JP6502746B2 - Oxygen sensor fault diagnosis device - Google Patents

Description

  The present invention relates to an oxygen sensor failure diagnosis device that detects an air-fuel ratio of air-fuel mixture from oxygen concentration in exhaust gas of an engine, and in particular, a failure diagnosis that diagnoses a failure of the characteristic changing function of an oxygen sensor whose output characteristics can be changed It relates to the device.

Conventionally, an exhaust gas purification catalyst (hereinafter simply referred to as "catalyst") in order to reduce harmful components such as HC (hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxide) contained in engine exhaust gas Post-treatment of exhaust gas using the As such a catalyst, it has an oxidation reaction of CO and HC and a reduction reaction of NOx at the same time, and has the function of converting it into harmless CO ₂ (carbon dioxide), H ₂ O (water), N ₂ (nitrogen) Former catalysts are generally used.

In the three-way catalyst, in order to obtain a high purification rate, it is necessary to control the air-fuel ratio of the air-fuel mixture in a narrow range near the stoichiometric air-fuel ratio (λ = 1) (air-fuel ratio feedback control). Therefore, in an exhaust gas purification system using such a three-way catalyst, a linear air-fuel ratio sensor (LAF sensor) is disposed upstream of the catalyst, and an oxygen sensor (O ₂ sensor) is disposed downstream of the catalyst. While performing “main feedback control” that corrects the fuel injection amount (feedback control) based on the output of the LAF sensor, the target air-fuel ratio of the main feedback control is corrected based on the output of the downstream oxygen sensor, Or what performs "sub feedback control" which corrects the amount of feedback corrections or fuel injection quantity of main feedback control is known (for example, refer to patent documents 1).

Here, Patent Document 1 discloses a technology (exhaust gas that can reduce exhaust emissions by maintaining the purification performance of the catalyst in a high state by making it possible to change the output characteristics of the oxygen sensor (O ₂ sensor) Purifiers) are disclosed. In this technology, in a system that performs sub-F / B (feedback) control based on the output of the oxygen sensor on the downstream side of the catalyst, a constant current circuit is provided outside the oxygen sensor to flow a constant current between the sensor electrodes. The output characteristics of the oxygen sensor can be changed.

  More specifically, in this technology, in order to enhance the detection response (lean sensitivity) at the time of change from rich to lean, oxygen is supplied from the atmosphere-side electrode layer to the exhaust-side electrode layer through the solid electrolyte layer. Constant current Ics (negative constant current Ics). In this case, by supplying oxygen from the atmosphere side to the exhaust side, the oxidation reaction is promoted with respect to the rich component (HC) present (remaining) around the exhaust side electrode layer, along with which the rich component is removed quickly it can. As a result, the lean component (NOx) easily reacts in the exhaust side electrode layer, and as a result, the responsiveness of the lean output of the oxygen sensor is improved.

  On the other hand, in order to enhance the detection response (rich sensitivity) at the time of change from lean to rich, a constant current Ics (positive value is supplied so that oxygen is supplied from the exhaust side electrode layer to the atmosphere side electrode layer through the solid electrolyte layer. Constant current Ics) flows. In this case, oxygen is supplied from the exhaust side to the air side, thereby promoting the reduction reaction of the lean component (NOx) present (residual) around the exhaust side electrode layer, along with which the lean component is removed quickly it can. As a result, the rich component (HC) easily reacts in the exhaust side electrode layer, and as a result, the responsiveness of the rich output of the oxygen sensor is improved.

JP, 2013-170453, A

  By the way, as described above, in the oxygen sensor capable of changing the output characteristics by applying a current to the oxygen sensor, when attempting to diagnose a failure of the characteristic changing function, that is, a method of diagnosing a failure of the characteristic changing function As, for example, it is considered that it is judged (diagnosed) as abnormal when the target current value (instruction value) of the current applied to the oxygen sensor and the actual current value (value of the current actually flowing) deviate. Be

  However, when such a failure diagnosis method is adopted, for example, if the target current value becomes zero and there is no discrepancy between the target current value and the actual current value after being determined as an abnormality, an abnormality occurs. Even if it is not resolved (that is, although it remains abnormal), it may be misjudged as normal.

