Patent Publication Number: US-2009229251-A1

Title: Exhaust purification control device and exhaust purification system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority to Japanese Patent Application No. 2008-066536 filed on Mar. 14, 2008, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exhaust purification control device and an exhaust purification system that determines abnormalities of a fuel addition valve. 
     2. Description of the Related Art 
     Exhaust purification systems are known. For example, JP-A-2003-172185 describes an exhaust purification system where harmful components in an exhaust discharged from an internal combustion engine are removed by an exhaust treatment device provided in an exhaust passage. The harmful components are purified by a fuel added into the exhaust passage from a fuel addition valve. 
     A NO x  catalyst, a diesel particulate filter (DPF), or the like are provided as the exhaust treatment device. The NO x  catalyst removes NO x  from the exhaust, and the DPF removes particulates from the exhaust. 
     In a conventional exhaust purification system, foreign materials can become attached to or trapped in a slide portion of the fuel addition valve so that stoppage or defective sliding of the slide portion may occur. Alternatively, electrical malfunctions of the fuel addition valve can result in an always open state or always closed state and a proper fuel amount cannot be added into the exhaust passage from the fuel addition valve. 
     For example, when the fuel addition valve is not instructed to add fuel and is not driven to open, the fuel may be added into the exhaust passage from the fuel addition valve when stuck in an open or partially open state. In contrast, when the fuel addition valve is instructed to add fuel at a predetermined time so as to purify the harmful components removed by the exhaust treatment device, the fuel may not be added into the exhaust passage from the fuel addition valve, the fuel addition amount may be much less than the instructed fuel addition amount, or the fuel addition amount may be much more than the instructed fuel addition amount when the valve is stuck in a closed or partially closed state. 
     If the proper fuel amount cannot be added into the exhaust passage, the harmful components that cannot be removed by the exhaust treatment device may be discharged without the purification, or an unburned fuel may be discharged together with the exhaust. 
     SUMMARY OF THE INVENTION 
     In view of the above-described difficulty, an object is to provide an exhaust purification control device and an exhaust purification system using the same that determines presence or absence of abnormalities of the fuel addition valve configured to add fuel into the exhaust passage. 
     According to one aspect, an exhaust purification control device for an exhaust purification system having an exhaust treatment device located in an outlet passage of an internal combustion engine and a fuel addition valve, includes an actual A/F ratio detecting means for detecting an actual A/F ratio based on an output signal of an A/F ratio sensor located downstream of the fuel addition valve; an estimated A/F ratio calculating means for calculating an estimated A/F ratio based on a fuel amount injected into the internal combustion engine from a fuel injection valve, a fuel amount added into the outlet passage from the fuel addition valve, and an inlet air amount supplied into the internal combustion engine; an addition valve controlling means for instructing the fuel addition valve to add fuel into the outlet passage; and an addition valve abnormality determining means for determining whether the fuel addition valve is abnormal based on the actual A/F ratio and the estimated A/F ratio. 
     In the above configuration, the exhaust purification control device can determine presence or absence of abnormalities of the fuel addition valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a block diagram illustrating an exhaust purification system according to an embodiment; 
         FIG. 2  is a diagram illustrating an abnormality determination routine 1 in a non-driven state of a fuel addition valve; 
         FIG. 3  is a diagram illustrating an abnormality determination routine 1 in a driven state of the fuel addition valve; 
         FIG. 4  is a diagram illustrating an abnormality determination routine 2 in the non-driven state of the fuel addition valve; 
         FIG. 5  is a diagram illustrating an abnormality determination routine 2 in the driven state of the fuel addition valve; 
         FIG. 6  is a diagram illustrating an abnormality determination routine 3 in the non-driven state of the fuel addition valve; 
         FIG. 7  is a diagram illustrating an abnormality determination routine 3 in the driven state of the fuel addition valve; 
         FIG. 8  is a diagram illustrating an abnormality determination routine 4 in the non-driven state of the fuel addition valve; and 
         FIG. 9  is a diagram illustrating an abnormality determination routine 4 in the driven state of the fuel addition valve. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter, an embodiment will be described with reference to the drawings. An exhaust purification system according to a present embodiment is shown in  FIG. 1 . An exhaust purification system  100  of an embodiment is a system for purifying exhaust discharged from a diesel engine  10  into an outlet passage  200 . Hereinafter, the diesel engine is also referred to as an engine. The detailed explanation of the exhaust purification system  100  will be described below. 
