JP4613893B2 - Internal combustion engine exhaust gas purification catalyst temperature estimation device - Google Patents

Description

  The present invention relates to an exhaust purification catalyst temperature estimation device for an internal combustion engine.

  An exhaust purification catalyst used in an internal combustion engine is inactive at a low temperature immediately after the start of the internal combustion engine. Therefore, in order to determine the deterioration state of the exhaust purification catalyst, it is necessary to determine the purification ability of the exhaust purification catalyst after the exhaust purification catalyst temperature has sufficiently increased due to the amount of heat of the exhaust. For this reason, it is important to accurately estimate the exhaust purification catalyst temperature. As a technique for this purpose, a technique for estimating the exhaust purification catalyst temperature (catalyst bed temperature) based on the amount of heat given from the exhaust or the heat generated by the catalytic reaction is known (see, for example, Patent Document 1).

In such an exhaust purification catalyst, the upper limit value of the estimated temperature is set in accordance with the internal combustion engine speed and the intake pressure in order to determine the catalyst temperature with high accuracy, particularly from the viewpoint of preventing a high temperature leading to melting damage. The technique which performs is known (for example, refer patent document 2). There is also known a technique for calculating an estimated temperature at a rate of increase corresponding to an operation region (see, for example, Patent Document 3).
Japanese Patent Laying-Open No. 2004-60563 (page 6-7, FIG. 5) Japanese Patent Laid-Open No. 4-1437 (5th page, FIG. 4) JP 2006-37834 A (page 4, FIG. 2)

  However, in the methods of Patent Documents 2 and 3 for obtaining the catalyst temperature with high accuracy in this way, both the upper limit value of the estimated temperature and the rate of increase corresponding to the operation region are based on the exhaust temperature value. It does not consider that there is a limit to the heat transfer between the exhaust and the catalyst. That is, even if the exhaust temperature increases, the heat transfer coefficient does not increase corresponding to the increase in temperature, and the catalyst does not simply increase in temperature.

  For this reason, even if the exhaust gas temperature rises rapidly, a phenomenon that the catalyst temperature does not rise so much occurs. Therefore, in the prior art, it is easy to estimate the catalyst temperature higher than the actual temperature especially when the catalyst temperature rises. For this reason, it is estimated that the catalyst temperature is still low and activated despite not being fully activated, and various processes may be executed on the assumption that the catalyst activation is completed. This also applies to the case where the exhaust temperature is lowered, and the catalyst temperature does not decrease so much even if the exhaust temperature rapidly decreases.

  Further, when the catalyst is overheated, there is a case where processing is performed to increase the fuel and enrich the air-fuel ratio to lower the exhaust temperature. Small compared to stoiki. Therefore, in the conventional technique that does not consider enrichment, it is easy to estimate the temperature higher than the actual temperature especially when the catalyst temperature rises.

  An object of the present invention is to calculate the estimated catalyst temperature with high accuracy by taking into consideration heat transfer between the exhaust gas of the internal combustion engine and the exhaust purification catalyst, or taking into account enrichment of the air-fuel ratio. is there.

In the following, means for achieving the above object and its effects are described.
The exhaust purification catalyst temperature estimation device for an internal combustion engine according to claim 1 is an exhaust purification catalyst temperature estimation device for an internal combustion engine that estimates the temperature of the exhaust purification catalyst on the basis of the operating state of the internal combustion engine, the exhaust flow rate or the exhaust gas A catalyst estimated temperature calculating means for calculating a catalyst temperature change amount based on a physical quantity reflecting the flow rate and a previously estimated catalyst estimated temperature, and calculating a catalyst estimated temperature using the catalyst temperature change amount; and Estimated temperature change limit setting means for limiting the amount of catalyst temperature change calculated by the temperature calculation means , and the estimated temperature change limit setting means includes the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and the previously calculated catalyst. An upper limit is provided for the amount of change in catalyst temperature based on the estimated temperature .

  The estimated catalyst temperature calculated by the estimated catalyst temperature calculating means is calculated by using the catalyst temperature change amount. The catalyst temperature change amount is a value calculated based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and the estimated catalyst temperature calculated last time. The amount of change in catalyst temperature is related to the transfer of heat by heat transfer between the exhaust and the exhaust purification catalyst. This heat transfer is not simply determined by the temperature difference between the exhaust and the exhaust purification catalyst, and since the exhaust flows at a high speed, there is a limit to the amount of heat exchanged with the exhaust purification catalyst. is there.

  Therefore, instead of determining the catalyst temperature change amount only by the temperature difference between the exhaust gas and the exhaust purification catalyst, it is possible to reflect the heat transfer limit by setting a limit on the catalyst temperature change amount.

For this reason, compared with the case where the amount of change in the catalyst temperature is determined only by the temperature difference between the exhaust gas and the exhaust gas purification catalyst, the change rate of the estimated catalyst temperature is not unlimited and is a change close to reality. Thus, by setting a limit on the amount of change in catalyst temperature, heat transfer between the exhaust gas and the exhaust purification catalyst can be taken into consideration, and the estimated catalyst temperature can be calculated with high accuracy.
In addition, especially when it is desired to detect the purification ability by capturing the timing when the exhaust purification catalyst is activated, it is determined that the temperature is actually low and inactive, but the temperature is calculated and activated. I want to avoid. For this reason, by setting an upper limit on the amount of change in the catalyst temperature, it is possible to prevent at least the estimated catalyst temperature from overshooting and prevent the estimated catalyst temperature from showing an active temperature for the exhaust purification catalyst in an inactive temperature state. it can.

  The exhaust gas purification catalyst temperature estimation device for an internal combustion engine according to claim 2, wherein the estimated catalyst temperature calculation means includes the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously calculated estimated catalyst temperature. The estimated catalyst temperature using one or both of the catalyst temperature change amount of the catalyst temperature change amount due to heat release from the exhaust purification catalyst and the catalyst temperature change amount due to the catalytic reaction in the exhaust purification catalyst Is calculated.

  In order to calculate the estimated catalyst temperature in this way, in addition to the catalyst temperature change amount based on the exhaust flow rate or the physical quantity and the previously estimated catalyst temperature, the catalyst temperature change amount due to heat release from the exhaust purification catalyst and the exhaust gas One or both of the catalyst temperature change amounts of the catalyst temperature change amount due to the catalytic reaction in the purification catalyst may be used. As a result, the estimated catalyst temperature can be calculated with higher accuracy.