The present invention has been made to solve the above-mentioned problems, and a failure diagnosis apparatus for diagnosing a failure in the characteristic changing function of an oxygen sensor (O ₂ sensor) whose output characteristic can be changed It is an object of the present invention to provide an oxygen sensor failure diagnosis apparatus capable of preventing erroneous determination as being normal.

  The fault diagnostic device for oxygen sensor according to the present invention is a fault diagnostic device that diagnoses a fault in a characteristic change function of an oxygen sensor whose output characteristic can be changed according to a current value to be applied. Target current setting means for setting a target current value to be applied to the oxygen sensor according to the target current change detection means for detecting whether or not the target current value set by the target current setting means is changing; Based on the current value, a current is applied to the oxygen sensor, and it is determined whether the characteristic changing means is normal or not based on the characteristic changing means that changes the output characteristic of the oxygen sensor And a diagnostic result mask means for invalidating the diagnosis result by the fault diagnosis means while the target current value is not changed after the characteristic change means is determined to be abnormal. To.

  According to the failure diagnosis apparatus for an oxygen sensor according to the present invention, whether or not the characteristic changing means is normal is diagnosed based on the deviation between the target current value and the actual current value. However, after the characteristic changing means is determined to be abnormal, the diagnosis result by the failure diagnosing means is invalidated (masked) while the target current value is not changing. Therefore, for example, even if the target current value becomes zero after being determined to be abnormal and there is no divergence between the target current value and the actual current value, it is possible to prevent an erroneous determination as normal. As a result, it is possible to prevent erroneous determination as normal at the time of failure (at the time of abnormality).

  In the failure diagnosis apparatus for an oxygen sensor according to the present invention, when the target current value starts to move after the characteristic changing unit is determined to be abnormal, the diagnosis result mask unit validates the diagnosis result by the failure diagnosis unit. Is preferred.

  In this case, when the target current value starts moving after the characteristic changing means is determined to be abnormal, the diagnosis result is made effective. Therefore, when the target current value starts moving again and the actual current value starts moving following the target current value (that is, when the abnormality is eliminated), it is possible to return to the normal determination.

  In the failure diagnosis apparatus for an oxygen sensor according to the present invention, the target current change detection means holds the minimum value and the maximum value of the target current value, and based on the deviation between the held minimum value and the maximum value, It is preferable to detect whether or not the target current value is changing.

  In this case, while the minimum value and the maximum value of the target current value are held, whether or not the target current value is changed is detected based on the deviation between the held minimum value and the maximum value. Therefore, it is possible to detect whether or not the target current value is changing easily and accurately.

  In the failure diagnosis apparatus for an oxygen sensor according to the present invention, the minimum value and the maximum value of the target current value held by the target current change detection unit when the characteristic diagnosis unit is judged to be abnormal by the failure diagnosis unit. It is preferable to clear each.

  In this case, when it is determined that the characteristic changing means is abnormal, each of the minimum and maximum values of the target current value held is cleared (that is, the peak hold value is reset). Here, if the minimum value and the maximum value of the target current value are maintained even after being diagnosed as abnormal, it is determined that the target current value is changing, for example, the target current value becomes zero, and the target If the difference between the current value and the actual current value disappears, it is misjudged as normal even if the abnormality is not eliminated (that is, although it remains abnormal). However, since each of the minimum value and the maximum value of the target current value is cleared and it is determined that the target current value is not changed, the diagnosis result by the failure diagnosis means is invalidated, so that the characteristic change means is erroneously normal. It is possible to prevent the determination.

  In the failure diagnosis apparatus for an oxygen sensor according to the present invention, when the failure diagnosis unit determines that the characteristic changing unit is abnormal, and the failure diagnosis unit determines that the characteristic changing unit is normal, the diagnosis result It is preferable that the target current setting unit sets the target current value to zero when the determination result is invalidated by the mask unit.

  In this case, when it is determined that the characteristic changing unit is abnormal, and when the failure diagnosis unit determines that the characteristic changing unit is normal, but the diagnosis result is invalidated by the diagnosis result mask unit. The target current value is made zero, and the application of the current to the oxygen sensor is stopped. Therefore, it is possible to prevent the output characteristic from being changed in a state where the normal determination is made erroneously.

  In the failure diagnosis device for an oxygen sensor according to the present invention, it is preferable that the oxygen sensor be disposed downstream of the exhaust gas purification catalyst that purifies the exhaust gas of the engine.

