Patent Publication Number: US-2009235645-A1

Title: Exhaust purification system, control apparatus and control method therefor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-76106 filed on Mar. 24, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to an exhaust purification system for an internal combustion engine, which includes an oxidation catalyst provided upstream an exhaust purification device in an exhaust passage of an internal combustion engine and an exhaust fuel valve provided to supply additive fuel into the exhaust passage so that exhaust temperature is raised by the oxidation reaction of the additive fuel in the oxidation catalyst, and a control apparatus and a control method for the exhaust purification system. 
     BACKGROUND OF THE INVENTION 
     In some conventional exhaust purification systems (for example, JP 9-222009A), an oxidation catalyst is provided upstream an exhaust purification device in an exhaust passage of an internal combustion engine so that the exhaust temperature is raised by the oxidation reaction of additive fuel supplied into the exhaust passage. 
     As the exhaust purification device, a diesel particulate filter (DPF) or the like is used to collect particulates in the exhaust emission of a diesel engine. Fuel is supplied as additive fuel into the exhaust passage, when the DPF is to be regenerated. In this instance, the additive fuel is oxidized in the oxidation catalyst and the exhaust temperature rises. As a result, the particulates collected by the DPF are burned and thus the exhaust gas is purified. 
     In place of such a DPF, which burns the particulates by the heat of reaction of the additive fuel in the oxidation catalyst, it is also possible to supply additive fuel into an exhaust passage to raise exhaust temperature by the heat of reaction of the additive fuel in an oxidation catalyst so that the exhaust temperature may be raised quickly to promote exhaust purification in an exhaust purification device when the exhaust temperature is low. 
     In such exhaust purification systems, a fuel injection valve of an internal combustion engine is driven to attain post-injection after normal main injection to supply additive fuel into the engine or an exhaust fuel injection valve provided in an exhaust passage is driven to directly supply additive fuel into the exhaust passage. This post-injection is attained in the exhaust stroke of the engine and hence does not contribute to the normal combustion of fuel nor to motive power generation. 
     If the exhaust fuel valve is used, the exhaust temperature sometimes does not rise sufficiently even when the exhaust fuel valve is driven to inject the additive fuel into the exhaust passage. It is not possible to specify the reason why the exhaust temperature does not rise sufficiently, that is, whether the additive fuel does not react in the oxidation catalyst because of failure (abnormality) of the oxidation catalyst in spite of the exhaust fuel valve operating normally, or whether the additive fuel is not supplied because of failure of the exhaust fuel valve in spite of the oxidation catalyst operating normally. As a result, the oxidation catalyst or the exhaust fuel valve may have to be replaced with a new one unnecessarily to raise the exhaust temperature. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an exhaust purification system, a control apparatus and a control method, which can determine whether an insufficient exhaust temperature rise is caused by abnormality of an exhaust fuel valve or an oxidation catalyst provided in an exhaust passage of an internal combustion engine. 
     According to one aspect, an exhaust purification system for an internal combustion engine has an exhaust fuel valve, an oxidation catalyst, an exhaust purification device in an exhaust passage thereof and an exhaust purification control apparatus. The exhaust fuel valve is for supplying additive fuel into the exhaust passage, and the oxidation catalyst is provided upstream the exhaust purification device so that the additive fuel supplied from the exhaust fuel valve raises exhaust temperature by oxidation reaction. The exhaust purification control apparatus is configured to determine a catalyst exhaust temperature in the oxidation catalyst based on an output signal of a temperature sensor provided in the exhaust passage, to control a first addition of fuel from the exhaust fuel valve into the exhaust passage and a second addition of fuel supplied from an engine fuel valve as a post-injection of the engine fuel valve, and to check whether the oxidation catalyst or the exhaust fuel valve is abnormal based on the catalyst exhaust temperatures determined when the first addition of fuel and the second addition of fuel are instructed, respectively. 
