JP2006250945A - Temperature control of exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide temperature controls of an exhaust gas sensor which can stably control temperature of the exhaust gas sensor element section to the desired temperature, even if exhaust gas temperature varies. <P>SOLUTION: This controls estimates or detects temperature of the exhaust gas, flowing through an exhaust air passage 3 and then uses the estimated or detected value to control the temperature of the sensor element section on the exhaust gas sensor 8 (O<SB>2</SB>sensor) to the predefined target temperature via a heater. When estimating exhaust gas temperature around the sensor 8 allocated position, the exhaust air passage 3 up to the sensor 8 is partitioned into a plurality of partial exhaust air passage 3a-3d, to sequentially estimate exhaust gas temperature of each partial exhaust air passage 3a-3d from an exhaust port 2 side of an engine 1. Estimating of the exhaust gas temperature is performed, by using an algorithm that takes into account the heat transfer between exhaust gas and passage products 6a, 6b, 7 of the exhaust air passage 3, or the heat release to the atmosphere. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a temperature control device for an exhaust gas sensor provided in an exhaust passage of an internal combustion engine.

The exhaust passage of the internal combustion engine is often provided with an exhaust gas sensor for detecting a physical quantity related to the component state of the exhaust gas such as the component concentration of the exhaust gas for the purpose of controlling the operation of the internal combustion engine and monitoring the state of the exhaust gas purification system. The exhaust gas sensor is disposed at a required position of the exhaust passage so that an element portion sensitive to the component state of the exhaust gas to be detected contacts the exhaust gas flowing through the exhaust passage. For example, an air-fuel ratio sensor such as an O ₂ sensor is provided upstream or downstream of the catalyst for the purpose of controlling the air-fuel ratio of the internal combustion engine so as to maintain the purification performance of the exhaust gas purification catalyst provided in the exhaust passage. Be placed.

In addition, this type of exhaust gas sensor is provided with a heater for heating the element part for the purpose of raising temperature and activating the element part to perform its original function and removing foreign matter adhering to the element part. Some are built-in. For example, the air-fuel ratio sensor such as the O ₂ sensor is usually (see, for example Patent Document 1) the electric heater is provided to heat the element, after starting operation of the internal combustion engine, the O ₂ sensor by electric heater The element portion is activated by heating and maintained in its active state.
JP 2000-304721 A

By the way, as shown in FIG. 3 described later, the O ₂ sensor is used only in a very narrow range Δ (range in the vicinity of the theoretical air-fuel ratio) of the air-fuel ratio of the exhaust gas represented by the oxygen concentration of the exhaust gas to which the element portion is sensitive. The output voltage Vout changes with a large gradient with respect to the change in the air-fuel ratio (the sensitivity to the change in the air-fuel ratio becomes high sensitivity). The change in the output voltage Vout of the O ₂ sensor (slope with respect to the air-fuel ratio) is very small in the air-fuel ratio area on the rich side and the air-fuel ratio area on the lean side of the highly sensitive range Δ. Further, the output characteristics of the O ₂ sensor (such as the inclination of the high-sensitivity portion described above) change under the influence of the temperature of the element portion. Therefore, in the case performs air-fuel ratio control, O only ₂ possible output characteristics of the sensor stably maintained the required characteristics, performed satisfactorily and thus the air-fuel ratio control using the output of such O ₂ sensor Therefore, it is desired to maintain the temperature of the element portion of the O ₂ sensor at a desired temperature as stably as possible.

In addition to the O ₂ sensor, many exhaust gas sensors have an output characteristic that is influenced by the temperature of the element portion. Therefore, when controlling an internal combustion engine or the like using the output of the exhaust gas sensor, the control is good. Therefore, it is preferable to maintain the temperature of the element part of the exhaust gas sensor at a desired temperature as stably as possible. Further, even when the element part is heated with a heater in order to clean the element part of the exhaust gas sensor, the temperature of the element part of the exhaust gas sensor is set to a desired temperature in order to perform the cleaning well. It is preferred to maintain the temperature.

  On the other hand, for example, as disclosed by the present applicant in Patent Document 1, the temperature of the element part of the exhaust gas sensor (the air-fuel ratio sensor in the case of Patent Document 1) is estimated, and according to the estimated temperature of the element part It is known that a suitable output characteristic of the exhaust gas sensor can be obtained by performing energization control of a heater (electric heater) so that the temperature of the element portion becomes a desired temperature. In this publication, the heater energization current and applied voltage are detected and the resistance value of the heater is determined from the detected values, and the temperature of the element part of the exhaust gas sensor is estimated based on the resistance value of the heater. Like to do.

  However, in the thing of the said patent document 1, a heater is controlled based only on the estimated value of the temperature of an element part. For this reason, when the operating state such as the load of the internal combustion engine changes frequently and the temperature of the exhaust gas changes frequently, it is difficult to ensure the temperature of the element portion stably at a desired temperature. It becomes. Such an inconvenience is also caused by detecting the temperature of the element portion directly by the temperature sensor and controlling the heater in accordance with the detected temperature.

  The present invention has been made in view of such a background, and provides an exhaust gas sensor temperature control device capable of stably controlling the temperature of an element part of an exhaust gas sensor to a desired temperature even when the exhaust gas temperature changes. For the purpose.

  In order to achieve such an object, the present invention is an exhaust gas sensor temperature control device that is disposed in an exhaust passage of an internal combustion engine and has an element portion that contacts exhaust gas flowing through the exhaust passage and a heater that heats the element portion. An exhaust gas temperature sensor disposed at a location separated from the exhaust gas sensor in the exhaust gas flow direction in order to detect the temperature of the exhaust gas flowing through the exhaust passage, and at least the temperature of the exhaust gas by the exhaust gas temperature sensor. Exhaust gas temperature estimating means for sequentially estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, and the exhaust gas temperature in the vicinity of the location of the exhaust gas sensor. Heater control means for controlling the heater so that the temperature of the element portion of the exhaust gas sensor becomes a predetermined target temperature using an estimated value of temperature It is characterized in.

  In an exhaust system of an internal combustion engine, the exhaust gas temperature sensor may be arranged at a required location in the exhaust passage for a purpose other than the temperature control of the element part of the exhaust gas sensor (for example, the purpose of grasping the state of the exhaust gas purification device). is there. Such an exhaust gas temperature sensor is not necessarily provided in the vicinity of the location where the exhaust gas sensor is disposed, and is often disposed at a location separated from the exhaust gas sensor in the exhaust gas flow direction in the exhaust passage.

  According to the present invention, when the exhaust gas temperature sensor is arranged at a location away from the exhaust gas sensor, the exhaust gas in the vicinity of the location of the exhaust gas sensor is detected using the detected value of the temperature of the exhaust gas by the exhaust gas temperature sensor. The heater control means uses an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor in order to control the heater. According to this, since the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated using the detected value of the temperature of the exhaust gas by the exhaust gas temperature sensor, an exhaust gas temperature sensor is separately provided in the vicinity of the location of the exhaust gas sensor. Therefore, the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed can be properly grasped. That is, it is possible to appropriately grasp the temperature of the exhaust gas that directly affects the temperature of the element part of the exhaust gas sensor. Then, by controlling the heater of the exhaust gas sensor using the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, the temperature of the element part of the exhaust gas sensor is reduced so as to reduce the influence of the temperature change of the exhaust gas sensor. Can be stably controlled to a predetermined target temperature (desired temperature).

  In this case, if the exhaust gas temperature sensor is located upstream of the exhaust gas sensor, the exhaust gas existing at the exhaust gas temperature sensor location at each point of time is transferred to the exhaust gas sensor location with a time delay according to the exhaust gas flow rate. To reach. In addition, when the exhaust gas temperature sensor is located downstream of the exhaust gas sensor, the exhaust gas present at the exhaust gas sensor arrangement location at each time point reaches the exhaust gas temperature sensor arrangement location with a time delay corresponding to the exhaust gas flow rate. To do. Therefore, the exhaust gas temperature estimation means estimates the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is located using at least the detected value of the exhaust gas temperature by the exhaust gas temperature sensor and the data representing the flow velocity of the exhaust gas.

  In this way, in consideration of the time delay until the exhaust gas reaches the sensor located on the upstream side of the exhaust gas temperature sensor and the exhaust gas sensor from the sensor located on the downstream side, It is possible to appropriately estimate the instantaneous instantaneous gas temperature. Eventually, by controlling the heater using the estimated value of the exhaust gas temperature, the temperature control of the element part of the exhaust gas sensor can be performed more favorably.

  Further, when the exhaust gas temperature sensor and the exhaust gas sensor are relatively separated from each other, the exhaust gas temperature estimation means includes an exhaust passage from the vicinity of the exhaust gas temperature sensor to the vicinity of the exhaust gas sensor. Is divided into a plurality of partial exhaust passages in advance along the flow direction of the exhaust gas. Of the plurality of partial exhaust passages, the exhaust gas temperature of the partial exhaust passage closest to the exhaust gas temperature sensor is estimated using at least the detected value of the exhaust gas temperature by the exhaust gas temperature sensor and the data representing the exhaust gas flow velocity. In addition, the exhaust gas temperature in each partial exhaust passage other than the partial exhaust passage closest to the exhaust gas temperature sensor is at least estimated value of the exhaust gas temperature in the partial exhaust passage adjacent to the partial exhaust passage on the exhaust gas temperature sensor side, and the exhaust gas flow velocity. And the estimated value of the temperature of the exhaust gas in the partial exhaust passage closest to the exhaust gas sensor is obtained as the estimated value of the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is located.

  In this way, the temperature of the exhaust gas in each partial exhaust passage between the vicinity of the exhaust gas temperature sensor and the vicinity of the exhaust gas sensor is sequentially and accurately determined starting from the vicinity of the exhaust gas temperature sensor. It can be obtained. Then, by obtaining an estimated value of the temperature of the exhaust gas in the partial exhaust passage closest to the exhaust gas sensor as an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor Can improve the accuracy.

  By the way, in the present invention, the exhaust gas temperature estimating means takes into account heat transfer between a passage formation forming an exhaust passage in the vicinity of the location where the exhaust gas sensor is disposed and an exhaust gas flowing through the passage formation. It is preferable to estimate the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is arranged using the constructed estimation algorithm. In particular, the exhaust gas temperature estimating means is configured to transfer heat between a passage formation that forms an exhaust passage from the vicinity of the exhaust gas sensor to a vicinity of the exhaust gas temperature sensor and the exhaust gas flowing through the passage formation. It is preferable to estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor by an estimation algorithm constructed in consideration of the above.

  Further, in the present invention, when the temperature of the exhaust gas in each partial exhaust passage is estimated as described above, the exhaust gas temperature estimation means includes a passage formation that forms each partial exhaust passage and the inside of the passage formation. It is preferable to estimate the temperature of the exhaust gas in each partial exhaust passage by an estimation algorithm constructed in consideration of heat transfer with the flowing exhaust gas.

  That is, when exhaust gas flows through the exhaust passage, heat transfer occurs between the passage formation material forming the exhaust passage and the exhaust gas, and the heat transfer affects the temperature of the exhaust gas. Therefore, the accuracy of the estimated value can be further improved by estimating the temperature of the exhaust gas by the estimation algorithm considering the heat transfer between the exhaust gas and the passage formation through which the exhaust gas flows as described above.

  Further, in the present invention, the exhaust gas temperature estimation means is based on an estimation algorithm constructed in consideration of heat radiation from a passage formation forming an exhaust passage in the vicinity of the location where the exhaust gas sensor is disposed to the outside atmosphere. It is preferable to estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor. In particular, the exhaust gas temperature estimation means is configured such that the exhaust gas temperature estimation means dissipates heat from a passage formation that forms an exhaust passage from the vicinity of the exhaust gas temperature sensor to the vicinity of the exhaust gas temperature sensor. More preferably, the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated by an estimation algorithm constructed in consideration of the above.

  Further, in the present invention, when the temperature of the exhaust gas in each partial exhaust passage is estimated as described above, the exhaust gas temperature estimation means transfers the passage formation material forming the respective partial exhaust passage to the outside atmosphere. It is preferable to estimate the temperature of the exhaust gas in each partial exhaust passage by an estimation algorithm constructed in consideration of heat dissipation.

  That is, when the exhaust gas flows through the exhaust passage, heat is released from the passage formation forming the exhaust passage to the atmosphere, and the heat release affects the temperature of the exhaust gas. Therefore, the accuracy of the estimated value can be increased by estimating the temperature of the exhaust gas by the estimation algorithm considering the heat radiation from the passage formation through which the exhaust gas flows to the atmosphere as described above. In particular, when heat transfer between the exhaust gas and the passage formation is taken into consideration, the accuracy of the estimated value of the exhaust gas temperature can be effectively increased.

  Further, in the present invention, the exhaust gas passage from the vicinity of the exhaust gas sensor arrangement location to the exhaust gas temperature sensor arrangement location is included as a passage formation that forms part of the exhaust gas passage. In this case, it is preferable that the exhaust gas temperature estimating means estimates the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is arranged by an estimation algorithm constructed in consideration of heat generation of the catalyst.

  Furthermore, in the present invention, when estimating the temperature of the exhaust gas in each partial exhaust passage as described above, at least one of the plurality of partial exhaust passages is exhaust gas purification as a passage formation that forms the partial exhaust passage. The exhaust gas temperature estimating means preferably estimates the temperature of the exhaust gas in the partial exhaust passage containing the catalyst by an estimation algorithm constructed in consideration of heat generation of the catalyst. It is.

  That is, the exhaust gas purifying catalyst generates heat due to the purifying action (oxidation, reduction reaction, etc.) of the exhaust gas flowing therethrough, and the generated heat affects the temperature of the exhaust gas. Therefore, the accuracy of the estimated value can be increased by estimating the temperature of the exhaust gas by the estimation algorithm considering the heat generation of the catalyst as described above. In particular, the accuracy of the estimated value of the exhaust gas temperature can be effectively increased by considering heat transfer between the exhaust gas and the passage formation and heat radiation from the passage formation to the atmosphere.

  In the present invention, in order to estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor in consideration of the heat transfer between the exhaust gas and the passage formation as described above, the exhaust gas temperature estimation means includes at least the exhaust gas sensor. While sequentially acquiring data representing the temperature of the passage formation forming the exhaust passage in the vicinity of the location of the exhaust gas, the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is obtained using the data representing the temperature of the passage formation. presume. In this way, data representing the temperature of the passage formation that forms the exhaust passage in the vicinity of the exhaust gas sensor is sequentially acquired, and the temperature of the exhaust gas in the vicinity of the exhaust gas sensor is estimated using the data. Thus, it is possible to estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor in a form that considers the temperature change of the exhaust gas accompanying heat transfer between the passage formation in the vicinity of the location of the exhaust gas sensor and the exhaust gas. And the accuracy of the estimated value can be increased.

  Further, as described above, when estimating the temperature of the exhaust gas in each partial exhaust passage, the exhaust gas temperature estimation means sequentially acquires data representing the temperature of the passage formation material forming each partial exhaust passage, The temperature of the exhaust gas in the partial exhaust passage is estimated using data representing the temperature of the passage formation material forming each partial exhaust passage. By doing so, the temperature of the exhaust gas in each partial exhaust passage can be estimated in a form that takes into account the temperature change of the exhaust gas accompanying heat transfer between the passage formation and the exhaust gas in each partial exhaust passage. The accuracy of the estimated value can be increased. As a result, the accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed can be improved.

  Note that the data representing the temperature of the passage formation may be data detected using a temperature sensor, or may be estimated appropriately from other parameters.

