Patent Application
20110023465
The present invention relates to an exhaust purification system of an internal combustion engine.
The exhaust gas in a diesel engine, gasoline engine, or other internal combustion engines contains ingredients such as carbon monoxide (CO), unburnt fuel (HC), nitrogen oxides (NOX), and particulate matter (PM). An internal combustion engine is provided with an exhaust purification system for purifying these ingredients.
As a method of removing nitrogen oxides, it is known to arrange in an engine exhaust passage an NOX storage reduction catalyst that stores NOX temporarily and reduces the NOX when releasing it. The NOX storage reduction catalyst stores NOX when the air-fuel ratio of the exhaust gas is lean. When the NOX stored amount has reached an allowable amount, making the air-fuel ratio of the exhaust gas rich or stoichiometric will cause the stored NOX to be released. The released NOX is reduced to N2 by carbon monoxide or another reducing agent contained in the exhaust gas. The NOX storage reduction catalyst has an NOX absorbent for storing NOX. The NOX absorbent contains an alkali metal, alkali earth metal, etc., but these alkali metal and alkali earth metal are known to scatter.
Japanese Patent Publication (A) No. 2003-83052 discloses an exhaust purification system provided with a storage catalyst to which at least one metal selected from a group comprising alkali metals and alkali earth metals is added as an absorbent and with a three-way catalyst arranged at a downstream side of the storage catalyst and to which an acidic substance having an alkali trapping function is added. It is disclosed that the system is able to prevent the alkali metal and the like from scattering and flowing into the three-way catalyst and the three-way catalyst from falling in performance.
Japanese Patent Publication (A) No. 2007-247589 discloses a catalyst diagnosis system provided with a storing material arranged in the exhaust passage of an engine and storing or releasing toxic ingredients in the exhaust, a scattering detecting means for detecting a scattered amount of potassium etc. contained in the storing material, and a diagnosing means for diagnosing a deteriorated state based on the scattered amount detected by the scattering detecting means. It is disclosed that this catalyst diagnosis system is capable of diagnosing an upper limit value of storage ability.
Japanese Patent Publication (A) No. 2002-21538 discloses an exhaust purification catalyst system adding potassium to an NOX catalyst as an NOX absorbent, providing a three-way catalyst at a downstream side of the NOX catalyst, and providing a phosphorus-carrying alkali metal trapping means between the NOX catalyst and the three-way catalyst. It is disclosed that this catalyst system is able to prevent potassium from reaching the three-way catalyst at the downstream side by reacting the potassium vaporizing and scattering from the NOX catalyst with phosphorus to trap it at an alkali metal trapping means.
Patent Literature
An NOX storage reduction catalyst can store NOX using an absorbent containing an alkali metal etc. On the other hand, a catalyst metal can be made to hold NOX. For example, to purify the NOX contained in the exhaust gas, if forming the catalyst metal by silver, the catalyst metal can hold the NOX. With this exhaust treatment device, it is possible to have the inflowing NOX held at the catalyst metal in the state of silver nitrate.
In this regard, the inventors discovered that if arranging an exhaust treatment device including a catalyst metal containing silver in exhaust gas of a predetermined temperature or higher, the NOX purification ability will fall. Particularly, they discovered that if repeatedly arranging it in exhaust gas of a predetermined temperature or higher, the NOX purification ability will drop.
For example, when an exhaust purification system is provided with a particulate filter and regenerating the particulate filter, the exhaust gas becomes a high temperature. Due to the exhaust gas becoming a high temperature, the other exhaust treatment devices arranged in the engine exhaust passage will also become a high temperature. If such an exhaust purification system is provided with an exhaust treatment device including a catalyst metal containing silver, the NOX purification ability will drop.
The present invention has as its object to provide an exhaust purification system of an internal combustion engine provided with an NOX holding material including a catalyst metal containing silver and suppressing a drop in the NOX purification ability.
An exhaust purification system of an internal combustion engine according to the present invention comprising an NOX holding material arranged in an engine exhaust passage, having a catalyst metal containing silver, holding NOX contained in the exhaust gas in the form of silver nitrate at the catalyst metal when an air-fuel ratio of inflowing exhaust gas is lean, and releasing the held NOX if the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich. The NOX holding material has a scatter temperature at which catalyst metal scatters in the form of silver nitrate if the temperature rises. When it is time to perform control to raise the temperature of the NOX holding material to the scatter temperature or above, the system makes the air-fuel ratio of the exhaust gas flowing into the NOX holding material a stoichiometric air-fuel ratio or rich to thereby make the NOX holding material release the held NOX.
In the above-described invention, the exhaust purification system may comprise an NOX storage reduction catalyst arranged in the engine exhaust passage downstream of the NOX holding material, including a catalyst metal and an NOX absorbent holding NOX, holding the NOX contained in the exhaust gas at the NOX absorbent when the air-fuel ratio of the inflowing exhaust gas is lean, and releasing the held NOX when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich, the NOX storage reduction catalyst holds SOX besides NOX, and when it is time to perform sulfur poisoning recovery control raising the temperature of the NOX storage reduction catalyst to an SOX releasable temperature and making the air-fuel ratio of the exhaust gas flowing into the NOX storage reduction catalyst the stoichiometric air-fuel ratio or rich so as to release the SOX, the NOX holding material is made to release the held NOX.
In the above-described invention, the exhaust purification system may comprise a particulate filter arranged in the engine exhaust passage and trapping particulate matter contained in the exhaust gas, and when it is time to perform regeneration control raising the temperature of the particulate filter to the temperature where the trapped particulate matter burns, the NOX holding material is made to release the held NOX.