  In this case, since the oxygen sensor is disposed downstream (after the catalyst) of the exhaust purification catalyst that purifies the exhaust gas of the engine, sub feedback control can be performed with high accuracy. Therefore, for example, the λ point (inflection point) of the oxygen sensor output can be rich shifted into the catalyst window, and sub F / B control can be performed even in a region where the oxygen sensor output sensitivity is low (rich output side), It is possible to reduce emissions (especially NOx).

  According to the present invention, in a failure diagnosis apparatus that diagnoses a failure in the characteristic changing function of an oxygen sensor whose output characteristics can be changed, it is possible to prevent erroneous determination as normal at the time of failure.

It is a figure showing the composition of the fault diagnosis device of the oxygen sensor concerning an embodiment. Changes in target current value, actual current value, normal / abnormal determination result, target current hold value (minimum value and maximum value) when the characteristic variable unit (λ variable circuit) changes from a normal state to an abnormal state It is a timing chart which shows an example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals are used for the same or corresponding parts. Further, in the respective drawings, the same elements are denoted by the same reference numerals, and duplicate explanations will be omitted.

  First, the configuration of the oxygen sensor failure diagnosis device 1 according to the embodiment will be described with reference to FIG. FIG. 1 is a view showing the configuration of an oxygen sensor failure diagnosis device 1 and an engine 10 to which the oxygen sensor failure diagnosis device 1 is applied.

  The engine 10 is, for example, a horizontally opposed four-cylinder gasoline engine. The engine 10 is an in-cylinder injection type engine that directly injects fuel into a cylinder (in a cylinder). In the engine 10, the air taken in from the air cleaner 16 is throttled by an electronically controlled throttle valve (hereinafter simply referred to as “throttle valve”) 13 provided in the intake pipe 15, passes through the intake manifold 11, and passes through to the engine 10. It is sucked into each of the formed cylinders. Here, the amount of air drawn from the air cleaner 16 is detected by an air flow meter 14 disposed between the air cleaner 16 and the throttle valve 13. Further, a vacuum sensor 30 for detecting the pressure in the intake manifold 11 (intake manifold pressure) is disposed inside the collector portion (surge tank) constituting the intake manifold 11. Further, a throttle opening degree sensor 31 for detecting the opening degree of the throttle valve 13 is disposed in the throttle valve 13.

  In the cylinder head, an intake port 22 and an exhaust port 23 are formed for each cylinder (only one bank is shown in FIG. 1). Each of the intake port 22 and the exhaust port 23 is provided with an intake valve 24 and an exhaust valve 25 for opening and closing the intake port 22 and the exhaust port 23. The intake cam pulley and the intake camshaft are relatively rotated between the intake camshaft and the intake cam pulley that drive the intake valve 24 to continuously change the rotational phase (displacement angle) of the intake camshaft with respect to the crankshaft 10a. A variable valve timing mechanism 26 is provided to advance and retard the valve timing (opening and closing timing) of the intake valve 24. The variable valve timing mechanism 26 variably sets the open / close timing of the intake valve 24 according to the engine operating state.

  Similarly, between the exhaust camshaft and the exhaust cam pulley, the exhaust cam pulley and the exhaust camshaft are relatively rotated to continuously change the rotational phase (displacement angle) of the exhaust camshaft relative to the crankshaft 10a. A variable valve timing mechanism 27 for advancing and retarding the valve timing (opening and closing timing) of the exhaust valve 25 is disposed. The variable valve timing mechanism 27 variably sets the open / close timing of the exhaust valve 25 according to the engine operating state.

  Each cylinder of the engine 10 is provided with an injector 12 for injecting fuel into the cylinder. The injector 12 directly injects the fuel pressurized by a high pressure fuel pump (not shown) into the combustion chamber of each cylinder.

  Further, an ignition plug 17 for igniting the air-fuel mixture and an igniter built-in coil 21 for applying a high voltage to the ignition plug 17 are attached to the cylinder head of each cylinder. In each cylinder of the engine 10, a mixture of the intake air and the fuel injected by the injector 12 is ignited by the spark plug 17 and burns. Exhaust gas after combustion is exhausted through the exhaust pipe 18.