  As described above, when estimating the temperature of the exhaust gas near the location of the exhaust gas sensor using the data representing the temperature of the passage formation in the vicinity of the location of the exhaust gas sensor, more specifically, the exhaust gas temperature The estimation means at least determines a temperature change amount per predetermined time of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed in accordance with a temperature gradient in the flow direction of the exhaust gas in the vicinity of the location where the exhaust gas sensor is located and a flow rate of the exhaust gas. In the vicinity of the location of the exhaust gas sensor based on a thermal model expressed as the sum of the temperature change component and the temperature change component according to the deviation between the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the temperature of the passage formation The exhaust gas temperature change amount is sequentially obtained, and the obtained temperature change amount is cumulatively added to the initial value set at the start of operation of the internal combustion engine. Estimating the temperature of the exhaust gas in the vicinity of the location of the sensor.

  Further, when estimating the temperature of the exhaust gas in each partial exhaust passage using data representing the temperature of the passage formation material forming each partial exhaust passage, the exhaust gas temperature estimating means The temperature change amount per predetermined time of the exhaust gas includes a temperature change component according to the temperature gradient in the flow direction of the exhaust gas in the partial exhaust passage and the flow rate of the exhaust gas, the temperature of the exhaust gas in the partial exhaust passage, and the partial exhaust passage. Based on the thermal model expressed as the sum of the temperature change components according to the deviation from the temperature of the passage formation, the exhaust gas temperature change amount in each partial exhaust passage is sequentially obtained, and the obtained temperature change amount is For each partial exhaust passage, the temperature of the exhaust gas in each partial exhaust passage is estimated by cumulatively adding to the initial value set at the start of operation of the internal combustion engine.

  Here, in the thermal model, the temperature change component corresponding to the temperature gradient in the exhaust gas flow direction and the exhaust gas flow velocity is an exhaust gas whose temperature is not constant in the exhaust gas flow direction (this is mainly a change in the operating state of the internal combustion engine). This means a temperature change component of exhaust gas (temperature change component at a location targeted by a thermal model) that is generated as a result of movement. In addition, the temperature change component corresponding to the deviation between the temperature of the passage formation and the temperature of the exhaust gas is the temperature change component of the exhaust gas accompanying the heat transfer between the passage formation and the exhaust gas (at the location targeted by the thermal model). Temperature change component). Therefore, it is possible to accurately obtain the temperature change amount of the exhaust gas every predetermined time based on such a thermal model. Then, this temperature change amount is cumulatively added to the initial value set at the start of the operation of the internal combustion engine (predicted value of the temperature of the exhaust gas at the start of the operation of the internal combustion engine at the location targeted by the thermal model). The estimated value of temperature can be obtained with high accuracy. As a result, the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed can be accurately estimated.

  Regarding the temperature gradient of the exhaust gas necessary for obtaining the temperature change amount per predetermined time based on the thermal model, in the present invention, for example, when the exhaust gas sensor is disposed at a location relatively close to the exhaust gas temperature sensor. The temperature gradient of the exhaust gas near the location of the exhaust gas sensor is calculated from the latest value of the estimated value of the exhaust gas temperature near the location of the exhaust gas sensor and the latest value of the exhaust gas temperature detected by the exhaust gas temperature sensor. Can be sought.

  Further, in the present invention, when estimating the temperature of the exhaust gas in the plurality of partial exhaust passages, for example, the latest value of the estimated value of the exhaust gas temperature in each partial exhaust passage and the partial exhaust passage adjacent to the partial exhaust passage The exhaust gas temperature gradient in the partial exhaust passage can be obtained from the latest estimated value of the exhaust gas temperature.

  Further, the temperature change component corresponding to the deviation between the temperature of the passage formation and the temperature of the exhaust gas is obtained from, for example, the latest value of the data representing the temperature of the passage formation and the latest value of the estimated value of the exhaust gas. be able to.

  As described above, in the present invention using the data representing the temperature of the passage formation to estimate the exhaust gas temperature, the exhaust gas temperature estimation means includes at least an estimated value of the exhaust gas temperature and a passage formation in the vicinity of the location where the exhaust gas sensor is disposed. It is preferable to sequentially estimate the temperature of the passage formation using data representing the atmospheric temperature outside the object, and use the estimated value of the temperature of the passage formation as the data representing the temperature of the passage formation. In particular, when estimating the temperature of exhaust gas in a plurality of partial exhaust passages, the exhaust gas temperature estimating means includes at least an estimated value of the temperature of exhaust gas in each of the partial exhaust passages and a passage formation forming the partial exhaust passage. The temperature of the passage formation forming each partial exhaust passage is sequentially estimated using data representing the external atmospheric temperature, and the estimated value of the temperature of the passage formation forming each partial exhaust passage is calculated. It is preferably used as the data representing temperature.

  In this way, by estimating the temperature of the passage formation together with the estimation of the temperature of the exhaust gas, data representing the temperature of the passage formation can be acquired without using a temperature sensor, and the cost can be reduced. Can be reduced. And in this case, by using the estimated value of the exhaust gas temperature and the data representing the atmospheric temperature for the estimation of the temperature of the passage formation, heat transfer between the passage formation and the exhaust gas flowing through the interior, The temperature of the passage formation can be estimated in a form that considers the heat release from the passage formation to the atmosphere, and the accuracy of the estimated value of the temperature can be increased.

  Normally, an internal combustion engine is provided with an atmospheric temperature sensor for detecting the atmospheric temperature for operation control, and if the detected value of the atmospheric temperature sensor is used as the data representing the atmospheric temperature. Good.

  As described above, when estimating the temperature of the passage formation in the vicinity of the location where the exhaust gas sensor is disposed, more specifically, the exhaust gas temperature estimation means is configured to change the temperature change amount per predetermined time of the passage formation. However, at least in the vicinity of the location where the exhaust gas sensor is disposed, a temperature change component corresponding to a deviation between the temperature of the exhaust gas and the temperature of the passage formation, and a temperature change corresponding to a deviation between the temperature of the passage formation and the atmospheric temperature On the basis of a thermal model expressed as including a component, and sequentially estimating the temperature change amount of the passage formation, and cumulatively adding the estimated value of the temperature change amount to the initial value set at the start of operation of the internal combustion engine. Thus, the temperature of the passage formation is estimated.

  Further, when estimating the temperature of the passage formation that generates each of the partial exhaust passages, the exhaust gas temperature estimation means has a temperature change amount per predetermined time of the passage formation that forms each of the partial exhaust passages. A temperature change component according to a deviation between at least the temperature of the exhaust gas in the partial exhaust passage and the temperature of the passage formation forming the partial exhaust passage, and a temperature change according to the deviation between the temperature of the passage formation and the atmospheric temperature On the basis of a thermal model expressed as including a component, and sequentially estimating the temperature change amount of the passage formation, and calculating the estimated value of the temperature change amount for each passage formation of each partial exhaust passage. The accumulated temperature of each partial exhaust passage is estimated by cumulatively adding to the initial value set at the start.

  Here, in the thermal model, the temperature change component according to the deviation between the temperature of the exhaust gas and the temperature of the passage formation is a temperature change component of the passage formation accompanying heat transfer between the passage formation and the exhaust gas ( This means a temperature change component at a location targeted by the thermal model. Also, the temperature change component according to the deviation between the temperature of the passage formation and the atmospheric temperature is the temperature change component of the passage formation accompanying the heat radiation from the passage formation to the atmosphere (the temperature at the target location of the thermal model). Change component). Therefore, it is possible to accurately obtain the temperature change amount of the passage formation for each predetermined time based on such a thermal model. Then, by cumulatively adding this amount of temperature change to the initial value set at the start of operation of the internal combustion engine (predicted value of the temperature of the passage formation at the start of operation of the internal combustion engine at the location targeted by the thermal model), The estimated value of the temperature of the passage formation can be obtained with high accuracy. As a result, the temperature of the exhaust gas can be accurately estimated using the estimated value of the temperature of the passage formation.

  The temperature change component component according to the deviation between the temperature of the passage formation and the temperature of the exhaust gas is obtained from, for example, the latest value of the estimated value of the temperature of the passage formation and the latest value of the estimated value of the exhaust gas. be able to. Moreover, the temperature change component according to the deviation between the temperature of the passage formation and the atmospheric temperature can be obtained from the latest value of the estimated value of the temperature of the passage formation and the latest value of the data representing the atmospheric temperature.

  In particular, when estimating the temperature of the exhaust gas and the temperature of the passage formation in the plurality of partial exhaust passages, at least one of the plurality of partial exhaust passages is a passage formation that forms the partial exhaust passage. When the exhaust gas purifying catalyst is included, the thermal model corresponding to the partial exhaust passage containing the catalyst calculates the temperature change amount per unit time of the passage formation of the partial exhaust passage. A temperature change component according to the deviation between the temperature of the exhaust gas in the gas and the temperature of the passage formation forming the partial exhaust passage, a temperature change component according to the deviation between the temperature of the passage formation and the atmospheric temperature, A model expressed as a sum of temperature change components corresponding to the flow velocity is preferable.

  In such a thermal model, the temperature change component corresponding to the flow rate of the exhaust gas means the temperature change component of the catalyst (passage formation) accompanying heat generation by the exhaust gas purification action of the catalyst. That is, as the flow rate of exhaust gas increases, the amount of exhaust gas that the catalyst reacts per predetermined time increases, so the amount of heat generated by the catalyst increases. For this reason, the temperature change component of the catalyst accompanying the heat generation of the catalyst corresponds to the flow rate of the exhaust gas. And based on such a thermal model, the amount of temperature change per predetermined time of the passage formation in the partial exhaust passage containing the catalyst can be accurately estimated. As a result, the accuracy of the estimated value of the temperature of the passage formation can be increased.

  Further, as described above, when the exhaust gas temperature or the temperature of the passage formation is estimated by accumulating the amount of temperature change every predetermined time to the initial value, the initial value is at least the atmosphere at the start of the operation of the internal combustion engine. It is preferable that the temperature is set according to the engine temperature of the internal combustion engine. According to this, it is possible to appropriately set the initial values of the exhaust gas temperature and the passage formation temperature at the start of the operation of the internal combustion engine.

  In the present invention, when the heater control means uses the estimated value of the exhaust gas temperature by the exhaust gas temperature estimation means to control the heater, the heater control means represents the temperature of the element part of the exhaust gas sensor. While acquiring data sequentially, the control input to the heater is added with at least the input component according to the temperature of the element part of the exhaust gas sensor and the control input component according to the estimated value of the exhaust gas temperature by the exhaust gas temperature estimating means It is preferable that the heater is sequentially calculated and the heater is controlled in accordance with the calculated control input.

  As described above, the control input includes the input component corresponding to the temperature of the element portion of the exhaust gas sensor, that is, the feedback component, and the input component corresponding to the estimated value of the exhaust gas temperature, that is, the feedforward component corresponding to the exhaust gas temperature. Thus, by calculating the control input, the temperature of the element part of the exhaust gas sensor can be stably controlled to the target temperature.

  The data representing the temperature of the element unit may be data directly detected by a temperature sensor attached to the element unit (detected value of the temperature of the element unit). The temperature of the element unit may be estimated by an appropriate algorithm considering heat transfer, heat transfer between the element unit and exhaust gas, and the estimated value may be used as data representing the temperature of the element unit.

In the present invention, examples of the exhaust gas sensor include an O ₂ sensor disposed on the downstream side of the exhaust gas purification catalyst device. In this case, when the air-fuel ratio of the exhaust gas is controlled so as to maintain the output voltage of the O ₂ sensor at a predetermined value in order to ensure the required purification performance by the catalyst device, the air-fuel ratio control is improved satisfactorily. In carrying out, it is preferable to control the temperature of the element portion of the O ₂ sensor to a predetermined target temperature (for example, 800 ° C.) of 750 ° C. or higher.

  Before describing embodiments of the present invention, reference examples related to embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram schematically showing the overall configuration of the apparatus of this reference example. In FIG. 1, reference numeral 1 denotes an engine (internal combustion engine) mounted on, for example, an automobile or a hybrid vehicle. Exhaust gas generated by the engine 1 burning a mixture of fuel and air is supplied to an exhaust port 2 of the engine 1. It is discharged to the atmosphere side through the communicating exhaust passage 3. In the exhaust passage 3, catalyst devices 4 and 5 for purifying exhaust gas are sequentially inserted from the upstream side. Of the exhaust passage 3, an upstream portion of the catalyst device 4 (a portion between the exhaust port 2 and the catalyst device 4), a portion between the catalyst devices 4, 5, and a downstream portion of the catalyst device 5 Are constituted by exhaust pipes 6a, 6b and 6c, which are tubular passage formations.

  Each of the catalyst devices 4 and 5 incorporates a catalyst 7 (a three-way catalyst in this reference example). The catalyst 7 is a honeycomb-structured passage formation, and exhaust gas flows through the catalyst 7. The catalyst devices 4 and 5 may be of an integrated structure (for example, two catalyst beds made of a three-way catalyst in the same case are built in the upstream portion and the downstream portion).

In the apparatus of the present reference example, the air-fuel ratio of the exhaust gas of the engine 1 is controlled so as to ensure particularly good purification performance of the catalyst device 4 (CO, HC, NOx purification performance by the catalyst device 4). In order to perform this air-fuel ratio control, an O ₂ sensor 8 is disposed in the exhaust passage 3 (exhaust passage formed by the exhaust pipe 6b) between the catalyst devices 4 and 5, and the exhaust gas upstream of the catalyst device 4 is exhausted. A wide area air-fuel ratio sensor 9 is arranged in the passage 3 (exhaust passage formed by the exhaust pipe 6a).

Here, the O ₂ sensor 8 corresponds to the exhaust gas sensor of the present invention, and the basic structure and characteristics thereof will be further described. As schematically shown in FIG. 2, the O ₂ sensor 8 has a bottomed cylindrical element portion 10 (mainly made of a solid electrolyte that easily allows oxygen ions to pass, for example, stable zirconia (ZrO ₂ + Y ₂ O ₃ )). The element portion 10 is coated with porous platinum electrodes 11 and 12 on the outer surface and the inner surface, respectively. In addition, a rod-shaped ceramic heater 13 as an electric heater is inserted into the element unit 10 in order to perform temperature rise / activation, temperature control, etc. of the element unit 10, and around the ceramic heater 13. The space is filled with air having a constant oxygen concentration (a constant oxygen partial pressure). The O ₂ sensor 8 is attached to the exhaust pipe 6b via the sensor housing 14 so that the outer surface of the tip of the element part 10 is in contact with the exhaust gas in the exhaust pipe 6b.

  In FIG. 2, reference numeral 15 denotes a cylindrical protector for preventing foreign matter from hitting the element portion 10 in the exhaust pipe 6 b, and the element portion 10 in the exhaust pipe 6 b is drilled in the protector 15. The exhaust gas is contacted through a plurality of holes (not shown).

In the O ₂ sensor 8 having such a structure, the oxygen in the exhaust gas is disposed between the platinum electrodes 11 and 12 due to the difference between the oxygen concentration of the exhaust gas contacting the outer surface of the tip of the element portion 10 and the oxygen concentration of the air inside the element portion 10. An electromotive force according to the concentration is generated. The O ₂ sensor 8 outputs an output voltage Vout obtained by amplifying the electromotive force with an amplifier (not shown).