In the above-described invention, the exhaust purification system preferably performs control estimating the amount of catalyst metal remaining at the NOX holding material when catalyst metal scatters from the NOX holding material, and reduces the NOX amount exhausted to the engine exhaust passage from the engine body in accordance with the drop in the amount of remaining catalyst metal.
In the above-described invention, the exhaust purification system preferably performs control making the air-fuel ratio of exhaust gas flowing into the NOX holding material the stoichiometric air-fuel ratio or rich so as to release NOX when a held amount of NOX of the NOX holding material exceeds a predetermined held amount judgment value, estimates the amount of catalyst metal remaining at the NOX holding material when the catalyst metal scatters from the NOX holding material, and decreases the held amount judgment value in accordance with the drop in the amount of remaining catalyst metal.
In the above-described invention, the exhaust purification system preferably comprises an NOX selective reducing catalyst arranged in the engine exhaust passage downstream of the NOX holding material and selectively reducing NOX by feeding a reducing agent, estimates the amount of catalyst metal remaining at the NOX holding material when catalyst metal scatters from the NOX holding material, and increases the feed amount of reducing agent to the NOX selective reducing catalyst in accordance with the drop in the amount of remaining catalyst metal.
In the above-described invention, the exhaust purification system preferably estimates the amount of catalyst metal remaining at the NOX holding material when catalyst metal scatters from the NOX holding material, and estimates the NOX amount flowing out from the NOX holding material based on the remaining amount of catalyst metal.
According to the present invention, it is possible to provide an exhaust purification system of an internal combustion engine provided with an NOX holding material including a catalyst metal containing silver and suppressing a drop in the NOX purification ability.
The exhaust purification system of an internal combustion engine in a first embodiment will be explained with reference from
The internal combustion engine is provided with an engine body 1. Further, the internal combustion engine is provided with an exhaust purification system. The engine body 1 includes combustion chambers 2 as cylinders, electronic control type fuel injectors 3 for injecting fuel to the respective combustion chambers 2, an intake manifold 4, and an exhaust manifold 5.
The intake manifold 4 is connected through an intake duct 6 to the outlet of a compressor 7a of an exhaust turbocharger 7. An inlet of the compressor 7a is connected through an intake air detector 8 to an air cleaner 9. A throttle valve 10 driven by a step motor is arranged inside the intake duct 6. Further, a cooling device 11 is arranged in the intake duct 6 for cooling the intake air flowing inside the intake duct 6. In the example shown in
On the other hand, the exhaust manifold 5 is connected to the inlet of a turbine 7b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7b is connected to an exhaust treatment device purifying the exhaust gas exhausted from the engine body 1.
The exhaust purification system in the present embodiment is provided with a particulate filter 16. The particulate filter 16 is an exhaust treatment device removing particulate matter contained in the exhaust gas. The particulate filter 16 is connected through an exhaust pipe 12 to the outlet of the turbine 7b. The exhaust purification system in the present embodiment is provided with an NOX holding material 13. The NOX holding material 13 is an exhaust treatment device for purifying the NOX contained in the exhaust gas. The NOX holding material 13 in the present embodiment is arranged inside the engine exhaust passage downstream of the particulate filter 16.
Between the exhaust manifold 5 and the intake manifold 4, an exhaust gas recirculation (hereinafter referred to as an “EGR”) passage 18 is arranged for exhaust gas recirculation. An electronic control type EGR control valve 19 is arranged in the EGR passage 18. Further, around the EGR passage 18 is arranged a cooling device 20 for cooling the EGR gas flowing through the inside of the EGR passage 18. In the embodiment shown in
The fuel injectors 3 are connected through fuel feed tubes 21 to a common rail 22. The common rail 22 is connected through an electronic control type variable discharge fuel pump 23 to a fuel tank 24. The fuel stored in the fuel tank 24 is supplied by the fuel pump 23 to the inside of the common rail 19. The fuel supplied to the inside of the common rail 22 is supplied through the fuel feed tubes 21 to the fuel injectors 3.
An electronic control unit 30 is comprised of a digital computer. The electronic control unit 30 in the present embodiment functions as the control device of the exhaust purification system. The electronic control unit 30 includes components connected with each other by a bi-directional bus 31 such as a ROM (read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34, input port 35, and output port 36.
The ROM 32 is a read-only storage device. The ROM 32 stores in advance information such as maps necessary for control. The CPU 34 can make perform any calculation or judgment. The RAM 33 is a read-write storage device. The RAM 33 can store operation history and other information or temporarily store calculation results.
Downstream of the particulate filter 16, a temperature sensor 26 is arranged as a temperature detection device for detecting the temperature of the particulate filter 16. Downstream of the NOX holding material 13, a temperature sensor 27 is arranged as a temperature detection device for detecting the temperature of the NOX holding material 13. Upstream of the NOX holding material 13, an air-fuel ratio sensor 28 is arranged for detecting the air-fuel ratio of the exhaust gas flowing into the NOX holding material 13. A pressure difference sensor 29 is attached to the particulate filter 16 for detecting the pressure difference before and after the particulate filter 16. The output signals of these temperature sensors 26 and 27, air-fuel ratio sensor 28, and pressure difference sensor 29 are input through the corresponding AD converter 37 to the input port 35.
The output signal of the intake air detector 8 is input through a corresponding AD converter 37 to the input port 35. An accelerator pedal 40 is connected to a load sensor 41 generating an output voltage proportional to the depression amount of the accelerator pedal 40. The output voltage of the load sensor 41 is input through a corresponding AD converter 37 to the input port 35. Further, a crank angle sensor 42 is connected to the input port 35, generating an output pulse every time the crankshaft rotates by for example 15°. The output of the crank angle sensor 42 can be used to detect the rotational frequency of the engine body.
