JP6379683B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  For example, Patent Document 1 discloses a phase spectrum (Phase 2) obtained by changing the fuel injection amount of a specific cylinder of an internal combustion engine and performing frequency analysis on a detection signal detected by an air-fuel ratio sensor upstream of the catalyst in the exhaust passage. ) And a power spectrum (Power 2), it is disclosed that the response deterioration of the air-fuel ratio sensor is detected.

JP 2008-185035 A

  However, in such Patent Document 1, the phase spectrum (Phase2) and the power spectrum (Power2) are calculated from the detection value of the air-fuel ratio sensor only for detecting the response deterioration of the air-fuel ratio sensor. The second frequency component calculation unit is necessary, and the manufacturing cost may increase accordingly.

The control apparatus for an internal combustion engine according to the present invention comprises an imbalance detecting means capable of detecting an exhaust air / fuel ratio imbalance between cylinders from an amplitude and phase of the exhaust air / fuel ratio detected by an air / fuel ratio sensor during a predetermined sampling period. The amplitude of the detection signal detected by the air-fuel ratio sensor while the fuel injection amount of one cylinder among all the cylinders is continuously increased for a predetermined period from the fuel injection amount of the other cylinders by a predetermined amount Is greater than or equal to a predetermined value, and the detection signal detected by the air-fuel ratio sensor is less than the predetermined value with respect to the arrival timing of the exhaust gas from the cylinder where the fuel is increasing, the air-fuel ratio sensor is normal. a fuel ratio sensor diagnosing means for determining that there is a air-fuel ratio feedback control execution means for exhaust air-fuel ratio detected by the air-fuel ratio sensor is performed a feedback control so that the target air-fuel ratio, the upper During fuel increase by the fuel increase control means stops the feedback control of the air-fuel ratio. Then, after the diagnosis by the air-fuel ratio sensor diagnostic means is sequentially performed on all the cylinders, it is determined whether or not the air-fuel ratio sensor is normal. The target air-fuel ratio fixed at a predetermined value during the fuel increase may be canceled after a predetermined time has elapsed after the fuel increase is completed.

  According to the present invention, the failure diagnosis of the air-fuel ratio sensor can be performed using the imbalance detection means, and the presence or absence of the failure of the air-fuel ratio sensor can be accurately determined without causing an increase in manufacturing cost.

The system block diagram of the control apparatus of the internal combustion engine which concerns on this invention. The block diagram which shows the outline | summary of control of an internal combustion engine. Explanatory drawing which showed typically the peak timing and amplitude of the exhaust air fuel ratio at the time of active pulse implementation. The map figure used for the failure diagnosis of an air fuel ratio sensor. Timing chart when active pulse is performed. The flowchart which shows the flow of control of the internal combustion engine in 1st Example. The flowchart which shows the flow of control of the internal combustion engine in 2nd Example. Explanatory drawing which shows an example of the fluctuation | variation of the exhaust air fuel ratio in a state without imbalance. It is explanatory drawing which shows an example of the fluctuation | variation of the exhaust air-fuel ratio in a state with imbalance, Comprising: (a) shows the case where the fuel injection amount of the cylinder without imbalance is increased, (b) shows the cylinder with imbalance This shows a case where the fuel injection amount is increased. It is explanatory drawing which shows an example of the fluctuation | variation of the exhaust air fuel ratio in a state with imbalance, Comprising: (a) shows the case where the fuel injection amount of the cylinder with imbalance is increased, (b) shows the cylinder without imbalance This shows a case where the fuel injection amount is increased.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system configuration diagram showing a control device for an internal combustion engine 1 according to the present invention.

  An intake passage 4 is connected to the combustion chamber 2 of the internal combustion engine 1 via an intake valve 3, and an exhaust passage 6 is connected via an exhaust valve 5.

  The intake passage 4 is provided with an air flow meter 7 for detecting an intake flow rate (intake air amount), and an electronic control type whose opening degree is controlled by an ECU (engine control unit) 9 via an actuator 8 by a control signal. The throttle valve 10 is arranged. The throttle valve 10 is integrally provided with a throttle sensor 11 that detects the opening degree of the throttle valve 10 (throttle opening degree), and the throttle opening degree is closed-loop controlled to the target opening degree based on the detection signal. .

