Patent Application
20190275465
The present invention relates to an abnormality diagnosis system for an exhaust gas purification apparatus.
A known exhaust gas purification apparatus includes a selective catalytic reduction NOx catalyst (also referred to as “SCR catalyst” hereinafter) capable of reducing NOx contained in the exhaust gas of an internal combustion engine by using ammonia as a reducing agent and a reducing agent suppler that supplies ammonia or a precursor of ammonia as a reducing agent to the exhaust gas.
It is known to diagnose abnormality of the SCR catalyst in such an exhaust gas purification apparatus on the basis of the NOx concentration in the region upstream of the SCR catalyst and the NOx concentration in the region downstream of the SCR catalyst, in other words, on the basis of the NOx removal rate of the SCR catalyst.
Patent Literature 1 discloses abnormality diagnosis of an SCR catalyst based on the ammonia concentration in the region downstream of the SCR catalyst. In the technology disclosed in Patent Literature 1, reducing agent is supplied to the exhaust gas at a location upstream of the SCR catalyst to reduce NOx. Diagnosis as to abnormality of the SCR catalyst is made based on the concentration of ammonia slipping out of the SCR catalyst.
According to the aforementioned prior art, the abnormality diagnosis of the SCR catalyst is performed based on the fact that ammonia tends to slip out of the SCR catalyst when the SCR catalyst has some abnormality. However, the amount of ammonia adsorbed in the SCR catalyst at the time when the condition for performing the abnormality diagnosis is met can be small depending on the structure of the exhaust gas purification apparatus or the operation state of the internal combustion engine. Then, if the quantity of reducing agent supplied is small, there may be cases where ammonia does not slip out of the SCR catalyst even if the SCR catalyst has an abnormality.
Therefore, in order for abnormality diagnosis of the SCR catalyst to be carried out successfully on the basis of the ammonia concentration in the exhaust gas in the region downstream of the SCR catalyst, it is necessary that a proper amount of ammonia be adsorbed in the SCR catalyst. However, the amount of ammonia adsorbed in the SCR catalyst may not be proper for abnormality diagnosis of the SCR catalyst at the time when the abnormality diagnosis is required to be performed in some cases. In such cases, it may be difficult to perform the abnormality diagnosis at an adequate frequency.
The present invention has been made in view of the above problem, and an object of the present invention is to enable abnormality diagnosis of the SCR catalyst to be performed at an adequate frequency.
According to a first aspect of the present invention, there is provided an abnormality diagnosis system for an exhaust gas purification apparatus that is applied to an exhaust gas purification apparatus including a reducing agent suppler provided in an exhaust passage of an internal combustion engine to supply ammonia or a precursor of ammonia as a reducing agent into the exhaust passage, a selective catalytic reduction NOx catalyst provided in the exhaust passage downstream of said reducing agent suppler to reduce NOx in exhaust gas by ammonia, and measure configured to measure the ammonia concentration in the exhaust gas downstream of said selective catalytic reduction NOx catalyst; wherein said abnormality diagnosis system comprises a controller comprising at least one processor configured to perform abnormality diagnosis of said selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by said measure. Said controller estimates an ammonia adsorption amount defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst on the assumption that said selective catalytic reduction NOx catalyst is normal; performs supply control to supply, by said reducing agent suppler, said reducing agent in a predetermined fixed supply quantity for diagnosis larger than the quantity of reducing agent that is supplied by said reducing agent suppler for the purpose of reduction of NOx by said selective catalytic reduction NOx catalyst, when said abnormality diagnosis is performed; performs abnormality diagnosis of said selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by said measure when said reducing agent is supplied by said supply control; and performs reducing control to reduce the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst in such a way as to make said ammonia adsorption amount after the completion of said supply control performed next time larger than a slip start adsorption amount in abnormal condition defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst at which slip of ammonia out of said selective catalytic reduction NOx catalyst starts if said selective catalytic reduction NOx catalyst is in a condition in which said selective catalytic reduction NOx catalyst is diagnosed to have an abnormality by said abnormality diagnosis and smaller than a slip start adsorption amount in normal condition defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst at which slip of ammonia out of said selective catalytic reduction NOx catalyst starts if said selective catalytic reduction NOx catalyst is in a normal condition, at a specific time after the completion of said abnormality diagnosis performed last time and before the start of said abnormality diagnosis performed next time, if said ammonia adsorption amount is larger than a specific upper limit adsorption amount at said specific time.
The above-described abnormality diagnosis system performs the supply control to supply the supply quantity for diagnosis of reducing agent by the reducing agent suppler when performing the abnormality diagnosis. According to the first aspect of the present invention, the supply quantity for diagnosis is a predetermined fixed quantity larger than the quantity of reducing agent that is supplied by the reducing agent suppler for the purpose of reduction of NOx by the selective catalytic reduction NOx catalyst (which will also be referred to as the “SCR catalyst” hereinafter). The quantity of reducing agent that is supplied by the reducing agent suppler for the purpose of reduction of NOx by the selective catalytic reduction NOx catalyst will also be referred to as the “quantity required for reduction” hereinafter. The quantity required for reduction is the quantity of reducing agent that is supplied for the purpose of reducing NOx during normal operation of the internal combustion engine. The supply quantity for diagnosis is a predetermined quantity.
If the above-described supply control is performed when the SCR catalyst is normal, the amount of ammonia adsorbed in the SCR catalyst tends to be relatively large because the reducing agent is supplied in the supply quantity for diagnosis larger than the quantity required for reduction. If the ammonia adsorption amount after the completion of this control (which will also be referred to as the “adsorption amount after supply control” hereinafter) is larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition, ammonia will not slip out of the SCR catalyst if the SCR catalyst is normal, and ammonia will slip out of the SCR catalyst if the SCR catalyst has an abnormality. The ammonia adsorption amount is the estimated value of the amount of ammonia adsorbed in the SCR catalyst that is estimated on the assumption that the SCR catalyst is normal. When ammonia slips out of the SCR catalyst, the ammonia concentration is measured by the measure. Thus, abnormality diagnosis of the SCR catalyst can be performed on the basis of the ammonia concentration measured by the measure when the reducing agent is supplied by the supply control. When performing the abnormality diagnosis of the SCR catalyst in this way, the controller may determine whether or not the SCR catalyst has an abnormality by a known technique. For example, the SCR catalyst may be diagnosed to have an abnormality when the ammonia concentration measured by the measure reaches or exceeds a threshold concentration.
In the above-described abnormality diagnosis system, since the adsorption amount after supply control tends to be relatively large, the ammonia adsorption amount at the time when abnormality diagnosis is performed next time tends to be larger than the specific upper limit amount, if the rate of decrease of the ammonia adsorption amount from the adsorption amount after supply control after the completion of the supply control is relatively low. The specific upper limit adsorption amount mentioned above is an upper limit of the ammonia adsorption amount at which the abnormality diagnosis of the SCR catalyst is allowed to be performed. For instance, the specific upper limit adsorption amount is defined as such an ammonia adsorption amount that if the reducing agent is supplied in the supply quantity for diagnosis larger than the quantity required for reduction in the process of abnormality diagnosis in the state in which the ammonia adsorption amount is larger than the specific upper limit adsorption amount, the adsorption capacity of the SCR catalyst is exceeded even if the SCR catalyst is normal and slip of ammonia out of the SCR catalyst can result. Therefore, if the reducing agent is supplied in the supply quantity for diagnosis larger than the quantity required for reduction in the process of the next abnormality diagnosis in a circumstance in which the ammonia adsorption amount at that time is larger than the specific upper limit adsorption amount, ammonia that the SCR catalyst even in a normal condition cannot adsorb can slip out of it. To avoid this, the above-described abnormality diagnosis system performs the reducing control at a specific time before the time when the abnormality diagnosis is performed next time, if the ammonia adsorption amount is larger than the specific upper limit adsorption amount.
After the reducing control is started at the aforementioned specific time, the amount of ammonia adsorbed in the SCR catalyst is reduced. The reducing control reduces the amount of ammonia adsorbed in the SCR catalyst taking account of the predetermined supply quantity for diagnosis in such a way as to make the ammonia adsorption amount after the completion of the next supply control larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. Even when the SCR catalyst is in normal conditions, the ammonia adsorption capacity of the SCR catalyst changes depending on the degree of deterioration of the SCR catalyst. The slip start adsorption amount in normal condition may be defined as the amount of ammonia adsorbed in the SCR catalyst at which slip of ammonia out of the SCR catalyst starts in the case where the SCR catalyst is in a specific deteriorated condition in which the SCR catalyst is regarded to be normal.
As the reducing agent is supplied in the quantity for diagnosis larger than the quantity required for reduction in the process of the next abnormality diagnosis, the ammonia adsorption amount, which is the amount of ammonia adsorbed in the SCR catalyst that is estimated on the assumption that the SCR catalyst is normal, changes to an amount larger than the slip start amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. This resultant adsorption amount will also be referred to as “specific state adsorption amount” hereinafter. Then, if the SCR catalyst is normal, ammonia will not slip. When the supply control is performed in the process of the next abnormality diagnosis, ammonia does not slip if the SCR catalyst is normal but slips if the SCR catalyst has an abnormality. Thus, the controller can make a diagnosis as to abnormality of the SCR catalyst according to the predetermined timing of performing the abnormality diagnosis.
