JP2007113920A - Heater controller of exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To early activate an air-fuel ratio sensor while preventing an element crack from being caused in the air-fuel ratio sensor by adhesion of moisture in an exhaust pipe, and to reduce the cost and the load on a controller. <P>SOLUTION: The heater controller determines whether the exhaust pipe temperature is increased to a temperature providing a moisture non-occurring state where moisture does not cause dew condensation in the exhaust pipe, based on whether or not the element resistance R of the air-fuel ratio sensor is a predetermined value R0 or lower. In a period when the element resistance R is higher than the predetermined value R0 immediately after engine start (moisture does not cause dew condensation in the exhaust pipe), energization to the heater is forbidden to prevent the element crack of the air-fuel ratio sensor, and the ignition timing of the engine is delayed to forcibly increase the temperature of the exhaust gas to rapidly increase the temperature of the exhaust pipe. Then, at the time when the element resistance R becomes the predetermined value R0 or lower (moisture non-occurring state is provided), the energization to the heater is started and is controlled so that the element temperature is rapidly increased to an activation temperature, and the delay control of the ignition timing is finished. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heater control device for an exhaust gas sensor that controls a heater for heating a sensor element of an exhaust gas sensor to control the temperature of the sensor element.

  In an electronically controlled internal combustion engine in recent years, an exhaust gas sensor (an air-fuel ratio sensor, an oxygen sensor, etc.) that detects an air-fuel ratio, rich / lean, etc. of exhaust gas is provided in an exhaust pipe, and an actual operation is performed based on the output of the exhaust gas sensor. The fuel injection amount, the intake air amount, and the like are feedback-controlled so that the air-fuel ratio matches the target air-fuel ratio. Generally, an exhaust gas sensor has poor detection accuracy unless the temperature of the sensor element is raised to the activation temperature. Therefore, a heater is incorporated in the exhaust gas sensor, and the sensor element is heated by the heater from the start of the internal combustion engine to activate the exhaust gas sensor. To promote

  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 exhaust pipe temperature is low immediately after the start of the internal combustion engine, the exhaust gas containing water vapor is contained in the exhaust pipe. Since it is cooled, 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 Publication No. 6-90167), when a temperature sensor is attached to the exhaust pipe and the exhaust pipe temperature detected by this temperature sensor is equal to or lower than a predetermined temperature, In some cases, it is determined that condensed water is present and heating of the exhaust gas sensor by the heater is prohibited.

Further, as described in Patent Document 2 (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 this exhaust gas calorific value (or exhaust gas) is calculated. The temperature of the exhaust pipe 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. There is one in which heating of an exhaust gas sensor by a heater is started when the exhaust pipe temperature rises to a temperature at which moisture does not condense in the exhaust pipe.
Japanese Patent Publication No. 6-90167 (first page, etc.) JP 2002-48749 A (2nd page, etc.)

  However, in the techniques disclosed in Patent Documents 1 and 2, the exhaust pipe is warmed up after the internal combustion engine is started, and the exhaust pipe temperature is a temperature at which moisture does not condense in the exhaust pipe (that is, element cracking of the exhaust gas sensor occurs due to adhesion of moisture). The exhaust gas sensor is heated by the heater after waiting for the temperature to rise, and the activation of the exhaust gas sensor is delayed, and the start of air-fuel ratio feedback control is delayed by that amount, resulting in worse exhaust emissions. There is a problem of doing.

  In addition, the technique disclosed in Patent Document 1 requires a new temperature sensor for detecting the exhaust pipe temperature, and there is a disadvantage that the cost increases accordingly. In the technique of Patent Document 2, 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 a 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 becomes complicated and the calculation load of the control device increases.

  The present invention has been made in view of these circumstances. Therefore, the object of the present invention is to activate the exhaust gas sensor early while preventing element cracking of the exhaust gas sensor due to adhesion of moisture in the exhaust passage. Another object of the present invention is to provide a heater control device for an exhaust gas sensor that can satisfy the demands for cost reduction and load reduction of the control device.

