JP2016205322A - Inspection method of sensor with heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method of a sensor with a heater which can suppress the generation of an element crack at the inspection of the sensor.SOLUTION: A control device 80 stores a detection value of a NOx sensor 150 when a sensor element is in an activated state by activation energization in an engine stop state to a storage device. Then, after storing the detection value of the NOx sensor 150, electricity-carrying to the heater 150a arranged at the NOx sensor 150 is stopped for a prescribed period of time, and the sensor element is cooled. Next, after the completion of the cooling of the sensor element, the detection value which is stored in the storage device is displayed on a diagnosis tool 500. Then, the presence or absence of an abnormality of the NOx sensor 150 is determined by a maintenance person on the basis of the detection value which is displayed on the diagnosis tool 500, and after the detection value is displayed on the diagnosis tool 500, an engine start by the maintenance person is permitted.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for inspecting a sensor with a heater.

  A sensor provided with a heater is provided in the exhaust passage of the internal combustion engine for early activation of the sensor element. Examples of such a sensor with a heater include a NOx sensor, an air-fuel ratio sensor, an oxygen sensor, and an HC sensor.

  Here, if the heater element is energized while the condensed water of the exhaust gas is attached to the sensor element and the temperature of the sensor element rises rapidly, the sensor element may be damaged by a sudden temperature change, so-called element cracking may occur. There is.

  Therefore, in order to suppress such element cracking, when energizing the heater, first, a relatively low power is supplied to evaporate the condensed water adhering to the sensor element. After that, activation energization is performed in which electric power that can raise the temperature of the sensor element to the activation temperature is supplied to the heater (for example, Patent Document 1).

JP 2004-69644 A

  As a method for checking the presence or absence of the abnormality of the sensor described above, for example, the detection value of the sensor in the activated state when the engine is stopped is displayed on the display device, and the displayed detection value is a normal range according to the atmospheric composition. If the value is within the range, it is determined that there is no abnormality in the sensor. On the other hand, if the sensor is out of the normal range, it can be determined that the sensor is abnormal. As an example, in the case of a NOx sensor, for example, it can be determined that the sensor is normal if the detected value of the sensor when the engine is stopped is generally less than 10 ppm. On the other hand, when it exceeds the normal value, it can be determined as abnormal.

  Here, since the temperature of the sensor in the activated state is high, when the engine is started at such a high temperature state, the condensed water present in the exhaust passage is blown away by the exhaust and the sensor There is a risk of adhesion to the element and element cracking.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for inspecting a sensor with a heater that can suppress the occurrence of element cracking during inspection of the sensor.

  A method for inspecting a sensor with a heater that solves the above problem is a method for inspecting a sensor with a heater provided in an exhaust passage of an internal combustion engine, wherein the sensor element of the sensor is heated to an activation temperature. A step of performing preheating energization to supply lower power to the heater than when performing energization energization to supply the heater with possible power, a step of performing the activation energization after performing the preheating energization, and the activity Storing the detected value of the sensor when the sensor element is in an activated state by energization energization, and storing the detected value of the sensor, and then energizing the heater is stopped for a predetermined period. The process of cooling the sensor element and the process of displaying the detection value stored in the storage device on the display device after the cooling of the sensor element is completed in order in the engine stop state. Thereby determining the presence or absence of an abnormality of the sensor based on the detected values displayed on the display device, permits the engine start after the detected value is displayed on the display device.

  According to this method, in a state where the engine is stopped, the sensor element whose temperature is increased by the energization by activation is cooled by stopping the energization to the heater for a predetermined period. When the cooling of the sensor element is completed, the detection value of the sensor is displayed on the display device, and the presence / absence of the abnormality of the sensor is determined / inspected based on the displayed value. Further, after the detection value of the sensor is displayed on the display device, the engine start is permitted.

  Since the sensor element is cooled before the engine start is permitted in this manner, the temperature of the sensor element is sufficiently lower than the activation temperature when the engine is started. Therefore, even if the condensed water present in the exhaust passage is discharged to the exhaust and adheres to the sensor element as the engine is started, the sensor element is low in temperature, so that the occurrence of element cracking can be suppressed. Accordingly, it is possible to suppress the occurrence of element cracking during sensor inspection.

