JP2010159720A - Diagnostic device for air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conduct an accurate diagnosis whether a rich signal of an air-fuel ratio sensor is properly output during a normal operation. <P>SOLUTION: When a state in which an intake-air volume Ga is equal to or greater than a predetermined value Ga0 is kept for a predetermined time period or longer (c1≥c10), determination is made whether an air-fuel ratio sensor on downstream side of the exhaust emission purifying catalyst is outputting a rich signal. When the rich signal is output, if it is determined that the output voltage Vr is equal to or smaller than a normal output Vr0 which is not influenced by dew condensation of sensor element, and the rich signal has been continually output for a predetermined time period or longer (c2≥c20), it is diagnosed that the rich signal is output properly. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for diagnosing an air-fuel ratio sensor that detects an air-fuel ratio in response to oxygen in exhaust gas of an internal combustion engine.

  In Patent Document 1, an air-fuel ratio sensor is provided on the upstream side and the downstream side of an exhaust purification catalyst of an internal combustion engine, and in an apparatus that feedback-controls the air-fuel ratio based on the output of these air-fuel ratio sensors, It is disclosed that rich / lean output determination is performed by comparing an output value with a reference value.

JP-A-8-21283

  The air-fuel ratio sensor (oxygen sensor) used on the downstream side of the catalyst includes a sensor element interposed between the atmosphere and the exhaust, and has an exhaust air-fuel ratio corresponding to the difference in oxygen partial pressure between the atmosphere and the exhaust. A detection signal is output.

  In this type of air-fuel ratio control device, in order to perform the air-fuel ratio control normally, a diagnosis of whether the downstream air-fuel ratio sensor normally outputs a rich signal and a lean signal (hereinafter, the former is a rich output diagnosis, The latter is called lean output diagnosis).

  These rich output diagnosis and lean output diagnosis are preferably performed during normal operation without performing special operation for diagnosis in order to suppress deterioration in driving performance, fuel consumption, and the like.

  By the way, if the sensor element is damaged and the exhaust gas flows into the atmospheric chamber inside the element through the damaged portion, the difference in oxygen partial pressure inside and outside the sensor element becomes small and a rich signal may not be output even if it is rich. There is (hereinafter, such sensor element damage is referred to as element cracking).

  Therefore, it is necessary to avoid that the rich signal is determined to be normal for an air-fuel ratio sensor that has caused element cracking. A rich signal may be output.

  If a rich output diagnosis is performed after separately diagnosing the presence or absence of element cracks, the accuracy can be ensured, but the number of diagnoses increases and becomes complicated.

  For this reason, conventionally, the rich output diagnosis during the normal operation is not performed, and the diagnosis is performed by a special operation for diagnosis, for example, active control in which the air-fuel ratio is forcibly switched and controlled to be rich or lean. However, the diagnosis by such special driving for the rich output diagnosis has led to deterioration of driving performance, fuel consumption, and the like.

  The present invention has been made paying attention to such a conventional problem, and has made it possible to perform a rich output diagnosis of an air-fuel ratio sensor with high accuracy even during normal operation even for an air-fuel ratio sensor in which an element crack has occurred. An object of the present invention is to provide an air-fuel ratio sensor diagnostic apparatus.

For this reason, the present invention includes a sensor element disposed in the exhaust passage of the internal combustion engine and interposed between the atmosphere and the exhaust, and detecting the exhaust air / fuel ratio according to the difference in oxygen partial pressure between the atmosphere and the exhaust. For an air-fuel ratio sensor that outputs a signal,
Rich output diagnostic means for diagnosing whether the air-fuel ratio sensor normally outputs a rich signal;
Rich output diagnosis permission means for permitting diagnosis by the rich output diagnosis means when it is determined that a predetermined diagnosis permission condition is satisfied;
A diagnostic device for an air-fuel ratio sensor comprising:
Means for detecting the amount of intake air;
The rich diagnosis permission means sets the predetermined diagnosis permission condition that a state where the intake air amount is equal to or greater than a predetermined value continues for a predetermined time.