In this case, the characteristic (output characteristic) of the output voltage Vout of the O ₂ sensor 8 with respect to the oxygen concentration of the exhaust gas or the air-fuel ratio of the exhaust gas ascertained from the oxygen concentration is basically shown by a solid line a in FIG. Such a characteristic (so-called Z curve characteristic) is obtained. 3 is a graph showing the output characteristics of the O ₂ sensor 8 when the temperature of the element unit 10 is 800 ° C., more specifically. The relationship between the temperature of the element unit 10 and the output characteristics of the O ₂ sensor 8 will be described later.

As can be seen from the graph a in FIG. 3, the output characteristic of the O ₂ sensor 8 is generally only in a state where the air-fuel ratio represented by the oxygen concentration of the exhaust gas is in a narrow air-fuel ratio region Δ near the stoichiometric air-fuel ratio. The output voltage Vout changes with high sensitivity almost linearly with respect to the air-fuel ratio of the exhaust gas. That is, in the air-fuel ratio range Δ (hereinafter referred to as the high-sensitivity air-fuel ratio range Δ), the gradient of the change in the output voltage Vout with respect to the change in the air-fuel ratio (the gradient of the output characteristic graph) becomes large. Then, in the air-fuel ratio region on the rich side and the air-fuel ratio region on the lean side with respect to the high-sensitivity air-fuel ratio region Δ, the slope of the change in the output voltage Vout with respect to the change in the air-fuel ratio of the exhaust gas (the slope of the graph of the output characteristics) It will be minute.

The wide-area air-fuel ratio sensor 9 is an air-fuel ratio sensor disclosed by the applicant of the present invention in, for example, Japanese Patent Application Laid-Open No. 4-369471, though detailed description thereof is omitted here, and is wider than the O ₂ sensor 8. This is a sensor that generates an output voltage KACT that varies linearly with respect to the air-fuel ratio of exhaust gas in the air-fuel ratio range. In the following description, the output voltage Vout of the O ₂ sensor 8 and the output voltage KACT of the wide area air-fuel ratio sensor 9 may be simply referred to as outputs Vout and KACT, respectively.

The apparatus of this reference example further includes a control unit 16 that performs processing such as air-fuel ratio control of exhaust gas and temperature control of the element portion 10 of the O ₂ sensor 8. The control unit 16 is constituted by a microcomputer including a CPU, a RAM, and a ROM (not shown). The O ₂ sensor 8 and the wide area air-fuel ratio sensor 9 are used to execute a control process described later. Output Vout and KACT are input, and the engine 1 rotational speed NE (rotational speed) and intake pressure PB (specifically, the absolute pressure of the intake pipe internal pressure of the engine 1) from a sensor (not shown) provided in the engine 1 are input. Data indicating the detected value such as the atmospheric temperature TA is given.

The control unit 16 includes, as functional means for the processing, an air-fuel ratio control means 17 for controlling the air-fuel ratio of the exhaust gas of the engine 1, and a sensor temperature control means 18 for controlling the temperature of the element portion 10 of the O ₂ sensor 8. It has.

The air-fuel ratio control means 17 is provided in the catalyst device 4 so as to ensure good purification performance (purification rate) of CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) by the catalyst device 4. The process which controls the air fuel ratio of the exhaust gas supplied from 1 is performed. Here, when the O ₂ sensor 8 having the output characteristics as described above is arranged on the downstream side of the catalyst device 4, the air-fuel ratio of the exhaust gas supplied to the catalyst device 4 (the air-fuel ratio of the exhaust gas upstream of the catalyst device 4) is set. By controlling the air-fuel ratio so that the output Vout of the O ₂ sensor 8 is set to a predetermined value Vop (see FIG. 3), the catalytic device 4 has good purification performance of CO, HC, NOx. 4 can be ensured regardless of the deterioration state.

Therefore, the air-fuel ratio control means 17, the predetermined value Vop as the target value of the output Vout of the O ₂ sensor 8, the catalytic converter the output Vout of the O ₂ sensor 8 at the target value Vop from the engine 1 so as to settle and maintain The air-fuel ratio of the exhaust gas supplied to 4 is controlled. In this air-fuel ratio control, for example, the target air-fuel ratio of the exhaust gas supplied to the catalyst device 4 is determined by feedback control processing so that the output Vout of the O ₂ sensor 8 converges to the target value Vop, and the target air-fuel ratio is set to a wide range. This is executed by adjusting the fuel supply amount of the engine 1 by feedback control processing so that the output KACT (detected value of the air / fuel ratio) of the air / fuel ratio sensor 9 is converged. Note that more specific processing of the air-fuel ratio control means 17 does not form the essence of the present invention, and thus detailed description thereof will be omitted. For example, the applicant of the present application disclosed in Japanese Patent Application Laid-Open No. 11-324767. This is carried out as described in [0071] to [0362] of the specification disclosed in the above.

Incidentally, the output characteristics of the O ₂ sensor 8 change under the influence of the temperature of the element unit 10. For example, the output characteristics of the O ₂ sensor 8 when the temperature of the element unit 10 is 800 ° C., 750 ° C., 700 ° C., and 600 ° C. are shown as a solid line graph a, a broken line graph b, and an alternate long and short dash line in FIG. The characteristic is as shown by the graph b in FIG. In this case, as is apparent with reference to FIG. 3, when the temperature of the element portion 10 changes particularly in a temperature range lower than 750 ° C., the O ₂ sensor 8 in the vicinity of the theoretical air-fuel ratio (the highly sensitive air-fuel ratio range Δ). The change slope (sensitivity) of the output Vout, the level of the output Vout on the rich side with respect to the high sensitivity air-fuel ratio range Δ, and the like are likely to change. When the temperature of the element unit 10 is 750 ° C. or higher, the change in the output characteristic of the O ₂ sensor 8 with respect to the temperature change of the element unit 10 becomes minute, and the output characteristic becomes almost constant.

Since the output characteristic of the O ₂ sensor 8 changes depending on the temperature state of the element unit 10 as described above, the controllability (stability and speed response) by the air-fuel ratio control means 17 may be deteriorated depending on the temperature state. There is. This is because, in controlling the air-fuel ratio of the exhaust gas so as to maintain the output Vout of the O ₂ sensor 8 at a certain target value Vop, the output characteristics of the O ₂ sensor 8 near the stoichiometric air-fuel ratio, that is, the high This is because the output characteristics in the sensitivity air-fuel ratio range Δ tend to have a large influence on the controllability. Further, the target value Vop of the output Vout of the O ₂ sensor 8 so that the exhaust gas purification performance by the catalyst 7 of the catalyst device 4 is kept good is also the temperature state of the element portion 9 particularly in a temperature range lower than 750 ° C. It depends on. Accordingly, in order to satisfactorily perform air-fuel ratio control (control to maintain the output Vout of the O ₂ sensor 8 at the target value Vop) by the air-fuel ratio control means 17 and to ensure good purification performance of the catalyst device 4. The temperature of the element portion 10 of the O ₂ sensor 8 is preferably basically maintained at a constant temperature.

In this case, in the O ₂ sensor 8, if the temperature of the element unit 10 is maintained at a temperature of 750 ° C. or higher, the output characteristics of the O ₂ sensor 8 become substantially constant and stable as described above. Further, according to the knowledge of the inventors of the present application, when the temperature of the element unit 10 is maintained at a temperature of 750 ° C. or higher, for example, 800 ° C., the exhaust gas purification performance by the catalyst 7 of the catalyst device 4 can be maintained satisfactorily. the target value Vop for the output Vout of a O ₂ sensor 8, portions denoted with the reference numeral Y in the graph a in FIG. 3, i.e., the slope of the graph a of the output characteristic of the O ₂ sensor 8 along with the enrichment of the air-fuel ratio An inflection point Y that switches from a large inclination to a small inclination is present. At this time, air-fuel ratio control that maintains the output Vout of the O ₂ sensor 8 at the target value Vop can be performed satisfactorily. This is presumably because the sensitivity to the air-fuel ratio of the output Vout of the O ₂ sensor 8 at the inflection point Y is an appropriate sensitivity that is neither excessive nor excessive.

For this reason, in the present reference example, the sensor temperature control means 18 controls the temperature of the element portion 10 of the O ₂ sensor 8 to a desired temperature via the ceramic heater 13. The desired temperature is basically a temperature of 750 ° C. or higher, for example, 800 ° C. The control process of the sensor temperature control means 18 will be described in detail below.

As shown in FIG. 4, the sensor temperature control means 18 classifies the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed in the exhaust passage 3 (the location of the intermediate portion of the exhaust pipe 6b). An exhaust gas temperature observer 19 (exhaust gas temperature estimating means) that sequentially estimates and an element temperature observer that estimates the temperature T _O2 of the element portion 10 of the O ₂ sensor 8 and the temperature Tht of the ceramic heater 13 using the estimated value of the exhaust gas temperature Tgd. 20, target value setting means 21 for setting the target value R of the temperature of the element unit 10, the estimated value of the temperature T _O2 of the element unit 10 and the temperature Tht of the ceramic heater 13, the target value R, and the estimation of the exhaust gas temperature Tgd A heater controller 22 (heater control means) is provided that performs energization control of the ceramic heater 13 (control of power supplied to the ceramic heater 13) using the value.

  In this reference example, the ceramic heater 13 is subjected to energization control (PWM control) by applying a pulse voltage to a heater energization circuit (not shown), and the power supplied to the ceramic heater 13 is It is defined by the pulse voltage duty DUT (ratio of the pulse width to one period of the pulse voltage). For this reason, the heater controller 22 uses the duty DUT of the pulse voltage applied to the heater energizing circuit as a control input (operation amount) for controlling the ceramic heater 13, and adjusts the duty DUT to thereby adjust the ceramic heater 13. The power supplied to the heater 13 and thus the amount of heat generated by the heater 13 are controlled. The duty DUT generated by the heater controller 22 is also used in the calculation process of the element temperature observer 20.

In this reference example, the exhaust temperature observer 19 extends the exhaust passage 3 (exhaust passage 3 upstream of the O ₂ sensor 8) from the exhaust port 2 of the engine 1 to the location where the O ₂ sensor 8 is disposed. The exhaust port 2 (exhaust passage 3) is divided into a plurality of (for example, four in this reference example) partial exhaust passages 3a to 3d along the existing direction (exhaust gas flow direction) and at a predetermined cycle time (period). The temperature of the exhaust gas at the inlet portion) and the temperature of the exhaust gas in each of the partial exhaust passages 3a to 3d (specifically, the temperature of the exhaust gas at the downstream end of each of the partial exhaust passages 3a to 3d) are estimated in order from the upstream side. Is. Of these partial exhaust passages 3a to 3d, the partial exhaust passages 3a and 3b are partial exhausts obtained by dividing the exhaust passage 3 (exhaust passage formed by the exhaust pipe 6a) on the upstream side of the catalyst device 4 into two. The partial exhaust passage 3c is a partial exhaust passage (exhaust passage formed inside the catalyst 7 of the catalyst device 4) from the inlet to the outlet of the catalyst device 4, and the partial exhaust passage 3d is an outlet of the catalyst device 4. This is a partial exhaust passage from the location where the O ₂ sensor 8 is disposed. The algorithm of the exhaust temperature observer 19 is constructed as follows.

  First, the exhaust gas temperature at the exhaust port 2 of the engine 1 is basically in a steady operation state of the engine 1 (specifically, in an operation state in which the engine speed NE and the intake pressure PB are kept constant). This corresponds to the engine speed NE and the intake pressure PB. Therefore, the exhaust gas temperature at the exhaust port 2 is basically estimated based on a map determined based on, for example, experiments in advance from the detected values of the rotational speed NE and the intake pressure PB as parameters representing the operating state of the engine 1. be able to. However, when the operating state of the engine 1 (the rotational speed NE or the intake pressure PB) fluctuates, heat exchange between the exhaust gas and the wall near the exhaust port 2, the combustion chamber of the engine 1, etc. The exhaust gas temperature has a response delay with respect to the exhaust gas temperature obtained from the map as described above (hereinafter referred to as basic exhaust gas temperature TMAP (NE, PB)).

  Therefore, in this reference example, the exhaust gas temperature observer 19 calculates the basic exhaust gas temperature TMAP () from the detected value (latest detected value) of the rotational speed NE of the engine 1 and the intake pressure PB at every predetermined cycle time (calculation processing period). After obtaining NE, PB) from the map, the exhaust gas temperature Texg at the exhaust port 2 is further set to follow the primary exhaust gas temperature TMAP (NE, PB) with a first order lag as shown in the following equation (1). Estimate sequentially.

  Here, k in equation (1) is the number of the arithmetic processing cycle of the exhaust temperature observer 19. Ktex is a coefficient (delay coefficient) determined based on experiments and the like in advance, and 0 <Ktex <1. In this reference example, the intake pressure PB of the engine 1 has a meaning as a parameter representing the intake air amount of the engine 1. Therefore, for example, when a flow sensor that directly detects the intake air amount is provided, the output of the flow sensor (the detected value of the intake air amount) may be used instead of the detected value of the intake pressure PB. .

  Using the estimated value of the exhaust gas temperature Texg of the exhaust port 2 thus obtained, the temperature of the exhaust gas in each of the partial exhaust passages 3a to 3e is estimated as described below. First, for convenience of explanation, generally, as shown in FIG. 5, heat transfer in a case where a fluid flows in a circular tube 23 extending in the Z-axis direction in the atmosphere while exchanging heat with the tube wall of the circular tube 23 will be described. To do. Here, it is assumed that the fluid temperature Tg and the tube wall temperature Tw (hereinafter referred to as the circular tube temperature Tw) are functions Tg (t, z) and Tw (t, z) between the time t and the position z in the Z-axis direction. The thermal conductivity of the tube wall of the circular tube 23 is assumed to be infinite in the radial direction and “0” in the Z-axis direction. The heat transfer between the fluid and the tube wall of the circular tube 23 and the heat transfer between the tube wall of the circular tube 23 and the atmosphere outside thereof are proportional to the respective temperature differences according to Newton's cooling law. Shall. At this time, the following equations (2-1) and (2-2) hold.

  Here, Sg, ρg, and Cg are the density, specific heat, and channel cross-sectional area of the fluid, respectively, Sw, ρw, and Cw are the density, specific heat, and cross-sectional area of the tube wall of the circular tube 23, and V is the fluid that flows through the circular tube 23, respectively. , TA is the atmospheric temperature outside the circular tube 23. U is the inner peripheral length of the circular tube 23, α1 is the heat transfer coefficient between the fluid and the tube wall of the circular tube 23, and α2 is the heat transfer coefficient between the tube wall of the circular tube 23 and the atmosphere. It is assumed that the atmospheric temperature TA is kept constant around the circular tube 23.

  When these formulas (2-1) and (2-2) are arranged, the following formulas (3-1) and (3-2) are obtained.

  However, in these formulas (3-1) and (3-2), a, b and c are constants, and a = α1 · U / (Sg · ρg · cg), b = α1 · U / (Sw Ρw · cw), c = α 2 · U / (Sw · ρw · cw).

  The first term on the right side of the equation (3-1) represents the temporal change rate (temperature change amount per unit time) of the fluid temperature Tg according to the temperature gradient in the fluid flow direction at the position z and the fluid flow velocity. Advection term to represent. Further, the second term on the right side of the equation (3-1) is the temporal change rate of the fluid temperature Tg according to the deviation between the fluid temperature Tg and the tube temperature Tw at the position z (temperature change amount per unit time). That is, it is a heat transfer term representing the temporal change rate of the fluid temperature Tg accompanying the heat transfer between the fluid and the tube wall of the circular tube 23. Therefore, this equation (3-1) indicates that the temporal change rate ∂Tg / ∂t of the fluid temperature Tg at the position z depends on the temperature change component of the advection term and the temperature change component of the heat transfer term. It shows that it becomes a thing (the sum total of those temperature change components).