  A catalyst converter 13 for purifying exhaust gas is provided in the exhaust passage 6 on the downstream side of the exhaust manifold 12 that collects the exhaust of each cylinder.

  A first air-fuel ratio sensor 14 that detects the air-fuel ratio of the exhaust gas in the exhaust passage 6 is provided upstream of the catalytic converter 13. The first air-fuel ratio sensor 14 is a wide area type air-fuel ratio sensor that can obtain an output corresponding to the value of the air-fuel ratio.

  A second air-fuel ratio sensor 15 that detects the air-fuel ratio of the exhaust gas in the exhaust passage 6 is provided downstream of the catalytic converter 13. The second air-fuel ratio sensor 15 is an oxygen sensor that detects only rich and lean air-fuel ratios. As the second air-fuel ratio sensor 15, the above-described wide-range air-fuel ratio sensor can be used.

  A spark plug 16 is disposed on the top of the combustion chamber 2. A fuel injection valve 17 that directly injects fuel into the combustion chamber 2 is disposed on the side of the combustion chamber 2 on the intake passage 4 side.

  Further, the internal combustion engine 1 includes a crank angle sensor 18 for detecting the engine rotational speed and the crank angle position, an accelerator opening sensor 19 for detecting an opening (depression amount) of an accelerator pedal operated by a driver, Various sensors such as a water temperature sensor 20 for detecting the cooling water temperature of the internal combustion engine 1 and a vehicle speed sensor 21 for detecting the vehicle speed are provided.

  Detection signals from various sensors such as the air flow meter 7 and the crank angle sensor 18 are input to the ECU 9. The ECU 9 includes a microcomputer that includes a CPU, a ROM, a RAM, and the like. The ECU 9 controls the injection amount and injection timing of the fuel injection valve 17, the ignition timing by the ignition plug 16, the throttle opening degree, and the like based on the detection signals from the various sensors described above, and the exhaust air-fuel ratio between the cylinders. The fuel injection amount feedback control (cylinder-by-cylinder air-fuel ratio feedback control) is carried out for each cylinder in order to reduce the variation of the cylinder.

  In the cylinder-by-cylinder air-fuel ratio feedback control, the fuel injection amount is controlled for each cylinder so that the variation in the exhaust air-fuel ratio between the cylinders becomes small. That is, using the detection value of the crank angle sensor 18, the exhaust air-fuel ratio is detected at the timing when the exhaust from each cylinder reaches the position of the first air-fuel ratio sensor 14 located downstream of the collection portion of the exhaust manifold 12, and the cylinder The fuel injection amount of each cylinder is individually controlled so that the variation in the exhaust air-fuel ratio is reduced. By the cylinder-by-cylinder air-fuel ratio feedback control, the internal combustion engine 1 is controlled so that the average value of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 as a whole becomes close to the target air-fuel ratio.

  FIG. 2 is a block diagram showing an outline of control of the internal combustion engine 1 in the present embodiment.

  In S1, the cylinder intake air amount is calculated based on the detected value of the air flow meter 7. In S2, the rotational speed of the internal combustion engine 1 is calculated based on the detection value of the crank angle sensor 18. In S3, the crank angle of the crankshaft is calculated based on the detected value of the crank angle sensor 18.

  In S4, the timing at which the exhaust of each cylinder reaches the position of the first air-fuel ratio sensor 14 is calculated using the cylinder intake air amount calculated in S1 and the engine speed calculated in S2, and the exhaust of each cylinder is calculated. The sample timing for detecting the air-fuel ratio is calculated.

  In S5, it is determined whether a permission condition for performing cylinder-by-cylinder air-fuel ratio feedback control (cylinder-by-cylinder A / FF / B) is satisfied. The cylinder-by-cylinder air-fuel ratio feedback control is permitted when the first air-fuel ratio sensor 14 is determined to be normal after execution of an active pulse (details will be described later). When the permission condition for performing the cylinder-by-cylinder air-fuel ratio feedback control is satisfied, S6 to S8 are performed, and a cylinder-by-cylinder F / B correction amount to be described later is calculated.

