JP2014025355A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device stably executing fresh air blow-by detection control in an ordinary exhaust system configuration.SOLUTION: At a time of occurrence of fresh air blow-by, peak points appear during a valve overlap period and a period corresponding to an exhaust stroke of each cylinder, respectively, so that the number of peak points in one cycle is equal to a twofold of the number of cylinders. By way of example, the number of peak points in one cycle is eight for a four-cylinder engine. Therefore, in fresh air blow-by detection control, the number of peak points in one cycle is measured and it is determined that fresh air blow-by occurs if the number of peak points in one cycle is equal to the twofold of the number of cylinders.

Description

  The present invention relates to a control device for an internal combustion engine mounted on a vehicle such as an automobile, and more particularly to a control device for an internal combustion engine having a scavenge detection function.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-175201), a control device for an internal combustion engine having a function of detecting a scavenge (a blow-through of fresh air into an exhaust system) is known. It has been. In the prior art, two exhaust ports provided in one cylinder are connected to different exhaust passages, and scavenging is generated in one exhaust passage. And scavenging is detected based on the difference between the air-fuel ratio detected in one exhaust passage and the air-fuel ratio detected in the other exhaust passage.

  Another conventional technique is disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2008-75549). In this prior art, the air-fuel ratio (air-fuel ratio calculated value) calculated based on the amount of air charged in the cylinder and the fuel injection amount is compared with the air-fuel ratio (sensor detected air-fuel ratio) detected by the air-fuel ratio sensor. To detect the occurrence of scavenging. This detection method utilizes the fact that when the air-fuel ratio sensor detects oxygen in the fresh air that has blown through the exhaust system, the sensor-detected air-fuel ratio shifts to the lean side as compared to the calculated air-fuel ratio. The occurrence is detected.

JP 2008-175201 A JP 2008-75549 A

  In the prior art described in Patent Document 1, scavenging is detected based on the exhaust air-fuel ratio on the premise that scavenging is generated only in one of the two exhaust passages. However, in the conventional technology, it is difficult to detect the occurrence of scavenging unless the exhaust system configuration as described above is assumed. In addition, scavenge generation conditions vary depending on exhaust pressure drop due to variations in exhaust muffler specifications, low pressure environment in high altitudes, etc., so scavenge detection control in general exhaust system configurations There is a problem that it is difficult to stably execute.

  Further, in the conventional technique described in Patent Document 2, if a sensor output value shift (deviation of the sensor output value offset with respect to the theoretical air-fuel ratio) or the like occurs due to an individual difference of the air-fuel ratio sensor, a change with time, or the like, Since an error also occurs in the relationship between the fuel ratio and the calculated air-fuel ratio, there is a problem that the detection accuracy of the scavenge is lowered.

  The present invention has been made to solve the above-described problems. The object of the present invention is based on the output of the air-fuel ratio sensor without being affected by the configuration of the exhaust system or the deviation of the sensor output value. An object of the present invention is to provide a control device for an internal combustion engine that can stably detect the occurrence of scavenging.

A first invention includes an air-fuel ratio sensor that is provided in an exhaust passage of an internal combustion engine and detects an exhaust air-fuel ratio, and a detection device that detects the occurrence of scavenging based on an output value of the air-fuel ratio sensor,
The detection device includes:
A peak that detects one predetermined point as a peak point among a maximum point where the output value of the air-fuel ratio sensor reverses from an increasing tendency to a decreasing tendency and a minimum point where the output value reverses from a decreasing tendency to an increasing tendency Point detection means;
Scavenge determination means for determining whether or not scavenge has occurred based on the relationship between the number of peak points appearing in one cycle of the internal combustion engine and the number of cylinders of the internal combustion engine;
It is characterized by providing.

  According to a second aspect of the present invention, the scavenge determining means determines that scavenging has occurred when the number of appearance of the peak point per cycle is twice the number of cylinders.

  According to a third aspect of the present invention, when the occurrence of scavenging is detected, the scavenging rate is estimated based on the amount of change when the output value of the air-fuel ratio sensor changes between the adjacent maximum and minimum points. Means.

According to a fourth aspect of the present invention, when the occurrence of scavenging is detected, the scavenging rate is estimated based on the amount of change when the output value of the air-fuel ratio sensor changes between the adjacent maximum and minimum points. Means,
When air-fuel ratio control is executed to feedback-control the exhaust air-fuel ratio so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio, the target air-fuel ratio is based on the estimated value of the scavenging rate. Correction means for correcting the fuel ratio.

  According to a fifth invention, the correction means has data representing a relationship between a deviation amount of the output value of the air-fuel ratio sensor with respect to a true value of the exhaust air-fuel ratio and an estimated value of the scavenging rate, The target air-fuel ratio is corrected based on the deviation amount of the output value calculated by the estimated value of the scavenging rate.

  According to the first invention, it is possible to easily determine whether or not scavenging has occurred based on the relationship between the number of peak points appearing in one cycle and the number of cylinders of the internal combustion engine. Moreover, at the time of detecting the peak point, for example, while periodically reading the output value of the air-fuel ratio sensor, detection is performed based on the difference, so even if there is an error due to the offset deviation of the sensor output value, etc. This error is canceled when the difference is calculated, and the peak point can be reliably detected. In addition, the output value of the air-fuel ratio sensor tends to fluctuate depending on the configuration of the exhaust system, etc., whereas the increasing / decreasing tendency of the sensor output value is stable when the output value fluctuates (offset) as a whole. ing. Therefore, the occurrence of scavenging can be accurately and stably detected without being affected by the exhaust system configuration, sensor output value deviation, and the like.

