JP6753151B2 - Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine - Google Patents

Description

The present invention relates to an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine.

It is necessary to branch the exhaust pipe between SCRF (filter coated with SCR) and SCR (selective catalytic reduction type catalyst), and provide an exhaust control valve and a cooling element in this branch pipe to cool the exhaust. In some cases, an exhaust gas purification system for an internal combustion engine has been proposed that controls the temperature of the exhaust gas flowing into the SCR by increasing the amount of exhaust gas passing through the branch pipe according to the target catalyst temperature (for example, patent). Reference 1).

Japanese Unexamined Patent Publication No. 2015-86848

By the way, in the above-mentioned exhaust gas purification system, the temperature of the exhaust flowing into the SCR is not controlled in consideration of the fluctuation of the cooling capacity of the cooling element (exhaust gas cooling device). Therefore, when the cooling capacity of the cooling element is temporarily excessive, there is a concern that the catalyst temperature of SCR becomes lower than the active temperature range and the NOx purification rate of SCR decreases.

An object of the present invention is to suppress deterioration due to overheating of the selective reduction catalyst device and decrease in the NOx purification rate, while reducing the NOx purification rate of the selective reduction catalyst device due to a temporary increase in the cooling capacity of the exhaust gas cooling device. It is an object of the present invention to provide an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine.

The exhaust gas purification system of the internal combustion engine of the present invention for achieving the above object is provided with a urea water supply device and a selective reduction catalyst device in order from the upstream side in the exhaust passage of the internal combustion engine. In the gas purification system, a branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and at a branch point from the exhaust passage to the branch passage. A flow path switching device is provided, and an SCR temperature detection device is provided inside the selective reduction type catalyst device or in the exhaust passage on the upstream side or the downstream side of the selective reduction type catalyst device, and the exhaust gas cooling device is provided. The control device that controls the exhaust gas purification system by providing a cooling temperature detection device in the branch passage on the downstream side has a detection value of the SCR temperature detection device equal to or higher than a preset cooling start temperature threshold. At times, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage, and the cooling capacity of the exhaust gas cooling device is based on the detection value of the cooling temperature detecting device. The temperature range of the selective reduction catalyst device, which is controlled so that the NOx purification rate of the selective reduction catalyst device becomes equal to or higher than a preset purification rate threshold, is set as an appropriate temperature range, and the upper limit of the appropriate temperature range is defined as the cooling. In addition to setting the start temperature threshold, the target temperature range is set within the appropriate temperature range, and the detection value of the SCR temperature detection device is continuously set within the target temperature range for a preset time. When included, the flow path switching device is controlled to control the flow of exhaust gas from the branch passage to the exhaust passage .
Alternatively, the exhaust gas purification system of the internal combustion engine of the present invention for achieving the above object is an internal combustion engine in which a urea water supply device and a selective reduction catalyst device are provided in order from the upstream side in the exhaust passage of the internal combustion engine. In the exhaust gas purification system of the above, a branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and the branch from the exhaust passage to the branch passage is provided. A flow path switching device is provided at a point, and an SCR temperature detection device is provided inside the selective reduction type catalyst device or in the exhaust passage on the upstream side or downstream side of the selective reduction type catalyst device to cool the exhaust gas. A cooling temperature detection device is provided in the branch passage on the downstream side of the device, and the control device that controls the exhaust gas purification system has a detection value of the SCR temperature detection device equal to or higher than a preset cooling start temperature threshold. When this happens, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage, and the cooling capacity of the exhaust gas cooling device is set to the detection value of the cooling temperature detecting device. Based on the control, the temperature range of the selective reduction catalyst device in which the NOx purification rate of the selective reduction catalyst device is equal to or higher than a preset purification rate threshold is set as the appropriate temperature range, and the upper limit of this appropriate temperature range is set. The cooling start temperature threshold is set, and the target temperature range is set within the appropriate temperature range, and the detection value of the SCR temperature detection device is included in the appropriate temperature range, but the target temperature range. When the temperature is lower than the lower limit of the above, the flow path switching device is controlled to switch the flow of exhaust gas from the branch passage to the exhaust passage.
Alternatively, the exhaust gas purification system of the internal combustion engine of the present invention for achieving the above object is an internal combustion engine in which a urea water supply device and a selective reduction catalyst device are provided in order from the upstream side in the exhaust passage of the internal combustion engine. In the exhaust gas purification system of the above, a branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and the branch from the exhaust passage to the branch passage is provided. A flow path switching device is provided at a point, and the flow path switching device is configured as a flow rate adjusting device capable of flowing exhaust gas to both the exhaust passage and the branch passage, and further, the inside of the selective reduction type catalyst device. Alternatively, the exhaust passage on the upstream side or the downstream side of the selective reduction type catalyst device is provided with an SCR temperature detection device, and the branch passage on the downstream side of the exhaust gas cooling device is provided with a cooling temperature detection device. When the control device that controls the exhaust gas purification system reaches or equal to the preset cooling start temperature threshold value of the SCR temperature detection device, the control device controls the flow path switching device to control the exhaust gas. The flow is switched from the exhaust passage to the branch passage, the cooling capacity of the exhaust gas cooling device is controlled based on the detection value of the cooling temperature detection device, and the flow of the exhaust gas is controlled between the exhaust passage and the branch passage. When switching between, as the fluctuation amount of the detection value of the cooling temperature detection device increases, the fluctuation amount of the flow rate of the exhaust gas passing through the branch passage is set small to control the flow rate adjusting device. It is configured as follows.