  An air-fuel ratio sensor 19F is attached downstream of the collecting portion of the exhaust pipe 18 and upstream of an exhaust purification catalyst 20 described later. The air-fuel ratio sensor 19F can output a signal corresponding to the concentration of oxygen in the exhaust gas and the concentration of unburned gas (that is, a signal corresponding to the air-fuel ratio of the mixture), and can linearly detect the air-fuel ratio. A fuel ratio sensor (LAF sensor) is used. An air-fuel ratio sensor (hereinafter also referred to as "LAF sensor") 19F functions as an air-fuel ratio detection unit described in the claims.

More specifically, the LAF sensor 19F has a structure in which an atmosphere-side electrode is provided on one surface of an oxygen ion conductor such as ZrO ₂ and a diffusion resistance layer and an exhaust-side electrode are provided on the other surface. When a voltage is applied between the electrodes, O ₂ is carried from the internal atmosphere in the rich region (pumping). On the other hand, in the lean region, O ₂ is transported from the exhaust gas side through the diffusion resistance layer. The pump current Ip flowing along with the movement of these O ₂ is proportional to the unburned gas concentration in the rich region, and is proportional to the O ₂ concentration in the exhaust gas in the lean region. Therefore, the LAF sensor 19F can linearly detect the air-fuel ratio from the lean region to the rich region.

An exhaust purification catalyst 20 is disposed downstream of the LAF sensor 19F. The exhaust purification catalyst 20 is a three-way catalyst, which simultaneously oxidizes hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas and reduces nitrogen oxides (NOx), thereby reducing harmful gas components in the exhaust gas. Is purified to harmless carbon dioxide (CO ₂ ), water vapor (H ₂ O) and nitrogen (N ₂ ).

Downstream of the exhaust purification catalyst 20, on the air-fuel ratio of the mixture from the oxygen concentration in the exhaust gas of the engine 10 - off of oxygen sensor for detecting (rear O ₂ sensor) 19R are provided. The oxygen sensor 19R, for example, coats platinum on the inner and outer surfaces of a bag-like cylinder (solid electrolyte layer) made of zirconium dioxide, and generates an electromotive force by the difference in oxygen concentration between the outer side in contact with exhaust and the inner side in contact with the atmosphere. Further, the oxygen sensor 19R of the present embodiment is configured such that the output characteristics of the oxygen sensor 19R can be changed by causing a constant current to flow between the sensor electrodes with a constant current circuit provided outside the oxygen sensor 19R.

  More specifically, in order to enhance the detection response (lean sensitivity) at the time of change from rich to lean, it is determined that oxygen is supplied from the atmosphere-side electrode layer to the exhaust-side electrode layer through the solid electrolyte layer. A current (negative constant current) flows. As a result, the output characteristic line shifts to the rich side (more specifically, shifts to the rich side and the electromotive force decreasing side). In this case, the sensor output becomes lean even if the actual air-fuel ratio is in the rich region near the stoichiometry. That is, as the output characteristic of the oxygen sensor 19R, the detection response (lean sensitivity) at the time of lean change is enhanced.

  On the other hand, in order to enhance the detection response (rich sensitivity) at the time of change from lean to rich, a constant current (positive current) is supplied so that oxygen is supplied from the exhaust side electrode layer to the atmosphere side electrode layer through the solid electrolyte layer. Constant current). Thereby, the output characteristic line shifts to the lean side (more specifically, shifts to the lean side and the electromotive force increase side). In this case, the sensor output is rich even if the actual air-fuel ratio is in the lean region near the stoichiometric. That is, as the output characteristic of the oxygen sensor 19R, the detection response (rich sensitivity) at the time of rich change is enhanced.

  In addition to the air flow meter 14, the LAF sensor 19F, the oxygen sensor 19R, the vacuum sensor 30, and the throttle opening sensor 31, the cam angle sensor 32 for performing cylinder discrimination of the engine 10 is attached near the camshaft of the engine 10. It is done. Further, in the vicinity of the crankshaft 10 a of the engine 10, a crank angle sensor 33 for detecting the rotational position of the crankshaft 10 a is attached. Here, at the end of the crankshaft 10a, for example, a timing rotor 33a having 34 teeth projections with two missing teeth formed at intervals of 10 ° is attached, and the crank angle sensor 33 is of the timing rotor 33a. By detecting the presence or absence of the protrusion, the rotational position of the crankshaft 10a is detected. As the cam angle sensor 32 and the crank angle sensor 33, for example, an electromagnetic pickup type is used.

