Exhaust Purification Control Device And Exhaust Purification System

Abstract

An exhaust purification control device is provided for an exhaust purification system that includes an exhaust treatment device located in an outlet passage of an internal combustion engine and a fuel addition valve. The control device includes an actual air-fuel (A/F) ratio detecting means for detecting an actual A/F ratio based on an output signal of an A/F ratio sensor, an estimated A/F ratio calculating means for calculating an estimated A/F ratio, 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. The exhaust purification control device can thereby determine normal and abnormal operation of the fuel addition valve.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] 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

[0002] 1. Field of the Invention

[0003] The present invention relates to an exhaust purification control device and an exhaust purification system that determines abnormalities of a fuel addition valve.

[0004] 2. Description of the Related Art

[0005] 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.

[0006] A NO.sub.x catalyst, a diesel particulate filter (DPF), or the like are provided as the exhaust treatment device. The NO.sub.x catalyst removes NO.sub.x from the exhaust, and the DPF removes particulates from the exhaust.

[0007] 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.

[0008] 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.

[0009] 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

[0010] 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.

[0011] 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.

[0012] 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

[0013] 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:

[0014] FIG. 1 is a block diagram illustrating an exhaust purification system according to an embodiment;

[0015] FIG. 2 is a diagram illustrating an abnormality determination routine 1 in a non-driven state of a fuel addition valve;

[0016] FIG. 3 is a diagram illustrating an abnormality determination routine 1 in a driven state of the fuel addition valve;

[0017] FIG. 4 is a diagram illustrating an abnormality determination routine 2 in the non-driven state of the fuel addition valve;

[0018] FIG. 5 is a diagram illustrating an abnormality determination routine 2 in the driven state of the fuel addition valve;

[0019] FIG. 6 is a diagram illustrating an abnormality determination routine 3 in the non-driven state of the fuel addition valve;

[0020] FIG. 7 is a diagram illustrating an abnormality determination routine 3 in the driven state of the fuel addition valve;

[0021] FIG. 8 is a diagram illustrating an abnormality determination routine 4 in the non-driven state of the fuel addition valve; and

[0022] 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

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The exhaust purification system 100 includes an oxidation catalyst 110, a NO.sub.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.

[0029] 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.sub.x absorption material for NO.sub.x catalyst 112. The NO.sub.x catalyst 112 absorbs NO.sub.x in the exhaust and removes NO.sub.x from the exhaust. The NO.sub.x absorbed in the NO.sub.x catalyst 112 is reduced by the fuel added from the fuel addition valve 120 to purify the exhaust.

[0030] 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.

[0031] 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.sub.x absorbed in the NO.sub.x catalyst 112.

[0032] 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.sub.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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] When functioning as an addition timing detecting means, the ECU 140 estimates the NO.sub.x amount absorbed in the NO.sub.x catalyst 112 depending on an operating history of the engine 10 or a running distance of a vehicle. When the NO.sub.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.sub.x absorbed in the NO.sub.x catalyst 112.

[0037] When functioning as an addition valve controlling means, when the addition timing detecting means determines as the timing to reduce NO.sub.x absorbed in the NO.sub.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.

[0038] 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.sub.x amount absorbed in the NO.sub.x catalyst 112.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.sub.x absorbed in the NO.sub.x catalyst 112.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.sub.x amount absorbed in the NO.sub.x catalyst 112 reaches a predetermined value based on the running distance or the operating history.

[0059] 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.sub.x amount absorbed in the NO.sub.x catalyst 112 reaches a predetermined value based on the running distance or the operating history.

[0060] FIG. 2 shows abnormality determination routine 1 in the non-driven state of the fuel addition valve 120. The ECU 140 determines at S300 whether the fuel addition valve 120 is driven. When the fuel addition valve 120 is driven, corresponding to "YES" at S300, the ECU 140 finishes the routine.

[0061] When the fuel addition valve 120 is not driven, corresponding to "NO" at S300, the ECU 140 calculates the estimated A/F ratio at S302 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.

[0062] The ECU 140 detects the actual A/F ratio based on the output signal of the A/F sensor 136 at S304. The ECU 140 determines at S306 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.

[0063] When the difference D1 is equal to or less than the applied constant A, corresponding to "NO" at S306, 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.

[0064] 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.sub.x absorbed in the NO.sub.x catalyst 112 so that NO.sub.x is purified.

[0065] When the difference D1 is larger than the applied constant A, corresponding to "YES" at S306, 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 S310 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.

[0066] 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.

[0067] FIG. 3 shows abnormality determination routine 1 in the driven state of the fuel addition valve 120. The ECU 140 determines at S320 whether the fuel addition valve 120 is not driven. When the fuel addition valve 120 is not driven, corresponding to "YES" at S320, the ECU 140 finishes the routine.