Exhaust purifying catalyst temperature estimation equipment of an internal combustion engine according to claim 3 is the exhaust gas purifying catalyst temperature estimating apparatus for an internal combustion engine for estimating the temperature of the exhaust purification catalyst based on the operating state of the internal combustion engine, the exhaust flow rate or A catalyst temperature change amount is calculated based on a physical quantity reflecting the exhaust gas flow rate and a previously estimated catalyst estimated temperature, and together with the catalyst temperature change amount, the catalyst temperature change amount due to heat release from the exhaust purification catalyst and the exhaust gas purification. Catalyst estimated temperature calculation means for calculating the estimated catalyst temperature using one or both of the catalyst temperature change amounts due to the catalytic reaction at the catalyst, and the catalyst temperature change amount calculated by the estimated catalyst temperature calculation means Estimated temperature change limit setting means for setting a limit, and the estimated temperature change limit setting means includes the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature. The total catalyst temperature change amount of the catalyst temperature change amount based on the catalyst temperature change amount due to heat release from the exhaust purification catalyst and the catalyst temperature change amount of one or both of the catalyst temperature change amount due to the catalytic reaction in the exhaust purification catalyst Is provided with an upper limit .

  The estimated catalyst temperature calculated by the estimated catalyst temperature calculating means is calculated by using the catalyst temperature change amount. The catalyst temperature change amount is a value calculated based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and the estimated catalyst temperature calculated last time. The amount of change in catalyst temperature is related to the transfer of heat by heat transfer between the exhaust and the exhaust purification catalyst. This heat transfer is not simply determined by the temperature difference between the exhaust and the exhaust purification catalyst, and since the exhaust flows at a high speed, there is a limit to the amount of heat exchanged with the exhaust purification catalyst. is there.
  Therefore, instead of determining the catalyst temperature change amount only by the temperature difference between the exhaust gas and the exhaust purification catalyst, it is possible to reflect the heat transfer limit by setting a limit on the catalyst temperature change amount.
  For this reason, compared with the case where the amount of change in the catalyst temperature is determined only by the temperature difference between the exhaust gas and the exhaust gas purification catalyst, the change rate of the estimated catalyst temperature is not unlimited and is a change close to reality. Thus, by setting a limit on the amount of change in catalyst temperature, heat transfer between the exhaust gas and the exhaust purification catalyst can be taken into consideration, and the estimated catalyst temperature can be calculated with high accuracy.

  Further, as in the configuration of claim 3, in order to calculate the estimated catalyst temperature, in addition to the amount of change in the catalyst temperature based on the exhaust flow rate or the physical quantity and the estimated catalyst temperature calculated last time, the exhaust purification catalyst One or both of the catalyst temperature change amounts of the catalyst temperature change amount due to heat release from the catalyst and the catalyst temperature change amount due to the catalytic reaction in the exhaust purification catalyst may be used. As a result, the estimated catalyst temperature can be calculated with higher accuracy.

Further, the catalyst temperature change amount for providing the upper limit may be the total catalyst temperature change amount of the various catalyst temperature change amounts described above. In particular, the amount of change in the catalyst temperature based on the exhaust flow rate or the physical quantity reflecting the exhaust flow rate and the estimated catalyst temperature previously calculated contributes significantly to the estimated catalyst temperature as compared to the other catalyst temperature change amounts. Therefore, even if an upper limit is set for the total amount of change in the catalyst temperature, overshoot of the estimated catalyst temperature can be prevented at least, and the estimated catalyst temperature is active for the exhaust purification catalyst in an inactive temperature state. It can prevent showing temperature.

Wherein the exhaust gas purifying catalyst temperature estimating apparatus for an internal combustion engine according to claim 4, in any one of claims 1-3, wherein the estimated temperature change limit setting means, based on the physical quantity reflecting the exhaust gas flow rate or the exhaust flow rate It is characterized by switching the limit.

  The degree of heat transfer between the exhaust gas and the exhaust purification catalyst also changes depending on the degree of the exhaust gas flow rate. For this reason, based on the exhaust flow rate or the physical quantity reflecting the exhaust flow rate, by switching the limit set in the catalyst temperature change amount, heat transfer between the exhaust gas and the exhaust purification catalyst can be more appropriately considered, The estimated catalyst temperature can be calculated with higher accuracy.

The exhaust purification catalyst temperature estimation device for an internal combustion engine according to claim 5 , wherein, in claim 4 , the estimated temperature change limit setting means is configured such that the exhaust flow rate or the physical quantity reflecting the exhaust flow rate is greater than a reference value. An upper limit is set for the catalyst temperature change amount, and when the exhaust flow rate or a physical quantity reflecting the exhaust flow rate is smaller than a reference value, no upper limit is set for the catalyst temperature change amount.

  In this way, a reference value is set for the exhaust flow rate or a physical quantity that reflects the exhaust flow rate, and if it is larger than the reference value that affects the catalyst temperature change amount, an upper limit is set for the catalyst temperature change amount. The upper limit may not be set for the catalyst temperature change amount. This makes it possible to appropriately consider heat transfer between the exhaust gas and the exhaust purification catalyst, and to calculate the estimated catalyst temperature with high accuracy, rather than setting the upper limit uniformly.

The exhaust gas purification catalyst temperature estimation device for an internal combustion engine according to claim 6 , further comprising rich determination means for determining whether or not the combustion air-fuel mixture in the internal combustion engine is rich in any of claims 1 to 5 , The estimated temperature change limit setting means lowers the limit when the rich determination means determines that the temperature is rich.

  If the combustion mixture is rich, there is an exhaust cooling effect due to excess fuel. For this reason, if the combustion air-fuel mixture is rich, the temperature rise is lowered, so the limit is lowered. As a result, heat transfer between the exhaust gas and the exhaust gas purification catalyst is taken into consideration, and the amount of change in the catalyst temperature is limited to a lower value in consideration of air-fuel ratio enrichment. Can be calculated.

The exhaust purification catalyst temperature estimation device for an internal combustion engine according to claim 7 is an exhaust purification catalyst temperature estimation device for an internal combustion engine that estimates the temperature of the exhaust purification catalyst based on an operating state of the internal combustion engine, wherein the exhaust flow rate or the exhaust gas A catalyst estimated temperature calculating means for calculating a catalyst temperature change amount based on a physical quantity reflecting the flow rate and a previously estimated catalyst estimated temperature, and calculating an estimated catalyst temperature using the catalyst temperature change amount; and an internal combustion engine Rich determination means for determining whether or not the combustion mixture is rich, and if the rich determination means determines that the combustion mixture is rich, an upper limit is set on the catalyst temperature change amount calculated by the estimated catalyst temperature calculation means. An estimated temperature change limit setting means is provided.