Schematic which shows the internal combustion engine to which this is applied about one Embodiment of the inspection method of a sensor with a heater, and its periphery structure. The flowchart which shows the check procedure of the NOx sensor in the embodiment. The flowchart which shows the procedure of the forced electricity supply process in the embodiment. The timing chart which shows the change of the flag value by forced energization processing.

  Hereinafter, an embodiment in which an inspection method of a sensor with a heater is applied to a NOx sensor of a diesel engine (hereinafter referred to as “engine”) mounted on a vehicle will be described with reference to FIGS.

As shown in FIG. 1, a selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) 41 as a catalyst for reducing and purifying NOx in exhaust gas is disposed in the exhaust passage 26 of the engine 1.
A urea addition valve 230 for adding urea water to the exhaust is provided on the exhaust upstream side of the SCR catalyst 41. The urea water injected from the urea addition valve 230 is converted into ammonia by hydrolysis utilizing exhaust heat and is adsorbed by the SCR catalyst 41. Then, NOx is reduced and purified by the ammonia adsorbed on the SCR catalyst 41.

Further, a NOx sensor 150 for detecting the amount of NOx in the exhaust is provided on the exhaust downstream side of the SCR catalyst 41.
The NOx sensor 150 includes a sensor element sintered using zirconia or the like as a material, a heater 150a for heating the sensor element, and the like. By energizing the heater 150a, the sensor element is heated to reach the activation temperature, so that the NOx sensor 150 is activated and outputs a detection value corresponding to the amount of NOx in the exhaust passage 26. . The NOx sensor 150 corresponds to the heater-equipped sensor in the present embodiment.

  Various controls of the engine 1 are performed by the control device 80. The control device 80 includes a central processing control device (CPU), a storage device that stores various programs and maps in advance, a storage device that temporarily stores CPU calculation results, a timer counter, an input interface, an output interface, and the like. It is structured around a microcomputer. The control device 80 is connected to an ignition switch (hereinafter referred to as IG switch) 25 operated by a vehicle driver and various sensors.

Further, the control device 80 performs an abnormality diagnosis for determining whether or not there is an abnormality in the NOx purification performed by the SCR catalyst 41.
For this abnormality diagnosis, the control device 80 sets the NOx amount in the exhaust gas flowing into the SCR catalyst 41 as the first NOx amount N1, and calculates this based on the engine operating state. That is, the amount of NOx generated in the cylinder of the engine 1 is calculated based on the fuel injection amount injected into the engine 1, the fuel injection timing, the engine rotational speed, the intake air amount related to the air-fuel ratio, and the like. The value is the first NOx amount N1. Further, the NOx amount detected by the NOx sensor 150 provided in the exhaust passage 26 downstream of the SCR catalyst 41, that is, the NOx amount in the exhaust gas purified by the SCR catalyst 41 is defined as a second NOx amount N2, and the following equation (1 ) To calculate the NOx purification rate CF.

NOx purification rate CF = (first NOx amount N1−second NOx amount N2) / first NOx amount N1 × 100 (%) (1)

When the calculated NOx purification rate CF is equal to or less than the abnormality determination value ER, it is determined that the NOx purification is abnormal.

  In addition, the control device 80 is provided with a port for connecting a diagnostic tool 500 for abnormality diagnosis used by the engineer of the engine 1. The diagnostic tool 500 includes a display unit 500a that displays various sensor values, diagnosis results of the engine 1, and the like. The diagnostic tool 500 including the display unit 500a constitutes the display device.

  By the way, when it is determined by the control device 80 that there is an abnormality in the NOx purification, the mechanic inspects various devices related to the NOx purification in order to eliminate such abnormality. One of these is the NOx sensor 150.

Therefore, in the present embodiment, the NOx sensor 150 is inspected as follows.
FIG. 2 shows an inspection procedure of the NOx sensor 150 performed by the mechanic. Note that the diagnostic tool 500 is connected to the control device 80 in advance at the start of this inspection procedure.

First, the mechanic turns off the IG switch 25 to stop the engine 1 (S100).
Next, the mechanic operates the diagnostic tool 500 to set the sensor diagnostic mode (S110).

  Next, the maintenance person turns on the IG switch 25 to start energization of the control device 80 (S120). In step S120, the engine is not started through the operation of the IG switch 25. That is, the starter for starting the engine 1 is not energized.

  Next, the mechanic confirms whether or not the detection value of the NOx sensor 150 is displayed on the display unit 500a (S130). When the detection value of the NOx sensor 150 is not displayed (S130: NO), the confirmation in step S130 is performed until the detection value of the NOx sensor 150 is displayed.

