JP2009133238A - Diagnostic device for nox sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnostic device for a NOx sensor having high diagnosis accuracy with securing a stable diagnosis condition without receiving influence of operation of an internal combustion engine. <P>SOLUTION: A diagnosis part constructing a control part 17 diagnoses the NOx sensor 36 after a sufficient period passes from stop of an engine system 10 and an exhaust system 16 is sufficiently cooled. The diagnosis part diagnoses the NOx sensor 36 if outside air temperature detected by an outside air temperature sensor 13 and temperature in an exhaust passage 27 detected by a temperature sensor 35 get almost same. When temperature in the exhaust passage 27 and the outside air temperature are almost same, the engine system 10 is sufficiently cooled, and temperature of the NOx sensor 36 and the exhaust system 16 get into stable states. Consequently, influence of the operation conditions of the engine system 10 and residual heat existing in the exhaust system 16 are eliminated, for diagnosis of heating performance of a heater of the NOx sensor 36. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a NOx sensor diagnostic device, and more particularly to a NOx sensor diagnostic device that detects NOx contained in exhaust gas from an internal combustion engine.

The NOx sensor that detects the concentration of NOx in the exhaust gas needs to be regularly diagnosed in order to maintain its accuracy and detect the presence or absence of a failure at an early stage. On the other hand, during operation of the internal combustion engine, the temperature of the exhaust gas changes due to fluctuations in the load of the internal combustion engine and the like, and the diagnosis conditions tend to become unstable. Therefore, it is difficult to ensure the accuracy of the NOx sensor diagnosis during operation of the internal combustion engine. In view of this, it has been proposed to perform a diagnosis of the NOx sensor within the after-operation period of the control device after the operation of the internal combustion engine is stopped (see Patent Document 1). The internal combustion engine is in an after-operation state in which the operation of the control device continues for a predetermined period even after the operation is stopped. Therefore, in Patent Document 1, the NOx sensor is diagnosed during the after-motion period of the control device. After the operation of the internal combustion engine is stopped, a change in exhaust gas temperature or the like is small and the diagnosis condition is stabilized as compared with the operation of the internal combustion engine.
JP 2006-105965 A

  However, after the internal combustion engine has stopped operating, the diagnostic conditions are stable compared to during operation, but the exhaust gas temperature immediately before the internal combustion engine stops operating, the residual heat remaining in the exhaust system after stopping operation, Or there is a problem of being affected by outside temperature. Further, it is difficult to determine whether or not the residual heat after the operation of the internal combustion engine is stopped has a sufficient amount of heat for the diagnosis of the NOx sensor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a NOx sensor diagnostic device that ensures stable diagnostic conditions and high diagnostic accuracy without being affected by the operation of an internal combustion engine.

  According to the first or seventh aspect of the invention, the diagnosis means diagnoses the NOx sensor when the internal combustion engine stops operating and the temperature difference between the NOx sensor and the outside air temperature becomes a predetermined value or less. When the internal combustion engine stops operating, the temperature of the NOx sensor gradually decreases. When the temperature of the NOx sensor detected by the sensor temperature detection means approximates the outside air temperature detected by the outside air temperature sensor, the diagnosis of the NOx sensor is performed by the diagnosis means. Here, although it is desirable that the temperature of the NOx sensor and the outside air temperature are substantially the same, a temperature difference of about several tens of degrees Celsius may be set according to the required diagnostic accuracy of the NOx sensor. When the temperature of the NOx sensor is close to the outside air temperature, the temperatures of the internal combustion engine and the NOx sensor are stable and hardly change. Therefore, when diagnosing the heating performance by the heater of the NOx sensor, the influence of the surrounding heat, particularly the influence of the exhaust heat, is eliminated. Therefore, it is not affected by the operation of the internal combustion engine, a stable diagnostic condition can be secured, and the diagnostic accuracy of the NOx sensor can be improved.

  According to the second or third aspect of the invention, the heating performance of the heater is diagnosed based on the relationship between the energization period of the heater and the reached temperature. That is, in the case of the invention described in claim 2, based on the temperature of the heater reached within a preset energizing period, in the case of the invention described in claim 3, until the heater reaches a preset reached temperature. The heating performance of the heater is diagnosed based on the energization period. Therefore, the heater heating performance, that is, the diagnosis of the NOx sensor can be performed with a simple configuration.

  According to a fourth aspect of the present invention, the diagnosis means has correction means for correcting the energization period of the heater or the reached temperature of the heater according to the outside air temperature. For example, when the outside air temperature is low, the temperature reached by the heater within the same energization period is lower than when the outside air temperature is high. As described above, the energization period and the arrival period of the heater are affected by the outside air temperature. Therefore, in the invention described in claim 4, the energization period of the heater or the temperature reached by the heater is corrected by the correcting means based on the outside air temperature detected by the outside air temperature sensor. Therefore, the influence of the diagnostic accuracy of the NOx sensor due to the outside air temperature can be reduced.