  According to the second invention, when the scavenge is not generated, the number of appearance of the peak point per cycle is equal to the number of cylinders, whereas when the scavenge is generated, the number of appearance of the peak point per cycle. Is twice the number of cylinders. Using this characteristic, it can be easily determined that scavenging has occurred.

  According to the third invention, the change amount of the sensor output value between the local maximum point and the local minimum point adjacent to each other has a characteristic of increasing as the scavenging rate increases. By using this characteristic, the scavenge rate can be specifically estimated.

  According to the fourth aspect of the invention, the scavenge rate is specifically estimated based on the change amount of the sensor output value between the maximum point and the minimum point adjacent to each other, and the air-fuel ratio control is performed based on the estimated value of the scavenge rate. The target air-fuel ratio can be corrected. As a result, in the air-fuel ratio control, even when the output value of the air-fuel ratio sensor is deviated due to scavenging, feedback is performed so that the output value matches the target air-fuel ratio in which the deviation amount of the sensor output value is reflected. Since control can be performed, the true value of the air-fuel ratio can be matched with the target air-fuel ratio. Therefore, even when scavenging occurs, the exhaust air-fuel ratio can be stably controlled by air-fuel ratio control, and the disturbance of the exhaust air-fuel ratio and the deterioration of exhaust emission due to scavenging can be suppressed.

  According to the fifth aspect of the invention, since the correction means holds in advance the relationship between the scavenging rate and the sensor output value deviation amount as data, it easily calculates the sensor output value deviation amount based on the scavenge rate. be able to.

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. 6 is a timing chart showing valve timing, valve lift amount, exhaust gas state, and exhaust air / fuel ratio over one cycle when scavenging occurs. 6 is a timing chart showing an output value of an air-fuel ratio sensor and a crank signal when scavenging is not generated. 5 is a timing chart showing an output value of an air-fuel ratio sensor and a crank signal when scavenging occurs. It is explanatory drawing which shows an example of the method of detecting the peak point of a sensor output value. In Embodiment 1 of this invention, it is a flowchart which shows the control performed by ECU. In Embodiment 2 of this invention, it is a timing chart which shows the state of the exhaust gas at the time of scavenging generation | occurrence | production, and an exhaust air fuel ratio over 1 cycle. It is a timing chart which shows the variation | change_quantity when a sensor output value changes between the mutually adjacent maximum point and minimum point when a scavenge rate is low. It is a timing chart which shows the change amount when a sensor output value changes between mutually adjacent maximum points and minimum points when the scavenge rate is high. It is a timing chart which shows an example of the output value of an air fuel ratio sensor, the difference of an output value, the product of a difference, and output amplitude. In Embodiment 3 of this invention, it is a timing chart which shows the state of the exhaust gas at the time of scavenging generation | occurrence | production, and an exhaust air fuel ratio over 1 cycle. It is a timing chart which shows the state from which the average value of the sensor output value shifted | deviated to the rich side with respect to the true value of the air fuel ratio. In Embodiment 3 of this invention, it is a flowchart which shows the control performed by ECU. In Embodiment 4 of this invention, it is a characteristic diagram which shows the relationship between the deviation | shift amount of the output value of an air fuel ratio sensor, and a scavenge rate. FIG. 7 is an explanatory diagram showing a state in which a deviation of the air-fuel ratio occurs due to scavenging in the air-fuel ratio control of the prior art. In Embodiment 4 of this invention, it is explanatory drawing which shows the state which correct | amended the target air fuel ratio according to the scavenge rate by the target air fuel ratio correction control. In Embodiment 5 of this invention, it is a characteristic diagram which shows the relationship between the deviation | shift amount of a sensor output value, and a scavenge rate about each of the air-fuel ratio sensor and catalyst downstream sensor of a catalyst upstream. It is explanatory drawing which shows the behavior of each sensor output value when scavenging generate | occur | produces. In Embodiment 6 of this invention, it is a timing chart which shows the state of the exhaust gas at the time of scavenging generation | occurrence | production, and an exhaust air fuel ratio over 1 cycle. In Embodiment 6 of this invention, it is a flowchart which shows the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes an engine 10 as, for example, a multi-cylinder internal combustion engine. FIG. 1 shows one cylinder of a plurality of functions mounted on the engine 10. In this embodiment, a four-cylinder engine will be described as an example, but the present invention is applied to an internal combustion engine having an arbitrary number of cylinders including a single cylinder. In each cylinder of the engine 10, a combustion chamber 14 is formed by a piston 12, and the piston 12 is connected to a crankshaft 16 of the engine. The engine 10 also includes an intake passage 18 that sucks intake air into each cylinder, and an exhaust passage 20 through which exhaust gas is discharged from each cylinder. The intake passage 18 is provided with an electronically controlled throttle valve 22 that adjusts the intake air amount and an intercooler 24 that cools the intake air.

  The exhaust passage 20 is provided with a catalyst 26 such as a three-way catalyst for purifying exhaust gas. Each cylinder has a fuel injection valve 28 for injecting fuel into the intake port, a spark plug 30 for igniting an air-fuel mixture in the combustion chamber 14 (in-cylinder), and an intake port opened and closed with respect to the cylinder. An intake valve 32 that opens and an exhaust valve 34 that opens and closes the exhaust port with respect to the inside of the cylinder are provided. Further, the engine 10 includes a known turbocharger 36 that supercharges intake air using exhaust pressure. The turbocharger 36 includes a turbine 36 a provided in the exhaust passage 20 on the upstream side of the catalyst 26 and a compressor 36 b provided in the intake passage 18. The compressor 36b is driven by a turbine 36a that rotates by receiving exhaust pressure, and supercharges intake air. The exhaust passage 20 is provided with a waste gate valve 38 that bypasses the turbine 36a and distributes the exhaust gas.

