JP4706928B2 - Exhaust gas sensor heater control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maximally early activate an exhaust gas sensor, while preventing an element crack of the exhaust gas sensor with a heater by sticking of moisture in an exhaust pipe. <P>SOLUTION: Heater-off time Toff corresponding to the lowest temperature TPmin lowest among the cooling water temperature, the intake air temperature and the outside air temperature in starting, is calculated (Step 101 and 102). Afterwards, heater-off correction time Tofs1 corresponding to a difference &Delta;TP1 between the cooling water temperature TPwsta and the lowest temperature TPmin in starting (the difference &Delta;TP1 between the cooling water temperature TPwsta and the outside air temperature or the intake air temperature in starting, when engine stopping time is relatively short), is calculated. The heater-off time Toff is shortened as the difference &Delta;TP1 between the cooling water temperature TPwsta and the outside air temperature or the intake air temperature in stating becomes large, by correcting the heater-off time Toff by using this heater-off correction time Tofs1 (Step 103 to 106). Thus, the heater-off time Toff is shortened as the exhaust pipe temperature in starting becomes high. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an exhaust gas sensor heater control device for controlling a heater for heating a sensor element of an exhaust gas sensor.

  In an internal combustion engine that has been electronically controlled in recent years, an exhaust gas sensor (such as an air-fuel ratio sensor or an oxygen sensor) that detects an air-fuel ratio of exhaust gas, rich / lean, or the like is disposed in an exhaust pipe, and based on the output of the exhaust gas sensor The fuel injection amount and the like are feedback controlled so that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio. In general, since the exhaust gas sensor has low detection accuracy unless the temperature of the sensor element is raised to the activation temperature, the sensor element is heated by a heater built in the exhaust gas sensor to promote activation of the exhaust gas sensor.

  By the way, the exhaust gas of the internal combustion engine contains water vapor generated by the combustion reaction of fuel and air. When the temperature of the exhaust pipe is low immediately after the start of the internal combustion engine, the exhaust gas containing water vapor is Therefore, the water vapor in the exhaust gas may condense in the exhaust pipe, resulting in condensed water. For this reason, there is a possibility that the condensed water generated in the exhaust pipe immediately after the start adheres to the sensor element of the exhaust gas sensor. When the sensor element is heated with the heater immediately after the start, the high temperature sensor element heated by the heater is condensed water. “Element cracking” may occur due to local cooling (thermal strain) due to the adhesion of silicon.

  As a countermeasure, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-328821), when it is determined that the stop time from the stop to the start of the internal combustion engine is a short restart (that is, at the start) If the exhaust pipe temperature is high and it is determined that almost no condensed water is generated in the exhaust pipe), the heater is energized from the start, and if it is not restarted, There is a heater off time that is set, and when the heater off time has elapsed from the start, the exhaust pipe temperature is judged to have risen to a temperature at which no condensed water is generated in the exhaust pipe, and energization of the heater is started. .

  Further, as described in Patent Document 2 (Japanese Patent Publication No. 6-90167), a temperature sensor is attached to the exhaust pipe, and when the exhaust pipe temperature detected by this temperature sensor is lower than a predetermined temperature, it is condensed in the exhaust pipe. There is one that judges that water is present and prohibits heating of the exhaust gas sensor by the heater.

Further, as described in Patent Document 3 (Japanese Patent Laid-Open No. 2002-48749), an exhaust gas calorific value (or exhaust gas temperature) is calculated based on the operating state of the internal combustion engine, and the exhaust gas calorific value (or exhaust gas) is calculated. The exhaust pipe temperature is estimated based on the gas temperature) and the heat transfer model that mathematically models the heat transfer between the exhaust gas and the exhaust pipe and the heat transfer between the exhaust pipe and the outside air. In some cases, heating of the exhaust gas sensor by the heater is started when the tube temperature rises to a temperature at which moisture does not condense in the exhaust pipe.
JP 2003-328821 A (the second page etc.) Japanese Patent Publication No. 6-90167 (first page, etc.) JP 2002-48749 A (2nd page, etc.)

  By the way, the higher the exhaust pipe temperature at start-up, the shorter the time required for the exhaust pipe temperature to rise to a temperature at which condensed water does not occur after start-up, so the heater off necessary to prevent cracks in the exhaust gas sensor Time is also shortened.