If the ammonia adsorption amount is equal to or smaller than the specific upper limit adsorption amount at said specific time, the ammonia adsorption amount at the time when the next abnormality diagnosis is performed will be equal to or smaller than the specific upper limit adsorption amount. In that case, the reducing control is not performed at said specific time. When the SCR catalyst is normal, as the reducing agent is supplied in the supply quantity for diagnosis larger than the quantity required for reduction, a relatively large quantity of ammonia that would lead to slip of ammonia out of the SCR catalyst if the SCR catalyst were abnormal is adsorbed by the SCR catalyst in a normal condition. Hence, even though the ammonia adsorption amount is equal to or smaller than the specific upper limit adsorption amount, the ammonia adsorption amount tends to be relatively large at said specific time, though not larger than the specific upper limit adsorption amount.
By performing the above-described reducing control, the abnormality diagnosis system for an exhaust gas purification apparatus according to the first aspect of the present invention enables the abnormality diagnosis of the SCR catalyst based on the ammonia concentration in the region downstream of the SCR catalyst to be performed at an adequate frequency.
According to a second aspect of the present invention, there is provided an abnormality diagnosis system for an exhaust gas purification apparatus comprising a controller comprising at least one processor configured to perform abnormality diagnosis of said selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by said measure. Said controller estimates an ammonia adsorption amount defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst on the assumption that said selective catalytic reduction NOx catalyst is normal; performs supply control to supply, by said reducing agent suppler, said reducing agent in a supply quantity for diagnosis larger than the quantity of reducing agent that is supplied by said reducing agent suppler for the purpose of reduction of NOx by said selective catalytic reduction NOx catalyst, when said abnormality diagnosis is performed, and performs said supply control in such a way as to make said ammonia adsorption amount after the completion of said supply control larger than a slip start adsorption amount in abnormal condition defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst at which slip of ammonia out of said selective catalytic reduction NOx catalyst starts if said selective catalytic reduction NOx catalyst is in a condition in which said selective catalytic reduction NOx catalyst is diagnosed to have an abnormality by said abnormality diagnosis and smaller than a slip start adsorption amount in normal condition defined as the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst at which slip of ammonia out of said selective catalytic reduction NOx catalyst starts if said selective catalytic reduction NOx catalyst is in a normal condition; performs abnormality diagnosis of said selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by said measure when said reducing agent is supplied by said supply control; and performs reducing control to reduce the amount of ammonia adsorbed in said selective catalytic reduction NOx catalyst in such a way as to make said ammonia adsorption amount equal to or smaller than a specific upper limit adsorption amount, at a specific time after the completion of said abnormality diagnosis performed last time and before the start of said abnormality diagnosis performed next time, if said ammonia adsorption amount is larger than said specific upper limit adsorption amount at said specific time.
In the abnormality diagnosis system according to the second aspect of the present invention, the controller performs the supply control in such a way as to make the adsorption amount after supply control equal to the specific state adsorption amount. In other words, in the abnormality diagnosis system according to the second aspect of the present invention, the supply quantity for diagnosis may be a specific variable quantity larger than the quantity required for reduction. If the ammonia adsorption amount at said specific time is larger than the specific upper limit adsorption amount, the reducing control is performed at that time. This makes the ammonia adsorption amount equal or smaller than the specific upper limit adsorption amount. As described above, the specific upper limit adsorption amount is an upper limit of the ammonia adsorption amount at which the abnormality diagnosis of the SCR catalyst is allowed to be performed. If, for example, the quantity of ammonia is reduced by a fixed quantity by the reducing control, the ammonia adsorption amount after performing the reducing control varies in accordance with the ammonia adsorption amount before performing the reducing control. In this case, performing the reducing control and the above-descried supply control helps to adjust the ammonia adsorption amount after the completion of the supply control to the specific state adsorption amount.
If the reducing control is not performed although the ammonia adsorption amount is larger than the specific upper limit adsorption amount and the ammonia adsorption amount before performing the supply control is relatively large, it is sometime impossible to adjust the adsorption amount after supply control to the specific state adsorption amount only by the supply control. This is because the supply quantity for diagnosis is larger than the quantity required for reduction, and the minimum value of the supply quantity for diagnosis tends to be relatively large. If it is not possible to adjust the adsorption amount after supply control to the specific state adsorption amount only by the supply control, the next abnormality diagnosis cannot be performed. Therefore, if the ammonia adsorption amount is larger than the specific upper limit adsorption amount at said specific time, it is necessary to perform the reducing control to reduce the ammonia adsorption amount to an amount smaller than the specific upper limit adsorption amount so that the ammonia adsorption amount before performing the supply control will be prevented from being so large. This enables the abnormality diagnosis of the SCR catalyst to be performed at the predetermined timing of performing the abnormality diagnosis.
As described above, even if the ammonia adsorption amount is equal to or smaller than the specific upper limit adsorption amount at said specific time (in this case, the reducing control is not performed), the ammonia adsorption amount tends to be relatively large, though not larger than the specific upper limit adsorption amount. However, there can be cases where the ammonia adsorption amount is very small, depending on the operation state of the internal combustion engine or other factors. If the ammonia adsorption amount is very small at the time when the next abnormality diagnosis is performed (whether the reducing control is performed or not), a relatively large quantity of reducing agent may be supplied by the supply control so as to adjust the adsorption amount after supply control to the specific state adsorption amount. Thus, it is possible to adjust the adsorption amount after supply control to the specific state adsorption amount appropriately.
In the abnormality diagnosis system for an exhaust gas purification apparatus according to the second aspect of the present invention, by performing the above-described supply control and reducing control, it is possible to appropriately adjust the adsorption amount after supply to the specific state adsorption amount with the supply quantity for diagnosis larger than the quantity required for reduction. Moreover, performing the above-described reducing control enables the abnormality diagnosis of the SCR catalyst based on the ammonia concentration in the region downstream of the SCR catalyst to be performed at an adequate frequency.
The abnormality diagnosis system for an exhaust gas purification apparatus according to the second aspect of the present invention, wherein said controller may determine, when a condition for performing said abnormality diagnosis is met, said supply quantity for diagnosis on the basis of said ammonia adsorption amount at the time when said condition for performing said abnormality diagnosis is met in such a way that the sum of said ammonia adsorption amount at the time when said condition for performing said abnormality diagnosis is met and the quantity of ammonia derived from said supply quantity for diagnosis is larger than said slip start adsorption amount in abnormal condition and smaller than said slip start adsorption amount in normal condition. Said controller of said abnormality diagnosis system may supply said reducing agent in said supply quantity for diagnosis by said reducing agent suppler in said supply control. The supply quantity for diagnosis determined by said controller is larger than the quantity required for reduction.
As described above, the reducing control is performed at a specific time after the abnormality diagnosis is performed last time and before the abnormality diagnosis is performed next time. Hence, the ammonia adsorption amount may change from the time when the reducing control is performed to the time when the reducing control is performed next time. If the supply quantity for diagnosis is determined at the time when the condition for performing the abnormality diagnosis is met on the basis of the ammonia adsorption amount at the time when the condition for performing the abnormality diagnosis is met as in the above-described abnormality diagnosis system, the supply control can be performed with higher accuracy than in the case where, for example, the supply quantity for diagnosis is determined on the basis of the ammonia adsorption amount immediately after the completion of the reducing control.
Said controller may determine said supply quantity for diagnosis in such a way that the sum of said ammonia adsorption amount at the time when said condition for performing said abnormality diagnosis is met and the quantity of ammonia derived from said supply quantity for diagnosis is equal to or larger than an abnormality diagnosis enabling quantity defined as the sum of said slip start adsorption amount in abnormal condition and a specific measurable ammonia quantity and smaller than said slip start adsorption amount in normal condition.
The specific measurable ammonia quantity is determined taking account of measurement errors in measurement of the ammonia concentration by the measure etc. If the quantity of ammonia slipping out of the SCR catalyst smaller than the specific measurable ammonia quantity, it is sometimes difficult to measure the concentration of ammonia slipping out of the SCR catalyst, because the measurement can be affected by measurement errors etc. Moreover, for example, when an NOx sensor capable of measuring the concentration of NOx in the exhaust gas and having sensitivity to ammonia as well as NOx is used as the measure, it is sometimes difficult to measure the ammonia concentration accurately unless the ammonia concentration in the exhaust gas is relatively higher than the NOx concentration. The specific measurable ammonia quantity is determined taking account of this.