  Next, a system control system will be described. The system according to the present embodiment includes a sensor system including sensors 40 to 48 and an ECU (Electronic Control Unit) 50 that controls the operating state of the engine 10. First, the sensor system will be described. The crank angle sensor 40 outputs a signal (crank signal) synchronized with the rotation of the crankshaft 16. The air flow sensor 42 detects the intake air amount of the engine, and the intake pressure sensor 44 detects the intake pressure (supercharging pressure) of the engine. The air-fuel ratio sensor 46 is disposed upstream of the catalyst 26 and detects the exhaust air-fuel ratio as a continuous value. The catalyst downstream sensor 48 is configured by a sensor similar to the air-fuel ratio sensor 46 or an oxygen sensor, and is disposed on the downstream side of the catalyst 26. The oxygen sensor is a sensor that detects whether the exhaust air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio (stoichiometric). In addition to the above sensors, the sensor system includes various sensors necessary for engine and vehicle control (for example, a water temperature sensor that detects the temperature of engine cooling water, an accelerator sensor that detects the amount of accelerator operation by the driver, etc.) )It is included.

  The ECU 50 is configured by an arithmetic processing device including a storage circuit such as a ROM and a RAM and an input / output port. Each sensor is connected to the input side of the ECU 50, and various actuators including the throttle valve 22, the fuel injection valve 28, the spark plug 30, the waste gate valve 38, and the like are connected to the output side of the ECU 50. The ECU 50 constitutes a detection device that detects the occurrence of scavenging based on the output value of the air-fuel ratio sensor 46, as will be described later.

  Then, the ECU 50 controls the operation of the engine by driving each actuator based on the engine operation information detected by the sensor system. Specifically, the engine speed (engine speed) and the crank angle are detected based on the output of the crank angle sensor 40, and the load is determined based on the intake air amount detected by the airflow sensor 42 and the engine speed. calculate. Further, the fuel injection amount is calculated based on the engine speed, the load, etc., and the fuel injection timing and the ignition timing are determined based on the crank angle. In each cylinder, the fuel injection valve 28 is driven when the fuel injection timing comes, and the spark plug 30 is driven when the ignition timing comes. Thereby, the air-fuel mixture is combusted in each cylinder, and the engine 10 is operated. Further, the ECU 50 executes known air-fuel ratio control and air-fuel ratio learning control. In the air-fuel ratio control, the exhaust air-fuel ratio (fuel injection amount) is fed back based on the outputs of the air-fuel ratio sensor 46 and the catalyst downstream sensor 48 so that the exhaust air-fuel ratio matches a predetermined target air-fuel ratio (for example, stoichiometric or the like). Control. In the air-fuel ratio learning control, the feedback control amount obtained by the air-fuel ratio control is stored in the learning map.

[Features of Embodiment 1]
In general, when the valve overlap between the intake valve 32 and the exhaust valve 34 is large and the intake pressure is relatively high with respect to the exhaust pressure as in supercharging, fresh air in the intake system passes through the cylinder. Therefore, a phenomenon (scavenge) that blows directly into the exhaust system is likely to occur. When scavenging occurs, a torque shift with respect to the intake air amount, a change in the ignition timing correction amount, and the like occur. Therefore, in engine control, it is preferable to detect the occurrence of scavenging and execute control corresponding thereto. However, since the scavenge generation conditions change due to variations in the structure of the exhaust system and the temperature environment, it is difficult to stably generate scavenges using the absolute value of the sensor output value.

(Scavenge detection control)
For this reason, in the present embodiment, the scavenge detection control described below is executed, and the occurrence of scavenge is detected based on the inversion frequency of the output value of the air-fuel ratio sensor 46. FIG. 2 is a timing chart showing valve timing, valve lift amount, exhaust gas state, and exhaust air-fuel ratio over one cycle (720 ° C.) when scavenging occurs. This figure exemplifies a 4-cylinder engine having cylinders # 1 to # 4. “# 1 intake” and “# 1 exhaust” mean the intake stroke and exhaust stroke of the # 1 cylinder, respectively. “IN · EX” means an intake valve and an exhaust valve. In the following description, the output value of the air-fuel ratio sensor 46 may be simply expressed as “sensor output value”.

  As shown in FIG. 2, in any cylinder where the valve overlap period has not arrived and no scavenging has occurred, the exhaust gas generated by the combustion in the rich state is exhausted from the cylinder. The sensor output value becomes rich. On the other hand, when a valve overlap period arrives in any cylinder and scavenging occurs, the mixture of the combustion gas and fresh air is exhausted, so the sensor output value is at least scavenging. It is relatively lean compared to the output value in the absence. Therefore, in a situation where the scavenging generation condition is satisfied, the operation of reversing the sensor output value from rich to lean to rich is repeated every time scavenging occurs in each cylinder in one cycle. In the above description, “lean” means relative lean based on at least “rich”, and does not necessarily mean lean based on the stoichiometric air-fuel ratio.

