Exhaust purification control device and exhaust purification system of internal combustion engine

Inactive Publication Date: 2010-05-20
DENSO CORP
8 Cites 46 Cited by

AI-Extracted Technical Summary

Problems solved by technology

Therefore, if the addition quantity of the reducing agent is decreased, there is a possibility that a purification rate of the nitrogen oxides lowers.
That is, ...
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Method used

[0063]The first processing shown in FIG. 4 is to decrease the urea addition quantity when the urea deposit accumulation quantity on the inner wall of the exhaust passage 40 increases. More specifically, in the present embodiment, the urea addition quantity Qur is decreased when the urea deposit accumulation quantity Dur (explained later) becomes equal to or larger than a threshold value β and the exhaust gas temperature Tex is equal to or lower than threshold temperature γ. The condition that the exhaust gas temperature Tex is equal to or lower than the threshold temperature γ is used in order to accurately determine the situation where the urea deposit accumulation quantity Dur increases. In FIG. 4, the decrease control of the urea solution addition quantity Qur is performed at time t3 when the exhaust gas temperature Tex becomes equal to or lower than the threshold temperature y. By performing the decrease control of the urea solution addition quantity Qur in this way, the increase of the accumulation quantity Dur of the urea deposit onto the inner wall of the exhaust passage 40 can be inhibited suitably.
[0072]The third processing shown in FIG. 6 is to increase the exhaust gas temperature Tex to or over the maximum value of the decomposition start temperature of the above-described deposit at higher speed than the increase speed of the exhaust gas temperature Tex accompanying the acceleration request of the diesel engine 10 when the acceleration of the diesel engine 10 is requested. More specifically, the processing is to increase the exhaust gas temperature Tex stepwise to 300 degrees C. Since the exhaust gas temperature Tex increases when the acceleration request occurs, the deposit having accumulated on the inner wall of the exhaust passage 40 decomposes. However, since the decomposition start temperature differs among the components of the deposit, it is difficult to determine timing and amount of emergence of the ammonia. Therefore, the exhaust gas temperature Tex is increased stepwise (as shown by mark B in FIG. 6) to facilitate anticipation of the amount of emergence of the ammonia resulting from the decomposition of the deposit. Thus, it can be facilitated to adjust the urea solution addition quantity Qur, which is added from the urea solution addition valve 62, to suitable quantity.
[0080]When the determination result in S22 is affirmative, the temperature increase control shown in FIG. 5 is performed in S30. When the processing of S30 completes or the determination result in S20 is affirmative, the process proceeds to S32. In S32, as shown in FIG. 5, the proces...
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Benefits of technology

[0036]The above-described eleventh example aspect of the present invention has the decreasing device...
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Abstract

If it is determined that accumulation quantity of deposit on an inner wall of an exhaust passage is equal to or larger than a predetermined value, addition quantity of urea solution from a urea solution addition valve is decreased. Thereafter, exhaust gas temperature is increased rapidly when request torque of a diesel engine increases. Thus, the deposit having accumulated on the inner wall of the exhaust passage is decomposed at once and is supplied to a urea SCR as ammonia.

Application Domain

Electrical controlInternal combustion piston engines +4

Technology Topic

Exhaust gasUrea +4

Image

  • Exhaust purification control device and exhaust purification system of internal combustion engine
  • Exhaust purification control device and exhaust purification system of internal combustion engine
  • Exhaust purification control device and exhaust purification system of internal combustion engine

Examples

  • Experimental program(2)