  With such a configuration, when the amount of intake air is small, even if the air-fuel ratio sensor is cracked, it is difficult for the exhaust to enter the atmosphere side, and the rich signal may be misdiagnosed as normal due to noise or the like. However, since the condition for diagnosis is that the intake air amount is more than the predetermined value for a predetermined period of time, if the element is cracked, the exhaust will flow from the damaged part of the sensor element to the atmosphere inside the element. It is possible to reliably avoid erroneous determination that the rich signal is normally output without the oxygen partial pressure difference being kept sufficiently small and the air-fuel ratio sensor not outputting the rich signal.

  Therefore, a high-accuracy rich output diagnosis can be performed even during normal operation without separately performing element crack diagnosis, and a special diagnostic operation need not be performed more than necessary.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows schematic structure of the internal combustion engine provided with the diagnostic apparatus of the air fuel ratio sensor concerning embodiment of this invention. A cross section showing a sensor element peripheral portion of an air-fuel ratio sensor (oxygen sensor) on the downstream side of the catalyst used for air-fuel ratio feedback control of the internal combustion engine. 7 is a flowchart showing a main routine for diagnosis of the air-fuel ratio sensor on the downstream side of the catalyst. The flowchart which shows the front | former stage of the rich output diagnosis (subroutine) of the air fuel ratio sensor of a catalyst downstream side. The flowchart which shows the back | latter stage of the rich output diagnosis (subroutine) of the air-fuel ratio sensor of the catalyst downstream side.

  FIG. 1 shows a schematic configuration of an internal combustion engine including an air-fuel ratio sensor diagnostic apparatus according to an embodiment of the present invention.

  The internal combustion engine 1 includes an intake passage 2 and an exhaust passage 3, and an air flow meter 4 that detects an intake air amount Ga, a throttle valve 5 that adjusts the intake air amount, and a fuel injection valve 6 at an intake port portion. Is arranged. The throttle valve 5 is driven by an electrically-operated throttle actuator 7. An exhaust purification catalyst (hereinafter also simply referred to as “catalyst”) 8 is disposed in the exhaust passage 3, and an upstream air-fuel ratio sensor 9 and a downstream air-fuel ratio sensor 10 are respectively provided upstream and downstream of the catalyst 8. It is arranged.

  Intake air (fresh air) is introduced into the combustion chamber 12 from the intake valve 11 that opens in the intake stroke via the intake passage 2. A spark plug 13 is attached to the combustion chamber 12.

  The fuel injected into the intake port from the fuel injection valve 6 is introduced into the combustion chamber 12 while being mixed with the intake air, ignited by the spark plug 13 and ignited and combusted, and the combustion exhaust is opened in the exhaust stroke. The exhaust valve 14 is discharged to the exhaust passage 3.

  The catalyst 8 simultaneously purifies CO, HC and NOx which purify exhaust by oxidizing HC and CO in the exhaust and reducing NOx in the exhaust in a state where combustion near the stoichiometric air-fuel ratio is performed. It consists of a three-way catalyst that can. The three-way catalyst also stores oxygen in the exhaust when the air-fuel ratio of the exhaust passing through it is leaner than the stoichiometric air-fuel ratio, and releases the stored oxygen when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. It has an oxygen storage function.

  The upstream air-fuel ratio sensor 9 is configured to linearly detect the exhaust air-fuel ratio, and the downstream air-fuel ratio sensor 10 has a large change in output voltage with the reference air-fuel ratio (theoretical air-fuel ratio) as a boundary. It is constituted by a so-called oxygen sensor that detects whether the air-fuel ratio is richer or leaner than the reference air-fuel ratio.

  Therefore, the downstream air-fuel ratio sensor 10 can determine whether rich exhaust gas (containing a lot of HC and CO) or lean exhaust gas (containing a lot of NOx) has flowed out downstream of the catalyst 8.