  However, in the technique of Patent Document 1 described above, when setting the heater off time, the heater off time is simply set according to the cooling water temperature without considering the exhaust pipe temperature at the time of starting. It may not be possible to set an appropriate value, the heater off time may be longer than necessary, and activation of the exhaust gas sensor may be delayed. There is a drawback that it gets worse.

  Moreover, in the technique of the above-mentioned Patent Document 2, it is necessary to newly provide a temperature sensor for detecting the exhaust pipe temperature.

  Further, in the technique of Patent Document 3, the exhaust gas heat quantity (or exhaust gas temperature) is calculated based on the operating state of the internal combustion engine, and the exhaust gas heat quantity (or exhaust gas temperature) and the heat transfer model are used. Since it is necessary to calculate the exhaust pipe temperature, there is a disadvantage that the calculation process of the exhaust pipe temperature is complicated and the calculation load of the control device increases.

  The present invention has been made in consideration of these circumstances. Therefore, the object of the present invention is to activate the exhaust gas sensor as early as possible while preventing element cracking of the exhaust gas sensor, and to reduce the cost. It is an object of the present invention to provide a heater control device for an exhaust gas sensor that can satisfy the demands for reducing the load on the control and control device.

To achieve the above object, the invention according to claim 1 is provided with a heater for heating the sensor element of the exhaust gas sensor provided in the exhaust passage of the internal combustion engine, and after a predetermined heater off time has elapsed since the start of the internal combustion engine. In the heater control device of the exhaust gas sensor that starts heating the sensor element by the heater, the heater off time is corrected by the heater off time correction means according to the difference between the cooling water temperature at the previous stop of the internal combustion engine and the cooling water temperature at the current start. der those such that is, specifically, to correct so as to shorten the extent the heater off time difference between the previous coolant temperature and the current start time of the cooling water temperature at the time of stop of the internal combustion engine is small It is what.

More downtime of the inner combustion engine increases, the temperature of the exhaust passage at the time of starting is low, and, since the difference between the coolant temperature and the current start time of the cooling water temperature at the previous stop is large, the previous stop The difference between the cooling water temperature of this time and the cooling water temperature at the start of this time is information reflecting the exhaust passage temperature at the start. Therefore, if the heater off time is corrected according to the difference between the coolant temperature at the previous stop and the coolant temperature at the current start, the heater off time can be changed according to the exhaust passage temperature at the start. As a result, the time required for the exhaust passage temperature to rise to a temperature at which condensed water does not occur after the start according to the exhaust passage temperature at the start (that is, the heater off time necessary to prevent cracking of the exhaust gas sensor element) Can be set to an appropriate value by changing the heater off time, and the exhaust gas sensor can be activated as early as possible while preventing cracks in the exhaust gas sensor due to moisture adhering to the exhaust passage. can do.

The present invention is characterized in that the heater off time is corrected to be shorter as the difference between the cooling water temperature at the previous stop of the internal combustion engine and the cooling water temperature at the current start is smaller. The shorter the stop time of the internal combustion engine, the smaller the difference between the coolant temperature at the previous stop and the coolant temperature at the current start, and the exhaust passage temperature at the start becomes higher. If correction is made so that the heater-off time is shortened as the difference between the water temperature and the cooling water temperature at the time of the start becomes smaller, the exhaust passage temperature at the start increases to a temperature at which no condensed water is generated after the start. Accordingly, the heater off time can be shortened correspondingly to the shortening of the time required to do so, and the exhaust gas sensor can be activated earlier.

  Hereinafter, the best mode for carrying out the present invention will be described using two Examples 1 and 2.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 that detects the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 for introducing air into each cylinder of the engine 11, and a fuel injection valve 21 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 20 of each cylinder. Yes. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of each ignition plug 22.

  On the other hand, the exhaust pipe 23 (exhaust passage) of the engine 11 is provided with an exhaust gas sensor 24 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or rich / lean of the exhaust gas. A heater (not shown) for heating the sensor element is built in (or attached externally). A catalyst 25 such as a three-way catalyst for purifying exhaust gas is provided on the downstream side of the exhaust gas sensor 24.

  A cooling water temperature sensor 26 that detects the cooling water temperature and a crank angle sensor 28 that outputs a pulse signal each time the crankshaft 27 of the engine 11 rotates a predetermined crank angle are attached to the cylinder block of the engine 11. Based on the output signal of the crank angle sensor 28, the crank angle and the engine speed are detected. The outside air temperature sensor 30 detects the outside air temperature, and the intake air temperature sensor 31 detects the intake air temperature.