Example

Second Embodiment
[0095]Next, a second embodiment of the present invention will be described with reference to the drawings, focusing on the differences from the first embodiment.
[0096]In the present embodiment, the addition quantity of the urea solution added by the urea solution addition valve 62 is calculated based on the NOx purification rate Rnox. The NOx purification rate Rnox is calculated based on the both sensing values of the upstream NOx sensor 56 and the downstream NOx sensor 60.
[0097]FIG. 8 shows a procedure of purification processing of the nitrogen oxides according to the present embodiment. The ECU 80 repeatedly performs the processing, for example, in a predetermined cycle. Processing in FIG. 8 corresponding to the processing in FIG. 7 is indicated with the same step number as in FIG. 7.
[0098]As shown in FIG. 8, in the present embodiment, as the execution condition of the decrease control of the urea solution addition quantity Qur in the case where the idling is not performed presently, a condition that increase speed of the accumulation quantity Dur is equal to or higher than threshold speed Sth is used (refer to S24a) in place of the condition that the accumulation quantity Dur is equal to or larger than the threshold value β. Thus, the excessive increase of the accumulation quantity of the deposit on the inner wall of the exhaust passage 40 can be surely avoided. When the increase speed of the accumulation quantity is very high, the NOx concentration in the exhaust gas lowers. Therefore, even if the decrease control of the urea solution addition quantity Qur is performed, the NOx purification rate Rnox does not fall.
[0099]In the present embodiment, the urea solution addition quantity Qur is set based on the NOx purification rate Rnox. Therefore, even if there is a situation where the NOx concentration in the exhaust gas falls, it does not necessarily lead directly to decrease of the set urea solution addition quantity Qur. Therefore, as in the present embodiment, it is specifically effective to perform the processing for decreasing the urea solution addition quantity Qur when the increase speed of the accumulation quantity Dur is high.
Modified Embodiments
[0100]The above described embodiments may be modified and implemented as follows, for example.
[0101]In the above embodiments, the exhaust temperature sensor 58 is provided to sense the exhaust gas temperature. Alternatively, the exhaust gas temperature may be estimated by using a parameter indicating an operation state of the diesel engine 10 as an input. Such the parameter may be fuel injection quantity, the rotation speed or the like, for example.
[0102]In the above-described second embodiment, a condition that the accumulation quantity is equal to or larger than the threshold value β may be used as the start condition of the decrease control of the urea solution addition quantity in addition to the condition that the increase speed of the accumulation quantity is equal to or higher than the threshold speed Sth.