  These sensors are connected to an electronic control unit (hereinafter referred to as "ECU") 50. Further, the ECU 50 includes a water temperature sensor 34 for detecting the temperature of the cooling water of the engine 10, an oil temperature sensor 35 for detecting the temperature of the lubricating oil, and an accelerator pedal opening degree for detecting the depression amount of the accelerator pedal, that is, the opening degree of the accelerator pedal. Various sensors such as a sensor 36 and a vehicle speed sensor 37 for detecting the speed of the vehicle are also connected.

  The ECU 50 is a microprocessor for performing calculations, a ROM for storing programs for causing the microprocessor to execute each process, a RAM for storing various data such as calculation results, and a backup RAM for storing the stored contents by a 12V battery. , And an input / output I / F. The ECU 50 also includes an injector driver for driving the injector 12, an output circuit for outputting an ignition signal, and a motor driver for driving the electric motor 13a for opening and closing the electronically controlled throttle valve 13.

  In the ECU 50, the cylinder is determined from the output of the cam angle sensor 32, and the rotational angular velocity and the engine rotational speed are obtained from the output of the crank angle sensor 33. Further, in the ECU 50, based on the detection signals input from the various sensors described above, various items such as intake air amount, intake pipe negative pressure, accelerator pedal opening degree, air-fuel ratio of air-fuel mixture, and water temperature and oil temperature of the engine 10 Information is acquired. Then, the ECU 50 comprehensively controls the engine 10 by controlling various devices such as the fuel injection amount, the ignition timing, and the throttle valve 13 based on the acquired various information.

In particular, the ECU 50 functions to prevent erroneous determination as normal when the characteristic changing function of the oxygen sensor (O ₂ sensor) 19R whose output characteristics can be changed fail (at the time of abnormality) )have. Therefore, the ECU 50 includes the λ variable circuit 51 and functionally includes the target current setting unit 52, the target current change detection unit 53, and the diagnosis result mask unit 54. Further, the λ variable circuit 51 functionally includes a characteristic variable unit 511 and a failure diagnosis unit 512. In the ECU 50, each function of the target current setting unit 52, the target current change detection unit 53, and the diagnosis result mask unit 54 is realized by the program stored in the ROM being executed by the microprocessor.

  The λ variable circuit 51 is, for example, an IC or the like, and functionally includes the characteristic change unit 511 and the failure diagnosis unit 512 as described above. The characteristic variable unit 511 includes a current application circuit, and changes the output characteristic of the oxygen sensor 19R by applying a current to the oxygen sensor 19R based on a target current value (details will be described later). That is, the inflection point (λ point) of λ (excess air ratio) of the oxygen sensor 19R is shifted (in particular, it is shifted to increase the NOx sensitivity). The property changing unit 511 functions as a property changing unit described in the claims.

  The failure diagnosis unit 512 reads the current value (actual current value) actually applied to the oxygen sensor 19R, and based on the deviation between the target current value and the actual current value, determines whether the characteristic variable unit 511 is normal or not. judge. That is, the failure diagnosis unit 512 determines that the characteristic variable unit 511 is abnormal (faulty) when the target current value and the actual current value deviate by a predetermined value or more. The failure diagnosis unit 512 functions as a failure diagnosis unit described in the claims.

  The determination result by the failure diagnosis unit 512 is output to the diagnosis result mask unit 54 via, for example, a communication line (not shown). Also, the target current value is received via the communication line.

  The target current setting unit 52 sets a target current value to be applied to the oxygen sensor 19R according to a target change amount (target shift amount) of the output characteristic (λ point) of the oxygen sensor 19R. That is, the target current setting unit 52 functions as target current setting means described in the claims.

  More specifically, when the target current setting unit 52 increases the detection response (lean sensitivity) at the time of change from rich to lean, oxygen is transmitted from the atmosphere-side electrode layer to the exhaust-side electrode layer through the solid electrolyte layer. The target current value is set to flow a negative constant current to be supplied. On the other hand, the target current setting unit 52 supplies oxygen from the exhaust-side electrode layer to the atmosphere-side electrode layer through the solid electrolyte layer in the case where the detection response (rich sensitivity) at the time of change from lean to rich is enhanced. Set the target current value so that a positive constant current flows. The target current set by the target current setting unit 52 is transmitted to the characteristic variable unit 511 (λ variable circuit 51) through the communication line as described above.

