JP2009013991A - Malfunction detection device for air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably detect malfunction of responsiveness of an air-fuel ratio sensor. <P>SOLUTION: The air-fuel ratio sensor 32 is arranged in an exhaust pipe 24 of an engine 10. An ECU 40 calculates an air-fuel ratio correcting amount for matching an air-fuel ratio detected value detected from an air-fuel ratio sensor signal with a target value. Variation data of the air-fuel ratio detected value to a rich side and to a lean side are calculated and variation data of the air-fuel correcting amount to a rich side and to a lean side are calculated. In accordance with the variation data of the calculated air-fuel ratio detected value to the rich side and to the lean side and the variation data of the calculated air-fuel ratio correcting amount to the rich side and to the lean side, the responsiveness of the sensor is detected each time during variation to the rich side and during variation to the lean side. The malfunction of the air-fuel ratio sensor 32 is detected in accordance with the detected responsiveness of the sensor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an abnormality detection device for an air-fuel ratio sensor.

  Conventionally, an air-fuel ratio sensor is provided in an exhaust pipe of an internal combustion engine, and an air-fuel ratio detector (exhaust air-fuel ratio) of exhaust gas discharged from the internal combustion engine is detected by a detection signal of the air-fuel ratio sensor. Has been put to practical use. In recent years, a linear A / F sensor or the like that can linearly detect the air-fuel ratio is used as the air-fuel ratio sensor. In the air-fuel ratio control system using this air-fuel ratio detection device, air-fuel ratio feedback control is performed so that the detected air-fuel ratio is stabilized at the target value, and as a result, exhaust emission has been successfully improved.

In such a case, it is premised that the air-fuel ratio sensor is functioning normally in order to realize good air-fuel ratio control, and various abnormality detection devices for detecting the presence or absence of abnormality of the air-fuel ratio sensor have been proposed. . For example, in Patent Document 1 (Japanese Patent Laid-Open No. Hei 4-237785), the air-fuel ratio feedback coefficient is changed in the vicinity of the theoretical air-fuel ratio, and deterioration diagnosis of the air-fuel ratio sensor is performed based on the air-fuel ratio sensor output response characteristics at that time. It was. In Patent Document 2 (Japanese Patent Laid-Open No. 10-169501), the speed change amount when the air-fuel ratio detected by the air-fuel ratio sensor fluctuates and the speed change amount when the air-fuel ratio correction coefficient fluctuates are calculated. At the same time, the speed change amounts are compared, and the abnormality of the air-fuel ratio sensor is diagnosed based on the comparison result.
Japanese Patent Laid-Open No. 4-278551 JP-A-10-169501

  In each of the above-mentioned patent documents, attention is paid to the output responsiveness of the air-fuel ratio sensor, and the sensor abnormality is detected based on the responsiveness state. However, in the air-fuel ratio sensor, the sensor responsiveness when changing to the rich side is detected. Among the sensor responsiveness when changing to the lean side, it is also conceivable that the responsiveness abnormality appears only on one side. In other words, as is generally known, an air-fuel ratio sensor has a solid electrolyte body such as zirconia and a pair of electrodes arranged so as to sandwich the solid electrolyte body, and exhaust gas according to the amount of oxygen ions conducted between the electrodes. The oxygen concentration (ie, air / fuel ratio) is detected. In this case, if the reaction speed differs between the electrodes due to factors such as sensor differences and changes over time, there will be a difference between the response when the air-fuel ratio changes to the rich side and the response when the air-fuel ratio changes to the lean side. . In such a situation, in each of the above-mentioned patent documents, both the rich side change and the lean side change are judged at the same time. Therefore, there is a possibility that the abnormality cannot be detected correctly when the responsiveness deteriorates only on one side.

  On the other hand, when detecting the output responsiveness of the air-fuel ratio sensor, even if the air-fuel ratio sensor is in an abnormal state (for example, a response delay state), the air-fuel ratio becomes the target air-fuel ratio (for example, target air-fuel ratio = theoretical air-fuel ratio). In the controlled state, the situation is hardly reflected in the sensor detection value, the air-fuel ratio correction coefficient, and the like. Therefore, it has been a problem in performing responsiveness detection.

  The first object of the present invention is to provide an abnormality detection device for an air-fuel ratio sensor that can preferably detect an abnormality in the response of the air-fuel ratio sensor, and can reliably detect the state of change in response. A second object is to provide an air-fuel ratio sensor responsiveness detecting device.

  In the first aspect of the present invention, the air-fuel ratio is forcibly changed to the rich side and the lean side during the air-fuel ratio feedback control. Similarly, the variation data of the air-fuel ratio detection value detected from the air-fuel ratio sensor signal during the air-fuel ratio feedback control to the rich side and the lean side are calculated, respectively, and the calculated air-fuel ratio detection value rich side and lean values are calculated. Based on the change amount data to the side, the responsiveness of the air-fuel ratio sensor is detected for each of the change to the rich side and the change to the lean side. Then, an abnormality of the air-fuel ratio sensor is detected based on the detected responsiveness of the air-fuel ratio sensor. Particularly, abnormality detection of the sensor is performed based on change amount data when the air-fuel ratio detection value changes to the rich side due to forced fluctuation of the air-fuel ratio and when the air-fuel ratio detection value changes to the lean side.

  As described above, when the dynamic characteristics of the air-fuel ratio sensor change due to changes over time, only the response to the rich side or the response to the lean side of the air-fuel ratio sensor changes greatly, leading to an abnormal state. There seems to be something. According to the first aspect of the present invention, since the responsiveness to the rich side and the responsiveness to the lean side of the air-fuel ratio sensor are individually detected, it is possible to suitably detect the responsiveness abnormality of the air-fuel ratio sensor. It becomes possible. In addition, because the air-fuel ratio is forcibly fluctuated to the rich side and the lean side, sufficient change amount data can be obtained when the air-fuel ratio changes to the rich side or the lean side, and highly reliable sensor abnormality detection is realized. it can.

  In the second aspect of the invention, the sensor responsiveness for each of the change to the rich side and the change to the lean side is compared with a predetermined reference value, and an abnormality of the air-fuel ratio sensor is detected according to the result. Is done. In this case, a change in responsiveness caused by a change with time can be monitored by comparison with a reference value. It is also conceivable to set the predetermined reference value based on the initial value in the sensor initial state.

  In the invention according to claim 3, the change amount data at the time of rich side change is compared with the change amount data at the time of lean side change, and whether the rich side responsive abnormality or the lean side responsive abnormality is based on the magnitude relationship between them. Is determined.

  According to a fourth aspect of the present invention, the change speed or the change acceleration is preferably calculated as the change amount data of the air-fuel ratio detection value.

  According to the fifth aspect of the present invention, a responsiveness parameter that makes the responsiveness of the air-fuel ratio sensor equal for each of the change to the rich side and the change to the lean side is calculated, and based on the responsiveness parameter An abnormality of the air-fuel ratio sensor is detected. In this case, if there is a difference in responsiveness between the rich side change and the lean side change, the responsiveness parameter changes greatly. Thus, sensor abnormality can be detected.

  When the air-fuel ratio is forcibly changed, the period and amplitude of the air-fuel ratio change may be fixed, but may be variably set as follows. In the invention according to claim 6, at least one of the cycle or the amplitude of the air-fuel ratio fluctuation is set based on the operating state of the internal combustion engine each time. In this case, although the operating state of the internal combustion engine changes sequentially, air-fuel ratio fluctuation control in a state following the change is possible.

  When the air-fuel ratio is forcibly changed, for example, in a low rotation / low load region, the exhaust gas flow rate is small and the exhaust gas flow velocity is small, so it takes time until the air-fuel ratio detection value changes from the change in the fuel injection amount. On the other hand, in the high rotation / high load region, since the exhaust gas flow rate is large and the exhaust gas flow velocity is fast, it does not take time for the air-fuel ratio detection value to change from the change in the fuel injection amount. Therefore, as described in claim 7, in the low rotation / low load region of the internal combustion engine, the cycle of air-fuel ratio fluctuation is increased or the amplitude is increased, and in the high rotation / high load region of the internal combustion engine, the cycle of air-fuel ratio fluctuation is increased. It is preferable to shorten or reduce the amplitude. As a result, even if the engine operating state changes, the rich / lean side air-fuel ratio fluctuation can be performed in substantially the same period, and the reliability of sensor response abnormality detection is improved.

