JP4951612B2 - Diagnostic device and control device for internal combustion engine - Google Patents

Description

  The present invention relates to a diagnostic apparatus for an internal combustion engine that detects an abnormality of a linear air-fuel ratio sensor that detects an exhaust air-fuel ratio of the internal combustion engine.

  A catalyst is installed in the exhaust pipe of the internal combustion engine, an air-fuel ratio sensor for detecting exhaust components is attached upstream and downstream of the catalyst, the fuel amount is corrected based on the value of the air-fuel ratio sensor, and exhaust is efficiently performed with the catalyst. There is an exhaust system to purify. Since the performance of the exhaust system depends on the purification performance of the catalyst and the performance of the air-fuel ratio sensor, a diagnostic device for monitoring these performances is provided.

  Here, as an example of a method of diagnosing the air-fuel ratio sensor upstream of the catalyst, a method of monitoring the response time of the upstream air-fuel ratio sensor output when the air-fuel ratio is forcibly excited is proposed (for example, Patent Document 1). Yes.

JP-A-8-220051

  In the conventional air-fuel ratio sensor, only the rich (lean) or light (lean) of the ternary point (stoichiki) with the best purification efficiency of the catalyst is known. On the other hand, the linear air-fuel ratio sensor can detect how rich or lean the stoichiometry is, and can realize more precise air-fuel ratio feedback control. Here, two main deterioration modes of the linear air-fuel ratio sensor are listed. The first response deterioration is a failure in which the response is delayed from the normal time due to clogging of the sensor or the like. The second gain deterioration is a failure in which the response becomes smaller than normal due to poisoning of the sensor element or abnormality of the current detection circuit, or conversely becomes larger. These deteriorations in response and gain are factors that cause exhaust deterioration due to erroneous determination in catalyst diagnosis or abnormal air-fuel ratio feedback control.

  However, the above-described invention is a diagnostic method for detecting only an abnormality (response deterioration) in the response delay of the upstream air-fuel ratio sensor. In particular, the detection sensitivity abnormality (gain deterioration) in the linear air-fuel ratio sensor that linearly detects the exhaust air-fuel ratio is detected. Not enough consideration has been given to this.

  The present invention has been made in view of such circumstances, and an object of the present invention is to disclose an internal combustion engine diagnostic device that separately detects response deterioration and gain deterioration of a linear air-fuel ratio sensor, This is to prevent misdiagnosis.

  In order to achieve the above-mentioned object, a response deterioration / gain deterioration detecting means for separately detecting response deterioration, which is a response abnormality of the linear air-fuel ratio sensor, and gain deterioration, which is an abnormality in detection sensitivity, is provided. Inside, there is provided a diagnostic signal generation means for giving an air-fuel ratio fluctuation lower than the normal air-fuel ratio control (frequency 1 Hz or less).

  Further, the present invention uses the air-fuel ratio fluctuation by the diagnostic signal generation means also for catalyst diagnosis.

  Furthermore, the present invention includes an abnormality warning means for warning the operation of gain degradation of the linear air-fuel ratio sensor.

  By implementing the present invention, exhaust deterioration and erroneous diagnosis due to a failure of the linear air-fuel ratio sensor can be prevented. Furthermore, by implementing the present invention, exhaust deterioration due to failure of the linear air-fuel ratio sensor and erroneous diagnosis of catalyst diagnosis can be prevented. Furthermore, by implementing the present invention, the driver can be warned of an abnormality even when only gain deterioration occurs.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram of the control system of the direct injection internal combustion engine 107. The intake air introduced into the cylinder 107b is taken from the inlet portion 102a of the air cleaner 102, passes through an air flow meter (air flow sensor) 103 which is one of the operating state measuring means of the internal combustion engine, and is electrically controlled to control the intake flow rate. The collector 106 is entered through the throttle body 105 in which the throttle valve 105a is accommodated. A signal representing the intake air flow rate is output from the airflow sensor 103 to a control unit 115 which is an internal combustion engine controller.