     An inlet filter  12 , a supercharger  14 , an intercooler  18 , a throttle valve  20 , an exhaust gas recirculation (EGR) valve  22  are provided in an inlet passage  202  for introducing air into a combustion chamber  204  of the engine  10 . The introduction of a charge from the supercharger  14  is controlled by a bypass valve  16 . 
     A high-pressure pump  30  as a fuel supply pump pressurizes a fuel drawn into a pressurizing chamber from a fuel tank  32  by a reciprocating motion of a plunger. The fuel amount discharged from the high-pressure pump  30  is controlled by a metering valve that controls the fuel amount drawn into the high-pressure pump  30 . The metering valve is not shown in the drawing. 
     Pressurized fuel output by the high-pressure pump  30  is stored in a common-rail  34  at a predetermined high pressure depending on operating condition of the engine  10 . Pressure in a control chamber is controlled so that a fuel injection valve  36  controls opening and closing of an ejection hole by a nozzle needle. Plural fuel injection valves  36  are located in each of cylinders and injects the fuel stored at the high pressure in the common-rail  34  into each of the cylinders. In one combustion cycle of the diesel engine  10 , the fuel injection valve  36  performs multistage injections including a pilot injection and a post injection or the like before or after a main injection that generates main torque. 
     An inlet air amount sensor  40 , an inlet air temperature sensor  42  and an inlet air pressure sensor  44  detect the amount, the temperature and the pressure of the air drawn into the combustion chamber  204  from the inlet passage  202 , respectively. A pressure sensor  46  detects the pressure of the fuel in the common-rail  34 . 
     The exhaust purification system  100  includes an oxidation catalyst  110 , a NO x  catalyst  112 , a DPF  114 , a fuel addition valve  120 , outlet air temperature sensors  130 ,  132 ,  134 , an A/F (A/F) ratio sensor  136 , a differential pressure sensor  138  and an electronic control unit (ECU)  140 . 
     A honeycomb structural body is configured to provide support for an oxidation catalyst  110  such as platinum. The oxidation catalyst  110  oxidizes harmful components in the exhaust such as hydrocarbon and carbon monoxide so that the exhaust is purified. The honeycomb structural body further provides support for a NO x  absorption material for NO x  catalyst  112 . The NO x  catalyst  112  absorbs NO x  in the exhaust and removes NO x  from the exhaust. The NO x  absorbed in the NO x  catalyst  112  is reduced by the fuel added from the fuel addition valve  120  to purify the exhaust. 
     The DPF  114  holds a honeycomb structural body made of porous ceramics. Inlet portions and outlet portions of exhaust passages formed along a flowing direction of the outlet air in the honeycomb structural body of the DPF  114  are sealed alternately. Particulates in the exhaust are drawn from the exhaust passages in which the inlet portions are not sealed and the outlet portions are sealed. Then, the particulates are captured in fine pores of bulkheads of the honeycomb structural body configuring the exhaust passages when the exhaust passes through the bulkheads. The exhaust flows out from the exhaust passages, in which the inlet portions are sealed and the outlet portions are not sealed. 
     The fuel addition valve  120  is a solenoid valve, and is located upstream of the oxidation catalyst  110 . The fuel addition valve  120  adds fuel pressurized by the high-pressure pump  30  into the outlet passage  200  located upstream of the oxidation catalyst  110  by injecting. The fuel added by the fuel addition valve  120  reduces NO x  absorbed in the NO x  catalyst  112 . 
     The outlet air temperature sensor  130  is located between the supercharger  14  and the oxidation catalyst  110 , the outlet air temperature sensor  132  is located between the oxidation catalyst  110  and the NO x  catalyst  112 , and the outlet air temperature sensor  134  is located downstream of the DPF  114 . The outlet air temperature sensors  130 ,  132 ,  134  detect the temperature of the outlet air in the outlet passage  200 . The A/F sensor  136  outputs a linear signal corresponding to oxygen concentration in the exhaust, and is located downstream of the DPF  114 . The differential pressure sensor  138  detects the pressure difference between the upstream side and the downstream side of the DPF  114 . 