  Outputs of these various sensors are input to a control circuit (hereinafter referred to as “ECU”) 29. The ECU 29 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount of the fuel injection valve 21 according to the engine operating state. The ignition timing of the spark plug 22 is controlled.

  At that time, the ECU 29 feedback-controls the fuel injection amount and the like so that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio based on the output of the exhaust gas sensor 24, so that the air-fuel ratio of the exhaust gas becomes the purification window of the catalyst 25. Thus, the exhaust gas purification efficiency of the catalyst 25 is increased. Further, since the exhaust gas sensor 24 has poor detection accuracy unless the temperature of the sensor element rises to the activation temperature (for example, 750 ° C.), the ECU 29 sets the heater of the exhaust gas sensor 24 so that the temperature of the sensor element becomes the activation temperature. The energization is controlled to control the heating of the sensor element.

  By the way, the exhaust gas of the engine 11 contains water vapor generated by the combustion reaction of fuel and air. When the temperature of the exhaust pipe 23 is low immediately after the engine 11 is started, the exhaust gas containing water vapor is exhausted. Since it is cooled in the pipe 23, the water vapor in the exhaust gas may condense in the exhaust pipe 23 to produce condensed water. For this reason, there is a possibility that the condensed water generated in the exhaust pipe 23 immediately after the start adheres to the sensor element of the exhaust gas sensor 24. When the sensor element is heated by the heater immediately after the start, the high-temperature sensor element heated by the heater However, “element cracking” may occur due to local cooling (thermal strain) due to adhesion of condensed water.

  As a countermeasure, the ECU 29 determines that the temperature of the exhaust pipe 23 has risen to a temperature at which condensed water is not generated in the exhaust pipe 23 when a predetermined heater-off time has elapsed since the start of the engine. The heating of the sensor element is started.

  At that time, the ECU 29 executes a heater-off time setting program shown in FIG. 2 described later to set the heater-off time Toff in accordance with the lowest temperature TPmin that is the lowest among the cooling water temperature, the intake air temperature, and the outside air temperature at the time of starting. In addition to calculating, the heater off correction time Tofs1 is calculated according to the difference ΔTP1 between the cooling water temperature TPwsta and the minimum temperature TPmin at the start, and the heater off correction time Tofs1 is subtracted from the heater off time Toff corresponding to the minimum temperature TPmin. The heater off time Toff is set.

  Hereinafter, the processing content of the heater-off time setting program of FIG. 2 executed by the ECU 29 will be described. The heater off time setting program shown in FIG. 2 is executed when the engine is started. When this program is started, first, in step 101, the lowest temperature among the cooling water temperature, the intake air temperature, and the outside air temperature at the start is calculated as the minimum temperature TPmin. At that time, if the engine stop time from the previous engine stop to the current engine start is relatively short, the cooling water temperature at the time of starting becomes higher than the outside air temperature or the intake air temperature, so the outside air temperature or the intake air temperature is the lowest temperature. TPmin.

  Thereafter, the process proceeds to step 102, where the heater off time Toff corresponding to the minimum temperature TPmin is calculated by a map or a mathematical formula. In general, the lower the minimum temperature TPmin (the lowest temperature among the cooling water temperature, the intake air temperature, and the outside air temperature at the start) is, the lower the exhaust pipe temperature at the start is, and the exhaust pipe temperature is not generated after the start. Since the time required to rise to the temperature (that is, the heater off time required to prevent cracking of the exhaust gas sensor 24) becomes longer, the heater off time Toff map or formula shows that the heater off time decreases as the minimum temperature TPmin decreases. Toff is set to be long.

  Thereafter, the process proceeds to step 103, and the cooling water temperature TPwsta at the start is read. Then, the process proceeds to step 104, and a difference ΔTP1 between the cooling water temperature TPwsta at the start and the minimum temperature TPmin is calculated. At that time, when the engine stop time is relatively short, the outside air temperature or the intake air temperature becomes the minimum temperature TPmin, and therefore the difference ΔTP1 between the cooling water temperature TPwsta at the start and the outside air temperature or the intake air temperature is calculated.