    
    
     
       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 schematic diagram showing an exhaust purification system according to an embodiment of the present invention; 
         FIG. 2  is a flowchart showing an example of abnormality check routine executed in the embodiment; and 
         FIG. 3  is a flowchart showing another example of abnormality check routine executed in the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1 , an exhaust purification system  100  is provided for purifying gas exhausted from a four-cylinder four-stroke diesel engine  10  into an exhaust passage  210 . 
     The engine  10  has an intake passage  200 , in which a turbocharger  12  is provided to supply compressed air and an intercooler  14  for cooling the compressed air before being supplied into the engine  10 . The intake passage  200  and the exhaust passage  210  are connected to each other via an exhaust gas recirculation (EGR) passage, which recirculates a part of the exhaust gas of the engine  10  through an EGR cooler  18  and an EGR valve  16  when the EGR valve  16  is opened. 
     A fuel supply pump  20 , which is a high-pressure pump having a reciprocating plunger, is provided to suction fuel from a fuel tank  22  and pressurize the fuel. The amount of pressurized fuel discharged or supplied from the fuel supply pump  20  is regulated by regulating the amount of fuel suctioned into the pump  20  by a metering valve (not shown). 
     The fuel supply pump  20  is coupled to a common rail  24 , which accumulates the pressurized fuel supplied from the fuel supply pump  20  and maintains the fuel at a predetermined high pressure determined in accordance with engine operating conditions. The common rail  24  is coupled to each engine fuel injection valve (engine fuel valve)  26  of the engine  10  to supply the accumulated fuel to the engine fuel injection valve  26 . The engine fuel injection valve  26  is an electromagnetically operable valve, in which a nozzle needle opens and closes an injection port in accordance with a pressure in a control chamber as known well. 
     The engine fuel injection valve  26  is mounted on each cylinder of the engine  10  to inject the fuel accumulated in the common rail  24  into the corresponding cylinder. As described below, the engine fuel injection valve  26  is driven multiple times in one combustion cycle (four strokes) of the engine  10  to attain not only normal main injection for generation of motive power but also a pilot injection before the main injection and a post-injection after the main injection. 
     An intake air sensor  30  is provided in the intake passage  200  at the upstream side of the turbocharger  12  to detect the amount of air suctioned into the engine  10 . A pressure sensor  32  is provided in the common rail  24  to detect the pressure of the accumulated fuel in the common rail  24 . A fuel level sensor  34  is provided in the fuel tank  22  to detect the level of fuel in the fuel tank  22 . 
     The exhaust purification system  100  includes a diesel oxidation catalyst (DOC)  110 , a diesel particulate filter (DPF)  112  provided as an exhaust purification device, a selective catalytic reduction (SCR) catalyst  120 , an exhaust fuel injection valve (exhaust fuel valve)  130 , a cut-off valve  132 , two exhaust temperature sensors  140 , a differential pressure sensor  142 , and an electronic control unit (ECU)  150 . The ECU  150  is connected to various sensors and actuators described above. 
     The DOC  110  and the DPF  112  are encased in the same casing in such a manner that the DOC  110  is provided upstream the DPF  112  and downstream the exhaust fuel injection valve  130  in the exhaust passage  210 . The DOC  110  is provided to oxidize additive fuel supplied into the exhaust passage  210  by the exhaust fuel injection valve  130  so that the oxidation reaction of the additive fuel in the DOC  110  raises the exhaust temperature. 
     The DPF  112  is formed of a porous ceramic in a honeycomb structure. The inlet sides and the outlet sides of exhaust passages formed in the exhaust flow direction in the honeycomb structure are sealed alternately. The exhaust gas thus flows through the DPF  112  from some exhaust passages, which have open inlets and sealed outlets, to the other exhaust passages, which have sealed inlets and open outlets. The DPF  112  collects particulates in the exhaust gas in micropores of partition walls, which separate the exhaust passages of the honeycomb structure, when the exhaust gas passes by the partition walls. 