  In order to achieve the above object, the invention according to claim 1 is directed to a heater for an exhaust gas sensor that controls a heater for heating a sensor element of an exhaust gas sensor provided in an exhaust passage of an internal combustion engine to control the temperature of the sensor element. In the control device, the exhaust gas temperature rise control means raises the temperature of the exhaust gas of the internal combustion engine when moisture is condensed in the exhaust passage, and the judgment means makes the exhaust passage based on the resistance value (impedance) of the sensor element. It is determined whether or not moisture is not condensed (hereinafter referred to as “moisture-free” state), and when it is determined that moisture is not generated, the temperature of the sensor element is increased to the activation temperature by the heater control means. The heater is controlled to raise the temperature.

  In this configuration, the temperature of the exhaust gas of the internal combustion engine can be forcibly raised immediately after the start of the internal combustion engine when the exhaust passage temperature is low and moisture is condensed in the exhaust passage. The temperature of the exhaust passage can be quickly raised by heat to quickly evaporate the condensed water in the exhaust passage, and the time until a moisture-free state can be shortened. When it is determined that the moisture is not generated, the heater is controlled so as to raise the temperature of the sensor element to the activation temperature, thereby preventing the element of the exhaust gas sensor from being cracked due to adhesion of moisture in the exhaust passage. However, heater control for raising the temperature of the sensor element to the activation temperature can be started earlier than before, and the exhaust gas sensor can be activated earlier.

  Further, after the internal combustion engine is started, the exhaust passage and the sensor element are heated by the heat of the exhaust gas flowing in the exhaust passage, and the temperature of the exhaust passage and the temperature of the sensor element rise in the same way. Since the resistance value of the sensor element changes according to the above, the resistance value of the sensor element is information reflecting the temperature of the exhaust passage. Therefore, if the resistance value of the sensor element is monitored as in the present invention, it can be accurately determined whether or not the temperature of the exhaust passage has been raised to a temperature at which moisture does not occur. In addition, if it is determined whether or not moisture is not generated based on the resistance value of the sensor element, there is no need to newly provide a temperature sensor for detecting the exhaust passage temperature, the cost can be reduced, and the exhaust passage temperature can be reduced. It is not necessary to perform complicated calculation processing for calculation, and the calculation load of the control device can be reduced.

  In this case, as in claim 2, it may be determined whether or not the moisture is not generated based on a resistance value of the sensor element or a temperature converted from the resistance value. In this way, it is possible to determine whether or not the temperature of the exhaust passage has been raised to a temperature at which moisture does not occur based on the resistance value of the sensor element (that is, the temperature of the sensor element).

  In the meantime, in the present invention, the sensor element may be preheated by energizing the heater within a temperature range in which element cracking due to moisture adhesion does not occur during the period from the start of the internal combustion engine to the absence of moisture. However, when the sensor element is preheated by the heater, the temperature of the sensor element becomes higher than the temperature of the exhaust passage by the amount preheated by the heater, and the temperature of the exhaust passage and the resistance value of the sensor element (temperature of the sensor element) Since the relationship is shifted, the determination accuracy of the moisture non-occurrence state based on the resistance value of the sensor element is lowered. Even in this case, if the detection value or determination condition of the resistance value of the sensor element is corrected according to the preheated amount by the heater, the determination accuracy of the moisture non-occurrence state based on the resistance value of the sensor element can be secured. Correction processing becomes necessary.

  Therefore, as described in claim 3, it is preferable to prohibit the heating of the sensor element by the heater until it is determined that the moisture is not generated. In this way, the exhaust passage temperature and the resistance value of the sensor element (the temperature of the sensor element) are determined by heating the sensor element by the heater before it is determined that the moisture is not generated based on the resistance value of the sensor element. Can be accurately determined whether moisture is not generated based on the resistance value of the sensor element, and there is no need for preheating correction processing by the heater. There is an advantage that the load can be reduced. In addition, by prohibiting heating of the sensor element by the heater until it is determined that the moisture is not generated, it is possible to more reliably prevent the element of the exhaust gas sensor from being cracked due to adhesion of moisture.

