Patent Publication Number: US-7707999-B2

Title: Exhaust protecting device and protecting method for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application claims priority to Japanese Patent Application No. 2006-202205 and Japanese Patent Application No. 2007-174134, the contents of which are incorporated herein in their entirety. 
   TECHNICAL FIELD 
   The disclosed devices and methods relate to protecting an internal combustion engine exhaust system, and more particularly to protecting exhaust system components including, among other components, the exhaust manifold. 
   BACKGROUND 
   Japanese Patent Application Laid-Open (JP-A) No. 63-045444 discloses that the exhaust gas temperature can be detected in order to protect an exhaust system component. Specifically, when the temperature increases excessively, the fuel feed rate is increased and corrected to decrease the exhaust gas temperature. 
   JP-A 2004-177179 discloses that an internal resistance (impedance) of a sensor element of an air/fuel (A/F) ratio sensor (oxygen sensor) arranged in an exhaust system can be measured and used to estimate the temperature of the exhaust gas. 
   In both JP-A 63-045444 and JP-A 2004-177179, the fuel feed rate is increased when the exhaust gas temperature reaches a predetermined temperature. However, the temperature increase of the exhaust manifold or other similar elements that have a large heat capacity lags behind the increase in the exhaust gas temperature. Increasing the fuel feed rate immediately after the exhaust gas temperature reaches a exhaust system components occurs and can therefore reduce the fuel efficiency of the engine. 
   SUMMARY 
   The exemplary teachings of this disclosure address the above-described problems, and recognize that it is desirable to protect the exhaust system by performing a fuel increment without also deteriorating the fuel efficiency. 
   Thus, exemplary teachings related to exhaust system protection devices and methods follow. When an estimated value of the exhaust gas temperature reaches a predetermined temperature, a fuel increment is delayed for a calculated period of time. The calculated delay period is based on the change ratio of the exhaust gas temperature. The fuel increment proceeds at the conclusion of the delay period. 
   Setting the delay period of a fuel increment as described above enables the fuel increment to be implemented with consideration of the actual temperature increase of an exhaust system component which is to be protected. Accordingly, the exhaust system component can be protected while minimizing any deterioration in fuel efficiency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the claims are not limited to the illustrated embodiments, an appreciation of various aspects of the system is best gained through a discussion of various examples thereof. Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent the embodiments, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the embodiments described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary embodiments of the present invention are described in detail by referring to the drawings as follows. 
       FIG. 1  is a system diagram of an engine and exhaust system showing one embodiment; 
       FIG. 2  is a control circuit diagram for an Air-to-Fuel (A/F) ratio sensor; 
       FIG. 3  is a flow chart of an exhaust gas temperature estimation routine; 
       FIG. 4  is a flow chart of a fuel increment control routine; 
       FIG. 5  is a timing chart of exhaust gas temperature estimation and fuel increment control; 
       FIG. 6  is a timing chart showing the exhaust gas temperature and the temperature of an exhaust manifold at the time when idling proceeds to a fuel increment stage; 
       FIG. 7  is a timing chart showing the exhaust gas temperature and the temperature of the exhaust manifold at the time when a middle load proceeds to the fuel increment stage; and 
       FIG. 8  is a chart of engine rotational speed and load displaying the A/F Ratio Feedback Area and the Fuel Increment Area. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a system diagram of an internal combustion engine and exhaust system. An engine cylinder shown generally in  FIG. 1  includes a combustion chamber  3 , a piston  2 , and an intake valve  5  and an exhaust valve  6  surrounding an ignition plug  4 . 
   Intake path  7  includes an electrically controlled throttle valve  8  upstream of an intake manifold. The intake path  7  further includes an electromagnetic fuel injection valve  9 , facing an intake port of a cylinder head, within each branch of the intake manifold that allows for the injection of fuel having a predetermined pressure to the valve head of intake valve  5 . However, a direct injection type fuel injection valve may be employed instead. 
   An exhaust gas purification catalyst  11  is provided downstream of the exhaust manifold within a gathering part of the exhaust gas path  10 . 