  Thereafter, the routine proceeds to step 105, where the heater off correction time Tofs1 corresponding to the difference ΔTP1 between the cooling water temperature TPwsta and the minimum temperature TPmin at the start is calculated with reference to the map of the heater off correction time Tofs1 shown in FIG.

  3 is a difference ΔTP1 between the cooling water temperature TPwsta at the start and the minimum temperature TPmin (when the engine stop time is relatively short, the cooling water temperature TPwsta at the start and the outside air temperature or the intake air temperature The heater OFF correction time Tofs1 is increased and the heater OFF time Toff is shortened as the difference ΔTP1) increases.

  When the engine stop time is relatively short, the shorter the engine stop time, the larger the difference ΔTP1 between the cooling water temperature TPwsta at the start and the outside air temperature or the intake air temperature, and the exhaust pipe temperature at the start increases. If the difference ΔTP1 between the cooling water temperature TPwsta at the start and the outside air temperature or the intake air temperature is increased, the heater off time Toff is corrected so that the exhaust pipe temperature at the start becomes higher. The heater off time Toff can be shortened corresponding to the shortening of the time required to rise to a temperature at which it does not occur.

Thereafter, the routine proceeds to step 106, where the heater off time Toff is corrected by subtracting the heater off correction time Tofs1 from the heater off time Toff corresponding to the minimum temperature TPmin to set the final heater off time Toff.
Toff = Toff -Tofs1
The processing of these steps 105 and 106 serves as a heater off time correction means in the claims.

  In the first embodiment described above, paying attention to the fact that the difference ΔTP1 between the cooling water temperature TPwsta at the start and the outside air temperature (or the intake air temperature) is information reflecting the exhaust pipe temperature at the start. Since the heater off time Toff is corrected according to the difference ΔTP1 between the cooling water temperature TPwsta and the outside air temperature (or the intake air temperature), the heater off time Toff can be changed according to the exhaust pipe temperature at the start. As a result, the higher the exhaust pipe temperature at the start, the longer the time required for the exhaust pipe temperature to rise to a temperature at which condensed water is not generated after the start (that is, the heater off time necessary to prevent cracking of the exhaust gas sensor 24). ) Is shortened, the heater off time Toff can be shortened. As a result, it is possible to activate the exhaust gas sensor 24 as early as possible and start air-fuel ratio feedback control as early as possible, while preventing element cracking of the exhaust gas sensor 24 due to moisture adhering to the exhaust pipe 23, thereby improving exhaust emission. Can be made.

  Moreover, since the difference between the cooling water temperature and the outside air temperature (or intake air temperature) at the time of starting is used as information on the exhaust pipe temperature at the time of starting, there is no need to newly provide a temperature sensor for detecting the exhaust pipe temperature, thereby reducing the cost. In addition, there is an advantage that it is not necessary to perform complicated calculation processing for calculating the exhaust pipe temperature, and the calculation load on the ECU 29 can be reduced.

  In the first embodiment, the lowest temperature among the cooling water temperature, the intake air temperature, and the outside air temperature at the start is set as the minimum temperature TPmin, and the heater OFF correction is performed according to the difference ΔTP1 between the cooling water temperature TPwsta at the start and the minimum temperature TPmin. Although the time Tofs1 is calculated, the heater-off correction time Tofs1 is calculated according to the difference ΔTP1 between the cooling water temperature TPwsta at the start and the outside air temperature, or the cooling water temperature TPwsta at the start and the intake air temperature The heater off correction time Tofs1 may be calculated according to the difference ΔTP1.

Next, Embodiment 2 of the present invention will be described with reference to FIGS.
In the first embodiment, the heater-off correction time Tofs1 is calculated according to the difference ΔTP1 between the cooling water temperature TPwsta and the minimum temperature TPmin at the time of starting. In the second embodiment, the heater-off time setting program of FIG. Is executed, the heater off correction time Tofs2 is calculated according to the difference ΔTP2 between the cooling water temperature TPwstp at the previous engine stop and the cooling water temperature TPwsta at the current engine start.

  In the heater off time setting program shown in FIG. 4, first, in step 201, the minimum temperature Tmin among the cooling water temperature, the intake air temperature, and the outside air temperature at the start is calculated, and then the process proceeds to step 202, where the heater off according to the minimum temperature TPmin is calculated. The time Toff is calculated by a map or a mathematical formula.