  Further, as a specific method for raising the temperature of the exhaust gas, it is preferable to retard the ignition timing of the internal combustion engine and raise the temperature of the exhaust gas as in claim 4. Thus, if the ignition timing is retarded, the combustion timing of the in-cylinder mixture can be delayed to approach the valve opening timing of the exhaust valve, and the temperature of the exhaust gas can be increased efficiently.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
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 for detecting 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 the 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 air-fuel ratio sensor 24 (exhaust gas sensor) for detecting the air-fuel ratio of the exhaust gas. The air-fuel ratio sensor 24 includes a heater (heater for heating the sensor element). (Not shown) is built-in (or externally attached). A catalyst 25 such as a three-way catalyst for purifying exhaust gas is provided on the downstream side of the air-fuel ratio sensor 24.

  The cylinder block of the engine 11 includes a coolant temperature sensor 26 that detects the coolant temperature, and a crank angle sensor 28 that outputs a crank angle signal (pulse signal) every time the crankshaft 27 of the engine 11 rotates a predetermined crank angle. It is attached. Based on the crank angle signal of the crank angle sensor 28, the crank angle and the engine speed are detected.

  Outputs of these various sensors are input to an engine 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 detects the air-fuel ratio of the exhaust gas based on the output of the air-fuel ratio sensor 24, and feedback-controls the fuel injection amount so that the detected air-fuel ratio matches the target air-fuel ratio. The air-fuel ratio sensor 24 has poor detection accuracy unless the temperature of the sensor element (hereinafter referred to as “element temperature”) rises to the activation temperature (for example, 750 ° C.). The element temperature is detected based on the element resistance value), and the sensor element is heated by controlling the energization of the heater so that the element temperature becomes the activation temperature.

  By the way, the exhaust pipe 23 and the sensor element of the air-fuel ratio sensor 24 are heated by the heat of the exhaust gas flowing through the exhaust pipe 23 after the engine is started, and the temperature of the exhaust pipe 23 and the temperature of the sensor element rise in the same way. Since the element resistance value changes according to the temperature rise of the sensor element, the element resistance value is information reflecting the temperature of the exhaust pipe 23. Therefore, if the element resistance value is monitored, it can be accurately determined whether or not the temperature of the exhaust pipe 23 has been raised to a temperature at which no moisture is condensed in the exhaust pipe 23.

  Focusing on this point, the ECU 29 executes a heater control program shown in FIG. 2 to be described later, so that the temperature of the exhaust pipe 23 depends on whether the element resistance value R of the air-fuel ratio sensor 24 is equal to or less than a predetermined value R0. It is determined whether or not the temperature has been raised to a temperature at which no moisture is condensed in the exhaust pipe 23. Generally, as shown in FIG. 3, the air-fuel ratio sensor 24 has a characteristic that the element resistance value decreases as the element temperature increases. Therefore, whether or not the element resistance value R is equal to or less than a predetermined value R0 (that is, the element temperature). It is possible to determine whether or not the temperature of the exhaust pipe 23 has been raised to a temperature at which no moisture is generated.

  Then, as shown in the time chart of FIG. 4, immediately after the engine is started, until the element resistance value R of the air-fuel ratio sensor 24 is greater than a predetermined value R0, that is, until the temperature of the exhaust pipe 23 is in a moisture-free state. During a period when the temperature is not raised (a period during which moisture is condensed in the exhaust pipe 23), energization of the heater is prohibited. Accordingly, heating of the sensor element by the heater is prohibited, and element cracking of the air-fuel ratio sensor 24 due to adhesion of moisture in the exhaust pipe 23 is prevented. Further, the temperature of the exhaust gas is forcibly raised by retarding the ignition timing of the engine 11 and delaying the combustion timing of the in-cylinder mixture so as to approach the valve opening timing of the exhaust valve. As a result, the temperature of the exhaust pipe 23 is quickly raised by the heat of the exhaust gas to evaporate the condensed water in the exhaust pipe 23, and the time until a moisture-free state in which no moisture is condensed in the exhaust pipe 23 is reached. To shorten.