  FIG. 2 shows a schematic configuration of the downstream air-fuel ratio sensor (oxygen sensor) 10. The downstream air-fuel ratio sensor 10 includes a cover 31 and is assembled in the exhaust passage 3 so that the cover 31 is exposed to the exhaust.

  The cover 31 is provided with a hole (not shown) for guiding exhaust therein, and a sensor element 32 is disposed inside the cover 31. The sensor element 32 has a tubular structure with one end (the lower end in FIG. 2) closed, and the outer surface of the tubular structure is covered with a diffusion resistance layer 33. The diffusion resistance layer 33 is a heat-resistant porous material such as alumina and has a function of regulating the diffusion speed of exhaust gas in the vicinity of the surface of the sensor element 32.

An exhaust side electrode 34, a solid electrolyte layer 35, and an atmosphere side electrode 36 are provided inside the diffusion resistance layer 33. The exhaust side electrode 34 and the atmosphere side electrode 36 are electrodes made of a noble metal having a high catalytic action such as Pt, and are electrically connected to a control circuit described later. The solid electrolyte layer 35 is a sintered body containing ZrO ₂ or the like and has a characteristic of conducting oxygen ions.

  An air chamber 37 that is open to the atmosphere is formed inside the sensor element 32. A heater 38 for heating the sensor element 32 is disposed in the atmospheric chamber 37. The sensor element 32 exhibits stable output characteristics at an activation temperature of about 400 ° C. The heater 38 is electrically connected to the control circuit, and can heat and maintain the sensor element 32 at an appropriate temperature.

  As various sensors for detecting the operating state of the engine, in addition to the air flow meter 4, the upstream air-fuel ratio sensor 9, the downstream air-fuel ratio sensor 10, the accelerator opening sensor 15 for detecting the accelerator opening ACC, and the engine rotational speed NE are used. A rotation speed sensor 16 for detecting, a throttle sensor 17 for detecting the opening degree of the throttle valve 5, a water temperature sensor 18 for detecting the cooling water temperature as the engine temperature, and the like are arranged. The detection signals from these sensors are used for various controls. Input to an ECU (electronic control unit) 20 to be performed.

  By the way, the purification efficiency by the catalyst (three-way catalyst) 8 is strongly influenced by the air-fuel ratio of the air-fuel mixture, and in order to simultaneously purify the HC, CO, and NOx, the air-fuel ratio of the air-fuel mixture is in the range near the stoichiometric air-fuel ratio. Must be set to Therefore, after the air-fuel ratio sensors 9 and 10 are activated and the air-fuel ratio can be detected, basically, to make the catalyst 8 function effectively, the air-fuel ratio of the mixture is set to the center of the above range. Air-fuel ratio control is performed.

  The ECU 20 controls the air-fuel ratio by controlling the throttle valve 5 and the fuel injection valve 6 according to the operating conditions of the internal combustion engine 1 and the vehicle that are grasped based on the detection signals from the sensors. Feedback control). The outline of the air-fuel ratio control by the ECU 20 is as follows.

  First, the target intake air amount is calculated according to the detected values of the accelerator opening ACC, the engine speed NE, etc., and the throttle valve 5 is opened so that the intake air amount Ga according to the target intake air amount is obtained. To control.

  On the other hand, the basic fuel injection amount for obtaining the theoretical air-fuel ratio is calculated with respect to the actual intake air amount detected by the air flow meter 4.

  An air-fuel ratio feedback correction for feedback-correcting the basic fuel injection amount based on the deviation between the air-fuel ratio upstream of the catalyst 8 detected by the upstream air-fuel ratio sensor 9 and the target air-fuel ratio, that is, the theoretical air-fuel ratio. Calculate the amount.