  The estimated catalyst temperature calculated by the estimated catalyst temperature calculating means is calculated based on the amount of change in the catalyst temperature. This amount of change in catalyst temperature is related to the transfer of heat between the exhaust gas and the exhaust gas purification catalyst. However, if the combustion mixture is rich, there is an exhaust cooling effect due to excess fuel. Therefore, when heat is transferred from the exhaust to the exhaust purification catalyst, that is, when the amount of change in the catalyst temperature is on the temperature increase side, the degree of the temperature increase is also suppressed.

  Therefore, the amount of change in the catalyst temperature is not determined only by the temperature difference between the exhaust gas and the exhaust purification catalyst, but when the combustion mixture is rich, an upper limit is set for the amount of change in the catalyst temperature. As a result, enrichment of the air-fuel ratio can be taken into account, and the estimated catalyst temperature can be calculated with high accuracy.

In the exhaust purification catalyst temperature estimating apparatus for an internal combustion engine according to claim 8, in claim 7, wherein the estimated temperature change limit setting means, limit limits of relative said catalyst temperature variation and high degree of rich combustion mixture It is characterized by lowering.

  When the richness of the combustion mixture is high, the fuel is excessively increased and the exhaust cooling effect is increased. Therefore, if the degree of richness is high, the estimated catalyst temperature can be calculated with high accuracy by lowering the upper limit.

In the exhaust purification catalyst temperature estimating apparatus for an internal combustion engine according to claim 9, in any one of claims 1-8, wherein the estimated temperature change limit setting means, at the time of fuel cut to lower the limit of the catalyst temperature variation It is characterized by.

  When the fuel is cut, the combustion in the combustion chamber of the internal combustion engine stops, and the exhaust temperature decreases rapidly. Accordingly, since the exhaust purification catalyst is only cooled, the limit of the amount of change in the catalyst temperature is lowered when the fuel is cut. As a result, it is possible to quickly cope with a decrease in the exhaust temperature, and to calculate the estimated catalyst temperature with high accuracy.

In the exhaust purification catalyst temperature estimating apparatus for an internal combustion engine according to claim 10, in claim 9, wherein the estimated temperature change limit setting means sets the limit of the upper limit for the catalyst temperature variation in the value of 0 or less at the time of fuel cut It is characterized by doing.

  As described above, by setting the upper limit to 0 or less when the fuel is cut, a value that temporarily increases the amount of change in the catalyst temperature may be set for the responsiveness in the arithmetic processing immediately after the fuel cut. Therefore, even when the fuel is cut, it is possible to respond quickly to a decrease in the exhaust temperature, and a highly accurate estimated catalyst temperature can be obtained.

The exhaust gas purification catalyst temperature estimating apparatus for an internal combustion engine according to claim 11 is characterized in that, in any one of claims 1 to 10 , the physical quantity reflecting the exhaust gas flow rate is an intake air flow rate of the internal combustion engine.

  Even if the exhaust flow rate is not directly measured, the intake flow rate and the exhaust flow rate are proportional to each other, so that the intake flow rate can be used as a physical quantity that reflects the exhaust flow rate. In the control of the internal combustion engine, the intake flow rate is usually measured and used for various controls. By using the intake flow rate data, the internal combustion engine can be controlled as described above without particularly increasing the number of sensors. An exhaust purification catalyst temperature estimation device can be realized.

[Embodiment 1]
FIG. 1 shows an internal combustion engine (a gasoline engine in the present embodiment) 2 mounted on a vehicle and an electronic control unit (hereinafter referred to as “ECU”) for controlling an internal combustion engine having a function as an exhaust purification catalyst temperature estimation device. ) 4 is a schematic configuration diagram. The internal combustion engine 2 is a four-cylinder internal combustion engine here, but in FIG. The number of cylinders may be another number of cylinders, for example, 3 cylinders, 6 cylinders, or 8 cylinders. In FIG. 1, one intake valve 2a and one exhaust valve 2b are shown for each cylinder, but a 4-valve engine or a 5-valve engine may be used.

  The output of the internal combustion engine 2 is finally transmitted as traveling driving force to the wheels via the transmission. The internal combustion engine 2 is provided with a spark plug 8 that ignites the air-fuel mixture in the combustion chamber 6. The combustion chamber 6 is provided with an intake port 10 that is opened and closed by an intake valve 2a. A fuel injection valve 14 that injects fuel toward the intake port 10 is provided in an intake manifold 12 connected to the intake port 10 for each cylinder. Is provided. The intake manifold 12 is connected to a surge tank 16, and a throttle valve 20 whose opening degree is adjusted by a motor 18 is provided in the intake passage 17 on the upstream side of the surge tank 16. The intake air amount GA is adjusted by the throttle opening degree TA which is the opening degree of the throttle valve 20. The throttle opening degree TA is detected by the throttle opening degree sensor 22 and read into the ECU 4. The intake air amount GA is detected by an intake air amount sensor 24 provided on the upstream side of the throttle valve 20 and read into the ECU 4. The fuel injection valve 14 may be an in-cylinder injection type gasoline engine that directly injects fuel into the combustion chamber 6.

  Further, the combustion chamber 6 is provided with an exhaust port 26 that is opened and closed by an exhaust valve 2 b, and a catalytic converter 30 is disposed in the middle of an exhaust passage 28 connected to the exhaust port 26. An exhaust purification catalyst 30 a such as a three-way catalyst is disposed in the catalytic converter 30. An air-fuel ratio sensor 32 that outputs a signal corresponding to the air-fuel ratio AF of the air-fuel mixture burned in the combustion chamber 6 based on the exhaust component is disposed upstream of the catalytic converter 30 in the exhaust passage 28.