  In the invention according to claim 5, the sensor temperature detecting means detects the temperature of the NOx sensor based on a period after the operation of the internal combustion engine is stopped. The temperature of the internal combustion engine decreases with the elapse of the period by stopping the operation. That is, when a sufficient period elapses after the operation of the internal combustion engine is stopped, the temperature difference between the exhaust system of the internal combustion engine provided with the NOx sensor and the outside air temperature becomes small. Thus, the temperature of the NOx sensor is estimated based on the elapsed time since the operation of the internal combustion engine was stopped without activating a temperature sensor that detects the temperature of the NOx sensor, for example, as the sensor temperature detecting means. In this case, the temperature sensor is not essential as a configuration. Therefore, the NOx sensor can be diagnosed in a short period of time, and an increase in the number of parts and a complicated structure can be suppressed.

  According to the sixth aspect of the present invention, the sensor temperature detecting means determines whether to perform the diagnosis of the NOx sensor based on the difference between the temperature of the exhaust passage through which the exhaust flows and the outside air temperature. The exhaust passage temperature sensor is provided inside the exhaust passage, for example, to directly detect the temperature of the exhaust passage, or indirectly detects the temperature of the exhaust passage by detecting the temperature of the exhaust pipe forming the exhaust passage. To detect. Since the NOx sensor is provided in the exhaust passage, the temperature of the exhaust passage indirectly indicates the temperature of the NOx sensor. Thereby, the sensor temperature detection means improves the temperature detection accuracy of the NOx sensor. Therefore, the diagnostic accuracy of the NOx sensor can be further increased.

  In the invention according to claim 8, the diagnosis means stops the diagnosis of the heating performance of the heater when the outside air temperature is below a predetermined value. For example, when the outside air temperature is extremely low, such as below zero, the power consumed by the heater of the NOx sensor increases. Therefore, the load on the battery increases, which may affect the next start of the internal combustion engine. Therefore, when the outside air temperature is low, the diagnosis unit stops diagnosing the heating performance of the heater. Therefore, the battery can be protected.

  According to the ninth aspect of the invention, the diagnosis of the heating performance of the heater is stopped when the voltage of the battery is equal to or lower than a predetermined value. The heater consumes a relatively large amount of power. Therefore, when the voltage of the battery is lowered due to a decrease or deterioration of the charge amount of the battery, when the heater is energized, a further load is applied to the battery. Therefore, there is a risk of affecting the next start of the internal combustion engine. Therefore, when the battery voltage is equal to or lower than the predetermined value, the diagnosis unit stops diagnosing the heating performance of the heater. Therefore, the battery can be protected.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of an engine system to which a NOx sensor diagnostic device according to the present invention is applied will be described with reference to the drawings.
(Engine system configuration)
First, an embodiment of an engine system to which the NOx sensor diagnostic device of the present invention shown in FIG. 1 is applied will be described.
The engine system 10 includes an engine 11 as an internal combustion engine, an exhaust purification device 12, and an outside air temperature sensor 13. As the engine 11, for example, a piston engine such as a gasoline engine or a diesel engine, or any internal combustion engine such as a gas turbine engine can be applied. This embodiment demonstrates the example which applies a gasoline engine as an engine. The engine 11 includes an engine body 14, an intake system 15, an exhaust system 16, and a control unit 17. The engine body 14 has a piston 19 that reciprocates inside the cylinder 18. The cylinder 18 is provided with an injector 21 for injecting fuel. The injector 21 injects fuel into a combustion chamber 22 formed between the cylinder 18 and the piston 19. The injector 21 is supplied with fuel from a fuel tank (not shown). In the case of the present embodiment, the engine 11 shows a so-called direct injection type in which fuel is injected from the injector 21 into the combustion chamber 22. The fuel supply format of the engine 11 is not limited to the direct injection type, and any method such as a so-called premixing type can be selected.

  The intake system 15 has an intake pipe portion 24 that forms an intake passage 23. The intake pipe 24 has one end connected to the engine body 14 and the other end open to the atmosphere. The intake pipe portion 24 has an air filter 25 at the end on the side open to the atmosphere. The intake air is removed by the air filter 25 and then sucked into the engine body 14 via the intake passage 23 formed by the intake pipe portion 24. The intake system 15 has a throttle 26. The throttle 26 opens and closes the intake passage 23 to control the flow rate of intake air flowing through the intake passage 23. An intake valve (not shown) is provided at the end of the intake passage 23 on the combustion chamber 22 side. Opening and closing of the intake valve interrupts the inflow of intake air from the intake passage 23 to the combustion chamber 22. The flow rate of the intake air sucked into the combustion chamber 22 may be controlled according to the opening / closing timing and the opening / closing amount of the intake valve instead of the throttle 26.