  In the invention according to claim 8, every time the air-fuel ratio detection value reaches the target air-fuel ratio, the target air-fuel ratio is alternately switched between the rich-side target air-fuel ratio and the lean-side target air-fuel ratio. Thereby, the air-fuel ratio fluctuation between the rich-side target air-fuel ratio and the lean-side target air-fuel ratio can be realized in the shortest time while realizing the desired air-fuel ratio fluctuation on the rich side and the lean side.

  According to the ninth aspect of the invention, during the air-fuel ratio feedback control, change amount data of the air-fuel ratio detection value to the rich side and the lean side are respectively calculated, and the change amount of the air-fuel ratio detection value to the rich side and the lean side is calculated. Based on the data, the responsiveness of the air-fuel ratio sensor is detected for each of the change to the rich side and the change to the lean side. Further, an abnormality of the air-fuel ratio sensor is detected based on the responsiveness of the air-fuel ratio sensor. Further, the calculation of the change amount data of the air-fuel ratio detection value is permitted or prohibited based on the change behavior of the air-fuel ratio correction amount.

  In the invention according to claim 10, change amount data of the air-fuel ratio detected value detected from the air-fuel ratio sensor signal during the air-fuel ratio feedback control to the rich side or the lean side is calculated, and also during the air-fuel ratio feedback control. The change amount data of the air-fuel ratio correction amount to the rich side or lean side is calculated, and the responsiveness of the air-fuel ratio sensor is detected based on the change amount data of the air-fuel ratio detection value and the change amount data of the air-fuel ratio correction amount. The In particular, the calculation of the change amount data of the air-fuel ratio detection value and the change amount data of the air-fuel ratio correction amount is permitted or prohibited based on the change behavior of the air-fuel ratio correction amount.

  In short, the responsiveness of the air-fuel ratio sensor changes due to a change with time or the like, and the change in responsiveness can be detected based on the change amount data of the air-fuel ratio detection value or the change amount data of the air-fuel ratio correction amount. However, even in an air-fuel ratio sensor in which a responsiveness change has occurred, in a state where the air-fuel ratio is controlled in the vicinity of the target air-fuel ratio, etc. There is a problem that it is difficult to be reflected in the amount change data, and accurate response detection cannot be performed. On the other hand, the calculation of each change amount data of the air-fuel ratio detection value and the air-fuel ratio correction amount is permitted or prohibited based on the change behavior of the air-fuel ratio correction amount, thereby reliably detecting the state of responsiveness change. Is possible. It is possible to prevent erroneous detection of responsiveness.

  In the invention according to claim 11, each change amount data of the air-fuel ratio detection value and the air-fuel ratio correction amount is changed only when the variation range of the air-fuel ratio correction amount to the rich side or the lean side within a predetermined time exceeds the specified value. Calculation is allowed. When the variation range of the air-fuel ratio correction amount to the rich side or the lean side within a predetermined time exceeds a specified value, it is considered that the air-fuel ratio deviation is large and the situation of the responsiveness change of the air-fuel ratio sensor appears clearly. Therefore, the sensor response can be detected well.

  As one form of the change in the response of the air-fuel ratio sensor, there is a change in the response time from the change in the gas atmosphere around the air-fuel ratio sensor until the sensor output starts to change. In the case of such a responsiveness change, the behavior of the air-fuel ratio detection value after the sensor output starts to react does not change from that in the normal state. Therefore, the responsiveness change cannot be accurately grasped only by the change amount data of the air-fuel ratio detection value. On the other hand, in the invention according to the twelfth aspect, the delay time from the start of the calculation of the change amount data of the air-fuel ratio correction amount to the start of the calculation of the change amount data of the air-fuel ratio detection value is set, and the delay time has elapsed. At this timing, calculation of change amount data of the air-fuel ratio detection value is permitted. Therefore, even if the response time until the sensor output starts to change changes in the sensor response can be accurately detected.

  In the case of the twelfth aspect, as described in the thirteenth aspect, the delay time is set based on a transport delay time from a change in the fuel supply amount to the internal combustion engine to a gas atmosphere change around the air-fuel ratio sensor. Good. In this case, it is preferable to set the delay time based on the engine operation state in each case.

  In the invention described in claim 14, after the calculation of the variation data of the air-fuel ratio correction amount is permitted, the calculation permission period is limited by a predetermined specified time. In other words, if the calculation of the change amount data of the air-fuel ratio correction amount is started and then continued without any time limit, the responsiveness change state may be gradually unclear. For example, if the response is delayed until the sensor output starts changing from the gas atmosphere change but the output behavior after the start of the reaction does not change from normal, the response change is detected as time passes. It will become increasingly difficult. On the other hand, by providing a time limit as described above, a change in sensor responsiveness can be reliably detected.

  In the invention according to claim 15, when the variation range of the air-fuel ratio correction amount to the rich side exceeds the specified value, the air-fuel ratio detection value changes to the lean side, or the air-fuel ratio correction amount to the lean side. When the air-fuel ratio detection value changes to the rich side when the change width exceeds the specified value, calculation of change amount data for the air-fuel ratio detection value is prohibited. In this case, when detecting the sensor responsiveness, it is possible to reduce the variation of the air-fuel ratio detection value due to noise or temporary combustion fluctuation.

  According to the sixteenth aspect of the present invention, the air-fuel ratio is forcibly changed to the rich side and the lean side, and when the air-fuel ratio detection value changes to the rich side as the air-fuel ratio changes, or the air-fuel ratio detection value is set to the lean side. The responsiveness of the air-fuel ratio sensor is detected based on change amount data at the time of change. In this case, it is possible to sufficiently obtain change amount data when the air-fuel ratio changes to the rich side or the lean side, and it is possible to realize highly reliable sensor response detection.

  When the air-fuel ratio is forcibly changed, the period and amplitude of the air-fuel ratio change may be fixed, but may be variably set as follows. In the invention described in claim 17, at least one of the cycle or the amplitude of the air-fuel ratio fluctuation is set based on the operating state of the internal combustion engine each time. In this case, although the operating state of the internal combustion engine changes sequentially, air-fuel ratio fluctuation control in a state following the change is possible.

  When the air-fuel ratio is forcibly changed, for example, in a low rotation / low load region, the exhaust gas flow rate is small and the exhaust gas flow velocity is small, so it takes time until the air-fuel ratio detection value changes from the change in the fuel injection amount. On the other hand, in the high rotation / high load region, since the exhaust gas flow rate is large and the exhaust gas flow velocity is fast, it does not take time for the air-fuel ratio detection value to change from the change in the fuel injection amount. Accordingly, as described in claim 18, the cycle of the air-fuel ratio fluctuation is lengthened or increased in the low rotation / low load region of the internal combustion engine, and the air fuel ratio fluctuation cycle is increased in the high rotation / high load region of the internal combustion engine. It is preferable to shorten or reduce the amplitude. As a result, even if the engine operating state changes, the rich / lean side air-fuel ratio fluctuation can be performed in substantially the same period, and the reliability of sensor response detection is improved.

  According to the nineteenth aspect of the invention, every time the air-fuel ratio detection value reaches the target air-fuel ratio, the target air-fuel ratio is alternately switched between the rich-side target air-fuel ratio and the lean-side target air-fuel ratio. Thereby, the air-fuel ratio fluctuation between the rich-side target air-fuel ratio and the lean-side target air-fuel ratio can be realized in the shortest time while realizing the desired air-fuel ratio fluctuation on the rich side and the lean side.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-vehicle multi-cylinder gasoline engine that is an internal combustion engine. In the control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount. And control of ignition timing. First, an overall schematic configuration diagram of the engine control system will be described with reference to FIG.

  In the engine 10 shown in FIG. 1, an air cleaner 12 is provided at the most upstream portion of the intake pipe 11, and an air flow meter 13 for detecting the intake air amount is provided downstream of the air cleaner 12. A throttle valve 14 whose opening is adjusted by an actuator such as a DC motor and a throttle opening sensor 15 for detecting the throttle opening are provided on the downstream side of the air flow meter 13. A surge tank 16 is provided downstream of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. The surge tank 16 is connected to an intake manifold 18 that introduces air into each cylinder of the engine 10. In the intake manifold 18, an electromagnetically driven fuel injection that injects fuel near the intake port of each cylinder. A valve 19 is attached.

  An intake valve 21 and an exhaust valve 22 are respectively provided in the intake port and the exhaust port of the engine 10, and an air / fuel mixture is introduced into the combustion chamber 23 by the opening operation of the intake valve 21, and the exhaust valve 22. By the opening operation, the exhaust gas after combustion is discharged to the exhaust pipe 24. A spark plug 27 is attached to the cylinder head of the engine 10 for each cylinder, and a high voltage is applied to the spark plug 27 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 27, and the air-fuel mixture introduced into the combustion chamber 23 is ignited and used for combustion.