Further, in the exhaust gas purification method for an internal combustion engine of the present invention for achieving the above object, a urea water supply device and a selective reduction catalyst device are provided in the exhaust passage of the internal combustion engine in order from the upstream side, and the urea water supply. The exhaust passage on the upstream side of the device is provided with a branch passage having an exhaust gas cooling device in parallel with the exhaust passage, and a flow path switching device is provided at a branch point from the exhaust passage to the branch passage. In the exhaust gas purification method of an internal combustion engine, when the temperature of the selective reduction type catalyst device becomes equal to or higher than a preset cooling start temperature threshold value, the flow path switching device is controlled to control the flow of exhaust gas. While switching from the exhaust passage to the branch passage, the cooling capacity of the exhaust gas cooling device is controlled based on the temperature of the exhaust gas immediately after passing through the exhaust gas cooling device, and the NOx purification rate of the selective reduction type catalyst device is determined in advance. The temperature range of the selective reduction type catalyst device that is equal to or higher than the set purification rate threshold is set as the appropriate temperature range, the upper limit of the appropriate temperature range is set as the cooling start temperature threshold, and the temperature range is further within the appropriate temperature range. A target temperature range is set, and when the temperature of the selective reduction catalyst device is continuously included in the target temperature range for a preset set time, the flow path switching device is controlled to exhaust the air. This method is characterized by controlling the flow of gas from the branch passage to the exhaust passage .
Alternatively, the exhaust gas purification method for an internal combustion engine of the present invention for achieving the above object includes a urea water supply device and a selective reduction catalyst device in the exhaust passage of the internal combustion engine in this order from the upstream side, and supplies the urea water. The exhaust passage on the upstream side of the device is provided with a branch passage having an exhaust gas cooling device in parallel with the exhaust passage, and a flow path switching device is provided at a branch point from the exhaust passage to the branch passage. In the exhaust gas purification method of an internal combustion engine, when the temperature of the selective reduction type catalyst device becomes equal to or higher than a preset cooling start temperature threshold value, the flow path switching device is controlled to control the flow of exhaust gas. While switching from the exhaust passage to the branch passage, the cooling capacity of the exhaust gas cooling device is controlled based on the temperature of the exhaust gas immediately after passing through the exhaust gas cooling device, and the NOx purification rate of the selective reduction type catalyst device is determined in advance. The temperature range of the selective reduction type catalyst device that is equal to or higher than the set purification rate threshold is set as the appropriate temperature range, the upper limit of the appropriate temperature range is set as the cooling start temperature threshold, and the temperature range is further within the appropriate temperature range. A target temperature range is set, and the flow path switching device is controlled when the temperature of the selective reduction type catalyst device is included in the appropriate temperature range but is lower than the lower limit of the target temperature range. The method is characterized in that the flow of exhaust gas is controlled to be switched from the branch passage to the exhaust passage.