  3 and 4 are timing charts showing the output value of the air-fuel ratio sensor and the crank signal when the scavenge is not generated and when it is generated. These drawings illustrate the case of a four-cylinder engine. First, when scavenging is not occurring, the exhaust air-fuel ratio fluctuates due to the difference in air-fuel ratio between the cylinders each time an exhaust stroke is performed in each cylinder. As a result, as shown in FIG. 3, the number of peak points P equal to the number of cylinders appears in one cycle in the output waveform of the air-fuel ratio sensor 46. Here, the peak point P is defined as a local maximum point at which the output value of the sensor reverses from an increasing tendency to a decreasing tendency, for example. An increasing trend is a tendency for the sensor output value to increase as the crank angle increases (the tendency for the sensor output waveform to rise to the right), and a decreasing trend is a decrease in the sensor output value as the crank angle increases. The tendency (the tendency of the sensor output waveform to fall to the right). In the present invention, a minimum point where the output value of the air-fuel ratio sensor 46 reverses from a decreasing tendency to an increasing tendency may be used as the peak point P.

  In this way, when scavenging is not occurring, the peak point P appears at a time corresponding to the exhaust stroke of each cylinder, so the number N of peak points P appearing in one cycle is equal to the number of cylinders M of the engine. (N = M). For example, in a four-cylinder engine, the number N of peaks in one cycle is four. On the other hand, when scavenging occurs, as described above, inversion (peak point) of the sensor output value caused by scavenging also appears at the time corresponding to the valve overlap period of each cylinder. That is, when scavenging occurs, as shown in FIG. 4, peak points P appear at the timing corresponding to the valve overlap period and the exhaust stroke of each cylinder, so the number N of peak points in one cycle is It is equal to twice the number M. For example, in a four-cylinder engine, the number N of peak points in one cycle is eight. Therefore, in the scavenge detection control, the number N of peak points in one cycle is measured, and it is determined that scavenging has occurred when the following equation 1 is satisfied.

[Equation 1]
N = M × 2

  Further, the peak point P of the sensor output value is detected by the detection method shown in FIG. FIG. 5 is an explanatory diagram showing an example of a method for detecting the peak point of the sensor output value. As shown in this figure, the ECU 50 calculates the difference between the previous sensor output value and the current sensor output value while reading the sensor output value at a constant calculation cycle. When the difference in sensor output value changes from a positive value to a negative value, this point is detected as a peak point P of the sensor output value, and a counter for counting the peak points is increased. Thereby, the number N of peak points can be measured for each cycle. The counter is cleared to zero every time one cycle elapses. Further, when a minimum point is used as the peak point P, the counter may be incremented when the difference between the sensor output values changes from a negative value to a positive value. Furthermore, the period during which the number N of peak points is measured is not necessarily one cycle, as will be described later.

[Specific Processing for Realizing Embodiment 1]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 6 is a flowchart of control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the engine. In the routine shown in FIG. 6, first, in step 100, the number N of peak points P of sensor output values appearing in one cycle is measured by the method described above. Next, in step 102, it is determined whether or not the number N is equal to twice the number of cylinders (M × 2). If this determination is established, the routine proceeds to step 104 where it is determined that scavenging has occurred. If the determination in step 102 is not established, the process proceeds to step 106, and it is determined that no scavenging has occurred.

  As described above, according to the present embodiment, it is easily determined whether scavenging has occurred based on the relationship between the number N of peak points P appearing in one cycle and the number M of engine cylinders. be able to. In addition, when the peak point P is detected, the output value of the air-fuel ratio sensor 46 is periodically read and the detection is performed based on the difference. Therefore, even if there is an error due to the offset deviation of the output value. This error is canceled when the difference is calculated, and the peak point P can be reliably detected. Further, the output value of the air-fuel ratio sensor 46 is likely to fluctuate depending on the configuration of the exhaust system and the like, but the increasing / decreasing tendency of the sensor output value is stable when the output value fluctuates (offset) as a whole. doing. Therefore, according to the present embodiment, it is possible to accurately and stably detect the occurrence of scavenging without being affected by the configuration of the exhaust system, the deviation of the sensor output value, and the like.

  In the first embodiment, step 100 in FIG. 6 shows a specific example of the peak point detection means, and steps 102 to 106 show a specific example of the scavenge determination means. In the first embodiment, the case where the number N of peak points in one cycle (720 ° C. A) is measured is exemplified. However, an object of the present invention is to detect a state where the number of appearances per peak cycle (appearance frequency) is equal to twice the number of cylinders. Therefore, the measurement period of the number N is not necessarily limited to one cycle, and may be set to an arbitrary period such as 180 ° C. A, 360 ° C. A, or the like. In this configuration, when the ratio of (number N of peak points / measurement period) is equal to the ratio of (twice the number of cylinders M / 1 cycle), it may be determined that scavenging has occurred. For example, in a 4-cylinder engine, when peak points appear at a ratio of (2/180 ° C. A) and (4/360 ° C. A), it may be determined that scavenging has occurred.

  In the first embodiment, a four-cylinder engine has been described as an example. However, the present invention is not limited to this, and can be applied to an engine having a single cylinder and an arbitrary number of cylinders of two or more cylinders. For example, in the case of a 6-cylinder engine, when 12 peak points P per cycle appear, and in the case of an 8-cylinder engine, when 16 peak points P appear per cycle, scavenging occurs. What is necessary is just to determine with a thing.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, in addition to the same configuration and control as in the first embodiment, the scavenge rate (the amount of fresh air blown into the exhaust system by scavenging / the total amount of air in the cylinder) is estimated. Yes. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
FIG. 7 is a timing chart showing the exhaust gas state and the exhaust air / fuel ratio over one cycle when scavenging occurs in the second embodiment of the present invention. As described above, when scavenging occurs (when the scavenging generation condition is satisfied), the output value of the air-fuel ratio sensor 46 indicates that the mixed gas of fresh air and combustion gas blown into the exhaust system is the air-fuel ratio sensor. The air is leaned in a period A (blow-through period) A reaching 46 and enriched in a period B in which only the combustion gas reaches the air-fuel ratio sensor 46 (blow-off stop period) B. Accordingly, the sensor output value changes (vibrates) alternately on the rich side and the lean side.