Example

[0103]In the above-described first embodiment, the urea solution addition quantity is set based on the NOx concentration in the exhaust gas. Alternatively, the urea solution addition quantity may be set based on the NOx purification rate in the urea SCR 52 as in the second embodiment, for example. Alternatively, a device or a section for estimating ammonia adsorption quantity in the urea SCR 52 may be provided, and the urea solution addition quantity may be set based on the estimated adsorption quantity.
[0104]In the above-described second embodiment, the urea solution addition quantity is set based on the NOx purification rate in the urea SCR 52. Alternatively, for example, a device or a section for estimating the ammonia adsorption quantity in the urea SCR 52 may be provided, and the urea solution addition quantity may be set based on the estimated adsorption quantity. Alternatively, for example, as in the above-described first embodiment, the urea solution addition quantity may be set based on the NOx concentration in the exhaust gas.
[0105]As mentioned above, it is thought that the case where the increase speed of the accumulation quantity is equal to or higher than the threshold speed Sth is a situation where the exhaust gas temperature is low and the NOx concentration in the exhaust gas is low. However, in the case where the urea solution addition quantity is set based on the NOx purification rate or the ammonia adsorption quantity in the urea SCR 52, there is a possibility that decrease of the urea solution addition quantity delays as compared to the case where the urea solution addition quantity is set based on the NOx concentration in the exhaust gas. Therefore, in the case where the NOx concentration of the exhaust gas discharged from the combustion chamber 28 of the diesel engine 10 is not used as the direct input parameter of the estimation of the urea solution addition quantity, it is specifically effective to perform the decrease control of the urea addition quantity when the increase speed of the accumulation quantity is equal to or higher than the threshold speed Sth in order to promptly perform the decrease control of the urea addition quantity.
[0106]In the above-described embodiments, the decrease control of the urea solution addition quantity is performed when a condition of the conjunction between the condition that the accumulation quantity is equal to or larger than the threshold value β and the condition that the exhaust gas temperature is equal to or lower than the threshold temperature γ is established in the range of the operation other than the idling. Alternatively, for example, the decrease control of the urea solution addition quantity may be performed when the condition that the accumulation quantity is equal to or larger than the threshold value β is established, irrespective of the exhaust gas temperature.
[0107]In the above-described embodiments, the threshold value ε for the determination of the stop of the temperature increase control in the range of the operation other than the idling is set larger than the threshold value β for the determination of the start of the decrease control of the urea solution addition quantity. Alternatively, for example, the threshold value ε may be set equal to or smaller than the threshold value β. With such the configuration, the deposit accumulation quantity on the inner wall surface of the exhaust passage 40 can be sufficiently decreased even before the request torque of the diesel engine 10 increases.
[0108]In the above embodiments, the idling time is used as the estimate of the accumulation quantity of the urea pyrolysate during the idling. Alternatively, for example, accumulation quantity estimated based on a parameter correlated with the temperature of the exhaust system and the urea solution addition quantity may be used also during the idling. In the case where the accumulation quantity is estimated based on the parameter correlated with the temperature of the exhaust system and the urea solution addition quantity, the accumulation quantity may be estimated in accordance with the idling time during the idling such that the accumulation quantity increases with the idling time instead of using the above parameter and the urea solution addition quantity. With such the modification, the execution conditions of the temperature increase control of the exhaust gas temperature and the addition quantity decrease control can be equalized between the case where the idling is performed and the case where the idling is not performed.
[0109]The scheme of the estimation of the accumulation quantity of the deposit is not limited to those illustrated in the above-described embodiments and the modifications thereof. For example, estimation processing of the accumulation quantity in each estimation processing cycle may be performed based on the idling time and at least one of a parameter correlated with the temperature of the exhaust system and the urea solution addition quantity during the idling.
[0110]In the above-described embodiments, the temperature increase control of the exhaust gas temperature is stopped when the estimate of the accumulation quantity of the deposit becomes equal to or smaller than the threshold value β in the range of the operation other than the idling. Alternatively, for example, the temperature increase control may be stopped on a condition that the temperature increase control time reaches a predetermined time. In this case, the temperature increase control time serves as the parameter indicating the accumulation quantity of the deposit. That is, it is meant that the accumulation quantity decreases as the temperature increase control time lengthens.
[0111]in the above-described embodiments, the temperature increase control of the exhaust gas temperature is stopped when the temperature increase control time reaches the threshold time T2 in the idling range. Alternatively, for example, the temperature increase control may be stopped when the estimate of the accumulation quantity of the deposit becomes equal to or smaller than the threshold value β.
[0112]The fuel supply processing to the exhaust passage 40 performed to increase the exhaust gas temperature is not limited to the processing for performing the post-injection. For example, in the case where another injector for injecting the fuel into the exhaust passage 40 is provided separately, processing for injecting the fuel into the exhaust passage 40 with the another injector may be performed.
[0113]The transmission used for increasing the exhaust gas temperature is not limited to the above-described CVT 35. For example, a transmission with discrete gear ratios may be used.
[0114]The control for increasing the exhaust gas temperature is not limited to the control that increases the exhaust gas temperature to approximately 300 degrees C. For example, control that increases the exhaust gas temperature over 300 degrees C. may be used. In this case, it is thought that the deposit in the exhaust passage 40 decomposes at once into the ammonia. Therefore, it is thought that the estimation of the ammonia supply quantity to the urea SCR 52 is made much easier.
[0115]The purification device for purifying the nitrogen oxides in the exhaust gas is not limited to the above-described urea SCR 52. For example, a selective reduction catalyst that uses a reducing agent, which is different from the urea solution and is added to the exhaust gas upstream of the catalyst, may be used. The present invention can be effectively applied to such the case if there is a possibility that deposit containing multiple components having different decomposition start temperatures accumulates because of the reducing agent when the inner wall surface temperature of the exhaust passage 40 is low. In this case, it is desirable to set the target temperature of the temperature increase processing of the exhaust gas temperature to or over the maximum value among the decomposition start temperatures of the components of the deposit.
[0116]The internal combustion engine is not limited to the compression ignition internal combustion engine such as the diesel engine. Alternatively, for example, even if the internal combustion engine is a spark ignition internal combustion engine such as a direct injection gasoline engine, the present invention can be effectively applied to the engine if a selective reduction catalyst is used for the purification of NOx.
[0117]While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
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Description & Claims & Application Information

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