  The ECU 4 is composed mainly of a digital computer, and receives signals from sensors that detect the operating state of the internal combustion engine 2 in addition to the throttle opening sensor 22, the intake air amount sensor 24, and the air-fuel ratio sensor 32 described above. Here, an accelerator opening sensor 36 that detects the accelerator opening ACCP that is the amount of depression of the accelerator pedal 34, an internal combustion engine speed sensor 38 that detects the internal combustion engine speed NE from the rotation of the crankshaft, and the rotational phase of the intake camshaft. A signal is input from a reference crank angle sensor 40 that determines a reference crank angle from the reference crank angle sensor 40. Further, a signal representing the internal combustion engine coolant temperature THW is detected from the coolant temperature sensor 42, a signal representing the intake air temperature THA is detected from the intake air temperature sensor 44 disposed in the air cleaner at the tip of the intake passage 17, and the rotation speed of the output shaft of the transmission is detected. A signal representing the vehicle speed SPD is input from the vehicle speed sensor 46.

  The ECU 4 controls the fuel injection timing, the fuel injection amount, the ignition timing, and the intake air of the internal combustion engine 2 by a control signal for the fuel injection valve 14, the ignition plug 8, or the throttle valve motor 18 based on the detection contents from each sensor described above. Adjust the amount. The fuel injection amount is feedback-controlled by the output of the air-fuel ratio sensor 32 so that the target air-fuel ratio, here, the air-fuel mixture reaches the stoichiometric air-fuel ratio. Control is also performed to enrich the air-fuel mixture by increasing the fuel injection amount to prevent catalyst overheating.

  Further, at the time of idling, the ECU 4 adjusts the throttle opening TA so that the idling target rotational speed NT is set in accordance with the state of the internal combustion engine 2 (cooling water temperature THW, air conditioner load, etc.), especially after the warm-up is completed. Idle speed feedback control is being executed. Note that when the throttle valve 20 is not an electronically controlled throttle, idle speed feedback control may be executed by intake air amount control by ISCV bypassing the throttle valve 20.

  Next, a flowchart of the catalyst temperature estimation process executed by the ECU 4 is shown in FIG. This process is a process that is repeatedly executed at regular time intervals. The steps in the flowchart corresponding to the individual processing contents are represented by “S˜”.

  First, the values of the intake air amount GA (g / s), the vehicle speed SPD (km / h), and the intake air temperature THA (° C.) calculated by the ECU 4 from the signals of the intake air sensor 24, the vehicle speed sensor 46, and the intake air temperature sensor 44 described above. Is read into the working memory (S100).

  Next, the steady operation catalyst temperature Texq is calculated from the intake air amount GA measured this time using the map MAPtexq shown in FIG. 3 (S102). When the internal combustion engine 2 is in a steady operation state, the exhaust flow rate and the catalyst temperature of the exhaust purification catalyst 30a have a unique correspondence, but there is also a unique relationship between the intake air amount GA (corresponding to the intake air flow rate) and the exhaust flow rate. Correspondence exists. Therefore, a unique correspondence also exists between the intake air amount GA as a physical quantity reflecting the exhaust flow rate and the catalyst temperature. By obtaining this correspondence relationship by experiment with a standard internal combustion engine of the same type as the internal combustion engine 2, as shown in FIG. 3, the correspondence relationship between the intake air amount GA and the catalyst temperature can be obtained as a map MAPtexq. The catalyst temperature Texq during steady operation can be calculated from the intake air amount GA.

  Next, according to Equation 1, the catalyst temperature change amount ΔTexq due to exhaust per control cycle of the present process in the exhaust purification catalyst 30a is calculated from the catalyst temperature Texq during steady operation and the estimated catalyst temperature CatT obtained in the previous control cycle. Calculate (S104).

[Formula 1] ΔTexq ← (Texq−CatT) · Kexq / n
Here, the coefficient Kexq is a coefficient reflecting the exchange of heat between the exhaust and the exhaust purification catalyst 30a based on heat transfer per control cycle, and the positive numerical value n is a value representing a time delay.

Next, it is determined whether or not the catalyst temperature change amount ΔTexq due to the exhaust gas calculated by the equation 1 is equal to or less than an upper limit value DTmax representing the upper limit (S106).
When the flow rate of the exhaust gas is high, the exhaust gas is discharged from the catalytic converter 30 while the heat quantity of the exhaust gas is not sufficiently transmitted to the exhaust gas purification catalyst 30a. In this case, the amount of heat is not transmitted from the exhaust to the exhaust purification catalyst 30a as calculated based on the heat transfer coefficient shown in the above equation 1. The upper limit value DTmax is provided to determine and limit the state in which the catalyst temperature change amount ΔTexq is set to be higher than the actual temperature increase. This upper limit value DTmax is a value obtained by experiments and analysis by changing various exhaust gas flow rates for a standard internal combustion engine of the same type as the internal combustion engine 2. In the internal combustion engine 2 of the present embodiment, the upper limit value DTmax is obtained as 10 ° C./s.

  Here, if ΔTexq ≦ DTmax (yes in S106), there is no particular restriction on the catalyst temperature change amount ΔTexq due to exhaust. On the other hand, if ΔTexq> DTmax (No in S106), the upper limit value DTmax is set to the catalyst temperature change amount ΔTexq as shown in Equation 2 (S108).

[Formula 2] ΔTexq ← DTmax
In this way, a limit is set for the catalyst temperature change amount ΔTexq based on the amount of heat from the exhaust, and a value exceeding the upper limit value DTmax is prevented from being set.

  If it is determined yes in step S106, or after step S108, the amount of heat generated between the outer surface of the catalytic converter 30 and the outside air per the control cycle of the present processing in the exhaust purification catalyst 30a is calculated according to Equation 3. A catalyst temperature change amount ΔToutq due to the transfer is calculated (S110).

[Formula 3] ΔToutq ← SPD · (THA-CatT) · Kout
Here, the coefficient Kout is a coefficient reflecting the transfer of heat amount by heat transfer between the exhaust purification catalyst 30a and the outside air through the outer wall of the catalytic converter 30 per control cycle. The higher the vehicle speed SPD, the greater the amount of heat exchanged with the outside air, so the vehicle speed SPD is multiplied as shown in Equation 3 above. This catalyst temperature change amount ΔToutq is normally negative, and the amount of heat given and received in this case represents the amount of heat released.

  Next, from the map MAPrac representing the relationship between the estimated catalyst temperature CatT and the catalyst temperature change amount ΔTracq due to the catalyst reaction, the catalyst temperature change amount ΔTracq due to the heat of formation of the catalyst reaction is calculated based on the estimated catalyst temperature CatT (S112). Here, there is a unique correspondence between the estimated catalyst temperature CatT and the catalyst temperature change amount ΔTracq due to the catalytic reaction. Therefore, the relationship between the estimated catalyst temperature CatT and the catalyst temperature change ΔTracq due to the catalytic reaction is previously mapped by experiment and analysis for a standard internal combustion engine of the same type as the internal combustion engine 2, and this map is used as the map MAPrac.