  The exhaust pipe 24 is provided with a catalyst 31 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas, and the air-fuel ratio of the air-fuel mixture is detected on the upstream side of the catalyst 31 with exhaust gas as a detection target. An air-fuel ratio sensor 32 (linear A / F sensor or the like) is provided for detecting the above. Further, the cylinder block of the engine 10 includes a coolant temperature sensor 33 that detects the coolant temperature, and a crank angle sensor 34 that outputs a rectangular crank angle signal for each predetermined crank angle of the engine (for example, at a cycle of 30 ° CA). It is attached.

  The outputs of the various sensors described above are input to the ECU 40 that controls the engine. The ECU 40 is configured mainly by a microcomputer including a CPU, a ROM, a RAM, and the like, and executes various control programs stored in the ROM, so that the fuel injection amount and ignition of the fuel injection valve 19 according to the engine operating state. The ignition timing by the plug 27 is controlled. In particular, in the fuel injection amount control, an air-fuel ratio correction coefficient FAF is calculated as an air-fuel ratio correction amount based on the deviation between the air-fuel ratio (detected air-fuel ratio) detected by the air-fuel ratio sensor 32 and the target air-fuel ratio. The air-fuel ratio F / B control using the correction coefficient FAF is performed.

  Here, the configuration of the air-fuel ratio sensor 32 will be described with reference to FIG. The air-fuel ratio sensor 32 has a sensor element 50 having a laminated structure, and FIG. 9 shows a cross-sectional configuration of the sensor element 50. Actually, the sensor element 50 has a long shape extending in a direction orthogonal to the paper surface of FIG. 9, and the entire element is accommodated in a housing or an element cover.

  The sensor element 50 includes a solid electrolyte layer 51, a diffusion resistance layer 52, a shielding layer 53, and an insulating layer 54, which are stacked on the upper and lower sides of the drawing. A protective layer (not shown) is provided around the element 50. The rectangular plate-shaped solid electrolyte layer 51 is made of a partially stabilized zirconia sheet, and a pair of upper and lower electrodes 55 and 56 are arranged opposite to each other with the solid electrolyte layer 51 interposed therebetween. The electrodes 55 and 56 are made of platinum Pt or the like. The diffusion resistance layer 52 is composed of a porous sheet for introducing exhaust gas into the electrode 55, and the shielding layer 53 is composed of a dense layer for suppressing permeation of exhaust gas. Each of these layers 52 and 53 is formed by molding a ceramic such as alumina or zirconia by a sheet forming method or the like, but has different gas permeability due to the difference in the average pore diameter and porosity of the porosity.

  The insulating layer 54 is made of ceramics such as alumina and zirconia, and an air duct 57 is formed at a portion facing the electrode 56. In addition, a heater 58 made of platinum Pt or the like is embedded in the insulating layer 54. The heater 58 is a heating element that generates heat when energized from a battery power source, and the entire element is heated by the generated heat. In the following description, the electrode 55 is also referred to as a diffusion layer side electrode, and the electrode 56 is also referred to as an atmosphere side electrode.

  In the sensor element 50, the surrounding exhaust gas is introduced from the side portion of the diffusion resistance layer 52 and reaches the diffusion layer side electrode 55. When the exhaust gas is lean, oxygen in the exhaust gas is decomposed at the diffusion layer side electrode 55 by applying a voltage between the electrodes 55, 56, is ionized, passes through the solid electrolyte layer 51, and then flows from the atmosphere side electrode 56 to the atmosphere duct 57. Discharged. At this time, a current flows in the direction from the atmosphere side electrode 56 to the diffusion layer side electrode 55, and a sensor signal corresponding to the current level is output. On the other hand, when the exhaust gas is rich, oxygen in the atmosphere duct 57 is decomposed by the atmosphere side electrode 56, ionized and passes through the solid electrolyte layer 51 and then discharged from the diffusion layer side electrode 55. And it reacts with unburned components such as HC and CO in the exhaust gas. At this time, a current flows in the direction from the diffusion layer side electrode 55 to the atmosphere side electrode 56, and a sensor signal corresponding to the current level is output.

  As described above, in the air-fuel ratio sensor 32 (sensor element 50), the oxygen decomposition reaction or the like is performed by the diffusion layer side electrode 55 and the atmosphere side electrode 56. Sensor response is different at each lean. This difference in responsiveness is caused by individual sensor differences and changes over time. If the sensor responsiveness is different, it is considered that the air-fuel ratio control is adversely affected. Therefore, in the air-fuel ratio detection apparatus according to the present embodiment, the responsiveness abnormality of the air-fuel ratio sensor 32 is detected based on the sensor response when changing to the rich side and the sensor response when changing to the lean side. The details will be described below.

  FIG. 2 is a functional block diagram showing the configuration of the air-fuel ratio detection device by function, and each of these functions will be briefly described. In the air-fuel ratio adjustment unit M1, an air-fuel ratio correction coefficient FAF is calculated based on the deviation between the corrected air-fuel ratio φm fetched from the air-fuel ratio sensor signal processing unit M5 described later and the target air-fuel ratio. The air-fuel ratio correction coefficient storage unit M2 stores at least the current value and the previous value of the air-fuel ratio correction coefficient FAF, and the corrected air-fuel ratio storage unit M3 stores at least the current value and the previous value of the corrected air-fuel ratio φm. . The responsiveness detection unit M4 calculates a responsiveness parameter (parameter α) representing the responsiveness of the air-fuel ratio sensor 32 to the rich side and the lean side based on the air-fuel ratio correction coefficient FAF and the corrected air-fuel ratio φm. In the air-fuel ratio sensor signal processing unit M5, the corrected air-fuel ratio φm is calculated based on the detected air-fuel ratio φsig calculated from the air-fuel ratio sensor signal and the parameter α. The sensor abnormality detection unit M6 detects an abnormality of the air-fuel ratio sensor 32 based on the parameter α output from the responsiveness detection unit M4. Here, the air-fuel ratio will be described as an excess fuel ratio (fuel amount / air amount), but there is no problem even if a configuration using an excess air ratio is used instead.

  FIG. 3 is a flowchart showing FAF calculation processing in the air-fuel ratio adjustment unit M1. In FIG. 3, first, in step S101, it is determined whether or not an air-fuel ratio F / B condition is satisfied. The air-fuel ratio F / B condition includes, for example, that the coolant temperature is equal to or higher than a predetermined temperature, is not in a high rotation / high load state, and that the air-fuel ratio sensor 32 is in an active state. If the condition is satisfied, the process proceeds to step S102, where the air-fuel ratio deviation err is calculated from the target air-fuel ratio φref and the corrected air-fuel ratio φm (err = φref−φm). Thereafter, in step S103, an air-fuel ratio correction coefficient FAF is calculated by the following equation based on a well-known PI control method.

FAF = KFp · err + KFi · Σerr
KFp is a proportional constant, and KFi is an integral constant. The method for calculating the air-fuel ratio correction coefficient FAF is not limited, and the FAF value is calculated using a model that reflects the past FAF value and calculates the current value of the FAF value, or a model that represents the dynamic behavior of the engine 10. Anything can be applied arbitrarily.

  If the air-fuel ratio F / B condition is not satisfied, the process proceeds to step S104, and the air-fuel ratio correction coefficient FAF is set to 1.

  Next, FIGS. 4 to 6 are flowcharts showing calculation processing in the responsiveness detection unit M4, and FIG. 4 is a flowchart showing FAF change rate calculation processing for calculating the change rate of the air-fuel ratio correction coefficient FAF. FIG. 5 is a flowchart showing the φm change rate calculation process for calculating the change rate of the corrected air-fuel ratio φm, and FIG. 6 is a flowchart showing the parameter α calculation process.

  First, in the FAF change speed calculation process of FIG. 4, in step S201, it is determined whether or not the air-fuel ratio correction coefficient FAF is currently being calculated, and the process proceeds to step S202 on condition that the FAF calculation is being performed. In step S202, the change amount ΔFAF is calculated from the difference between the current value FAF (k) and the previous value FAF (k−1) of the air-fuel ratio correction coefficient. Thereafter, in step S203, it is determined whether or not the change amount ΔFAF of the air-fuel ratio correction coefficient is larger than zero. Here, ΔFAF> 0 means that the fuel injection amount by the fuel injection valve 19 is corrected to the increase side, and accordingly the air-fuel ratio changes to the rich side.