  The throttle body 105 is provided with a throttle sensor 104, which is one of the operating state measuring means of the internal combustion engine for detecting the opening degree of the electric throttle valve 105a, and its signal is also output to the control unit 115. It has become so.

  The air sucked into the collector 106 is distributed to the intake pipes 101 connected to the cylinders 107b of the internal combustion engine 107, and then guided to the combustion chambers 107c of the cylinders 107b.

  On the other hand, fuel such as gasoline is primarily pressurized from the fuel tank 108 by the fuel pump 109 and regulated to a constant pressure by the fuel pressure regulator 110 and is secondarily pressurized to a higher pressure by the high-pressure fuel pump 111. To the common rail.

  The high-pressure fuel is injected from the injector 112 provided in each cylinder 107b into the combustion chamber 107c. The fuel injected into the combustion chamber 107 c is ignited by the spark plug 114 by the ignition signal that has been increased in voltage by the ignition coil 113.

  The cam angle sensor 116 attached to the camshaft of the exhaust valve outputs a signal for detecting the phase of the camshaft to the control unit 115. Here, the cam angle sensor may be attached to the camshaft on the intake valve side. In addition, a crank angle sensor 117 is provided on the crankshaft shaft to detect the rotation and phase of the crankshaft of the internal combustion engine, and its output is input to the control unit 115.

  Further, an air-fuel ratio sensor 118 provided upstream of the catalyst 120 in the exhaust pipe 119 detects oxygen in the exhaust gas and outputs a detection signal to the control unit 115. Here, the cylinder injection internal combustion engine has been described. However, the present invention is not limited to this and can be applied to a port injection internal combustion engine in which the injector 112 is attached to the intake port.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 shows an outline of a diagnostic apparatus for an internal combustion engine that detects an abnormality of a linear air-fuel ratio sensor (LAF sensor) upstream of the catalyst. An injector 203 is provided at the intake port. A linear air-fuel ratio sensor 204 is provided upstream of the catalyst 205 installed midway in the exhaust pipe 207. An air-fuel ratio sensor 206 is provided on the downstream side of the catalyst 205. In normal A / F control (in the control mode for controlling the air-fuel ratio), the fuel is increased or decreased at a frequency greater than 1 Hz and less than or equal to 3 Hz. Here, the frequency in the A / F control will be described. The control unit 115 in FIG. 1 detects the air-fuel ratio in the exhaust pipe by means of a linear air-fuel ratio sensor installed in the exhaust pipe so that the air-fuel ratio in the engine becomes a predetermined air-fuel ratio. Based on this, the amount of fuel supplied from the injector is adjusted. The frequency of the fuel amount increase / decrease supplied from the injector at this time is the frequency in the A / F control.

  The diagnostic apparatus of this embodiment detects the exhaust air / fuel ratio when the fuel is increased or decreased by 1 Hz or less by the diagnostic signal generating means B201 (diagnostic mode) by the linear air / fuel ratio sensor, and the response deterioration / gain deterioration detecting means 2 shows a diagnostic apparatus for an internal combustion engine that separately detects response deterioration and gain deterioration by B202. Preferably, the low frequency range that is the diagnostic mode is 0.3 Hz or more in consideration of exhaust deterioration and drivability.

  Next, the diagnostic principle of this embodiment will be described. FIG. 3 shows gain characteristics and phase characteristics of the linear air-fuel ratio sensor. Regarding the linear air-fuel ratio sensors, A is normal, A ′ is response deterioration, A ″ indicates gain characteristics when gain is deteriorated, B is normal, B ′ is response deterioration, and B ″ is gain. The phase characteristic at the time of deterioration is shown. That is, the response deterioration is a phenomenon in which the gain is shifted to the left (low frequency side) in the figure (A → A ′) and the phase is delayed (B → B ′) from the normal state. On the other hand, gain degradation is a phenomenon in which the gain characteristic shifts downward (lower gain side) than when it is normal (A → A ″). The phase does not change (B and B ″) due to gain degradation. Here, if the deterioration detection is performed using the normal A / F control frequency (greater than 1 Hz and 3 Hz or less), the gain changes in both the response deterioration and the gain deterioration, so that normality and deterioration can be distinguished. It is very difficult to discriminate between response deterioration and gain deterioration (a in FIG. 3). However, in the low frequency range c (for example, 1 Hz or less), the gain decreases only when the gain is deteriorated, and the phase is delayed only when the response is deteriorated. Therefore, by focusing attention on the gain range c ′ in detection of gain degradation and focusing on the phase range c ″ in detection of response degradation, response degradation and gain degradation can be easily separated and detected.

