JP2005140742A - Apparatus for diagnosing deterioration in sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose deterioration in a sensor precisely regarding an apparatus for diagnosing deterioration in the sensor for vehicles, in which the response speeds differ, depending on the active state. <P>SOLUTION: The apparatus for diagnosing deterioration in the sensor diagnoses deterioration, with respect to an oxygen concentration sensor, or the like, provided at the exhaust passage of an internal combustion engine. A sensor, such as the oxygen concentration sensor, changes the response time, depending on the temperature and allows the response speed to be faster, the higher the temperature is. The oxygen concentration sensor, having these characteristics, have a relatively high response speed at high temperatures, even if it has deteriorated, so that the difference in the response speed, as compared with a normal sensor becomes small, making accurate determination difficult. Therefore, the apparatus for diagnosing deterioration in the sensor diagnoses deterioration in an inactive state, in which the difference between the response speed of the normal sensor and that of a deteriorated sensor appears marked; namely, when the temperature of the sensor is low, diagnosing of deterioration is conducted. As a result of this, diagnosis of deterioration can be carried out with high accuracy. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a deterioration diagnosis apparatus for a vehicle sensor whose response varies depending on an active state, and relates to a deterioration diagnosis apparatus that can accurately diagnose deterioration of a sensor.

  In automobiles and the like, sensors that detect temperature, gas flow rate, and the like are installed at various locations. For example, an oxygen concentration sensor (hereinafter simply referred to as “oxygen sensor”) whose output changes in response to oxygen concentration is provided in an exhaust passage of an automobile. This oxygen sensor indirectly detects an air / fuel ratio (hereinafter referred to as “A / F”). The A / F detected by the oxygen sensor is output to an ECU (Engine Control Unit) that is a computer for controlling the vehicle, and the fuel injection amount and the like are controlled based on this A / F.

  As described above, the ECU of an automobile or the like can control each component based on the detection result from the sensor and can diagnose whether such a sensor is normal. Specifically, the ECU can diagnose the deterioration of the oxygen sensor. For example, in the technique described in Patent Document 1, the oxygen sensor is activated with a heater in the oxygen sensor at a high temperature, and after activation, the A / F is changed to rich and lean, and the oxygen sensor at that time The deterioration of the response of the oxygen sensor is diagnosed by observing the output. The diagnosis is performed after the sensor is activated by the heater as described above, because the oxygen sensor has a characteristic that the sensor has good response in the activated state.

  However, even when the oxygen sensor is deteriorated, if the temperature of the oxygen sensor is high, the response time becomes relatively fast, and therefore, the difference from the response time of the normal oxygen sensor may be small. . Therefore, when the oxygen sensor is activated, the difference in response between the normal oxygen sensor and the deteriorated oxygen sensor becomes small, and there is a problem that the accuracy of the deterioration diagnosis decreases.

JP-A-10-141122

  The present invention has been made to solve such problems, and the object of the present invention is to provide a deterioration diagnosis that can accurately diagnose the deterioration of a vehicle sensor whose response varies depending on the active state. To provide an apparatus.

  In one aspect of the present invention, there is provided a deterioration diagnosis apparatus for a vehicle sensor having a property that a difference in response between a normal sensor and a deteriorated sensor is larger in an inactive state than in an active state, wherein the sensor is in an inactive state It is characterized in that deterioration diagnosis is performed when the

  The sensor deterioration diagnosis apparatus performs a deterioration diagnosis of a sensor installed in a vehicle or the like. The sensor on which the deterioration diagnosis is performed has an active state and an inactive state. Further, this sensor has a characteristic that when it is in an inactive state, a difference in response between a normal sensor and a deteriorated sensor appears remarkably. Therefore, the deterioration diagnosis device performs deterioration diagnosis on a sensor having such characteristics when the sensor is in an inactive state. As a result, the sensor deterioration diagnosis apparatus can accurately determine a deteriorated sensor.