When the supply control is performed to supply the reducing agent in the supply quantity for diagnosis determined as above by the reducing agent suppler, the adsorption amount after supply control is made equal to or larger than the abnormality diagnosis enabling quantity and smaller than the slip start adsorption amount in normal condition. Then, if the SCR catalyst has an abnormality, a quantity of ammonia larger than the specific measurable ammonia quantity will slip out of the SCR catalyst when the supply control is performed. Then, the measure can measure the concentration of ammonia with relatively high accuracy. Therefore, the controller can make a diagnosis of the SCR catalyst with relatively high accuracy.
By performing the supply control to supply the reducing agent in the supply quantity for diagnosis as described above, the above-described abnormality diagnosis system enables the abnormality diagnosis of the SCR catalyst based on the ammonia concentration in the region downstream of the SCR catalyst to be performed with as high accuracy as possible. Executing the above-described reducing control enables the abnormality diagnosis with such high accuracy to be performed at an adequate frequency.
According to the present invention, the exhaust gas purification apparatus may further include an NOx removing catalyst provided in the exhaust passage upstream of said selective catalytic reduction NOx catalyst to reduce NOx in the exhaust gas. In the exhaust gas purification apparatus configured as above, a somewhat large part of NOx discharged from the internal combustion engine is removed by the NOx removing catalyst provided in the exhaust passage upstream of the SCR catalyst, and the NOx concentration in the exhaust gas flowing into the SCR catalyst is relatively low. In consequence, the quantity of ammonia available for reduction of NOx is relatively low. Hence, after the supply control is performed once, the rate of decrease of the ammonia adsorption amount from the adsorption amount after supply control tends to be low. In that case, as described above, the ammonia adsorption amount at the time when abnormality diagnosis is performed next time tends to be larger than the specific upper limit adsorption amount. In this state, if the reducing agent is supplied when the abnormality diagnosis is performed next time, ammonia that the SCR catalyst cannot adsorb may slip even if the SCR catalyst is normal.
Therefore, the abnormality diagnosis system for an exhaust gas purification apparatus according to the present invention is configured to perform the reducing control at the specific time if the ammonia adsorption amount at that time is larger than the specific upper limit adsorption amount, thereby enabling the abnormality diagnosis of the SCR catalyst to be performed at an adequate frequency.
Said controller of the abnormality diagnosis system for an exhaust gas purification apparatus according to the present invention may perform, as said reducing control, at least one of catalyst temperature raising control for raising the temperature of said selective catalytic reduction NOx catalyst and NOx flow rate increasing control for increasing the flow rate of NOx flowing into said selective catalytic reduction NOx catalyst.
The amount of ammonia that the SCR catalyst can adsorb changes depending on the temperature of the SCR catalyst, and raising the temperature of the SCR catalyst can reduce the amount of ammonia adsorbed in the SCR catalyst. Increasing the flow rate of NOx flowing into the SCR catalyst can also reduce the amount of ammonia adsorbed in the SCR catalyst, because a relatively large quantity of ammonia is consumed in reduction of the increased quantity of NOx.
According to a third aspect of the present invention, there is provided an abnormality diagnosis system for an exhaust gas purification apparatus that is applied to an exhaust gas purification apparatus including a reducing agent suppler provided in an exhaust passage of an internal combustion engine to supply ammonia or a precursor of ammonia as a reducing agent into the exhaust passage, a selective catalytic reduction NOx catalyst provided in the exhaust passage downstream of the reducing agent suppler to reduce NOx in exhaust gas by ammonia, and a measure configured to measure the ammonia concentration in the exhaust gas downstream of the selective catalytic reduction NOx catalyst; wherein said abnormality diagnosis system comprises a controller comprising at least one processor configured to perform abnormality diagnosis of the selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by the measure. Said controller estimates an ammonia adsorption amount in abnormal condition defined as the amount of ammonia adsorbed in the selective catalytic reduction NOx catalyst on the assumption that the selective catalytic reduction NOx catalyst is in a condition that is diagnosed as abnormal by the abnormality diagnosis; estimates an ammonia adsorption amount in normal condition defined as the amount of ammonia adsorbed in the selective catalytic reduction NOx catalyst on the assumption that the selective catalytic reduction NOx catalyst is in a normal condition; performs, when the abnormality diagnosis is to be performed, supply control for diagnosis to supply the reducing agent by the reducing agent suppler in such a way as to make the ammonia adsorption amount in abnormal condition larger than a first predetermined adsorption amount that is equal to or larger than a slip start adsorption amount in abnormal condition and to make the ammonia adsorption amount in normal condition smaller than a second predetermined adsorption amount that is equal to or smaller than a slip start adsorption amount in normal condition, the slip start adsorption amount in abnormal condition being defined as the amount of ammonia adsorbed in the selective catalytic reduction NOx catalyst at which slip of ammonia out of the selective catalytic reduction NOx catalyst starts if the selective catalytic reduction NOx catalyst is in a condition that is diagnosed as abnormal by the abnormality diagnosis, and the slip start adsorption amount in normal condition being defined as the amount of ammonia adsorbed in the selective catalytic reduction NOx catalyst at which slip of ammonia out of the selective catalytic reduction NOx catalyst starts if the selective catalytic reduction NOx catalyst is in a normal condition; and performs abnormality diagnosis of the selective catalytic reduction NOx catalyst on the basis of the ammonia concentration measured by the measure while the supply control for diagnosis is performed.
The abnormality diagnosis system according to the third aspect of the present invention estimates the ammonia adsorption amount in abnormal condition and the ammonia adsorption amount in normal condition by the controller. The ammonia adsorption amount in abnormal condition is the amount of ammonia adsorbed in the selective catalytic reduction NOx catalyst (SCR catalyst) on the assumption that the SCR catalyst is in a condition that is diagnosed as abnormal by the abnormality diagnosis. That is, the ammonia adsorption amount in abnormal condition is the amount of ammonia adsorbed in the SCR catalyst that is estimated on the assumption that the SCR catalyst is in a condition that is diagnosed as abnormal. The ammonia adsorption amount in normal condition is the amount of ammonia adsorbed in the SCR catalyst on the assumption that the SCR catalyst is in a normal condition. That is, the ammonia adsorption amount in abnormal condition is the amount of ammonia adsorbed in the SCR catalyst that is estimated on the assumption that the SCR catalyst is in a condition that is diagnosed as normal. When the abnormality diagnosis is to be performed, the controller performs the supply control for diagnosis so as to make the ammonia adsorption amount in abnormal condition larger than the first predetermined adsorption amount that is equal to or larger than the slip start adsorption amount in abnormal condition and to make the ammonia adsorption amount in normal condition smaller than the second predetermined adsorption amount that is equal to or smaller than the slip start adsorption amount in normal condition.
When the supply control for diagnosis is performed as above, ammonia does not slip out of the SCR catalyst if the SCR catalyst is in a normal condition but slips out of the SCR catalyst if the SCR catalyst has an abnormality. Therefore, the controller is configured to perform abnormality diagnosis on the basis of the ammonia concentration measured by the measure while the supply control for diagnosis is performed.
According to the third aspect of the present invention, it is possible to adjust the amount of ammonia adsorbed in the SCR catalyst to an amount suitable for abnormality diagnosis of the SCR catalyst based on the concentration of ammonia slipping out of the SCR catalyst by performing the supply control for diagnosis. This enables abnormality diagnosis of an SCR catalyst to be performed at an adequate frequency.
The present invention enables abnormality diagnosis of an SCR catalyst to be performed at an adequate frequency.
In the following, modes for carrying out the present invention will be specifically described as embodiments for illustrative purposes with reference to the drawings. It should be understood that the dimensions, materials, shapes, relative arrangements, and other features of the components that will be described in connection with the embodiments are not intended to limit the technical scope of the present invention only to them, unless stated otherwise.
In the following, an embodiment of the present invention will be described with reference to the drawings.
The internal combustion engine 1 has a fuel injection valve 3 that injects fuel into a cylinder 2. If the internal combustion engine 1 is a spark-ignition internal combustion engine, the fuel injection valve 3 may be adapted to inject fuel into an intake port.
The internal combustion engine 1 is connected with an intake passage 4. The intake passage 4 is provided with an air flow meter 40 and a throttle valve 41. The air flow meter 40 outputs an electrical signal representing the quantity (or mass) of intake air flowing in the intake passage 4. The throttle valve 41 is arranged in the intake passage 4 downstream of the air flow meter 40. The throttle valve 41 can vary the channel cross sectional area in the intake passage 4 to adjust the intake air quantity of the internal combustion engine 1.