  Then, the three catalyst temperature change amounts ΔTexq, ΔToutq, and ΔTracq calculated as described above are summed as shown in Equation 4 to set the total catalyst temperature change amount ΔTcat (S114).

[Formula 4] ΔTcat ← ΔTexq + ΔToutq + ΔToutq
Next, the estimated catalyst temperature CatT is corrected as shown in Equation 5 based on the catalyst temperature change amount ΔTcat determined in this way to calculate a new estimated catalyst temperature CatT (S116).

[Formula 5] CatT ← CatT + ΔTcat
Thus, this process is temporarily terminated. Thereafter, the above-described process is repeated for each control cycle, and the estimated catalyst temperature CatT is updated.

  An example of the control in the present embodiment is shown in the timing chart of FIG. Before the timing t0, the catalyst temperature change amount ΔTexq is equal to or less than the upper limit value DTmax (= 10 ° C./s) in the above equation 1, and is thus added to the total catalyst temperature change amount ΔTcat as it is. However, when the catalyst temperature change amount ΔTexq in the equation 1 becomes larger than the upper limit value DTmax (t0 to t1), the value of the upper limit value DTmax as the catalyst temperature change amount ΔTexq with respect to the total catalyst temperature change amount ΔTcat in the equation 4. Will be added. For this reason, the estimated catalyst temperature CatT shows a change close to the actual catalyst temperature. If the upper limit value DTmax is not set for the catalyst temperature change amount ΔTexq as shown by the broken line, the estimated catalyst temperature CatT will overshoot the actual catalyst temperature. For this reason, for example, even if it is attempted to catch the warm-up completion of the exhaust purification catalyst 30a at the estimated catalyst temperature CatT, it may be determined that the warm-up is completed at an early stage even though it is still in a cold state.

  In the configuration described above, the relationship with the claims is that steps S100 to S104 and S110 to S116 of the catalyst temperature estimation process (FIG. 2) are the processes as the estimated catalyst temperature calculation means, and steps S106 and S108 are the estimated temperature change limit setting. It corresponds to processing as means.

According to the first embodiment described above, the following effects can be obtained.
(I). In the catalyst temperature estimation process (FIG. 2), three catalyst temperature changes ΔTexq, ΔToutq, and ΔTracq are calculated to obtain the estimated catalyst temperature CatT (S102, S104, S110, S112). Thus, the estimated catalyst temperature CatT is calculated in consideration of the intake air amount GA as a physical quantity reflecting the exhaust flow rate, the heat radiation from the exhaust purification catalyst 30a, and the catalytic reaction in the exhaust purification catalyst 30a (S114, S116).

  Of these three catalyst temperature change amounts ΔTexq, ΔToutq, ΔTracq, the catalyst temperature change amount ΔTexq due to exhaust is related to heat transfer between the exhaust and the exhaust purification catalyst 30a. This heat transfer is not simply determined by the temperature difference between the exhaust gas to which the exhaust purification catalyst 30a is exposed, and there is an amount of heat that cannot be transferred depending on the exhaust flow rate. There is also a limit to the exchange of heat between the two. For this reason, there is a limit on the catalyst temperature change amount ΔTexq due to exhaust.

  As a result, the total catalyst temperature change amount ΔTcat finally calculated becomes a catalyst temperature change amount close to reality. In this way, it is possible to calculate the estimated catalyst temperature CatT with high accuracy.

  In particular, the upper limit (upper limit value DTmax) is set as a limit because it is important for the warm-up completion timing determination on the temperature increase side of the catalyst temperature (S106, S108). Accordingly, even when determining the deterioration state of the exhaust purification catalyst 30a, it can be determined at an appropriate warm-up completion timing, so that it is erroneously determined that the exhaust purification catalyst 30a that has not deteriorated in the unwarmed state has deteriorated. Is prevented.

  (B). Although the contribution to the total catalyst temperature change amount ΔTcat is small, the catalyst temperature change amount ΔToutq due to the transfer of heat from the outer surface of the catalytic converter 30 and the catalyst temperature change amount ΔTracq due to the heat generated by the catalytic reaction are calculated, This is used to calculate the total catalyst temperature change amount ΔTcat. For this reason, it is possible to calculate the estimated catalyst temperature CatT with higher accuracy.

[Embodiment 2]
In the present embodiment, the catalyst temperature estimation process as shown in FIG. 5 is repeatedly executed at regular time intervals. In this process, the value of the upper limit value DTmax is switched by the intake air amount GA, which is a physical quantity that reflects the exhaust gas flow rate as in the map MAPdtmax shown in FIG.

  In the catalyst temperature estimation processing (FIG. 5) of the present embodiment, the upper limit value DTmax is calculated from the map MAPdtmax shown in FIG. 6 based on the intake air amount GA after step S200 (S105). The determination in step S106 is made based on the upper limit value DTmax calculated in this way. Steps S106 and S108 are the same processes as those in FIG. 2 shown in the first embodiment. Further, step S200 is the same as the process of steps S100 to S104 of FIG. 2, and step S210 is the same as the process of steps S110 to S116 of FIG. Other configurations are the same as those of the first embodiment.

  In the map MAPdtmax in FIG. 6, the upper limit value DTmax is lowered as the intake air amount GA is increased. This is because the larger the intake air amount GA, the higher the flow rate of the exhaust gas, and the amount of heat exchanged with the exhaust purification catalyst 30a is not sufficiently performed.

  Note that the upper limit value DTmax may be changed stepwise instead of gradually as shown in FIG. As a specific example, as shown in FIG. 7, the upper limit value DTmax is set with an intake air amount equal to or higher than the intake air amount GAs set on the high flow rate side as a reference value, and the upper limit value DTmax is not set with an intake air amount smaller than the intake air amount GAs. May be. For example, in the flowchart of FIG. 5, the upper limit value DTmax is set to a large value (eg, 500 ° C./s) that is not normally possible when the intake air amount is smaller than the intake air amount GAs in step S105, so that it is always determined as yes in step S106. May be. Alternatively, steps S106 and S108 may be jumped.