   The operations of the electrically controlled throttle valve  8  and the fuel injection valve  9  are controlled by an engine control unit (hereinafter referred to as ECU)  20 . The ECU  20  receives input signals from at least a crank angle sensor  21 , an accelerator pedal opening sensor  22 , an air flow meter  23 , a water temperature sensor  24 , an air-to-fuel (hereinafter referred to as A/F) ratio sensor (oxygen sensor)  25 . The crank angle sensor  21  can output a crank angle signal in synchronization with the engine rotation to detect the crank angle position and the engine rotational speed Ne. The accelerator pedal opening sensor  22  detects the depression amount (accelerator pedal opening) APO of the accelerator pedal. The air flow meter  23  detects the intake air amount Qa within the intake path  7  upstream of the electrically controlled throttle valve  8 . The water temperature sensor  24  detects an engine coolant temperature Tw. The A/F ratio sensor (oxygen sensor)  25  detects the air-to-fuel ratio of exhaust gas upstream of the catalyst  11  of the exhaust gas path  10 . The outside air-temperature sensor  26  detects the outside temperature of the vehicle. The vehicle speed sensor  27  detects the vehicle speed. The ECU  20  controls the opening of the electrically controlled throttle valve  8  in response mainly to the accelerator pedal opening APO to control the intake air amount. 
   Further, the ECU  20  calculates a standard fuel injection amount Tp=K·Qa/Ne (K is a constant number) from the intake air amount Qa and the engine rotational speed Ne. This standard amount Tp is then adjusted using an A/F ratio feedback correction coefficient α and various correction coefficients COEF to calculate a final fuel injection amount Ti=Tp·α·COEF. The ECU  20  outputs a fuel injection pulse with a pulse width corresponding to the Ti to the fuel injection valve  9  of each cylinder in synchronization with the engine rotation to control the fuel injection amount. 
   The A/F ratio feedback correction coefficient α stoichiometrically controls the A/F ratio in response to the output of the A/F ratio sensor  25  (real A/F ratio). The real A/F ratio and an objective A/F ratio (stoichiometric value) are compared under an A/F ratio feedback control condition to set increments/decrements of α through proportional integration control (reference value is 1). 
   At least a fuel increment correction coefficient Kfuel is included in various correction coefficients COEF (COEF=1+ . . . +Kfuel). The fuel increment correction coefficient Kfuel is 0 during normal operation. When the exhaust gas temperature increases excessively, Kfuel is set to a value greater than zero after the A/F ratio feedback control is stopped (α is fixed to the reference value or a previous value) to increase the fuel injection amount, so that the A/F ratio can be enriched. The Kfuel value may be increased as the operating conditions of the engine proceed to a greater load and a higher rotational speed. 
     FIG. 2  is a control circuit diagram for the A/F ratio sensor  25 , which includes a sensor element  31  and a heater  32  for heating the sensor element. The heater  32  is arranged adjacent to the sensor element  31  of the A/F ratio sensor  25 . The heater  32  heats the sensor element  31  anytime it is cold due to inactivity. The heater is operated by appling a battery voltage VB through a switching element  33 . 
   The output voltage Vs of the sensor element  31  of the A/F ratio sensor  25  changes linearly in response to the A/F ratio. A predetermined voltage Vcc (for example, 5 V) for measuring the internal resistance is applied to the sensor element  31  through a switching element  34  and a reference resistance R 0 . Therefore, when the switching element  34  is turned ON, the voltage for measuring the internal resistance is raised on the output Vs of the sensor element  31 . 
   A central processing unit (CPU)  35  in the ECU  20  turns the switching element  33  ON anytime the sensor is cold to heat the sensor element  31  by the heater  32 . Further, while setting the ON/OFF state of the switching element  34 , which applies an internal resistance measuring voltage Vcc, CPU  35  reads the output Vs of the sensor element  31  through a filter (smoothing circuit)  36  and an A/D converter  37  at a predetermined timing. The sensor output Vs is read while the switching element  34  is in an OFF state, so that the A/F ratio can be detected in response to the value. The sensor output Vs is read while the switching element  34  is in an ON state, so that the internal resistance of the sensor element  31  can be measured in response to the value. The exhaust gas temperature (element temperature) can be estimated based on the measurement. 