  Here, the active pulse in the present specification means a fuel corresponding to enrich the exhaust air / fuel ratio of a predetermined cylinder among all cylinders of the internal combustion engine 1 as compared with the exhaust air / fuel ratio of other cylinders. It is to change the fuel injection pulse of the injection valve 17. By performing the active pulse, the fuel injection amount of a predetermined cylinder among all the cylinders of the internal combustion engine 1 is continuously increased by a predetermined amount for a predetermined period of time than the fuel injection amount of the other cylinders. . That is, when the active pulse is performed, the target fuel injection amount of one predetermined cylinder is increased by a predetermined amount from the target fuel injection amount of the other cylinders continuously for a predetermined period.

  In S6, the exhaust air-fuel ratio (A / F) of each cylinder is detected from the detection value of the first air-fuel ratio sensor 14 at the timing calculated in S4. In S7, an exhaust air-fuel ratio deviation (A / F deviation), which is the difference between the exhaust air-fuel ratio of each cylinder and its average value, is calculated for each cylinder. In S8, the fuel injection amount correction amount (cylinder F / B correction amount) is calculated for each cylinder so that the exhaust air-fuel ratio deviation (A / F deviation) of each cylinder calculated in S7 is reduced. As a result of correcting the fuel injection amount for each cylinder by the correction amount of the fuel injection amount for each cylinder (F / B correction amount for each cylinder), the entire internal combustion engine 1 is detected by the first air-fuel ratio sensor 14. The average value of the exhaust air / fuel ratio is controlled to be close to the theoretical air / fuel ratio. That is, the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 is controlled to be the stoichiometric air-fuel ratio by correcting the fuel injection amount using the cylinder-specific F / B correction amount for each cylinder.

  Here, S5 to S8 correspond to cylinder-by-cylinder air-fuel ratio feedback control execution means. This cylinder-by-cylinder air-fuel ratio feedback control executing means can detect the exhaust air-fuel ratio imbalance between the cylinders from the amplitude and phase of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 during a predetermined sampling period. This corresponds to imbalance detection means. Further, the cylinder-by-cylinder air-fuel ratio feedback control execution means controls the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 to be the target air-fuel ratio, and corresponds to the air-fuel ratio feedback control execution means. is there.

  In S9, the fuel injection amount for each cylinder is calculated using the calculated correction amount of the F / B correction amount for each cylinder calculated in S8 or the active pulse correction amount described later. The fuel injection valve 17 of each cylinder injects fuel by the fuel injection amount calculated in S9.

  In S10, it is determined whether or not an active pulse permission condition is satisfied. The active pulse permission condition is, for example, an active pulse when the engine speed is in a predetermined speed range, the operating state of the internal combustion engine 1 is in a predetermined load range, and the coolant temperature is equal to or higher than a predetermined temperature. It is determined that the permission condition is satisfied.

  Specifically, the engine speed is between a predetermined upper limit speed R1 and a predetermined lower limit speed R2, and the fuel injection time (fuel injection amount) of the fuel injection valve 17 is set in advance. Is determined between the upper limit injection time T1 and the lower limit injection time T2 and the cooling water temperature is equal to or higher than the preset temperature D1. If the active pulse has already been performed after the start of the internal combustion engine 1 and the failure diagnosis of the first air-fuel ratio sensor 14 has been completed (when the active pulse has been completed), the next time even if the active pulse permission condition is satisfied. The active pulse is not executed until the next operation (after the start by the key-on operation by the next driver).

  In S11, a target air-fuel ratio is calculated. During the execution of the active pulse, the target air-fuel ratio is fixed to the stoichiometric air-fuel ratio. When the execution of the active pulse is completed, the fixed target air-fuel ratio to the stoichiometric air-fuel ratio is released after several cycles have elapsed from the end of the active pulse (two rotations of the crankshaft are defined as one cycle). That is, the fixed target air-fuel ratio to the stoichiometric air-fuel ratio is released after a predetermined time has elapsed after the end of the active pulse.