[0068] When the fuel addition valve 120 is driven, corresponding to "NO" at S320, the ECU 140 calculates the estimated A/F ratio at S322 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.

[0069] The ECU 140 detects the actual A/F ratio based on the output signal of the A/F sensor 136 at S324. The ECU 140 determines at S326 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.

[0070] When the difference D2 is larger than the applied constant B, corresponding to "YES" at S326, 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 S328 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.

[0071] When the difference D2 is equal to or less than the applied constant B, corresponding to "NO" at S326, the ECU 140 determines at S330 whether the difference D1 between the estimated A/F ratio and the actual A/F ratio is larger than an applied constant C.

[0072] When the difference D1 is equal to or less than the applied constant C, corresponding to "NO" at S330, the ECU 140 determines at S332 that the fuel addition valve 120 adds the instructed fuel addition amount in the driven state and the fuel addition valve 120 is normal.

[0073] When the difference D1 is larger than the applied constant C, corresponding to "YES" at S330, 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 S334 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.

[0074] 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.

[0075] FIG. 4 shows abnormality determination routine 2 in the non-driven state of the fuel addition valve 120. The ECU 140 determines at S340 whether the A/F sensor 136 is abnormal or whether the fuel addition valve 120 is driven.

[0076] When the A/F sensor 136 is abnormal or the fuel addition valve 120 is driven, corresponding to "YES" at S340, 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 S340, the ECU 140 performs S342 to S350. Because S342 to S350 are substantially same as S302 to S310 in FIG. 2, the description thereof is omitted for simplicity.

[0077] However, an applied constant D used when the difference D1 is determined at S346, is desirably set to be smaller than the applied constant A at S306 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.

[0078] FIG. 5 shows abnormality determination routine 2 for a driven state of the fuel addition valve 120. The ECU 140 determines at S360 whether the A/F sensor 136 is abnormal or whether the fuel addition valve 120 is not driven.

[0079] When the A/F sensor 136 is abnormal or the fuel addition valve 120 is not driven, corresponding to "YES" at S360, 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 S360, the ECU 140 performs S362 to S374. Because S362 to S374 are substantially same with S322 to S334 in FIG. 3, the description thereof is omitted for simplicity.

[0080] However, an applied constant E used when the difference D2 is determined at S366, is desirably set to be smaller than the applied constant B at S326 in FIG. 3. In addition, an applied constant F used when the difference D1 is determined at S370, is desirably set to be smaller than the applied constant C at S330 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.

[0081] FIG. 6 shows abnormality determination routine 3 in the non-driven state of the fuel addition valve 120. The ECU 140 determines at S380 whether the DPF 114 is regenerated by the post injection or whether the fuel addition valve 120 is driven.

[0082] When the DPF 114 is regenerated by the post injection or the fuel addition valve 120 is driven, corresponding to "YES" at S380, 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 S380, the ECU 140 performs S382 to S390. Because S382 to S390 are substantially same with S302 to S310 in FIG. 2, the description thereof is omitted for simplicity.

[0083] However, an applied constant G used when the difference D1 is determined at S386, is desirably set to be smaller than the applied constant A at S306 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.

[0084] FIG. 7 shows abnormality determination routine 3 in the driven state of the fuel addition valve 120. The ECU 140 determines at S400 whether the DPF 114 is regenerated by the post injection or whether the fuel addition valve 120 is not driven.

[0085] When the DPF 114 is regenerated by the post injection or the fuel addition valve 120 is not driven, corresponding to "YES" at S400, 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 S400, the ECU 140 performs S402 to S414. Because S402 to S414 are substantially same with S322 to S334 in FIG. 3, the description thereof is omitted for simplicity.

[0086] However, an applied constant H used when the difference D2 is determined at S406, is desirably set to be smaller than the applied constant B at S326 in FIG. 3. In addition, an applied constant I used when the difference D1 is determined at S410, is desirably set to be smaller than the applied constant C at S330 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.

[0087] FIG. 8 shows abnormality determination routine 4 in the non-driven state of the fuel addition valve 120. The ECU 140 determines at S420 whether the A/F sensor 136 is abnormal or whether the fuel addition valve 120 is driven.

[0088] When the A/F sensor 136 is abnormal or the fuel addition valve 120 is driven, corresponding to "YES" at S420, 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 S420, the ECU 140 determines at S422 whether the DPF 114 is regenerated by the post injection. When the DPF 114 is regenerated by the post injection, corresponding to "YES" at S422, the ECU 140 finishes the routine.

[0089] When the DPF 114 is not regenerated, corresponding to "NO" at S422, the ECU 140 performs S424 to S432. Because S424 to S432 are substantially same with S302 to S310 in FIG. 2, the description thereof is omitted for simplicity.