  Further, the oxygen storage state or oxygen release state of the catalyst 8 is estimated based on the air-fuel ratio downstream of the catalyst 8 detected by the downstream air-fuel ratio sensor 10, and the correction to the air-fuel ratio feedback correction amount is made based on this estimation. Do. In this correction process, the sub-feedback correction amount calculated based on the output of the downstream air-fuel ratio sensor 10 is corrected to increase or decrease, and the air-fuel ratio feedback correction amount is corrected by the sub-feedback correction amount. Specifically, while the downstream air-fuel ratio sensor 10 is outputting a rich signal, the sub-feedback correction amount is decremented by a certain amount to the minus side so that the air-fuel ratio of the air-fuel mixture changes by a certain amount toward lean. Will be increased. On the other hand, while the downstream air-fuel ratio sensor 10 is outputting a lean signal, the sub feedback correction amount is increased by a certain amount to the plus side so that the air-fuel ratio of the air-fuel mixture approaches the rich side by a certain amount.

  The basic fuel injection amount is corrected by the air-fuel ratio feedback correction amount corrected by the sub feedback correction amount that is increased or decreased in this manner, and the corrected final fuel injection amount is injected from the fuel injection valve 6. Feedback control of the air-fuel ratio. By such air-fuel ratio feedback control, the purification action of the catalyst 8 is effectively utilized.

  On the other hand, in order to perform such air-fuel ratio feedback control normally, the air-fuel ratio sensors 9 and 10 are diagnosed.

  Hereinafter, diagnosis during normal operation including rich output diagnosis of the downstream air-fuel ratio sensor 10 according to the present invention will be described. Here, the normal operation refers to a state in which the vehicle is normally operated without performing a special operation for this type of diagnosis. During the normal operation, the air-fuel ratio feedback control is basically performed, and at the time of acceleration, the air-fuel ratio control is performed so that the air-fuel ratio is transiently rich. Therefore, the air-fuel ratio downstream of the catalyst 8 is at least rich. There is a period.

  Therefore, if the downstream air-fuel ratio sensor 10 has a function of normally outputting the rich signal, the rich signal should be output when the air-fuel ratio downstream of the catalyst 8 becomes rich during normal operation. The rich output diagnosis is performed based on the output history of the rich signal.

  The diagnosis of the downstream air-fuel ratio sensor 9 will be described with reference to the flowcharts shown in FIGS. FIG. 3 shows the main flow.

  In step S1, it is determined whether the precondition is satisfied. Specifically, after the start of the engine 1 and before the end of the rich output diagnosis, the diagnosis result such as disconnection or short circuit of the air-fuel ratio sensor output system is normal, and the battery voltage is not less than a predetermined value. For example, it is determined whether all the conditions for executing the rich output diagnosis are satisfied.

  When the precondition is not satisfied, this routine is terminated. When the precondition is satisfied, the process proceeds to step S2.

  In step S2, it is determined whether or not the determination that the downstream air-fuel ratio sensor 10 is in an active state has been completed. This activation determination is performed by determining whether the elapsed time after startup, the integrated value of the intake air amount or the fuel injection amount is equal to or greater than a set value set as a value that activates the downstream air-fuel ratio sensor 10 or the like. It can be carried out.

  When it is determined that the downstream air-fuel ratio sensor 10 is active, the process proceeds to step S3, and it is shown whether or not the lean signal is normally output by the lean output diagnosis of the downstream air-fuel ratio sensor 10. The lean output diagnosis flag value is determined by the subroutine that does not. The lean output diagnosis is continued for a predetermined time or more accurately, whether there is a history that the downstream air-fuel ratio sensor 10 has output a lean signal during normal operation in which the exhaust air-fuel ratio becomes lean. It can be determined by whether there is a history of lean signal output.

  When it is determined that the lean signal of the downstream air-fuel ratio sensor 10 is normally output, the process proceeds to step S4, and the rich output diagnosis according to the present invention diagnoses that the rich signal is normally output. Is determined by the value of the rich output diagnosis flag by a subroutine to be described later.

  If the rich signal is also a normal diagnosis result, the process proceeds to step S5, where the downstream air-fuel ratio sensor 10 is diagnosed as normal, and otherwise, the routine is terminated without making a normal determination.