  On the other hand, when the detected value of the NOx sensor 150 is displayed (S130: YES), the presence / absence of abnormality of the NOx sensor 150 is determined based on the displayed detected value (S140). In step S140, the detected value displayed on the display unit 500a, that is, the detected value of the NOx sensor 150 in a state where the engine is stopped and the exhaust passage 26 is filled with the atmosphere is normal according to the atmospheric composition. If the value is within the range, it is determined that the NOx sensor 150 has no abnormality. On the other hand, if it is out of the normal range, it is determined that the NOx sensor 150 is abnormal. As an example, if the displayed detection value is less than about 10 ppm, it is determined as normal. On the other hand, when the displayed detection value exceeds the normal value, it is determined as abnormal. It should be noted that the amount of NOx in the atmosphere may exceed 10 ppm along streets with heavy traffic or where other diesel vehicles are operating. It is desirable to change.

  Then, the engine start by the mechanic is permitted (S150). The permission to start the engine in step S150 indicates that the engine start is permitted on the display unit 500a, or the engine start is permitted when the detected value is displayed on the display unit 500a in a maintenance procedure manual or the like. A method of writing an explanation to do so is conceivable.

Then, the inspection of the NOx sensor is finished.
Next, after the diagnostic tool 500 is set to the sensor diagnostic mode in the procedure in step S110, the IG switch 25 is turned on in the procedure in step S120, thereby energizing the control device 80. Then, the control device 80 forcibly energizes the heater 150a in order to activate the NOx sensor 150 and output the detected value.

Hereinafter, forced energization of the heater 150a will be described with reference to FIGS. FIG. 3 shows a procedure of forced energization processing, and FIG. 4 shows changes in various flag values and the like due to the forced energization processing.
As shown in FIG. 3, when this process is started, it is first determined whether or not there is a sensor diagnosis request from the diagnostic tool (S200). The determination in step S200 is performed immediately after the IG switch 25 is turned on and energization of the control device 80 is started, as shown at time t1 in FIG. When the diagnostic tool 500 is not set to the sensor diagnostic mode, it is determined that there is no request for sensor diagnosis (S200: NO), and this process ends.

  On the other hand, when the diagnostic tool 500 is set to the sensor diagnostic mode in the procedure of step S110, it is determined that there is a sensor diagnostic request from the diagnostic tool (S200: YES), and at time t1 in FIG. As shown, the pre-energization flag is set to “ON” almost simultaneously with the ON operation of the IG switch 25 (S210). When this pre-energization flag is set to “ON”, electric power that can raise the temperature of the NOx sensor 150 to the activation temperature is supplied to the heater 150a. The preheating energization process is performed. It should be noted that the amount of heat generated by the heater 150a during the preheating energization is adjusted to an amount of heat that can evaporate the condensed water without causing element cracking even if condensed water adheres to the sensor element.

  Next, after the IG switch 25 is turned on, in other words, after the preliminary energization flag is set to “ON”, it is determined whether or not the specified time TP1 has elapsed (S220). The specified time TP1 is set in advance with a time required for evaporation of the condensed water by the preheating energization.

  When the specified time TP1 has not elapsed since the IG switch 25 was turned on (S220: NO), the determination process of step S220 is repeatedly executed until the specified time TP1 has elapsed.

  On the other hand, when the specified time TP1 has elapsed since the IG switch 25 was turned on (S220: YES), as shown at time t2 in FIG. 4, the preheating energization flag is set to “OFF” and the preheating energization is terminated. (S230).

  Next, when the preheating energization is completed, since the condensed water is not attached to the sensor element, activation energization is performed to supply the heater 150a with electric power that can raise the NOx sensor 150 to the activation temperature. However, there is no risk of element cracking. Therefore, as shown at time t3 in FIG. 4, the activation energization flag is set to “ON” in order to perform activation energization (S240). When the activation energization flag is set to “ON”, an activation energization process for supplying the maximum power that can be energized to the heater 150a is performed. Note that the power for activation energization is not necessarily limited to such maximum power, and may be any power that can raise the NOx sensor 150 to the activation temperature.