  One aspect of the above-described sensor deterioration diagnosis apparatus is a vehicle sensor having a property that a difference in response between the normal sensor and the deteriorated sensor is larger in the inactive state than in the active state. The sensor is characterized in that the response is slower than the active state. The sensor for which the deterioration diagnosis is performed has good responsiveness when in an active state and decreases in responsiveness when in an inactive state. Even if a sensor having such characteristics is deteriorated, if the sensor is in an active state, a difference in response with a normal sensor becomes small, and accurate deterioration determination tends to be difficult. is there. Therefore, the sensor deterioration diagnosis apparatus performs deterioration diagnosis when the sensor is in an inactive state in which a difference in response between a normal sensor and a deteriorated sensor is noticeable.

  In another aspect of the sensor deterioration diagnostic apparatus, the inactive state refers to a state in which the temperature of the sensor is equal to or lower than a predetermined temperature, sensor temperature detecting means for detecting the temperature of the sensor, and the sensor temperature Deterioration diagnosis means for performing deterioration diagnosis when is below the predetermined temperature. The active state of the sensor changes depending on the temperature, and the responsiveness is good when the sensor is in an active state where the temperature of the sensor is high. Even if the sensor is deteriorated, if the temperature of the sensor is high, the response is good and it is difficult to determine whether or not the sensor is deteriorated. Therefore, the sensor deterioration diagnosis device performs deterioration diagnosis when the sensor is in an inactive state, that is, when the temperature of the sensor is equal to or lower than a predetermined temperature. Thereby, the sensor which has deteriorated can be distinguished with sufficient accuracy.

  In another aspect of the sensor deterioration diagnostic apparatus, a temperature increasing means for increasing the temperature of the sensor, and a means for stopping the temperature increasing means when the sensor temperature is equal to or higher than the predetermined temperature. Prepare. Since the sensor has a characteristic of good responsiveness in an active state at a high temperature, the output from the sensor can be obtained immediately by raising the temperature of the sensor by the temperature raising means. . The sensor deterioration diagnosis apparatus performs the deterioration diagnosis when the sensor temperature is equal to or lower than the predetermined temperature. Therefore, when the sensor temperature is equal to or higher than the predetermined temperature, the temperature increasing means is stopped and the sensor temperature is predetermined. Wait until the temperature falls below the temperature, and perform a diagnosis after the temperature of the sensor falls below the predetermined temperature.

  Another aspect of the sensor deterioration diagnosis apparatus includes a sensor response time detection unit that detects a response time of the sensor, and the deterioration diagnosis unit detects the sensor if the sensor response time is a predetermined time or less. If the sensor response time is equal to or longer than the predetermined time, the sensor is diagnosed as degraded. As the sensor response time, when the sensor deterioration diagnostic device forcibly changes the state so that the sensor output changes, the sensor output reaches the second output value from the predetermined first output value. The time required until the time can be used. If the response time calculated in this way is longer than a predetermined response time set in advance, the sensor deterioration diagnosis apparatus diagnoses that the sensor has deteriorated.

  In another aspect of the sensor deterioration diagnosis apparatus, the inactive state may be a state after the engine is started until the temperature of the sensor reaches the predetermined temperature.

  In another aspect of the sensor deterioration diagnostic apparatus, the inactive state is a state in which the temperature of the sensor becomes equal to or lower than the predetermined temperature after the temperature of the sensor once reaches the predetermined temperature. Can do.

  In a preferred embodiment, the sensor may be an oxygen sensor or an A / F sensor that detects oxygen concentration. An oxygen sensor or an A / F sensor is a sensor whose output changes in response to oxygen concentration. The output from the oxygen sensor is used as A / F in the vehicle. As described above, this oxygen sensor also has a characteristic that the responsiveness is good in the active state and the responsiveness falls in the inactive state, and even if the sensor is deteriorated, the active state If so, the difference between normal sensor response and difference will be small. Therefore, it is possible to accurately perform the deterioration diagnosis of the oxygen sensor and the A / F sensor by the above-described deterioration diagnosis device.