  In S12, a feedback correction coefficient at the time of feedback control is calculated so that the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 becomes the target air-fuel ratio. During the execution of the active pulse, the feedback correction coefficient is fixed to “1 (100%)” or the feedback correction coefficient immediately before the execution of the active pulse. That is, during the execution of the active pulse, the exhaust air / fuel ratio feedback control is stopped such that the exhaust air / fuel ratio detected by the first air / fuel ratio sensor 14 becomes the target air / fuel ratio. In this embodiment, the feedback correction coefficient is fixed to “1 (100%)” during the execution of the active pulse. The exhaust air / fuel ratio feedback control is resumed simultaneously with the end of the active pulse. That is, the feedback correction coefficient is unfixed simultaneously with the end of the active pulse.

  In this way, the target air-fuel ratio is released from being fixed to the stoichiometric air-fuel ratio after a few cycles have elapsed since the end of the active pulse, and the feedback correction coefficient is released immediately after the end of the active pulse. The amplitude of the exhaust air / fuel ratio can be quickly converged after the active pulse ends.

  Further, by fixing the feedback correction count when the active pulse is performed, it is possible to prevent a decrease in the detectability of the exhaust air / fuel ratio waveform detected by the first air / fuel ratio sensor 14.

  In S13, an active pulse correction amount is calculated. The active pulse correction amount is a correction coefficient for increasing and correcting the fuel injection amount of the active pulse execution cylinder, and is set in advance as a predetermined constant.

  In S14, the phase and amplitude of the rich / lean peak of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 during the execution of the active pulse are detected. Here, the rich / lean peak phase and amplitude of the exhaust air-fuel ratio in S14 are detected using the processing functions used in S6 and S7 described above.

  More specifically, as shown in FIG. 3, the exhaust air-fuel ratio lean peak (maximum value) and rich peak (minimum value) detected by the first air-fuel ratio sensor 14 for a predetermined number of cycles after the start of the active pulse. Detect the phase and magnitude. By performing the active pulse, the exhaust air-fuel ratio of the cylinder in which the fuel injection amount is increased becomes relatively rich, and the exhaust air-fuel ratio characteristics detected by the first air-fuel ratio sensor 14 are shown in FIG. 3 as a whole. Thus, the waveform vibrates at a predetermined cycle.

  Further, the rich peak timing and the lean peak timing that are average values of the exhaust air / fuel ratio peak timing during a predetermined number of cycles, and the A / F amplitude that is the average value of the exhaust air / fuel ratio amplitude during a predetermined number of cycles, Is calculated. The A / F amplitude is an average value of the difference between AF1 and AFr.

  It should be noted that the exhaust gas air-fuel ratio detection value waveform detected by the first air-fuel ratio sensor 14 is unstable in several cycles immediately after the execution of the active pulse. Data for calculating peak timing, lean peak timing, and A / F amplitude is not taken.

  In S15, failure diagnosis of the first air-fuel ratio sensor 14 is performed using the rich peak timing, lean peak timing, and A / F amplitude detected in S14.

  Specifically, as shown in FIG. 4, the rich peak timing and the lean peak timing detected in S14 are within a range of ± 90 deg CA with respect to a predetermined median value, and the A / F amplitude detected in S14 is When it is equal to or greater than the predetermined amplitude determination threshold, it is determined that the first air-fuel ratio sensor 14 is normal. When one of the rich peak timing and the lean peak timing is outside the range of ± 90 degCA with respect to the predetermined median value, or when the A / F amplitude is smaller than the predetermined amplitude determination threshold, the first air-fuel ratio It is determined that the sensor 14 is abnormal.

  That is, S10 to S15 are air-fuel ratio sensor diagnostic means for performing failure diagnosis of the first air-fuel ratio sensor 14, and whether or not the first air-fuel ratio sensor 14 is in a state in which the cylinder-by-cylinder air-fuel ratio feedback control is executable Determine.

  The rich peak timing median and lean peak timing median are fixed values that are calculated in advance using, for example, the median of the permitted range of engine speed and fuel injection amount, which are active pulse permission conditions.

  The amplitude determination threshold value is an amplitude value that is detected when the exhaust air-fuel ratio between the cylinders is in a predetermined imbalance state and the output value of the first air-fuel ratio sensor 14 is the lower limit value of variation during production. It is a fixed value calculated in advance.