     As will be appreciated, the ECU  140  as an exhaust purification control device is configured with a CPU, a RAM, a ROM and a flash memory, none of which are shown in the drawings. The ECU  140  determines the operating condition of the engine  10  depending on the output signals of the above-described sensors, and controls operations of the bypass valve  16  of the supercharger  14 , the throttle valve  20 , the EGR valve  22 , the metering valve of the high-pressure pump  30 , the fuel injection valve  36  and the fuel addition valve  120  depending on the operating condition of the engine  10 . 
     For example, the ECU  140  controls the injection timing and the injection amount of the fuel injection valve  36  and the injection pattern of the multistage injections depending on the operating condition of the engine  10 . The ECU  140  drives the fuel addition valve  120  to control the fuel addition into the outlet passage  200  from the fuel addition valve  120 . 
     The ECU  140  can function as several means described below based on control programs stored in a memory device such as the ROM and the flash memory of the ECU  140 . 
     When functioning as an addition timing detecting means, the ECU  140  estimates the NO x  amount absorbed in the NO x  catalyst  112  depending on an operating history of the engine  10  or a running distance of a vehicle. When the NO x  amount reaches a predetermined value, such as be reaching or approaching an acceptable value, the ECU  140  determines a timing associated with adding the fuel from the fuel addition valve  120  to reduce NO x  absorbed in the NO x  catalyst  112 . 
     When functioning as an addition valve controlling means, when the addition timing detecting means determines as the timing to reduce NO x  absorbed in the NO x  catalyst  112 , the ECU  140  drives the fuel addition valve  120  in connection with an instruction to add fuel into the outlet passage  200 . 
     The amount of fuel to be added by operation of the fuel addition valve  120  in connection with the instruction of the ECU  140 , may be a constant fixed amount or may be changed depending on the NO x  amount absorbed in the NO x  catalyst  112 . 
     When functioning as an actual A/F ratio detecting means, the ECU  140  detects an actual A/F ratio that can be determined by the inlet air amount drawn into the engine  10 , the fuel amount injected from the fuel injection valve  36  and the fuel amount added from the fuel addition valve  120 , depending on the output signal of the A/F sensor  136 . 
     When functioning as an estimated A/F ratio calculating means, the ECU  140  calculates an estimated A/F ratio based on the inlet air amount detected from the output signal of the inlet air amount sensor  40 , the fuel injection amount instructed to be injected by the fuel injection valve  36 , and the fuel addition amount instructed be added by the fuel addition valve  120 . If the fuel addition valve  120  is not instructed to add fuel, the fuel addition amount instructed to be added becomes zero for the purpose of calculating the estimated A/F ratio. 
     When functioning as an A/F sensor abnormality determining means, the ECU  140  determines that the A/F sensor  136  is abnormal when the output signal of the A/F sensor  136  does not change, and, for example, is fixed to a High or Low level. 
     When functioning as an addition valve abnormality determining means, the ECU  140  determines whether the amount of fuel to be added based on the instruction is actually added to the outlet passage  200  from the fuel addition valve  120  based on the difference between the actual A/F ratio detected by the actual A/F ratio detecting means and the estimated A/F ratio calculated by the estimated A/F ratio calculating means, and determines whether the fuel addition valve  120  is abnormal. 
     Hereinafter, the abnormality determination by the ECU  140  with respect to the fuel addition valve  120  in non-driven state and driven state of the fuel addition valve  120  will be described. The non-driven state means that the ECU  140  does not provide an instruction to the fuel addition valve  120  to add fuel, and the driven state means that the ECU  140  provides an instruction to the fuel addition valve  120  to add fuel. 
     In the non-driven state of the fuel addition valve  120 , when the fuel addition valve  120  is normal, the fuel is not added into the exhaust passage  200  from the fuel addition valve  120 . Thus, as described above, the instructed fuel addition amount with respect to the fuel addition valve  120  becomes zero in calculating the estimated A/F ratio. 