  FIG. 4 shows an example of a deterioration index based on the principle of FIG. The air-fuel ratio is periodically oscillated in the low frequency range by the diagnostic signal generation means shown in FIG. In this case, in the response deterioration, the cycle of the air-fuel ratio (detected air-fuel ratio) detected by the sensor is longer than the cycle of the air-fuel ratio (target air-fuel ratio) that the generating means tries to give due to the phase delay. On the other hand, when the gain decreases due to gain deterioration, the amplitude of the detected air-fuel ratio becomes smaller than the amplitude of the target air-fuel ratio because of the gain decrease. Therefore, the ratio of the detected air-fuel ratio period to the target air-fuel ratio period (response deterioration index = detected air-fuel ratio period / target air-fuel ratio period) is used as the response deterioration index. Further, the ratio of the peak of the detected air-fuel ratio amplitude to the peak of the target air-fuel ratio amplitude (gain deterioration index = the peak of the detected air-fuel ratio amplitude / the peak of the target air-fuel ratio amplitude) is used as the gain deterioration index. By using these two indices, response deterioration and gain deterioration can be easily separated and diagnosed according to the degree of deterioration.

Next, the conventional air-fuel ratio sensor (O ₂ sensor) diagnosis and the linear air-fuel ratio sensor diagnosis of this embodiment will be compared with reference to FIGS. In the conventional air-fuel ratio sensor diagnosis, since the O ₂ sensor is the diagnosis target, the deterioration detection target is only response deterioration. For example, as shown in FIG. 5, the horizontal axis is the frequency of the exhaust air-fuel ratio (input signal) generated by the diagnostic generation signal B201 shown in FIG. 2, and the vertical axis is a sensor installed in the exhaust pipe. It is set as the sensor detection cycle (cycle) to be detected at the time. With respect to the frequency of the exhaust air-fuel ratio (input signal) generated by the diagnostic generation signal B201 on the horizontal axis, there is a predetermined sensor detection cycle (cycle) that is actually detected by a sensor installed in the exhaust pipe on the vertical axis. If it is greater than or equal to the value, it is determined that the response of the sensor has deteriorated. However, in the conventional method, it is difficult to detect gain deterioration regardless of the period when the gain is normal. On the other hand, there is also a method of detecting deterioration from gain characteristics in the conventional method, for example, a method of detecting deterioration from a decrease in gain characteristics at a control frequency (greater than 1 Hz and 3 Hz or less). However, in this method, as shown in FIG. 6, there is a possibility that it is determined that the gain is deteriorated even though the sensor is normal. Although a slight response deterioration has occurred, b is within a normal range as a sensor. In the case of “a”, no response deterioration occurs, but gain deterioration occurs remarkably, and the sensor is in an abnormal range. Therefore, the gain deterioration cannot be detected correctly in the range where there is an intersection D between a which is only gain deterioration and b where the sensor is normal. In order to detect such gain degradation, an input signal with a low frequency (1 Hz or less) is required. In this embodiment, by focusing on the gain characteristics of the low frequency response, gain degradation that cannot be detected by the conventional method. Can be detected.