     Although not shown in  FIG. 1 , a urea fluid supply valve is provided between the DPF  112  and the SCR catalyst  120  to supply urea fluid into the exhaust passage  210 , so that the urea fluid supplied from the urea fluid supply valve is adsorbed in the SCR catalyst  120 . The urea fluid adsorbed in the SCR catalyst  120  is hydrolyzed and decomposed into ammonia and carbon dioxide, when the exhaust temperature rises above a predetermined temperature. The ammonia produced by the hydrolysis of the urea fluid reduces nitrogen dioxides in the exhaust gas in the SCR catalyst  120 . 
     The exhaust fuel injection valve  130  is an electromagnetically-operated valve controlled by the ECU  150  and provided in the exhaust passage  210  upstream the DOC  110 . The exhaust fuel injection valve  130  is coupled to the fuel supply pump  20  to directly inject the pressurized fuel as additive fuel into the exhaust passage  130  upstream the DOC  110 . This additive fuel is oxidized in the DOC  110  and generates oxidation reaction heat, which raises the exhaust temperature in the DOC  110 . 
     The cut-off valve  132  is also an electromagnetically-operated valve and controlled by the ECU  132  to open and close the fuel passage from the fuel supply pump  20  to the exhaust fuel injection valve  130 . The cut-off valve  132  opens the fuel passage to allow fuel flow when the engine  10  is started and closes the same to prevent the fuel flow when the engine  10  is stopped. The two exhaust temperature sensors  140  are provided upstream the DOC  110  and between the DOC  110  and the DPF  112 , respectively to detect the exhaust temperatures (catalyst temperatures) upstream and downstream the DOC  110 . The differential pressure sensor  142  is provided to detect a pressure difference (differential pressure) between the pressures upstream the DOC  110  and downstream the DPF  112 . 
     The ECU  150  is provided as an exhaust purification control apparatus and is configured with a CPU, a RAM, a ROM, a flash memory and the like as known well in the art. The ECU  150  determines engine operating conditions based on the output signals of the various sensors, and controls operations of the actuators such as the EGR valve  16 , the metering valve of the fuel supply pump  20 , the fuel injection valves  26  and the exhaust fuel injection valve  130  based on the determined engine operating conditions, 
     Specifically, the ECU  150 , particularly the CPU, is programmed to control the fuel injection timing, the fuel injection amount and the fuel injection patterns of multi-stage fuel injections of the engine fuel injection valve  26 . The ECU  150  is programmed to control the addition of fuel supplied directly into the exhaust passage  210  as the additive fuel by driving the exhaust fuel injection valve  130 . 
     The ECU  150  is programmed to function as the following means, that is, temperature determination means, regeneration timing determination means, fuel control means, and abnormality check means. 
     (Catalyst Exhaust Temperature Determination) 
     The ECU  150  is programmed to determine the catalyst exhaust temperature in the DOC  110  form the output signals of the two exhaust temperature sensors. 
     (Regeneration Timing Determination) 
     The ECU  150  is programmed to determine the differential pressure of the upstream and the downstream of the DPF  112  based on the output signal of the differential pressure sensor  142 . The ECU  150  is programmed to check whether the determined differential pressure is greater than a predetermined pressure and the DPF  112  is clogged with the collected particulates. The ECU  150  is programmed to determine in this instance that it is time to regenerate the DPF  112  by adding fuel into the exhaust passage  210  from the exhaust fuel injection valve  130 . 
     If the additive fuel is supplied directly into the exhaust passage  210 , the additive fuel is oxidized in the DOC  110 . This oxidation reaction produces reaction heat and raises the exhaust temperature sufficiently. As a result, the particulates collected in the DPF  112  are burned with the raised exhaust temperature. Thus the DPF  112  is regenerated to be able to collect further particulates anew. 
     (Fuel Control) 
     The ECU  150  is programmed to instruct the direct addition of fuel (first addition of fuel) directly into the exhaust passage  210  by the exhaust fuel injection valve  130  and the indirect addition of fuel (second addition of fuel) into the exhaust passage  210  by the engine fuel injection valve  26  as the post-injection of the engine fuel injection valve  26  in the exhaust stroke. The addition of fuel is instructed in either one of the following orders (1) and (2). 