On the other hand, the output port 36 has the fuel injectors 3, throttle valve 10 drive step motor, EGR control valve 19, and fuel pump 23 connected to it through corresponding drive circuits 38.
The particulate filter 16 is a filter that removes carbon fine particles, sulfates and other ionic fine particles and other particulate matter (particulate) contained in the exhaust gas. The particulate filter has, for example, a honeycomb structure and has a plurality of flow passages extending in the direction of gas flow. In the plurality of flow passages, flow passages with a sealed downstream end and flow passages with a sealed upstream end are alternatively formed. The partition walls of the flow passages are formed from a porous material such as cordierite. When exhaust gas passes through the partition wall, the particulate is trapped.
In the present invention, the ratio of air and fuel (hydrocarbons) of exhaust gas fed to the engine intake passage, combustion chamber, or engine exhaust passage is called the air-fuel ratio (A/F) of the exhaust gas. Further, in the present invention, “hold” is used in the sense including “adsorb” and “store”.
The NOX holding material 13 adsorbs the NOX contained in the exhaust gas at the catalyst metal 49 when the air-fuel ratio of the exhaust gas is lean. The NOX contained in the exhaust gas is held in the form of silver nitrate at the catalyst metal 49. Further, the NOX is held through oxygen at the catalyst metal 49. As opposed to this, when the air-fuel ratio of the exhaust gas is rich or stoichiometric, the NOX held at the catalyst metal 49 is released. The released NOX is reduced by the unburnt hydrocarbons, carbon monoxide, and the like contained in the exhaust gas into N2.
The NOX holding material has a maximum amount of NOX that it can hold, that is, a holdable amount. If the NOX held amount reaches the holdable amount, it can no longer hold NOX. That is, it can no longer remove the NOX contained in the exhaust gas. In the present embodiment, when the NOX amount held in the NOX holding material exceeds a predetermined held amount judgment value, NOX purge control is carried out for making the NOX holding material release the NOX. The held amount judgment value in the present embodiment is a value smaller than the NOX holdable amount of the NOX holding material.
Referring to
During normal operation, as shown by the injection pattern B, the main injection FM may be performed alone without the pilot injection FP. In the present embodiment, the injection pattern where the pilot injection FP is performed will be taken as an example for the explanation. When operating under the injection pattern A during normal operation, the air-fuel ratio of the exhaust gas exhausted from the engine body is lean.
By performing the after injection, the air-fuel ratio of the exhaust gas can be lowered. In the present embodiment, control is performed to reduce the intake air amount flowing into the combustion chamber. Referring to
Referring to
By performing the NOX purge control, at the time t2, the NOX amount held in the NOX holding material becomes substantially zero. At the time t2, the NOX purge control is ended and the normal operating state is shifted to. In the present embodiment, the NOX purge control is carried out for a predetermined period of time. Further, in the NOX purge control, a map of the released amount of NOX as a function of the injection amount of the fuel in the combustion chamber and the engine rotational frequency etc. may be used to calculate the released amount of NOX.
Referring to
Further, the inventors discovered that if the temperature of the NOX holding material 13 rises, the catalyst metal 49 carried on the catalyst carrier 48 will scatter in the form of silver nitrate. The inventors discovered that silver nitrate separates from the catalyst carrier 48 if at the boiling point or more. The inventors discovered that, if, for example, the silver nitrate becomes approximately 450° C. or more, it separates from the catalyst carrier 48. In the present invention, the lowest temperature at which silver nitrate scattering occurs is referred to as the “scatter temperature”. If the catalyst metal 49 scatters in the form of silver nitrate, the amount of catalyst metal contained in the NOX holding material decreases. Therefore, for example, the holdable amount that can be held in the NOX holding material decreases. Further, the reduction ability when reducing NOX to N2 falls. In this way, the NOX purification rate of the NOX holding material falls.
Referring to
In regeneration of the particulate filter, the temperature of the particulate filter is raised to a temperature at which the particulate matter burns or higher. In the present embodiment, the particulate filter is raised to a target temperature or higher. By making the air-fuel ratio of the exhaust gas lean in this state, the deposited particulate matter is made to burn. The deposited particulate matter is removed.
In the regeneration control of the particulate filter 16, the particulate filter 16 is raised to, for example, 600° C. or higher. In the present embodiment, the temperature of the exhaust gas exhausted from the engine body is raised to 600° C. or more. Therefore, the temperature of the NOX holding material 13 becomes the scatter temperature at which the catalyst metal scatters or more.
In the present embodiment, before regeneration control of the particulate filter, NOX purge control of the NOX holding material is performed. This makes the NOX held at the catalyst metal be released. By making the NOX be released, the catalyst metal returns to the form of silver. In the form of silver, the scattering of catalyst metal can be avoided even if at the scatter temperature or more. Therefore, by making the NOX be released, it is possible to suppress the scattering of the catalyst metal.
In the present embodiment, when it is time to perform the regeneration control of the particulate filter, the NOX purge control in the NOX holding material is performed. In the example shown in
At the time t2, the particulate filter regeneration control is started. At the time t2, the intake air amount is restored. The air-fuel ratio of the exhaust gas exhausted from the engine body becomes lean. In the present embodiment, even after the time t2, the after injection FA is continued to raise the temperature of the particulate filter.
Referring to
Referring to
Along with the temperature rise of the particulate filter 16, the temperature of the NOX holding material 13 also rises at the same time. The temperature of the NOX holding material exceeds the scatter temperature. However, the NOX holding material does not hold NOX, that is, does not contain silver nitrate, so scattering of the catalyst metal can be avoided.