  4 and 5 show the flow of the rich output diagnosis subroutine.

  In step S11, the intake air amount Ga detected by the air flow meter 4 is read.

  In step S12, it is determined whether the intake air amount Ga is a predetermined value Ga0 or more.

  When it is determined that the value is equal to or greater than the predetermined value Ga0, the process proceeds to step S13, the counter C1 is counted up, and then the process proceeds to step S15.

  When it is determined that the value is less than the predetermined value Ga0, the process proceeds to step S14, the count value c1 of the counter C1 is reset to 0, and this flow is exited.

  In step S15, it is determined whether the count value c1 is equal to or greater than a predetermined value c10.

  When it is determined that the count value c1 is equal to or greater than the predetermined value c10, that is, the duration of the state in which the intake air amount Ga is equal to or greater than the predetermined value Ga0, the process proceeds to step S16 and Ga is determined to be less than the predetermined value. When it is done, this flow is exited.

  In other words, if the intake air amount Ga is less than the predetermined value Ga0 or is not less than the predetermined value Ga0 and does not continue for the predetermined time t1, the normal determination of the rich signal is avoided.

  In step S16, it is determined whether the downstream air-fuel ratio sensor 10 is outputting a rich signal. When the rich signal is not output, the process proceeds to step S17, and after resetting a count value c2 of a rich signal output duration measuring counter C2 to be described later to 0, this flow is exited.

  When it is determined that the rich signal is output, the process proceeds to step S18, and it is determined whether the output voltage Vr of the rich signal is maintained at a predetermined value Vr0 or less. The predetermined value Vr0 is set to be equal to or lower than the upper limit value of the normal output when the air-fuel ratio is rich.

  When it is determined that the output voltage Vr is maintained below the predetermined value Vr0, the process proceeds to step S19, and when it is determined that the output voltage Vr is greater than the predetermined value Vr0, the rich output normal determination is not performed. Exit this flow.

  This may increase the output voltage Vr of the downstream air-fuel ratio sensor 10 due to leakage of the current in the heater output circuit due to condensation of the sensor element. Such a signal may be referred to as a normal rich signal. This is to avoid the erroneous determination and the normal determination of the rich signal being made.

  In step S19, the counter C2 for measuring the output continuation time of a normal rich signal whose output voltage Vr is equal to or less than the predetermined value Vr0 is counted up, and then the process proceeds to step S20.

  In step S20, it is determined whether the count value c2 of the counter C2 is equal to or greater than the predetermined value c20. If the count value c2 is less than the predetermined value c20, the process exits this flow.

  When the count value c2 reaches the predetermined value c20, that is, the high intake air amount state in which the intake air amount Ga is equal to or greater than the predetermined value Ga0 continues for a predetermined time t2 and is not an abnormal output due to condensation or the like. When the normal rich signal is continuously output for a predetermined time or longer, the process proceeds to step S21, where the downstream air-fuel ratio sensor 10 diagnoses that the rich signal is normally output and sets the rich output diagnosis flag to 1. .

  With this configuration, the following operational effects can be obtained.

  Even if the sensor element 32 of the downstream air-fuel ratio sensor 10 is damaged (element cracking), if the intake air amount is small or the intake air amount Ga is temporarily large, the rich exhaust is detected by the sensor. This is a situation in which it is difficult to enter the atmosphere chamber inside the element, and a rich signal may be output and it may be determined to be normal.

  Therefore, since the rich output diagnosis is performed on the condition that the state where the intake air amount Ga is large continues for a predetermined time t1 or more, if the sensor element is cracked, it is erroneously output if the rich signal is output normally. It is possible to reliably avoid being diagnosed.

  Accordingly, the rich output diagnosis can be performed with high accuracy during the normal operation without performing the element crack diagnosis separately, and the special operation for the diagnosis, for example, every time the signal output of the downstream air-fuel ratio sensor is inverted. In addition, by changing the fuel injection amount, active control or the like for reversing the target air-fuel ratio between rich (for example, target air-fuel ratio = 14.1) and lean (for example, target air-fuel ratio = 15.1) is performed more than necessary. Can be avoided, and driving performance and fuel consumption can be maintained well.