  In addition, the first term on the right side of the equation (3-2) is the temporal change rate (temperature change amount per unit time) of the tube temperature Tw according to the deviation between the tube temperature Tw and the fluid temperature Tg at the position z. ), That is, a heat transfer term representing a temporal change rate of the tube temperature Tw accompanying heat transfer between the fluid at the position z and the tube wall of the tube 23. Further, the second term on the right side of the equation (3-2) is the rate of change over time of the tube temperature Tw according to the deviation between the tube temperature Tw at the position z and the external atmospheric temperature TA (temperature per unit time). Change amount), that is, a heat radiation term representing a temporal change rate of the tube temperature Tw according to heat radiation from the tube wall of the circular tube 23 to the atmosphere at the position z. Expression (3-2) shows that the temporal change rate ∂Tw / ∂t of the tube temperature Tw at the position z corresponds to the temperature change component of the heat transfer term and the temperature change component of the heat release term. (The sum of these temperature change components).

  When these equations (3-1) and (3-2) are rewritten and rearranged by the difference method, the following equations (4-1) and (4-2) are obtained.

  These formulas (4-1) and (4-2) are the position z, the fluid temperature Tg (t, z) and the tube temperature Tw (t, z) at time t, and the position z immediately upstream (upstream side). ) At the position z-Δz at the time t, the fluid temperatures Tg (t + Δt, z) and Tw (t at the next time t + Δt at the position z are obtained. t + Δt, z) can be obtained and these equations are connected in series to obtain the fluid temperature Tg and the tube temperature Tw at the positions z + Δz, z + 2Δz,. Means that you can. That is, initial values of Tg and Tw (initial values at t = 0) at each position z, z + Δz, z + 2Δz,... Are given, and an arbitrary origin (for example, a circle) of the circular tube 23 in the Z-axis direction is given. If the fluid temperature Tg (t, 0) at the inlet of the tube 23 is given (here, z−Δz = 0), each time t, t + Δt at positions z, z + Δz, z + 2Δz,. Tg and Tw at t + 2Δt,... can be calculated.

  In this case, the fluid temperature Tg (t, z) at the position z is a temperature change component corresponding to the flow velocity V and the temperature gradient at the position z at a predetermined time (the second term of the equation (4-1) is The temperature change component (temperature change component represented by the third term of the equation (4-1)) according to the deviation between the fluid temperature Tg and the tube temperature Tw at the position z, and the initial value. It can be calculated by cumulative addition (integration) to Tg (0, z). The same applies to the other positions z + Δz, z + 2Δz,. Further, the circular tube temperature Tw (t, z) at the position z is a temperature change component (formula (4-2)) corresponding to the deviation between the fluid temperature Tg at the position z and the circular tube temperature Tw at every predetermined time. Temperature change component represented by the second term of the above), and a temperature change component (temperature change component represented by the third term of the equation (4-2)) according to the deviation of the circular tube temperature Tw and the atmospheric temperature TA at the position z. , And can be calculated by accumulating (integrating) the initial value Tw (0, z).

  Therefore, in this reference example, the exhaust gas temperature observer 19 uses the model equations (4-1) and (4-2) as basic equations, and sets the exhaust gas temperatures in the partial exhaust passages 3a to 3d as follows. Ask.

  First, among the partial exhaust passages 3a to 3d, each of the partial exhaust passages 3a and 3b is formed using the exhaust pipe 6a as a passage formation. And in this reference example, in order to estimate the temperature of the exhaust gas in these partial exhaust passages 3a, 3b, the exhaust gas flow velocity and the temperature gradient (in the exhaust gas flow direction) as in the case described with respect to the circular tube 23. Temperature change according to the temperature gradient), heat transfer between the exhaust gas and the exhaust pipe 6a, and heat radiation from the exhaust pipe 6a to the atmosphere are considered.

  In this case, the estimated value of the exhaust gas temperature Tga in the partial exhaust passage 3a is combined with the estimated value of the temperature Twa of the exhaust pipe 6a (hereinafter referred to as the exhaust pipe temperature Twa) in the partial exhaust passage 3a, together with the processing of the exhaust temperature observer 19. Each cycle time is obtained by the following model formulas (5-1) and (5-2). Further, the estimated value of the exhaust gas temperature Tgb in the partial exhaust passage 3b is combined with the estimated value of the exhaust pipe temperature Twb in the partial exhaust passage 3b for each cycle time of the processing of the exhaust temperature observer 19 (6 -1) and (6-2). More specifically, the exhaust gas temperature Tga and the exhaust pipe temperature Twa obtained by the equations (5-1) and (5-2) are estimated values of temperatures in the vicinity of the downstream end of the partial exhaust passage 3a. Similarly, the exhaust gas temperature Tgb and the exhaust pipe temperature Twb obtained by the equations (6-1) and (6-2) are estimated values of temperatures in the vicinity of the downstream end of the partial exhaust passage 3b in more detail.

  Dt in these formulas (5-1), (5-2), (6-1), and (6-2) is a processing cycle (cycle time) of the exhaust temperature observer 19, and the formula (4) -1), which corresponds to Δt in (4-2). The value of dt is predetermined. Further, La and Lb in the equations (5-1) and (6-1) are the lengths (fixed values) of the partial exhaust passages 3a and 3b, respectively, and correspond to Δz in the equation (4-1). In addition, Aa, Ba, and Ca in formulas (5-1) and (5-2) and Ab, Bb, and Cb in formulas (6-1) and (6-2) are represented by formula (4-1), respectively. ) And (4-2) are model coefficients corresponding to a, b, and c, and their values are set (identified) based on experiments and simulations in advance. Further, Vg in the equations (5-1) and (6-1) is a parameter indicating the flow rate of exhaust gas (this is obtained as described later), and corresponds to V in the equation (4-1). is there.

  Here, the exhaust gas temperature Texg (k) (the exhaust gas temperature at the exhaust port 2) necessary for calculating the new estimated value Tga (k + 1) of the exhaust gas temperature Tga by the equation (5-1) is basically Is the latest value obtained by the equation (1). Similarly, the exhaust gas temperature Tga (k) (exhaust gas temperature in the partial exhaust passage 3a) necessary for calculating the new estimated value Tgb (k + 1) of the exhaust gas temperature Tgb by the equation (6-1) is basically The latest value obtained by the equation (5-1) is used for. Further, the atmospheric temperature TA (k) necessary for the calculation of the equations (5-2) and (6-2) is an atmospheric temperature sensor (not shown) (this is a sensor provided in the engine 1 in this reference example). The latest value of the atmospheric temperature detected by (used) is used. Further, in this reference example, the flow velocity parameter Vg necessary for the calculations of the equations (5-1) and (6-1) is calculated from the latest detected values of the engine speed NE and the intake pressure PB according to the following equation (7 ) Is used.

  NEBASE and PBBASE in the equation (7) are a predetermined rotation speed and a predetermined intake pressure, respectively, which are set to, for example, the maximum rotation speed of the engine 1 and 760 mmHg (≈101 kPa). The flow velocity parameter Vg calculated by the equation (7) is proportional to the exhaust gas flow velocity, and Vg ≦ 1.

  The initial values Tga (0), Twa (0), Tgb (0), Twb (0) of the estimated values of the exhaust gas temperature Tga and the exhaust pipe temperature Twa, and the exhaust gas temperature Tgb and the exhaust pipe temperature Twb are In the reference example, the atmospheric temperature detected by the atmospheric temperature sensor (not shown) at the start of operation of the engine 1 (when the engine 1 is started) is set.

  Next, the partial exhaust passage 3c is an exhaust passage formed using the catalyst 7 of the catalyst device 4 as a passage formation product. The catalyst 7 is self-heated by the exhaust gas purification action (specifically, oxidation / reduction reaction), and the heat generation amount (heat generation amount per unit time) is approximately proportional to the flow rate of the exhaust gas. This is because the exhaust gas component that reacts with the catalyst 7 per unit time increases as the flow rate of the exhaust gas increases.

  Therefore, in this reference example, regarding the estimation of the exhaust gas temperature in the partial exhaust passage 3c, in order to accurately perform the estimation, the exhaust gas and the catalyst 7 of the catalyst device 4 in accordance with the temperature change according to the flow velocity and the temperature gradient of the exhaust gas. In addition to considering the heat transfer between the catalyst 7 and the heat radiation from the catalyst 7 to the atmosphere, the self-heating of the catalyst 7 is further considered.

  In this case, the estimated value of the exhaust gas temperature Tgc in the partial exhaust passage 3c is combined with the estimated value of the temperature Twc of the catalyst 7 forming the partial exhaust passage 3c (hereinafter referred to as the catalyst temperature Twc) in the processing of the exhaust temperature observer 19. For each cycle time, the following model formulas (8-1) and (8-2) are used. More specifically, the exhaust gas temperature Tgc and the catalyst temperature Twc determined by the equation (8-1) are estimated values of the temperature at the downstream end (near the outlet of the catalyst device 4) of the partial exhaust passage 3a.

  Lc in the equation (8-1) is the length (fixed value) of the partial exhaust passage 3c and corresponds to Δz in the equation (4-1). In addition, Ac, Bc, and Cc in the equations (8-1) and (8-2) are model coefficients corresponding to a, b, and c in the equations (4-1) and (4-2), respectively. These values are set (identified) based on experiments and simulations in advance. Further, the fourth term on the right side of the equation (8-2) represents a temperature change component of the catalyst 7 due to self-heating of the catalyst 7 of the catalyst device 4 (temperature change amount per cycle of the treatment of the exhaust temperature observer 19). And is proportional to the flow velocity parameter Vg. Dc in the fourth term is a model coefficient whose value is set (identified) in advance based on experiments and simulations, like Ac to Cc. Therefore, the equation (8-2) corresponds to the right side of the equation (4-2) added with a temperature change component accompanying self-heating of the passage formation material (here, the catalyst 7).

  The meanings and values of dt and Vg in the formulas (8-1) and (8-2) are the same as those in the formulas (5-1) to (6-2). Further, the value of TA used in the calculation of Expression (8-2) is the same as that used in Expressions (5-2) and (6-2). Further, the initial values Tgc (0) and Twc (0) of the exhaust gas temperature Tgc and the catalyst temperature Twc are the start values of the engine 1 in this reference example, as in the case of the equations (5-1) to (6-2). It is the detected value of the atmospheric temperature at the time.

  Next, the partial exhaust passage 3d is an exhaust pipe 6b similar to the partial exhaust passages 3a and 3b. Therefore, the exhaust temperature Tgd and the exhaust pipe temperature Twd (more specifically, the temperature at the downstream end of the partial exhaust passage 3d) of the partial exhaust passage 3d are the same as those in the equations (5-1) to (6-2). It is determined by model formulas (9-1) and (9-2).

  Ld in the equation (9-1) is the length (fixed value) of the partial exhaust passage 3d, and corresponds to Δz in the equation (4-1). In addition, Ad, Bd, and Cd in the equations (9-1) and (9-2) are model coefficients corresponding to a, b, and c in the equations (4-1) and (4-2), respectively. These values are set (identified) based on experiments and simulations in advance.

  The meanings and values of dt and Vg in the formulas (9-1) and (9-2) are the same as those in the formulas (5-1) to (6-2). Further, the value of TA used in the calculation of Expression (9-2) is the same as that used in Expressions (5-2), (6-2), and (8-2). Further, the initial values Tgd (0) and Twd (0) of the estimated values of the exhaust gas temperature Tgd and the catalyst temperature Twd are the same as those in the expressions (5-1) to (6-2) at the start of operation of the engine 1. It is the detected value of the atmospheric temperature.

By the processing of the exhaust temperature observer 19 described above, the estimated values of the exhaust gas temperatures Texe, Tga, Tgb, Tgc, and Tgd of the exhaust port 2 and the partial exhaust passages 3a to 3d of the engine 1 are obtained from the upstream side at each cycle time. Asked in order. In this case, the estimated value of the exhaust gas temperature Tgd in the partial exhaust passage 3d on the most downstream side corresponds to the temperature of the exhaust gas in the vicinity of the location where the O ₂ sensor 8 is disposed, and the estimated value of the exhaust gas temperature Tgd is the O ₂ sensor. 8 is obtained as an estimated value of the exhaust gas temperature in the vicinity of the arrangement position.

The algorithm for the estimation process of the exhaust gas temperature observer 19 is represented as a block diagram as shown in FIG. In FIG. 6, the model formula of the formula (1) is the exhaust port heat model 24, the model formulas of the formulas (5-1) and (5-2), and the formulas (6-1) and (6-2). CAT pre-exhaust system heat models 25 and 26, and equations (8-1) and (8-2) are model equations for CAT part exhaust system heat model 27, equations (9-1) and (9- The model formula 2) is referred to as a post-CAT exhaust system heat model 28. As shown in the drawing, the detected values of the rotational speed NE of the engine 1 and the intake pressure PB are given to the thermal models 24 to 28. Note that NE and PB given to the exhaust port heat model 24 are for obtaining the basic exhaust gas temperature TMAP, and NE and PB given to the exhaust system heat models 25 to 28 are values for the flow velocity parameter Vg. Is for. Further, the detected value of the atmospheric temperature TA is given to the exhaust system thermal models 25 to 28. The pre-CAT exhaust system heat model 25, the pre-CAT exhaust system heat model 26, the CAT part exhaust system heat model 27, and the post-CAT exhaust system heat model 28 are each one of the upper heat models 24, 25, 26. , 27 are provided with estimated values of exhaust gas temperatures Texg, Tga, Tgb, Tgc, respectively, and finally the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed by the post-CAT exhaust system thermal model 28. A value is obtained.

  In this reference example, an atmospheric temperature sensor provided in the engine 1 is used to estimate the temperatures of the passage formations (exhaust pipe 6a, catalyst 7 of the catalyst device 4, exhaust pipe 6b) of the partial exhaust passages 3a to 3d. However, it is also possible to separately arrange an atmospheric temperature sensor outside the exhaust passage 3 and use the detected value of the atmospheric temperature sensor.

Next, the element temperature observer 20 will be described. In this reference example, the element temperature observer 20 is configured to transfer heat between the element portion 10 of the O ₂ sensor 8 and the exhaust gas in contact with the element portion 10 and a ceramic heater 13 (hereinafter simply referred to as “heat source”). The temperature T _O2 of the element unit 10 is sequentially estimated at a predetermined cycle time in consideration of heat transfer with the heater 13). In order to perform this estimation, the temperature Tht of the heater 13 is also estimated. In this case, in the estimation process of the temperature Tht of the heater 13, heat transfer between the heater 13 and the element unit 10 is taken into consideration, and heat generation of the heater 13 accompanying power supply to the heater 13 is taken into consideration. The estimation algorithm of the element temperature observer 20 that performs such estimation processing is constructed as described below.

That is, the element temperature observer 20 has an estimated value of the temperature T _O2 (hereinafter referred to as element temperature T _O2 ) of the element portion 10 of the O ₂ sensor 8 and an estimated value of the temperature Tht of the heater 13 (hereinafter referred to as heater temperature Tht). Are sequentially obtained at predetermined cycle times by the following model equations (10-1) and (10-2), respectively.