From the time t3 to the time t4, the particulate matter deposited on the particulate filter can be made to burn. At the time t4, the deposited amount of particulate matter reaches the lower limit judgment value. At the time t4, the regeneration control is ended. The deposited amount on the particulate filter reaching the lower limit judgment value can be detected for example from the output of the pressure difference sensor 29 arranged at the particulate filter 16. At the time t4 on, normal operation is performed.
In the present embodiment, when it is time to perform the regeneration control of the particulate filter, NOX purge control of the NOX holding material is performed. When it is time to perform control to increase the temperature of the NOX holding material to the scatter temperature or more, the NOX purge control is performed to cause the release of the NOX held at the NOX holding material. Due to this configuration, it is possible to suppress scattering of the catalyst metal of the NOX holding material when the temperature of the NOX holding material is at the scatter temperature or above. The drop in the NOX purification ability of the NOX holding material can be suppressed.
In this regard, the NOX purge control in the present embodiment performs the after injection FA in the combustion chamber. Therefore, the temperature of the exhaust gas rises as the air-fuel ratio of the exhaust gas drops. When starting the NOX purge control, sometimes the NOX holding material already has a high temperature. In such cases, when performing the NOX purge control, the temperature of the NOX holding material is liable to become the scatter temperature or more.
At step 101, it is judged if there is a regeneration request for the particulate filter. At step 101, when there is no regeneration request for the particulate filter, this control is ended. When there is a regeneration request for the particulate filter, the routine proceeds to step 102.
At step 102, it is judged if the NOX amount held in the NOX holding material is greater than zero. That is, it is judged if NOX is held in the NOX holding material. When at step 102 the NOX amount held in the NOX holding material is zero, this control is ended. When at step 102 the NOX amount held in the NOX holding material is greater than zero, the routine proceeds to step 103.
At step 103, NOX purge control is started. In the present embodiment, in the combustion chamber, in addition to main injection FM, after injection FA is performed. The temperature of the exhaust gas rises, so the temperature of the NOX holding material rises.
Next, at step 104, during the period where NOX purge control is performed, it is judged if the bed temperature of the NOX holding material is a predetermined temperature judgment value or more. When at step 104 the temperature of the NOX holding material is the temperature judgment value for suspending the NOX purge control or more, the routine proceeds to step 105. That is, when the temperature of the NOX holding material is liable to reach the silver nitrate scatter temperature, the routine proceeds to step 105. This temperature judgment value is a temperature sufficiently lower than the scatter temperature so that even if the NOX purge control is continued for a predetermined period, the temperature of the NOX holding material does not reach the scatter temperature of the silver nitrate.
At step 105, the NOX purge control is suspended. In the present embodiment, the NOX purge control is suspended for a predetermined length of time. Step 105 is not limited to this. A lower limit temperature judgment value may be set in advance and the NOX purge control may be suspended until the temperature of the NOX holding material becomes the lower limit temperature judgment value or less.
Next, the routine proceeds to step 102, where this control is repeated. Further, when at step 104 the bed temperature of the NOX holding material is less than the temperature judgment value, the routine proceeds to step 102. At step 102, it is judged again if the NOX amount held in the NOX holding material is greater than zero. When the NOX amount held in the NOX holding material is zero, this control is ended.
After the predetermined length of time has passed, at the time t3, NOX purge control is restarted. At the time t3, the bed temperature of the NOX holding material is a temperature lower than the temperature judgment value. By performing the NOX purge control from the time t3 to the time t4, the NOX amount held in the NOX holding material becomes substantially zero.
In the second NOX purge control, when the bed temperature of the NOX holding material is becomes the predetermined temperature judgment value or more, the NOX purge control is suspended. By employing this control, during the NOX purge control period, it is possible to avoid the temperature of the NOX holding material becoming the scatter temperature or more in the state where the NOX holding material contains silver nitrate. In this way, the NOX purge control may be performed intermittently.
In the present embodiment, by performing the after injection in addition to the main injection, the air-fuel ratio of the exhaust gas flowing into the NOX holding material is made the stoichiometric or rich, however, the invention is not limited to this. Any device making the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich can be employed.
Further, a fuel addition valve may be arranged upstream of the NOX holding material in the engine exhaust passage for feeding unburnt fuel. The fuel from the fuel addition valve that is used can be the same fuel as the engine body for example. The fuel addition valve can be controlled by the electronic control unit for example. By feeding unburnt fuel from the fuel addition valve, it is possible to make the air-fuel ratio of the exhaust gas flowing into the NOX holding material the stoichiometric air-fuel ratio or rich.
The exhaust purification system of the internal combustion engine in the present embodiment has the particulate filter arranged at an upstream side of the NOX holding material, but the invention is not limited to this. The particulate filter may also be arranged at a downstream side of the NOX holding material. Further, the exhaust purification system of the internal combustion engine may be provided with an NOX selective reducing catalyst, oxidation catalyst, NOX storage reduction catalyst, or other exhaust treatment device. Further, the NOX holding material may be any exhaust treatment device so long as it includes a catalyst metal containing silver and treats NOX.
In the present embodiment, as control whereby the temperature of the NOX holding material rises to the scatter temperature or above, the particulate filter regeneration control was used as an example for the explanation. However, when it is time to perform any control whereby the temperature of the NOX holding material rises to the scatter temperature or above, the NOX purge control is carried out to remove silver nitrate from the NOX holding material thereby allowing the suppression of a drop in NOX purification ability.
The internal combustion engine in the present embodiment is arranged in an automobile, but the invention is not limited to this. The present invention can be applied to any internal combustion engine.