  Further, for example, when the injected fuel stays in the cylinder as in the case of in-cylinder injection, the air-fuel ratio in the cylinder becomes rich as the scavenging rate increases, and this air-fuel ratio becomes the sensor output during the blow-off stop period B. It is reflected in the value. That is, the sensor output value during the blow-off stop period B becomes richer as the scavenging rate is higher. On the other hand, the mixed gas of the rich combustion gas discharged from the cylinder and the scavenged fresh air becomes relatively lean as the fresh air ratio increases. That is, the sensor output value in the blow-through period A becomes leaner as the scavenging rate is higher.

  Therefore, when scavenging occurs, the amount of change (amplitude) when the sensor output value changes between the adjacent maximum and minimum points is higher as the scavenging rate is higher, as shown in FIGS. There are increasing properties. 8 and 9 are timing charts showing the amount of change in the sensor output value when the scavenging rate is low and when it is high. By paying attention to the above characteristics, in the present embodiment, when the occurrence of scavenging is detected, the scavenging is based on the amount of change when the sensor output value changes between the adjacent maximum and minimum points. The rate is estimated.

Next, the scavenging rate estimation method will be described in detail with reference to FIG. FIG. 10 is a timing chart showing an example of the output value of the air-fuel ratio sensor, the difference between the output values, the product of the differences, and the output amplitude. First, FIG. 10A shows the output value of the air-fuel ratio sensor 46, and FIG. 10B shows the difference between the output values. Here, the n-th output value of the sensor output to be read at a constant calculation period as the X _n, if this the (n-th) the difference between the output value of the previous (n-1 th) and Y _n, The difference Y _n is expressed by the following equation (2).

[Equation 2]
_{Y n = X n -X n-} 1

Further, when the product Z _n of the difference Y _n between the current time and the previous time is defined by the following equation 3, the product Z _n is between output values X _n and X _n−1 as shown in FIG. When there is a local maximum or minimum point, the value is negative. Otherwise, the value is zero or more. That is, the maximum point and minimum point of the sensor output value can be approximately detected as the point at which the product Z _n is a negative value.

[Equation 3]
Z _n = Y _n × Y _n-1

Therefore, in this embodiment, based on the following equation number 4, for example, that the product Z _n is a negative value in the K-th from (n = a), that the product Z _n is a negative value in the K + 1 th ( The difference Y _n up to n = b) is integrated to calculate the output amplitude W. The output amplitude W corresponds to the amount of change when the sensor output value changes between the maximum point and the minimum point adjacent to each other.

[Equation 4]

  As a result, as shown in FIG. 10 (4), the output amplitude W is integrated between the adjacent maximum and minimum points as an integration interval, and cleared to zero at the end of the integration interval. Further, in the present embodiment, the correlation coefficient S between the output amplitude W and the scavenge rate Rs is set in advance based on actual measurement or the like. Therefore, the scavenge rate Rs is calculated by the following equation (5).

[Equation 5]
Rs = W × S

  According to the present embodiment configured as described above, in addition to the effects of the first embodiment, the scavenge rate Rs can be specifically estimated. Thereby, generation | occurrence | production of scavenging can be detected and the control corresponding to scavenging rate Rs can be performed, and the controllability of an engine can be improved. In the second embodiment, the formulas 2 to 5 show specific examples of the estimation means.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIGS. In the present embodiment, in addition to the same configuration and control as in the first embodiment, the feedback operation of the air-fuel ratio control is stopped when the occurrence of scavenging is detected. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 3]
FIG. 11 is a timing chart showing the state of exhaust gas and the exhaust air / fuel ratio over one cycle when scavenging occurs in the third embodiment of the present invention. In the blow-by period A, the mixed gas of combustion gas and fresh air reaches the air-fuel ratio sensor 46, so that the sensor output value basically has a lean tendency. However, the hydrogen component in the combustion gas burned in the rich state has a characteristic that the air-fuel ratio sensor 46 is easily detected. For this reason, even if the actual component ratio of the mixed gas is lean with respect to the stoichiometry, the sensor output value is likely to be rich, and when the time average of the sensor output value is obtained, the average value is calculated as shown in FIG. In some cases, it may shift to the rich side from the true value of. FIG. 12 is a timing chart showing a state where the average value of the sensor output values is shifted to the rich side with respect to the true value of the air-fuel ratio. When such a deviation of the sensor output value occurs, an error also occurs in the feedback control amount by the air-fuel ratio control, and the controllability deteriorates.

  For this reason, in this embodiment, when the occurrence of scavenging is detected by the scavenging detection control, the feedback operation of the air-fuel ratio control is stopped. As a result, it is possible to avoid a decrease in the accuracy of the air-fuel ratio control due to the occurrence of scavenging, and it is possible to maintain the exhaust emission favorably. In the present invention, when the occurrence of scavenging is detected, it is preferable to stop not only the air-fuel ratio control but also other control using the air-fuel ratio (such as air-fuel ratio learning control).