  As another application example, the sensor may be an exhaust temperature sensor that detects the temperature of exhaust gas.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a part of a vehicle 200a to which a sensor deterioration diagnosis apparatus according to one embodiment of the present invention is applied.

In FIG. 1, a vehicle 200 a includes an engine 101, an exhaust passage 102, an ECU 105, and an oxygen sensor (O ₂ sensor) 106. In the present embodiment, the deterioration diagnosis device is mainly configured by the ECU 105, and diagnoses whether or not the oxygen sensor 106 is deteriorated.

  As the engine 101, for example, an internal combustion engine such as a gasoline engine or a diesel engine can be used.

  Exhaust gas discharged from the engine 101 flows through the exhaust passage 102 and is discharged. An oxygen sensor 106 that can detect the oxygen concentration in the exhaust gas is disposed in the middle of the exhaust passage 102. The oxygen sensor 106 is a sensor that changes the output value of the electric signal in response to the oxygen concentration of oxygen flowing through the exhaust passage 102.

  As the oxygen sensor 106, for example, a sensor in which platinum is coated on the inner and outer surfaces of a zirconia element can be used. The oxygen sensor 106 uses a mechanism in which electric power is generated by a difference in oxygen concentration between the inner and outer surfaces of the sensor. In other words, when the oxygen concentration difference between the atmosphere introduced into the sensor (which contains a lot of oxygen) and the exhaust gas outside the sensor (which does not contain so much oxygen) is larger, the voltage difference is larger and there is no difference in oxygen concentration. There is no voltage difference. Therefore, if the engine 101 is in a lean state (lean combustion state), the output voltage of the oxygen sensor 106 is small because there is less fuel and oxygen is contained in the exhaust gas after combustion. Since there is little oxygen left in the exhaust gas, the output voltage of the oxygen sensor 106 increases. The output voltage S1 from the oxygen sensor 106 is input to an ECU (Engine Control Unit) 105, and air-fuel ratio feedback control (fuel injection amount control) of the engine 101 is performed.

  The ECU 105 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). In the present embodiment, the ECU 105 acquires an electrical signal indicating the oxygen concentration (that is, an electrical signal indicating A / F) S1 from the oxygen sensor 106. Further, the ECU 105 calculates the element impedance of the oxygen sensor 106 based on the value of the current flowing through the element of the oxygen sensor 106. Then, the ECU 105 calculates the temperature of the oxygen sensor 106 (that is, the element temperature) from the calculated element impedance. In the oxygen sensor 106, since there is a correlation between the element impedance inside the sensor and the sensor temperature, the temperature of the oxygen sensor 106 can be known by detecting the element impedance inside the sensor.

  The ECU 105 also calculates the response time of the oxygen sensor 106. The ECU 105 diagnoses the deterioration of the oxygen sensor 106 based on the temperature and response time of the oxygen sensor 106 described above. Further, the ECU 105 supplies an instruction signal S3 including the fuel injection amount to the engine 101 based on the oxygen concentration obtained from the oxygen sensor 106, and performs feedback control of air fuel consumption.

  Next, an outline of the deterioration diagnosis of the oxygen sensor 106 according to this embodiment performed by the ECU 105 will be described. First, the reason why the sensor temperature is used as a determination factor in the deterioration diagnosis of the oxygen sensor 106 will be described. It is known that the responsiveness of the oxygen sensor 106 changes depending on whether the sensor is active or inactive. In other words, the response speed of the oxygen sensor 106 changes depending on the temperature.