  In the case where the target current setting unit 52 determines that the characteristic variable unit 511 is abnormal by the failure diagnosis unit 512, and the characteristic diagnosis unit 512 determines that the characteristic variable unit 511 is normal, When the determination result is invalidated by the result mask unit 54 (details will be described later), that is, when the characteristic variable unit 511 (λ variable circuit 51) is broken, zero is set as the target current value. Therefore, the application of the current to the oxygen sensor 19R is stopped (the λ variable control is stopped).

  The target current change detection unit 53 detects whether or not the target current value is changing. That is, the target current change detection unit 53 functions as a target current change detection unit described in the claims. More specifically, the target current change detection unit 53 holds (peak hold) the minimum value and the maximum value of the target current value, and the target according to the deviation between the held minimum value and the maximum value. It is detected whether or not the current value is changing. That is, when the deviation between the held minimum value and the maximum value is equal to or more than a predetermined value, it is determined that the target current value is changing. Information on whether or not the target current value is detected, which is detected by the target current change detection unit 53, is output to the diagnosis result mask unit 54.

  When target voltage change detection unit 53 determines that characteristic change unit 511 (λ variable circuit 51) is abnormal by failure diagnosis unit 512, each of the minimum value and the maximum value of the target current value held therein is Clear (reset the peak hold value).

  The diagnosis result mask unit 54 invalidates the diagnosis result by the fault diagnosis unit 512 while the target current value does not change after the fault diagnosis unit 512 determines that the characteristic variable unit 511 (λ variable circuit 51) is abnormal. To (mask). Therefore, after the fault diagnosis unit 512 determines that the characteristic variable unit 511 (λ variable circuit 51) is abnormal, for example, even if the target current value becomes zero and the difference between the target current value and the actual current value disappears, While the target current value does not change, the diagnosis result by the fault diagnosis unit 512 is invalidated (that is, the abnormality determination is maintained). Thus, the diagnosis result mask unit 54 functions as a diagnosis result mask unit described in the claims.

  However, the diagnostic result mask unit 54 determines that the target current value starts to move after the characteristic variable unit 511 (λ variable circuit 51) is determined to be abnormal (the target current change detection unit 53 determines that the target current value has started to move). If it is determined that the diagnosis result of the failure diagnosis unit 512 is valid.

  The warning light (MIL) 59 lights up when the characteristic variable unit 511 (λ variable circuit 51) is determined to be abnormal and the application of the current to the oxygen sensor 19R is stopped (when λ variable control is stopped). And warn the driver. The lighting of the warning light 59 is controlled by the ECU 50.

  Then, the timing chart which shows operation | movement of the failure diagnosis apparatus 1 of the oxygen sensor mentioned above is shown in FIG. FIG. 2 shows the target current value, actual current value, normal / abnormal determination result, target current hold value (minimum value and minimum value) when the characteristic variable unit 511 (λ variable circuit 51) changes from the normal state to the abnormal state. 3 is a timing chart showing an example of the change of the maximum value). In FIG. 2, the horizontal axis represents time, and the vertical axis represents the target current value (mA), the actual current value (mA), the abnormality determination result of the characteristic variable unit 511 by the failure diagnosis unit 512, and the diagnosis result in order from the upper stage. They are an abnormality determination result (mask result) by the mask unit 54, a target current hold value (minimum value), and a target current hold value (maximum value) (mA).

  As shown in FIG. 2, between time t1 and t2, the target current value rises in a step-like manner (stepwise), and the actual current value rises so as to follow the increase in the target current value. go. Therefore, the deviation between the target current value and the actual current value is less than the predetermined value, and it is determined that the characteristic variable unit 511 (λ variable circuit 51) is normal. Therefore, the normality / abnormality determination result of the characteristic variable unit 511 by the failure diagnosis unit 512 and the normality / abnormality determination result (mask result) by the diagnosis result mask unit 54 are both normal (0). The target current hold value (minimum value) is maintained at zero, and the target current hold value (maximum value) is held at a peak in accordance with the increase of the target current value and rises in a step-like manner.