  When ΔFAF> 0, the process proceeds to step S204, and the change rate ΔFAFR of the air-fuel ratio correction coefficient when changing to the rich side is calculated by the following equation.

ΔFAFR (k) = ΔFAFR (k−1) + ksm1 (ΔFAF (k) −ΔFAF (k−1))
In the above equation, ksm1 is an annealing rate.

  If ΔFAF ≦ 0, the process proceeds to step S205, and the change rate ΔFAFL of the air-fuel ratio correction coefficient when changing to the lean side is calculated by the following equation.

ΔFAFL (k) = ΔFAFL (k−1) + ksm1 (ΔFAF (k) −ΔFAF (k−1))
As described above, the change rates ΔFAFR and ΔFAFL of the air-fuel ratio correction coefficient are calculated as change amount data of the air-fuel ratio correction amount at the time of rich change and lean change.

  Next, in the φm change rate calculation process of FIG. 5, in step S301, it is determined whether or not the corrected air-fuel ratio φm is currently being calculated, and the process proceeds to step S302 on condition that φm is being calculated. In step S302, the amount of change Δφm is calculated from the difference between the current value φm (k) of the corrected air-fuel ratio and the previous value φm (k−1). Thereafter, in step S303, it is determined whether or not the change amount Δφm of the corrected air-fuel ratio is greater than zero. Here, Δφm> 0 means that the excess fuel ratio increases and the air-fuel ratio changes to the rich side.

  If Δφm> 0, the process proceeds to step S304, and the correction air-fuel ratio change rate ΔφmR when changing to the rich side is calculated by the following equation.

ΔφmR (k) = ΔφmR (k−1) + ksm2 (Δφm (k) −Δφm (k−1))
In the above equation, ksm2 is an annealing rate.

  If Δφm ≦ 0, the process proceeds to step S305, and the change rate ΔφmL of the corrected air-fuel ratio when changing to the lean side is calculated by the following equation.

ΔφmL (k) = ΔφmL (k−1) + ksm2 (Δφm (k) −Δφm (k−1))
Thus, the corrected air-fuel ratio change rates ΔφmR and ΔφmL are calculated as change amount data of the air-fuel ratio detection value at the time of rich change and lean change.

  In the parameter α calculation process of FIG. 6, in step S401, the ratio compR (= ΔφmR (k) between the change rate ΔφmR of the corrected air-fuel ratio and the change rate ΔFAFR of the air-fuel ratio correction coefficient when the air-fuel ratio changes to the rich side. / ΔFAFR (k)) and a ratio compL (= ΔφmL (k) / ΔFAFL (k) between the change rate ΔφmL of the corrected air-fuel ratio and the change rate ΔFAFL of the air-fuel ratio correction coefficient when the air-fuel ratio changes to the lean side )) Is calculated.

Thereafter, in step S402, the ratio compRL between the calculated compR and compL is calculated. In the subsequent step S403, the parameter α is calculated using a PI compensator for setting compRL to the target value (= 1). That is,
e = compRL-1
α = 1 + kp · e + ki (Σe)
The parameter α is calculated as follows. Note that kp is a proportionality constant and ki is an integration constant.

  Thus, compR and compL are calculated as responsiveness data of the air-fuel ratio sensor 32 at the time of rich change and lean change, and the parameter α is calculated as a responsiveness parameter.

  By the way, in the present embodiment, the air-fuel ratio sensor signal processing is performed using the phase advance filter, and the transfer function is expressed by the following equation (1). A is the median value of the sensor time constant.

また、連続時間を離散時間に変換するための双一次ｓ−ｚ変換は次の（２）式で表される。（２）式において、ｈ＝２／Ｔ（Ｔはサンプル周期）である。

In addition, bilinear sz conversion for converting continuous time to discrete time is expressed by the following equation (2). In the equation (2), h = 2 / T (T is a sampling period).

上記（２）式により、上記（１）式は次の（３）式となる。

From the above equation (2), the above equation (1) becomes the following equation (3).

上記（３）式を差分方程式に展開すると、次の（４）式が得られる。

When the above equation (3) is expanded into a difference equation, the following equation (4) is obtained.

Ｙはフィルタ出力、Ｕはフィルタ入力である。上記（４）式により、フィルタ入力である検出空燃比φｓｉｇに対して位相進み処理が実施され、その結果、修正空燃比φｍが算出できる。

Y is a filter output, and U is a filter input. According to the above equation (4), the phase advance process is performed on the detected air-fuel ratio φsig that is the filter input, and as a result, the corrected air-fuel ratio φm can be calculated.

  FIG. 7 is a flowchart showing sensor signal processing in the air-fuel ratio sensor signal processing unit M5.

  In FIG. 7, in step S <b> 501, it is determined whether an execution condition for sensor signal processing is satisfied. The execution conditions include, for example, that the air-fuel ratio sensor 32 has not failed and that the sensor 32 is in an active state. In step S502, it is determined whether the air-fuel ratio is changing in a rich direction. Specifically, the difference between the previous value and the current value of the detected air-fuel ratio φsig is obtained, and if the “current value−previous value” is positive, it is determined that the air-fuel ratio is changing in the rich direction.

  If the rich condition is changed when the execution condition is satisfied (ie, if step S502 is YES), the process proceeds to step S503, and the parameter α is initialized to 1. When the lean direction is changed (NO in step S502), the process proceeds to step S504 as it is, and the phase advance process is performed using the equation (4). Thus, the detected air-fuel ratio φsig is corrected according to the parameter α when the air-fuel ratio changes to the lean side, and the corrected air-fuel ratio φm is calculated.

  FIG. 8 is a flowchart showing sensor abnormality detection processing in the sensor abnormality detection unit M6.

  In FIG. 8, in step S601, compR, compL, compRL, and parameter α calculated in the arithmetic processing of FIG. 6 are read. In subsequent steps S602 to S605, sensor abnormality is detected from the read compR, compL, compRL, and parameter α. The presence or absence of is determined. That is, in step S602, it is determined whether or not compR> K1, and in step S603, whether or not compL> K2 is determined (however, K1 = K2 is also possible). In step S604, it is determined whether or not K3 <compRL <K4. In step S605, it is determined whether α> K5. At this time, K1 to K5 are responsiveness abnormality determination values, and in particular, K3 <1, K4> 1.

  Here, when the rich side change or lean side change of the corrected air-fuel ratio φm is excessively large with respect to the rich side change or lean side change of the air-fuel ratio correction coefficient FAF, steps S602 and S603 become YES, and the rich side When the sensor response on the lean side is greatly different, steps S604 and S605 are YES.

  And if all of step S602-S605 are NO, it will progress to step S606 and will determine that the air fuel ratio sensor 32 is normal. If any of steps S602 to S605 is YES, the process proceeds to step S607, and it is determined that a responsiveness abnormality has occurred in the air-fuel ratio sensor 32. Incidentally, when it is determined that a sensor abnormality has occurred, an abnormality warning lamp is turned on and an abnormality warning is given to the driver or the like. Then, appropriate measures such as repair or replacement of the air-fuel ratio sensor 32 are urged. In addition, abnormality diagnosis data (diag data) is stored in a backup memory or the like, and fail-safe processing such as interruption of air-fuel ratio F / B control is performed. Note that the present invention is not limited to the configuration in which the abnormality is detected by all of steps S602 to S605, and the abnormality may be detected only by any one of them (for example, steps S604 and S605).

  According to the embodiment described above in detail, the following excellent effects can be obtained.

  Since the responsiveness when the air-fuel ratio sensor 32 changes on the rich side and the responsiveness when the lean-side change changes are individually detected, the dynamic characteristics of the air-fuel ratio sensor 32 can be known from the responsiveness data. The response abnormality of the air-fuel ratio sensor 32 can be suitably detected based on the characteristics.

Further, from the ratio between the change amount data (ΔφmR, ΔφmL) of the corrected air-fuel ratio φm and the change amount data (ΔFAFR, ΔFAFL) of the air-fuel ratio correction coefficient FAF for each of the change to the rich side and the change to the lean side. Since the response data (compR, compL) is calculated, the response data is obtained by comparing the change in the corrected air-fuel ratio φm with the change in the air-fuel ratio correction coefficient FAF. Therefore, the reliability of the responsiveness data is increased, and the abnormality detection of the air-fuel ratio sensor 32 can be more suitably performed.
(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment.