According to the exhaust gas purification system of the internal combustion engine and the exhaust gas purification method of the internal combustion engine of the present invention, the cooling capacity of the exhaust gas cooling device can be suppressed while suppressing deterioration due to overheating of the selective reduction catalyst device and reduction of the NOx purification rate. It is possible to suppress a decrease in the NOx purification rate of the selective reduction catalyst device due to a temporary excess.

Further, since the temperature of the exhaust gas flowing into the selective reduction catalyst device is controlled based on the cooling capacity of the exhaust gas cooling device, urea supplied from the urea water supply device located upstream of the selective reduction catalyst device is used. The temperature of this exhaust gas can be reliably maintained in a temperature range in which the hydrolysis reaction of water to ammonia is promoted.

It is a figure which shows the structure of the exhaust gas purification system of the internal combustion engine of this invention. It is a figure which shows the relationship between the temperature of a selective reduction type catalyst apparatus and NOx purification rate. It is a figure which shows the control flow of the exhaust gas purification method of the internal combustion engine of this invention. It is a figure which shows the structure of the exhaust gas purification system of the internal combustion engine of the prior art.

Hereinafter, the exhaust gas purification system of the internal combustion engine and the exhaust gas purification method of the internal combustion engine according to the embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the exhaust gas purification system 1 of the present invention has an oxidation catalyst device (DOC) 11, a fine particle collection device 12, and a urea water supply device in this order from the upstream side to the exhaust passage (exhaust pipe) 10 of the engine 2. 15. This system is provided with a selective catalytic reduction (SCR) 13.

The oxidation catalyst device 11 is configured by supporting a noble metal catalyst (oxidation catalyst) that oxidizes hydrocarbons (HC), carbon monoxide (CO), etc. of the exhaust gas G on a base material forming a honeycomb structure. As the noble metal catalyst, a platinum (Pt) -based catalyst that oxidizes hydrocarbons to water and carbon dioxide and carbon monoxide to carbon dioxide is preferable.

Since the oxidation reaction of hydrocarbons and carbon monoxide by this noble metal catalyst is an exothermic reaction, the temperature of the exhaust gas G rises due to this heat generation. Utilizing this, when a high temperature exhaust gas G is required such as during forced PM regeneration control of the fine particle collecting device 12, it is included in the exhaust gas G passing through the exhaust passage 10 on the upstream side of the oxidation catalyst device 11. The exhaust gas G is heated in temperature by temporarily increasing the amount of hydrocarbons and oxidizing the increased amount of hydrocarbons in the oxidation catalyst device 11.

As a method for temporarily increasing the amount of hydrocarbons, for example, a method of post-injecting fuel in the cylinder 2a of the engine 2 or a method of performing fuel post-injection in the exhaust passage 10 on the upstream side of the oxidation catalyst device 11 is used. There is a method of injecting fuel from this fuel injection device by providing an injection device (not shown).

The fine particle collecting device 12 is configured to include a filter inside the particulate matter (PM) in the exhaust gas G in order to collect the particulate matter (PM). This filter is a monolith honeycomb type wall flow type filter in which inlets and outlets of porous ceramic honeycomb cells (channels) are alternately sealed.

Exhaust gas G flows in from the entrance of the unsealed cell of the fine particle collecting device 12, and passes through the PM collecting wall formed at the boundary between the adjacent outlet and the unsealed cell. , The exit flows out from the exit of the unsealed cell. The PM contained in the exhaust gas G is collected by the wall for collecting PM, but the amount of PM collected is limited. Therefore, before the PM collection amount reaches the limit value, the high-temperature exhaust gas G is passed through the inside of the fine particle collection device 12, and the heat of the exhaust gas G collects the particles inside the fine particle collection device 12. Forced PM regeneration control that burns and removes the generated PM is regularly performed.

The selective reduction type catalyst device 13 produces ammonia (NH ₃ ) produced by hydrolyzing the urea water U injected from the urea water supply device 15 provided in the exhaust passage 10 on the upstream side by the heat of the exhaust gas G. As a reducing agent, it is a device that purifies nitrogen oxides (NOx) contained in exhaust gas G into nitrogen (N ₂ ).