     Thereby, when the fuel addition valve  120  is normal and is closed in the non-driven state, the actual A/F ratio detected by the ECU  140  based on the output signal of the A/F sensor  136 , becomes a value corresponding to the case that the fuel addition amount is zero. Therefore, considering errors in the inlet air amount sensor  40 , the A/F sensor  136 , or other sensors, the actual A/F ratio falls within a predetermined range with respect to the estimated A/F ratio. 
     Despite the non-driven state, when the mechanical abnormality such as the fixation or the electrical abnormality may occur, the fuel addition valve  120  opens and adds fuel. Thereby, the actual A/F ratio detected by the ECU  140  based on the output signal of the A/F sensor  136 , becomes out of the predetermined range. 
     Therefore, in the non-driven state of the fuel addition valve  120 , the ECU  140  can determine whether opening abnormality, in which the fuel addition valve  120  opens and adds fuel despite the non-driven state, occurs based on the actual A/F ratio and the estimated A/F ratio. 
     During normal functioning, in the driven state of the fuel addition valve  120 , the amount of fuel associated with the instruction is added into the exhaust passage  200  from the fuel addition valve  120  so as to reduce NO x  absorbed in the NO x  catalyst  112 . 
     Thereby when the fuel addition valve  120  is normal and adds fuel of the instructed addition amount in the driven state, the value of the actual A/F ratio detected by the ECU  140  based on the output signal of the A/F sensor  136 , corresponds to a fuel addition amount from the fuel addition valve  120  equal to the instructed fuel addition amount. Therefore, considering errors or the like, the value of the actual A/F ratio falls within a predetermined range with respect to the estimated A/F ratio. 
     However, when a mechanical abnormality occurs that, for example, causes the valve to stick leading to defective sliding or an electrical abnormality occurs in the fuel addition valve  120 , a fuel addition abnormality occurs in which the fuel addition valve  120  is stuck in a closed position and does not add fuel despite the driven state or the fuel addition valve  120  partially opens and adds fuel but the fuel addition amount is too little. Thereby, the actual A/F ratio detected by the ECU  140  based on the output signal of the A/F sensor  136 , falls outside of the predetermined range with respect to the estimated A/F ratio. 
     In addition, when a mechanical abnormality such as sticking or an electrical abnormality occurs in the fuel addition valve  120 , the fuel addition valve  120  opens and adds fuel by in connection with an instruction to add fuel, but the fuel addition amount is too much because of the opening abnormality. Thereby, the actual A/F ratio detected by the ECU  140  based on the output signal of the A/F sensor  136 , falls outside of the predetermined range with respect to the estimated A/F ratio. 
     Therefore, in the driven state of the fuel addition valve  120 , the ECU  140  can determine whether a closing abnormality exists in which the fuel addition valve  120  closes and does not add fuel despite the driven state and the fuel addition amount is too little, or whether an opening abnormality exists in which the fuel addition valve  120  adds fuel but the fuel addition amount is too much. 
     In case that particulates trapped in the DPF  114  are burned by the post injection of the fuel injection valve  36  so as to regenerate the DPF  114 , it is difficult to determine whether the abnormality that causes the actual A/F ratio to fall outside of the predetermined range results from the post injection or the fuel addition valve  120  during the post injection. 
     Thus, when the fuel injection valve  36  performs the post injection so as to regenerate the DPF  114 , the ECU  140  stops the abnormality determination with respect to the fuel addition valve  120 . Thereby, the ECU  140  can be prevented from making an incorrect determination of whether the fuel addition valve  120  is abnormal based on the actual A/F ratio and the estimated A/F ratio during the post injection by the fuel injection valve  36 . 
     Furthermore, the ECU  140  stops the abnormality determination with respect to the fuel addition valve  120  when the A/F sensor  136  is abnormal. Thereby, the ECU  140  can be prevented from making an incorrect determination of whether the fuel addition valve  120  is abnormal based on the actual A/F ratio detected based on an incorrect output signal of the A/F sensor  136 , and the estimated A/F ratio. 
     When the A/F sensor  136  is normal, the ECU  140  controls the instructed fuel addition amount with respect to the fuel addition valve  120  based on the actual A/F ratio detected from the output signal of the A/F sensor  136 . 