  Thereafter, energization of the heater is started when the element resistance value R of the air-fuel ratio sensor 24 becomes equal to or less than the predetermined value R0, that is, when the temperature of the exhaust pipe 23 is raised to a temperature at which no moisture is generated. Then, the energization of the heater is controlled so that the element temperature is quickly raised to the activation temperature, the ignition timing retarding control is terminated, and the ignition timing is returned to the normal value.

  Hereinafter, the processing content of the heater control program of FIG. 2 executed by the ECU 29 will be described. The heater control program shown in FIG. 2 is executed at a predetermined cycle while the ECU 29 is turned on, and serves as a heater control means in the claims.

  When this program is started, first, in step 101, the temperature of the exhaust pipe 23 rises to a temperature at which no moisture is generated depending on whether the element resistance value R of the air-fuel ratio sensor 24 is equal to or less than a predetermined value R0. Determine if it has been warmed. Here, the predetermined value R0 is set to an element resistance value corresponding to the minimum temperature of the exhaust pipe 23 necessary for a moisture-free state or a temperature slightly higher than that. The process of step 101 serves as a determination means in the claims.

  If it is determined in step 101 that the element resistance value of the air-fuel ratio sensor 24 is greater than the predetermined value R0, that is, it is not in a moisture-free state (moisture is condensed in the exhaust pipe 23). Then, the process proceeds to Step 102, where energization of the heater is prohibited and heating of the sensor element by the heater is prohibited, thereby preventing element cracking of the air-fuel ratio sensor 24 due to adhesion of moisture in the exhaust pipe 23. The process of step 102 serves as a heater prohibiting means in the claims.

  Thereafter, the routine proceeds to step 103 where the ignition timing of the engine 11 is retarded and the temperature of the exhaust gas is forcibly increased. As a result, the temperature of the exhaust pipe 23 is quickly raised by the heat of the exhaust gas to evaporate the condensed water in the exhaust pipe 23, and the time until a moisture-free state in which no moisture is condensed in the exhaust pipe 23 is reached. To shorten. The processing in step 103 serves as exhaust gas temperature rise control means in the claims.

  Thereafter, in step 101, when it is determined that the element resistance value R of the air-fuel ratio sensor 24 is equal to or less than the predetermined value R0, that is, in a moisture-free state, the routine proceeds to step 104, where energization of the heater is permitted. Thus, energization of the heater is controlled so that the element temperature is quickly raised to the activation temperature. Thereafter, the routine proceeds to step 105, where the ignition timing retarding control is terminated, and the ignition timing is returned to the normal value.

  In the present embodiment described above, when the temperature of the exhaust pipe 23 is low immediately after the engine is started and moisture is condensed in the exhaust pipe 23, the exhaust gas temperature of the engine 11 is forcibly controlled by retarding the ignition timing. Therefore, the temperature of the exhaust pipe 23 can be quickly raised by the heat of the exhaust gas to quickly evaporate the condensed water in the exhaust pipe 23, and moisture in the exhaust pipe 23 can be evaporated. It is possible to shorten the time until a moisture-free state where no condensation occurs. Then, when it is determined that the moisture is not generated, energization of the heater is started, and the heater is controlled so as to quickly raise the element temperature to the activation temperature. Heater control that raises the element temperature to the activation temperature can be started earlier than before while preventing the element cracking of the air-fuel ratio sensor 24 due to adhesion, and the air-fuel ratio sensor is activated earlier so that the air-fuel ratio feedback is achieved earlier. Control can be started and exhaust emission can be improved.

  In addition, since it is determined whether or not moisture is not generated based on the element resistance value of the air-fuel ratio sensor 24, it is not necessary to newly provide a temperature sensor for detecting the exhaust pipe temperature, and the cost can be reduced. In addition, there is an advantage that it is not necessary to perform a complicated calculation process for calculating the exhaust pipe temperature, and the calculation load on the ECU 29 can be reduced.