  The failure diagnosis of the first air-fuel ratio sensor 14 is performed only when the active pulse is continuously performed a predetermined number of times. In other words, when the active pulse permission condition is not satisfied before the active pulse is executed a predetermined number of times (the required number of times of active), the active pulse is not completed, and the failure diagnosis of the first air-fuel ratio sensor 14 is performed. Not implemented.

  FIG. 5 is a timing chart showing an example when the active pulse is performed in the present embodiment.

  After the internal combustion engine is started, the active pulse permission condition described above is satisfied at the timing of time t1, and the active pulse is started.

  At the timing of time t2, the active pulse permission condition is not satisfied, and the active pulse ends. Between time t1 and time t2, since the number of active pulses has not reached the required number of active times, failure diagnosis of the first air-fuel ratio sensor 14 using rich peak timing, lean peak timing, and A / F amplitude is not performed. . The active pulse normality determination variable indicating the failure diagnosis result of the first air-fuel ratio sensor 14 is “1” when the failure diagnosis result is normal, and is “0” when the failure diagnosis is not completed or the failure diagnosis result is abnormal. It has become.

  Since the diagnosis of the air-fuel ratio sensor by the active pulse is performed every time the internal combustion engine 1 is started, the MIL lamp is not turned on until the diagnosis is confirmed, and the cylinder-by-cylinder air-fuel ratio feedback control is not performed.

  When the above-described active pulse permission condition is satisfied again at the timing of time t3, the active pulse is started again.

  When the number of active pulses reaches the required number of times at the timing of time t4, the active pulses are terminated and a failure diagnosis of the first air-fuel ratio sensor 14 is performed. In this example, the A / F amplitude detected between time t3 and time t4 is equal to or greater than the amplitude determination threshold and is not shown in FIG. 5, but is detected between time t3 and time t4. Since the rich peak timing and the lean peak timing are within the range of ± 90 degCA with respect to the predetermined median value, the active pulse normality determination variable is switched from “0” to “1” at the timing of time t4.

  As described above, in this embodiment, the failure diagnosis of the first air-fuel ratio sensor 14 is performed by performing the active pulse on a predetermined one cylinder of the internal combustion engine 1.

  Note that, at time t1 to time t2 and from time t3 to time t4, the active pulse is applied to the predetermined cylinder, so that the feedback correction coefficient (ALPHA) and the target air-fuel ratio (TGABFE) are fixed to predetermined values, respectively. Is done.

  FIG. 6 is a flowchart showing a flow of control of the internal combustion engine 1 in the present embodiment. In S21, it is determined whether or not the internal combustion engine 1 is in operation. If the internal combustion engine 1 is in operation, the process proceeds to S22. In S22, it is determined whether or not the active pulse has been completed, that is, whether or not the failure diagnosis of the first air-fuel ratio sensor 14 has been completed. If the active pulse has not been completed and the failure diagnosis of the first air-fuel ratio sensor 14 has not been completed, the process proceeds to S23, and if not, the process proceeds to S27. In S23, it is determined whether or not an active pulse permission condition is satisfied. If the permission condition is satisfied, the process proceeds to S24. In S24, an active pulse is performed on one predetermined cylinder of the internal combustion engine 1. In S25, it is determined whether or not the fuel injection increased by the active pulse has been continuously performed a predetermined number of times. If it has been performed the predetermined number of times, the process proceeds to S26, and if not, the process proceeds to S23. In S26, the failure determination of the first air-fuel ratio sensor 14 is performed. If it is determined in S26 that the first air-fuel ratio sensor 14 is normal, the process proceeds to S27, and if it is determined that there is an abnormality, the process proceeds to S30. In S27, cylinder-by-cylinder air-fuel ratio feedback control is performed. In S28, an imbalance amount with respect to the target air-fuel ratio of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 is calculated for each cylinder of the internal combustion engine 1. In S29, it is determined whether or not the imbalance amount of each cylinder calculated in S28 is larger than a preset threshold value. If any one of the imbalance amounts of each cylinder is larger than the threshold value, the process proceeds to S30, and if not, the process proceeds to S31. In S30, a warning lamp (MIL) is turned on. On the other hand, in S31, the warning lamp (MIL) is not turned on.