  The exhaust system 16 has an exhaust pipe portion 28 that forms an exhaust passage 27. The exhaust pipe portion 28 has one end connected to the engine body 14 and the other end open to the atmosphere via a muffler (not shown). Exhaust gas is discharged from the engine body 14 to the atmosphere via an exhaust passage 27 formed by the exhaust pipe portion 28. An exhaust valve (not shown) is provided at the end of the exhaust passage 27 on the combustion chamber 22 side. By opening and closing the exhaust valve, the exhaust gas flowing out from the combustion chamber 22 to the exhaust passage 27 is interrupted.

  The control unit 17 is an ECU (Electronic Control Unit) that controls the entire engine system 10 including the engine 11 and the exhaust purification device 12. As shown in FIG. 2, the control unit 17 includes a microcomputer having a CPU 31, a ROM 32, and a RAM 33. The control unit 17 is connected to another control device of the engine system 10 via an in-vehicle LAN (not shown). The control unit 17 outputs a drive signal to the injector 21 based on a depression amount of an accelerator pedal (not shown). The controller 17 controls the opening / closing period of the injector 21, that is, the fuel injection amount by outputting a drive signal to the injector 21.

As shown in FIG. 1, the exhaust purification device 12 includes a three-way catalyst 34, a temperature sensor 35, and a NOx sensor 36. The three-way catalyst 34, the temperature sensor 35, and the NOx sensor 36 are all provided in the exhaust system 16. When the three-way catalyst 34 reaches the activation temperature, the hydrocarbon (HC) contained in the exhaust is oxidized into water (H ₂ O) and carbon dioxide (CO ₂ ). Further, the three-way catalyst 34 reduces nitrogen oxide (NOx) contained in the exhaust gas to nitrogen (N ₂ ).
The temperature sensor 35 is provided in the exhaust pipe portion 28 that forms the exhaust passage 27. The temperature sensor 35 is composed of a temperature measuring element such as a thermistor, for example. The temperature sensor 35 outputs an electrical signal according to the temperature of the exhaust passage 27. The controller 17 detects the temperature of the exhaust passage 27 based on the electrical signal output from the temperature sensor 35.

  The NOx sensor 36 is provided on the downstream side of the three-way catalyst 34 in the exhaust flow direction in the exhaust system 16. The NOx sensor 36 detects the concentration of NOx contained in the exhaust flowing through the exhaust passage 27. The NOx sensor 36 has a known structure including a sensor element 41 and a heater 42 as shown in FIG. The sensor element 41 has a pair of electrodes (not shown), for example. A solid electrolyte is sandwiched between the pair of electrodes of the sensor element 41. The heater 42 heats the sensor element 41. Thereby, the sensor element 41 is heated to the activation temperature by the heater 42.

  The outside air temperature sensor 13 detects the air temperature outside the engine system 10 shown in FIG. For example, when the engine system 10 is mounted on a vehicle, the outside air temperature sensor 13 detects the outside air temperature of the vehicle. The outside air temperature sensor 13 outputs an electrical signal according to the outside air temperature. The control unit 17 detects the outside air temperature based on the electric signal output from the outside air temperature sensor 13. Therefore, the outside air temperature sensor 13 and the control unit 17 constitute outside air temperature detecting means in the claims. The outside air temperature sensor 13 can be shared with, for example, an outside air temperature sensor provided in a vehicle air conditioner (not shown).

Next, the configuration of the diagnostic device for the NOx sensor 36 will be described in detail.
As shown in FIG. 2, the diagnostic device 50 includes the control unit 17 of the engine system 10, the outside air temperature sensor 13, the temperature sensor 35, and the NOx sensor 36. The control unit 17 is a microcomputer having the CPU 31, the ROM 32, and the RAM 33 as described above. The control unit 17 includes a sensor output reading unit 51, an energization control unit 52, a heater temperature detection unit 53, an outside air temperature detection unit 54, an exhaust passage temperature detection unit 55, and a diagnosis unit 56. The sensor output reading unit 51 is connected to the sensor element 41 of the NOx sensor 36. An electrical signal corresponding to the NOx concentration output from the sensor element 41 is input to the sensor output reading unit 51. The controller 17 detects the concentration of NOx contained in the exhaust flowing through the exhaust passage 27 based on the electrical signal input to the sensor output reading unit 51.

  The energization control unit 52 is connected to the heater 42 of the NOx sensor 36. The energization control unit 52 turns on or off the energization of the heater 42. Thereby, supply of electric power from a battery (not shown) is intermittently supplied to the heater 42. The heater temperature detection unit 53 detects the temperature of the heater 42. In the case of this embodiment, the heater temperature detection unit 53 detects the voltage applied from the energization control unit 52 to the heater 42 and the current supplied to the heater 42. The heater temperature detection unit 53 detects the temperature of the heater 42 from the relationship between the voltage applied to the heater 42 and the current supplied to the heater 42. The outside air temperature detection unit 54 is connected to the outside air temperature sensor 13. The electrical signal output from the outside air temperature sensor 13 according to the outside air temperature is input to the outside air temperature detecting unit 54. The control unit 17 detects the outside air temperature based on the electric signal input to the outside air temperature detecting unit 54.