[0090] However, an applied constant J used when the difference D1 is determined at S428, is desirably set to be smaller than the applied constant A at S306 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.

[0091] FIG. 9 shows abnormality determination routine 4 in the driven state of the fuel addition valve 120. The ECU 140 determines at S440 whether the A/F sensor 136 is abnormal or whether the fuel addition valve 120 is not driven.

[0092] When the A/F sensor 136 is abnormal or the fuel addition valve 120 is not driven, corresponding to "YES" at S440, 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 S440, the ECU 140 determines at S442 whether the DPF 114 is regenerated by the post injection. When the DPF 114 is regenerated by the post injection, corresponding to "YES" at S422, the ECU 140 finishes the routine.

[0093] When the DPF 114 is not regenerated, corresponding to "NO" at S442, the ECU 140 performs S444 to S456. Because S444 to S456 are substantially same with S322 to S334 in FIG. 3, the description thereof is omitted for simplicity.

[0094] However, an applied constant K used when the difference D2 is determined at S448, is desirably set to be smaller than the applied constant B at S326 in FIG. 3. In addition, an applied constant L used when the difference D1 is determined at S452, is desirably set to be smaller than the applied constant C at S330 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.

[0095] 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.

[0096] 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

[0097] In the above embodiment, the oxidation catalyst 110, the NO.sub.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.sub.x absorbed in the NO.sub.x catalyst 112.

[0098] In addition, the fuel may be injected from the fuel addition valve 120 to regenerate the DPF 114. At least one of the NO.sub.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.sub.x absorbed in the NO.sub.x catalyst 112 and/or to regenerate the DPF 114.

[0099] In the above-described case, the abnormality determination routines shown in FIG. 2 to FIG. 5 can be applied.

[0100] 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.

[0101] The located position of the A/F sensor 136 is not limited to the downstream of the NO.sub.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.sub.x catalyst 112.

[0102] 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.

[0103] 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.

[0104] 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.

Claims

1. An exhaust purification control device capable of placement in an exhaust purification system that includes an exhaust treatment device located in an outlet passage of an internal combustion engine and a fuel addition valve, the exhaust purification control device comprising: an actual air-fuel (A/F) ratio detecting means for detecting an actual A/F ratio based on an output signal from 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 injection amount of fuel injected into the internal combustion engine from a fuel injection valve, a fuel addition amount of the fuel to be 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 the fuel addition amount 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.

2. The exhaust purification control device according to claim 1, wherein the addition valve abnormality determining means determines whether the fuel addition valve is abnormal based on the actual A/F ratio and the estimated A/F ratio in a non-driven state in which the addition valve controlling means does not instruct the fuel addition valve to add the fuel addition amount.

3. The exhaust purification control device according to claim 1, wherein the addition valve abnormality determining means determines whether the fuel addition valve is abnormal based on the actual A/F ratio and the estimated A/F ratio in a driven state in which the addition valve controlling means instructs the fuel addition valve to add the fuel addition amount.

4. The exhaust purification control device according to claim 1, further comprising: an A/F ratio sensor abnormality determining means for determining whether the A/F ratio sensor is abnormal, wherein the addition valve abnormality determining means stops an abnormality determination with respect to the fuel addition valve when the A/F ratio sensor is determined to be abnormal.

5. The exhaust purification control device according to claim 1, wherein the exhaust treatment device includes a NO.sub.x catalyst configured to reduce NO.sub.x removed from the exhaust by the fuel addition amount added from the fuel addition valve.

6. The exhaust purification control device according to claim 5, wherein the exhaust treatment device further includes a filter configured to remove a particulate from the exhaust.

7. The exhaust purification control device according to claim 6, wherein the particulate removed by the filter is burned by a second fuel injection amount of the fuel from of a post injection performed by the fuel injection valve, and the addition valve abnormality determining means stops an abnormality determination with respect to the fuel addition valve in the post injection.

8. The exhaust purification control device according to claim 6, wherein the particulate removed from the exhaust is burned by the fuel addition amount added from the fuel addition valve so that the filter is regenerated.

9. An exhaust purification system comprising: an exhaust treatment device provided in an outlet passage of an internal combustion engine and configured to remove a component in an exhaust discharged from the internal combustion engine; a fuel addition valve configured to purify the harmful component removed by the exhaust treatment device by adding an fuel addition amount of fuel into the outlet passage; an A/F ratio sensor located downstream of the fuel addition valve; and the exhaust purification control device including: an actual air-fuel (A/F) ratio detecting means for detecting an actual A/F ratio based on an output signal from 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 injection amount of the fuel injected into the internal combustion engine from a fuel injection valve, the fuel addition amount of fuel to be 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 the fuel addition amount of the 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.