Referring to
At the NOX storage reduction catalyst, when the air-fuel ratio of the exhaust gas is lean, the NO contained in the exhaust gas is oxidized on the catalyst metal 46 and becomes NO2. The NO2 is stored in the form of nitrate ions NO3− in the NOX absorbent 47. As opposed to this, when the air-fuel ratio of the exhaust gas is rich or the stoichiometric air-fuel ratio, the nitrate ions NO3− in the NOX absorbent 47 are released in the form of NO2 from the NOX absorbent 47. The released NOX is reduced to N2 by the unburnt hydrocarbons and carbon monoxide contained in the exhaust gas.
Referring to
Further, when the temperature of the exhaust gas becomes high, mainly the NOX absorbent 47 of the NOX storage reduction catalyst 17 stores NOX. For example, when the engine body runs for a long period of time at a high speed, sometimes the temperature of the exhaust gas rises and the NOX holding ability of the NOX holding material 13 falls. In such a case as well, the NOX storage reduction catalyst 17 can store NOX.
In the NOX holding material 13, when the NOX held amount exceeds an allowable value, NOX purge control can be performed to release and reduce the NOX.
At the NOX storage reduction catalyst 17, the NOX amount stored in the NOX storage reduction catalyst is calculated. When the NOX amount stored in the NOX storage reduction catalyst 17 exceeds the allowable amount, NOX release control is performed. In the NOX release control, the air-fuel ratio of the exhaust gas flowing into the NOX storage reduction catalyst 17 can be made the stoichiometric air-fuel ratio or rich so as to make the NOX storage reduction catalyst 17 release the NOX and reduce the NOX to N2.
The NOX stored amount in the NOX storage reduction catalyst 17 can be estimated by the output signal of the NOX sensor 53 arranged at the upstream side of the NOX storage reduction catalyst 17. Based on the output signal of the NOX sensor 53, the NOX amount flowing into the NOX storage reduction catalyst 17 can be estimated. Through cumulative addition of the NOX amounts flowing into the NOX storage reduction catalyst 17 per unit time, it is possible to calculate the NOX stored amount of the NOX storage reduction catalyst 17 at any time.
Estimation of the NOX amount stored in the NOX storage reduction catalyst 17 is not limited to this. Any device can be used. For example, a map or the like may be used to calculate the NOX amount flowing out from the NOX holding material and calculate the NOX amount stored in the NOX storage reduction catalyst.
In this way, by arranging the NOX holding material 13 in the engine exhaust passage and arranging the NOX storage reduction catalyst 17 at the downstream side of the NOX holding material 13, NOX can be purified with a high purification rate in a broad range of temperature of the exhaust gas from low temperature to high temperature. Further, if compared with an exhaust purification system arranging only an NOX storage reduction catalyst in the engine exhaust passage, the NOX holding material can purify the NOX, so it is possible to make the NOX storage reduction catalyst smaller in size. The NOX holding material can use silver or another catalyst metal, so it is possible to slash the amount of platinum and other precious metals used in the NOX storage reduction catalyst.
In the present embodiment, the NOX holding material 13 is arranged at the upstream side and the NOX storage reduction catalyst 17 is arranged at the downstream side. The NOX holding material 13 may also be arranged downstream of the NOX storage reduction catalyst 17. However, for example, when the exhaust gas is a high temperature, sometimes NOX flows out from the NOX holding material 13. By arranging the NOX holding material 13 upstream of the NOX storage reduction catalyst 17, the NOX flowing out from the NOX holding material 13 can be purified at the NOX storage reduction catalyst 17. Therefore, the NOX holding material 13 is preferably arranged at the further upstream side from the NOX storage reduction catalyst 17.
In this regard, exhaust gas contains SOX, that is, SO2. If SO2 flows into the NOX storage reduction catalyst 17, it is oxidized at the catalyst metal 46 and becomes SO3. This SO3 is absorbed by the NOX absorbent 47 and forms BaSO4 for example. The sulfate BaSO4 is stable and does not break down easily. With simply only making the air-fuel ratio of the exhaust gas rich, the sulfate BaSO4 does not break down and remains as it is. Therefore, the NOX amount that can be stored by the NOX storage reduction catalyst falls. The NOX storage reduction catalyst therefore suffers from sulfur poisoning.
To recover from the sulfur poisoning, the temperature of the NOX storage reduction catalyst is raised up to a temperature where SOX can be released. Further, sulfur poisoning recovery control is performed making the air-fuel ratio of the exhaust gas flowing into the NOX storage reduction catalyst rich or the stoichiometric air-fuel ratio. By performing sulfur poisoning recovery control, it is possible to make the NOX storage reduction catalyst release the SOX.
The SOX amount stored in the NOX storage reduction catalyst can for example be calculated from a map of the SOX amount exhausted from the engine body per unit time as a function of the rotational frequency of the engine body and the fuel injection amount. This map is stored in the electronic control unit for example. By cumulatively adding the SOX amount stored per unit time calculated according to the operating state, it is possible to estimate the SOX amount stored in the NOX storage reduction catalyst at any time. In the present embodiment, when the SOX amount stored in the NOX storage reduction catalyst exceeds the allowable value, sulfur poisoning recovery control is performed.
Referring to
In this regard, when performing the sulfur poisoning recovery control, the temperature of the exhaust gas becomes high. The temperature of the exhaust gas is raised to 650° C. or more for example. The temperature of the NOX holding material 13 becomes the scatter temperature or more. Therefore, in the NOX holding material 13, when NOX is held, the catalyst metal scatters in the form of silver nitrate. In the present embodiment, when it is time to perform the sulfur poisoning recovery control, the NOX purge control is performed. That is, in the same way as how NOX purge control is performed before the regeneration control of the particulate filter in the first embodiment, the NOX purge control is performed before the sulfur poisoning recovery control.