     The ECU  150  is programmed to set the amount of additive fuel of the exhaust fuel injection valve  130  at a fixed amount or a variable amount corresponding to the output signal of the differential pressure sensor  142 . 
     The amount of fuel (additive fuel) injected as the post-injection and the number of times of the post-injections need be determined so that whether the DOC  110  is normal or abnormal may be checked based on the catalyst exhaust temperature. It is preferred for this reason that the amount of fuel and the number of times of the post-injections are set to be less than the amount of fuel and the number of times of post-injections required to regenerate the DPF  112 . 
     (1) Post-Injection After Additive Fuel Injection by Exhaust Fuel Injection Valve  130   
     The ECU  150  instructs, at the time of regeneration of the DPF  112 , the exhaust fuel injection valve  130  to inject the additive fuel. The ECU  150  instructs the engine fuel injection valve  26  to inject the additive fuel as the post-injection if the engine fuel injection valve  26  is normal, when the catalyst exhaust temperature does not rise sufficiently and remains below a predetermined temperature although the exhaust fuel injection valve  130  has been instructed to inject the additive fuel. 
     The ECU  150  instructs the engine fuel injection valve  26  to perform the post-injection, when the catalyst exhaust temperature has risen above the predetermined temperature T 1 . If the post-injection is performed in the exhaust stroke, a part of the additive fuel will adhere to the cylinder wall of the engine  10 . This fuel will leak out through the sliding part with the piston and possibly dilute lubricating oil. 
     However, the amount of fuel and the number of times of the post-injection of the engine fuel injection valve  26  can be reduced by instructing the engine fuel injection valve  26  to attain the post-injection only when the catalyst exhaust temperature does not rise sufficiently in spite of the instruction of the injection of additive fuel to the exhaust fuel injection valve  26  at the time of regeneration of the DPF  112 . 
     (2) Additive Fuel Injection by Exhaust Fuel Injection Valve  130  After Post-Injection 
     The ECU  150  instructs the engine fuel injection valve  26  to inject the additive fuel as the post-injection at the time of regeneration of the DPF  112  if the engine fuel injection valve  26  is normal. 
     The amount of fuel (additive fuel) injected as the post-injection and the number of times of the post-injections need be determined so that whether the DOC  110  is normal or abnormal may be checked based on the catalyst exhaust temperature. It is preferred for this reason that the amount of fuel and the number of times of the post-injections are set to be less than the amount of fuel and the number of times of post-injections required to regenerate the DPF  112 . 
     The ECU  150  instructs the exhaust fuel injection valve  130  to inject the additive fuel into the exhaust passage  210  directly, when the engine fuel injection valve  26  has been instructed to perform the post-injection and the catalyst exhaust temperature has risen above a predetermined temperature. The ECU  150  does not instruct the exhaust fuel injection valve  130  to inject the additive fuel, when the engine fuel injection valve  26  has been instructed to perform the post-injection but the catalyst exhaust temperature does not rise and remains below the predetermined temperature. 
     The ECU  150  is programmed to thus control, based on the catalyst exhaust temperature attained in response to one of the instructions of additive fuel injection to the exhaust fuel injection valve  130  and the engine fuel injection valve  26 , whether the other fuel injection of additive fuel should be instructed. 
     (Abnormality Check) 
     The ECU  150  is further programmed to determine the catalyst exhaust temperature in either one of the following orders of additive fuel injection (1) and (2). 
     The ECU  150  is still further programmed to check whether the DOC  110  is abnormal or the exhaust fuel injection valve  130  is abnormal based on two catalyst exhaust temperatures, one temperature is a result of the direct injection of the additive fuel into the exhaust passage  210  by the exhaust fuel injection valve  130  and the other temperature is a result of the post-injection of the additive fuel into the engine  10  by the engine fuel injection valve  26 . 
     (1) Post-Injection After Additive Fuel Injection by Exhaust Fuel Injection Valve  130   
     The ECU  150  checks whether the catalyst exhaust temperature has risen above the predetermined temperature as a result of instruction of the additive fuel injection by the exhaust fuel injection valve  130  at the time of the regeneration of the DPF  112 . 