Equation (10-1) shows that the temperature change amount of the element unit 10 for each cycle time is the exhaust gas temperature Tgd (exhaust gas temperature of the partial exhaust passage 3d) and the element temperature T _{O2 in the} vicinity of the location where the O ₂ sensor 8 is disposed. Change component (the second term on the right side of the equation (10-1)) according to the deviation of the element, that is, the temperature change component accompanying the heat transfer between the element unit 10 and the exhaust gas in contact therewith, and the element temperature T _O2 In accordance with the temperature change component (third term on the right side of the equation (10-1)), that is, the temperature change component accompanying heat transfer between the element unit 10 and the ceramic heater 13. It is shown that it becomes a thing (total of those temperature change components).

In addition, the expression (10-2) indicates that the temperature change amount of the heater 13 for each cycle time is a temperature change component corresponding to a deviation between the element temperature T _O2 and the heater temperature Tht (second on the right side of the expression (10-2)). ), That is, a temperature change component accompanying heat transfer between the element unit 10 and the heater 13 and a temperature change component according to a duty DUT generated by the heater controller 22 as described later, that is, power supply to the heater 13. It is shown that the temperature change component according to the heat generation of the heater 13 due to (the sum of those temperature change components) is obtained.

  Note that Ax, Bx, Cx, and Dx in the expressions (10-1) and (10-2) are model coefficients whose values are set (identified) in advance based on experiments and simulations. Further, dt is a processing period (cycle time) of the element temperature observer 20, and in this reference example, the processing time of the exhaust temperature observer 19 described above (the dt in the equations (5-1) to (9-2)). ) Is set to the same value.

Here, the latest value of the duty DUT calculated by the heater controller 22 as described later is used as the DUT (k) necessary for the calculation of Expression (10-2). Further, the initial values T _O2 (0) and Tht (0) of the estimated values of the element temperature T _O2 and the heater temperature Tht are detected values of the atmospheric temperature at the start of operation of the engine 1 in this reference example.

With the algorithm described above, the element temperature observer 20 sequentially calculates estimated values of the element temperature T _O2 and the heater temperature Tht.

  Next, the heater controller 22 will be described. The heater controller 22 sequentially generates a duty DUT as a control input (operation amount) to the heater 13 by an optimal predictive control algorithm, and controls the power supplied to the heater 13 by the duty DUT.

In this case, in this reference example, the deviation between the element temperature T _O2 and the target value with respect to the deviation, the amount of change of the deviation per predetermined time (this corresponds to the change speed of the deviation), and the predetermined time of the heater temperature Tht Focusing on the amount of change for each (this corresponds to the rate of change of the heater temperature Tht), these are used as state quantities relating to the control target of the heater controller 22, and a model equation for the control target is introduced. The algorithm of the heater controller 22 is constructed as described below.

First, a model expression to be controlled will be described. When attention is paid to the change amounts ΔT _O2 and ΔTht of the element temperature T _O2 and the heater temperature Tht per predetermined time, these change amounts ΔT _O2 and ΔTht are the model equations (10-1) and (10) relating to the element temperature observer 20, respectively. 10-2) is given by the following equations (11-1) and (11-2).

In these equations (11-2) and (11-2), ΔT _O2 (k) = T _O2 (k + 1) −T _O2 (k), ΔTht (k) = Tht (k + 1) − Tht (k), ΔTgd (k) = Tgd (k + 1) −Tgd (k), ΔDUT (k) = DUT (k + 1) −DUT (k).

Next, the target value of the element temperature T _O2 is R, and a deviation e (deviation for each predetermined cycle time; hereinafter referred to as element temperature deviation e) between them is defined by the following equation (12).

  At this time, the change amount Δe of the element temperature deviation e for each cycle time (hereinafter referred to as the element temperature deviation change amount Δe) is expressed by the following equation (13) based on the equations (11-1) and (12). Given.

In Equation (13), Δe (k) = e (k + 1) −e (k) and ΔR (k) = R (k + 1) −R (k). In the derivation process of the equation (13), a relational expression ΔT _O2 = Δe (k) + ΔR (k) (which is based on the equation (12)) is used.

Further, when the relational expression of ΔT _O2 = Δe (k) + ΔR (k) is applied to the expression (11-2), the following expression (14) is obtained.

  Here, when the state quantity vector X0 (k) = (e (k), Δe (k), ΔTht (k)) T is introduced (T means transposition), the equations (14), (15) and , E (k + 1) = e (k) + Δe (k) and the following equation (15) is obtained.

  In the equation (15), R0, G, and Gd are vectors defined by the proviso of the equation (15), respectively, and Φ and Gr are matrices defined by the proviso of the equation (15), respectively. .

  This formula is a basic formula of a model to be controlled related to the control process of the heater controller 22.

In the above description, the cycle of the control process by the heater controller 22 is made the same as the cycle dt of the calculation process of the exhaust temperature observer 19 and the element temperature observer 20. For this reason, dt is used in the vectors G and Gd and the matrices Φ and Gr in equation (15). In this case, it is desirable that the calculation processing of the exhaust temperature observer 19 and the element temperature observer 20 be performed at a relatively fast cycle (for example, a cycle of 20 to 50 msec) in order to improve the accuracy of temperature estimation. However, regarding the control process of the heater controller 22, the response speed of the change in the element temperature with respect to the control input (duty DUT) is relatively slow (about several Hz in terms of frequency). It may be longer than the period dt of the arithmetic processing of the observer 19 and the element temperature observer 20. Further, in the optimal predictive control described later, the future value of the target value R of the element temperature T _O2 needs to be stored and held for a certain time, so that if the control processing cycle of the heater controller 22 is short, the target value R The storage capacity of the memory increases.

  Therefore, in this reference example, the control processing cycle (cycle time) of the heater controller 22 is set to a value dtc (for example, 300 to 500 msec) longer than the calculation processing cycle dt of the exhaust temperature observer 19 and the element temperature observer 20. ing.

  For this reason, in this reference example, the model formula to be controlled by the heater controller 22 is rewritten from the formula (15) to the following formula (16) using the cycle dtc of the control process of the heater controller 22.

  This equation (16) is a model equation of the control object that is actually used in the algorithm of the control process of the heater controller 22. Here, n in the equation (16) indicates the number of the cycle dtc of the control process of the heater controller 22.

Using this model formula, the algorithm for the control process of the heater controller 22 (the algorithm for optimal predictive control) is constructed as follows. The target value R of the element temperature T _O2 is set to the future after the Mr step (after the time of Mr times the control process cycle dtc of the heater controller 22) with respect to the model formula of the formula (16). It is assumed that the exhaust gas temperature Tgd serving as a disturbance input is maintained at the current value until the future after the Md step (after Md times the cycle dtc of the control process of the heater controller 22). In the following description, Mr is referred to as a target value prediction time, and Md is referred to as an exhaust gas temperature prediction time. These prediction times Mr and Md are integer values expressed in units of one cycle dtc of the control process of the heater controller 22.

  At this time, the controller that generates the control input ΔDUT that minimizes the value of the evaluation function J0 in the following equation (17) is the optimum foreseeing servo controller.

  Here, M in the equation (17) is a larger one of the target value prediction time Mr and the exhaust gas temperature prediction time Md, that is, M = max (Mr, Md). Q0 and H0 are weight matrices for adjusting the convergence of the state vector X0 and the power (magnitude) of the control input ΔDUT, respectively. In this case, since X0 is a cubic vector, Q0 is a 3-by-3 diagonal matrix. Since ΔDUT is a scalar, H0 is also a scalar. In this reference example, in order to reduce the power consumption by the heater 13, for example, Q0 is set to a unit matrix (a diagonal matrix in which all diagonal components are “1”), while H0 is a pair of the matrix Q0. It is set to a large value (for example, 1000) compared to the corner component. Further, regarding the target value prediction time Mr and the exhaust gas temperature prediction time Md, in this reference example, the cycle of the control process of the heater controller 22 is set to 300 to 500 msec, Mr is set to 20, for example, and Md is set to 10, for example. Is set.

  The control input ΔDUT that minimizes the value of the evaluation function of the equation (17) is given by the following equation (18).

  In the equation (18), F0 of the first term on the right side is a cubic row vector (Fs0, Fe0, Fx0), Fr0 (i) (i = 1, 2,..., Mr) of the second term on the right side (term of Σ). ) Are secondary row vectors (Fr01 (i), Fr02 (i)), and Fdt of the third term on the right side is a scalar, and is given by the following equations (19-1) to (19-3), respectively.

  In this case, P in these equations (19-1) to (19-3) is a matrix satisfying the Riccati equation of the following equation (20-1) (in this case, a 3 × 3 matrix), and ζ is This is a matrix (3 × 3 matrix in this case) given by the following equation (20-2).

  G, Gr, Gd, and Φ in the formulas (19-1) to (19-3) and the formulas (20-1) and (20-2) are defined in the proviso of the formula (16). is there. Further, H0 and Q0 are weight matrices (in this case, H0 is a scalar) of the evaluation function J0 in the equation (17).

  Here, the second term (Σ term) on the right side of the equation (18) is rewritten using the components of Fr0 and R0 (see the proviso in the equations (19-2) and (16)), When arranged, the following equation (21) is obtained.

  While substituting this equation (21) into equation (18), the first term on the right side of equation (18) is the component of F0 and X0 (see the proviso of equations (19-1) and (16) above). Thus, the above equation (18) is expressed by the following equation (22).

  At this time, the control input DUT (n) to be generated by the heater controller 22 is a cumulative addition of ΔDUT (1), ΔDUT (2),..., ΔDUT (n) to the initial value DUT (0). From the above equation (22), the following equation (23) is obtained.

  Then, the initial value term of the equation (23), that is, the sixth term (the term of Fe 0 · e (0)) to the tenth term (the term of DUT (0)) of the equation (23) are all “0”. Thus, an equation for calculating the control input DUT (n) that is actually generated by the heater controller 22 is obtained as the following equation (24).

  This equation (24) is an arithmetic equation for sequentially calculating the control input DUT (n) (duty) for controlling the heater 13 by the heater controller 22. That is, the heater controller 22 sequentially calculates the control input DUT (n) for each cycle time (period) of the control process of the heater controller 22 by the equation (24), and illustrates the pulse voltage of the duty DUT (n) as shown in the figure. The power supplied to the heater 13 is adjusted by applying it to the heater energizing circuit. The first to third terms (from the term including Σe (j) to the term including Tht (n)) of the equation (24) are control input components (feedback components) corresponding to the element temperature deviation e and the heater temperature Tht. Hereinafter, this component is referred to as an optimum F / B component Uopfb). Further, the fourth term (ΣFr (i) · R (n + i) term) on the right side of the equation (24) is a control input component (feed forward component) corresponding to the target value R. This component is hereinafter referred to as the optimum target value F. The fifth term (term including Tgd (n)) is a control input component (feed forward component) corresponding to the exhaust gas temperature Tgd (which functions as a disturbance to the controlled object). Hereinafter, this component is referred to as an optimum disturbance F / F component Uopfd). In this way, the heater controller 22 that obtains the DUT as the control input by the equation (24) is represented as a block diagram as shown in FIG.

  Here, as Fs0, Fe0, and Fx0 necessary for obtaining the control input DUT (n) by the equation (24), values calculated in advance according to the equation (19-1) are used. As Fr (i) (i = 0, 1,..., Mr), a value calculated in advance according to the equations (21) and (19-2) is used. Further, a value calculated in advance according to the equation (19-3) is used for Fdt. Note that the values of these coefficients Fs0, Fe0, Fx0, Fr (i), and Fdt do not necessarily need to be the values as defined, but may be adjusted as appropriate through simulations and experiments.

  Further, the heater temperature Tht and the exhaust gas temperature Tgd necessary for the calculation of the equation (24) are obtained by the latest value of the estimated value of the heater temperature Tht obtained by the element temperature observer 20 and the exhaust temperature observer 19, respectively. The latest value of the estimated value of the exhaust gas temperature Tgd is used.

Further, the element temperature deviation e required for the calculation of the equation (24) is the latest value of the estimated value of the element temperature T _O2 obtained by the element temperature observer 20, and the target value prediction time by the target value setting means 21. It is calculated from the target value R set at the cycle time before Mr.

Here, the target value setting means 21 basically sets a temperature of 750 ° C. or higher (for example, 800 ° C. in this reference example) at which the output characteristics of the O ₂ sensor 8 become stable and good, and the heater controller 22. The target value R of the temperature of the element unit 10 is set at the same cycle time as the cycle time (period) of the process. In this case, the target value setting means 21 sets the target value R to be set at each cycle time from the current cycle time to the target value prediction time in order to perform the processing by the heater controller 22 by the above-described optimal prediction control algorithm. It is set as a target value R (n + Mr) after Mr, and is stored and held in time series for the target value prediction time Mr. That is, Mr + 1 target values R (n), R (n + 1),..., R (n + Mr) are stored and held while being sequentially updated. Then, the target value R used for obtaining the element temperature deviation e required for the calculation of the equation (24) is set and stored by the target value setting means 21 as described above at the cycle time before the target value prediction time Mr. The held value R (n). Further, the target values R (n), R (n + 1),..., R (n + Mr) stored and held as described above are the fourth term (R (n + i)) of the equation (24). Is used to determine the value of the term of Σ including.

If the target value R of the element temperature T _O2 is set to a high temperature such as 800 ° C. from the start of operation of the engine 1, moisture or the like adheres to the element portion 10 of the O ₂ sensor 8 at the start of operation of the engine 1. In such a case, there is a possibility that the element unit 10 may be damaged by stress accompanying rapid heating. For this reason, in this reference example, the target value setting means 21 sets the target value R of the element temperature T _{O2 to} a temperature lower than 750 ° C. until a predetermined time (for example, 15 seconds) elapses after the operation of the engine 1 is started. For example, the temperature is set to 600 ° C.

  Next, the overall processing of the apparatus of this reference example, particularly the sensor temperature control means 12, will be described.

  When the engine 1 is started and its operation is started, the sensor temperature control means 12 executes the main routine process shown in the flowchart of FIG. 8 with a predetermined cycle time. The execution cycle of this main routine is shorter than the processing cycle dt of the exhaust temperature observer 19 and the element temperature observer 20, and therefore shorter than the processing cycle dtc of the target value setting means 21 and the heater controller 22.

  The sensor temperature control means 12 first acquires detected values of the engine speed NE, the intake pressure PB, and the atmospheric temperature TA (STEP 1), and further for one cycle of processing of the target value setting means 21 and the heater controller 22. The value of the countdown timer COPC for counting the time dtc is determined (STEP 2). The value of the countdown timer COPC is initialized to “0” when the engine 1 is started.

Then, when COPC = 0, the sensor temperature control means 12 newly sets the timer setting time TM1 corresponding to the control processing cycle dtc of the target value setting means 21 and the heater controller 22 as the value of COPC. (STEP 3) A process for setting the target value R of the element temperature T _O2 of the O ₂ sensor 8 and a process for calculating the duty DUT of the heater 13 are sequentially executed by the target value setting means 21 and the heater controller 22, respectively ( STEP4, 5). If COPC ≠ 0 in STEP2, the sensor temperature control means 12 counts down the value of COPC in STEP5 and omits the processes in STEP4 and 5. Therefore, the processing of STEPs 4 and 5 is executed at a cycle dtc defined by the timer setting time TM1.

  More specifically, the processing of STEPs 4 and 5 is performed as follows. First, the processing of STEP 4 by the target value setting means 21 is executed as shown in the flowchart of FIG.

In the processing of STEP4 by the target value setting means 21, first, the value of the parameter TSH representing the elapsed time after the engine 1 is started is compared with a predetermined value XTM (STEP4-1). At this time, when TSH ≦ XTM, that is, when the engine 1 is in a state immediately after the start of operation, the target value setting means 21 prevents damage to the element portion 10 of the O ₂ sensor 8 as described above. Therefore, the target value R of the element temperature T _O2 is set to a low temperature (for example, 600 ° C.) (STEP 4-2). More specifically, the target value R set here is the target value R (n + Mr) after the target value prediction time Mr from the present time.