  Further, in the present embodiment, since the condition is that the output voltage Vr of the rich signal is equal to or less than the predetermined value Vr0, it is possible to avoid erroneous determination due to an increase in the output voltage due to condensation, and the rich signal is output for a predetermined time t2. Since continuous output is added to the conditions, the diagnostic accuracy can be further improved.

  Further, in this embodiment, an air-fuel ratio sensor comprising a wide-range air-fuel ratio sensor that linearly detects the air-fuel ratio upstream of the exhaust purification catalyst, and an oxygen sensor that detects air-fuel ratio rich and lean downstream of the catalyst. Is applied to the diagnosis of the downstream air-fuel ratio sensor in a system that performs air-fuel ratio feedback control based on the detection values of these two air-fuel ratio sensors. Can be applied to the rich output diagnosis of the oxygen sensor.

  Furthermore, the air-fuel ratio sensor to which the present invention is applied is not limited to the oxygen sensor, and includes a sensor element interposed between the atmosphere and the exhaust, and corresponds to the difference in oxygen partial pressure between the atmosphere and the exhaust. Any air-fuel ratio sensor that outputs an exhaust air-fuel ratio detection signal may be used, and the air-fuel ratio may be detected linearly.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Air flow meter 5 ... Throttle valve 6 ... Fuel injection valve 7 ... Throttle actuator 8 ... Exhaust purification catalyst 9 ... Upstream air-fuel ratio sensor 10 ... Downstream air-fuel ratio sensor 15 ... Accelerator opening sensor 16 ... rotational speed sensor 17 ... throttle sensor 18 ... water temperature sensor 20 ... ECU
32 ... Sensor element 37 ... Air chamber 38 ... Heater

Claims (5)

An air-fuel ratio that is disposed in an exhaust passage of an internal combustion engine, includes a sensor element interposed between the atmosphere and exhaust, and outputs a detection signal of an exhaust air-fuel ratio according to a difference in oxygen partial pressure between the atmosphere and the exhaust For the sensor
Rich output diagnostic means for diagnosing whether the air-fuel ratio sensor normally outputs a rich signal;
Rich output diagnosis permission means for permitting diagnosis by the rich output diagnosis means when it is determined that a predetermined diagnosis permission condition is satisfied;
A diagnostic device for an air-fuel ratio sensor comprising:
Means for detecting the amount of intake air;
The rich diagnosis permission means sets the predetermined diagnosis permission condition that a state where the intake air amount is equal to or greater than a predetermined value continues for a predetermined time.   The air-fuel ratio sensor diagnosis apparatus according to claim 1, wherein the air-fuel ratio sensor is an oxygen sensor having a characteristic that an output value largely changes with a reference air-fuel ratio as a boundary.   The diagnostic apparatus for an air-fuel ratio sensor according to claim 1 or 2, wherein the predetermined diagnosis permission condition includes that the output of the air-fuel ratio sensor is equal to or less than a normal output upper limit value when rich.   The rich output diagnosis means diagnoses that the air-fuel ratio sensor is normally outputting the rich signal when it detects that the rich signal of the air-fuel ratio sensor has been continuously output for a predetermined time. The diagnostic apparatus for an air-fuel ratio sensor according to any one of claims 3 to 4.   The air-fuel ratio sensor is a downstream air-fuel ratio sensor disposed on the downstream side of the exhaust purification catalyst, and an upstream air-fuel ratio sensor that outputs an exhaust air-fuel ratio detection signal is disposed on the upstream side of the exhaust purification catalyst. 5. The engine according to claim 1, further comprising air-fuel ratio control means for performing air-fuel ratio feedback control based on air-fuel ratio detection values of the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor. A diagnostic apparatus for an air-fuel ratio sensor as described.

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