     The catalyst exhaust temperature should rise above the predetermined temperature, if the exhaust fuel injection valve  130  has injected the additive fuel into the exhaust passage  210  and the injected additive fuel has been oxidized in the DOC  110 . In this instance, the ECU  150  determines that both the exhaust fuel injection valve  130  and the DOC  110  are normal. 
     The ECU  150  determines that at least one of the exhaust fuel injection valve  130  and the DOC  110  is abnormal, if the catalyst exhaust temperature does not rise above the predetermined temperature in spite of the instruction of the additive fuel injection to the exhaust fuel injection valve  130 . 
     In this instance, the ECU  150  instructs the engine fuel injection valve  26  to inject the additive fuel as the post injection if the engine fuel injection valve  26  is normal. The ECU  150  checks whether the catalyst exhaust temperature has risen above the predetermined temperature based on the output signals of the exhaust temperature sensors  140  as a result of the instruction of the post-injection to the engine fuel injection valve  26 . 
     As far as the engine fuel injection valve  26  has no abnormality and operates normally, the exhaust temperature will be raised above the predetermined temperature by the post-injection if the DOC  110  is normal. In this instance, the ECU  150  determines that the DOC  110  is normal. 
     The ECU  150  determines that the DOC  110  does not operate normally and is abnormal, if the catalyst exhaust temperature does not rise above and remains below the predetermined temperature in spite of the instruction of the post-injection to the engine fuel injection valve  26 . 
     The predetermined temperatures, with which the detected catalyst exhaust temperature is compared, may be the same or different between the case when the additive fuel injection is instructed to the exhaust fuel injection valve  130  and the case when the additive fuel injection by the post-injection is instructed to the engine fuel injection valve  130 . 
     If the DOC  110  is abnormal, the exhaust temperature in the DOC  110  will not rise above and remain below the predetermined temperature whether the additive fuel is injected by the exhaust fuel injection valve  130 . Therefore, in this instance, it is impossible to check whether the exhaust fuel injection valve  130  is normal or abnormal. 
     If the amount of fuel and the number of times of the post-injections are set to respective values, which are less than those required to regenerate the DPF  112 , the predetermined temperature, with which the detected catalyst exhaust temperature caused by the post-injection of the engine fuel injection valve  26  is compared, is set to be less than that, with which the detected catalyst exhaust temperature caused by the additive fuel injection by the exhaust fuel injection valve  130  is compared. 
     (2) Additive Fuel Injection by Exhaust Fuel Injection Valve After Post-Injection 
     The ECU  150  instructs the engine fuel injection valve to inject fuel as the post-injection at the time of regenerating the DPF  112 , if the engine fuel injection valve  26  is normal. 
     The ECU  150  checks whether the catalyst exhaust temperature detected from the output signals of the exhaust temperature sensors  140  has risen above the predetermined temperature after the instruction of the post-injection to the engine fuel injection valve  26 . As far as the engine fuel injection valve  26  is normal and attains the post-injection, the exhaust temperature will rise above the predetermined temperature if the DOC  110  is normal. In this instance, the ECU  150  determines that the DOC  110  is normal. 
     If the exhaust temperature does not rise above the predetermined temperature in spite of the instruction of the post-injection to the engine fuel injection valve  26 , the ECU  150  determines that the DOC  110  does not operate normally and hence is abnormal. If the DOC  110  is abnormal, the exhaust temperature will remain below the predetermined temperature whether the additive fuel is injected from the exhaust fuel injection valve  130 . As a result, it is impossible to check whether the exhaust fuel injection valve  130  is normal or abnormal. In this instance, the ECU  150  does not instruct the exhaust fuel injection valve  130  to inject the additive fuel even if it is the time to regenerate the DPF  112 . 
     If the catalyst exhaust temperature has risen above the predetermined temperature subsequent to the instruction of the post-injection, the ECU  150  instructs the additive fuel injection to the exhaust fuel injection valve  130  thereby to regenerate the DPF  112 . In this instance, since it is confirmed that the DOC  110  is normal from the result of the post-injection, the exhaust temperature will rise above the predetermined temperature if the exhaust fuel injection valve  130  is normal. 