If TSH> XTM in STEP 4-1, the target value setting means 21 uses the current detected value of the atmospheric temperature TA (obtained in STPE 1 in FIG. 8) to a predetermined data table. Based on this, the target value R of the element temperature T _O2 is set (STEP 4-3). The target value R set here is basically a predetermined value of 750 ° C. or higher (800 ° C. in this reference example) when the atmospheric temperature TA is about room temperature (eg, TA ≧ 0 ° C.). However, when the atmospheric temperature TA is low (for example, TA <0 ° C.) such as when the engine 1 is operated in a cold region, the heater 13 has a target value R of the element temperature T _O2 as high as 800 ° C. The temperature is likely to become excessively high. And in this reference example, when the temperature of the heater 13 becomes excessively high due to the overheat prevention processing of the heater 13 described later, the energization to the heater 13 is avoided in order to avoid failure (disconnection, melting damage, etc.) of the heater 13. Is forcibly canceled. Therefore, in this reference example, in STEP 4-3, when the atmospheric temperature TA is low (for example, TA <0 ° C.), the target value R of the element temperature T _O2 is slightly lower than the normal value (for example, 750 ° C. ≦ ≤ R <800 ° C.).

  Note that the target value R set in STEP 4-3 is similar to the target value R set in STEP 4-2. More specifically, the target value R (n + Mr) after the target value prediction time Mr from the present time. is there.

  After the target value R (= R (n + Mr)) is newly set in STEP4-2 or 4-3 as described above, the target value setting means 21 sets the target value R to the target value prediction time Mr. The values of Mr + 1 buffers RBF (0), RBF (1),..., RBF (Mr) for storing and holding are updated in STEPs 4-4 and 4-5. Thereby, the process of STEP4 is completed.

  In this case, in STEP 4-4, the value of RBF (j) is set to the current value of RBF (j + 1) in order for Mr buffers RBF (j) (j = 0, 1,..., Mr−1). Processing to update the value is executed. Note that the value held so far in the buffer RBF (0) is deleted. In STEP 4-5, the value of the buffer RBF (Mr) is updated to the target value R newly set in STEP 4-2 or 4-3. The values of the buffers RBF (0), RBF (1),..., RBF (Mr) updated in this way are R (n) and R (n + 1) in the fourth term of the equation (24), respectively. ), ..., R (n + Mr). The values of the buffers RBF (0), RBF (1),..., RBF (Mr) are initialized to predetermined values (for example, target values set in STEP4-2) when the engine 1 is started.

Next, the processing of STEP5 by the heater controller 22 is executed as shown in the flowchart of FIG. In the processing of STEP5, first, the current value T _O2 (n) of the estimated value of the element temperature T _O2 and the buffer RBF (0) (= R (n)), that is, the target before the target value prediction time Mr. An element temperature deviation e (n) = T _O2 (n) −RBF (0) between them is calculated from the target value R set by the value setting means 21 (STEP 5-1).

  Next, the heater controller 22 determines the values of the flags F / A and F / B (STEP5-2). Here, the flag F / A is a flag whose value is set to “0” or “1” in the limit processing to be described later of the duty DUT, and F / A = 1 is a predetermined upper limit value predetermined by the duty DUT. Alternatively, it means a state where the duty is forcibly limited to the lower limit value, and F / A = 0 means a state where the value of the duty DUT is not restricted (upper limit value> DUT> lower limit value). The flag F / B is a flag set to “1” in a state where energization to the heater 13 is forcibly cut off by an overheat prevention process of the heater 13 described later. The initial values of the flags F / A and F / B are “0”.

  If F / A = F / B = 0 in the determination in STEP5-2, the heater controller 22 adds the current value of Σe (j) in the first term of the equation (24) to the current value in STEP5-1. Is added to the calculated deviation e (n) (STEP 5-3). Thereby, the deviation e (n) is obtained by cumulative addition (integration) every cycle time dtc of the process of the heater controller 22. The initial value of Σe (j) is “0”.

  If F / A = 1 or F / B = 1 in the determination of STEP5-2, the current value of the duty DUT is not a normal normal value, so the heater controller 22 performs the processing of STEP5-4. The process proceeds to the next STEP 5-4, and the value of Σe (j) is held at the current value.

Next, the heater controller 22 uses the current value (latest value) of the element temperature deviation e (n) obtained in STEP 5-1, the current value of the cumulative addition value Σe (j), etc. An arithmetic operation is performed to calculate the current value DUT (n) of the DUT that is a control input to the heater 13 (STEP 5-4). That is, the current value of the deviation e (n) obtained in STEP 5-1, the current value of the cumulative addition value Σe (j), the current value Tht (n) of the estimated value of the heater temperature Tht, and the buffer RBF ( 0), RBF (1),..., RBF (Mr) current values (= R (n), R (n + 1),..., R (n + Mr)) and exhaust gas temperature Tgd (O ₂ The present value Tgd (n) of the estimated value of the exhaust gas temperature at the location where the sensor 8 is arranged) and predetermined coefficients Fs0, Fe0, Fx0, Fr (i) (i = 0, 1,..., Mr), From the value of Fdt, the duty DUT (n) is calculated by the equation (24). The estimated value of the heater temperature Tht and the estimated value of the exhaust gas temperature Tgd are set as the initial values of the atmospheric temperature TA detected at that time when the engine 1 is started (when the engine 1 is started). Then, at the stage where the processing of the exhaust temperature observer 19 and the element temperature observer 20 has not been executed yet, those initial values are used for the calculation of the equation (24). After the processing of both observers 19 and 20 is executed, the latest value of the estimated value obtained by each of the observers 19 and 20 is used for the calculation of Expression (24).

  Next, the heater controller 22 executes the limit process of the duty DUT (n) calculated in STEP 5-4 in STEPs 5-5 to 5-11. That is, it is determined whether the duty DUT (n) is smaller than a predetermined lower limit value (for example, “0”) (STEP 5-5). If DUT (n) <lower limit value, DUT (n) Is forcibly reset to the “lower limit value” (STEP 5-6). At this time, the value of the flag F / A (flag used in STEP5-2) is set to "1" (STEP5-7).

  If DUT (n) ≧ lower limit value, it is further determined whether or not the duty DUT (n) is larger than a predetermined upper limit value (for example, 100%) (STEP 5-8). At this time, if DUT (n)> the upper limit value, the value of DUT (n) is forcibly reset to the “upper limit value” (STEP 5-9). At this time, the value of the flag F / A is set to “1” (STEP 5-10). When the lower limit value ≦ DUT (n) ≦ the upper limit value, the value of DUT (n) is maintained and the value of the flag F / A is set to “0” (STEP 5-11). Thus, the process of STEP5 by the heater controller 22 ends.

  Returning to the processing of the main routine of FIG. 8, the sensor temperature control means 12 next executes the processing shown in STEPs 7 to 13. This process is a process for preventing overheating of the heater 13. First, in STEP 7, the current value (latest value) of the estimated value of the heater temperature Tht is equal to or greater than a predetermined upper limit value THTLMT (eg, 930 ° C.). It is determined whether or not. In this case, in this reference example, basically, when Tht ≧ THTLMT, in order to prevent the heater 13 from being damaged, the energization of the heater 13 is forcibly cut off. However, the estimated value of Tht may temporarily rise above the upper limit value THTLMT due to the influence of disturbance or the like. Therefore, in this reference example, when the state where Tht ≧ THTLMT continues for a predetermined time (for example, 3 seconds, hereinafter referred to as the heater OFF delay time) or longer, the energization of the heater 13 is cut off.

  For this reason, if Tht <THTLMT in STEP 7, the sensor temperature control means 12 sets the value of the countdown timer TMHTOFF for measuring the heater OFF delay time to a predetermined value TM2 corresponding to the heater OFF delay time. (STEP 8). In this case, since the heater 13 is not turned off, the sensor temperature control means 12 sets the value of the flag F / B (the flag used in STEP5-2 in FIG. 10) to “0”. (STEP 9).

  On the other hand, if Tht ≧ THTLMT in STEP 7, the sensor temperature control means 12 counts down the value of the countdown timer TMHTOFF by “1” (STEP 10), and then the value of the countdown timer TMHTOFF becomes “0”. It is determined whether or not the heater OFF delay time TM2 has elapsed in the state of Tht ≧ THTLMT (STEP 11).

  If TMHTOFF ≠ 0 at this time, the value of the flag F / B is set to “0” in STEP9. If TMHTOFF = 0, the current value of the duty DUT is forcibly reset to “0” (STEP 12), and the value of the flag F / B is set to “1” (STEP 13). .

  If the value of the flag F / B is set to “0” in STEP 9, the sensor temperature control means 12 applies the pulse voltage according to the current value of the duty DUT (the latest value calculated in the processing of STEP 5). A heater energizing circuit (not shown) is applied to energize the heater 13 with electric power corresponding to the duty DUT. If the value of the flag F / B is set to “1” in STEP 12, the sensor temperature control means 12 does not apply a pulse voltage to the energization circuit of the heater 12. Turn off the power.

  After executing the processing related to STEP7 to STEP13 (overheat prevention processing of the heater 13) as described above, the sensor temperature control means 12 then performs one cycle of the processing of the exhaust temperature observer 19 and the element temperature observer 20. The value of the countdown timer COBS for counting the time dt is determined (STEP 14). The value of the countdown timer COBS is initialized to “0” when the engine 1 is started.

When COBS = 0, the sensor temperature control means 12 sets a timer set time TM3 (which is shorter than TM1 of STEP 3) corresponding to the processing period dt of the exhaust temperature observer 19 and the element temperature observer 20. After newly setting the COBS value (STEP 15), a process for estimating the exhaust gas temperature Tgd (the exhaust gas temperature in the vicinity of the location where the O ₂ sensor 8 is disposed) and a process for estimating the element temperature T _O2 (a process for estimating the heater temperature Tht) Are executed by the exhaust temperature observer 19 and the element temperature observer 20 (STEP 16). If COBS ≠ 0 in STEP14, the processes in STEP15 and STEP16 are omitted. Therefore, the processing of STEP16 is executed at a cycle dt defined by the timer setting time TM3. The process described above is the process of the main routine in FIG.

More specifically, the processing of STEP 16 is performed as shown in the flowchart of FIG. That is, the sensor temperature control means 12 first executes the processing of STEP16-1 to STEP16-6 sequentially by the exhaust temperature observer 19, and obtains the estimated value of the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed. In STEP16-1, the flow velocity parameter Vg is obtained by the equation (7) using the current detected value of the engine speed NE and the intake pressure PB (the latest value acquired in STEP1). The value of the flow velocity parameter Vg is forcibly set to Vg = 1 when the calculation result of the equation (7) exceeds “1” due to over-rotation of the engine 1 or the like.

  Next, the exhaust temperature observer 19 calculates an estimated value of the exhaust gas temperature Texg at the exhaust port 2 of the engine 1 based on the equation (1) (STEP 16-2). That is, the basic exhaust gas temperature TMAP (NE, PB) is obtained from a current map of the engine speed NE and the intake pressure PB using a predetermined map, and the TMAP (NE, PB) and the exhaust gas temperature Texg are estimated. The right side of the equation (1) is calculated using the current value Texg (k-1) (value obtained in STEP16-2 at the previous cycle time) and the value of the predetermined coefficient Ktex. . Thereby, a new estimated value Texg (k) of the exhaust gas temperature Texg is calculated. In this reference example, during the idling operation of the engine 1 and during fuel cut, the basic exhaust gas temperature TMAP used for the calculation of Expression (1) is set to a predetermined value corresponding to each operation state. Like to do. Further, as described above, the estimated value of the exhaust gas temperature Texg is such that the atmospheric temperature TA detected at the time of starting operation (starting) of the engine 1 is set as the initial value Texg (0). When the calculation of the expression (1) is performed for the first time after the operation is started, the initial value Texg (0) is used as the value of Texg (k-1).

  Next, the exhaust temperature observer 19 calculates an estimated value of the exhaust gas temperature Tga and an estimated value of the exhaust pipe temperature Twa in the partial exhaust passage 3a based on the equations (5-1) and (5-2) (STEP 16). -3). That is, the current value Tga (k) of the estimated value of the exhaust gas temperature Tga (value obtained in STEP16-3 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twa (STEP16- at the previous cycle time). 3), the current value of the estimated value of the exhaust gas temperature Texg previously calculated in STEP 16-2, the current value of the flow velocity parameter Vg calculated in STEP 16-1, and a predetermined model coefficient A new estimated value Tga (k + 1) of the exhaust gas temperature Tga is obtained by calculating the right side of the equation (5-1) using the value of Aa and the value of the processing period dt of the exhaust gas temperature observer 19. Ask.

  Further, the current value Tga (k) of the estimated value of the exhaust gas temperature Tga (value obtained in STEP16-3 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twa (STEP16- at the previous cycle time) 3) and the value of the model coefficients Ba and Ca determined in advance and the value of the processing cycle dt of the exhaust gas temperature observer 19 are used to calculate the right side of the equation (5-2). Thus, a new estimated value Twa (k + 1) of the exhaust pipe temperature Twa is obtained.

  Note that the estimated values of the exhaust gas temperature Tga and the exhaust pipe temperature Twa are determined as follows when the engine 1 is started (started) and the atmospheric temperature TA detected at that time is the initial value Tga (0), Twa. Is set as (0), and the initial values Tga (0) and Twa (0) are respectively calculated when the calculations of the equations (5-1) and (5-2) are performed for the first time after the engine 1 is started. Used as values of Tga (k-1) and Twa (k-1).

  Next, the exhaust temperature observer 19 calculates an estimated value of the exhaust gas temperature Tgb and an estimated value of the exhaust pipe temperature Twb in the partial exhaust passage 3b based on the equations (6-1) and (6-2) (STEP 16). -4). That is, the current value Tgb (k) of the estimated value of the exhaust gas temperature Tgb (the value obtained in STEP16-4 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twb (STEP16− at the previous cycle time). 4), the current value of the estimated value of the exhaust gas temperature Tga previously calculated in STEP 16-3, the current value of the flow velocity parameter Vg calculated in STEP 16-1, and a predetermined model coefficient A new estimated value Tgb (k + 1) of the exhaust gas temperature Tgb is obtained by calculating the right side of the equation (6-1) using the value of Ab and the value of the processing period dt of the exhaust gas temperature observer 19. Ask.

  Further, the current value Tgb (k) of the estimated value of the exhaust gas temperature Tgb (the value obtained in STEP16-4 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twb (STEP16- at the previous cycle time). 4), the value of model coefficients Bb and Cb determined in advance, and the value of the cycle dt of the processing of the exhaust temperature observer 19 are used to calculate the right side of the equation (6-2). Thus, a new estimated value Twb (k + 1) of the exhaust pipe temperature Twb is obtained.

  Note that the estimated values of the exhaust gas temperature Tgb and the exhaust pipe temperature Twb are the initial values Tgb (0), Twb of the atmospheric temperature TA detected at the time of starting the engine 1 (starting) as described above. Is set as (0), and when the calculations of equations (6-1) and (6-2) are performed for the first time after the operation of the engine 1 is started, their initial values Tgb (0) and Twb (0) are respectively set. Used as values of Tgb (k-1) and Twb (k-1).