The internal combustion engine 1 is connected with an exhaust passage 5. The exhaust passage 5 is provided with a first NOx sensor 53, an NOx storage reduction catalyst 50 (which will be also referred to as the “NSR catalyst 50” hereinafter), a second NOx sensor 54, a urea solution addition valve 52, a temperature sensor 56, a selective catalytic reduction NOx catalyst 51 (which will be also referred to as the “SCR catalyst 51” hereinafter), and a third NOx sensor 55, which are arranged in order along the direction of exhaust gas flow in the exhaust passage 5. The NSR catalyst 50 chemically stores or physically adsorbs NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio higher than the stoichiometric air-fuel ratio, and releases NOx and promotes the reaction of the released NOx and reductive components in the exhaust gas, such as hydrocarbon (HC) and/or carbon monoxide (CO) in the exhaust gas when the air-fuel ratio of the exhaust gas is a rich air-fuel ratio lower than the stoichiometric air-fuel ratio. The SCR catalyst 51 has the function of reducing NOx in the exhaust gas using ammonia as a reducing agent. The urea solution addition valve 52 arranged upstream of the SCR catalyst supplies aqueous urea solution to the exhaust gas flowing in the exhaust passage 5, so that the urea solution is supplied to the SCR catalyst 51. Thus, urea as a precursor of ammonia is supplied to the SCR catalyst 51. The urea thus supplied is hydrolyzed to produce ammonia, and the ammonia thus produced is adsorbed by the SCR catalyst 51. The ammonia adsorbed by the SCR catalyst 51 serves as a reducing agent to reduce NOx in the exhaust gas. The urea solution addition valve 52 may be replaced by an ammonia addition valve that adds ammonia gas to the exhaust gas. The exhaust passage 5 may be provided with a filter that traps PM in the exhaust gas.
The first NOx sensor 53, the second NOx sensor 54, and the third NOx sensor 55 each output an electrical signal representing the NOx concentration in the exhaust gas. The temperature sensor 56 outputs an electrical signal representing the temperature of the exhaust gas. The NOx sensor is a sensor that measures the NOx concentration in the exhaust gas, and the NOx sensor detects ammonia also as NOx. The third NOx sensor 55 as such outputs an electrical signal representing the combined concentration of NOx and ammonia in the exhaust gas in the region downstream of the SCR catalyst 51.
An electronic control unit (ECU) 10 is provided for the internal combustion engine 1. The ECU 10 controls the operation state of the internal combustion engine 1. The ECU 10 is electrically connected with various sensors such as an accelerator position sensor 7 and a crank position sensor 8 as well as the aforementioned air flow meter 40, the first NOx sensor 53, the second NOx sensor 54, the third NOx sensor 55, and the temperature sensor 56. The accelerator position sensor 7 outputs an electrical signal representing the amount of operation of the accelerator pedal that is not shown in the drawings (or the accelerator opening degree). The crank position sensor 8 outputs an electrical signal representing the rotational position of the engine output shaft (or the crankshaft) of the internal combustion engine 1. The output signals of these sensors are input to the ECU 10. The ECU 10 calculates the engine load of the internal combustion engine 1 on the basis of the output signal of the accelerator position sensor 7 and calculates the engine speed of the internal combustion engine 1 on the basis of the output signal of the crank position sensor 8. Moreover, the ECU 10 estimates the flow rate of the exhaust gas flowing into the SCR catalyst 51 on the basis of the output value of the air flow meter 40 and estimates the temperature of the SCR catalyst 51 on the basis of the output value of the temperature sensor 56. The flow rate of the exhaust gas flowing into the SCR catalyst 51 will be also referred to as the “exhaust gas flow rate”, and the temperature of the SCR catalyst 51 will be also referred to as the “SCR catalyst temperature” hereinafter. While in the illustrative configuration shown in
Now, the NOx concentration measured by the first NOx sensor 53, the second NOx sensor 54, and the third NOx sensor 55 in the exhaust gas purification apparatus having the NSR catalyst 50 and the SCR catalyst 51 according to the embodiment will be described with reference to
As shown in
In the case of the exhaust gas purification apparatus according to the embodiment in which the difference between the NOx concentration in the region upstream of the SCR catalyst 51 and the NOx concentration in the region downstream of the SCR catalyst 51 is relatively small when the SCR catalyst 51 is normal, the NOx removal rate with the SCR catalyst 51 does not drop greatly even when the SCR catalyst 51 has an abnormality in some cases. For this reason, if abnormality diagnosis of the SCR catalyst is performed based on the NOx removal rate, the accuracy of diagnosis may be deteriorated. Moreover, in the exhaust gas purification apparatus according to the embodiment, if the NOx removal rate with the SCR catalyst 51 is calculated based on the difference between the NOx concentration in the region upstream of the SCR catalyst 51 and the NOx concentration in the region downstream of the SCR catalyst 51, the calculated NOx removal rate is apt to be affected relatively greatly by measurement errors of the NOx concentrations. Hence, if abnormality diagnosis of the SCR catalyst is performed based on the NOx removal rate, there is a possibility that a correct diagnosis cannot be made.
Next, we will discuss a case where the SCR catalyst is normal and a case where the SCR catalyst 51 is abnormal in comparison in abnormality diagnosis of the SCR catalyst 51 using ammonia slipping out of the SCR catalyst 51, with reference to
In this SCR catalyst 51, the amount of ammonia that the SCR catalyst 51 can adsorb changes depending on the degree of progress of deterioration (or the degree of deterioration) even when the SCR catalyst 51 is in a normal condition. The solid curve C1 shown in
As shown in
In the exhaust gas purification apparatus according to the embodiment, a large part of NOx discharged from the internal combustion engine 1 is stored, adsorbed, or reduced by the NSR catalyst 50, and consequently the NOx concentration in the exhaust gas flowing into the SCR catalyst 51 is low, as described above. Then, the quantity of NOx reduced in the SCR catalyst 51 is small, and therefore the quantity of urea solution supplied by the urea solution addition valve 52 for reduction of NOx or the quantity of ammonia supplied is small. As shown in
As shown in
As will be understood from the above, in the exhaust gas purification apparatus according to the embodiment, which is configured in such a way that the NOx concentration in the exhaust gas flowing into the SCR catalyst 51 is relatively low, when the abnormality diagnosis of the SCR catalyst 51 is performed using ammonia slipping out of the SCR catalyst 51, it is not possible to perform the abnormality diagnosis of the SCR catalyst 51 correctly based on the ammonia concentration in the region downstream of the SCR catalyst 51, unless the quantity of ammonia supplied is larger than Q1 and smaller than Q2, in other words, unless urea solution is supplied to the exhaust gas through the urea solution addition valve 52 in a quantity large enough that a relatively large quantity of ammonia that will lead to slip of ammonia out of the SCR catalyst 51 if the SCR catalyst is abnormal will be adsorbed by the SCR catalyst 51 if the SCR catalyst is normal. For this reason, in the apparatus according to the embodiment, the ECU 10 is configured to supply urea solution through the urea solution addition valve 52 in a supply quantity for diagnosis that will be described later when performing the abnormality diagnosis.
In the control shown in
As shown in
The aforementioned supply quantity for diagnosis is a predetermined fixed quantity larger than the quantity of urea solution that is supplied by the urea solution addition valve 52 for the purpose of reduction of NOx by the SCR catalyst 51. The latter quantity will also be referred to as the “quantity required for reduction” hereinafter. The quantity required for reduction is the quantity of urea solution that is supplied for the purpose of reduction of NOx during the normal operation of the internal combustion engine 1. The supply quantity for diagnosis is a predetermined quantity. In this embodiment, the aforementioned control of supplying urea solution through the urea solution addition valve 52 in the predetermined fixed quantity larger than the quantity required for reduction when performing the abnormality diagnosis will be referred to as the “supply control”.
As shown in
The change of the ammonia adsorption amount Qad1 to Qad2 shown in
As shown in
Ammonia slips out of the SCR catalyst 51 as above, and the ammonia concentration is measured by the third NOx sensor 55. Thus, it is possible to diagnose abnormality of SCR catalyst 51 based on the ammonia concentration in the region downstream of the SCR catalyst 51.
Referring back to
To avoid the above situation, if the ammonia adsorption amount is larger than the specific upper limit adsorption amount Qadth at a specific time after the completion of the latest abnormality diagnosis and before the start of the next abnormality diagnosis, the ECU 10 performs control for reducing the amount of ammonia adsorbed in the SCR catalyst 51 so as to make the ammonia adsorption amount after the completion of the next supply control larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in a normal condition. In this embodiment, this control performed by the ECU 10 will be referred to as the “reducing control”.
The reducing control performed at the aforementioned specific time will be described with reference to
As shown in
As above, the catalyst temperature raising control is started at time t23 to raise the SCR catalyst temperature to the specific temperature Tcth or higher, and the SCR catalyst temperature rises to reach or exceed the specific temperature after the lapse of a certain delay time since time t23. Since the amount of ammonia that the SCR catalyst 51 can adsorb changes depending on the SCR catalyst temperature, the decrease in the quantity of ammonia achieved by the catalyst temperature raising control can be controlled by adjusting the specific temperature Tcth, which includes adjusting the SCR catalyst temperature that is made equal to or higher than the specific temperature Tcth by the catalyst temperature raising control, or by adjusting the time at which the SCR catalyst temperature is made equal to or higher than the specific temperature Tcth. In the catalyst temperature raising process, the amount of ammonia adsorbed in the SCR catalyst 51 is reduced taking account of the supply quantity for diagnosis (Qsum1) so as to make the ammonia adsorption amount after the completion of the next supply control larger than the slip start adsorption amount in abnormal condition Qada and smaller than the slip start adsorption amount in normal condition Qadn. The slip start adsorption amount in normal condition Qadn may be an amount that may vary depending on the specific deterioration condition. Specifically, the slip start adsorption amount in normal condition Qadn may be either an amount that varies depending on the condition of deterioration of the SCR catalyst 51 during the operation of the internal combustion engine 1 or an amount corresponding to a predetermined fixed deterioration condition that does not depend on the condition of deterioration of the SCR catalyst 51 during the operation of the internal combustion engine 1.