     Next, the abnormality determination with respect to the fuel addition valve  120  in the exhaust purification system  100  will be described with reference to the abnormality determination routines shown in  FIG. 2  to  FIG. 9 . 
     In the routines in  FIG. 2  to  FIG. 9 , a routine for the non-driven state is regularly executed at a predetermined running distance. Alternatively, the routine is executed before the fuel addition valve  120  is instructed to add fuel when the ECU  140  determines that the NO x  amount absorbed in the NO x  catalyst  112  reaches a predetermined value based on the running distance or the operating history. 
     In the routines in  FIG. 2  to  FIG. 9 , a routine for the driven state is executed when the fuel addition valve  120  is instructed to add fuel, such as when the ECU  140  determines that the NO x  amount absorbed in the NO x  catalyst  112  reaches a predetermined value based on the running distance or the operating history. 
       FIG. 2  shows abnormality determination routine 1 in the non-driven state of the fuel addition valve  120 . The ECU  140  determines at S 300  whether the fuel addition valve  120  is driven. When the fuel addition valve  120  is driven, corresponding to “YES” at S 300 , the ECU  140  finishes the routine. 
     When the fuel addition valve  120  is not driven, corresponding to “NO” at S 300 , the ECU  140  calculates the estimated A/F ratio at S 302  based on the amount of inlet air detected from the output signal of the inlet air amount sensor  40 , the fuel injection amount associated with an instruction to the fuel injection valve  36 , and the fuel addition amount associated with an instruction to the fuel addition valve  120 . 
     The ECU  140  detects the actual A/F ratio based on the output signal of the A/F sensor  136  at S 304 . The ECU  140  determines at S 306  whether a difference D1 between the estimated A/F ratio and the actual A/F ratio is larger than an applied constant A set in advance in consideration of errors of each of sensors. 
     When the difference D1 is equal to or less than the applied constant A, corresponding to “NO” at S 306 , the ECU  140  determines that the fuel addition valve  120  does not add fuel in the non-driven state and the fuel addition valve  120  is normal. 
     If the fuel addition valve  120  is normal, the ECU  140  drives the fuel addition valve  120  at a predetermined time to add fuel into the outlet passage  200 . Then, the fuel reduces NO x  absorbed in the NO x  catalyst  112  so that NO x  is purified. 
     When the difference D1 is larger than the applied constant A, corresponding to “YES” at S 306 , the actual A/F ratio is less than the estimated A/F ratio, that is, the fuel amount shown by the actual A/F ratio is more than the fuel amount shown by the estimated A/F ratio. Therefore, the ECU  140  determines at S 310  that the fuel addition valve  120  is experiencing an opening abnormality in that the fuel addition valve  120  continues to add fuel despite being in the non-driven state. 
     When the fuel addition valve  120  is determined to be abnormal, the ECU  140  stops driving the fuel addition valve  120  even at the predetermined time, and provides information regarding the presence of the abnormality of the fuel addition valve  120  by operation of a warning light, a warning beep, a warning display or the like. 
       FIG. 3  shows abnormality determination routine 1 in the driven state of the fuel addition valve  120 . The ECU  140  determines at S 320  whether the fuel addition valve  120  is not driven. When the fuel addition valve  120  is not driven, corresponding to “YES” at S 320 , the ECU  140  finishes the routine. 
     When the fuel addition valve  120  is driven, corresponding to “NO” at S 320 , the ECU  140  calculates the estimated A/F ratio at S 322  based on the inlet air amount detected from the output signal of the inlet air amount sensor  40 , the fuel injection amount provided in connection with an instruction to the fuel injection valve  36 , and the fuel addition amount provided in connection with an instruction to the fuel addition valve  120 . 
     The ECU  140  detects the actual A/F ratio based on the output signal of the A/F sensor  136  at S 324 . The ECU  140  determines at S 326  whether a difference D2 between the actual A/F ratio and the estimated A/F ratio is larger than an applied constant B set in advance based on consideration of errors of each of sensors. 