     If the catalyst exhaust temperature remains below the predetermined temperature in spite of the instruction of the additive fuel injection to the exhaust fuel injection valve  130 , the ECU  150  determines that the exhaust fuel injection valve  130  is abnormal. 
     (Abnormality Check) 
     The abnormality check and determination processing for the DOC  110  and the exhaust fuel injection valve  130 , which are executed by the ECU  150 , particularly by its CPU, is described next in detail with reference to  FIGS. 2 and 3 . The routines of  FIGS. 2 and 3  are repeated normally at every predetermined interval. 
     (Abnormality Check Routine  1 ) 
     In this routine shown in  FIG. 2 , the ECU  150  first instructs the exhaust fuel injection valve  130  to inject the first additive fuel based on the catalyst exhaust temperature and then instructs the engine fuel injection valve  26  to inject the second additive fuel as the post-injection. 
     More specifically, the ECU  150  checks whether the regeneration of DPF  112  is necessary based on the output signal of the differential pressure sensor  142 , that is, whether it is the time for DPF regeneration (S 300 ). If the output signal of the sensor  142  indicates that it is not the DPF regeneration time yet (S 300 : NO), this routine is ended. 
     If it is the DPF regeneration time (S 300 : YES), the ECU  150  instructs the exhaust fuel injection valve  130  to inject the first additive fuel directly into the exhaust passage  210  (S 302 ) thereby to activate the DOC  110 . The ECU  150  checks whether the catalyst exhaust temperature has risen above a first predetermined temperature TI based on the output signals or the exhaust temperature sensors  140  (S 304 ). 
     If the catalyst exhaust temperature has risen above the predetermined temperature T 1  ( 5304 : YES), the ECU  150  determines that the DOC  110  and the exhaust fuel injection valve  130  are both normal (S 306 , S 308 ) and ends this routine. 
     If the catalyst exhaust temperature has not risen and is below the predetermined temperature T 1  (S 304 : NO), the ECU  150  determines that at least either one of the DOC  110  and the exhaust fuel injection valve  130  is abnormal. In this instance, the ECU  150  checks whether the engine fuel injection valve  26  operates normally (S 310 ). This check may be made by monitoring whether the engine rotation speed changes in correspondence to fuel injections by the engine fuel injection valve  26  or whether the cylinder pressure changes in correspondence to combustions in the cylinder. If the engine fuel injection valve  26  is not normal (S 310 : NO), the ECU  150  ends this routine. 
     If the engine fuel injection is valve  26  is normal (S 310 : YES), the ECU  150  instructs the engine fuel injection valve  26  to inject the second additive fuel in the exhaust stroke as the post-injection (S 312 ) to activate DOC  110 . 
     The ECU  150  then checks whether the catalyst exhaust temperature has risen above a second predetermined temperature T 2  in response to the post-injection by the engine fuel injection valve  26  ( 5312 ). If the catalyst exhaust temperature does not rise above the predetermined temperature T 2  (S 314 : NO), the ECU  150  determines that the DOC  110  is abnormal (S 316 ) and end this routine 
     If the catalyst exhaust temperature rises above the second predetermined temperature T 2  (S 314 : YES), the ECU  150  determines that the DOC  110  is normal (S 318 ) but the exhaust fuel injection valve  130  is abnormal ( 5320 ), thus ending this routine. 
     (Abnormality Check Routine  2 ) 
     In the routine shown in  FIG. 3 , the ECU  150  instructs first the engine fuel injection valve  26  to inject the second additive fuel as the post-injection and thereafter instructs the exhaust fuel injection valve  130  to inject the first additive fuel into the exhaust passage  120  directly based on the catalyst exhaust temperature, 
     More specifically, the ECU  150  checks whether it is the time to regenerate the DPF  112  based on the output signal of the differential pressure sensor  142  ( 5330 ). If it is not the time for regeneration (S 330 : NO), the ECU  150  ends this routine. 