  Even in an air-fuel ratio sensor in which a responsiveness abnormality has occurred, in a state where the air-fuel ratio is controlled in the vicinity of the target air-fuel ratio, etc., the state of the responsiveness abnormality is the change amount data (ΔφmR, ΔφmL) It is considered that it is difficult to reflect the change amount data (ΔFAFR, ΔFAFL) of the air-fuel ratio correction amount. Therefore, in the present embodiment, the calculation of each change amount data of the air-fuel ratio detection value and the air-fuel ratio correction amount is permitted or prohibited on the basis of the change behavior of the air-fuel ratio correction amount (air-fuel ratio correction coefficient FAF). We will improve the detection accuracy of sexual abnormalities.

  FIG. 10 is a flowchart showing the entire flow of the sensor abnormality detection process in the present embodiment, and abnormality detection of the air-fuel ratio sensor 32 is performed based on the flowchart. The process in FIG. 10 is executed by the ECU 40 at a predetermined time period, for example.

  In FIG. 10, first, in step S710, an abnormality detection execution condition is determined. Specifically, for example, the engine speed, load, water temperature, active state of the air-fuel ratio sensor 32, etc. are monitored, and the execution condition is satisfied if the engine 10 has been warmed up and is in the middle rotation / medium load operation. Determine that you are doing. When the execution condition is satisfied, the process proceeds to the subsequent step S720. When the execution condition is not satisfied, the present process is terminated.

  When the abnormality detection execution condition is satisfied, the air-fuel ratio forced variation process (step S720), the FAF change rate calculation process (step S730), the φm change rate calculation process (step S740), the parameter α calculation process (step S750), and the sensor signal process. (Step S760) and sensor abnormality detection processing (Step S770) are sequentially performed.

  Of the above processes, the air-fuel ratio forced variation process (step S720) is shown in FIG. 11, the FAF change rate calculation process (step S730) is shown in FIG. 12, and the φm change rate calculation process (step S740) is shown in FIG. Each of these processes will be described in turn below. Since parameter α calculation processing (step S750), sensor signal processing (step S760), and sensor abnormality detection processing (step S770) can be applied to FIGS.

  First, in the air-fuel ratio forced variation process of FIG. 11, in step S801, it is determined whether or not it is the calculation timing of the cycle and amplitude of the air-fuel ratio variation. For example, it is determined whether or not the air-fuel ratio inversion timing has reached (1/2 of the fluctuation cycle described later). If the calculation timing is not reached, the present process is terminated. If it is the calculation timing, the period and amplitude of the air-fuel ratio fluctuation are calculated in steps S802 and S803. At this time, the fluctuation cycle and the amplitude may be variably set according to the engine operating state. For example, the characteristic cycle shown in FIG. 16 is used, and the fluctuation cycle and the amplitude are calculated according to the engine speed and load at that time. According to the characteristic of FIG. 16, the fluctuation period is long and the amplitude is set large in the low rotation / low load operation region, and the fluctuation period is short and the amplitude is set small in the high rotation / high load operation region. In other words, comparing the low rotation / low load state with the high rotation / high load state, the former has a low exhaust gas flow rate and low flow velocity, so the response of the actual air-fuel ratio is slow, and the latter has a high exhaust gas flow rate and high flow rate. Real air-fuel ratio response is fast. In this situation, if the fluctuation period and amplitude are set as shown in FIG. 16, the response of the actual air-fuel ratio on the rich side and lean side can be made substantially the same under any operating condition. However, it is also possible to use a setting method using mathematical formulas instead of setting the fluctuation period and amplitude using the map. It is possible to variably set only one of the period or amplitude of the air-fuel ratio fluctuation.

  Thereafter, in step S804, it is determined whether the current air-fuel ratio fluctuation is a rich fluctuation or a lean fluctuation based on the state of the enrichment flag. In the case of rich fluctuation (riching flag = 1), the process proceeds to step S805, where the value obtained by subtracting the forced fluctuation amplitude from the base target air-fuel ratio is set as the target air-fuel ratio and the riching flag is cleared. In the case of lean fluctuation (enrichment flag = 0), the process proceeds to step S806, where the value obtained by adding the forced fluctuation amplitude to the base target air-fuel ratio is set as the target air-fuel ratio and the enrichment flag is set.

  The determination of whether or not enrichment may be performed may be determination based on the target air-fuel ratio at that time, in addition to the determination based on the above-described enrichment flag. Further, a period counter for counting the inversion period may be provided, and the determination may be made based on the counter value. The counter may be set to rich / lean, or may be rich / lean shared.

  Next, in the FAF change speed calculation process of FIG. 12, in step S901, it is determined whether or not the air-fuel ratio correction coefficient FAF is currently being calculated, and the process proceeds to step S902 on the condition that the FAF calculation is being performed. . In step S902, the change amount ΔFAF1 is calculated from the difference between the current value FAF (k) of the air-fuel ratio correction coefficient and the previous value FAF (k−1). In subsequent step S903, the current value FAF of the air-fuel ratio correction coefficient is calculated. The amount of change ΔFAF2 is calculated from the difference between (k) and the previous value FAF (k−3). In the following description, in order to distinguish ΔFAF1 and ΔFAF2, the former is also referred to as a first change amount ΔFAF1, and the latter is also referred to as a second change amount ΔFAF2. The second change amount ΔFAF2 is calculated from the difference between the current value FAF (k) of the air-fuel ratio correction coefficient and the previous value FAF (k−3), and the second change amount ΔFAF2 It may be calculated from the difference from the value FAF (k−2), or may be calculated from the difference between the current value FAF (k) and the previous value FAF (k−4). In this case, an optimal time interval may be set for each engine.

  Thereafter, in step S904, it is determined whether or not the calculated second change amount ΔFAF2 of the air-fuel ratio correction coefficient is equal to or larger than a predetermined rich side determination value krich. If ΔFAF2 <krich, the ΔFAFR calculation permission flag is cleared in step S905. In step S906, it is determined whether or not the calculated second change amount ΔFAF2 of the air-fuel ratio correction coefficient is equal to or less than a predetermined lean determination value klean. If ΔFAF2> klean, the ΔFAFL calculation permission flag is cleared in step S907, and the process is terminated. Here, the ΔFAFR calculation permission flag is a flag for permitting calculation of the rich side change speed ΔFAFR of the air-fuel ratio correction coefficient, and the ΔFAFL calculation permission flag is a flag for permitting calculation of the lean side change speed ΔFAFL of the air-fuel ratio correction coefficient. 1 represents calculation permission, and 0 represents calculation disapproval. That is, when the change width of the air-fuel ratio correction coefficient FAF within a predetermined period does not exceed the specified value (when klean <ΔFAF2 <krich), the rich-side change speed ΔFAFR and the lean-side change speed ΔFAFL of the air-fuel ratio correction coefficient are both It is not calculated.

  If ΔFAF2 ≧ krich, the process proceeds to step S910, and the rich side change rate ΔFAFR of the air-fuel ratio correction coefficient is calculated. If ΔFAF2 ≦ klean, the process proceeds to step S920, and a process of calculating the lean side change rate ΔFAFL of the air-fuel ratio correction coefficient is performed.

  The ΔFAFR calculation process will be described with reference to FIG. In step S911, it is determined whether or not the ΔFAFR calculation permission flag is 0. If the flag = 0, in step S912, the ΔFAFR calculation permission flag is set to 1 and the ΔFAFR calculation period flag is set to 1. In a succeeding step S913, a predetermined value is set in the ΔFAFR calculation period timer. That is, after ΔFAF2 ≧ krich is established, the setting process of each flag and timer is performed only at the first time when the ΔFAFR calculation permission flag is in the clear state. The ΔFAFR calculation period timer is a time measuring means that is decremented every predetermined time by another process (not shown) after the predetermined value is set.

  Thereafter, in step S914, it is determined whether or not the timer value is greater than 0. If the timer value is greater than 0, the rich side change rate ΔFAFR of the air-fuel ratio correction coefficient is calculated by the following equation in step S915.

ΔFAFR (k) = ΔFAFR (k−1) + ksm1 (ΔFAF1 (k) −ΔFAF1 (k−1))
In the above equation, ksm1 is an annealing rate.

  If the timer value ≦ 0, the ΔFAFR calculation period flag is cleared in step S916. That is, after the timer value reaches 0, the rich side change speed ΔFAFR is not calculated.