  Specifically, the relationship between the activity of the oxygen sensor 106 and the response will be described with reference to FIG. FIG. 2 shows the temperature of the oxygen sensor 106 on the horizontal axis and the response time of the oxygen sensor 106 on the vertical axis. Here, the characteristic A1 shows an example of the measurement result of the normal (that is, not deteriorated) oxygen sensor 106, and the characteristic A2 shows an example of the measurement result of the deteriorated oxygen sensor 106. It can be seen from FIG. 2 that the response time of the normal oxygen sensor 106 and the response time of the oxygen sensor 106 that have deteriorated also become shorter, that is, the response speed becomes faster as the sensor temperature increases. It can also be seen that the response time of the normal oxygen sensor 106 is consistently shorter than the response time of the degraded oxygen sensor 106. In the inactive state where the temperature of the oxygen sensor 106 is low, the difference between the response time of the normal oxygen sensor 106 and the response time of the deteriorated oxygen sensor 106 is significant, but the oxygen sensor 106 is hot. It can be seen that the difference in response time becomes small when the active state is reached.

  As described above, in the present embodiment, the deterioration diagnosis is performed in a state where a difference in response between the normal oxygen sensor 106 and the deteriorated oxygen sensor 106 appears remarkably, that is, in an inactive state where the temperature of the oxygen sensor 106 is low. Specifically, a predetermined threshold is set for the response time of the oxygen sensor 106, the temperature of the oxygen sensor 106 is set to a predetermined temperature or less to be inactive, and the measured response time of the oxygen sensor 106 is larger or smaller than the threshold. The deterioration diagnosis is performed by determining whether or not. As described above, the deteriorated oxygen sensor 106 can be accurately determined.

  Next, a method for detecting the response time of the oxygen sensor 106 will be described with reference to FIG. In FIG. 3, the horizontal axis indicates time (msec), and the vertical axis indicates the output (V) of the oxygen sensor 106. A characteristic B1 shows an example of an output waveform of the oxygen sensor 106. The response time of the oxygen sensor 106 is calculated by periodically changing the A / F (Air by Fuel) between the rich state and the lean state (fuel lean state) and observing the output of the oxygen sensor 106 at that time. To do. In the example of FIG. 3, A / F is periodically changed between a rich state and a lean state. The output of the oxygen sensor 106 varies between 0V and 1V. When the output is 0.45V, the A / F is in a stoichiometric state (when the A / F is the stoichiometric air-fuel ratio), and the output is 0.45. When it is V or higher, the A / F is in a rich state, and when it is 0.45 V or lower, the A / F is in a lean state. Here, the response time of the oxygen sensor 106 is, for example, the value obtained by adding the predetermined voltage amount to 0.45 V from the value obtained by subtracting the predetermined voltage amount from 0.45 V (predetermined voltage “V1” in FIG. 3). It can be the time required to reach (the predetermined voltage “V2” in FIG. 3). Then, the ECU 105 compares the target response time recorded in a memory (not shown) with the detected response time. The ECU 105 determines that the oxygen sensor 106 is normal if the detected response time is shorter than the target response time, and determines that the oxygen sensor 106 is deteriorated if it is longer than the target response time.

  In the present embodiment, an example in which deterioration diagnosis is performed on the oxygen sensor 106 that detects the oxygen concentration is shown. You can also Further, the deterioration diagnosis device of the present invention can be applied not only to the oxygen concentration sensor but also to all sensors whose response varies depending on the active state, for example, for deterioration diagnosis of an exhaust temperature sensor that detects the temperature of exhaust gas. Can be applied. Further, the place where the sensor to be subjected to deterioration diagnosis is arranged is not limited to the exhaust passage of the internal combustion engine. Further, the application of the deterioration diagnosis apparatus of the present invention is not limited to only a vehicle having an internal combustion engine.

[Deterioration diagnosis device]
Below, the Example of the deterioration diagnosis apparatus of the sensor which concerns on this invention is described. FIG. 4 is a schematic block diagram illustrating a partial configuration of a vehicle to which the oxygen sensor deterioration diagnosis apparatus according to the embodiment of the present invention is applied.