  Thereafter, the process proceeds to step 203, and the coolant temperature TPwstp at the previous engine stop is read. The cooling water temperature TPwstp when the engine is stopped is a cooling water temperature detected immediately before the previous engine stop, and is stored in a rewritable nonvolatile memory such as a backup RAM that can hold a stored value even when the engine is stopped.

  Thereafter, the process proceeds to step 204, and after reading the coolant temperature TPwsta at the time of the current engine start, the process proceeds to step 205, where the difference ΔTP2 between the coolant temperature TPwstp at the previous engine stop and the coolant temperature TPwsta at the time of the current engine start. Is calculated.

  Thereafter, the routine proceeds to step 206, and referring to the map of the heater-off correction time Tofs2 shown in FIG. 5, the heater-off according to the difference ΔTP2 between the cooling water temperature TPwstp at the previous engine stop and the cooling water temperature TPwsta at the current engine start-up. The correction time Tofs2 is calculated.

  The map of the heater-off correction time Tofs2 in FIG. 5 shows that the heater-off correction time Tofs2 increases as the difference ΔTP2 between the coolant temperature TPwstp at the previous engine stop and the coolant temperature TPwsta at the current engine start decreases, and the heater-off time Toff Is set to be shorter.

  The shorter the engine stop time, the smaller the difference ΔTP2 between the coolant temperature TPwstp at the previous engine stop and the coolant temperature TPwsta at the current engine start, and the exhaust pipe temperature at the start increases. If the difference ΔTP2 between the cooling water temperature TPwstp at this time and the cooling water temperature TPwsta at the time of starting the engine becomes smaller, the heater off time Toff is corrected to be shorter. As the exhaust pipe temperature at the start becomes higher, the exhaust pipe temperature becomes higher after the start. The heater off time Toff can be shortened corresponding to the shortening of the time required to rise to a temperature at which condensed water is not generated.

Thereafter, the process proceeds to step 207, where the heater off time Toff is corrected by subtracting the heater off correction time Tofs2 from the heater off time Toff corresponding to the minimum temperature TPmin to set the final heater off time Toff.
Toff = Toff -Tofs2
The processing of these steps 206 and 207 serves as a heater off time correction means in the claims.

  In the second embodiment described above, attention is paid to the fact that the difference ΔTP2 between the cooling water temperature TPwstp at the previous engine stop and the cooling water temperature TPwsta at the current engine start reflects the exhaust pipe temperature at the start. The heater off time Toff is corrected according to the difference ΔTP2 between the coolant temperature TPwstp at the previous engine stop and the coolant temperature TPwsta at the current engine start, so the heater off time according to the exhaust pipe temperature at the start. Toff can be changed, and substantially the same effect as in the first embodiment can be obtained.

  In the first and second embodiments, the lowest temperature among the cooling water temperature, the intake air temperature, and the outside air temperature at the start is set as the minimum temperature TPmin, and the heater off time Toff corresponding to the minimum temperature TPmin is calculated. However, the lower one of the cooling water temperature and the outside air temperature at the start is set as the minimum temperature TPmin, or the lower one of the cooling water temperature and the intake air temperature at the start is set as the minimum temperature TPmin. You may make it do.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. It is a flowchart which shows the flow of a process of the heater off time setting program of Example 1. FIG. It is a figure which shows notionally an example of the map of the heater OFF correction | amendment time of Example 1. FIG. It is a flowchart which shows the flow of a process of the heater off time setting program of Example 2. FIG. It is a figure which shows notionally an example of the map of the heater OFF correction | amendment time of Example 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe (exhaust passage), 24 ... Exhaust gas sensor, 26 ... Cooling water temperature sensor, 29 ... ECU (heater off time correction means), 30 ... outside air temperature sensor, 31 ... intake air temperature sensor

Claims (1)

A heater control for an exhaust gas sensor that includes a heater for heating a sensor element of an exhaust gas sensor provided in an exhaust passage of the internal combustion engine and starts heating the sensor element by the heater after a predetermined heater off time has elapsed since the start of the internal combustion engine In the device
A heater off time correction means for correcting the heater off time according to the difference between the cooling water temperature at the previous stop of the internal combustion engine and the cooling water temperature at the time of the current start ,
The heater off time correction means corrects the heater off time so that the heater off time is shortened as the difference between the cooling water temperature at the previous stop of the internal combustion engine and the cooling water temperature at the current start is smaller. Control device.

Images