  At time t2, for example, it is assumed that a sticking file is generated and the actual current value decreases to 0 (mA). Here, since the deviation between the target current hold value (minimum value) and the target current hold value (maximum value) is equal to or greater than a predetermined value, it is determined that the target current value is changing. On the other hand, since the deviation between the target current value and the actual current value deviates by a predetermined value or more, the characteristic variable means 511 (λ variable circuit 51) is determined to be abnormal (fault). Then, the normality / abnormality judgment result of the characteristic variable hand portion 511 by the failure diagnosis unit 512 and the normal / abnormality judgment result (mask result) by the diagnosis result mask unit 54 both transition from normal (0) to abnormality (1). At this time, the target current hold value (minimum value) and the target current hold value (maximum value) are reset (cleared) and become zero.

  Thereafter, assuming that the target current value becomes zero at time t3, the difference between the target current value and the actual current value disappears, so that the normal / abnormal determination result of the characteristic variable unit 511 by the failure diagnosis unit 512 is zero (normal). Return to Here, as described above, since the target current hold value (maximum value) is cleared at time t2, the deviation between the target current hold value (minimum value) and the target current hold value (maximum value) is zero. It is determined that the target current value has not changed. Therefore, in the diagnosis result mask unit 54, the normal / abnormal determination result by the failure diagnosis unit 512 is invalidated. Therefore, the normal / abnormal determination result (mask result) by the diagnostic result mask unit 54 is maintained at 1 (abnormal). After that, until the target current value starts moving at time t4, the normal / abnormal determination result by the failure diagnosis unit 512 is invalidated (masked).

  After that, for example, assuming that the failure (sticking failure) of the characteristic variable unit 511 (λ variable circuit 51) is eliminated between time t3 and t4, the target current value starts moving at time t4, and the actual current value becomes the target current. Follow the value and start moving. Here, since the target current hold value (maximum value) increases, the deviation between the target current hold value (minimum value) and the target current hold value (maximum value) becomes equal to or greater than a predetermined value, and the target current value changes. It is determined that Therefore, the determination result of the failure diagnosis unit 512 is not invalidated by the diagnosis result mask unit 54, and the normality / abnormality determination result of the characteristic variable unit 511 by the failure diagnosis unit 512 and the normality / abnormality determination by the diagnosis result mask unit 54. Both results (mask results) are considered normal (0).

  As described above in detail, according to the present embodiment, it is determined whether the characteristic variable unit 511 (λ variable circuit 51) is normal or not based on the deviation between the target current value and the actual current value That is, when the deviation deviates from the predetermined value abnormally, it is determined to be abnormal). Here, when it is determined that the characteristic variable unit 511 (λ variable circuit 51) is abnormal, thereafter, while the target current value does not change, the diagnosis result by the failure diagnosis unit 512 is invalidated. Therefore, for example, even if the target current value becomes zero after the fault diagnosis unit 512 determines that the characteristic variable unit 511 (λ variable circuit 51) is abnormal, even if the difference between the target current value and the actual current value disappears, It is possible to prevent erroneous determination as normal. As a result, it is possible to prevent erroneous determination as normal at the time of failure (at the time of abnormality).

  According to the present embodiment, when the target current value starts to move after the characteristic variable unit 511 (λ variable circuit 51) is determined to be abnormal, the diagnosis result by the failure diagnosis unit 512 is validated. Therefore, when the target current value starts moving again and the actual current value starts to move following the target current value (that is, when the abnormality is eliminated), it is possible to return to the normal determination.

  According to the present embodiment, the minimum value and the maximum value of the target current value are held (peak hold), and the target current value is changed based on the deviation between the held minimum value and the maximum value. Is detected. Therefore, it is possible to detect whether or not the target current value is changing easily and accurately.

  According to the present embodiment, when it is determined that the characteristic variable unit 511 (λ variable circuit 51) is abnormal, each of the minimum value and the maximum value of the target current value held is cleared (ie, the peak hold value). Is reset). Here, if the minimum value and the maximum value of the target current value are maintained even after being diagnosed as abnormal, it is determined that the target current value is changing, for example, the target current value becomes zero, and the target If the difference between the current value and the actual current value disappears, it will be misjudged as normal even if the abnormality is not resolved (that is, although it remains abnormal). However, each of the minimum value and the maximum value of the target current value is cleared, and it is determined that the target current value is not changed, whereby the diagnosis result is invalidated. It is possible to

  According to the present embodiment, when it is determined by the failure diagnosis 512 that the characteristic variable unit 511 is abnormal, and when the failure diagnosis unit 512 determines that the characteristic variable unit 511 is normal, the diagnosis result mask unit When the determination result is invalidated by 54, the target current value is made zero, and the application of the current to the oxygen sensor 19R is stopped (the λ variable control is stopped). Therefore, it is possible to prevent the output characteristic from being changed in a state where the normal determination is made erroneously (despite the abnormality).

