Title:
EXHAUST PURIFICATION SYSTEM, CONTROL APPARATUS AND CONTROL METHOD THEREFOR
Kind Code:
A1


Abstract:
An exhaust gas purification control apparatus for an internal combustion engine instructs an exhaust fuel valve to inject additive fuel when a diesel particulate filter is to be regenerated, and determines that both the exhaust fuel valve and an oxidation catalyst are normal if an exhaust temperature rises. If the exhaust temperature does not rise, the control apparatus instructs an engine fuel valve to inject additive fuel as a post-injection. If the exhaust temperature does not rise, the control apparatus determines that the oxidation catalyst is abnormal. If the exhaust temperature rises, the control apparatus determines that the oxidation catalyst is normal but the exhaust fuel valve is abnormal.



Inventors:
Noda, Yoshihiro (Ichinomiya-city, JP)
Application Number:
12/372148
Publication Date:
09/24/2009
Filing Date:
02/17/2009
Assignee:
DENSO CORPORATION (Kariya-city, JP)
Primary Class:
Other Classes:
60/297, 60/299
International Classes:
F01N9/00
View Patent Images:



Primary Examiner:
TRAN, DIEM T
Attorney, Agent or Firm:
NIXON & VANDERHYE, PC (ARLINGTON, VA, US)
Claims:
What is claimed is:

1. An exhaust purification control apparatus for an internal combustion engine having an exhaust fuel valve, an oxidation catalyst and an exhaust purification device in an exhaust passage thereof, the exhaust fuel valve being for supplying additive fuel into the exhaust passage and the oxidation catalyst being 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 comprising: temperature determination means 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; fuel control means configured 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 abnormality check means configured to check whether the oxidation catalyst or the exhaust fuel valve is abnormal based on the catalyst exhaust temperatures determined when the fuel control means has instructed the first addition of fuel and the second addition of fuel, respectively.

2. The exhaust purification control apparatus according to claim 1, wherein: the fuel control means is configured to instruct the second addition of fuel as the post-injection when the catalyst exhaust temperature, which is determined when the first addition of fuel by the exhaust fuel valve is instructed, is lower than a first predetermined temperature; the abnormality check means is configured to determine that the oxidation catalyst and the exhaust fuel valve are normal, when the catalyst exhaust temperature becomes greater than the first predetermined temperature in response to the first addition of fuel; the abnormality check means is configured to determine that the oxidation catalyst is abnormal, when the catalyst exhaust temperature is less than a second predetermined temperature in response to the second addition of fuel, which is instructed when the catalyst exhaust temperature is less than the first predetermined temperature; and the abnormality check means is configured to determine that the oxidation catalyst is normal and the exhaust fuel valve is abnormal, when the catalyst exhaust temperature becomes greater than the second predetermined temperature in response to the second addition of fuel.

3. The exhaust purification control apparatus according to claim 1, wherein: the fuel control means is configured to instruct the first addition of fuel by the exhaust fuel valve when the catalyst exhaust temperature, which is determined when the second addition of fuel by the engine fuel valve is instructed, becomes greater than a second predetermined temperature; the abnormality check means is configured to determine that the oxidation catalyst is normal, when the catalyst exhaust temperature becomes greater than the second predetermined temperature in response to the second addition of fuel; the abnormality check means is configured to determine that the exhaust fuel valve is normal, when the catalyst exhaust temperature becomes greater than a first predetermined temperature in response to the first addition of fuel, which is instructed when the catalyst exhaust temperature is greater than the second predetermined temperature in response to the second addition of fuel; and the abnormality check means determines that the exhaust fuel valve is abnormal, when the catalyst exhaust temperature is less than the first predetermined temperature in response to the first addition of fuel.

4. The exhaust purification control apparatus according to claim 1, wherein the exhaust purification device includes a particulate filter.