In this way, by performing the NOX purge control when it is time to perform the sulfur poisoning recovery control, it is possible to eliminate the NOX holding material holding NOX in the form of silver nitrate. When performing the sulfur poisoning recovery treatment, the scattering of the catalyst metal can be avoided even when the temperature of the NOX holding material is the scatter temperature or more. The drop in the NOX purification ability of the NOX holding material can therefore be suppressed.
In the present embodiment, control similar to the second NOX purge control in the first embodiment was used as an example for the explanation, but the invention is not limited to this. Control similar to the first NOX purge control in the first embodiment can also be performed.
The rest of the configuration, actions, and effects are similar to those of the first embodiment. The explanations are not repeated here.
Referring to
In the operation of the internal combustion engine, sometimes it is difficult to predict the inflow of high temperature exhaust gas into the NOX holding material. For example, when an operating state where the rotational frequency of the engine body is extremely high and the fuel injection amount in the combustion chamber is large is sustained for a long period of time, the temperature of the exhaust gas flowing into the NOX holding material becomes high. Further, when the distance between the NOX holding material and the engine body is short, the temperature of the exhaust gas flowing into the NOX holding material rises. In such cases, sometimes the NOX holding material ends up exceeding the scatter temperature of the catalyst metal. When the NOX holding material holds NOX, the catalyst metal scatters in the form of silver nitrate.
At step 112, it is judged if the temperature of the NOX holding material is the scatter temperature of the catalyst metal or more. When the temperature of the NOX holding material is less than the scatter temperature, this control is ended. When the temperature of the NOX holding material is the scatter temperature or more, the routine proceeds to step 113.
At step 113, the scattered amount of the catalyst metal is estimated. In the present embodiment, a map of the scattered amount of the catalyst metal is used. At step 113, the scattered amount of the catalyst metal at this time is calculated.
Referring to
The exhaust purification system of an internal combustion engine for performing the first operational control in the present embodiment is provided with an NOX holding material (for example see
Next, the second operational control in this present embodiment will be explained. The second operational control is operational control for the exhaust purification system of the second embodiment. Referring to
At step 121, it is judged if the scattered amount of the catalyst metal of the NOX holding material is greater than zero. That is, it is judged if the catalyst metal scatters. When the scattered amount of the catalyst metal of the NOX holding material is zero, the routine proceeds to step 122. At step 122, when the scatter amount of the catalyst metal is zero, a map of the NOX amount flowing out from the NOX holding material is selected based on the temperature of the NOX holding material.
At step 121, when the scatter amount of the catalyst metal of the NOX holding material is greater than zero, the routine proceeds to step 123. At step 123, the amount of catalyst metal of the NOX holding material is detected.
Next, at step 124, a map of the NOX amount flowing out from the NOX holding material is selected. The NOX amount flowing out from the NOX holding material 13 corresponds to the NOX amount stored in the NOX storage reduction catalyst 17. In the present embodiment, the NOX amount flowing out from the NOX holding material 13 is calculated by the map.
A plurality of maps are created in advance for the NOX amount flowing out from the NOX holding material corresponding to each temperature and catalyst metal amount and are stored in the ROM 32 of the electronic control unit 30 for example. These maps are made so that when the amount of catalyst metal of the NOX holding material becomes lower, the NOX amount flowing out from the NOX holding material becomes larger.
Referring to
At step 125, using the selected map, the NOX stored amount of the NOX storage reduction catalyst is calculated. By cumulatively adding the NOX amounts NOXB flowing in per unit time, the NOX amount stored in the NOX storage reduction catalyst at any time can be calculated. That is, by adding the current calculated NOX amount flowing into the NOX storage reduction catalyst to the previously calculated NOX stored amount, the NOX stored amount can be calculated.
In this way, in the second operational control of the present embodiment, the amount of catalyst metal remaining at the NOX holding material when the catalyst metal scatters from the NOX holding material is calculated. Based on the remaining amount of the catalyst metal, the NOX amount flowing out from the NOX holding material is calculated, and the NOX amount stored in the NOX storage reduction catalyst is calculated.
At part of the time period from the time t2 to the time t5, the catalyst metal of the NOX holding material scatters due to a predetermined operating state. The amount of the catalyst metal of the NOX holding material decreases along with the scattering of the catalyst metal. At the time tX, the amount of catalyst metal of the NOX holding material becomes the judgment value for modifying the map of the NOX amount flowing out from the NOX holding material or less. Therefore, at normal operation from the time t4 on, the map for calculating the NOX amount flowing out from the NOX holding material is modified. At step 124 of
Therefore, in the operation from the time t4 on, the interval of NOX release control becomes shorter. The length of time from the time t4 to the time t5 becomes shorter than the length of time from the time t2 to the time t3.
The map is updated according to the scatter amount of the catalyst metal in this way. By estimating the NOX amount flowing out from the NOX holding material based on the amount of remaining catalyst metal, the NOX amount flowing out from the NOX holding material can be more accurately estimated. Therefore, in the present embodiment, it is possible to more accurately estimate the NOX amount stored in the NOX storage reduction catalyst. This can suppress the inflow of an amount of NOX larger than the estimated NOX amount into the NOX storage reduction catalyst and saturation of the NOX storage reduction catalyst. The outflow of NOX from the NOX storage reduction catalyst can be avoided.
The NOX selective reducing catalyst 14 in the present embodiment can selectively reduce NOX using ammonia as a reducing agent. The NOX selective reducing catalyst can be comprised from zeolite adsorbing ammonia and containing iron or other transition metals. Further, it can be comprised from a titanic-vanadium-based catalyst not having an ammonia adsorbing function. The NOX selective reducing catalyst 14 in the present embodiment is comprised from ammonia adsorption type Fe zeolite.