In FIG. 4, a vehicle 200 b includes an engine 101, an exhaust passage 102, a front catalyst 103, a rear catalyst 104, an ECU 105, an A / F sensor 107, and an oxygen (O ₂ ) sensor 108. In the present embodiment, the deterioration diagnosis apparatus is mainly configured by the ECU 105, and can determine whether or not the A / F sensor 107 or the oxygen sensor 108 is deteriorated.

  As the engine 101, for example, an internal combustion engine such as a gasoline engine or a diesel engine can be used.

  Exhaust gas discharged from the engine 101 flows through the exhaust passage 102. A front catalyst 103 is provided in the upstream exhaust passage 102, and a rear catalyst is provided in the downstream exhaust passage 102. Exhaust gas discharged from the engine 101 is purified by the front catalyst 103 and the rear catalyst 104 provided in the exhaust passage. The front catalyst 103 and the rear catalyst 104 remove NOx (nitrogen oxide), SOx (sulfur oxide), CO (carbon monoxide), particulate matter (PM), and the like in the exhaust gas. be able to. As the front catalyst 103 and the rear catalyst 104, a three-way catalyst, an occlusion reduction type NOx catalyst, a particulate matter removal filter, or the like can be used.

  In the exhaust passage 102, an A / F sensor 107 is provided on the upstream side of the front catalyst 103, and an oxygen sensor 108 is provided between the front catalyst 103 and the rear catalyst 104. Both the A / F sensor 107 and the oxygen sensor 108 output electrical signals (that is, signals corresponding to A / F) S11 and S13 corresponding to the oxygen concentration of the exhaust gas flowing through the exhaust passage 102. As described above, by detecting the A / F using the two oxygen sensors of the A / F sensor 107 and the oxygen sensor 108 in combination, the air-fuel ratio feedback control of the engine 101 can be performed with high accuracy.

  In this embodiment, the A / F sensor 107 and the oxygen sensor 108 are provided with heaters 120 and 122 for heating the sensor element. As described above, since the oxygen concentration sensor has a high response speed when the temperature is high, the oxygen concentration is detected after being heated by a heater to be in an active state. As a result, the A / F sensor 107 and the oxygen sensor 108 can immediately output the electrical signals S11 and S13 indicating the oxygen concentration. The output signals of the A / F sensor 107 and the oxygen sensor 108 are supplied to the ECU 105.

  The ECU 105 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). In the present embodiment, the ECU 105 acquires electrical signals S11 and S13 indicating the oxygen concentration from the A / F sensor 107 and the oxygen sensor 108. Further, the ECU 105 calculates the element impedance of the oxygen sensor 106 based on the current values flowing through the elements of the A / F sensor 107 and the oxygen sensor 108, and the temperatures of the A / F sensor 107 and the oxygen sensor 108 are calculated from the calculated element impedance. To decide. In an oxygen sensor or the like, since there is a correlation between the element impedance inside the sensor and the sensor temperature, the temperature of the sensor can be known by detecting the element impedance inside the sensor.

  Further, the ECU 105 supplies an instruction signal S3 including the fuel injection amount to the engine 101 based on the oxygen concentration obtained from the A / F sensor 107 and the oxygen sensor 108, and performs feedback control of the air fuel consumption.

  Also in the A / F sensor 107 and the oxygen sensor 108 of this embodiment, as described above, in the inactive state where the temperature of the sensor is low, the difference in response time between the normal sensor and the sensor sensor that has deteriorated. However, there is a characteristic that a difference in response time becomes small in an active state where the sensor is at a high temperature. Accordingly, when the response time obtained from the normal A / F sensor 107 and the oxygen sensor 108 and the response time obtained from the deteriorated sensor are significantly different from each other, that is, when the sensor temperature is low. Perform deterioration diagnosis. Specifically, a predetermined threshold is provided for the response times of the A / F sensor 107 and the oxygen sensor 108, the temperature of the A / F sensor 107 and the oxygen sensor 108 is set to a predetermined temperature or less, and the measured response time of the sensor is measured. Deterioration diagnosis is performed depending on whether it is larger or smaller than the corresponding threshold value. As described above, it is possible to accurately determine a deteriorated sensor.