5. An exhaust purification system for an internal combustion engine having an exhaust passage comprising: an exhaust fuel valve provided in the exhaust passage for supplying additive fuel into the exhaust passage; an oxidation catalyst provided in the exhaust passage for causing oxidation reaction of the additive fuel; a temperature sensor for outputting a signal corresponding to an exhaust temperature in the oxidation catalyst; an exhaust purification device provided downstream the oxidation catalyst for purifying harmful components in emissions exhausted from the internal combustion engine; and an exhaust purification control apparatus according to claim 1.

6. A control method for an exhaust purification system for an internal combustion engine having an exhaust passage comprising an engine fuel valve provided on the engine for supplying fuel into the engine, an exhaust fuel valve provided in the exhaust passage for supplying additive fuel into the exhaust passage, an oxidation catalyst provided in the exhaust passage for causing oxidation reaction of fuel in exhaust gas of the engine, and an exhaust purification device provided downstream the oxidation catalyst for purifying exhaust gas of the engine, the control method comprising: instructing the exhaust fuel valve and the engine fuel valve to supply first additive fuel into the exhaust passage and second additive fuel into the engine, respectively, at different timings, the second additive fuel being supplied into the engine in an exhaust stroke of the engine; checking whether temperature in the oxidation catalyst has risen in response to each instruction of supply of the first additive fuel and the second additive fuel; and determining which one of the exhaust fuel valve and the oxidation catalyst is abnormal based on check results of temperatures in the oxidation catalyst.

7. The control method according to claim 6, wherein: the checking compares the temperature in the oxidation catalyst with a first predetermined temperature and a second predetermined temperature when the supply of the first additive fuel and the second additive fuel are instructed, respectively; and the first predetermined temperature is higher than the second predetermined temperature.

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 T1. 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 (S300). If the output signal of the sensor 142 indicates that it is not the DPF regeneration time yet (S300: NO), this routine is ended.

If it is the DPF regeneration time (S300: YES), the ECU 150 instructs the exhaust fuel injection valve 130 to inject the first additive fuel directly into the exhaust passage 210 (S302) 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 (S304).

If the catalyst exhaust temperature has risen above the predetermined temperature T1 (5304: YES), the ECU 150 determines that the DOC 110 and the exhaust fuel injection valve 130 are both normal (S306, S308) and ends this routine.

If the catalyst exhaust temperature has not risen and is below the predetermined temperature T1 (S304: 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 (S310). 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 (S310: NO), the ECU 150 ends this routine.

If the engine fuel injection is valve 26 is normal (S310: 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 (S312) to activate DOC 110.

The ECU 150 then checks whether the catalyst exhaust temperature has risen above a second predetermined temperature T2 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 T2 (S314: NO), the ECU 150 determines that the DOC 110 is abnormal (S316) and end this routine

If the catalyst exhaust temperature rises above the second predetermined temperature T2 (S314: YES), the ECU 150 determines that the DOC 110 is normal (S318) 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 (S330: NO), the ECU 150 ends this routine.

If it is the time for DPF regeneration (S330: YES), the ECU 150 checks whether the engine fuel injection valve 26 normally operates to inject fuel (S332). If the engine fuel injection valve 26 does not normally inject fuel (S332: NO), the ECU 150 ends this routine.

If the engine fuel injection valve 26 normally injects fuel (S332: YES), the ECU 150 instructs the engine fuel injection valve 26 to inject the second additive fuel as the post-injection (S334) for activating the DOC 110. The ECU 150 then checks whether the catalyst exhaust temperature has risen above the second predetermined temperature T2 in correspondence to the post-injection (S336). If the catalyst exhaust temperature has not risen above the predetermined temperature T2 (S336: NO), the ECU 150 determines that the DOC 110 is abnormal (S338) and ends this routine.

If the catalyst exhaust temperature has risen above the predetermined temperature T2 in response to the post-injection (S336: YES), the ECU 150 determines that the DOC 110 is normal (S340). 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 (S344).

If the catalyst exhaust temperature does not rise and remains below the predetermined temperature T1 (S344: NO), the ECU 150 determines that the exhaust fuel injection valve 130 is abnormal (S346). If the catalyst exhaust temperature has risen above the predetermined temperature T1 (S344: 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.