     When the difference D2 is larger than the applied constant B, corresponding to “YES” at S 326 , the actual A/F ratio is larger than the estimated A/F ratio, that is, the fuel amount shown by the actual A/F ratio is less than the fuel amount shown by the estimated A/F ratio. As a result, the ECU  140  determines at S 328  that the fuel addition valve  120  is experiencing a closing abnormality in that the fuel addition valve  120  closes and does not add fuel despite being in the driven state or the fuel addition valve  120  partially opens and adds fuel but the fuel addition amount is too little. 
     When the difference D2 is equal to or less than the applied constant B, corresponding to “NO” at S 326 , the ECU  140  determines at S 330  whether the difference D1 between the estimated A/F ratio and the actual A/F ratio is larger than an applied constant C. 
     When the difference D1 is equal to or less than the applied constant C, corresponding to “NO” at S 330 , the ECU  140  determines at S 332  that the fuel addition valve  120  adds the instructed fuel addition amount in the driven state and the fuel addition valve  120  is normal. 
     When the difference D1 is larger than the applied constant C, corresponding to “YES” at S 330 , the actual A/F ratio is less than the estimated A/F ratio, that is, the fuel amount shown by the actual A/F ratio is greater than the fuel amount shown by the estimated A/F ratio. Therefore, the ECU  140  determines at S 334  that the fuel addition valve  120  is experiencing an opening abnormality in that the fuel addition amount added by the fuel addition valve  120  is larger than the instructed fuel addition amount. 
     When the fuel addition valve  120  is experiencing the opening abnormality or the closing abnormality, the ECU  140  stops driving the fuel addition valve  120  even at the predetermined time, and provides information regarding the presence of the abnormality of the fuel addition valve  120  by operation of a warning light, a warning beep, a warning display or the like. 
       FIG. 4  shows abnormality determination routine 2 in the non-driven state of the fuel addition valve  120 . The ECU  140  determines at S 340  whether the A/F sensor  136  is abnormal or whether the fuel addition valve  120  is driven. 
     When the A/F sensor  136  is abnormal or the fuel addition valve  120  is driven, corresponding to “YES” at S 340 , the ECU  140  finishes the routine. When the A/F sensor  136  is normal and the fuel addition valve  120  is not driven, corresponding to “NO” at S 340 , the ECU  140  performs S 342  to S 350 . Because S 342  to S 350  are substantially same as S 302  to S 310  in  FIG. 2 , the description thereof is omitted for simplicity. 
     However, an applied constant D used when the difference D1 is determined at S 346 , is desirably set to be smaller than the applied constant A at S 306  in  FIG. 2  because of enhanced reliability. For example, by setting the constant D smaller than A, in the routine that does not determine the abnormality of the A/F sensor  136  in  FIG. 2  and the routine that determines the abnormality of the A/F sensor  136  in  FIG. 4 , reliability of the value of the actual A/F ratio in the routine of  FIG. 4  is higher than that of  FIG. 2 . 
       FIG. 5  shows abnormality determination routine 2 for a driven state of the fuel addition valve  120 . The ECU  140  determines at S 360  whether the A/F sensor  136  is abnormal or whether the fuel addition valve  120  is not driven. 
     When the A/F sensor  136  is abnormal or the fuel addition valve  120  is not driven, corresponding to “YES” at S 360 , the ECU  140  finishes the routine. When the A/F sensor  136  is normal and the fuel addition valve  120  is driven, corresponding to “NO” at S 360 , the ECU  140  performs S 362  to S 374 . Because S 362  to S 374  are substantially same with S 322  to S 334  in  FIG. 3 , the description thereof is omitted for simplicity. 
     However, an applied constant E used when the difference D2 is determined at S 366 , is desirably set to be smaller than the applied constant B at S 326  in  FIG. 3 . In addition, an applied constant F used when the difference D1 is determined at S 370 , is desirably set to be smaller than the applied constant C at S 330  in  FIG. 3  because of reliability. By setting the constants as noted above, in the routine that does not determine the abnormality of the A/F sensor  136  in  FIG. 3  and in the routine that determines the abnormality of the A/F sensor  136  in  FIG. 5 , reliability of the value of the actual A/F ratio in the routine of  FIG. 5  is higher than that of  FIG. 3 . 
       FIG. 6  shows abnormality determination routine 3 in the non-driven state of the fuel addition valve  120 . The ECU  140  determines at S 380  whether the DPF  114  is regenerated by the post injection or whether the fuel addition valve  120  is driven. 