  In the configuration described above, the relationship with the claims is that the steps S200 and S210 of the catalyst temperature estimation process (FIG. 5) are the processes as the estimated catalyst temperature calculation means, and the steps S105, S106 and S108 are the estimated temperature change limit setting means. It corresponds to the process.

According to the second embodiment described above, the following effects can be obtained.
(I). While producing the effect of the first embodiment and switching the upper limit value DTmax based on the intake air amount GA, heat transfer between the exhaust gas and the exhaust purification catalyst 30a can be more appropriately taken into consideration, and high accuracy is achieved. The estimated catalyst temperature CatT can be calculated.

[Embodiment 3]
In the present embodiment, the catalyst temperature estimation process as shown in FIG. 8 is repeatedly executed at regular time intervals. In this process, the upper limit value DTmax is fixed to 0 (° C./s) when the fuel is cut. That is, in the catalyst temperature estimation process (FIG. 8) of the present embodiment, it is determined whether or not a fuel cut is not executed after step S300 (S120). If the fuel cut is not being executed (yes in S120), the process proceeds to step S106. If the fuel cut is being executed (no in S120), the upper limit value DTmax is set to 0 (° C./s) (S122), and the process proceeds to step S106.

  Steps S106 and S108 are the same processes as those in FIG. 2 shown in the first embodiment. Further, step S300 is the same as the process of steps S100 to S104 of FIG. 2, and step S310 is the same as the process of steps S110 to S116 of FIG. Other configurations are the same as those of the first embodiment.

  At the time of fuel cut, the exhaust temperature is lowered and the exhaust purification catalyst 30a is only cooled and the temperature does not rise. Therefore, the upper limit value DTmax = 0 (° C./s). The upper limit value DTmax may be set to a value (minus) smaller than 0 (° C./s).

  In the above-described configuration, the relationship with the claims is that steps S300 and S310 of the catalyst temperature estimation process (FIG. 8) are the processes as the estimated catalyst temperature calculation means, and steps S120, S122, S106 and S108 are the estimated temperature change limits. It corresponds to processing as means.

Note that step S105 of FIG. 5 may be executed after step S300.
According to the third embodiment described above, the following effects can be obtained.
(I). The effects of the first embodiment can be produced, and the catalyst estimated temperature CatT can be calculated with higher accuracy since the exhaust temperature can be quickly reduced due to the fuel cut.

(B). If step S105 of FIG. 5 is executed, the effect of the second embodiment is also produced.
[Embodiment 4]
In the present embodiment, the catalyst temperature estimation process as shown in FIG. 9 is repeatedly executed at regular time intervals. In this process, during the air-fuel ratio enrichment process, the upper limit value DTmax is decreased by the decrease correction value drich. That is, in the catalyst temperature estimation process (FIG. 9) of the present embodiment, it is determined whether or not the air-fuel ratio enrichment is not executed after step S400 (S130). For example, in the fuel injection amount control, determination is made based on whether the fuel increase coefficient is “1” or a value exceeding “1” in order to prevent catalyst overheating. The determination may be made based on the output value of the air-fuel ratio sensor 32.

  If enrichment is not being executed (yes in S130), an initial value is set to the upper limit value DTmax (S131), and the process proceeds to step S106. If enrichment is being executed (no in S130), after the process of setting the value obtained by subtracting the decrease correction value drich from the initial value is set to the upper limit value DTmax (S132), the process proceeds to step S106.

  Steps S106 and S108 are the same processes as those in FIG. 2 shown in the first embodiment. Further, step S400 is the same as the process of steps S100 to S104 of FIG. 2, and step S410 is the same as the process of steps S110 to S116 of FIG. Other configurations are the same as those of the first embodiment.

The fuel for the increased amount for enrichment has a cooling effect due to evaporation heat, so the exhaust temperature is lower than that during stoichiometric. For this reason, the upper limit value DTmax is lowered corresponding to the enrichment.
In the configuration described above, the relationship with the claims is that the steps S400 and S410 of the catalyst temperature estimation process (FIG. 9) are the processes as the estimated catalyst temperature calculation means, and the steps S132, S106 and S108 are the estimated temperature change limit setting means. In step S130, step S130 corresponds to processing as rich determination means.

  Note that step S105 of FIG. 5 may be executed after step S400. In this case, the upper limit value DTmax calculated from the map MAPdtmax in FIG. 6 or 7 is used as the initial value in steps S131 and S132.

According to the fourth embodiment described above, the following effects can be obtained.
(I). In addition to the effects of the first embodiment, the amount of catalyst temperature change ΔTexq due to exhaust gas is limited to a smaller value in consideration of the richness of the air-fuel ratio. The estimated catalyst temperature CatT can be calculated.

(B). If step S105 of FIG. 5 is executed, the effect of the second embodiment is also produced.
[Embodiment 5]
In the present embodiment, the catalyst temperature estimation process as shown in FIG. 10 is repeatedly executed at regular time intervals. In this process, during the air-fuel ratio enrichment process (no in S140), the map MAPtexq representing the relationship between the intake air amount GA used in step S102 and the steady-state catalyst temperature Texq is switched from the contents shown in FIG. 3 to FIG. (S142). That is, as shown in FIG. 11, the exhaust temperature decreases due to the heat of fuel evaporation in the rich combustion (solid line) than in the normal stoichiometric combustion (broken line), so the relationship between the intake air amount GA and the catalyst temperature Texq during steady operation is Even if the intake air amount GA is the same, the catalyst temperature Texq during steady operation decreases according to the degree of enrichment.

  Accordingly, in the catalyst temperature estimation process (FIG. 10), if the air-fuel ratio enrichment is not being executed (yes in S140), the map MAPtexq (FIG. 3) is used without being switched in step S102. Then, based on the obtained catalyst temperature Texq during steady operation, the catalyst temperature change amount ΔTexq due to exhaust is calculated by the above equation 1 (S104), and finally the estimated catalyst temperature CatT is updated (S500).

  However, if enrichment of the air-fuel ratio is being executed (no in S140), the catalyst temperature Texq during steady operation depends on the degree of enrichment in step S142, here, the value of the fuel increase coefficient (> 1). The low-switched map MAPtexq (FIG. 11) is used in step S102. The catalyst temperature change amount ΔTexq due to exhaust is calculated by the above equation 1 based on the steady-state catalyst temperature Texq calculated in this map MAPtexq (FIG. 11) (S104), and finally the estimated catalyst temperature CatT is updated. (S500).