  Next, it is determined whether or not the element temperature stabilization flag is “ON” (S250). This element temperature stabilization flag is set to “ON” when the temperature of the sensor element of the NOx sensor 150 is equal to or higher than the activation temperature, and is set to “OFF” when the temperature of the sensor element is lower than the activation temperature. Flag. The element temperature stabilization flag is a flag set in the control device provided in the NOx sensor 150 and is a signal value output from the NOx sensor 150 to the control device 80.

  When the element temperature stability flag is not “ON” (S250: NO), the determination process of step S250 is repeatedly executed until the element temperature stability flag is “ON”.

  On the other hand, as shown at time t4 in FIG. 4, when the element temperature stabilization flag is “ON” (S250: YES), the cooling counter is reset to “0” (S260). The value of the cooling counter gradually increases with time while the above-described element temperature stabilization flag is “OFF”. Therefore, as shown in FIG. 4, the element temperature stabilization flag is “OFF” immediately after the IG switch 25 is turned on. Therefore, the element temperature stability flag is turned “ON” immediately after the IG switch 25 is turned on. Until just before, the value of the cooling counter gradually increases. When the element temperature stabilization flag is “ON” (time t4), the cooling counter is reset to “0”.

Here, the detection value of the NOx sensor 150 is unstable and the reliability is low until a certain amount of time elapses after the element temperature stabilization flag is turned “ON”.
Therefore, it is next determined whether or not the specified time TP2 has elapsed since the element temperature stabilization flag was turned "ON" (S270). The specified time TP2 is set in advance with a time required until the detected value of the NOx sensor 150 is stabilized after the element temperature stabilization flag is turned “ON”. If the detected value of the NOx sensor 150 is stable immediately after the element temperature stabilization flag is set to “ON”, the process of step S270 can be omitted.

  Then, when the specified time TP2 has not elapsed since the element temperature stabilization flag is set to “ON” (S270: NO), the determination process of step S270 is repeatedly executed until the specified time TP2 has elapsed.

  On the other hand, when the specified time TP2 has elapsed after the element temperature stabilization flag is turned “ON” (S270: YES), the activation flag is set to “ON” as shown at time t5 in FIG. 4 (S280). ). When the activation flag is set to “ON”, the NOx amount is detected by the NOx sensor 150.

  Next, the detection value of the NOx sensor 150 when the activation flag is set to “ON”, that is, the detection value of the NOx sensor 150 when the NOx sensor 150 is activated by activation energization is controlled. A step of storing in the storage device in the device 80 is performed (S290).

  When the detection value of the NOx sensor 150 is stored in this way, since the detection value for sensor inspection is completed, the activation energization flag is set to “OFF” as shown at time t6 in FIG. Energization is stopped (S300). A process of cooling the sensor element is performed by stopping energization of the heater 150a.

  Next, it is determined whether or not the element temperature flag is turned “OFF” due to the temperature drop of the sensor element due to the stop of energization of the heater 150a (S310). When the element temperature flag is not “OFF” (S310: NO), the process of step S310 is repeatedly executed until the element temperature flag is “OFF”.

  By the way, when the energization of the heater 150a is stopped, the temperature of the sensor element rapidly decreases. Therefore, as shown at time t6 in FIG. 4, the element is activated at approximately the same time as the activation energization flag is set to “OFF”. The temperature flag is also “OFF”.

  When the element temperature flag is “OFF” (S310: YES), since the NOx sensor 150 is in an inactive state, the activation flag is “OFF” as shown at time t6 in FIG. (S320).

  Here, if it is determined in step S310 that the element temperature stability flag is “OFF”, the cooling counter restarts the measurement of the cooling counter, as shown after time t6 in FIG. It gradually increases from “0”.

  Next, it is determined whether or not the cooling counter that gradually increases with time has reached the cooling determination value α (S330). As the cooling determination value α, the temperature of the sensor element that has become equal to or higher than the activation temperature due to the activation energization is reduced to such an extent that no element cracking occurs even if condensed water adheres by stopping energization of the heater 150a. The value of the cooling counter corresponding to the required cooling period is preset.

When the cooling counter is less than the cooling determination value α (S330: NO), the process of step S340 is repeatedly executed until the cooling counter becomes equal to or higher than the cooling determination value α.
On the other hand, when the cooling counter becomes equal to or larger than the cooling determination value α (S330: YES), the preheating energization flag is set to “ON” again as shown at time t7 in FIG. The temperature of the sensor element whose temperature is lower than the activation temperature is kept. If it is not necessary to keep the sensor element warm, the process of step S340 can be omitted.