  Specifically, the inactive state in which the sensor is at a low temperature refers to (1) a period until the sensor temperature reaches a predetermined temperature corresponding to the active state after the engine start of the vehicle, and (2) once the sensor temperature is activated. When it rises to a predetermined temperature corresponding to the state and then falls below a predetermined temperature, it is included.

  As a sensor inactive state, the sensor deterioration is diagnosed before the sensor temperature reaches a predetermined temperature after the engine of the vehicle is started, so that the sensor value is detected before starting other control of the vehicle using the detection value of the sensor. Degradation can be determined. For example, when it is determined that the sensor has deteriorated, necessary countermeasures can be taken against the deterioration before the control using the sensor is started. Therefore, it becomes possible to appropriately control the vehicle using the detection value of the sensor.

  In addition, when the sensor temperature is raised to a predetermined temperature corresponding to the active state and then lowered to a predetermined temperature or less as a sensor inactive state, a sensor deterioration diagnosis is performed by diagnosing sensor deterioration. It is possible to prevent erroneous determination of the presence or absence of sensor degradation due to the above. That is, if the sensor temperature does not rise to a predetermined temperature because the sensor temperature detection device is out of order, the sensor deterioration is not determined. When the sensor is actually in the active state when the sensor temperature is above the predetermined temperature and the sensor deterioration diagnosis is performed by determining that the sensor temperature is below the predetermined temperature, that is, inactive due to a failure of the sensor temperature detection device, etc. Therefore, the difference in response between the normal sensor and the deteriorated sensor is small, and the possibility of misjudgment regarding sensor deterioration increases. Therefore, once the sensor temperature rises to a predetermined temperature corresponding to the active state and then falls below the predetermined temperature, that is, when the sensor temperature is normally detected, the sensor deterioration is diagnosed. Such erroneous determination can be prevented.

  The ECU 105 calculates response times of the A / F sensor 107 and the oxygen sensor 108 by a method similar to the method described with reference to FIG. That is, the ECU 105 periodically changes the A / F between the rich state and the lean state by controlling the fuel injection amount inside the engine 101 by the control signal S3. For example, as shown in FIG. The time required for the voltage to reach the predetermined level V2 from the predetermined level V1 is calculated. Then, the ECU 105 compares the target response time recorded in a memory (not shown) with the detected response time. The ECU 105 determines that the A / F sensor 107 or the oxygen sensor 108 is normal if the detected response time is shorter than the target response time, and determines that the A / F sensor 107 or the oxygen sensor 108 is deteriorated if it is longer than the target response time.

[Deterioration diagnosis processing]
Next, sensor deterioration diagnosis processing according to the present embodiment will be described with reference to the flowchart of FIG.

  The process shown in FIG. 5 is mainly performed by the ECU 105. In this process, the ECU 105 performs deterioration diagnosis on the A / F sensor 107 shown in FIG. 4 based on the temperature of the sensor and the response time of the sensor. It is assumed that the sensor deterioration diagnosis process is executed once for each start of the engine 101.

  First, in step S101, the ECU 105 determines whether or not a diagnosis execution condition is satisfied. For example, the ECU 105 reads the load state of the engine 101 and determines that the diagnosis execution condition is satisfied when the load is not high. This is because in the deterioration diagnosis process, as described above, the deterioration diagnosis is performed by periodically changing the A / F of the engine 101 between the rich state and the lean state, so that the engine 101 is adversely affected in a high load state. It is. Therefore, the diagnosis execution condition is determined in advance so as to be satisfied when the vehicle is traveling relatively stably.

  If the diagnosis execution condition is not satisfied (step S101; No), the process returns to step S101 to make a determination again.