  The exhaust passage temperature detector 55 is connected to the temperature sensor 35. An electrical signal corresponding to the temperature of the exhaust passage 27 output from the temperature sensor 35 is input to the exhaust passage temperature detector 55. The control unit 17 detects the temperature of the exhaust passage 27 based on the electrical signal input to the exhaust passage temperature detection unit 55. The temperature sensor 35 may be arranged in the exhaust passage 27 to directly detect the temperature of the exhaust passage 27, or may be configured to indirectly detect the temperature of the exhaust passage 27 from the temperature of the exhaust pipe portion 28. The NOx sensor 36 is provided in the exhaust passage 27. Therefore, the temperature of the exhaust passage 27 detected by the temperature sensor 35 and the control unit 17 substantially matches the temperature of the NOx sensor 36. Thereby, the temperature sensor 35 and the control part 17 in this embodiment are equivalent to the sensor temperature detection means of a claim.

  The diagnosis unit 56 diagnoses the NOx sensor 36 according to the computer program recorded in the ROM 32. The diagnosis unit 56 constitutes the diagnostic means of the claims. Hereinafter, the diagnosis flow of the NOx sensor 36 in the diagnosis unit 56 will be described.

(First embodiment of NOx sensor diagnosis)
A first embodiment of the diagnosis of the NOx sensor 36 will be described based on FIGS. 3 and 4.
The main relay (not shown) of the control unit 17 starts autonomously at a predetermined interval when an ignition switch (not shown) of the engine system 10 is turned off. When the main relay is activated, the control unit 17 executes various computer programs including diagnosis of the NOx sensor 36. At this time, the interval at which the main relay is activated can be arbitrarily set, for example, within a range from several minutes to several tens of minutes.

  When the computer program is executed by the activation of the main relay, the diagnosis unit 56 determines whether or not the engine system 10 is in operation (S101). For example, when the ignition switch is off, it is highly likely that the engine system 10 has stopped operating, but the diagnosis unit 56 determines whether the engine system 10 is in operation for confirmation, and whether the engine system 10 It is determined whether or not the engine is in a starting state. The diagnosis unit 56 detects the state of the engine system 10 based on, for example, the amount of fuel injected from the injector 21 or the rotational speed of the engine 11 detected by a rotation sensor (not shown).

  When determining that the engine system 10 is stopped in step S101, the diagnosis unit 56 determines whether or not the diagnosis of the NOx sensor 36 is performed after the engine system 10 is stopped (S102). The diagnosis of the NOx sensor 36 only needs to be performed once between the stop of the engine system 10 and the next start. Therefore, if the diagnosis of the NOx sensor 36 is performed once after the engine system 10 is stopped, further diagnosis of the NOx sensor 36 is unnecessary. Therefore, if the diagnosis of the NOx sensor 36 is performed once after the engine system 10 is stopped, the diagnosis unit 56 ends the process.

  If the diagnosis unit 56 determines in step S102 that the diagnosis of the NOx sensor 36 is not performed after the engine system 10 is stopped, the diagnosis unit 56 determines whether or not a diagnosis execution condition is satisfied (S103). Here, the diagnosis unit 56 determines whether or not the difference between the outside air temperature and the temperature of the exhaust passage 27 is equal to or less than a predetermined value as a diagnosis execution condition. That is, the diagnosis unit 56 determines whether or not the difference between the outside air temperature detected by the outside air temperature sensor 13 and the temperature of the exhaust passage 27 detected by the temperature sensor 35 is a predetermined value or less. Since the NOx sensor 36 is provided in the exhaust passage 27 as described above, the temperature of the exhaust passage 27 approximates the temperature of the NOx sensor 36. Therefore, the diagnosis unit 56 determines whether the diagnosis execution condition is satisfied by regarding the temperature of the exhaust passage 27 as the temperature of the NOx sensor 36. The diagnosis unit 56 may be configured to estimate the temperature of the NOx sensor 36 by multiplying the temperature of the exhaust passage 27 detected by the temperature sensor 35 by a predetermined coefficient.

  When the difference between the outside air temperature and the temperature of the exhaust passage 27 is equal to or less than a predetermined value, the exhaust system 16 and the NOx sensor 36 of the engine system 10 are sufficiently cooled and the temperature is considered to be stable. Therefore, the diagnosis unit 56 determines whether or not the temperature of the exhaust system of the engine system 10 is close to the outside air temperature and is sufficiently cooled. In this case, it is desirable that the difference between the outside air temperature and the temperature of the exhaust passage 27 is almost 0, that is, the outside air temperature and the temperature of the exhaust passage 27 substantially coincide. This is because it is considered that the exhaust system 16 of the engine system 10 is sufficiently cooled when the outside air temperature and the temperature of the exhaust passage 27 substantially coincide. However, in consideration of detection errors of the outside air temperature sensor 13 and the temperature sensor 35, the predetermined value of the difference between the outside air temperature and the temperature of the exhaust passage 27 may be set to, for example, about several degrees Celsius to several tens of degrees Celsius. That is, the predetermined value of the difference between the outside air temperature set here and the temperature of the exhaust passage 27 depends on the accuracy required for the diagnosis of the NOx sensor 36, the detection accuracy of the outside air temperature sensor 13 and the temperature sensor 35, and the like. It may be arbitrarily set within the range of 0 ° C. to several tens of ° C.