  Then, as shown at time t7 in FIG. 4, a step of displaying the detected value of the NOx sensor 150 stored in step S290 on the display unit 500a of the diagnostic tool 500 is performed (S350), and this process is terminated.

Next, the operation of this embodiment will be described.
In the engine stop state, the activation energization flag is set to “ON” in step S240, whereby activation energization is performed on the heater 150a.

  The sensor element heated to high temperature by this energization is cooled by stopping the energization to the heater 150a for a period corresponding to the cooling determination value α through the execution from step S300 to step S330.

  When the cooling of the sensor element is completed, the detected value stored when the NOx sensor 150 is activated in step S290 is displayed on the diagnostic tool 500 in step S350.

  In step S140 of FIG. 2, the NOx sensor 150 is inspected by determining whether or not the NOx sensor 150 is abnormal based on the detection value displayed on the diagnostic tool 500. Then, in step S150 of FIG. 2, after the detected value is displayed on the diagnostic tool 500, the engine start is permitted.

  Thus, before the engine start is permitted, a period for cooling the sensor element, that is, a period for stopping the energization of the heater 150a until the cooling counter reaches the cooling determination value α is provided. The temperature of the sensor element is sufficiently lower than the activation temperature.

According to this embodiment described above, the following effects can be obtained.
(1) A period for cooling the sensor element is provided before permitting engine start. Therefore, when the engine is started, the temperature of the sensor element is sufficiently lower than the activation temperature. Therefore, even if the condensed water existing in the exhaust passage 26 is discharged to the exhaust and adheres to the sensor element as the engine is started, the sensor element is low in temperature, so that the occurrence of element cracking can be suppressed. . Therefore, it is possible to suppress the occurrence of element cracks when the NOx sensor 150 is inspected.

  (2) By performing preheating energization, the condensed water adhering to the sensor element can be evaporated. Therefore, activation energization can be performed without causing element cracking, and the NOx sensor can be activated early during inspection. Accordingly, the inspection time can be shortened.

  (3) The detected value is displayed on the diagnostic tool 500 after the cooling of the sensor element is completed, and the engine start is permitted after the detected value is displayed on the diagnostic tool 500. Therefore, the maintenance person can easily know that the engine start is permitted by displaying the detection value on the diagnostic tool 500.

  (4) With the NOx sensor 150 attached to the exhaust passage 26, the NOx sensor 150 can be inspected without causing element cracking. Therefore, serviceability and work efficiency can be improved compared with the case where inspection is performed with the NOx sensor 150 removed from the exhaust passage 26.

  (5) After the sensor element cooling period has elapsed (step S340 in FIG. 3: YES), preheating energization is performed to keep the sensor element warm. Therefore, reattachment of condensed water to the sensor element can be suppressed. Further, since the sensor element is kept warm, the temperature of the sensor element can be raised to the activation temperature earlier when activation energization is performed as compared with the case where the temperature is not kept.

In addition, the said embodiment can also be changed and implemented as follows.
-The position and number of NOx sensors can be changed as appropriate.
In the above embodiment, the sensor with a heater is the NOx sensor 150, but another sensor with a heater such as an air-fuel ratio sensor, an oxygen sensor, or an HC sensor may be used.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 25 ... Ignition switch (IG switch), 26 ... Exhaust passage, 41 ... Selective reduction type NOx catalyst (SCR catalyst), 80 ... Control device, 150 ... NOx sensor, 150a ... Heater, 230 ... Urea addition valve, 500: diagnostic tool, 500a: display unit.

Claims (1)

A method for inspecting a sensor with a heater provided in an exhaust passage of an internal combustion engine,
Performing preheating energization for supplying power to the heater at a lower power than when performing activation energization for supplying the heater with power capable of raising the sensor element of the sensor to an activation temperature;
Performing the activation energization after performing the preheating energization;
Storing the detection value of the sensor when the sensor element is in an activated state by the activation energization in a storage device;
Storing the detection value of the sensor, and cooling the sensor element by stopping energization of the heater for a predetermined period;
After the cooling of the sensor element is completed, the process of displaying the detection value stored in the storage device on a display device is sequentially performed in the engine stop state,
A sensor with a heater that determines whether or not there is an abnormality in the sensor based on the detection value displayed on the display device, and permits engine start after the detection value is displayed on the display device. Inspection method.