  As described above, the internal combustion engine 1 according to the present embodiment performs the cylinder-by-cylinder air-fuel ratio feedback control, and uses the processing function used when the cylinder-by-cylinder air-fuel ratio feedback control is performed. Failure diagnosis of the first air-fuel ratio sensor 14 necessary for feedback control can be performed.

  In other words, in this embodiment, it is possible to perform failure diagnosis of the first air-fuel ratio sensor 14 on the upstream side of the catalytic converter 13 by using the existing cylinder-by-cylinder air-fuel ratio feedback control execution means, which increases the manufacturing cost. The presence or absence of failure of the first air-fuel ratio sensor 14 can be accurately determined without incurring.

  Further, the second upstream side of the catalytic converter 13 is not considered without considering the exhaust air / fuel ratio (the detected value of the second air / fuel ratio sensor 15) on the downstream side of the catalytic converter 13 which changes depending on the state of the catalytic converter 13 (whether it is deteriorated or activated). Since the failure diagnosis of the first air-fuel ratio sensor 14 can be performed, the failure diagnosis of the first air-fuel ratio sensor 14 upstream of the catalytic converter 13 is performed using the detection signal of the second air-fuel ratio sensor 15 downstream of the catalytic converter 13 In comparison with this, it is possible to accurately determine whether or not the first air-fuel ratio sensor 14 has failed.

  In the first embodiment described above, active pulses are performed only on one of all cylinders of the internal combustion engine 1 to determine whether or not the first air-fuel ratio sensor 14 has failed. It is also possible to sequentially apply active pulses to the cylinders in all the engines 1 and determine whether or not the first air-fuel ratio sensor 14 has failed based on the result.

  FIG. 7 is a flowchart showing a control flow of the internal combustion engine 1 in the second embodiment. In S41, it is determined whether or not the internal combustion engine 1 is in operation. If the internal combustion engine 1 is in operation, the process proceeds to S42. In S42, it is determined whether or not the active pulse has been completed, that is, whether or not the failure diagnosis of the first air-fuel ratio sensor 14 has been completed. If the active pulse has not been completed and the failure diagnosis of the first air-fuel ratio sensor 14 has not been completed, the process proceeds to S43, and if not, the process proceeds to S49. In S43, one of the cylinders of the internal combustion engine 1 for which no active pulse is performed is selected. In S44, it is determined whether or not an active pulse permission condition is satisfied. If the permission condition is satisfied, the process proceeds to S45. In S45, an active pulse is performed on the cylinder (#n cylinder) selected in S43. In S46, it is determined whether or not the fuel injection increased by the active pulse has been continuously performed a predetermined number of times for the currently selected cylinder. If the predetermined number of times has been performed, the process proceeds to S47. The process proceeds to S44. In S47, it is determined whether or not active pulses have been performed on all the cylinders of the internal combustion engine 1. If active pulses are not performed for all cylinders, the process proceeds to S43, and if active pulses are performed for all cylinders, the process proceeds to S48. In S48, failure determination of the first air-fuel ratio sensor 14 is performed. If it is determined in S48 that the first air-fuel ratio sensor 14 is normal, the process proceeds to S49, and if it is determined that there is an abnormality, the process proceeds to S52. In S49, cylinder-by-cylinder air-fuel ratio feedback control is performed. In S50, an imbalance amount with respect to the target air-fuel ratio of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 is calculated for each cylinder of the internal combustion engine 1. In S51, it is determined whether or not the imbalance amount of each cylinder calculated in S50 is larger than a preset threshold value. If at least one of the imbalance amounts of each cylinder is larger than the threshold value, the process proceeds to S52, and if not, the process proceeds to S53. In S52, a warning lamp (MIL) is turned on. On the other hand, in S53, the warning lamp (MIL) is not turned on.