After the ammonia adsorption amount has been reduced by the catalyst temperature raising control, the supply of urea solution through the urea solution addition valve 52 is restarted. Then, the supply control is started at time t3 at which the condition for performing the next abnormality diagnosis is met, and the urea solution is supplied in the quantity Qsum1 (represented by the hatched area in
The flow of control performed by the ECU 10 will be described with reference to
In this flow, firstly in step S101, the ammonia adsorption amount Qad is retrieved. In step S101, the ammonia adsorption amount Qad estimated by the known flow other than this flow is retrieved. As described above, the ammonia adsorption amount Qad is the amount of ammonia adsorbed in the SCR catalyst 51 that is estimated on the assumption that the SCR catalyst 51 is normal.
Then, in step S102, it is determined whether or not the ammonia adsorption amount Qad retrieved in step S101 is equal to or smaller than the specific upper limit adsorption amount Qadth. As described above, the specific upper limit adsorption amount Qadth is an upper limit of the ammonia adsorption amount at which the abnormality diagnosis of the SCR catalyst 51 is allowed to be performed, and it is defined, for example, as such an ammonia adsorption amount that if urea solution is supplied in the supply quantity for diagnosis in the process of abnormality diagnosis in the state in which the ammonia adsorption amount is larger than the specific upper limit adsorption amount Qadth, the adsorption capacity of the SCR catalyst is exceeded even if the SCR catalyst 51 is normal, possibly leading to slip of ammonia out of the SCR catalyst 51. The value of the specific upper limit adsorption amount Qadth is stored in the ROM of the ECU 10 in advance. If an affirmative determination is made in step S102, the ECU 10 executes the processing of step S103 next. If a negative determination is made in step S102, the ECU 10 executes the processing of step S117 next.
If an affirmative determination is made in step S102, then in step S103, it is determined whether or not the SCR catalyst temperature Tc is higher than a predetermined lower limit temperature Tcmin and lower than a predetermined upper limit temperature Tcmax. As described in the above description with
If an affirmative determination is made in step S103, then in step S104, it is determined whether or not the condition for performing the abnormality diagnosis of the SCR catalyst 51 is met. In step S104, an affirmative determination is made, for example, if the vehicle provided with the internal combustion engine 1 has travelled a predetermined distance or the internal combustion engine 1 has operated for a predetermined length of time after the completion of the latest abnormality diagnosis, or if the internal combustion engine 1 has been stopped and restarted afterward. The above specific conditions are merely for illustrative purposes; in step S104, a determination as to whether or not the condition for performing the abnormality diagnosis of the SCR catalyst 51 is met may be made based on any known technology. If an affirmative determination is made in step S104, the ECU 10 executes the processing of step S105 next. If a negative determination is made in step S104, the execution of this flow is terminated.
If an affirmative determination is made in step S104, then in step S105, the supply quantity for diagnosis Qsum is read. The supply quantity for diagnosis Qsum is the quantity of urea solution that is supplied through the urea solution addition valve 52 when the diagnosis is performed. The supply quantity for diagnosis Qsum is a predetermined fixed quantity larger than the quantity required for reduction, as described above. This value of the supply quantity for diagnosis Qsum is stored in the ROM of the ECU 10 in advance.
Then, in step S106, a urea solution supply time ts is calculated. The urea solution supply time ts is a length of time over which urea solution is to be supplied through the urea solution addition valve 52 when the abnormality diagnosis is performed. In step S106, on the basis of the supply quantity for diagnosis Qsum read in step S105, the urea solution supply time ts is calculated in such a way that urea solution is supplied at a supply rate that enables the SCR catalyst 51 to adsorb ammonia appropriately.
Then, in step S107, the supply of urea solution through the urea solution addition valve 52 is started. Urea solution will be supplied in the supply quantity for diagnosis Qsum read in step S105 by the urea solution addition valve 52 with the lapse of the urea solution supply time ts calculated in step S106 after the start of the supply of urea solution in step S107. Thus, when performing the abnormality diagnosis, the ECU 10 starts the supply control in step S107 to supply urea solution through the urea solution addition valve 52 in the supply quantity for diagnosis Qsum read in step S105.
Then, in step S108, it is determined whether or not the SCR catalyst temperature Tc is higher than the predetermined lower limit temperature Tcmin and lower than the predetermined upper limit temperature Tcmax. The processing of step S108 is the same as the processing of step S103 described above. Since the SCR catalyst Tc can change while the supply control is performed, the above described determination is made in step S108 with the current SCR catalyst temperature Tc during the supply control. If an affirmative determination is made in step S108, the ECU 10 executes the processing of step S109 next. If a negative determination is made in step S108, the ECU 10 executes the processing of step S116 next.
If an affirmative determination is made in step S108, then in step S109, it is determined whether or not the concentration Ca measured by the third NOx sensor 55 is lower than a threshold concentration Cath. The threshold concentration Cath is a threshold for determining slip of ammonia out of the SCR catalyst 51. If the measured concentration Ca is equal to or higher than the threshold concentration Cath, it is determined in the abnormality diagnosis of the SCR catalyst 51 performed by this flow that there is slip of ammonia. The threshold concentration Cath is stored in the ROM of the ECU 10 in advance. If an affirmative determination is made in step S109, the ECU 10 executes the processing of step S110 next. If a negative determination is made in step S109, the ECU 10 executes the processing of step S114 next.
If an affirmative determination is made in step S109, then in step S110, it is determined whether or not the urea solution supply time is calculated in step S106 has elapsed. If an affirmative determination is made in step S110, urea solution has been supplied through the urea solution addition valve 52 in the supply quantity for diagnosis Qsum. Then, the ECU 10 executes the processing of step S111 next. If a negative determination is made in step S110, then the ECU 10 returns to the processing of step S108, where the ECU 10 continues the supply of urea solution through the urea solution addition valve 52.
If an affirmative determination is made in step S110, then in step S111, the supply of urea solution through the urea solution supply valve 52 is stopped. Thus, the supply control is terminated in step S111.
Then, in step S112, it is determined that the SCR catalyst 51 is normal. The processing of step S112 executed in the case where the measured concentration Ca is equal to or lower than the threshold concentration Cath, while urea solution has been supplied in the supply quantity for diagnosis Qsum by the supply control. Then, in other words, the SCR catalyst 51 is in the state in which it is determined by the abnormality diagnosis of the SCR catalyst 51 performed by this flow that slip of ammonia out of the SCR catalyst 51 is not occurring while the ammonia adsorption amount is larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. Therefore, it may be concluded that the SCR catalyst 51 is normal. In contrast, the case in which the SCR catalyst is diagnosed as abnormal is, for example, a case in which the SCR catalyst 51 cannot remove NOx sufficiently, so that emissions exceed the OBD limit set by regulations, and it is determined that slip of ammonia out of the SCR catalyst 51 occurs while urea solution is being supplied so as to make the ammonia adsorption amount larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition, as will be described later in the description of step S115.
Then, in step S113, a counter Nc that controls the timing of performing the reducing control is initialized to zero. The reducing control will be described later. After the completion of the processing of step S113, the execution of this flow is terminated.
If a negative determination is made in step S109, then in step S114, the supply of urea solution through the urea solution addition valve 52 is stopped. The case in which the supply of urea solution through the urea solution addition valve 52 is stopped in step S114 is the case in which the supply control is terminated while the supply control is in progress because the measured concentration Ca reaches or exceeds the threshold concentration Cath while the supply control is being performed. In that case, the quantity of urea solution supplied has not reached the supply quantity for diagnosis Qsum.
Then, in step S115, it is determined that the SCR catalyst 51 has an abnormality. In the case which the processing of step S115 is executed, the SCR catalyst 51 is in the state in which it is determined by the abnormality diagnosis of the SCR catalyst 51 performed by this flow that slip of ammonia out of the SCR catalyst 51 is occurring while urea solution is being supplied so as to make the ammonia adsorption amount in the SCR catalyst 51 larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. Therefore, the ECU 10 can determine correctly that the SCR catalyst 51 has an abnormality. After the completion of the processing of step S115, the execution of this flow is terminated.