  By the way, in the present invention, the sensor element may be preheated by energizing the heater within a temperature range in which element cracking due to moisture adhesion does not occur during the period from the start of the engine to the absence of moisture, When the sensor element is preheated by the heater, the temperature of the sensor element becomes higher than the temperature of the exhaust passage by the amount preheated by the heater, and the temperature of the exhaust pipe 23 and the element resistance value of the air-fuel ratio sensor 24 (temperature of the sensor element). Therefore, the determination accuracy of the moisture non-occurrence state based on the element resistance value is lowered. Even in this case, if the detection value R or the determination value R0 of the element resistance value is corrected according to the preheated amount by the heater, the determination accuracy of the moisture non-occurrence state based on the element resistance value can be secured. Therefore, it is necessary to correct the preheating by the heater.

  In consideration of this point, in this embodiment, since the heater is prohibited from heating the sensor element until it is determined that the moisture is not generated based on the element resistance value, the moisture content is determined based on the element resistance value. Before it is determined that the state does not occur, it is possible to prevent the relationship between the temperature of the exhaust pipe 23 and the element resistance value (element temperature) due to heating of the sensor element by the heater, and moisture based on the element resistance value. It is possible to accurately determine whether or not it is a non-occurring state, and there is an advantage that a calculation process can be reduced because a preheating correction process by a heater is unnecessary. In addition, by prohibiting heating of the sensor element by the heater until it is determined that the moisture is not generated, it is possible to more reliably prevent element cracking of the air-fuel ratio sensor 23 due to moisture adhesion.

  Further, in the above embodiment, when the engine is started, the exhaust gas is determined when it is determined that the moisture is not generated (the moisture is condensed in the exhaust pipe 23) based on the element resistance value of the air-fuel ratio sensor 24. However, it is not in a water-free state based on temperature information of at least one of the cooling water temperature, the oil temperature, the intake air temperature, the outside air temperature, etc. (a state in which moisture is condensed in the exhaust pipe 23) It is also possible to raise the temperature of the exhaust gas when it is determined.

  In the above embodiment, the ignition timing is retarded to raise the temperature of the exhaust gas during the period from the start of the engine to the absence of moisture, but the fuel injection amount, air-fuel ratio, exhaust pipe The temperature of exhaust gas flowing through the exhaust pipe may be raised by controlling the amount of secondary air introduced into the exhaust pipe.

  In addition, the application range of the present invention is not limited to the heater control of the air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas. For example, the heater control of other exhaust gas sensors such as an oxygen sensor that detects rich / lean of the exhaust gas The present invention may be applied to.

It is a schematic block diagram of the whole engine control system in one Example of this invention. It is a flowchart which shows the flow of a process of a heater control program. It is a characteristic view showing the relationship between the element temperature of the air-fuel ratio sensor and the element resistance value. It is a time chart which shows the example of execution of heater control.

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 ... Air-fuel ratio sensor (exhaust gas sensor), 29 ... ECU (exhaust gas temperature rise control means, determination means, heater control means, heater prohibition means)

Claims (4)

In a heater control device for an exhaust gas sensor that controls a heater for heating a sensor element of an exhaust gas sensor provided in an exhaust passage of an internal combustion engine to control the temperature of the sensor element.
Exhaust gas temperature increase control means for increasing the temperature of the exhaust gas of the internal combustion engine when moisture is condensed in the exhaust passage;
Determination means for determining whether or not moisture is not condensed in the exhaust passage based on a resistance value of the sensor element (hereinafter referred to as “moisture-free state”);
And a heater control means for controlling the heater so as to raise the temperature of the sensor element to an activation temperature when it is determined by the determination means that the moisture is not generated. Gas sensor heater control device.   2. The exhaust gas sensor according to claim 1, wherein the determination unit determines whether or not the moisture is not generated based on a resistance value of the sensor element or a temperature converted from the resistance value. Heater control device.   3. The exhaust gas sensor according to claim 1, further comprising a heater prohibiting unit that prohibits heating of the sensor element by the heater until the determination unit determines that the moisture is not generated. Heater control device.   The heater control apparatus for an exhaust gas sensor according to any one of claims 1 to 3, wherein the exhaust gas temperature increase control means retards the ignition timing of the internal combustion engine to increase the temperature of the exhaust gas.

Images