  An example in which the internal combustion engine 1 is an in-line four cylinder will be described in detail. When there is no imbalance between the cylinders of the internal combustion engine 1, the exhaust air / fuel ratio detected by the first air / fuel ratio sensor 14 before the active pulse is not greatly changed as shown in FIG. On the other hand, when the active pulse is performed, the exhaust air-fuel ratio fluctuates so as to become the richest at the timing when the exhaust of the # 1 cylinder reaches. Therefore, failure diagnosis of the first air-fuel ratio sensor 14 can be performed using the peak timing of the exhaust air-fuel ratio and the A / F amplitude. Therefore, when there is no imbalance between the cylinders of the internal combustion engine 1, it is possible to determine whether or not the first air-fuel ratio sensor 14 has failed by performing an active pulse on one cylinder of the internal combustion engine 1.

  When the # 1 cylinder of the internal combustion engine 1 has an imbalance of -20% (when the fuel injection amount of the other cylinder is 100% and the fuel injection amount of the # 1 cylinder is 80%), FIG. As shown, the exhaust air-fuel ratio before the active pulse is detected detected by the first air-fuel ratio sensor 14 fluctuates so as to become the leanest when the exhaust of the # 1 cylinder reaches. When the active pulse for increasing the fuel injection amount by 20% is performed on the # 1 cylinder, the imbalance of the # 1 cylinder is canceled and the fluctuation of the exhaust air / fuel ratio detected by the first air / fuel ratio sensor 14 is almost eliminated. End up. Therefore, when the active pulse is applied to the cylinder having the invaras, the exhaust air / fuel ratio characteristic detected by the first air / fuel ratio sensor 14 becomes linear, so that the A / F amplitude is larger than the amplitude determination threshold value. As a result of failure diagnosis, it is determined that the first air-fuel ratio sensor 14 has a response deterioration.

  However, when the # 1 cylinder of the internal combustion engine 1 has an imbalance of -20%, when an active pulse for increasing the fuel injection amount by 20% is performed for the # 4 cylinder, as shown in FIG. Therefore, the fluctuation of the exhaust air-fuel ratio detected by the first air-fuel ratio sensor 14 becomes larger than before the active pulse is performed, and the exhaust air-fuel ratio of the # 4 cylinder becomes richer than before the active pulse is performed. Therefore, when the active pulse is performed on the cylinders other than the cylinder having the negative impulse, if the first air-fuel ratio sensor 14 is normal, the A / F amplitude becomes larger than the amplitude determination threshold value. Therefore, it is correctly determined that the first air-fuel ratio sensor 14 is normal.

  Further, when the # 4 cylinder of the internal combustion engine 1 has an imbalance of + 20% (when the fuel injection amount of the # 4 cylinder is 120% when the fuel injection amount of the other cylinder is 100%), FIG. ), The exhaust air-fuel ratio before active pulse detection detected by the first air-fuel ratio sensor 14 fluctuates so as to become the richest at the timing when the exhaust of the # 4 cylinder arrives. When an active pulse for increasing the fuel injection amount by 20% is performed on the # 1 cylinder, the exhaust air-fuel ratio becomes rich at the timing when the exhaust from the # 1 cylinder arrives, and the timing when the exhaust from the # 4 cylinder arrives But the exhaust air-fuel ratio becomes richer. Therefore, since the exhaust air-fuel ratio characteristic detected by the first air-fuel ratio sensor 14 has a lump-like waveform that becomes an extreme value on the rich side when the exhaust of the # 1 cylinder and the # 4 cylinder arrives, The peak timing of the air-fuel ratio deviates from the range within ± 90 deg CA with respect to the predetermined median value, and as a result of failure diagnosis, it is determined that the first air-fuel ratio sensor 14 has a phase shift failure.

  However, when the # 4 cylinder of the internal combustion engine 1 has an imbalance of + 20%, if an active pulse for increasing the fuel injection amount by 20% is performed on the # 4 cylinder, as shown in FIG. The fluctuation of the exhaust air / fuel ratio detected by the first air / fuel ratio sensor 14 becomes larger than before the execution of the active pulse, and the exhaust air / fuel ratio of the # 4 cylinder becomes richer than before the execution of the active pulse. Therefore, when an active pulse is performed on a cylinder with a positive impulse, if the first air-fuel ratio sensor 14 is normal, the peak timing of the exhaust air-fuel ratio is within ± 90 deg CA with respect to a predetermined median value. Therefore, as a result of the failure diagnosis, it is correctly determined that the first air-fuel ratio sensor 14 is normal.