  If the diagnosis execution condition is satisfied (step S101; Yes), the process proceeds to step S102. In step S102, the ECU 105 detects the temperature of the A / F sensor 107, and determines whether or not the detected sensor temperature is lower than a predetermined temperature X (° C.). The determination in step S102 is performed because the A / F sensor 107 is in an inactive state when the temperature is lower than the predetermined temperature X, and deterioration diagnosis is performed in the inactive state. . The temperature of the A / F sensor 107 is calculated by the ECU 105 based on the element impedance of the sensor indicated by the signal S11 supplied from the A / F sensor 107. Further, the predetermined temperature X is a temperature in which the sensor is in an inactive state, for example, in the example of FIG. 2, around 550 to 600 ° C. where a difference in response time between a normal sensor and a deteriorated sensor appears remarkably. be able to. The predetermined temperature X can be stored in advance in a memory in the ECU 105.

  If the vehicle 200b is after the engine is started, the temperature of the A / F sensor 107 is often equal to or lower than a predetermined temperature X. By performing the deterioration diagnosis in such a state, the deterioration diagnosis can be performed in advance before the control of the vehicle 200b using the detection value of the A / F sensor 107. As a result, the deterioration of the A / F sensor 107 can be dealt with before the control of the vehicle 200b is started, and the vehicle 200b can be favorably controlled.

  When the temperature of the A / F sensor 107 is higher than the predetermined temperature X (° C.) (step S102; No), the process proceeds to step S103. In step S103, the ECU 105 turns off the heater 120 attached to the A / F sensor 107. In the present invention, since the sensor deterioration diagnosis is performed at a low temperature when the sensor is in an inactive state, it is necessary to lower the sensor temperature to a predetermined temperature X (° C.) or less. To do. When the above process is completed, the process returns to step S101 and the diagnosis execution condition is determined again.

  By performing the processing in steps S102 and S103, the deterioration diagnosis is performed only when the A / F sensor 107 is once activated (predetermined temperature X or higher) and then the heater 120 is turned off and the predetermined temperature X or lower is reached. It can be performed. That is, a device that measures the temperature of the A / F sensor 107 (such as a circuit that calculates impedance in the ECU 105) has failed, and continues to indicate that the temperature is equal to or higher than the predetermined temperature X but lower than the predetermined temperature X. However, it is possible to prevent the deterioration diagnosis from being performed. By doing so, the sensor deterioration is determined only in a state in which the device for measuring the sensor temperature is correctly detecting the temperature, so the sensor deterioration is determined in a situation where the sensor temperature cannot be detected correctly. It is possible to prevent erroneous determination that the sensor has deteriorated but has not deteriorated.

  On the other hand, when the temperature of the A / F sensor 107 is lower than the predetermined temperature X (step S102; Yes), the process proceeds to step S104. In step S104, the ECU 105 calculates the response time of the A / F sensor 107. As shown in FIG. 3, the response time is such that the ECU 105 periodically changes the A / F between a rich state and a lean state until the output voltage of the A / F sensor 107 reaches a predetermined voltage V1 to V2. The time required for the calculation is calculated. Then, the process proceeds to step S105.

  In step S105, the ECU 105 determines whether or not the number of times of calculating the response time as described above exceeds a predetermined number Y. This is because the deterioration diagnosis process uses an average value of response times measured repeatedly Y times a predetermined number of times. In the present embodiment, determination is performed by repeatedly measuring in order to increase the reliability of the deterioration diagnosis. Therefore, if the number of times the response time is calculated does not exceed the predetermined number Y, the process returns to step S101 and the processes of steps S101 to S104 are performed again. The ECU 105 can update and record the number of times the response time of the A / F sensor 107 is calculated in the memory. Further, the response time of the A / F sensor 107 repeatedly measured is stored in the memory in the ECU 105.

  If the number of times the response time has been calculated exceeds the predetermined number Y (step S105; Yes), the process proceeds to step S106. In step S106, the ECU 105 calculates an average response time from the response time of the A / F sensor 107 calculated Y times. Then, the process proceeds to step S107.