  Steps S100, S102, and S104 are the same processing as the same step number in FIG. 2 shown in the first embodiment. Further, step S500 is the same as the processing of steps S110 to S116 in FIG. Other configurations are the same as those of the first embodiment.

  An example of processing according to this embodiment is shown in the timing chart of FIG. Before the timing t10, the fuel increase coefficient = 1 and the enrichment is not performed, so the map MAPtexq before switching (FIG. 3) is used. At the timing t10 to t11, the fuel increase coefficient> 1 and the air-fuel ratio of the air-fuel mixture is enriched. Therefore, the catalyst temperature Texq during steady operation is switched to a low value according to the value of the fuel increase coefficient (> 1). The map MAPtexq (FIG. 11) is used. Therefore, the estimated catalyst temperature CatT shows a change close to the actual catalyst temperature as shown by the solid line. If the map MAPtexq corresponding to the enrichment is not set, the estimated catalyst temperature CatT becomes higher than the actual catalyst temperature and overshoots as shown by the broken line in FIG.

  In the configuration described above, the relationship with the claims is that step S140 of the catalyst temperature estimation process (FIG. 11) is the process as the rich determination means, step S142 is the process as the relation switching means, and steps S100, S102, S104, S500 corresponds to the processing as the estimated catalyst temperature calculation means.

According to the fifth embodiment described above, the following effects can be obtained.
(I). The richness of the air-fuel ratio can be considered by switching the map MAPtexq to a relationship where the catalyst temperature Texq during steady operation is lower in consideration of the richness of the air-fuel ratio. Therefore, the catalyst temperature change amount ΔTexq due to exhaust can be appropriately calculated, and the estimated catalyst temperature CatT can be calculated with high accuracy.

[Embodiment 6]
In the present embodiment, the catalyst temperature estimation process as shown in FIG. 13 is repeatedly executed at regular time intervals. The upper limit setting of the catalyst temperature change amount ΔTexq by the upper limit value DTmax (not necessarily the same value as in the first embodiment) is performed only during the enrichment of the air-fuel ratio. Therefore, after step S600, it is determined whether air-fuel ratio enrichment is being executed (S150). If the enrichment of the air-fuel ratio is being executed (yes in S150), the upper limit of the catalyst temperature change amount ΔTexq is set (S106, S108). However, if the enrichment of the air-fuel ratio is not being executed (no in S150), the upper limit of the catalyst temperature change amount ΔTexq (S106, S108) is not set, and is set according to the above-described equation 1 on the step S600 side. The catalyst temperature change amount ΔTexq is used as it is in the calculation of the total catalyst temperature change amount ΔTcat in the above equation 4.

  Steps S106 and S108 are the same processes as those in FIG. 2 shown in the first embodiment. Further, step S600 is the same as the process of steps S100 to S104 of FIG. 2, and step S610 is the same as the process of steps S110 to S116 of FIG. Other configurations are the same as those of the first embodiment.

  In the configuration described above, the relationship with the claims is that step S150 of the catalyst temperature estimation process (FIG. 13) is a process as the rich determination means, steps S106 and S108 are a process as the estimated temperature change limit setting means, and step S600. , S610 corresponds to the processing as the estimated catalyst temperature calculation means.

According to the sixth embodiment described above, the following effects can be obtained.
(I). In the present embodiment, the limit for the catalyst temperature change amount ΔTexq is set by the upper limit value DTmax only during the enrichment of the air-fuel ratio. If the combustion mixture is rich, there is an exhaust cooling effect due to excess fuel. Therefore, when heat is transferred from the exhaust to the exhaust purification catalyst 30a, that is, when the catalyst temperature change amount ΔTexq is on the temperature increase side, the degree of temperature increase is also suppressed. As a result, enrichment of the air-fuel ratio can be taken into consideration, and the estimated catalyst temperature CatT can be calculated with high accuracy.

(B). The effect (b) of the first embodiment is produced.
[Other embodiments]
(A). In each of the above embodiments, instead of using the three catalyst temperature change amounts ΔTexq, ΔToutq, and ΔTracq, the total catalyst temperature change amount ΔTcat may be calculated using only two of the catalyst temperature change amounts ΔTexq and ΔToutq. . Alternatively, the total catalyst temperature change amount ΔTcat may be calculated using only two of the catalyst temperature change amounts ΔTexq and ΔTracq.

  The catalyst temperature change amount ΔTexq due to exhaust is the largest contribution to the total catalyst temperature change amount ΔTcat. Therefore, without calculating the total catalyst temperature change amount ΔTcat, the catalyst temperature change amount ΔTexq itself due to exhaust gas is used as the total catalyst temperature change amount. It may be used instead of ΔTcat.

  (B). Although the upper limit value DTmax is a fixed value in the sixth embodiment, the upper limit value DTmax may be decreased as the degree of richness increases, that is, as the fuel increase coefficient increases.

  (C). Except for the fifth embodiment, the upper limit is set as the limit of the catalyst temperature change amount ΔTexq in each of the above embodiments. However, the lower limit may be set to prevent undershoot when the exhaust gas temperature decreases.

  (D). In each embodiment except for the fifth embodiment, an upper limit is set for the catalyst temperature change amount ΔTexq due to exhaust. However, as described above, the catalyst temperature change amount ΔTexq due to exhaust is the largest contribution to the total catalyst temperature change amount ΔTcat. Therefore, even if an upper limit is set for the total catalyst temperature change amount ΔTcat, the estimated catalyst temperature CatT can be accurately determined. An effect that can be calculated is obtained.

  (E). In each of the above-described embodiments, the intake air amount GA is measured by the intake air amount sensor 24 disposed in the intake passage 17, and this intake air amount GA is used as a physical quantity that reflects the exhaust flow rate. In addition to this, when the intake pressure is measured, the exhaust flow rate (or intake air amount GA) may be obtained from a relationship between the intake pressure and the internal combustion engine speed NE by using a map or the like. If the exhaust flow rate can be measured directly in the exhaust passage 28, the exhaust flow rate may be used instead of the intake air amount GA.