[Specific Processing for Realizing Embodiment 3]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 13 is a flowchart of the control executed by the ECU in the third embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the engine. In the routine shown in FIG. 13, first, in steps 200 and 202, processing similar to that in steps 100 and 102 of the first embodiment (FIG. 6) is executed to determine whether scavenging has occurred.

  If the determination in step 202 is established, scavenging has occurred, so the routine proceeds to step 204, where it is determined whether air-fuel ratio control (feedback operation) is stopped. If the determination in step 204 is established, the air-fuel ratio control is stopped (OFF), so this routine is terminated as it is. On the other hand, if the determination in step 204 is not established, the air-fuel ratio control is being executed (ON), so the routine proceeds to step 206 and the air-fuel ratio control is stopped.

  On the other hand, if the determination in step 202 is not established and it is determined that scavenging has not occurred, the process proceeds to step 208 to determine whether air-fuel ratio control is being executed. If the determination in step 208 is satisfied, the routine is terminated as it is. If the determination in step 208 is not satisfied, the routine proceeds to step 210 and air-fuel ratio control is started.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, in addition to the same configuration and control as in the first embodiment, the deviation amount of the sensor output value described in the third embodiment is quantitatively calculated based on the scavenge rate, and the calculation result The target air-fuel ratio of air-fuel ratio control is corrected based on the above. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 4]
FIG. 14 is a characteristic diagram showing the relationship between the amount of deviation of the output value of the air-fuel ratio sensor and the scavenge rate in Embodiment 4 of the present invention. The characteristic line shown in this figure is obtained based on the data described in the third embodiment (FIG. 12). In the example shown in FIG. 14, the difference between the true value of the air-fuel ratio and the sensor output value is adopted as the deviation amount of the sensor output value, and the output value of the sensor is obtained by averaging the output values over a certain period of time. Is adopted. As shown in FIG. 14, the amount of deviation of the sensor output value is substantially proportional to the scavenge rate, and a primary correlation is established between the two. Therefore, in the present embodiment, the target air-fuel ratio of the air-fuel ratio control is corrected based on the estimated value of the scavenge rate Rs by the following target air-fuel ratio correction control.

(Target air-fuel ratio correction control)
This control is executed when the occurrence of scavenging is detected. First, the scavenging rate Rs is estimated by the estimation method described in the second embodiment or another known estimation method. Then, based on the estimated value of the scavenge rate Rs and a predetermined correlation coefficient AFgap, the deviation amount ΔX of the sensor output value is calculated by the following equation (6). The correlation coefficient AFgap is obtained, for example, as the slope of the characteristic line shown in FIG. 14 (correlation coefficient of the primary correlation), and represents the relationship between the estimated value of the scavenge rate Rs and the deviation amount ΔX of the sensor output value. It corresponds to data and is stored in the ECU 50 in advance. The deviation amount ΔX is defined based on the true value of the exhaust air / fuel ratio as shown in the following equation (7), and is set to a positive value when the sensor output value is shifted to the rich side. The

[Equation 6]
ΔX = Rs × AFgap
[Equation 7]
ΔX = true value of air-fuel ratio-sensor output value

  According to the equation (6), the deviation amount ΔX of the sensor output value can be estimated based on the scavenge rate. Therefore, in the next process, based on the estimated value of the deviation amount ΔX, the target air-fuel ratio AFref of the air-fuel ratio control is corrected by the following formula 8 to calculate the control input target AFreq. Here, the control input target AFreq corresponds to the corrected target air-fuel ratio, and is used as a virtual target air-fuel ratio for matching the sensor output value when the air-fuel ratio control is executed.

[Equation 8]
AFreq = AFref + ΔX

  Next, the effect of the target air-fuel ratio correction control will be described with reference to FIGS. FIG. 15 is an explanatory diagram showing a state in which a deviation of the air-fuel ratio occurs due to scavenging in the air-fuel ratio control of the prior art. FIG. 16 is an explanatory diagram showing a state in which the target air-fuel ratio is corrected according to the scavenge rate by the target air-fuel ratio correction control in the fourth embodiment of the present invention. In the prior art, as shown in FIG. 15, the sensor output value shifts to the rich side due to the occurrence of scavenging. Therefore, if the sensor output value is controlled to coincide with the target air-fuel ratio by air-fuel ratio control, the true value of the air-fuel ratio is The state is shifted to the lean side with respect to the target air-fuel ratio.

  In contrast, in the present embodiment, as shown in FIG. 16, when the occurrence of scavenging is detected, the deviation amount ΔX of the sensor output value can be calculated based on the scavenging rate Rs. Then, the target air-fuel ratio AFref can be corrected by the amount of deviation ΔX, and the control input target AFreq can be calculated. Thereby, in the air-fuel ratio control, feedback control can be performed so that the sensor output value matches the control input target AFreq in which the deviation amount ΔX is reflected. Therefore, the true value of the air-fuel ratio is set to the target air-fuel ratio AFref. Can be matched. Therefore, even when scavenging occurs, the exhaust air-fuel ratio can be stably controlled by air-fuel ratio control, and the disturbance of the exhaust air-fuel ratio and the deterioration of exhaust emission due to scavenging can be suppressed.

  In this embodiment, since the relationship between the scavenging rate Rs and the sensor output value deviation amount ΔX is stored in advance as the correlation coefficient AFgap, the deviation amount ΔX can be easily calculated based on the scavenging rate Rs. Can do. In particular, since it has been found that the relationship between the two is a linear correlation, a data map for calculating a deviation amount is not necessary, and the amount of memory used and the calculation load can be suppressed.