     FIG. 3  is a flow chart of an exhaust gas temperature estimation routine by the ECU. This routine exemplifies one possible exhaust gas temperature estimation mechanism or means. In S 1 , it is determined whether the heater  32  of the A/F ratio sensor  25  is in the OFF condition or not. Recognizing that the heater is forcibly turned OFF whenever possible, the process proceeds to S 2  only when the heater is in the off condition. In S 2 , the switching element  34  is turned ON in order to measure the internal resistance of the sensor element  31 . Thus, the internal resistance measuring voltage Vcc is applied to the sensor element  31 , and in this state, the sensor output Vs is read. The sensor output Vs read at this time may include an error due to a varying voltage in response to the A/F ratio. In order to correct any error, a correction can be performed while Vs=Vs−Vs′ where Vs′ is a sensor output at A/F ratio detection timing immediately before the internal resistance measuring voltage is applied. Detection of the A/F ratio is prohibited when the internal resistance is measured, while likewise measurement of the internal resistance is prohibited when the A/F ratio is detected. 
   In S 3 , an internal resistance Rs of the sensor element  31  is calculated in response to the sensor output Vs, which has been read and possibly corrected. Specifically, assuming that a current flowing in the sensor element  31  is i, the following formulas are obtained:
 
 Vs=i×Rs  
 
 Vcc−Vs=i×R 0
 
   Obtaining Rs=Vs/[(Vcc−Vs)/R 0 ]. Thus, the internal resistance Rs can be calculated. 
   In S 4 , an element temperature Ts is calculated by using the internal resistance Rs of the sensor element  31  with reference to a table and the like. The element temperature Ts is related to the internal resistance Rs in that the greater the Ts value, the smaller the Rs value. As a result of this known relationship, the element temperature Ts can be calculated by using the internal resistance Rs. 
   In S 5 , it is determined whether or not the internal combustion engine driving condition is a transition condition. Despite the fact that the exhaust gas temperature can be estimated with higher accuracy during normal engine operation when it is estimated through the element temperature (internal resistance), a correction is needed at a transition time due to a time lag that is generated as a result of heat mass of the sensor element part at a transition time. A plurality of factors such as whether the vehicle is accelerating, a change of the engine&#39;s operational region (the combination of the rotational speed and the load), and a change in the element temperature (internal resistance) determine whether the engine driving condition is a transition condition. If the internal combustion engine condition is a transition condition, the process proceeds to S 6  and S 7 . 
   In S 6 , a first correction coefficient K 1  is calculated based on the operational region as defined by the engine rotational speed and the load (fuel injection amount and the like) with reference to a map. K 1  is mapped to a value of 1 (no correction) in a lower rotational speed and lower load region, and to K 1 &gt;1 in a higher rotational speed and higher load region. This correction is required because the higher rotational speed and greater load result in an over estimate of the exhaust gas temperature Te under a transition condition. 
   In S 7 , a second correction coefficient K 2  is calculated based on the exhaust gas flow rate, which is determined from the intake air amount Qa and a reference table. This table lists values of K 2 =1 (no correction) for a lower exhaust gas flow rate (Qa), while providing values of K 2 &gt;1 for a higher exhaust gas flow rate (Qa). This correction is required because higher exhaust gas flow rates (Qa) result in an over estimate of the exhaust gas temperature Te under a transition condition. It is possible that the calculation of either K 1  or K 2 , or both, occurs during the routine in order to correct the estimated exhaust gas temperature Te. 
   If the internal combustion engine driving condition is not a transition condition (i.e. in the case of normal operation), the process proceeds to S 8 . In S 8 , the correction coefficients K 1  and K 2  are both set to 1 indicating that no correction is needed. Alternatively, they may be set to a value, which is smaller than the value under a transition condition. Thereafter, the process proceeds to S 9 . In S 9 , the exhaust gas temperature Te is set to the product of the element temperature (exhaust gas temperature standard value) Ts, the first correction coefficient K 1 , and second correction coefficients K 2  (Te=Ts*K 1 *K 2 ). 
     FIG. 4  presents a flow chart depicting the steps of one possible fuel increment control routine executed by an ECU. In S 11 , the operating region of the vehicle, as determined by the rotational speed and load of the engine, is analyzed to determine whether a fuel increment is required. Specifically, high rotational speeds and high loads would indicate that a fuel increment is required. If the engine is not operating in a region that requires a fuel increment, the present routine is finished leaving the state as is. However, when the operating region requires a fuel increment the process proceeds to S 12 . 