  Next, the ΔFAFL calculation process will be described with reference to FIG. In step S921, it is determined whether or not the ΔFAFL calculation permission flag is 0. If the flag = 0, in step S922, the ΔFAFL calculation permission flag is set to 1 and the ΔFAFL calculation period flag is set to 1. In a succeeding step S923, a predetermined value is set in the ΔFAFL calculation period timer. That is, after ΔFAF2 ≦ klean is established, the setting process of each flag and timer is performed only at the first time when the ΔFAFL calculation permission flag is in the clear state. The ΔFAFL calculation period timer is a time measuring means that is decremented every predetermined time by another process (not shown) after setting the predetermined value.

  Thereafter, in step S924, it is determined whether or not the timer value is greater than 0. If the timer value is greater than 0, the lean side change rate ΔFAFL of the air-fuel ratio correction coefficient is calculated by the following equation in step S925.

ΔFAFL (k) = ΔFAFL (k−1) + ksm1 (ΔFAF1 (k) −ΔFAF1 (k−1))
When the timer value ≦ 0, the ΔFAFL calculation period flag is cleared in step S926. That is, after the timer value reaches 0, the lean side change speed ΔFAFL is not calculated.

  The calculation procedure of the FAF change speed according to FIGS. 12 to 14 will be described more specifically based on the time chart of FIG. However, in FIG. 17, only the change to the lean side will be described.

  At timing t1, the second change amount ΔFAF2 (= FAF (k) −FAF (k−3)) becomes equal to or less than the lean determination value klean, and accordingly, the ΔFAFL calculation permission flag and the ΔFAFL calculation period flag are set to 1. At the same time, a predetermined value (kleantm in the figure) is set to the ΔFAFL calculation period timer. After this t1, the lean side change speed ΔFAFL of the air-fuel ratio correction coefficient is calculated. After that, when the value of the ΔFAFL calculation period timer becomes 0, the ΔFAFL calculation period flag is cleared (timing t2). Thereby, the calculation of the lean side change speed ΔFAFL is ended. That is, the calculation of ΔFAFL is started after the air-fuel ratio correction amount FAF has changed a prescribed amount, but the calculation period is limited by the timer value. Due to the time limit of the calculation period, for example, the response from the gas atmosphere change until the sensor output begins to change is delayed, but even if the output response after the start of the reaction does not change from normal, the sensor response Responsiveness can be detected reliably. Further, even when the air-fuel ratio correction coefficient FAF fluctuates in a period different from the air-fuel ratio fluctuation period (when hunting occurs), the responsiveness can be detected with high accuracy.

  Next, in the φm change rate calculation process of FIG. 15, in step S1001, it is determined whether or not the corrected air-fuel ratio φm is currently being calculated, and the process proceeds to step S1002 on the condition that φm is being calculated. In step S1002, the amount of change Δφm is calculated from the difference between the current value φm (k) of the corrected air-fuel ratio and the previous value φm (k−1). Thereafter, in step S1003, it is determined whether or not the ΔφmR calculation period flag is 1, and the process proceeds to step S1004 on the condition that the flag = 1. The ΔφmR calculation period flag is a flag that is set based on the set / clear timing of the ΔFAFR calculation period flag, and details thereof will be described later (the same applies to the ΔφmL calculation period flag described later).

  In step S1004, it is determined whether or not the amount of change Δφm in the corrected air-fuel ratio is greater than zero. Δφm> 0 means that the excess fuel ratio increases and the air-fuel ratio changes to the rich side. If Δφm> 0, the process proceeds to step S1005, and the rich side change rate ΔφmR of the corrected air-fuel ratio is calculated by the following equation.

ΔφmR (k) = ΔφmR (k−1) + ksm2 (Δφm (k) −Δφm (k−1))
In the above equation, ksm2 is an annealing rate.

  If Δφm ≦ 0 in step S1004, the process proceeds to step S1006, and ΔφmR (k) = ΔφmR (k−1) is set. That is, if ΔφmR calculation period flag = 1 but the change in the corrected air-fuel ratio φm is leaner, there is a possibility that φm may vary due to noise or temporary combustion fluctuations. Cancel the calculation of the rich side change speed ΔφmR of the corrected air-fuel ratio.

  If NO in step S1003, the process advances to step S1007 to determine whether or not the ΔφmL calculation period flag is 1, and the process advances to step S1008 on condition that the flag = 1. In step S1008, it is determined whether or not the change amount Δφm of the corrected air-fuel ratio is smaller than zero. Δφm <0 means that the excess fuel ratio decreases and the air-fuel ratio changes to the lean side. If Δφm <0, the process proceeds to step S1009 to calculate the lean side change rate ΔφmL of the corrected air-fuel ratio by the following equation.

ΔφmL (k) = ΔφmL (k−1) + ksm2 (Δφm (k) −Δφm (k−1))
If Δφm ≧ 0 in step S1008, the process proceeds to step S1010, and ΔφmL (k) = ΔφmL (k−1) is set. That is, if the ΔφmL calculation period flag = 1 but the change in the corrected air-fuel ratio φm is in a rich direction, there is a possibility that φm may vary due to noise or temporary combustion fluctuations. Cancel the calculation of the lean side change rate ΔφmL of the corrected air-fuel ratio.

  Note that if both of steps S1003 and S1007 are NO, the process ends without calculating the rich side change rate ΔφmR and the lean side change rate ΔφmL of the corrected air-fuel ratio.

  Hereinafter, the procedure for setting the ΔφmL calculation period flag will be described with reference to the time chart of FIG. Although explanation is omitted, the ΔφmL calculation period flag is set in the same procedure.

  In FIG. 18, for example, the ΔFAFL calculation period flag is set in each period from t11 to t13 and t15 to t17. In the first ΔFAF calculation period in FIG. 18, a predetermined value is set in the ΔφmL calculation start timer 1 when the ΔFAFL calculation period flag is set (t11), and a predetermined value is set in the ΔφmL calculation end timer 1 when the flag is cleared. (T13). Then, the ΔφmL calculation period flag is set when the ΔφmL calculation start timer 1 becomes 0 (t12), and the ΔφmL calculation period flag is cleared when the ΔφmL calculation end timer 1 becomes 0 (t14). In this case, the period (t12 to t14) in which the ΔφmL calculation period flag is set becomes the ΔφmL calculation period, and ΔφmL is calculated in this period. Looking at the ΔFAFL calculation period, the ΔφmL calculation period is provided with a predetermined time delay.

  In the second ΔFAF calculation period, the same processing is performed except that the ΔφmL calculation start timer 2 and the ΔφmL calculation end timer 2 are used, and as a result, the ΔφmL calculation period flag is set in the period from t16 to t18. Then, ΔφmL is calculated in the ΔφmL calculation period (t16 to t18). In this case, by using two sets of ΔφmL calculation start timer and ΔφmL calculation end timer, the ΔFAFL calculation period flag may be determined before each timer value becomes 0 (see t19 and after in the figure). The ΔφmL calculation period flag can be set without any trouble. However, it is also possible to employ a configuration in which only one set of ΔφmL calculation start timer and ΔφmL calculation end timer is used.

  The set times of the ΔφmL calculation start timers 1 and 2 and the ΔφmL calculation end timers 1 and 2 correspond to a delay time from the change amount data calculation of the air-fuel ratio correction coefficient FAF to the change amount data calculation of the corrected air-fuel ratio φm. In this case, the timer set time may be set based on the transport delay time from the change in the fuel injection amount to the change in the gas atmosphere around the air-fuel ratio sensor. Specifically, the timer set time is appropriately calculated from the engine operating state parameters (engine speed, load, etc.) using a map or a mathematical formula defined in advance by experiments or the like. However, if the engine operating range is defined as an execution condition, the set time can be set to a fixed value.

  As described above, according to the second embodiment, the following effect is newly obtained in addition to the effect of the first embodiment.

  Only when the variation range (ΔFAF2) of the air-fuel ratio correction coefficient FAF to the rich side or lean side exceeds the specified value, the change amount data (ΔφmR, ΔφmL) of the corrected air-fuel ratio φm and the change amount data of the air-fuel ratio correction coefficient FAF Since the calculation of (ΔFAFR, ΔFAFL) is permitted, the change amount data is calculated only in a state where the responsiveness abnormality state of the air-fuel ratio sensor 32 clearly appears, and as a result, the detection accuracy of the sensor responsiveness abnormality is improved. be able to.