     When the DPF  114  is regenerated by the post injection or the fuel addition valve  120  is driven, corresponding to “YES” at S 380 , the ECU  140  finishes the routine. When the DPF  114  is not regenerated and the fuel addition valve  120  is not driven, corresponding to “NO” at S 380 , the ECU  140  performs S 382  to S 390 . Because S 382  to S 390  are substantially same with S 302  to S 310  in  FIG. 2 , the description thereof is omitted for simplicity. 
     However, an applied constant G used when the difference D1 is determined at S 386 , is desirably set to be smaller than the applied constant A at S 306  in  FIG. 2  because of reliability. For example, by setting the constants as noted, in the routine that does not determine whether the DPF  114  is regenerated in  FIG. 2  and in the routine that determines whether the DPF  114  is regenerated in  FIG. 4 , reliability of the value of the estimated A/F ratio in the routine of  FIG. 6  is higher than that of  FIG. 4  due to variability of the injection amount of the post injection for regenerating the DPF  114 . 
       FIG. 7  shows abnormality determination routine 3 in the driven state of the fuel addition valve  120 . The ECU  140  determines at S 400  whether the DPF  114  is regenerated by the post injection or whether the fuel addition valve  120  is not driven. 
     When the DPF  114  is regenerated by the post injection or the fuel addition valve  120  is not driven, corresponding to “YES” at S 400 , the ECU  140  finishes the routine. When the DPF  114  is not regenerated and the fuel addition valve  120  is driven, corresponding to “NO” at S 400 , the ECU  140  performs S 402  to S 414 . Because S 402  to S 414  are substantially same with S 322  to S 334  in  FIG. 3 , the description thereof is omitted for simplicity. 
     However, an applied constant H used when the difference D2 is determined at S 406 , is desirably set to be smaller than the applied constant B at S 326  in  FIG. 3 . In addition, an applied constant I used when the difference D1 is determined at S 410 , is desirably set to be smaller than the applied constant C at S 330  in  FIG. 3  because of reliability. For example, in the routine that does not determine whether the DPF  114  is regenerated in  FIG. 3  and in the routine that determines whether the DPF  114  is regenerated in  FIG. 7  reliability of the value of the estimated A/F ratio in the routine of  FIG. 7  is higher than that of  FIG. 3 . 
       FIG. 8  shows abnormality determination routine 4 in the non-driven state of the fuel addition valve  120 . The ECU  140  determines at S 420  whether the A/F sensor  136  is abnormal or whether the fuel addition valve  120  is driven. 
     When the A/F sensor  136  is abnormal or the fuel addition valve  120  is driven, corresponding to “YES” at S 420 , the ECU  140  finishes the routine. When the A/F sensor  136  is normal and the fuel addition valve  120  is not driven, corresponding to “NO” at S 420 , the ECU  140  determines at S 422  whether the DPF  114  is regenerated by the post injection. When the DPF  114  is regenerated by the post injection, corresponding to “YES” at S 422 , the ECU  140  finishes the routine. 
     When the DPF  114  is not regenerated, corresponding to “NO” at S 422 , the ECU  140  performs S 424  to S 432 . Because S 424  to S 432  are substantially same with S 302  to S 310  in  FIG. 2 , the description thereof is omitted for simplicity. 
     However, an applied constant J used when the difference D1 is determined at S 428 , is desirably set to be smaller than the applied constant A at S 306  in  FIG. 2  because of reliability. For example, in the routine that does not determine the abnormality of the A/F sensor  136  and whether the DPF  114  is regenerated in  FIG. 2  and in the routine that determines the abnormality of the A/F sensor  136  and whether the DPF  114  is regenerated in  FIG. 8 , reliability of the value of the actual A/F ratio and the estimated A/F ratio in the routine of  FIG. 8  is higher than that of  FIG. 2 . 
       FIG. 9  shows abnormality determination routine 4 in the driven state of the fuel addition valve  120 . The ECU  140  determines at S 440  whether the A/F sensor  136  is abnormal or whether the fuel addition valve  120  is not driven. 