  Next, the exhaust temperature observer 19 calculates an estimated value of the exhaust gas temperature Tgc and an estimated value of the catalyst temperature Twc in the partial exhaust passage 3c based on the equations (8-1) and (8-2) (STEP 16- 5). That is, the current value Tgc (k) of the estimated value of the exhaust gas temperature Tgc (the value obtained in STEP16-5 at the previous cycle time) and the current value of the estimated value of the catalyst temperature Twc (STEP16-5 at the previous cycle time) The current value of the estimated value of the exhaust gas temperature Tgb previously calculated in STEP 16-4, the current value of the flow velocity parameter Vg calculated in STEP 16-1, and a predetermined model coefficient Ac. And the value of the period dt of the processing of the exhaust gas temperature observer 19 are used to calculate the right side of the equation (8-1) to obtain a new estimated value Tgc (k + 1) of the exhaust gas temperature Tgc. .

  Further, the current value Tgc (k) of the estimated value of the exhaust gas temperature Tgc (the value obtained in STEP16-5 at the previous cycle time) and the current value of the estimated value of the catalyst temperature Twc (STEP16-5 at the previous cycle time) The current value of the flow velocity parameter Vg calculated in STEP 16-1, the values of the model coefficients Bc, Cc, Dc and the value of the processing period dt of the exhaust gas temperature observer 19 determined in advance. The new estimated value Twc (k + 1) of the catalyst temperature Twc is obtained by calculating the right side of the equation (8-2).

  As described above, the estimated values of the exhaust gas temperature Tgc and the catalyst temperature Twc are the initial values Tgc (0), Twc ( 0), and when the calculations of equations (8-1) and (8-2) are performed for the first time after the engine 1 is started, their initial values Tgc (0) and Twc (0) are respectively set to Tgc. Used as the value of (k-1), Twc (k-1).

Next, the exhaust gas temperature observer 19 calculates the estimated value of the exhaust gas temperature Tgd in the partial exhaust passage 3d (in the vicinity of the location where the O ₂ sensor 8 is disposed) based on the equations (9-1) and (9-2) and An estimated value of the exhaust pipe temperature Twd is calculated (STEP 16-6). That is, the current value Tgd (k) of the estimated value of the exhaust gas temperature Tgd (the value obtained in STEP 16-6 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twd (STEP 16- at the previous cycle time). 6), the current value of the estimated value of the exhaust gas temperature Tgc previously calculated in STEP 16-5, the current value of the flow velocity parameter Vg calculated in STEP 16-1, and a predetermined model coefficient A new estimated value Tgd (k + 1) of the exhaust gas temperature Tgd is obtained by calculating the right side of the equation (9-1) using the value of Ad and the value of the processing period dt of the exhaust gas temperature observer 19. Ask.

  Further, the current value Tgd (k) of the estimated value of the exhaust gas temperature Tgd (the value obtained in STEP 16-6 at the previous cycle time) and the current value of the estimated value of the exhaust pipe temperature Twd (STEP 16- at the previous cycle time). 6) and the value of the model coefficients Bd and Cd determined in advance and the value of the cycle dt of the processing of the exhaust temperature observer 19 are used to calculate the right side of the equation (9-2). Thus, a new estimated value Twd (k + 1) of the exhaust pipe temperature Twd is obtained.

  Note that the estimated values of the exhaust gas temperature Tgd and the exhaust pipe temperature Twd are the initial values Tgd (0), Twd at the start of the operation of the engine 1 (starting) as described above. Is set as (0), and the initial values Tgd (0) and Twd (0) are respectively calculated when the equations (9-1) and (9-2) are calculated for the first time after the engine 1 is started. Used as values of Tgd (k-1) and Twd (k-1).

Next, the sensor temperature control means 12 executes the processing of STEP 16-7 by the element temperature observer 20, and the estimated values of the element temperature T _O2 and the heater temperature Tht of the O ₂ sensor 8 are calculated by the above equation (10-1), Obtained based on (10-2). That is, the current value T _O2 (k) of the estimated value of the element temperature T _O2 (value obtained in STEP 16-7 in the previous cycle time) and the current value Tht (k) of the estimated value of the heater temperature Tht (the previous value) (The value obtained in STEP16-7 in the cycle time), the current value of the estimated value of the exhaust gas temperature Tgd previously calculated in STEP6-6, the values of the predetermined model coefficients Ax and Bx, and the element temperature observer The new estimated value T _O2 of the element temperature T _O2 is calculated by performing the calculation of the right side of the equation (10-1) using the value of the processing cycle dt of 20 (= the processing cycle of the exhaust temperature observer 19). Find (k + 1).

Further, the current value T _O2 (k) of the estimated value of the element temperature T _O2 (the value obtained in STEP 16-7 at the previous cycle time) and the current value Tht (k) of the estimated value of the heater temperature Tht (the previous value) (The value obtained in STEP16-7 in the cycle time), the current value DUT (k) of the duty DUT, the values of the model coefficients Cx and Dx determined in advance, and the value of the cycle dt of the process of the element temperature observer 20 A new estimated value Tht (k + 1) of the heater temperature Tht is obtained by using the calculation of the right side of the equation (10-2).

Note that the estimated values of the element temperature T _O2 and the heater temperature Tht are the initial values T _O2 (0), the atmospheric temperature TA detected at the start of the operation of the engine 1 (starting) as described above. It is set as Tht (0), and when the calculations of the equations (10-1) and (10-2) are performed for the first time after the engine 1 starts operation, their initial values T _O2 (0), Tht (0) Are used as the values of T _O2 (k-1) and Tht (k-1), respectively. Further, the duty DUT (k) used in the equation (10-2) is basically the latest value obtained by the heater controller 22 in STEP 5 described above. However, when the value of the duty DUT is limited to “0” in STEP 12 (when the power supply to the heater 13 is cut off), the value is used in the equation (10-2).

The processing of the sensor temperature control means 12 described above, electric power supplied to the heater 13 of the O ₂ sensor 8 as the element temperature T _O2 of the O ₂ sensor 8 is maintained at the target value R is controlled. In this case, the target value R is normally set to 800 ° C., except immediately after the start of operation of the engine 1 or when the atmospheric temperature TA is considerably low. As a result, the output characteristic of the O ₂ sensor 8 can be stably maintained at a characteristic suitable for the air-fuel ratio control of the engine 1 (air-fuel ratio control for ensuring good purification performance by the catalyst device 4). The air-fuel ratio control can be performed satisfactorily, and the good purification performance of the catalyst device 4 can be reliably maintained.

In this reference example, the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is arranged is estimated by the exhaust gas temperature observer 19, and the exhaust gas is used to calculate the duty DUT for controlling the heater 13 to be energized by the heater controller 22. An estimate of the temperature Tgd is used. More specifically, the duty DUT as a control input for the control object of the heater controller 22 is a control input component (the first term (Σe () in the equation (24)) corresponding to the element temperature T _O2 (estimated value in this reference example). The term including j) and the second term (term including e (n))), as well as the control input component corresponding to the estimated value of the exhaust gas temperature Tgd which is a disturbance factor of the fluctuation of the element temperature T _O2 , that is, , Calculated as including the optimum disturbance F / F component Uopfd. The coefficient Fdt related to the optimum disturbance F / F component Uopfd is determined by the predictive control algorithm assuming that the current exhaust gas temperature continues until the exhaust gas temperature prediction time Md. As a result, the stability of the control of the element temperature T _{O2 to} the target value R can be effectively increased, and consequently the stability of the output characteristics of the O ₂ sensor 8 can be effectively increased.

Furthermore, in this reference example, the control input component corresponding to the target value R of the element temperature T _O2 (the target value R from the present to the target value prediction time Mr), that is, the optimum target value F / F component Uopfr The control input DUT is calculated including the components. For this reason, especially when the target value R is switched from the low temperature side temperature (600 ° C.) immediately after the start of operation of the engine 1 to the normal high temperature side temperature (750 ° C. to 800 ° C.), the control input DUT temporarily changes. It is possible to prevent an excessive increase (the element temperature T _O2 causes an overshoot with respect to the target value R). This also effectively increases the stability of the output characteristics of the O ₂ sensor 8.

Further, in the exhaust gas temperature Tgd estimation process, the exhaust passage 3 from the exhaust port 2 to the location where the O ₂ sensor 8 is disposed is divided into a plurality of partial exhaust passages 3a to 3d. Then, the exhaust gas temperature Texg at the exhaust port 2 of the engine 1 as the entrance of the partial exhaust passage 3a on the most upstream side is estimated using the detected values of the rotational speed NE and the intake pressure PB as parameters representing the operating state of the engine 1. In addition, the exhaust gas temperatures Tga, Tgb, Tgc, and Tgd of the partial exhaust passages 3a to 3d are upstream using the estimated values of the exhaust gas temperatures Texg, Tga, Tgb, and Tgc on the upstream side of the partial exhaust passages 3a to 3d. Estimated in order from the side. Further, at this time, heat transfer between the passage formation (exhaust pipe 6a, catalyst 7 of the catalyst device 4 and exhaust pipe 6b) forming the partial exhaust passages 3a to 3d and the exhaust gas, and from the passage formation to the atmosphere. The exhaust gas temperatures Tga, Tgb, Tgc, and Tgd are estimated together with the temperatures of the passages formed in the partial exhaust passages 3a to 3d (exhaust pipe temperatures Twa, Twb, Twd, and catalyst temperature Twc). In addition, in the estimation of the catalyst temperature Twc, the heat generation of the catalyst 7 of the catalyst device 4 is also taken into consideration. As a result, the estimated values of the exhaust gas temperatures Texg, Tga, Tgb, Tgc, and Tgd can be obtained in order and with high accuracy.

Thus, the estimated values of the exhaust gas temperatures Texg, Tga, Tgb, Tgc, Tgd, particularly the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is arranged can be accurately estimated. The optimum disturbance F / F component Uopfd corresponding to the above is suitable for compensating for the variation of the element temperature T _O2 due to the variation of the exhaust gas temperature Tgd. As a result, it is possible to satisfactorily control the element temperature T _{O2 to} the target value R.

In this reference example, the exhaust passage 3 from the exhaust port 2 to the location where the O ₂ sensor 8 is disposed is divided into four partial exhaust passages 3a to 3d, but the number of divisions is not necessarily four. However, it may be set as appropriate according to the length and layout of the exhaust system, the accuracy of the required estimated value, the calculation load, and the like. For example, the exhaust passage 3 in the portion of the exhaust pipe 6a may be divided into three or more, or the exhaust passage 3 in the portion of the catalyst device 4 may be divided into two or more.

In this reference example, the engine 1 is used as an initial value of the estimated values of the exhaust gas temperatures Texg, Tga, Tgb, Tgc, Tgd, exhaust pipe temperatures Twa, Twb, Twd, catalyst temperature Twc, element temperature T _O2 , and heater temperature Tht. However, the engine temperature at the start of operation of the engine 1 or the like may be used as the initial value, or depending on the atmospheric temperature TA and the engine temperature, the atmospheric temperature TA detected at the start of the operation may be used. An initial value may be set. Further, the initial value may be set such that the atmospheric temperature is used when the engine 1 is normally started, and the engine temperature is used when the engine 1 is restarted soon after the operation is stopped. The same applies to other reference examples and embodiments described later.

  Next, a first embodiment of the present invention will be described with reference to FIGS. In addition, since other embodiments to be described later including this embodiment are different from the above-described reference example only in a part of the configuration or function, the same configuration part or the same function part is that of the reference example. Detailed description will be omitted using the same reference numerals.

In the present embodiment, as shown in FIG. 12, an exhaust gas temperature sensor 29 for detecting the exhaust gas temperature Tx is attached to an intermediate portion of the exhaust pipe 6 a of the exhaust passage 3, and the exhaust gas temperature sensor 29 detects the exhaust gas temperature Tx. The value is given to the sensor temperature control means 12 (more specifically, the exhaust gas temperature observer 19) of the control unit 10 for the process of estimating the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed. The exhaust gas temperature sensor 29 does not have to be dedicated to the control process of the element temperature T _O2 of the O ₂ sensor 8, and has a purpose other than the control of the element temperature T _O2 (for example, enrichment of the air-fuel ratio). For example, it may be an existing one provided for the purpose of controlling exhaust gas temperature for catalyst protection.

In the present embodiment, the exhaust gas temperature observer 19 of the sensor temperature control means 12 uses the detected value of the exhaust gas temperature Tx by the exhaust gas temperature sensor 29, and the exhaust gas near the location where the O ₂ sensor 8 is disposed as described below. The temperature Tgd is estimated.

That is, in the present embodiment, the exhaust passage 3 from the place where the exhaust gas temperature sensor 29 is arranged to the place where the O ₂ sensor 8 is arranged is divided into three partial exhaust passages 3b to 3d. The partial exhaust passages 3c and 3d are the same as those in the reference example, and the partial exhaust passages 3b are the same as those in the reference example, or only differ in length. Corresponding to these three partial exhaust passages 3b to 3d, the algorithm of the exhaust temperature observer 19 is expressed by the above-described equations (6-1) and (6-2) as shown in FIG. The CAT pre-exhaust system thermal model 26 represented, the CAT part exhaust system thermal model 27 represented by the model expressions of the equations (8-1) and (8-2), and the equations (9-1) and (9 -2) and a post-CAT exhaust system heat model 28 represented by the model formula.

  In this case, as is apparent from comparison with the block diagram of FIG. 6, the algorithm of the exhaust system observer 19 in this embodiment includes the exhaust port thermal model 24 and the pre-CAT exhaust system thermal model 25 of the reference example. It is not done. In the present embodiment, the pre-CAT exhaust system thermal model 26 is provided with the detected value Tx of the exhaust gas temperature by the exhaust gas temperature sensor 29 as the value of “Tga” used for the calculation of the equation (6-1). This is the only difference from the algorithm of the exhaust temperature observer 19 of the reference example. That is, in the present embodiment, the pre-CAT exhaust system thermal model 26 uses the detected value Tx (latest value) of the exhaust gas temperature by the exhaust gas temperature sensor 29 as the value of “Tga” in Equation (6-1), The estimated value of the exhaust gas temperature Tgb at the downstream end of the exhaust passage 3b is sequentially obtained.

The processing of the sensor temperature control means 12 other than that described above is the same as that of the reference example. This embodiment differs from the above reference example only in that the detected value Tx of the exhaust gas temperature by the exhaust gas temperature sensor 29 is used to estimate the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed. It is. Also in the present embodiment, the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is arranged can be estimated appropriately and accurately. Therefore, the same effect as the reference example can be obtained.

In addition, although the said 1st Embodiment demonstrated the case where the exhaust gas temperature sensor 29 was provided in the intermediate part of the exhaust pipe 6a, this exhaust gas temperature sensor 29 may be provided in another location. For example, as shown in FIG. 14A, when an exhaust gas temperature sensor 29 for detecting an exhaust gas temperature Tx in the vicinity of the exhaust port 2 of the engine 1 is provided (second embodiment), FIG. The exhaust port heat model 24 is omitted, and the detected value (latest value) of the exhaust gas temperature Tx by the exhaust gas temperature sensor 29 is used as the value of “Texg” used in the calculation of the above equation (5-1). The heat model 25 is given. Thereby, the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed can be estimated.

Further, for example, as shown in FIG. 14B, when the exhaust gas temperature sensor 29 for detecting the exhaust gas temperature Tx in the vicinity of the entrance of the catalyst device 4 is provided (third embodiment), the exhaust gas shown in FIG. The port heat model 24 and the pre-CAT exhaust system heat models 25 and 26 are omitted, and the detected value (latest value) of the exhaust gas temperature Tx by the exhaust gas temperature sensor 29 is used for the calculation of the equation (8-1) “Tgb Is given to the CAT part exhaust system thermal model 27 as a value of "". Thereby, the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed can be estimated.