  Therefore, the active pulses are sequentially applied to all the cylinders, and an overall balance is determined from each failure diagnosis result at the time of executing each active pulse, whereby an imbalance occurs between the cylinders of the internal combustion engine 1. However, the presence or absence of failure of the first air-fuel ratio sensor 14 can be accurately determined.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust valve 6 ... Exhaust passage 7 ... Air flow meter 9 ... ECU
12 ... Exhaust manifold 13 ... Catalytic converter 14 ... First air-fuel ratio sensor

Claims (3)

An air-fuel ratio sensor that is located downstream of the exhaust manifold portion of the exhaust manifold and detects the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst;
An exhaust arrival timing calculating means capable of individually calculating the timing at which the exhaust from each cylinder reaches the air-fuel ratio sensor;
Imbalance detection means capable of detecting an exhaust air / fuel ratio imbalance between cylinders from the amplitude and phase of the exhaust air / fuel ratio detected by the air / fuel ratio sensor during a predetermined sampling period;
Fuel increase control means for increasing the fuel injection amount of one cylinder among all the cylinders by a predetermined amount continuously from the fuel injection amount of other cylinders when a predetermined permission condition is satisfied;
Air-fuel ratio fixing means for fixing the target air-fuel ratio during fuel increase by the fuel increase control means to a predetermined value;
Using the imbalance detection means, the amplitude of the detection signal detected by the air-fuel ratio sensor becomes a predetermined value or more during the fuel increase by the fuel increase control means, and the phase of the detection signal detected by the air-fuel ratio sensor An air-fuel ratio sensor diagnosing means for determining that the air-fuel ratio sensor is normal when the deviation is equal to or less than a predetermined value with respect to the arrival timing of the exhaust from the cylinder in which the fuel is increasing;
Air-fuel ratio feedback control execution means for performing feedback control so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor becomes the target air-fuel ratio,
During fuel increase by the fuel increase control means, the air-fuel ratio feedback control is stopped,
An internal-combustion-engine control apparatus characterized by determining whether or not the air-fuel ratio sensor is normal after sequentially performing diagnosis by the air-fuel ratio sensor diagnostic means for all cylinders . An air-fuel ratio sensor that is located downstream of the exhaust manifold portion of the exhaust manifold and detects the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst;
An exhaust arrival timing calculating means capable of individually calculating the timing at which the exhaust from each cylinder reaches the air-fuel ratio sensor;
Imbalance detection means capable of detecting an exhaust air / fuel ratio imbalance between cylinders from the amplitude and phase of the exhaust air / fuel ratio detected by the air / fuel ratio sensor during a predetermined sampling period;
Fuel increase control means for increasing the fuel injection amount of one cylinder among all the cylinders by a predetermined amount continuously from the fuel injection amount of other cylinders when a predetermined permission condition is satisfied;
Air-fuel ratio fixing means for fixing the target air-fuel ratio during fuel increase by the fuel increase control means to a predetermined value;
Using the imbalance detection means, the amplitude of the detection signal detected by the air-fuel ratio sensor becomes a predetermined value or more during the fuel increase by the fuel increase control means, and the phase of the detection signal detected by the air-fuel ratio sensor An air-fuel ratio sensor diagnosing means for determining that the air-fuel ratio sensor is normal when the deviation is equal to or less than a predetermined value with respect to the arrival timing of the exhaust from the cylinder in which the fuel is increasing
Air-fuel ratio feedback control execution means for performing feedback control so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor becomes the target air-fuel ratio,
  During fuel increase by the fuel increase control means, the air-fuel ratio feedback control is stopped,
The control apparatus for an internal combustion engine, wherein the air-fuel ratio fixing means releases the fixation of the target air-fuel ratio after a predetermined time has elapsed after the fuel increase by the fuel increase control means is completed. 3. The control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control executing means restarts the air-fuel ratio feedback control simultaneously with completion of fuel increase by the fuel increase control means.

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