   In S 12 , the operational region is stored immediately prior to a required fuel increment. Storage of the region is necessary because the ability of exhaust system components to tolerate a change in the exhaust gas temperature varies depending on the preceding operational region as shown in  FIGS. 6 and 7 . More specifically,  FIG. 6  shows a case in which the engine is idling prior to transitioning to a high load that necessitates a fuel increment. While idling, both the exhaust gas temperature and the temperature of the exhaust manifold are low. For this reason, even if the exhaust gas temperature reaches Tmax when the operational state transitions to a high load that necessitates a fuel increment, the amount of time that can elapse before the exhaust manifold reaches its maximum allowable temperature is longer than it would be had the engine been operating in excess of its idle speed and load. 
     FIG. 7  shows a case in which the engine is operating in a middle load region prior to transitioning to a high load region that necessitates a fuel increment. In the middle load operational region, both the exhaust gas temperature and the temperature of the exhaust manifold are high. For this reason, the amount of time that can elapse before the exhaust gas reaches a first predetermined temperature Tmax is shorter than the case of  FIG. 6 . Similarly, the amount of time that can elapse before the exhaust manifold reaches its maximum allowable temperature also becomes shorter than the case of  FIG. 6 . So in summary, the operating region immediately preceding a fuel increment is stored at S 12  due to the fact that the delay imposed before a fuel increment varies with respect to the engine&#39;s operating region prior to a fuel increment. 
   Returning to  FIG. 4 , next in S 13 , the exhaust gas temperature Te, is estimated and stored according to the previously described exhaust gas temperature estimation routine of  FIG. 3 . Then, in S 14 , the exhaust gas temperature Te is compared with the first predetermined temperature Tmax to determine whether Te≧Tmax. The predetermined temperature Tmax is a temperature at which the exhaust manifold reaches the allowable heat resistance. So, when the exhaust gas temperature exceeds the first predetermined temperature Tmax, a fuel increment is necessary because there is a possibility that the temperature of the exhaust manifold will exceed the maximum allowable heat resistance temperature. The first predetermined temperature Tmax is a comparison value used to identify such a situation. If Te≧Tmax as a result of the determination, the process proceeds to S 15 . In S 15 , an exhaust gas temperature change ratio ΔTe is calculated by obtaining the difference between a current time exhaust gas temperature and the Te that was stored in S 13 . 
   In S 16  the delay time until a fuel increment is calculated using the exhaust gas temperature change ratio ΔTe with reference to a predetermined table. Specifically, longer delay times are set for smaller exhaust gas temperature change ratio ΔTe values. Likewise, shorter delay times are set for larger exhaust gas temperature change ratio ΔTe values. Consequently, as shown in  FIG. 5 , the delay time is set such that a fuel increment begins when the temperature of the exhaust manifold which is to be protected reaches the allowable heat resistance temperature Tem. 
   In the exemplary illustration, as described above, the amount of time between the point in time when the exhaust gas temperature reaches the first predetermined temperature Tmax to time when the temperature of the exhaust manifold reaches the maximum allowable heat resistance temperature varies due to the engine&#39;s operating region immediately before the fuel increment. For this reason, the delay time set in S 16  is corrected in response to the operating region that existed immediately before the fuel increment. 
   It should be recognized that a portion of the heat absorbed by the manifold from the exhaust gas is radiated into the air surrounding the manifold. Thus, in the present embodiment, the delay time set in S 16  is additionally corrected for the amount of heat radiated from the exhaust manifold. This correction of the delay time is performed in S 17  to S 19 . 
   First, in S 17 , the operational region correction coefficient is read. As described above in S 6 , the operational region correction coefficient is a coefficient for setting the delay time such that higher loads and speeds immediately before a fuel increment result in shorter delay times. Further, in order to correct the delay time due to the heat radiated from the exhaust manifold, the outside air temperature Tout and the vehicle speed Vsp are read. 
   In S 18  (described in detail below), an outside air temperature correction coefficient DLYHOS#, which is set in response to the outside air temperature Tout, and a vehicle speed correction coefficient FUEHOS#, which is set in response to the vehicle speed Vsp, are multiplied by the delay time set in S 16  to yield a final delay time. A detailed description of the outside air temperature correction coefficient DLYHOS# set in response to the outside air temperature Tout and the vehicle speed correction coefficient FUEHOS# set in response to the vehicle speed Vsp follows. 