  Further, the diagnosis unit 56 determines the diagnosis condition based on the elapsed period after the engine system 10 is stopped instead of determining the diagnosis condition based on the temperature difference detected by the outside air temperature sensor 13 and the temperature sensor 35. May be. In other words, when a sufficient period of time elapses after the engine system 10 is stopped, the exhaust system 16 is sufficiently cooled, and the temperature of the exhaust system 16 becomes stable. Therefore, the diagnosis unit 56 may determine that the diagnosis condition is satisfied depending on whether or not a predetermined period has elapsed since the engine system 10 was stopped. Specifically, by counting the number of times the main relay is turned on and off in step S101, it is possible to detect an elapsed period after the ignition is turned off. When the diagnosis condition is determined based on the elapsed time since the engine system 10 was stopped, the temperature sensor 35 need not be activated. Therefore, the diagnosis of the NOx sensor 36 can be performed more easily and in a short period of time.

  Furthermore, in addition to the determination of the diagnosis execution condition based on the temperature of the exhaust system 16, the diagnosis unit 56 may determine the diagnosis execution condition according to the state of the battery (not shown) or the outside air temperature. Specifically, the diagnosis unit 56 determines that the diagnosis execution condition is not satisfied when the charge amount of the battery is reduced or when the battery is deteriorated. The diagnosis of the NOx sensor 36 energizes the heater 42 with relatively large power consumption. For this reason, if the diagnosis of the NOx sensor 36 is performed when the charge amount of the battery is reduced or the battery is deteriorated, the load applied to the battery increases. As a result, there is a risk of hindering the next start of the engine system 10. Therefore, the diagnosis unit 56 determines that the diagnosis execution condition is not satisfied when the charge amount of the battery is reduced or when the battery is deteriorated, and stops the diagnosis. Further, when the outside air temperature detected by the outside air temperature sensor 13 is extremely low, such as below zero, the diagnosis unit 56 determines that the diagnosis execution condition is not satisfied, and stops the diagnosis. This is because when the outside air temperature is extremely low, the power consumed by the heater 42 of the NOx sensor 36 becomes excessive, and the load applied to the battery may increase.

  As described above, when the diagnosis unit 56 determines that the diagnosis execution condition of the NOx sensor 36 is satisfied in step S103 as described above, the diagnosis unit 56 initializes the counter and sets C = 0 (S104). The diagnosis unit 56 has a counter (not shown) in its configuration. When the diagnosis unit 56 determines in step S103 that the diagnosis execution condition for the NOx sensor 36 is satisfied, the diagnosis unit 56 turns on the diagnosis execution flag. The diagnosis unit 56 starts energization of the heater 42 by turning on the diagnosis execution flag. The diagnosis unit 56 turns on the energization of the heater 42 via the energization control unit 52 (S105). The time when the energization of the heater 42 is started is t0 shown in FIG.

  When the energization of the heater 42 is turned on, the diagnosis unit 56 detects the temperature Th of the heater 42 (S106). The temperature Th of the heater 42 increases as the energization period elapses. The temperature Th of the heater 42 is detected by the heater temperature detection unit 53 based on the relationship between the voltage applied from the energization control unit 52 to the heater 42 and the current supplied to the heater 42 as described above. The temperature Th of the heater 42 detected here is the reached temperature in the claims. The detection of the temperature Th of the heater 42 is not limited to detection based on the relationship between the voltage and current of the heater 42, and is detected by, for example, a temperature sensor provided in the heater 42 or a resistance of an element provided in the vicinity of the heater 42. It is good also as a structure.

  The diagnosis unit 56 determines whether or not the temperature Th of the heater 42 detected in step S106, that is, the reached temperature of the heater 42 is higher than a preset temperature T1 (S107). Here, it is desirable to set the set temperature T1 to the activation temperature of the NOx sensor 36. The activation temperature of the NOx sensor 36 is set to a high temperature such as 700 ° C., for example. The set temperature T1 is not limited to the activation temperature of the NOx sensor 36, and may be set to an arbitrary temperature. By reducing the set temperature T1 within a range in which the diagnostic accuracy of the NOx sensor 36 is ensured, the power consumption in the heater 42 can be reduced.