  According to the present embodiment, since the oxygen sensor 19R is disposed downstream of the exhaust purification catalyst 20 that purifies the exhaust gas of the engine 10, sub feedback control can be performed with high accuracy. Therefore, for example, the λ point (inflection point) of the oxygen sensor output can be rich shifted into the catalyst window, and sub F / B control can be performed even in a region where the oxygen sensor output sensitivity is low (rich output side), It is possible to reduce emissions (especially NOx).

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, although the present invention is applied to a horizontally opposed engine as an example, the present invention is not limited to the horizontally opposed engine. For example, engines such as in-line type or V-type engine Can also be applied. In the above embodiment, the present invention is applied to a cylinder injection type engine as an example, but the present invention can also be applied to a port injection type engine or the like. Furthermore, although the case where the present invention is applied to a gasoline engine car has been described as an example in the above embodiment, the present invention relates to a vehicle having a driving power source other than a gasoline engine, for example, an engine and an electric motor. The present invention can also be applied to a source hybrid vehicle (HEV) and the like.

In the above embodiment, although the oxygen sensor (O ₂ sensor) 19R is disposed downstream of the exhaust purification catalyst 20, for example, a system having a configuration in which the oxygen sensor (O ₂ sensor) 19R is disposed upstream of the exhaust purification catalyst 20 It can also be done.

1 Failure diagnosis system for oxygen sensor 10 Engine 12 Injector 17 Spark plug 19F Air-fuel ratio sensor (LAF sensor)
19R oxygen sensor (O2 sensor)
31 Throttle opening sensor 32 Cam angle sensor 33 Crank angle sensor 50 ECU
DESCRIPTION OF SYMBOLS 51 λ variable circuit 511 Characteristic variable part 512 Failure diagnosis part 52 Target current setting part 53 Target current change detection part 54 Diagnostic result mask part 59 Warning light

Claims (6)

In a failure diagnosis apparatus which diagnoses a failure of a characteristic change function of an oxygen sensor capable of changing an output characteristic according to a value of an applied current,
Target current setting means for setting a target current value to be applied to the oxygen sensor according to a target change amount of the output characteristic of the oxygen sensor;
Target current change detection means for detecting whether or not the target current value set by the target current setting means is changing;
A characteristic changing unit that applies a current to the oxygen sensor based on the target current value to change an output characteristic of the oxygen sensor;
Failure diagnosis means for diagnosing whether the characteristic changing means is normal based on the deviation between the target current value and the actual current value;
An oxygen sensor comprising: diagnostic result mask means for invalidating the diagnostic result by the failure diagnostic means while the target variable value is not changed after the characteristic changing means is determined to be abnormal. Failure diagnosis device.   2. The diagnostic result mask unit according to claim 1, wherein when the target current value starts to move after the characteristic variable unit is determined to be abnormal, the diagnostic result mask unit makes the diagnostic result by the failure diagnostic unit effective. Oxygen sensor fault diagnosis device.   The target current change detection means holds the minimum value and the maximum value of the target current value, and determines whether the target current value changes based on the deviation between the held minimum value and the maximum value. An oxygen sensor failure diagnosis apparatus according to claim 1 or 2, characterized by detecting.   The target current change detection means is configured to clear each of the minimum value and the maximum value of the target current value held when it is determined that the characteristic change means is abnormal by the failure diagnosis means. The fault diagnostic device of the oxygen sensor according to claim 3.   When it is determined that the characteristic changing unit is abnormal by the failure diagnosis unit, and the characteristic changing unit is determined to be normal by the failure diagnosis unit, the judgment result is determined by the diagnosis result mask unit. The oxygen sensor failure diagnosis apparatus according to any one of claims 1 to 4, wherein the target current setting unit sets the target current value to zero when being invalidated. The oxygen sensor failure diagnosis device according to any one of claims 1 to 5, wherein the oxygen sensor is disposed downstream of an exhaust gas purification catalyst that purifies exhaust gas of an engine.

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