  FIG. 7 is an example of a block diagram for realizing the present invention. In the gain deterioration determination of FIG. 7, RABF (actual air-fuel ratio) is passed through a high-pass filter (HPF) at B701 to remove a direct current component and a drift component. Next, the absolute value is converted in B702, and the maximum value is searched in B703 to calculate the peak of the detected air-fuel ratio. Then, the gain deterioration index shown in FIG. 4 is calculated in the normalization process of B704, noise is removed by the average process in B705, and the gain is obtained when the average gain deterioration index output from B705 is outside the predetermined range in B706. It is determined that the gain is deteriorated, and a gain deterioration determination flag is set. On the other hand, in the response degradation determination, the B701 high-pass filter output is zero-cross detected by the B707 zero-cross detection, the zero-cross detection period is computed by the B708 period computation, and the response degradation index shown in FIG. 4 is computed by the B709 normalization process. In step B710, noise is removed by averaging processing. If the average response deterioration index output from B710 in B711 is larger than a predetermined value, it is determined that the response is deteriorated, and a response deterioration determination flag is set.

  FIG. 8 is an example of the time chart in FIG. 7 and shows how the zero value of the filter output is detected and the maximum value and period are calculated using this as a trigger. In this example, since deterioration index calculation can be performed twice in one cycle, it is possible to detect deterioration in a shorter time.

  FIG. 9 is an example when the deterioration of the linear air-fuel ratio sensor is actually detected by the block diagram shown in FIG. 7 at various vehicle speeds. The upper part of FIG. 9 shows the gain degradation index when there is gain degradation or response degradation. On the other hand, the lower part shows the response deterioration index when there is gain deterioration or response deterioration. When the gain deterioration on the horizontal axis of the left drawing of FIG. 9 is 100%, it indicates that there is no gain deterioration of the linear air-fuel ratio sensor. When the response deterioration on the horizontal axis of the right drawing is about 100 ms, the linear air-fuel ratio is It shows that there is no sensor response degradation. From this result, it is possible to detect a gain degradation of 50% or less or 150% or more as a gain degradation if the criterion for determining the gain degradation is 0.7 to 1.3. Similarly, if the criterion for determining response deterioration is 1.3, response deterioration of 300 ms or more can be detected as response deterioration. Here, it can be confirmed that the response deterioration index increases as the response deterioration increases, but has no sensitivity to gain deterioration, and the gain deterioration index increases or decreases according to the gain deterioration, but has no sensitivity with respect to the response deterioration.

  Next, FIG. 10 shows one experimental result showing the relationship between sensor deterioration and exhaust deterioration. FIG. 10 shows an exhaust deterioration margin when a rich or lean step disturbance is given during air-fuel ratio feedback control by the linear air-fuel ratio sensor. At this time, the catalyst installed in the exhaust pipe is normal. The two diagrams on the left are the results when the gain is degraded, while the two diagrams on the right are the results when the response is degraded. Response degradation is insensitive to step disturbance, while gain degradation worsens HC three times and NOx two times against step disturbance. This is because the feedback control by the linear air-fuel ratio sensor is controlled based on the deviation, and it is considered that the exhaust gas deteriorated because the deviation is different from the actual due to gain deterioration. However, since the catalyst is normal, the exhaust deterioration is caused by sensor gain deterioration. Therefore, if the sensor output is corrected according to the degree of deterioration, exhaust deterioration due to gain deterioration can be prevented.

  Next, FIG. 11 shows an example of a system that prevents exhaust deterioration due to gain deterioration by sensor correction. In the conventional system, the exhaust air / fuel ratio is corrected by directly using the output of the air / fuel ratio sensor for the air / fuel ratio correcting means B1103. However, the sensor deterioration detecting means B1101 in FIG. In B1102, the output of the air-fuel ratio sensor is corrected according to the degree of gain deterioration. For example, when the gain deterioration index is halved from the normal value, the exhaust performance similar to that in the normal state can be realized by doubling the output of the detected air-fuel ratio. In this way, by correcting the sensor output using the gain deterioration index, it is possible to construct a system that is robust against sensor deterioration that prevents exhaust deterioration even when gain deterioration occurs. Further, based on the gain deterioration detected by the sensor deterioration detection means B1101, the warning lamp B1106 is turned on to notify the driver of the abnormality. Here, the warning lamp includes, for example, outputting a trouble code, turning on a mill, and the like. Moreover, you may notify a driver | operator using an audio | voice. As a result, even when only gain degradation, which is an abnormality in detection sensitivity, has occurred, it is possible to warn the driver of the degradation.