The exhaust purification system is provided with a reducing agent feeding device feeding a reducing agent to the NOX selective reducing catalyst 14. In the present embodiment, ammonia is used as the reducing agent. The reducing agent feeding device contains a urea feed valve 55. The urea feed valve 55 is arranged in the engine exhaust passage at an upstream side of the NOX selective reducing catalyst 14. The urea feed valve 55 is formed so as to inject urea into the engine exhaust passage. The reducing agent feeding device in the present embodiment is made so as to feed urea, however, the invention is not limited to this. It may also be made so as to feed ammonia water.
The urea feed valve 55 is connected through a corresponding drive circuit 38 to the output port 36 of the electronic control unit 30. The urea feed valve 55 in the present embodiment is controlled by the electronic control unit 30 (see
If urea is fed from the urea feed valve 55 to the exhaust gas flowing in the engine exhaust passage, the urea is hydrolyzed. By the urea being hydrolyzed, ammonia and carbon dioxide are created. By the created ammonia being fed to the NOX selective reducing catalyst 14, the NOX selective reducing catalyst 14 reduces the NOX contained in the exhaust gas to nitrogen.
This exhaust purification system can purify the NOX at both the NOX holding material 13 and the NOX selective reducing catalyst 14 during normal operation. During normal operation of the engine body 1, it is possible to purify NOX by the NOX holding material 13 repeatedly holding the NOX and performing NOX purge control. Further, by feeding a reducing agent from the urea feed valve 55 to the NOX selective reducing catalyst 14, the NO selective reducing catalyst 14 can purify the NOX.
When the temperature of the exhaust gas is low, NOX can be removed from the exhaust gas by adsorption of NOX at the NOX holding material 13. When the temperature of the exhaust gas is high, the NOX purification rate in the NOX holding material 13 drops, however, by selectively reducing the NOX at the NOX selective reducing catalyst 14, NOX can be purified. In such a way, NOX can be purified at a wide range of temperature from low temperature to high temperature. Further, it is possible to slash the amount of use of platinum and other precious metals and purify NOX.
In the present embodiment, the NOX holding material 13 is arranged at the upstream side and the NOX selective reducing catalyst 14 is arranged at the downstream side. The NOX holding material 13 may also be arranged downstream of the NOX selective reducing catalyst 14. However, when the exhaust gas has a high temperature for example, sometimes NOX flows out from the NOX holding material 13. By arranging the NOX holding material 13 upstream of the NOX selective reducing catalyst 14, the NOX flowing out from the NOX holding material 13 can be purified by the NOX selective reducing catalyst 14. Therefore, the NOX holding material 13 is preferably arranged more to the upstream side than the NOX selective reducing catalyst 14.
At step 131, it is judged if the scatter amount of the catalyst metal of the NOX holding material is greater than zero. When at step 131 the scatter amount of the catalyst metal of the NOX holding material is zero, the routine proceeds to step 132. At step 132, a feed amount of urea set in advance is selected as the feed amount of urea from the urea feed valve. When at step 131 the scatter amount of the catalyst metal of the NOX holding material is greater than zero, the routine proceeds to step 133. At step 133, the amount of the catalyst metal of the NOX holding material 13 is detected.
Next, at step 134, the amount of urea fed from the urea feed valve 55 is calculated based on the amount of catalyst metal of the NOX holding material. The amount of urea fed from the urea feed valve can be calculated using a map of the urea feed amount per unit time as a function of the NOX amount NOXA per unit time flowing into the NOX holding material and the NOX amount held in the NOX holding material. A plurality of maps are created in advance for the urea amounts corresponding to different temperatures and catalyst metal amounts and are stored in the ROM 32 of the electronic control unit 30 for example. These maps are formed so that the smaller the amount of the catalyst metal of the NOX holding material, the greater the urea feed amount. The amount of urea fed from the urea feed valve can be calculated with such a urea feed amount map. The calculation of the feed amount of the urea is not limited to this. The amount may be calculated by any method based on the amount of the catalyst metal of the NOX holding material.
Next, at step 135, urea is fed from the urea feed valve by the urea feed amount selected at step 132 or the urea feed amount calculated at step 134. If the scatter amount of the catalyst metal is increased, the amount of catalyst metal of the NOX holding material decreases. If the amount of catalyst metal decreases, the NOX amount flowing out from the NOX holding material increases. Therefore, the NOX amount flowing into the NOX selective reducing catalyst increases. The feed amount of urea from the urea feed valve increases along with an increase of the inflow amount of NOX to the NOX selective reducing catalyst.
In the present embodiment, urea is intermittently injected from the urea feed valve. When increasing the feed amount of urea, the urea injection interval can be shortened. Further, the urea feed amount can be increased by increasing one injection amount.
Thus, in the third operational control of the present embodiment, the amount of the catalyst metal remaining in the NOX holding material when the catalyst metal scatters from the NOX holding material is estimated. The less the amount of catalyst metal remaining, the more the increase in the feed amount of the reducing agent of the NOX selective reducing catalyst. By employing this configuration, when the catalyst metal scatters at the NOX holding material, the purified amount of NOX at the NOX selective reducing catalyst on the downstream side can be increased, and the outflow of NOX from the NOX selective reducing catalyst can be suppressed.
In the present embodiment, a map is used to estimate the scatter amount of the catalyst metal, then the amount of the catalyst metal remaining in the NOX holding material is estimated, however, the invention is not limited to this. Any method may be used to estimate the amount of the catalyst metal remaining at the NOX holding material. For example, NOX sensors are arranged at the upstream side and at the downstream side of the NOX holding material. It is also possible to estimate the purification rate of NOX in the NOX holding material based on the NOX amount flowing into the NOX holding material and the NOX amount flowing out from the NOX holding material and estimate the amount of catalyst metal remaining at the NOX holding material from this NOX purification rate.