     When the A/F sensor  136  is abnormal or the fuel addition valve  120  is not driven, corresponding to “YES” at S 440 , the ECU  140  finishes the routine. When the A/F sensor  136  is normal and the fuel addition valve  120  is driven, corresponding to “NO” at S 440 , the ECU  140  determines at S 442  whether the DPF  114  is regenerated by the post injection. When the DPF  114  is regenerated by the post injection, corresponding to “YES” at S 422 , the ECU  140  finishes the routine. 
     When the DPF  114  is not regenerated, corresponding to “NO” at S 442 , the ECU  140  performs S 444  to S 456 . Because S 444  to S 456  are substantially same with S 322  to S 334  in  FIG. 3 , the description thereof is omitted for simplicity. 
     However, an applied constant K used when the difference D2 is determined at S 448 , is desirably set to be smaller than the applied constant B at S 326  in  FIG. 3 . In addition, an applied constant L used when the difference D1 is determined at S 452 , is desirably set to be smaller than the applied constant C at S 330  in  FIG. 3  because of simplicity. In the routine that does not determine the abnormality of the A/F sensor  136  and whether the DPF  114  is regenerated in  FIG. 3  and in the routine that determines the abnormality of the A/F sensor  136  and whether the DPF  114  is regenerated in  FIG. 9 , reliability of the value of the actual A/F ratio and the estimated A/F ratio in the routine of  FIG. 9  is higher than that of  FIG. 3 . 
     According to the above described embodiment, in the driven state and the non-driven state of the fuel addition valve  120 , the ECU  140  detects the actual A/F ratio from the output signal of the A/F sensor  136 , calculates the estimated A/F ratio based on the inlet air amount detected from the output signal of the inlet air amount sensor  40 , the fuel injection amount provided by instruction to the fuel injection valve  36 , and the fuel addition amount provided by instruction to the fuel addition valve  120 , and determines whether the fuel addition valve  120  is abnormal based on the actual A/F ratio and the estimated A/F ratio. 
     Thereby, when the fuel addition valve  120  is abnormal, proper treatments such as stopping to drive the fuel addition valve  120 , alerting the abnormality of the fuel addition valve  120  or the like can be performed. 
     OTHER EMBODIMENTS 
     In the above embodiment, the oxidation catalyst  110 , the NO x  catalyst  112  and the DPF  114  are used as the exhaust treatment device for removing the harmful components in the exhaust discharged from the engine  10 , and the fuel is injected from the fuel addition valve  120  to reduce NO x  absorbed in the NO x  catalyst  112 . 
     In addition, the fuel may be injected from the fuel addition valve  120  to regenerate the DPF  114 . At least one of the NO x  catalyst  112  and the DPF  114  may be provided, and the fuel may be injected from the fuel addition valve  120  to reduce NO x  absorbed in the NO x  catalyst  112  and/or to regenerate the DPF  114 . 
     In the above-described case, the abnormality determination routines shown in  FIG. 2  to  FIG. 5  can be applied. 
     The exhaust treatment device may be any configuration as long as the exhaust treatment device removes the harmful components in the exhaust and the removed harmful components that are purified by the fuel injected from the fuel addition valve  120 . 
     The located position of the A/F sensor  136  is not limited to the downstream of the NO x  catalyst  112  and the DPF  114  as the exhaust treatment device as long as the A/F sensor  136  is located downstream of the fuel addition valve  120 . For example, the A/F sensor  136  may be located upstream of the NO x  catalyst  112 . 
     In the above embodiment, functions of the addition timing detecting means, the addition valve controlling means, the actual A/F ratio detecting means, the estimated A/F ratio calculating means, the addition valve abnormality determining means and the A/F sensor abnormality determining means are accomplished by the ECU  140 , in which the functions are specified by the control programs. By contrast, at least a part of the functions of the above-described means may be accomplished by hardware, in which the function is specified by a circuit configuration in itself. 
     Furthermore, the internal combustion engine is not limited to the diesel engine A gasoline engine, an internal combustion engine using another fuel or the like may be used. 
     While the invention has been described with reference to various exemplary embodiments, it is to be understood that the invention is not limited to the embodiments and constructions discussed and described herein. The invention is intended to cover various modifications and equivalent arrangements.