1 is a schematic configuration diagram of a vehicle-mounted internal combustion engine and an ECU according to a first embodiment. The flowchart of the catalyst temperature estimation process which the said ECU performs. FIG. 4 is a configuration explanatory diagram of a map MAPtexq representing the relationship between the intake air amount GA and the catalyst temperature Texq during steady operation. 4 is a timing chart illustrating an example of control according to the first embodiment. 7 is a flowchart of catalyst temperature estimation processing according to Embodiment 2. The structure explanatory drawing of map MAPdtmax showing the relationship between the intake air amount GA and the upper limit DTmax. Structure explanatory drawing which shows another example of the said map MAPdtmax. 10 is a flowchart of a catalyst temperature estimation process according to the third embodiment. 10 is a flowchart of a catalyst temperature estimation process according to the fourth embodiment. 10 is a flowchart of a catalyst temperature estimation process according to the fifth embodiment. The structure explanatory view showing the change state of map MAPtexq. 10 is a timing chart illustrating an example of control according to the fifth embodiment. 10 is a flowchart of a catalyst temperature estimation process according to the sixth embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Internal combustion engine, 2a ... Intake valve, 2b ... Exhaust valve, 4 ... ECU, 6 ... Combustion chamber, 8 ... Spark plug, 10 ... Intake port, 12 ... Intake manifold, 14 ... Fuel injection valve, 16 ... Surge tank, DESCRIPTION OF SYMBOLS 17 ... Intake passage, 18 ... Throttle valve motor, 20 ... Throttle valve, 22 ... Throttle opening sensor, 24 ... Intake amount sensor, 26 ... Exhaust port, 28 ... Exhaust passage, 30 ... Catalytic converter, 30a ... Exhaust purification catalyst , 32 ... Air-fuel ratio sensor, 34 ... Accelerator pedal, 36 ... Accelerator opening sensor, 38 ... Internal combustion engine speed sensor, 40 ... Reference crank angle sensor, 42 ... Cooling water temperature sensor, 44 ... Intake temperature sensor, 46 ... Vehicle speed sensor .

Claims (11)

An exhaust purification catalyst temperature estimation device for an internal combustion engine that estimates the temperature of the exhaust purification catalyst based on the operating state of the internal combustion engine,
An estimated catalyst temperature calculating means for calculating a catalyst temperature change amount based on an exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature, and calculating an estimated catalyst temperature using the catalyst temperature change amount; ,
Estimated temperature change limit setting means for setting a limit on the catalyst temperature change amount calculated by the catalyst estimated temperature calculation means ,
The estimated temperature change limit setting means sets an upper limit for a catalyst temperature change amount based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature.
An exhaust gas purification catalyst temperature estimation device for an internal combustion engine. 2. The catalyst estimated temperature calculation means according to claim 1, wherein the catalyst estimated by the heat release from the exhaust purification catalyst is combined with a catalyst temperature change amount based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst temperature. An exhaust purification catalyst temperature estimation device for an internal combustion engine, wherein an estimated catalyst temperature is calculated using one or both of a temperature change amount and a catalyst temperature change amount of a catalyst temperature due to a catalytic reaction at the exhaust purification catalyst. . An exhaust purification catalyst temperature estimation device for an internal combustion engine that estimates the temperature of the exhaust purification catalyst based on the operating state of the internal combustion engine,
  A catalyst temperature change amount is calculated based on an exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature, and together with the catalyst temperature change amount, a catalyst temperature change amount due to heat radiation from the exhaust purification catalyst, A catalyst estimated temperature calculating means for calculating a catalyst estimated temperature using one or both of the catalyst temperature change amount and the catalyst temperature change amount due to a catalytic reaction in the exhaust purification catalyst;
  Estimated temperature change limit setting means for setting a limit on the catalyst temperature change amount calculated by the catalyst estimated temperature calculation means,
  The estimated temperature change limit setting means includes a catalyst temperature change amount based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature, a catalyst temperature change amount due to heat release from the exhaust purification catalyst, and An upper limit is set on the total catalyst temperature change amount of one or both of the catalyst temperature change amounts due to the catalytic reaction in the exhaust purification catalyst.
  An exhaust gas purification catalyst temperature estimation device for an internal combustion engine. The exhaust purification catalyst temperature estimation device for an internal combustion engine according to any one of claims 1 to 3 , wherein the estimated temperature change limit setting means switches the limit based on the exhaust flow rate or a physical quantity reflecting the exhaust flow rate. . 5. The estimated temperature change limit setting means according to claim 4 , wherein when the physical quantity reflecting the exhaust flow rate or the exhaust flow rate is larger than a reference value, an upper limit is set for the catalyst temperature change amount, and the exhaust flow rate or the exhaust flow rate is set. An exhaust purification catalyst temperature estimation device for an internal combustion engine, wherein an upper limit is not set for the catalyst temperature change amount when the reflected physical quantity is smaller than a reference value. In any one of Claims 1-5 , while providing the rich determination means which determines whether the combustion air-fuel | gaseous mixture in an internal combustion engine is rich,
The exhaust gas purification catalyst temperature estimation device for an internal combustion engine, wherein the estimated temperature change limit setting means lowers the limit when it is determined that the rich determination means is rich. An exhaust purification catalyst temperature estimation device for an internal combustion engine that estimates the temperature of the exhaust purification catalyst based on the operating state of the internal combustion engine,
An estimated catalyst temperature calculating means for calculating a catalyst temperature change amount based on an exhaust flow rate or a physical quantity reflecting the exhaust flow rate and a previously estimated catalyst estimated temperature, and calculating an estimated catalyst temperature using the catalyst temperature change amount; ,
Rich determination means for determining whether or not the combustion mixture in the internal combustion engine is rich;
An estimated temperature change limit setting means for setting an upper limit for the amount of change in catalyst temperature calculated by the estimated catalyst temperature calculating means when the rich determining means determines that the fuel is rich;
An exhaust purification catalyst temperature estimation device for an internal combustion engine, comprising: 8. The exhaust purification catalyst temperature estimation for an internal combustion engine according to claim 7 , wherein the estimated temperature change limit setting means lowers the upper limit of the catalyst temperature change amount when the richness of the combustion mixture is high. apparatus. In any one of claims 1-8, wherein the estimated temperature change limit setting means, at the time of fuel cut exhaust purifying catalyst temperature estimating apparatus for an internal combustion engine, characterized in that to lower the limit of the catalyst temperature variation. 10. The exhaust purification catalyst temperature estimation device for an internal combustion engine according to claim 9 , wherein the estimated temperature change limit setting means sets an upper limit for the catalyst temperature change amount to a value of 0 or less when the fuel is cut. In any of claims 1-10, the exhaust gas purifying catalyst temperature estimating device of the physical quantity is an internal combustion engine which is a intake air flow rate in an internal combustion engine that reflects the exhaust flow.

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