As described above, it is determined whether the SCR catalyst 51 is normal or has an abnormality by the comparison of the measured concentration Ca and the threshold concentration Cath in step S109. In other words, the abnormality diagnosis of the SCR catalyst 51 is performed on the basis of the concentration Ca measured by the third NOx sensor 55 when urea solution is supplied by the supply control. There may be a time lag from the time when urea solution is supplied by the urea solution addition valve 52 to the time when the concentration of ammonia derived from the supplied urea solution is measured by the third NOx sensor 55. Therefore, the abnormality diagnosis of the SCR catalyst 51 may be performed based on the measured concentration Ca that is obtained during and after the supply of urea solution by the urea solution addition valve 52.
If a negative determination is made in step S108, then in step S116, the supply of urea solution through the urea solution addition valve 52 is stopped. The case in which the supply of urea solution through the urea solution addition valve 52 is stopped in step S116 is the case in which the supply control is terminated while it is in progress because the SCR catalyst temperature Tc becomes equal to or lower than the predetermined lower limit temperature Tcmin or equal to or higher than the predetermined upper limit temperature Tcmax while the supply control is being performed. In that case, the quantity of urea solution supplied has not reached the supply quantity for diagnosis Qsum. After the completion of the processing of step S116, the execution of this flow is terminated. After the execution of this flow is terminated, the supply control is restarted if an affirmative determination is made in step S103 next time because the SCR catalyst temperature Tc becomes higher than the predetermined lower limit temperature Tcmin and lower than the predetermined higher limit temperature Tcmax, and an affirmative determination is made in steps S102 and S104 as well.
In the case where a negative determination is made in step S102, the counter Nc is incremented by 1 in step S117. In step S118, it is determined whether or not the value of the counter Nc reaches a predetermined value Ncth. The predetermined value Ncth is a threshold used to determine whether the reducing control is to be performed or not. When the counter Nc reaches this predetermined value Ncth, the reducing control is performed. The predetermined value Ncth is stored in the ROM of the ECU 10 in advance.
In step S102 in this flow, a determination is made as to whether the supply control is allowed to be performed with the current ammonia adsorption amount Qad at the timing of performing the next abnormality diagnosis, irrespective of whether the condition for performing the abnormality diagnosis of the SCR catalyst 51 is met or not. The case in which a negative determination is made in step S102 is the case in which it is considered that performing the supply control with the current ammonia adsorption amount Qad at the timing of performing the next abnormality diagnosis probably leads to slip of ammonia that the SCR catalyst 51 cannot adsorb even if the SCR catalyst 51 is normal. In that case, the reducing control is performed immediately to reduce the amount of ammonia adsorbed in the SCR catalyst 51 in preparation for the supply control performed in the next abnormality diagnosis. Alternatively, a waiting period may be provided before the start of the reducing control. In this embodiment, the reducing control is not performed until the value of the counter Nc reaches the predetermined value Ncth. In other words, in this flow, a waiting period is provided before the start of the reducing control, and the reducing control is performed at a specific time after the completion of the latest abnormality diagnosis and before the start of the next abnormality diagnosis. In cases where the ammonia adsorption amount Qad does not become equal to or smaller than the specific upper limit adsorption amount Qadth, the reducing control is started at the specific time.
The predetermined value Ncth is set, for example, as a value corresponding to the running time of the internal combustion engine 1 since the time at which the counter Nc is set to zero. When the counter Nc is initialized to zero in step S113, the ammonia adsorption amount Qad is apt to become larger than the specific upper limit adsorption amount Qadth, and therefore a negative determination tends to be made in step S102 after the counter Nc is initialized to zero in step S113. In that case, the counter Nc is incremented by 1 in step S117. Therefore, for example, if the specific time is defined as the time at which the running time of the internal combustion engine 1 reaches one hour after the completion of the abnormality diagnosis, the predetermined value Ncth is determined on the basis of the time specified above and the calculation interval of this flow. The time to perform the reducing control may be controlled by known technique without using the counter Nc in such a way that the reducing control is performed at the specific time after the completion of the latest abnormality diagnosis and before the start of the next abnormality diagnosis. If an affirmative determination is made in step S118, the ECU 10 executes the processing of S119 next. If a negative determination is made in step S119, the execution of this flow is terminated.
If an affirmative determination is made in step S118, then in step S119, a target reduction Qred in the quantity of ammonia in the reducing control is calculated. In step S119, the target reduction Qred is calculated as such a value that makes the ammonia adsorption amount after the completion of the next supply control larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition, taking account of the ammonia adsorption amount Qad retrieved in step S101 and the predetermined supply quantity for diagnosis Qsum.
Then in step S120, the reducing control is performed. In step S120, the above-described catalyst temperature raising control is performed as the reducing control. In the catalyst temperature raising control, adjustment of the specific temperature Tcth, which involves the adjustment of the SCR catalyst temperature, which is made equal to or higher than the specific temperature Tcth by the catalyst temperature raising control, and adjustment of the time over which the SCR catalyst temperature is made equal to or higher than the specific temperature Tcth are performed so that a reduction in the quantity of ammonia equal to the target reduction Qred calculated in step S119 will be achieved. After the completion of the processing of step S120, the execution of this flow is terminated. In step S120, NOx flow rate increasing control that will be described later may be performed as the reducing control.
The abnormality diagnosis system for the exhaust gas purification apparatus enables the abnormality diagnosis of the SCR catalyst 51 to be performed at an adequate frequency by executing the above-described control flow.
A second embodiment of the present invention will be described. In the above-described first embodiment, the supply quantity for diagnosis is a predetermined fixed quantity larger than the quantity required for reduction. In this embodiment, the supply quantity for diagnosis is a variable quantity larger than the quantity required for reduction. The components and the control processing in the second embodiment that are substantially the same as those in the above-described first embodiment will not be described further.
In the second embodiment, when the ammonia adsorption amount at the aforementioned specific time is larger than the predetermined upper limit adsorption amount, the reducing control is performed so as to make the ammonia adsorption amount equal to or smaller than the predetermined upper limit adsorption amount. Moreover, the supply control is performed so as to make the ammonia adsorption amount after the completion of the supply control larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. Performing the reducing control and the supply control helps to make the ammonia adsorption amount after the completion of the supply control larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition. This will be described in the following.
Similarly to
In the control shown in
In the above-described first embodiment, adjustment of the specific temperature Tcth, which involves the adjustment of the SCR catalyst temperature, which is made equal to or higher than the specific temperature Tcth by the catalyst temperature raising control, and adjustment of the time over which the SCR catalyst temperature is made equal to or higher than the specific temperature Tcth are performed in the catalyst temperature raising control so that a reduction in the quantity of ammonia equal to the target reduction Qred will be achieved. In the second embodiment, the specific temperature Tcth′ and the time over which the SCR catalyst temperature is made equal to or higher than the specific temperature Tcth′ may be determined in advance so that the reduction in the quantity of ammonia achieved by catalyst temperature raising control will be constant.
In the control shown in
The change of the ammonia adsorption amount caused by the next supply control shown in
As shown in
The supply quantity for diagnosis Qsum2 in the supply control performed in the next abnormality diagnosis is, for example, the smallest value of the supply quantity for diagnosis, which is a variable value. This is because the amount of ammonia Qad3 adsorbed in the SCR catalyst 51 before the supply of urea solution in next abnormality diagnosis is larger than the slip start adsorption amount in abnormal condition Qada as shown in FIG.
A control flow executed by the ECU 10 will be described with reference to
In the control flow shown in
By performing the above-described supply control and reducing control, it is possible to appropriately adjust the ammonia adsorption amount after the completion of the supply control to a value larger than the slip start adsorption amount in abnormal condition and smaller than the slip start adsorption amount in normal condition with the supply quantity for diagnosis larger than the quantity required for reduction. Executing the above-described control flow enables the abnormality diagnosis of the SCR catalyst 51 to be performed at an adequate frequency.
Modification
A modification of the above-described second embodiment will be described. The components and the control processing in this modification that are substantially the same as those in the above-described first embodiment will not be described further.
As shown in
In this modification, the supply control is performed in such a way as to make the ammonia adsorption amount after the completion of the supply control larger than the sum of the slip start adsorption amount in abnormal condition and a specific measurable ammonia quantity and smaller than the slip start adsorption amount in normal condition. The sum of the slip start adsorption amount in abnormal condition and the specific measurable ammonia quantity will also be referred to as the “abnormality diagnosis enabling quantity” hereinafter. The specific measurable ammonia quantity is determined taking account of measurement errors in the measurement of the ammonia concentration using the third NOx sensor 55 and other factors. The state in which a quantity of ammonia larger than the specific measurable ammonia quantity slips out of the SCR catalyst 51 corresponds to the state in which the aforementioned measurement difference is relatively large.
If the SCR catalyst 51 has an abnormality at the time when urea solution is supplied in the process of abnormality diagnosis, a quantity of ammonia substantially equal to Qad2 minus Qada will slip out of the SCR catalyst 51. This quantity of slipping ammonia is larger than the specific measurable ammonia quantity ΔQdet shown in
If the supply quantity for diagnosis is set as such a value that the sum of the ammonia adsorption amount Qad1 before the supply of urea solution in the abnormality diagnosis and the quantity of ammonia derived from the supply quantity for diagnosis is equal to or larger than the abnormality diagnosis enabling quantity Qdig defined as the sum of the slip start adsorption amount in abnormal condition Qada and the specific measurable ammonia quantity ΔQdet and smaller than the slip start adsorption amount in normal condition Qadn, the abnormality diagnosis of the SCR catalyst 51 can be performed based on the ammonia concentration in the region downstream of the SCR catalyst 51 with as high accuracy as possible.
