivable. In this aspect, when the afterburning is negligibly small, the total elapsed time atdcmax is not so long as compared with the main combustion time atdc, and further, the combustion duration time atdcint is not so long as compared with the main combustion time atdc. Paying attention to the ratio of the total elapsed time atdcmax to the combustion time atdc and the product of the ratio of the combustion duration atdcint to the main combustion time atdc, that is, the square of the main combustion time atdc of the product of the total elapsed time atdcmax and the combustion duration atdcint The combustion determination time atcombl5 is selected on the basis of the ratio R4 with respect to. That is, when the ratio R4 does not exceed the predetermined value Lb, the afterburning is assumed to be negligible, and the main combustion time atdc is selected as the combustion determination time atcombl5, while when the ratio R4 exceeds the predetermined value Lb. The total elapsed time atdcmax is selected as the combustion determination time atcombl5, and the combustion state is determined based on the combustion determination time atcombl5. Note that the predetermined value Lb is a limit value that can be determined that the total elapsed time atdcmax and the combustion duration time atdcint are not longer than the main combustion time atdc to an extent that the afterburning can be considered negligible, for example, 5. Is required.

  A schematic procedure of control by this combustion state determination program will be described with reference to FIG. 6 which is a flowchart.

  In step S31, the main combustion time atdc, the total elapsed time atdcmax, and the combustion duration time atdcint are measured. Then, the process proceeds to step S32.

  In step S32, a ratio R4 of the product of the total elapsed time atdcmax and the combustion duration time atdcint to the square of the main combustion time atdc is obtained, and then the process proceeds to step S33.

  In step S33, it is determined whether or not the ratio R4 exceeds a predetermined value Lb. If the ratio R4 exceeds the predetermined value Lb, the process proceeds to step S34. Otherwise, the process proceeds to step S35.

  In step S34, the total elapsed time atdcmax is set as the combustion determination time atcombl5, and the process proceeds to step S36.

  In step S35, the main combustion time atdc is set to the combustion determination time atcombl5, and the process proceeds to step S36.

  In step S36, it is determined whether or not the combustion determination time atcombl5 exceeds the combustion state deterioration determination threshold value L. When the combustion determination time atcombl5 exceeds the combustion state deterioration determination threshold L, the process proceeds to step S37. Otherwise, the process proceeds to step S38.

  In step S37, it is determined that the combustion state has deteriorated.

  In step S38, it is determined that the combustion state is good.

  The combustion state deterioration determination threshold value L is set to a value sufficiently longer than the main combustion time atdc when the air-fuel ratio is close to the theoretical air-fuel ratio.

  That is, even in this mode, when it can be considered that afterburning can be ignored, it is considered that only main combustion has occurred, and the combustion state is judged to exclude the influence of afterburning and the combustion state is deteriorated. It is possible to prevent erroneous determination as having been performed. Furthermore, since the ratio R4 of the product of the total elapsed time atdcmax and the combustion duration time atdcint to the square of the main combustion time atdc is a dimensionless number, the influence of other parameters is excluded when determining the specific gravity of the afterburning. And robustness can be improved.

  In the combustion time measurement program in the above-described embodiment, the measurement start time points of the total elapsed time atdcmax and the main combustion time atdc may be set at other time points near the top dead center instead of the top dead center. .

In addition, the combustion state determination method according to the present invention may be used not only at the time of cold start, but also when the O ₂ sensor fails and air-fuel ratio feedback control is impossible.

  In addition, various changes may be made without departing from the spirit of the present invention.

Schematic which shows the engine which concerns on one Embodiment of this invention. The block diagram of the electric circuit which performs the waveform shaping which concerns on the same embodiment. The flowchart which shows the flow of control in the combustion state determination program which concerns on the same embodiment. Action | operation explanatory drawing which concerns on the same embodiment. The flowchart which shows the flow of control in the combustion state determination program which concerns on the other embodiment of this invention. The flowchart which shows the flow of control in the combustion state determination program which concerns on the other embodiment of this invention. The flowchart which shows the flow of control in the combustion state determination program which concerns on the other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Engine 6 ... Control apparatus 18 ... Spark plug

Claims (2)

A combustion state determination method for detecting an ionic current generated for each ignition in a combustion chamber of an internal combustion engine and determining a combustion state based on a period of time during which the detected ionic current is equal to or greater than a threshold,
The main combustion time from the predetermined measurement start time including the top dead center after ignition to the time when the ion current based on the main combustion first generated after ignition falls below the threshold, and the post-combustion generated after the main combustion from the measurement start time And the total elapsed time until the point when the ion current based on the last one falls below the threshold and the period when the ion current based on all of the post-combustion generated after the main combustion from the measurement start point is equal to or greater than the threshold Measure the respective combustion durations combined with the main combustion time,
Combustion of an internal combustion engine, wherein one of the total elapsed time or the main combustion time is selected as a criterion for determining the combustion state based on at least one of the main combustion time or the total elapsed time and the combustion duration time State determination method. When the ratio of the combustion duration to the main combustion time exceeds a predetermined value, select the total elapsed time as a criterion for determining the combustion state,
2. The combustion state determination method for an internal combustion engine according to claim 1, wherein when the ratio of the combustion duration to the main combustion time is less than a predetermined value, the main combustion time is selected as a reference for determining the combustion state.

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