  If the diagnosis unit 56 determines in step S107 that the temperature Th of the heater 42 has not reached the set temperature T1, the diagnosis unit 56 advances the counter and sets C = C + 1 (S108). Then, the diagnosis unit 56 determines whether or not the count C of the counter advanced in step S108 is greater than a predetermined value C1 (S109). If the result of determination is that C> C1, the diagnosis unit 56 returns to step S106 and repeats step S106 to step S109. This predetermined value C1 of the count corresponds to a preset energization period to the heater 42, and corresponds to the timing t1 when the energization period has elapsed from t0 when energization is started in FIG.

  When determining that C> C1 in step S109, the diagnosis unit 56 determines that the heater 42 is abnormal and turns on the heater abnormality flag (S110). When the temperature C of the counter becomes larger than C1 without the temperature Th of the heater 42 reaching the set temperature T1, the energization period until the heater 42 reaches the set temperature T1 is set to a predetermined count value C1. It means that it is longer than the corresponding energization period. Therefore, it is considered that an abnormality has occurred in the heater 42 and the heating performance of the heater 42 has deteriorated. Therefore, the diagnosis unit 56 determines that the heater 42 is abnormal when the temperature Th of the heater 42 does not reach the set temperature T1 and the count C becomes larger than the predetermined value C1.

On the other hand, when the temperature Th of the heater 42 becomes higher than the set temperature T1 without reaching the predetermined value C1 in step S107, the diagnosis unit 56 determines that the heater 42 is normal and turns on the heater normal flag (S111). . Between Step S106 and Step S109, a loop is made while determining whether or not the count C of the counter is larger than C1 in Step S109. Therefore, if the temperature Th of the heater 42 has reached the set temperature T1 in step S107 during this loop, the energization period of the heater 42, that is, the count C of the counter is C1 or less. As a result, it is considered that no abnormality has occurred in the heater 42. Therefore, the diagnosis unit 56 turns on the heater normal flag.
When the heater abnormality flag is turned on in step S110 or the heater normal flag is turned on in step S111, the diagnosis unit 56 turns off the energization of the heater 42 (S112). Then, the diagnosis unit 56 turns on the diagnosis completion flag (S113). By turning on the diagnosis completion flag, in the next and subsequent routines, it is determined in step S102 that the diagnosis of the NOx sensor 36 is completed.

  As described above, in the first embodiment of the diagnosis of the NOx sensor 36, the NOx sensor 36 is diagnosed after the engine system 10 is stopped and a sufficient period has passed and the exhaust system 16 is sufficiently cooled. ing. When the temperature of the exhaust passage 27 becomes substantially the same as the outside air temperature, the temperatures of the NOx sensor 36 and the exhaust system 16 are stabilized. Therefore, the diagnosis of the heating performance of the heater 42 of the NOx sensor 36 eliminates the influence of the operating state of the engine system 10 or the residual heat remaining in the exhaust system 16. Therefore, stable diagnostic conditions can be ensured without being affected by the operating state of the engine system 10 and the diagnostic accuracy of the NOx sensor 36 can be increased.

  In the present embodiment, the heating performance of the heater 42 is diagnosed based on the period until the temperature of the heater 42 reaches a predetermined set temperature T1, that is, the count of the counter. Thereby, it is diagnosed whether the heater 42 of the NOx sensor 36 has a heating capability necessary to exhibit the function of the NOx sensor 36. Therefore, the diagnosis of the NOx sensor 36 can be performed reliably and with high accuracy. In this case, for example, a sensor for detecting the temperature of the heater 42 becomes unnecessary by detecting the temperature of the heater 42 from the relationship between the voltage applied to the heater 42 and the current supplied to the heater 42. Therefore, the NOx sensor 36 can be diagnosed with high accuracy without increasing the number of parts and complicating the structure.

  In the present embodiment, the diagnosis execution condition of the NOx sensor 36 is determined based on the temperature difference between the temperature of the exhaust passage 27 detected by the temperature sensor 35 and the outside air temperature detected by the outside air temperature sensor 13. When the temperature difference between the temperature of the exhaust passage 27 and the outside air temperature is a predetermined value or less, the exhaust system 16 is sufficiently cooled, and the temperature of the NOx sensor 36 provided in the exhaust passage 27 is considered to be stable. Therefore, when the diagnosis of the NOx sensor 36 is performed, the influence of heat remaining in the exhaust system 16 is reduced. On the other hand, instead of detecting the temperature of the exhaust passage 27 by the temperature sensor 35, the diagnosis execution condition may be determined based on the elapsed period from the stop of the engine system 10. In this case, it is not necessary to start the temperature sensor 35 that detects the temperature of the exhaust passage 27. Therefore, the diagnosis of the NOx sensor 36 can be performed in a shorter period of time and simpler processing.