  A delay time is set after permitting calculation of the change amount data of the air-fuel ratio correction coefficient FAF until the change amount data calculation of the corrected air-fuel ratio φm is permitted, and the change amount data of the corrected air-fuel ratio φm at the timing when the delay time has passed. Since the calculation is permitted, a sensor response abnormality can be accurately detected even when a response delay occurs until the sensor output starts to change.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

  In the above-described embodiment, it is an implementation requirement to calculate the parameter α set so as to eliminate the responsiveness to the rich side and the lean side. However, the configuration may be such that the parameter α is not calculated. Even if the parameter α is not calculated, the sensor responsiveness may be detected from the change data compR, compL, etc., and the abnormality detection of the air-fuel ratio sensor 32 may be performed based on the result.

  The rich side responsiveness abnormality and the lean side responsiveness abnormality may be determined separately. For example, in the sensor abnormality detection process of FIG. 8, if step S602 is YES, the rich side responsiveness abnormality is assumed, and if step S603 is YES, the lean side responsiveness abnormality is assumed. Further, in step S604, it is determined whether the rich responsiveness abnormality or the lean side responsiveness abnormality depends on whether compRL is out of the determination value.

  In the above-described embodiment, the corrected air-fuel ratio change rates ΔφmR, ΔφmL, and the air-fuel ratio correction factor change rates ΔFAFR, ΔFAFL are used as the air-fuel ratio detection value and the change amount data of the air-fuel ratio correction amount to the rich side or lean side. However, instead of this, it is possible to employ a configuration in which the change acceleration of the corrected air-fuel ratio and the change acceleration of the air-fuel ratio correction coefficient are used.

  In the above embodiment, the responsiveness detection unit M4 is configured to calculate the change amount data of the air-fuel ratio detection value using the corrected air-fuel ratio φm. Instead, the air-fuel ratio detection is performed using the detected air-fuel ratio φsig. A configuration may be employed in which value variation data is calculated.

  In the above embodiment, when the air-fuel ratio changes to the lean side, the corrected air-fuel ratio φm is calculated by performing the phase advance process on the detected air-fuel ratio φsig, but instead, the air-fuel ratio change to the rich side is calculated. At this time, the corrected air-fuel ratio φm may be calculated by applying a phase delay process to the detected air-fuel ratio φsig. Further, the correction method of the detected air-fuel ratio φsig is not limited to the phase advance / phase delay process, and other correction methods may be used. For example, the correction may be performed by multiplying the detected air-fuel ratio φsig by a predetermined correction coefficient.

  In the above-described embodiment, the responsiveness abnormality determination values K1 to K5 are used in detecting the sensor abnormality in FIG. 8, but the responsiveness abnormality determination values K1 to K5 are set based on the initial responsiveness value in the sensor initial state. It is good also as a structure to keep. Thereby, the responsiveness change from the sensor initial state can be monitored.

  In the first embodiment, air-fuel ratio changing means for forcibly changing the air-fuel ratio in a predetermined cycle is provided, and responsiveness detection of the air-fuel ratio sensor 32 and sensor abnormality detection are performed in a state where the air-fuel ratio change is performed. You may make it do. This air-fuel ratio fluctuation can be realized by the air-fuel ratio forced fluctuation processing of FIG. 11 in the second embodiment. Further, for example, air-fuel ratio fluctuation is performed by using air-fuel ratio dither control performed for the purpose of early activation of the catalytic converter at the cold start of the engine and improvement of catalyst purification efficiency (function regeneration) during normal operation. May be. Specifically, the air-fuel ratio is changed toward the rich side and the lean side at a cycle of about several Hz. In such a case, abnormality detection of the air-fuel ratio sensor 32 is performed using the air-fuel ratio detection value and the air-fuel ratio correction amount change data when the air-fuel ratio changes to the rich side or the lean side as the air-fuel ratio changes. Thereby, sufficient amount of change data when the air-fuel ratio changes to the rich side or the lean side can be obtained, and highly reliable sensor abnormality detection can be realized.

  When the air-fuel ratio is forcibly changed, every time the air-fuel ratio detection value reaches the target air-fuel ratio, the target air-fuel ratio may be alternately switched between the rich-side target air-fuel ratio and the lean-side target air-fuel ratio. . Specifically, the target air-fuel ratio is reversed as shown in FIG. In FIG. 19, the actual air-fuel ratio is indicated by a solid line, the air-fuel ratio detected value is indicated by a dotted line (where the common part with the actual air-fuel ratio is a solid line), and the target air-fuel ratio is indicated by a two-dot chain line. FIG. 19A is an example of a responsive abnormality such as a sensor output, and FIG. 19B is an example of an abnormality in which a delay time (dead time) from a gas atmosphere change to a sensor output change increases. . In each case, an example in which a responsive abnormality occurs only on the lean side is shown.

  In FIGS. 19A and 19B, both a1 and b1 correspond to a period in which responsive abnormality occurs, and both a2 and b2 correspond to a period in which responsiveness is normal. In this case, it is possible to detect an abnormality in responsiveness by comparing parameters in the periods a1 and b1 and the periods a2 and b2. In the configuration in which the air-fuel ratio is reversed when the detected air-fuel ratio coincides with the target air-fuel ratio, the air-fuel ratio can be changed in the shortest cycle while realizing the desired air-fuel ratio fluctuation on the rich side and the lean side.

  When detecting a sensor abnormality, only the change amount data of the air-fuel ratio detection value may be used without using the change amount data of the air-fuel ratio correction amount. Also with this configuration, sensor abnormality detection based on the dynamic characteristics of the air-fuel ratio sensor 32 is possible. In particular, when the air-fuel ratio is forcibly changed as described above, since the amount of change in the air-fuel ratio is known in advance, sensor abnormality detection using only the change amount data of the air-fuel ratio detection value becomes more effective. The change speed or change acceleration may be used as the change amount data of the air-fuel ratio detection value.

  In the second embodiment, the first change amount ΔFAF1 and the second change amount ΔFAF2 are calculated as the FAF change amounts in the FAF change speed calculation processing of FIGS. 12 to 14, but only one of them is calculated. Anyway. In this case, in the FAF change amount determination (steps S904 and S906) in FIG. 12, the ΔFAFR calculation (step S915) in FIG. 13, and the ΔFAFL calculation (step S925) in FIG. 14, the first change amount ΔFAF1 or the second change amount ΔFAF2 is determined. Arithmetic processing or the like is performed using either one of the data.

  In the second embodiment, for example, two flags (ΔFAFL calculation permission flag and ΔFAFL calculation period flag) are set when calculating the lean side change speed ΔFAFL of the air-fuel ratio correction coefficient (see FIG. 17 and the like). It is also possible to simplify the configuration by integrating two flags into one. The same applies to the calculation of the rich side change rate ΔFAFR.

  Various parameters such as the change amount data of the air-fuel ratio detection value and the change amount data of the air-fuel ratio correction amount are sequentially calculated, and may be calculated only at the timing immediately before the abnormality detection.

  Instead of realizing the air-fuel ratio sensor 23 as an abnormality detecting device, the air-fuel ratio sensor 32 can also be realized as a responsiveness detecting device. That is, in the latter case, the abnormality detection part is not an implementation requirement. The responsiveness detection result can be used for correction of the air-fuel ratio detection value, air-fuel ratio control, and the like.

It is a block diagram which shows the outline of the engine control system in embodiment of invention. It is a functional block diagram which shows the structure of an air fuel ratio detection apparatus. It is a flowchart which shows FAF calculation processing. It is a flowchart which shows the calculation process of FAF change speed. It is a flowchart which shows the calculation process of (phi) m change speed. It is a flowchart which shows the calculation process of parameter (alpha). It is a flowchart which shows a sensor signal process. It is a flowchart which shows a sensor abnormality detection process. It is sectional drawing which shows the structure of a sensor element. It is a flowchart which shows the whole flow of a sensor abnormality detection process. It is a flowchart which shows an air fuel ratio forced variation process. It is a flowchart which shows the calculation process of FAF change speed. It is a flowchart which shows the calculation process of (DELTA) FAFR. It is a flowchart which shows the calculation process of (DELTA) FAFL. It is a flowchart which shows the calculation process of (phi) m change speed. FIG. 5 is a characteristic diagram for setting a fluctuation period and amplitude at the time of forced air-fuel ratio fluctuation. It is a time chart for demonstrating the procedure which sets the calculation period of FAF change speed. It is a time chart for demonstrating the procedure which sets the calculation period of (phi) m change speed. It is a time chart for demonstrating another form of an air fuel ratio forced fluctuation | variation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 24 ... Exhaust pipe, 32 ... Air fuel ratio sensor, 40 ... ECU, M1 ... Air fuel ratio adjustment part, M5 ... Air fuel ratio sensor signal processing part, M6 ... Sensor abnormality detection part.