  In step S107, it is determined whether or not the average response time calculated in step S106 is smaller than a predetermined response time Z (msec). As the predetermined response time Z, for example, in the example of FIG. 2, 500 (msec), which can reliably determine whether or not the sensor is normal when the temperature of the sensor is 600 ° C. or lower, is used. it can. The predetermined response time X can be stored in advance in a memory in the ECU 105.

  If the average response time is shorter than the predetermined response time Z (msec) (step S107; Yes), in step S108, the ECU 105 determines that the A / F sensor 107 is normal (not deteriorated).

  On the other hand, if the average response time is longer than the predetermined response time Z (msec) (step S107; No), in step S109, the ECU 105 determines that the A / F sensor 107 has deteriorated. At this time, the ECU 105 performs control such as issuing a diagnosis code relating to the abnormality of the A / F sensor 107 and lighting an engine check lamp (not shown).

  As described above, it is possible to accurately determine a deteriorated sensor by performing a deterioration diagnosis process when the sensor temperature at which the difference in response between a normal sensor and a deteriorated sensor appears markedly is low. Can do.

1 is a block diagram of a part of a vehicle to which a deterioration diagnosis apparatus according to an embodiment of the present invention is applied. It is a figure which shows an example of the relationship between the temperature of an oxygen sensor, and a response speed. It is a figure which shows an example of the method of determining the response speed of an oxygen sensor. 1 is a block diagram of a part of a vehicle to which a deterioration diagnosis apparatus according to an embodiment of the present invention is applied. It is a flowchart which shows the deterioration diagnosis process based on the Example of this invention.

Explanation of symbols

101 Engine 102 Exhaust passage 103 Front catalyst 104 Rear catalyst 105 ECU
106, 108 Oxygen sensor 107 A / F sensor 120, 122 Heater 200a, 200b Vehicle

Claims (8)

A sensor deterioration diagnosis device for a vehicle having a property that a difference in response between a normal sensor and a deteriorated sensor is larger in an inactive state than in an active state, and the deterioration diagnosis is performed when the sensor is in an inactive state. A sensor deterioration diagnosis device characterized by that. The vehicle sensor having a property that the difference in response between the normal sensor and the deteriorated sensor is larger in the inactive state than in the active state is a sensor in which the response of the sensor in the inactive state is slower than the response in the active state. The sensor deterioration diagnosis apparatus according to claim 1, wherein the sensor deterioration diagnosis apparatus is provided. The inactive state refers to a state where the temperature of the sensor is equal to or lower than a predetermined temperature,
Sensor temperature detection means for detecting the temperature of the sensor;
The deterioration diagnosis device for a sensor according to claim 1, further comprising a deterioration diagnosis unit that performs a deterioration diagnosis when the sensor temperature is equal to or lower than the predetermined temperature. Temperature raising means for raising the temperature of the sensor;
The sensor deterioration diagnosis apparatus according to claim 3, further comprising: means for stopping the temperature raising means when the sensor temperature is equal to or higher than the predetermined temperature. Sensor response time detecting means for detecting the response time of the sensor;
If the sensor response time is a predetermined time or less, the deterioration diagnosis unit diagnoses that the sensor is not deteriorated,
5. The sensor deterioration diagnosis apparatus according to claim 3, wherein if the sensor response time is equal to or longer than the predetermined time, the sensor is diagnosed as being deteriorated. The sensor according to any one of claims 1 to 5, wherein the inactive state is a state until the temperature of the sensor reaches the predetermined temperature after the engine of the vehicle is started. Deterioration diagnosis device. The inactive state is a state in which the temperature of the sensor becomes equal to or lower than the predetermined temperature after the temperature of the sensor once reaches the predetermined temperature. Deterioration diagnosis device for sensor as described in 1. The deterioration diagnosis apparatus according to claim 1, wherein the sensor is an oxygen sensor or an A / F sensor that detects an oxygen concentration.

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