   When the outside air temperature is lower than a predetermined room temperature range, there is a greater amount of time between the time when the exhaust gas temperature reaches the first predetermined temperature Tmax to the time when an actual exhaust gas manifold temperature reaches the allowable heat resistance temperature due to the amount of heat discharged from the exhaust manifold to the atmosphere. The outside air temperature correction coefficient DLYHOS# corrects the optimum delay time based on any variation in the outside air temperature. 
   The outside air temperature correction coefficient DLYHOS# is set to 1, for example, when the outside air temperature Tout is in a room temperature range (0° C. to 30° C.). When the outside air temperature Tout is higher than the room temperature range, the amount of heat radiated from the exhaust manifold is less than the amount radiated in the room temperature range. Therefore, DLYHOS# is set to a value of 1 or less in order to reduce the delay time. Similarly, when the outside air temperature Tout is lower than the room temperature area, the amount of heat radiated from the exhaust manifold is greater than the amount radiated in the room temperature range. Therefore, DLYHOS# is set to a value of 1 or more in order to increase the delay time. 
   The vehicle speed correction coefficient FUEHOS# similarly corrects the optimum delay time in response to the amount of heat radiated from the exhaust manifold. The vehicle speed correction coefficient FUEHOS# increases the delay period at higher speeds because the amount heat dissipation is large when the vehicle speed is high. On the other hand, the delay period is reduced at low speeds because the amount of heat dissipation is small. Specifically, the vehicle speed correction coefficient FUEHOS# is 1 when the vehicle speed is zero, and increases to values greater than 1 as the vehicle speed becomes higher. Accordingly, an optimum delay period before a fuel increment can be calculated based on the operational state immediately before the fuel increment and the amount heat dissipation from the exhaust manifold (outside air temperature, vehicle speed, and the like) after the point in time when a fuel increment becomes necessary. 
   Next, in S 19 , a fuel increment correction coefficient Kfuel is set in fuel increment area. As shown in the map of  FIG. 8 , high loads and high speeds define an operating region of the engine in which A/F ratio feedback control is stopped in order to implement a fuel increment. The fuel increment correction coefficient Kfuel is set to larger values for higher and greater speeds and loads. The fuel increment correction coefficient Kfuel is set to 0 in A/F ratio feedback area. 
   As described above, at higher vehicle speeds Vsp a greater amount of heat is radiated from the exhaust manifold. For this reason, even when the fuel increment correction coefficient Kfuel set according to the map of  FIG. 8  is decreased, the temperature of the exhaust manifold can still be sufficiently decreased. Thus, in the process of S 19 , the fuel increment correction coefficient Kfuel that becomes the base value is corrected by multiplying it with the vehicle speed correction coefficient VSPHOS#. As described above, higher the vehicle speeds Vsp result in a smaller vehicle speed correction coefficient VSPHOS# being set, while lower vehicle speeds Vsp result in a larger vehicle speed correction coefficient VSPHOS# being set. So the resulting fuel increment correction coefficient Kfuel is smaller at high speeds and larger at low speeds. Similarly, the fuel increment correction coefficient Kfuel may be compensated in response to the outside air temperature Tout. 
   In S 20 , it is determined whether or not the delay time set in S 18  has elapsed. If it has elapsed, the process proceeds to the next step S 21 . In S 21 , the fuel increment is started in response to the fuel increment correction coefficient Kfuel set in S 19 . Specifically, the A/F ratio feedback control is stopped and the A/F ratio feedback correction coefficient α is fixed to a reference value or a previous value. As a consequence, the fuel injection amount Ti is corrected and increased to enrich the A/F ratio in order to decrease the exhaust gas temperature. 
   In S 22 , the exhaust gas temperature Te, which was last estimated through the exhaust gas temperature estimation routine of  FIG. 3 , is estimated again in order to ensure that there has been a decrease in the exhaust gas temperature. In S 23 , the exhaust gas temperature Te is compared with Tperm to determine whether or not Te≦Tperm. Tperm is a second predetermined temperature, a fuel increment completion temperature, which is lower than the first predetermined temperature Tmax. 