Claims (19)

An apparatus comprising an air-fuel ratio sensor installed in an exhaust passage of an internal combustion engine, and performing air-fuel ratio feedback control so that an air-fuel ratio detected value by the air-fuel ratio sensor matches a target value,
Air-fuel ratio changing means for forcibly changing the air-fuel ratio to the rich side and the lean side during the air-fuel ratio feedback control;
Similarly, air-fuel ratio detected value change calculating means for calculating change data of the air-fuel ratio detected value to the rich side and lean side during the air-fuel ratio feedback control,
Responsiveness detection for detecting the responsiveness of the air-fuel ratio sensor for each of the change to the rich side and the change to the lean side based on the change amount data to the rich side and the lean side of the calculated air-fuel ratio detection value Means,
An abnormality detection means for detecting an abnormality of the air-fuel ratio sensor based on the detected response of the air-fuel ratio sensor;
The abnormality detection means is based on change amount data when the air-fuel ratio detection value changes to the rich side and the air-fuel ratio detection value changes to the lean side in accordance with the air-fuel ratio fluctuation by the air-fuel ratio fluctuation means. An abnormality detection apparatus for an air-fuel ratio sensor, wherein abnormality detection of the sensor is performed.   The abnormality detection means compares the sensor responsiveness for each of the change to the rich side and the change to the lean side with a predetermined reference value, and detects an abnormality of the air-fuel ratio sensor according to the result. The abnormality detection device for an air-fuel ratio sensor according to claim 1.   The change amount data at the time of rich side change is compared with the change amount data at the time of change on the lean side, and it is determined whether the rich side responsiveness abnormality or the lean side responsiveness abnormality is based on the magnitude relationship between them. An air-fuel ratio sensor abnormality detection device.   The abnormality detection device for an air-fuel ratio sensor according to any one of claims 1 to 3, wherein a change speed or a change acceleration is calculated as change amount data of the air-fuel ratio detection value. A parameter calculating means for calculating a responsiveness parameter that equalizes the responsiveness of the air-fuel ratio sensor for each of the change to the rich side and the change to the lean side;
The abnormality detection device for an air-fuel ratio sensor according to any one of claims 1 to 4, wherein the abnormality detection means detects an abnormality of the air-fuel ratio sensor based on the response parameter.   6. The air-fuel ratio sensor abnormality detection according to claim 1, wherein the air-fuel ratio fluctuation means sets at least one of a cycle or an amplitude of the air-fuel ratio fluctuation based on an operating state of the internal combustion engine each time. apparatus.   The air-fuel ratio fluctuation means increases the air-fuel ratio fluctuation period or increases the amplitude in the low rotation / low load region of the internal combustion engine, and shortens or amplitudes the air-fuel ratio fluctuation period in the high rotation / high load region of the internal combustion engine. The abnormality detection device for an air-fuel ratio sensor according to claim 6, wherein   The air-fuel ratio fluctuation means amplifies the target air-fuel ratio to the rich side and the lean side, and each time the air-fuel ratio detection value reaches the target air-fuel ratio, the target air-fuel ratio is changed to the rich-side target air-fuel ratio and the lean side. The abnormality detection device for an air-fuel ratio sensor according to any one of claims 1 to 5, wherein the air-fuel ratio sensor is alternately switched with a target air-fuel ratio. An air-fuel ratio sensor installed in the exhaust passage of the internal combustion engine;
An apparatus for performing air-fuel ratio feedback control using the air-fuel ratio correction amount, comprising correction amount calculation means for calculating an air-fuel ratio correction amount for making the air-fuel ratio detection value detected from the air-fuel ratio sensor signal coincide with the target value And
Air-fuel ratio detected value change calculating means for calculating change data of the air-fuel ratio detected value to the rich side and lean side during the air-fuel ratio feedback control;
Responsiveness detection for detecting the responsiveness of the air-fuel ratio sensor for each of the change to the rich side and the change to the lean side based on the change amount data to the rich side and the lean side of the calculated air-fuel ratio detection value Means,
An abnormality detection means for detecting an abnormality of the air-fuel ratio sensor based on the responsiveness of the detected air-fuel ratio sensor;
Data calculation permission means for permitting or prohibiting the calculation of the change amount data of the air-fuel ratio detection value based on the change behavior of the air-fuel ratio correction amount;
An abnormality detection device for an air-fuel ratio sensor comprising: An air-fuel ratio sensor installed in the exhaust passage of the internal combustion engine;
Correction amount calculating means for calculating an air-fuel ratio correction amount for making the air-fuel ratio detection value detected from the signal of the air-fuel ratio sensor coincide with a target value, and performing air-fuel ratio feedback control using the air-fuel ratio correction amount Device to
Air-fuel ratio detected value change calculating means for calculating change data of the air-fuel ratio detected value to the rich side or lean side during the air-fuel ratio feedback control;
A correction amount change calculating means for calculating change data on the rich side or lean side of the air-fuel ratio correction amount during the air-fuel ratio feedback control,
In the air-fuel ratio sensor responsiveness detection apparatus, wherein the air-fuel ratio sensor responsiveness is detected based on the calculated air-fuel ratio detection value change amount data and the calculated air-fuel ratio correction amount change amount data.
A data calculation permission means for permitting or prohibiting the calculation of the change amount data of the air-fuel ratio detection value and the change amount data of the air-fuel ratio correction amount based on the change behavior of the air-fuel ratio correction amount. A responsiveness detection device for a fuel ratio sensor.   The data calculation permission means calculates the variation data of the air-fuel ratio detection value and the air-fuel ratio correction amount only when the variation range of the air-fuel ratio correction amount to the rich side or lean side within a predetermined time exceeds a specified value. The responsiveness detection device for an air-fuel ratio sensor according to claim 10, which is permitted.   The data calculation permission means sets a delay time from the start of calculating the change amount data of the air-fuel ratio correction amount to the start of the change amount data calculation of the air-fuel ratio detection value, and at the timing when the delay time has elapsed, The responsiveness detection device for an air-fuel ratio sensor according to claim 10 or 11, wherein calculation of detection value change amount data is permitted.   13. The air-fuel ratio sensor responsiveness detection according to claim 12, further comprising means for setting the delay time based on a transport delay time from a change in fuel supply amount to the internal combustion engine to a change in gas atmosphere around the air-fuel ratio sensor. apparatus.   The air-fuel ratio sensor according to any one of claims 10 to 13, wherein the data calculation permission means restricts the period during which the calculation is permitted after permitting the calculation of the variation data of the air-fuel ratio correction amount. Responsiveness detection device.   The data calculation permission means is configured to change the air-fuel ratio correction amount to the lean side when the air-fuel ratio correction value changes to the lean side when the air-fuel ratio correction amount changes to the rich side exceeds a specified value. The responsiveness detection of an air-fuel ratio sensor according to any one of claims 10 to 14, wherein when the air-fuel ratio detection value changes to a rich side when the air pressure exceeds a specified value, calculation of change amount data of the air-fuel ratio detection value is prohibited. apparatus.   Air-fuel ratio changing means for forcibly changing the air-fuel ratio to the rich side and the lean side, and when the air-fuel ratio detected value changes to the rich side in accordance with the air-fuel ratio fluctuation by the air-fuel ratio changing means, or the air-fuel ratio detected value is The responsiveness detection device for an air-fuel ratio sensor according to any one of claims 10 to 15, wherein the responsiveness of the air-fuel ratio sensor is detected based on change amount data when changing to the lean side.   The responsiveness detection device for an air-fuel ratio sensor according to claim 16, wherein the air-fuel ratio fluctuation means sets at least one of a cycle or an amplitude of the air-fuel ratio fluctuation based on an operating state of the internal combustion engine each time.   The air-fuel ratio fluctuation means increases the air-fuel ratio fluctuation period or increases the amplitude in the low rotation / low load region of the internal combustion engine, and shortens or amplitudes the air-fuel ratio fluctuation period in the high rotation / high load region of the internal combustion engine. The responsiveness detection device for an air-fuel ratio sensor according to claim 17, wherein   The air-fuel ratio fluctuation means amplifies the target air-fuel ratio to the rich side and the lean side, and each time the air-fuel ratio detection value reaches the target air-fuel ratio, the target air-fuel ratio is changed to the rich-side target air-fuel ratio and the lean side. The responsiveness detection device for an air-fuel ratio sensor according to claim 16, wherein the responsiveness detection apparatus alternately switches and sets the target air-fuel ratio.

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