  Next, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 12 shows an example of a catalyst diagnosis method. This system includes means for separating and detecting the abnormality of the sensor by increasing / decreasing the fuel injected from the injector by the diagnostic generating means (B1203) based on the rich lean inversion means (B1202). Catalyst deterioration detection means (B1201) for detecting catalyst deterioration from the outputs of the linear air-fuel ratio sensor and the downstream air-fuel ratio sensor is provided. As the catalyst deterioration index of the catalyst deterioration detection means (B1201), for example, the ratio of the trajectory lengths of the upstream and downstream sensors, the ratio of the inversion period, the ratio of the number of inversions, the correlation, and the like can be used.

  FIG. 13 shows the result of experimentally determining the catalyst deterioration index when the sensor deteriorates in the catalyst diagnosis method shown in FIG. In this experiment, correlation is used as a deterioration index, and the larger the correlation is, the more the catalyst is deteriorated. This is based on the fact that when the catalyst is deteriorated, the swing of the downstream air-fuel ratio sensor output becomes large due to the decrease in the oxygen adsorption capacity of the catalyst, and the correlation between this shake and the swing of the upstream air-fuel ratio sensor output becomes large. The same normal catalyst was used in all experiments. Although there is no sensitivity of the catalyst deterioration index (correlation) to gain deterioration, in response deterioration, the deterioration index (correlation) increases as the response deterioration degree increases. Therefore, even a normal catalyst may be erroneously determined as catalyst deterioration due to response deterioration. This is because the rich-lean inversion period becomes longer due to the response deterioration, and the air-fuel ratio is controlled with a long period exceeding the oxygen adsorption capacity of the normal catalyst. Also at this time, erroneous diagnosis can be prevented by correcting the sensor output in accordance with the response deterioration degree.

  FIG. 14 shows an example of a system that prevents erroneous determination of the catalyst by sensor correction. Description of the same components as those in FIG. 11 is omitted. The response deterioration index is calculated by the sensor deterioration detection unit B1401 to obtain the response deterioration degree, and the sensor output correction unit B1402 corrects the sensor output according to the response deterioration index. For example, if the response is delayed by 100 ms with respect to a normal sensor, the response may be advanced by 100 ms by phase advance compensation. By calculating the catalyst deterioration index by the catalyst deterioration detection means of B1403 using the sensor output corrected in this way and the output of the downstream air-fuel ratio sensor, the catalyst deterioration robust against the response deterioration can be realized.

  In the catalyst diagnosis method shown in FIG. 12, if the air-fuel ratio fluctuation of 1 Hz or less is generated in the diagnostic signal generation means in B1203, not only the catalyst diagnosis but also the linear air-fuel ratio sensor diagnosis can be performed. Reduction of exhaust can be realized.

  Next, another embodiment of the present invention will be described with reference to FIG.

  FIG. 15 is a flowchart for prohibiting the LAF sensor diagnosis when a fuel system abnormality is detected. In step S1501, it is determined whether there is an abnormality in the fuel system. Here, for example, the air-fuel ratio feedback correction coefficient becomes an upper limit or a lower limit value for a predetermined time, or the accelerator opening feedback correction coefficient during idling becomes an upper limit or a lower limit value for a predetermined time. What is necessary is just to judge abnormality of a fuel system. In step S1502, it is determined whether or not there is an abnormality in the fuel system. If there is an abnormality, the process proceeds to step S1503 and the LAF diagnosis prohibition flag is set to 1. In step S1504, it is determined whether the LAF diagnosis prohibition flag is 1. If the LAF diagnosis prohibition flag is 1, the process is terminated as it is. If the LAF diagnosis prohibition flag is not 1, the process advances to step S1505 to execute, for example, the LAF sensor diagnosis as described in the first embodiment. According to the present invention, it is possible to prevent erroneous diagnosis of LAF sensor diagnosis due to fuel system abnormality by prohibiting LAF sensor diagnosis when the fuel system is abnormal.