Embodiment 5 FIG.
Next, Embodiment 5 of the present invention will be described with reference to FIGS. In this embodiment, in addition to the same configuration and control as in the first embodiment, the detection accuracy of scavenge is improved by utilizing the deviation of the sensor output value described in the fourth embodiment. Yes. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 5]
As described above, when scavenging occurs, the sensor output value shifts to the rich side. This phenomenon is caused by the presence of unburned fuel around the air-fuel ratio sensor 46. The unburned fuel flows into the catalyst 26 together with fresh air blown into the exhaust system by scavenging, and reacts with oxygen in the fresh air in the catalyst. As a result, the gas flowing out of the catalyst 26 becomes the burned gas in which the combustion of the unburned fuel is almost completed. Therefore, as shown in FIG. 17, the catalyst downstream sensor 48 has the exhaust air / fuel ratio (or the exhaust gas in the exhaust gas). The amount of oxygen) can be accurately calculated.

  FIG. 17 is a characteristic diagram showing the relationship between the deviation amount of the sensor output value and the scavenge rate for each of the air-fuel ratio sensor and the catalyst downstream sensor upstream of the catalyst in the fifth embodiment of the present invention. As described above, the output value of the air-fuel ratio sensor 46 is shifted by an amount corresponding to the scavenge rate, whereas the catalyst downstream sensor 48 has a very small shift amount of the sensor output value caused by scavenging. . For this reason, in the present embodiment, the difference (AF2−AF1) between the output value AF1 of the air-fuel ratio sensor 46 disposed upstream of the catalyst 26 and the output value AF2 of the catalyst downstream sensor 48 is expressed by the following equation (9). If the condition is satisfied, it is determined that scavenging has occurred.

[Equation 9]
AF2-AF1> Ks

  Here, the scavenge determination value Ks is set on the basis of, for example, the maximum value of the difference (AF2-AF1) obtained in a state where no scavenging occurs, and is adjusted in consideration of variations in sensor output values. . FIG. 18 is an explanatory diagram showing the behavior of each sensor output value when scavenging occurs. As shown in this figure, when scavenging occurs, the output value AF1 on the upstream side shifts to the rich side (the output value decreases) according to the scavenging rate, whereas the output value AF2 on the downstream side is Since there is almost no change depending on the presence or absence of scavenging, the difference between the two (AF2−AF1) increases and exceeds the scavenging determination value Ks. Further, the scavenge determination process according to the above formula 9 is used in combination with the determination process (the formula 1) described in the first embodiment. As an example, a configuration may be adopted in which it is finally determined that scavenging has occurred when both equations 1 and 9 are satisfied.

  According to the present embodiment configured as described above, the occurrence of scavenging can be supplementarily detected based on the difference (AF2-AF1) in the sensor output value. Therefore, in addition to the same effect as the first embodiment, the scavenge detection accuracy can be further improved.

Embodiment 6 FIG.
Next, Embodiment 6 of the present invention will be described with reference to FIG. In this embodiment, in addition to the same configuration and control as in the first embodiment, the occurrence of scavenging is detected for each cylinder. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 6]
FIG. 19 is a timing chart showing the exhaust gas state and the exhaust air / fuel ratio over one cycle when scavenging occurs in the sixth embodiment of the present invention. This figure illustrates the case of a four-cylinder engine. Since scavenging is generated according to the balance between the intake pressure and the exhaust pressure, the ease of scavenging is likely to vary among cylinders. This variation between cylinders is caused by differences in the length and volume of the exhaust pipe of each cylinder. In the present embodiment, as shown in FIG. 19, the presence or absence of scavenging is determined for each cylinder based on the output value of the air-fuel ratio sensor 46 and the crank angle signal.

  More specifically, in the example shown in FIG. 19, the exhaust air-fuel ratio becomes rich at the crank angle corresponding to the blow-off stop period B of the cylinders # 1, # 4, and # 2, and corresponds to the blow-through period A of each cylinder. The exhaust air-fuel ratio is leaning at the crank angle. Therefore, it can be determined that scavenging has occurred in these cylinders. On the other hand, since the exhaust air / fuel ratio does not change at the crank angle corresponding to the blowout stop period B and the blowout period A of the # 3 cylinder, it can be determined that scavenging has not occurred in the # 3 cylinder. If the scavenge detection control described in the first embodiment is used in combination with these determination processes, the presence / absence of scavenging in each cylinder can be accurately detected. It is possible to execute appropriate response control.

Embodiment 7 FIG.
Next, a seventh embodiment of the present invention will be described with reference to FIG. In the present embodiment, in addition to the same configuration and control as in the first embodiment, the scavenge rate of the cylinder in which the scavenge has occurred is estimated for each cylinder. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 7]
In the present embodiment, by combining the control described in the second and sixth embodiments, the scavenge rate is estimated for each cylinder based on the change amount (amplitude) of the exhaust air-fuel ratio in each cylinder. The ignition timing of the cylinder is corrected based on the scavenging rate of the cylinder. Hereinafter, specific processing for realizing the above configuration will be described with reference to FIG.

  FIG. 20 is a flowchart of control executed by the ECU in the seventh embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the engine. In the routine shown in FIG. 20, first, in step 300, the exhaust air-fuel ratio amplitude Yx in the Xth cylinder (#X cylinder) is calculated by combining the control described in the second and sixth embodiments. Specifically, the amount of change when the sensor output value changes between the maximum point and the minimum point adjacent to each other at the crank angle corresponding to the #X cylinder is calculated as the amplitude Yx. Note that X indicates a cylinder number (for example, 1 to 4 in a four-cylinder engine).