   If Te is greater than Tperm, the process returns to S 22  to continue the fuel increment. Similarly, if Te is less than or equal to Tperm, the process proceeds to S 24  to end the fuel increment. Thus, the fuel increment continues until the exhaust gas temperature decreases to a value less than or equal to the second predetermined temperature Tperm which is lower than the first predetermined temperature Tmax, so that the exhaust gas temperature can be decreased reliably. 
   S 15  corresponds to an exhaust gas temperature change ratio calculation means, S 16  to S 18  correspond to a delay time set means, and S 21  to S 24  correspond to a fuel increment means. 
   As described above, even when there is a drastic increase in the exhaust gas temperature as shown in  FIG. 5 , there is a time lag before the exhaust gas temperature reaches the maximum allowable heat resistance temperature Tem of the exhaust manifold. When a fuel increment is employed as a means for reducing the exhaust gas temperature, fuel efficiency can be improved by delaying the fuel increment for a calculated period of time. The calculated delay period is based on the exhaust gas temperature change ratio (internal resistance change ratio) ΔTe. Therefore, the timing of fuel increments can be set precisely to reliably maintain the manifold temperature to the maximum allowable heat resistance temperature Tem or lower. 
   As a means for monitoring the exhaust gas temperature precisely, an A/F ratio sensor is employed. This A/F ratio sensor estimates the exhaust gas temperature through its internal resistance (element temperature) so that monitoring can be performed relatively correctly. Of course, an exhaust gas temperature sensor may be attached to an exhaust system to detect the exhaust gas temperature directly. 
   Further, the present illustration is constructed such that means (S 6 ) for setting the correction coefficient K 1  in response to the engine&#39;s operational region is provided so that the exhaust gas temperature estimated in response to the internal resistance of the A/F ratio sensor element is corrected by the correction coefficient K 1  at a transition time. Similarly means (S 7 ) for setting the correction coefficient K 2  in response to the exhaust gas flow rate is provided so that the exhaust gas temperature estimated in response to the internal resistance of the A/F ratio sensor is corrected by the correction coefficient K 2  at a transition time. With this configuration, the exhaust gas temperature can be estimated precisely even when there is a time lag is due to heat mass of the sensor element, which can occur during a transition time. 
   Further, according to one illustrative approach, a predetermined voltage for measuring the internal resistance is applied to the A/F ratio sensor element to read the sensor output. In response to this output, the internal resistance of the A/F ratio sensor element is measured. Consequently, the internal resistance can be measured precisely, whereby the accuracy of the exhaust gas temperature estimate (element temperature) can be improved. 
   The delay time is corrected for any heat radiated from the exhaust manifold in one embodiment while other embodiments may omit this step. An estimated value of the exhaust gas temperature or the first predetermined temperature may be corrected. 
   Although the operational state immediately before the fuel increment area is stored to correct the delay time in one embodiment, other embodiments may omit this step. Alternatively, the length of delay before a fuel increment can be corrected by monitoring the operational state immediately before the fuel increment for a predetermined period of time in order to estimate a temperature difference between the exhaust gas temperature and the exhaust manifold. 
   For example, even when the exhaust gas temperature reaches the first predetermined temperature Tmax as the engine transitions from an idling operating region to a middle load region, the temperature increase of the exhaust manifold is slow due to the heat capacity of the exhaust manifold. Further, assume that a driver continues to accelerate the vehicle such that the operational state enters the fuel increment region. In this case, the exhaust gas temperature and the temperature of the exhaust manifold before the engine reaches the fuel increment region are not in an equilibrium condition, that is in a state in which although the exhaust gas temperature is higher, the temperature of the exhaust manifold is lower compared to that. Thus, it is desirable to set the delay period before a fuel increment to a greater length than that shown in  FIG. 7 . 
   In such a situation, the operational state immediately before the fuel increment area is monitored for a predetermined period of time as described above. Thereby, the temperature difference between the exhaust gas temperature and the temperature of the exhaust manifold is estimated, so that an optimum delay time can be set even if the exhaust gas temperature and the temperature of the exhaust manifold are different from each other before the fuel increment area. 
   Although the discussion above generally relates to protecting the exhaust manifold, the disclosed systems and methods would be equally effective in protecting other exhaust system components such as an exhaust gas purification catalyst. 
   The preceding description has been presented only to illustrate and describe exemplary embodiments of the claimed invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. The scope of the invention is limited solely by the following claims.