     If it is the time for DPF regeneration (S 330 : YES), the ECU  150  checks whether the engine fuel injection valve  26  normally operates to inject fuel (S 332 ). If the engine fuel injection valve  26  does not normally inject fuel (S 332 : NO), the ECU  150  ends this routine. 
     If the engine fuel injection valve  26  normally injects fuel (S 332 : YES), the ECU  150  instructs the engine fuel injection valve  26  to inject the second additive fuel as the post-injection (S 334 ) for activating the DOC  110 . The ECU  150  then checks whether the catalyst exhaust temperature has risen above the second predetermined temperature T 2  in correspondence to the post-injection (S 336 ). If the catalyst exhaust temperature has not risen above the predetermined temperature T 2  (S 336 : NO), the ECU  150  determines that the DOC  110  is abnormal (S 338 ) and ends this routine. 
     If the catalyst exhaust temperature has risen above the predetermined temperature T 2  in response to the post-injection (S 336 : YES), the ECU  150  determines that the DOC  110  is normal (S 340 ). The ECU  150  instructs next the exhaust fuel injection valve  130  to inject the first additive fuel into the exhaust passage  210  for DPF activation ( 5342 ), and then checks again whether the catalyst exhaust temperature has arisen above the first predetermined temperature in response to the additive fuel injection by the exhaust fuel injection valve  130  (S 344 ). 
     If the catalyst exhaust temperature does not rise and remains below the predetermined temperature T 1  (S 344 : NO), the ECU  150  determines that the exhaust fuel injection valve  130  is abnormal (S 346 ). If the catalyst exhaust temperature has risen above the predetermined temperature T 1  (S 344 : YES), the ECU  150  determines that the exhaust fuel injection valve  130  is normal ( 5348 ) and ends this routine. 
     According to the present embodiment, the catalyst exhaust temperature detected following the instruction of additive fuel injection into the exhaust passage  210  by the exhaust fuel injection valve  130  and the catalyst exhaust temperature detected following the instruction of additive fuel injection as the post-injection by the engine fuel injection valve  26  are compared with the respective predetermined temperatures. 
     As a result, it can be checked whether the abnormality of at least either one of the DOT  110  or the exhaust fuel injection valve  130  has caused that the catalyst exhaust temperature does not rise above the predetermined temperature even if the additive fuel has been injected into the exhaust passage  210  by the exhaust fuel injection valve  130 . 
     The present embodiment described above may be modified in various ways 
     For example, a NOx catalyst may be provided in the exhaust passage  210  as an exhaust gas purifying device to thereby purify the NOx in the exhaust gas quickly, by injecting the additive fuel into the exhaust passage  210  and causing the oxidation reaction in the DOC  110 , which raises the exhaust temperature. 
     As far as the exhaust purification system includes an oxidation catalyst upstream an exhaust purification device to raise exhaust temperature by oxidation reaction of additive fuel injected by an exhaust fuel injection valve in the oxidation catalyst, the exhaust purification control apparatus may be used for gasoline or other fuel engines other than a diesel engine. 
     In place of instructing the additive fuel injection as the post-injection at the time of regenerating the DPF  112 , the additive fuel injection as the post-injection by the engine fuel injection valve  26  may be instructed at the time of starting or stopping the engine  10 . In this instance, too, it can be checked whether the DOC  110  and the exhaust fuel injection valve  130  are normal or abnormal based on the catalyst exhaust temperature 
     The functions of temperature determination, regeneration timing determination, fuel control and abnormality check may be realized wholly or partly by hardware circuits in place of software processing in the ECU  150 . 
     In place of taking the normality of the engine fuel injection valve  26  into consideration to check whether the DOC  110  and the exhaust fuel injection valve  130  are normal or abnormal, it may be so determined tentatively, irrespective of the normality or abnormality of the engine fuel injection valve  26 , that the DOC  110  is abnormal when the catalyst exhaust temperature in the DOC  110  does not rise in response to any of the additive fuel injections of the engine fuel injection valve  26  and the exhaust fuel injection valve  130 .