In this modification, in step S205 in
By performing the supply control to supply urea solution in the supply quantity for diagnosis Qsum thus calculated, the abnormality diagnosis of the SCR catalyst can be performed with as high accuracy as possible. Executing the above-described decreasing control enables the abnormality diagnosis of the SCR catalyst 51 with such high accuracy to be performed at an adequate frequency.
A third embodiment of the present invention will be described. The exhaust gas purification apparatus according to the above-described embodiments is provided with the NSR catalyst 50 for reducing NOx in the exhaust gas arranged in the exhaust passage 5 upstream of the SCR catalyst 51. In the exhaust gas purification apparatus according to the third embodiment, an NOx removing catalyst such as an NSR catalyst for reducing NOx in the exhaust gas is not provided in the exhaust passage 5 upstream of the SCR catalyst 51. The components and the control processing in the third embodiment that are substantially the same as those in the above-described embodiments will not be described further.
In the exhaust gas purification apparatus according to the above-descried embodiments, the NOx concentration in the exhaust gas flowing into the SCR catalyst 51 is low, because a large part of NOx discharged from the internal combustion engine 1 is stored, adsorbed, or reduced by the NSR catalyst 50. In the exhaust gas purification apparatus according to the third embodiment also, in which an NOx removing catalyst such as an NSR catalyst is not provided upstream of the SCR catalyst 51, the NOx concentration in the exhaust gas flowing into the SCR catalyst 51 can be low in some cases depending on the operation state of the internal combustion engine 1 or other factors. In such cases, by performing supply control in the process of abnormality diagnosis, abnormality diagnosis of the SCR catalyst 51 can be performed based on the ammonia concentration in the region downstream of the SCR catalyst 51. In the exhaust gas purification apparatus according to the third embodiment, executing the control flow shown in
A fourth embodiment of the present invention will be described with reference to
The NOx flow rate increasing control will be described with reference to
As shown in
After the NOx flow rate increasing control is started at time t23, the inflowing NOx flow rate increases. As the inflowing rate increases, a relatively large quantity of ammonia is consumed to reduce NOx flowing into the SCR catalyst 51. Therefore, when the NOx flow rate increasing control is performed, the ammonia adsorption amount decreases as shown in
When the NOx flow rate increasing control is performed in place of the catalyst temperature raising control in the first embodiment, the increase in the quantity of NOx and the length of time over which the NOx flow rate increasing control is performed may be varied depending on the target decrease Qred. When the NOx flow rate increasing control is performed in place of the catalyst temperature raising control in the second embodiment, the increase in the quantity of NOx and the length of time over which the NOx flow rate increasing control is performed may be determined in advance.
Now, a method of increasing the flow rate of NOx flowing into the SCR catalyst 51 in the exhaust gas purification apparatus having the NSR catalyst 50 arranged upstream of the SCR catalyst 51 will be described. As described above, the NSR catalyst 50 chemically stores or physically adsorbs NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio higher than the stoichiometric air-fuel ratio. The efficiency of such storage and adsorption tends to decrease with increasing amount of NOx chemically stored or physically adsorbed in the NSR catalyst 50. The amount of NOx chemically stored or physically adsorbed in the NOx catalyst will also be referred to as the “NOx storage amount” hereinafter. During normal operation of the internal combustion engine 1, NOx chemically stored or physically adsorbed in the NSR catalyst 50 (which will also be referred to as the “stored NOx”) is reduced by releasing the stored NOx and promoting the reaction of the released NOx and reductive components in the exhaust gas, before the efficiency of storage and adsorption (which will be also referred to as the “NOx storage efficiency) of NOx in the NSR catalyst 50 becomes low.
When the NOx flow rate increasing control is performed, the NOx storage efficiency is reduced by not performing the above-described reduction of NOx to let the NOx storage amount increase. In consequence, the flow rate of NOx that pass through the NSR catalyst 50 without being stored or adsorbed in the NSR catalyst 50 increases, leading to an increase in the flow rate of NOx flowing into the SCR catalyst 51.
When the NOx flow rate increasing control is performed, the quantity of EGR into the cylinder 2 of the internal combustion engine 1 is decreased. As the quantity of EGR into the cylinder 2 decreases, the combustion temperature tends to rise, leading to an increase in the quantity of NOx discharged from the internal combustion engine 1. As the quantity of NOx discharged from the internal combustion engine 1 increases, the flow rate of NOx flowing into the NSR catalyst 50 increases. Therefore, the NOx storage amount can be increased as quickly as possible. When the NOx storage amount is large and the NOx storage efficiency is low, increases in the flow rate of the NOx flowing into the NSR catalyst 50 lead to increases in the flow rate of NOx that passes through the NSR catalyst 50 without being stored or adsorbed in the NSR catalyst 50, and hence increases in the flow rate of NOx flowing into the SCR catalyst 51.
The above-described NOx flow rate increasing control should be performed when the SCR catalyst temperature falls within its active temperature range so that emissions will not be increased by this control. The method of increasing the flow rate of NOx flowing into the SCR catalyst 51 is not limited to the method described above, but other known methods may be employed.
The abnormality diagnosis system enables the abnormality diagnosis of the SCR catalyst 51 to be performed at an adequate frequency by performing the NOx flow rate increasing control as the reducing control in the control flow shown in
In the system according to the third embodiment, the ECU 10 estimates “an ammonia adsorption amount in abnormal condition” and “an ammonia adsorption amount in normal condition” in the SCR catalyst 51. The ammonia adsorption amount in abnormal condition is the amount of ammonia adsorbed in the SCR catalyst 51 under the assumption that the SCR catalyst is in a condition that is diagnosed as abnormal by the abnormality diagnosis. The ammonia adsorption amount in normal condition is the amount of ammonia adsorbed in the SCR catalyst 51 under the assumption that the SCR catalyst is in a normal condition.
The ECU 10 calculates the ammonia adsorption amount in abnormal condition and the ammonia adsorption amount in normal condition repeatedly at predetermined calculation intervals. A specific method of calculating the ammonia adsorption amount in the SCR catalyst 51 according to this embodiment will now be described with reference to
The adsorption amount calculation unit 120 calculates the present ammonia adsorption amount by integrating the amount of ammonia supplied to the SCR catalyst 51 (ammonia supply amount), the amount of ammonia consumed in reduction of NOx in the SCR catalyst 51 (ammonia consumption amount), and the amount of ammonia desorbed from the SCR catalyst 51 (ammonia desorption amount). Specifically, the adsorption amount calculation unit 120 includes a consumption amount calculation unit 121 and a desorption amount calculation unit 122. The consumption amount calculation unit 121 calculates an ammonia consumption amount as the amount of ammonia consumed in reduction of NOx in the SCR catalyst 51 through a specific period corresponding to the interval of calculation of the ammonia adsorption amount. The desorption amount calculation unit 122 calculates an ammonia desorption amount as the amount of ammonia desorbed from the SCR catalyst during the specific period. Moreover, the adsorption amount calculation unit 120 estimates an ammonia supply amount as the amount of ammonia supplied to the SCR catalyst 51 during the specific period. As described above, the ammonia supplied to the SCR catalyst is produced by hydrolysis of urea contained in urea solution added through the urea solution addition valve 52. Therefore, the ammonia supply amount can be estimated on the basis of the amount of urea solution added through the urea solution addition valve 52 during the specific period.
To the consumption amount calculation unit 121 are input the values of the NOx concentration in the exhaust gas flowing into the SCR catalyst 51 (inflowing NOx concentration), the exhaust gas flow rate, the temperature of the SCR catalyst (SCR catalyst temperature), and the ammonia adsorption amount in the SCR catalyst 51 calculated in the previous (i.e. the last) calculation (previous adsorption amount). The inflowing NOx concentration is measured by the second NOx sensor 54. The NOx removal rate with the SCR catalyst 51 relates to the exhaust gas flow rate, the SCR catalyst temperature, and the ammonia adsorption amount in the SCR catalyst 51. The consumption amount calculation unit 121 calculates the NOx removal rate that the SCR catalyst 51 is supposed to provide at the present time (which will be hereinafter referred to as the “estimated NOx removal rate”) from the values of the exhaust gas flow rate, the SCR catalyst temperature, and the previous adsorption amount input thereto. Moreover, the consumption amount calculation unit 121 calculates the amount of NOx flowing into the SCR catalyst 51 during the specific period (which will be hereinafter referred to as the “inflowing NOx amount”) from the values of the inflowing NOx concentration and the exhaust gas flow rate input thereto. Then, the consumption amount calculation unit 121 calculates the ammonia consumption amount from the estimated NOx removal rate and the inflowing NOx amount calculated as above. To the desorption amount calculation unit 122 are input the values of the SCR catalyst temperature and the previous adsorption amount. The desorption amount calculation unit 122 calculates the ammonia desorption amount from the values of the SCR catalyst temperature and the previous adsorption amount.