(Second Embodiment of NOx Sensor Diagnosis)
Next, a second embodiment of the diagnosis of the NOx sensor 36 will be described based on FIG. In addition, description is abbreviate | omitted about the procedure substantially the same as 1st Embodiment of the diagnosis of NOx sensor 36. FIG.
When the computer program is executed by the activation of the main relay, the diagnosis unit 56 determines whether or not the engine system 10 is in operation (S201). When determining that the engine system 10 is stopped, the diagnosis unit 56 determines whether the diagnosis of the NOx sensor 36 has been performed in the past (S202). When the diagnosis unit 56 determines that the diagnosis of the NOx sensor 36 is not performed, the diagnosis unit 56 determines whether or not the diagnosis execution condition is satisfied (S203). If the diagnosis unit 56 determines that the diagnosis execution condition is satisfied, the counter 56 initializes the counter to C = 0 (S204) and turns on the heater 42 (S205).

  When the energization of the heater 42 is turned on, the diagnosis unit 56 advances the count of the counter to C = C + 1 (S206). Then, the diagnosis unit 56 determines whether or not the count C advanced in step S206 is greater than a predetermined value C2 (S207). The diagnosis unit 56 repeats steps S206 and S207 until the count C becomes larger than the predetermined value C2. When determining that the count C is greater than C2 in step S207, the diagnosis unit 56 detects the temperature Th of the heater 42 (S208). The detection of the temperature Th of the heater 42 is performed in the same manner as in the first embodiment described above.

  The diagnosis unit 56 determines whether or not the temperature Th of the heater 42 detected in step S208, that is, the reached temperature is higher than a preset temperature T2. When the diagnosis unit 56 determines in step S209 that the temperature Th of the heater 42 has not reached the set temperature T2, the diagnosis unit 56 turns on the heater abnormality flag (S210). On the other hand, when determining that the temperature Th of the heater 42 has reached the set temperature T2 in step S209, the diagnosis unit 56 turns on the heater normal flag (S211).

The diagnosis unit 56 detects the temperature Th of the heater 42 when the period during which the heater 42 is energized, that is, the energization period, reaches the predetermined value C2 by repeating Step S206 and Step S207. Therefore, the diagnosis unit 56 can determine whether or not the temperature Th of the heater 42, that is, the reached temperature of the heater 42 has reached the set temperature T2 within a predetermined energization period. At this time, if the temperature Th of the heater 42 has reached the set temperature T2 in step S209, it is determined that the heating performance of the heater 42 is sufficiently ensured and the heater 42 is normal. On the other hand, if the temperature Th of the heater 42 does not reach the set temperature T2 in step S209, it is determined that the heating performance of the heater 42 is insufficient and the heater 42 is abnormal.
When the heater abnormality flag is turned on in step S210 or the heater normal flag is turned on in step S211 as a result of the determination in step S209, the diagnosis unit 56 turns off the power supply to the heater 42 (S212). Then, the diagnosis unit 56 turns on the diagnosis completion flag (S213).

As described above, in the second embodiment of the diagnosis of the NOx sensor 36, the temperature Th of the heater 42 reaches the set temperature T2 during a predetermined period, that is, the energization period of the heater 42 until the count of the counter reaches C2. The heating performance of the heater 42 is diagnosed based on whether or not it is. Thereby, it is diagnosed whether the heater 42 of the NOx sensor 36 has a heating capability necessary to exhibit the function of the NOx sensor 36. Therefore, the diagnosis of the NOx sensor 36 can be performed reliably and with high accuracy.
The diagnosis of the heater 42 may be determined based on the energization period until the temperature of the heater 42 reaches the set temperature T1 as in the first embodiment, and the predetermined energization of the heater 42 as in the second embodiment. The determination may be made based on whether or not the temperature of the heater 42 reaches the set temperature T2 within the period.

(Variation of NOx sensor diagnosis)
In the first embodiment described above, the set temperature T1 is set as a condition for determining the temperature of the heater 42, and the predetermined value C1 is set as a condition for determining the energization period. In the second embodiment, the set temperature T2 is set as a condition for determining the temperature of the heater 42, and the predetermined value C2 is set as a condition for determining the energization period. In the above-described embodiment, the set temperatures T1 and T2 and the predetermined values C1 and C2 of the energization period have been described as constants.
However, the set temperatures T1 and T2 and the predetermined values C1 and C2 of the energization period may be variables, or may be correction values with corrections as necessary. Specifically, the set temperatures T1 and T2 and the predetermined values C1 and C2 of the energization period may change according to the outside air temperature detected by the outside air temperature sensor 13. Moreover, it is good also as a structure which correct | amends preset temperature T1, T2 and predetermined value C1, C2 of an electricity supply period according to the outside temperature detected with the outside temperature sensor 13. FIG.