The rest of the configuration, actions, and effects are similar to the first or second embodiments, so the explanations are not repeated here.
Referring to
At step 141, it is judged if the amount of catalyst metal of the NOX holding material is a predetermined remainder judgment value or less. When at step 141 the amount of catalyst metal of the NOX holding material is greater than the predetermined remainder judgment value, this control is ended. When the amount of catalyst metal is the predetermined remainder judgment value or less, the routine proceeds to step 142.
At step 142, it is judged if the temperature of the NOX holding material is a predetermined temperature judgment value or less.
It will be understood that due to the catalyst metal scattering, the maximum amount that the NOX holding material can hold, that is, the NOX holdable amount, falls. It will be understood that the drop in the NOX holdable amount is large at the region where the bed temperature of the NOX holding material is low. In the present embodiment, a temperature judgment value is set in advance. For this temperature judgment value, it is possible to select the point where, for example, the NOX holdable amount becomes smaller than a predetermined value at the time when a predetermined amount of the catalyst metal scatters.
Referring to
Referring to
In the example shown in
Thus, the less the amount of catalyst metal remaining in the NOX holding material, the more the NOX amount exhausted from the engine body can be reduced. In the present embodiment, when the amount of catalyst metal of the NOX holding material is the remainder judgment value or less, the recirculation rate is increased by exactly a predetermined amount, however, the invention is not limited to this. The NOX amount exhausted from the engine body may also be adjusted according to the amount of the catalyst metal of the NOX holding material. For example, a plurality of remainder judgment values may be set and control performed to gradually reduce the NOX amount exhausted from the engine body as the amount of catalyst metal of the NOX holding material decreases.
In the first operational control in the present embodiment, exhausted NOX reduction control is performed when the bed temperature of the NOX holding material is the temperature judgment value or less. The first operational control is not limited to this. For example, a plurality of temperature judgment values may be set and control performed to gradually reduce the NOX amount exhausted from the engine body as the bed temperature of the NOX holding material drops.
At step 146, it is judged if the amount of catalyst metal of the NOX holding material is the remainder judgment value or less. When at step 146 the amount of catalyst metal of the NOX holding material is greater than the remainder judgment value, this control is ended. When at step 146 the amount of catalyst metal of the NOX holding material is the remainder judgment value or less, the routine proceeds to step 147.
At step 147, it is judged if there is an acceleration request for the vehicle. In the present embodiment, it is judged if the depression amount of the accelerator pedal is a depression judgment value or more. Referring to
At step 148, exhausted NOX reduction control is performed. As the exhausted NOX reduction control, in the same way as the first operational control of the present embodiment, the NOX amount exhausted from the engine body is reduced by control increasing the recirculation rate of the engine body.
When there is an acceleration request, the NOX amount exhausted per unit time increases. For example, the engine rotational frequency of the engine body increases and the NOX amount exhausted from the engine body per unit time increases. In the present embodiment, when the depression amount of the accelerator pedal is the depression judgment value or more, control is performed to reduce the NOX amount exhausted from the engine body.
At the time t1, the depression amount of the accelerator pedal becomes the depression judgment value or more. By depressing the accelerator pedal 40, the opening degree of the throttle valve 10 increases and the intake air amount increases. Therefore, the recirculation rate drops. In the present embodiment, control is performed so that the drop of the recirculation rate becomes smaller. That is, the recirculation rate is increased in the period from the time t1 to the time t2 so that the recirculation rate becomes larger than when exhausted NOX reduction control is not performed. By performing this control, the NOX amount exhausted from the engine body can be made smaller, and the NOX amount flowing out from the NOX holding material can be suppressed.
In the second operational control in the present embodiment, when the depression amount of the accelerator pedal is the depression judgment value or more, exhausted NOX reduction control is performed. The second operational control is not limited to this. For example, a plurality of depression judgment values may be set and control performed to reduce the NOX amount exhausted from the engine body gradually the larger the depression amount of the accelerator pedal.
The exhaust purification system in the present embodiment reduces the NOX amount exhausted from the engine body when in an operating state where the catalyst metal scatters from the NOX holding material and the NOX is liable to flow out from the NOX holding material. With this configuration, it is possible to suppress the outflow of NOX from the NOX holding material. Further, it is possible to suppress the outflow of NOX from the exhaust purification system of the internal combustion engine.
In the exhausted NOX reduction control in the present embodiment, control increasing the recirculation rate in the engine body is performed, however, the invention is not limited to this. Any control that reduces the NOX exhausted from the engine body may be performed. For example, the fuel injection timing in the combustion chamber may be retarded. For example, by retarding the injection timing of the main injection, the fuel temperature at the time of fuel combustion drops, and the NOX amount created can be reduced.
Further, in the present embodiment, control is performed to reduce the NOX amount exhausted from the engine body when the catalyst metal scatters and a predetermined NOX amount flows out from the NOX holding material, however, the invention is not limited to this. Exhausted NOX reduction control may be performed at any time when the catalyst metal scatters. For example, control may be performed reducing the NOX amount exhausted from the engine body gradually according to the scatter amount of the catalyst metal.
In the present embodiment, the exhaust purification system of an internal combustion engine in the first embodiment was used as an example for the explanation, however, the invention is not limited to this. The invention can be applied to any exhaust purification system of an internal combustion engine provided with an NOX holding material.
The rest of the configuration, actions, and effects are similar to those of either of the first to third embodiments, so the explanations are not repeated here.
The above embodiments can be appropriately combined. In the above drawings, the same or corresponding parts are assigned the same reference numerals. Note that, the above embodiments are illustrative and do not limit the present invention. Further, in the embodiments, modifications included in the claims are intended.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/059480 | 5/19/2009 | WO | 00 | 2/18/2010 |