  Next, in step 302, the scavenge rate Zx of the #X cylinder is calculated. Since a first-order correlation is established between the scavenge rate Zx and the exhaust air-fuel ratio amplitude Yx, the scavenge rate Zx is obtained by multiplying the amplitude Yx by an appropriate sensitivity coefficient K (correlation coefficient). Can do. Next, in step 304, the engine speed Ne and the load KL are obtained based on the output of the sensor system, and in step 306, the reference scavenging rate is obtained by referring to the data map based on these parameters Ne and KL. Zave is calculated. The reference scavenge rate Zave is defined as a reference value of the scavenge rate that does not require correction of the ignition timing, and is set in advance as a two-dimensional data map having parameters Ne and KL as arguments, for example.

  Next, in step 308, a difference Zgap (= Zx−Zave) between the scavenge rate Zx and the reference scavenge rate Zave is calculated, and it is determined whether or not the calculation result is zero. If the determination in step 308 is true, it is not necessary to correct the ignition timing. Therefore, in step 310, the ignition timing correction amount AOPgap is set to zero, and this routine is terminated. If the determination in step 308 is not established, the process proceeds to step 312.

  In step 312, the ignition timing correction coefficient S is calculated by referring to the data map based on the difference Zgap. This data map is preset as, for example, a one-dimensional data map using the difference Zgap as an argument. Subsequently, at step 314, the ignition timing correction amount AOPgap (= Zgap × S) is calculated by multiplying the difference Zgap by the ignition timing correction coefficient S, and this routine is terminated. The ignition timing correction amount AOPgap is reflected in the ignition timing of the #X cylinder. Note that the processing in steps 300 to 314 is executed in all cylinders (X = 1 to the number of cylinders) according to the crank angle.

  According to the present embodiment configured as described above, the following operational effects can be obtained. First, the valve overlap is set large under the operating conditions where scavenging occurs. For this reason, if there is variation among cylinders in the occurrence of scavenging, the internal EGR is almost zero in the scavenging cylinder due to the blow-through of fresh air, whereas in the non-scavenging cylinder, the valve overlap is large. Since no fresh air is blown out, the internal EGR increases. As a result, there is a large difference in the appropriate ignition timing (MBT, TK ignition timing, etc.) between the scavenging cylinder and the non-generating cylinder even if the amount of air flowing into the cylinder is equal. In contrast, in the present embodiment, since the scavenging rate can be estimated for each cylinder, the ignition timing can be optimized for each cylinder according to the scavenging state of each cylinder. Therefore, it is possible to correct the optimum ignition timing shift caused by the variation in the internal EGR between cylinders, and to improve the fuel consumption and torque.

  In the first to seventh embodiments, each configuration has been described individually. However, the present invention is not limited to this, and any two or more configurations that can be combined in the first to seventh embodiments are combined. In total, one system may be configured. In the embodiment, a four-cylinder engine has been described as an example. However, the present invention is not limited to this, and is applicable to an engine having an arbitrary number of cylinders including six cylinders and eight cylinders.

10 Engine (Internal combustion engine)
12 Piston 14 Combustion chamber 16 Crankshaft 18 Intake passage 20 Exhaust passage 22 Throttle valve 24 Intercooler 24
26 Catalyst 28 Fuel Injection Valve 30 Spark Plug 32 Intake Valve 34 Exhaust Valve 36 Supercharger 38 Waste Gate Valve 40 Crank Angle Sensor 42 Air Flow Sensor 44 Intake Pressure Sensor 46 Air Fuel Ratio Sensor 48 Catalyst Downstream Sensor 50 ECU (Detection Device)

Claims (5)

An air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine for detecting an exhaust air-fuel ratio;
A detection device that detects the occurrence of scavenging based on the output value of the air-fuel ratio sensor,
The detection device includes:
A peak that detects one predetermined point as a peak point among a maximum point where the output value of the air-fuel ratio sensor reverses from an increasing tendency to a decreasing tendency and a minimum point where the output value reverses from a decreasing tendency to an increasing tendency Point detection means;
Scavenge determination means for determining whether or not scavenge has occurred based on the relationship between the number of peak points appearing in one cycle of the internal combustion engine and the number of cylinders of the internal combustion engine;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the scavenging determination unit determines that scavenging has occurred when the number of appearances per cycle of the peak point is twice the number of cylinders.   Claims comprising estimation means for estimating the scavenge rate based on the amount of change when the output value of the air-fuel ratio sensor changes between a maximum point and a minimum point adjacent to each other when occurrence of scavenging is detected. Item 3. The control device for an internal combustion engine according to Item 1 or 2. An estimation means for estimating a scavenge rate based on an amount of change when the output value of the air-fuel ratio sensor changes between a maximum point and a minimum point adjacent to each other when occurrence of scavenging is detected;
When air-fuel ratio control is executed to feedback-control the exhaust air-fuel ratio so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio, the target air-fuel ratio is based on the estimated value of the scavenging rate. Correction means for correcting the fuel ratio;
The control device for an internal combustion engine according to claim 1, comprising:   The correction means has data representing the relationship between the deviation amount of the output value of the air-fuel ratio sensor with respect to the true value of the exhaust air-fuel ratio and the estimated value of the scavenge rate, and the data and the estimated value of the scavenge rate, The control apparatus for an internal combustion engine according to claim 4, wherein the target air-fuel ratio is corrected based on a deviation amount of the output value calculated by the equation (5).

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