  In the above description, a periodic signal as shown in FIG. 4 is used for diagnosis of the LAF sensor. However, the present invention can be applied not only to a periodic signal but also to a step response as shown in FIG. That is, in the detected air-fuel ratio when the target air-fuel ratio is changed stepwise in an open loop, the response deterioration index is the time constant of the detected air-fuel ratio, and the gain deterioration index is the average of the target air-fuel ratio after the step change and the detected air-fuel ratio. Can also detect response degradation and gain degradation separately.

The whole block diagram of a cylinder injection internal combustion engine. The outline | summary of the diagnostic apparatus of the internal combustion engine in this embodiment. The figure explaining the principle of this embodiment. An example of the deterioration parameter | index in this embodiment. An example of the conventional diagnostic method. The figure explaining the characteristic of this embodiment. An example of the block diagram which implement | achieves this embodiment. An example of the time chart in FIG. An example of the deterioration detection by this embodiment. An experimental result showing the relationship between sensor deterioration and exhaust deterioration. Outline of a control device for an internal combustion engine that is robust against gain deterioration. Overview of catalyst diagnostic method. An experimental result showing the relationship between sensor deterioration and catalyst diagnosis. An overview of a control device for an internal combustion engine that is robust against response deterioration. An example of a flowchart for prohibiting LAF sensor diagnosis when the fuel system is abnormal. Another example of the deterioration parameter | index in this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Intake pipe, 102 ... Air cleaner, 103 ... Air flow sensor, 104 ... Throttle sensor, 105 ... Throttle body, 106 ... Collector, 107 ... In-cylinder injection internal combustion engine, 109 ... Fuel pump, 111 ... High pressure fuel pump, 112 ... Injector , 113 ... ignition coil, 114 ... ignition plug, 115 ... control unit, 116 ... cam angle sensor, 117 ... crank angle sensor, 118 ... air-fuel ratio sensor.

Claims (5)

A diagnostic device for an internal combustion engine that is installed in an exhaust pipe of an internal combustion engine and diagnoses a linear air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas,
The diagnostic device comprises:
Diagnostic signal generating means for providing air-fuel ratio fluctuations;
Means for separating and detecting response deterioration and gain deterioration of the linear air-fuel ratio sensor;
Has a control mode for controlling the air-fuel ratio and the diagnostic mode for diagnosing the linear air-fuel ratio sensor, the diagnosis signal generating means is in the diagnostic mode, giving an air-fuel ratio varies significantly below 1Hz than 0 Hz,
A diagnostic apparatus, wherein a gain deterioration is determined based on an air-fuel ratio fluctuation detected by the linear air-fuel ratio sensor and an air-fuel ratio fluctuation controlled by the diagnostic signal generation means.   Determining the gain deterioration of the linear air-fuel ratio sensor based on a gain deterioration index which is a ratio of the peak of the air-fuel ratio detected by the linear air-fuel ratio sensor and the peak of the air-fuel ratio fluctuation controlled by the diagnostic signal generating means. The diagnostic apparatus according to claim 1, characterized in that:   The control device according to claim 1, wherein a gain characteristic of the linear air-fuel ratio sensor is corrected based on the gain deterioration index.   The diagnostic apparatus according to any one of claims 1 to 3, wherein the frequency of air-fuel ratio fluctuation for diagnosing the linear air-fuel ratio sensor by the diagnostic signal generation means is greater than 0 Hz and 1 Hz or less.   4. The diagnostic apparatus according to claim 1, wherein the frequency of air-fuel ratio fluctuation in a diagnostic mode for diagnosing the linear air-fuel ratio sensor by the diagnostic signal generation means is 0.3 Hz to 1 Hz.

Images