When the adsorption amount calculation unit 120 calculates the ammonia adsorption amount in abnormal condition, the consumption amount calculation unit 121 and the desorption amount calculation unit 122 calculate the ammonia consumption amount and the ammonia desorption amount respectively on the assumption that the SCR catalyst is in a condition that is diagnosed as abnormal by abnormality diagnosis. When the adsorption amount calculation unit 120 calculates the ammonia adsorption amount in normal condition, the consumption amount calculation unit 121 and the desorption amount calculation unit 122 calculate the ammonia consumption amount and the ammonia desorption amount respectively on the assumption that the SCR catalyst 51 is in a normal condition. The ammonia adsorption amount in abnormal condition is calculated by integrating the ammonia consumption amount and the ammonia desorption amount calculated on the assumption that the SCR catalyst 51 is in a condition that is diagnosed as abnormal by abnormality diagnosis and the ammonia supply amount. The ammonia adsorption amount in normal condition is calculated by integrating the ammonia consumption amount and the ammonia desorption amount calculated on the assumption that the SCR catalyst 51 is in a normal condition and the ammonia supply amount.
The method of estimating the ammonia adsorption amount in abnormal condition and the ammonia adsorption amount in normal condition is not limited to the above-described method. Other known methods of estimation may be employed instead.
In the third embodiment, when abnormality diagnosis of the SCR catalyst 51 is to be performed, supply control for diagnosis is performed. In the supply control for diagnosis, urea solution is supplied through the urea solution addition valve 52 in such a way as to make the ammonia adsorption amount in abnormal condition estimated by the ECU 10 larger than a first predetermined adsorption amount, which is equal to or larger than the slip start adsorption amount in abnormal condition, and to make the ammonia adsorption amount in normal condition estimated by the ECU 10 smaller than a second predetermined adsorption amount, which is equal to or smaller than the slip start adsorption amount in normal condition. Changes in the ammonia adsorption amount in abnormal condition and the ammonia adsorption amount in normal condition with the execution of the supply control for diagnosis will be described in the following with reference to
In
When ammonia is supplied to the SCR catalyst 51 by the supply control for diagnosis, the ammonia adsorption amount in abnormal condition and the ammonia adsorption amount in normal condition both increase as indicated by arrows in
When the ammonia adsorption amount in abnormal condition becomes larger than the first predetermined adsorption amount Qada1 with the supply of ammonia to the SCR catalyst 51 as illustrated in
As above, when performing abnormality diagnosis of the SCR catalyst 51, the system according to this embodiment performs the supply control for diagnosis to adjust the ammonia adsorption amount in the SCR catalyst 51 to an amount suitable for abnormality diagnosis of the SCR catalyst 51 based on ammonia slipping out of the SCR catalyst 51. This enables abnormality diagnosis of the SCR catalyst 51 to be performed at an adequate frequency.
A control process for abnormality diagnosis of the SCR catalyst 51 executed by the ECU 10 according to the embodiment will be described with reference to
In the process illustrated in
In step S302, the values of the ammonia adsorption amount in abnormal condition Qa and the ammonia adsorption amount in normal condition Qn at the present time are retrieved, which are estimated by a process other than this process. Then, in step S303, it is determined whether or not the ammonia adsorption amount in abnormal condition Qa at the present time retrieved in step S302 is smaller than the first predetermined adsorption amount Qada1 and the ammonia adsorption amount in normal condition Qn at the present time retrieved in step S302 is smaller than the second predetermined adsorption amount Qadn2. The first predetermined adsorption amount Qada1 and the second predetermined adsorption amount Qadn2 referred to in step S303 are values that are determined on the basis of the temperature of the SCR catalyst 51 at the present time. The ECU 10 has relationship between the temperature of the SCR catalyst 51 and the first predetermined adsorption amount Qada1 like that illustrated in
In step S304, it is determined whether or not it is possible to set a supply quantity for diagnosis Qsum0, which is defined as the quantity of urea solution to be supplied through the urea solution addition valve 52 in the supply control for diagnosis. The supply quantity for diagnosis Qsum0 is such a quantity that makes the ammonia adsorption amount in abnormal condition Qa larger than the first predetermined adsorption amount Qada1 and keeps the ammonia adsorption amount in normal condition Qn smaller than the second predetermined adsorption amount Qadn2 when this quantity of urea solution is added through the urea solution addition valve 51. In step S303, the ammonia adsorption amount in abnormal condition Qa and the ammonia adsorption amount in normal condition Qn after the execution of the supply control for diagnosis are estimated from the ammonia adsorption amount in abnormal condition Qa and the ammonia adsorption amount in normal condition Qn at the present time retrieved in step S302 and respective increases thereof resulting from the additional supply of urea solution through the urea solution addition valve 52. Specifically, the ECU 10 estimates the ammonia adsorption amount in abnormal condition Qa and the ammonia adsorption amount in normal condition Qn after the execution of the supply control for diagnosis, if executed, by the aforementioned adsorption amount calculation unit 120. Then, it is determined whether or not it is possible to set the supply quantity for diagnosis Qsum0 described above on the basis of the estimated values of the ammonia adsorption amount in abnormal condition Qa and the ammonia adsorption amount in normal condition Qn. If a negative determination is made in step S304, the execution of this flow is terminated this time. In other words, abnormality diagnosis of the SCR catalyst 51 based on the ammonia concentration in the region downstream of the SCR catalyst is enabled by performing the supply control for diagnosis according to this embodiment only when affirmative determinations are made in steps S303 and S304 before the supply control for diagnosis is performed.
If an affirmative determination is made in step S304, it may be concluded that it is possible to perform the supply control for diagnosis. Then, in step S305, a urea solution supply time ts is calculated on the basis of the supply quantity for diagnosis Qsum0, which can be set according to the determination in step S304. The urea solution supply time ts is a length of time over which urea solution is to be supplied through the urea solution addition valve 52 by the supply control for diagnosis. In other words, the urea solution supply time ts calculated in step S305 is the length of time taken to supply urea solution through the urea solution addition valve 52 in the supply quantity for diagnosis Qsum0.
Then, in step S306, supply of urea solution through the urea solution addition valve 52 is started. Thus, the supply control for diagnosis is started. Then, in step S307, it is determined whether or not the concentration Ca measured by the third NOx sensor 55 is lower than a threshold concentration Cath. The processing executed in step S307 is the same as that in step S109 in the process illustrated in
In step S308, it is determined whether or not the urea solution supply time ts calculated in step S305 has elapsed after the start of supply of urea solution through the urea solution addition valve 52 in step S306. If a negative determination is made in step S308, the processing of step S307 is executed again. If an affirmative determination is made in step S308, then in step S309 the supply of urea solution through the urea solution addition valve 52 is stopped. Thus, the supply control for diagnosis is ended. In this case, slip of ammonia out of the SCR catalyst 51 is not occurring even after urea solution has supplied through the urea solution addition valve 52 in the supply quantity for diagnosis Qsum0, in other words, even though the ammonia adsorption amount in abnormal condition Qa has exceeded the first predetermined adsorption amount Qada1. In consequence, it is determined then in step S310 that the SCR catalyst 52 is normal.
If a negative determination is made in step S307, the processing of step S311 is executed next. In step S311 also, the supply of urea solution through the urea solution addition valve 52 is stopped. In this case, slip of ammonia out of the SCR catalyst 51 has occurred while the supply of urea solution through the urea solution addition valve 52 up to the supply quantity for diagnosis Qsum0 is performed, in other words, while the ammonia adsorption amount in normal condition Qn is smaller than the second predetermined adsorption amount Qadn2. In consequence, it is determined then in step S312 that the SCR catalyst 52 has an abnormality.
In the above process, a determination as to whether or not the concentration Ca measured by the third NOx sensor is smaller than the threshold concentration Cath may be made as in step S307 at the time when the urea solution supply time is has elapsed from the start of the supply of urea solution through the urea solution addition valve 52. In this case also, if the concentration Ca measured by the third NOx sensor 55 is smaller than the threshold concentration Cath, the SCR catalyst 51 may be determined to be normal. If the concentration Ca measured by the third NOx sensor 55 is not smaller than the threshold concentration Cath, the SCR catalyst 51 may be determined to have an abnormality.
In the above-described process, when the condition for performing abnormality diagnosis of the SCR catalyst 51 is met, if affirmative determinations are made in steps S303 and S304, it is possible to perform abnormality diagnosis of the SCR catalyst 51 by performing the supply control for diagnosis. This enables abnormality diagnosis of the SCR catalyst 51 to be performed at an adequate frequency.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-228283 | Nov 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/042221 | 11/24/2017 | WO | 00 |