Further, for example, as shown in FIG. 14C, when an exhaust gas temperature sensor 29 for detecting an exhaust gas temperature Tx in the vicinity of the outlet of the catalyst device 4 is provided (fourth embodiment), the exhaust gas shown in FIG. The port heat model 24, the pre-CAT exhaust system heat models 25 and 26, and the CAT part exhaust system heat model 27 are omitted, and the detected value (latest value) of the exhaust gas temperature Tx by the exhaust gas temperature sensor 29 is expressed by the above equation (9− As the value of “Tgc” used in the calculation of 1), it is given to the exhaust system heat model 28 after CAT. Thereby, the exhaust gas temperature Tgd in the vicinity of the location where the O ₂ sensor 8 is disposed can be estimated.

  In any case of the second to fourth embodiments, other processes of the sensor temperature control means 12 (processes other than the process of estimating the exhaust gas temperature Tgd) may be the same as those in the reference example.

Although detailed description in the present specification is omitted, even if the exhaust gas temperature sensor is provided on the downstream side of the O ₂ sensor 8, the detected value of the exhaust gas temperature by the exhaust gas temperature sensor is used. It is also possible to estimate the exhaust gas temperature in the vicinity of the location where the _two sensors 8 are arranged. That is, as can be seen from the equation (4-1), if the exhaust gas temperature Tg (z) at the exhaust passage position z (exhaust gas flow direction position) is detected and grasped, the position is calculated in reverse. It is possible to estimate the exhaust gas temperature Tg (z-Δz) at a position z-Δz upstream of z. Therefore, it is possible to use the detection value of the exhaust gas temperature by the exhaust gas temperature sensor provided downstream of the O ₂ sensor 8, estimates the exhaust gas temperature in the vicinity of the location of the O ₂ sensor 8.

Further, in each of the embodiments described above, the temperature of the element unit 10 of the O ₂ sensor 8 is controlled to the target value R by the optimal predictive control algorithm, but other control algorithms (for example, normal PI control or The control input DUT may be generated by an algorithm that generates a control input DUT including a feedforward component corresponding to the exhaust gas temperature Tgd in the PID control.

In each of the above embodiments, the element temperature T _O2 of the O ₂ sensor 8 and the heater temperature Tht are estimated, but both of them may be detected directly by the temperature sensor. Alternatively, either one may be directly detected by a temperature sensor and the other may be estimated using the detected value.

In each of the above embodiments, the case where the element temperature T _O2 of the O ₂ sensor 8 is controlled has been described as an example. However, an exhaust gas sensor other than the O ₂ sensor 8 (for example, the wide-area air-fuel ratio sensor 9 or the moisture of the exhaust gas). It goes without saying that the present invention can also be applied to a humidity sensor or the like that generates an output corresponding to the content. In this case, an algorithm for estimating the exhaust gas temperature in the vicinity of the location of the exhaust gas sensor may be appropriately constructed depending on the location of the exhaust gas sensor. For example, when the exhaust gas sensor is arranged in the middle of the exhaust pipe 6a in FIG. 1R> 1, the thermal model of the above formula (1) and formulas (5-1) and (5-2) is used. The exhaust gas temperature in the vicinity of the location where the exhaust gas sensor is disposed can be estimated.

  Here, as the internal combustion engine, the present invention can be applied to a normal port injection internal combustion engine, an in-cylinder direct injection type spark ignition internal combustion engine, a diesel engine, and an internal combustion engine for an outboard motor. Needless to say.

The block diagram which shows the whole structure of the apparatus of the reference example relevant to embodiment of this invention. Sectional view showing the structure of the O ₂ sensor (exhaust gas sensor) provided in the apparatus of FIG 1. Graph showing the output characteristic of the O ₂ sensor in FIG. The block diagram which shows the functional structure of the sensor temperature control means with which the apparatus of FIG. 1 was equipped. Sectional drawing for demonstrating the process of the exhaust temperature observer with which the sensor temperature control means of FIG. 5 was equipped. The block diagram which shows the functional structure of the exhaust temperature observer with which the sensor temperature control means of FIG. 5 was equipped. The block diagram which shows the functional structure of the heater controller with which the sensor temperature control means of FIG. 5 was equipped. The flowchart which shows the whole process of the sensor temperature control means with which the apparatus of FIG. 1 was equipped. 9 is a flowchart showing subroutine processing of the flowchart of FIG. 9 is a flowchart showing subroutine processing of the flowchart of FIG. 9 is a flowchart showing subroutine processing of the flowchart of FIG. 1 is a block diagram showing the overall configuration of an apparatus according to a first embodiment of the present invention. The block diagram which shows the functional structure of the exhaust temperature observer with which the sensor temperature control means of the apparatus of FIG. 12 was equipped. (A) The block diagram which shows the principal part structure of the apparatus of 2nd Embodiment of this invention.

  (B) The block diagram which shows the principal part structure of the apparatus of 3rd Embodiment of this invention.

  (C) The block diagram which shows the principal part structure of the apparatus of 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 2 ... Exhaust port, 3 ... Exhaust passage, 3a-3d ... Partial exhaust passage, 6a, 6b ... Exhaust pipe (passage formation), 7 ... Catalyst (passage formation), 8 ... O ₂ sensors (exhaust gas sensors), 10 elements, 13 heaters, 19 exhaust gas temperature observers (exhaust gas temperature estimating means), 22 heater controllers (heater control means), 29 exhaust gas temperature sensors.

Claims (21)

A temperature control device for an exhaust gas sensor, which is disposed in an exhaust passage of an internal combustion engine and has an element portion that contacts exhaust gas flowing through the exhaust passage and a heater that heats the element portion,
In order to detect the temperature of the exhaust gas flowing through the exhaust passage, an exhaust gas temperature sensor disposed at a location separated from the exhaust gas sensor in the exhaust gas flow direction in the exhaust passage;
Exhaust gas temperature estimation means for sequentially estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using at least the detected value of the exhaust gas temperature by the exhaust gas temperature sensor and data representing the flow rate of the exhaust gas;
A heater control means for controlling the heater so that the temperature of the element portion of the exhaust gas sensor becomes a predetermined target temperature by using an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor. An exhaust gas sensor temperature control device.   The exhaust gas temperature estimating means divides the exhaust passage from the vicinity of the exhaust gas temperature sensor to the vicinity of the exhaust gas sensor into a plurality of partial exhaust passages along the flow direction of the exhaust gas. Among the partial exhaust passages, the exhaust gas temperature of the partial exhaust passage closest to the exhaust gas temperature sensor is estimated using at least the detected value of the exhaust gas temperature by the exhaust gas temperature sensor and data representing the flow rate of the exhaust gas, and the exhaust gas temperature Exhaust gas temperature in each partial exhaust passage other than the partial exhaust passage closest to the sensor, at least an estimated value of the exhaust gas temperature in the partial exhaust passage adjacent to the partial exhaust passage on the exhaust gas temperature sensor side, and data representing the exhaust gas flow rate Estimated value of the temperature of the exhaust gas in the partial exhaust passage closest to the exhaust gas sensor. Temperature control of the exhaust gas sensor according to claim 1, wherein the obtaining the estimated value of the temperature of the exhaust gas in the vicinity.   The exhaust gas temperature estimation means is based on an estimation algorithm constructed in consideration of heat transfer between a passage formation forming an exhaust passage in the vicinity of the location where the exhaust gas sensor is disposed and exhaust gas flowing in the passage formation. The exhaust gas sensor temperature control apparatus according to claim 1 or 2, wherein the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated.   The exhaust gas temperature estimation means considers heat transfer between a passage formation that forms an exhaust passage from the vicinity of the exhaust gas sensor to a vicinity of the exhaust gas temperature sensor and the exhaust gas flowing through the passage formation. The exhaust gas sensor temperature control apparatus according to claim 1, wherein the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated by an estimation algorithm constructed as described above.   The exhaust gas temperature estimation means uses an estimation algorithm constructed in consideration of heat transfer between the passage formation forming the partial exhaust passage and the exhaust gas flowing through the passage formation. The temperature control device for an exhaust gas sensor according to claim 2, wherein the temperature is estimated.   The exhaust gas temperature estimating means is provided in the vicinity of the location of the exhaust gas sensor by an estimation algorithm constructed in consideration of heat radiation from the passage formation forming the exhaust passage in the vicinity of the location of the exhaust gas sensor to the outside atmosphere. The temperature control device for an exhaust gas sensor according to any one of claims 1 to 5, wherein the temperature of the exhaust gas is estimated.   The exhaust gas temperature estimation means is an estimation algorithm constructed in consideration of heat radiation from a passage formation forming an exhaust passage from the vicinity of the exhaust gas temperature sensor to the vicinity of the exhaust gas temperature sensor to the outside atmosphere. The temperature control device for an exhaust gas sensor according to any one of claims 1 to 5, wherein the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed is estimated.   The exhaust gas temperature estimation means estimates the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor by an estimation algorithm constructed in consideration of heat radiation from the passage formation forming the partial exhaust passage to the outside atmosphere. The temperature control device for an exhaust gas sensor according to claim 2 or 5.   The exhaust passage from the vicinity of the exhaust gas sensor arrangement location to the vicinity of the exhaust gas temperature sensor arrangement location contains a catalyst for exhaust gas purification as a passage formation that forms part of the exhaust passage, and the exhaust gas temperature estimation 9. The apparatus according to claim 1, wherein the means estimates the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is arranged by an estimation algorithm constructed in consideration of heat generation of the catalyst. Exhaust gas sensor temperature control device.   At least one of the plurality of partial exhaust passages includes an exhaust gas purifying catalyst as a passage formation forming the partial exhaust passage, and the exhaust gas temperature estimating means includes the partial exhaust passage including the catalyst. The exhaust gas sensor temperature control apparatus according to any one of claims 2, 5, and 8, wherein the temperature of the exhaust gas is estimated by an estimation algorithm constructed in consideration of heat generation of the catalyst.   The exhaust gas temperature estimating means sequentially acquires data representing the temperature of a passage formation forming an exhaust passage at least in the vicinity of the location where the exhaust gas sensor is disposed, and uses the data representing the temperature of the passage formation to obtain the exhaust gas. The exhaust gas sensor temperature control device according to any one of claims 1 to 10, wherein the temperature of the exhaust gas in the vicinity of the sensor location is estimated.   The exhaust gas temperature estimating means sequentially acquires data representing the temperature of the passage formation forming the partial exhaust passages, while using the data representing the temperature of the passage formation forming the partial exhaust passages. 3. The exhaust gas sensor temperature control apparatus according to claim 2, wherein the temperature of the exhaust gas in the passage is estimated.   The exhaust gas temperature estimating means includes at least a temperature change amount per predetermined time of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed, a temperature gradient in the flow direction of the exhaust gas in the vicinity of the location where the exhaust gas sensor is disposed, and a flow rate of the exhaust gas. Of the exhaust gas sensor based on a thermal model expressed as the sum of the temperature change component according to the temperature difference and the temperature change component according to the deviation between the temperature of the exhaust gas near the location where the exhaust gas sensor is located and the temperature of the passage formation. The exhaust gas temperature change amount in the vicinity of the exhaust gas sensor is sequentially obtained, and the obtained temperature change amount is cumulatively added to the initial value set at the start of operation of the internal combustion engine. The temperature control apparatus for an exhaust gas sensor according to claim 11, wherein the temperature is estimated.   The exhaust gas temperature estimation means includes a temperature change component according to a temperature gradient in a flow direction of the exhaust gas in the partial exhaust passage and a flow rate of the exhaust gas, and a temperature change amount per predetermined time of the exhaust gas in each partial exhaust passage. The temperature change of the exhaust gas in each partial exhaust passage based on a thermal model expressed as the sum of the temperature change component corresponding to the deviation between the temperature of the exhaust gas in the partial exhaust passage and the temperature of the passage formation in the partial exhaust passage The amount of temperature change is sequentially obtained, and the obtained temperature change amount is cumulatively added to the initial value set at the start of operation of the internal combustion engine for each partial exhaust passage, thereby estimating the temperature of the exhaust gas in each partial exhaust passage. 13. The exhaust gas sensor temperature control device according to claim 12,   The exhaust gas temperature estimating means sequentially estimates the temperature of the passage formation using at least the estimated value of the temperature of the exhaust gas in the vicinity of the location where the exhaust gas sensor is located and the data representing the atmospheric temperature outside the passage formation, The exhaust gas sensor temperature control device according to claim 11 or 13, wherein an estimated value of the temperature of the passage formation is used as the data representing the temperature of the passage formation.   The exhaust gas temperature estimation means forms each partial exhaust passage by using at least an estimated value of the exhaust gas temperature of each partial exhaust passage and data representing the atmospheric temperature outside the passage formation forming the partial exhaust passage. 15. The temperature of the passage formation is sequentially estimated, and the estimated value of the temperature of the passage formation forming each partial exhaust passage is used as the data representing the temperature of the passage formation. Exhaust gas sensor temperature control device.   The exhaust gas temperature estimation means has a temperature change component according to a deviation between at least the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the temperature of the channel formation, so that the temperature change amount per predetermined time of the passage formation is And the temperature change amount of the passage formation based on a thermal model expressed as including a temperature change component corresponding to a deviation between the temperature of the passage formation and the atmospheric temperature, and the temperature change amount The exhaust gas sensor temperature control device according to claim 15, wherein the temperature of the passage formation is estimated by cumulatively adding the estimated value of the passage to an initial value set at the start of operation of the internal combustion engine.   In the exhaust gas temperature estimation means, the temperature change amount per predetermined time of the passage formation forming each partial exhaust passage is at least the temperature of the exhaust gas in the partial exhaust passage and the temperature of the passage formation forming the partial exhaust passage. And the temperature change amount of the passage formation based on a thermal model expressed as including a temperature change component according to the deviation of the passage formation and a temperature change component according to the deviation between the temperature of the passage formation and the atmospheric temperature. Are sequentially estimated, and the estimated value of the temperature change amount is cumulatively added to the initial value set at the start of operation of the internal combustion engine for each partial exhaust passage passage formation, thereby the temperature of the passage formation in each partial exhaust passage. The temperature control device for an exhaust gas sensor according to claim 16, wherein   At least one of the plurality of partial exhaust passages includes an exhaust gas purifying catalyst as a passage formation forming the partial exhaust passage, and the thermal model corresponding to the partial exhaust passage including the catalyst is: A temperature change component according to a deviation between the temperature of the exhaust gas in the partial exhaust passage and the temperature of the passage formation forming the partial exhaust passage; 19. A model expressed as a sum of a temperature change component according to a deviation between the temperature of the passage formation and the atmospheric temperature and a temperature change component according to a flow rate of exhaust gas. Exhaust gas sensor temperature control device.   The initial value is set according to at least the atmospheric temperature at the start of operation of the internal combustion engine and / or the engine temperature of the internal combustion engine, and any one of claims 13 and 14, and 17-19. The exhaust gas sensor temperature control device according to claim 1.   The heater control means sequentially obtains data representing the temperature of the element part of the exhaust gas sensor, and inputs a control input to the heater, at least an input component corresponding to the temperature of the element part of the exhaust gas sensor, and the exhaust gas temperature estimation 21. The control input component according to the estimated value of the exhaust gas temperature by the means is added and sequentially calculated, and the heater is controlled according to the calculated control input. The exhaust gas sensor temperature control device according to claim 1.

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