  Since the temperature of the heater 42 is increased by energization, the heater 42 is easily affected by the outside air temperature. For example, when the outside air temperature is low, the period during which the heater 42 is energized before reaching the predetermined temperature is longer than when the outside air temperature is high. Therefore, as shown in FIG. 6, the period required for the diagnosis of the NOx sensor 36 by the diagnosis unit 56 changes according to the outside air temperature. As a result, if the set temperatures T1 and T2 and the predetermined values C1 and C2 of the energization period are constant values, there is a possibility that an error may occur in the diagnosis result according to the outside air temperature. Therefore, a configuration may be adopted in which a correction unit is provided in the diagnosis unit 56, and the correction unit corrects the set temperatures T1 and T2 and the predetermined values C1 and C2 of the energization period according to the outside air temperature detected by the outside air temperature sensor 13. Thereby, the diagnostic accuracy of the heating performance of the heater 42 is improved. Therefore, the diagnosis of the NOx sensor 36 can be performed with high accuracy regardless of the outside air temperature condition.

In the above embodiments, the configuration in which the temperature of the NOx sensor 36 is indirectly detected from the temperature of the exhaust passage 27 has been described. However, a separate temperature sensor may be provided in the NOx sensor 36 and the temperature of the NOx sensor 36 may be directly detected.
The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

Schematic which shows the engine system to which the diagnostic apparatus of the NOx sensor by one Embodiment of this invention is applied. The block diagram which shows the diagnostic apparatus of the NOx sensor by one Embodiment of this invention Schematic which shows the flow of 1st Embodiment of the diagnosis of NOx sensor by the diagnostic apparatus of NOx sensor by one Embodiment of this invention. Schematic which shows the timing chart in 1st Embodiment of the diagnosis of the NOx sensor shown in FIG. Schematic which shows the flow of 2nd Embodiment of the diagnosis of NOx sensor by the diagnostic apparatus of NOx sensor by one Embodiment of this invention. Schematic showing the relationship between outside temperature and diagnosis period

Explanation of symbols

  In the drawings, 11 is an engine (internal combustion engine), 13 is an outside air temperature sensor (outside air temperature detecting means), 17 is a control unit (sensor temperature detecting means, outside air temperature detecting means), 27 is an exhaust passage, and 35 is a temperature sensor (sensor). (Temperature detection means, exhaust passage temperature sensor), 36 is a NOx sensor, 41 is a sensor element, 42 is a heater, 50 is a diagnostic device, and 56 is a diagnosis unit (diagnosis means, correction means).

Claims (9)

A diagnostic device for a NOx sensor comprising a sensor element for detecting the concentration of NOx contained in exhaust gas from an internal combustion engine and a heater for heating the sensor element to an activation temperature,
Sensor temperature detecting means for detecting the temperature of the NOx sensor;
Outside air temperature detecting means for detecting outside air temperature outside the NOx sensor;
When the internal combustion engine stops operation and the difference between the temperature of the NOx sensor detected by the sensor temperature detection means and the outside air temperature detected by the outside air temperature detection means is equal to or less than a predetermined value, the heater is energized, Diagnosing means for diagnosing the heating performance of the sensor element by the heater;
A diagnostic apparatus for a NOx sensor, comprising:   2. The NOx sensor diagnosis apparatus according to claim 1, wherein the diagnosis unit diagnoses the heating performance of the heater based on a temperature reached by the heater that has been reached in a preset energization period.   2. The NOx sensor diagnosis apparatus according to claim 1, wherein the diagnosis unit diagnoses the heating performance of the heater based on an energization period until the heater reaches a preset reached temperature. 3.   4. The NOx sensor diagnosis apparatus according to claim 2, wherein the diagnosis unit includes a correction unit that corrects the energization period or the reached temperature based on an outside air temperature detected by the outside air temperature detecting unit.   5. The NOx sensor according to claim 1, wherein the sensor temperature detection unit detects the temperature of the NOx sensor based on a period after the operation of the internal combustion engine is stopped. Diagnostic device. The sensor temperature detecting means has an exhaust passage temperature sensor for directly or indirectly detecting the temperature of the exhaust passage through which the exhaust gas of the internal combustion engine flows.
The diagnosis means determines whether or not to perform the diagnosis of the heating performance of the heater based on a difference between the temperature of the exhaust passage detected by the exhaust passage temperature sensor and the outside air temperature detected by the outside air temperature sensor. The NOx sensor diagnostic apparatus according to any one of claims 1 to 4, wherein the determination is performed.   The diagnosis means performs a diagnosis of the heating performance of the heater when the temperature of the NOx sensor detected by the sensor temperature detection means and the outside air temperature detected by the outside air temperature sensor are substantially the same. The diagnostic apparatus for a NOx sensor according to any one of claims 1 to 6.   The NOx sensor according to any one of claims 1 to 7, wherein the diagnosis unit stops the diagnosis of the heating performance of the heater when the outside air temperature detected by the outside air temperature sensor is equal to or lower than a predetermined value. Diagnostic equipment.   8. The NOx sensor diagnosis apparatus according to claim 1, wherein when the battery voltage is equal to or lower than a predetermined value, the diagnosis unit stops diagnosis of the heating performance of the heater. 9.

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