Ammonia that is not used for purifying NOx contained in the exhaust gas G is occluded inside the selective reduction catalyst device 13 or flows out (slip) to the exhaust passage 10 downstream of the selective reduction catalyst device 13. ). Further, the ammonia storage capacity (upper limit amount capable of storing ammonia) of the selective reduction catalyst device 13 decreases as the temperature of the selective reduction catalyst device 13 increases.

Further, a control device 40 for controlling the exhaust gas purification system 1 of the present invention is arranged. The control device 40 is a device that controls the supply amount of urea water U from the urea water supply device 15 based on the detection values of various sensors indicating the operating state of the engine 2.

As shown in FIG. 1, the exhaust gas purification system 1 of the present invention includes a branch passage 20 having an exhaust gas cooling device 21 in the exhaust passage 10 on the upstream side of the urea water supply device 15 in parallel with the exhaust passage 10. At the same time, the system is provided with a three-way valve (flow path switching device) 22 at the branch point from the exhaust passage 10 to the branch passage 20, which is different from the exhaust gas purification system 1X of the conventional internal combustion engine shown in FIG. There is.

Further, the SCR temperature detection sensor (SCR temperature detection device) 30 that detects the temperature of the selective reduction catalyst device 13 is placed inside the selective reduction catalyst device 13 (at this position in FIG. 1) or the selective reduction catalyst device. For cooling in the exhaust passage 10 on the upstream side or the downstream side of the 13 and for detecting the temperature of the exhaust gas Gb after passing through the exhaust gas cooling device 21 in the branch passage 20 on the downstream side of the exhaust gas cooling device 21. A temperature detection sensor (cooling temperature detection device) 31 is provided.

In the exhaust gas cooling device 21, cooling media such as air, engine cooling water, and radiator cooling water are circulated in the cooling medium passage (not shown) inside the exhaust gas cooling device 21, and are adjacent to the cooling medium passage. The exhaust gas Gb passing through the exhaust gas passage (not shown) is cooled by a cooling medium.

Further, regarding the installation position of the SCR temperature detection sensor 30, as shown in FIG. 1, the SCR temperature detection sensor 30 is provided inside the selective reduction catalyst device 13 to directly detect the temperature of the selective reduction catalyst device 13. However, the SCR temperature detection sensor 30 is provided in the exhaust passage 10 on the upstream side or the downstream side of the selective reduction catalyst device 13, and the detection value of the SCR temperature detection sensor 30 is selected by the selective reduction catalyst device 13. It may be substituted as the temperature.

Then, when the detection value T of the SCR temperature detection sensor 30 becomes equal to or higher than the cooling start temperature threshold T1, the control device 40 controls the three-way valve 22 to branch the flow of the exhaust gas G from the exhaust passage 10. It is configured to switch to 20 and control the cooling capacity of the exhaust gas cooling device 21 based on the detection value of the cooling temperature detection sensor 31.

Here, when the cooling start temperature threshold value T1 is equal to or higher than this threshold value, there is a concern that the thermal deterioration of the catalyst supported on the selective reduction catalyst device 13 may progress or the NOx purification rate may decrease. It is a value set in advance by an experiment or the like.

The cooling capacity of the exhaust gas cooling device 21 is the amount and temperature of the cooling medium such as air or engine cooling water that exchanges heat with the exhaust gas Gb to the exhaust gas cooling device 21. Further, the cooling capacity of the exhaust gas cooling device 21 is improved by increasing the flow amount of the cooling medium to the exhaust gas cooling device 21 or lowering the temperature of the cooling medium. On the contrary, the cooling capacity is lowered by reducing the distribution amount or raising the temperature of the cooling medium.

That is, in the exhaust gas purification system 1 of the internal combustion engine of the present invention, the temperature T of the selective reduction type catalyst device 13 is the selective reduction type during high load operation of the engine 2 or forced PM regeneration control of the fine particle collection device 12. When the temperature is high enough that the thermal deterioration of the catalyst carried on the catalyst device 13 progresses or the NOx purification rate may decrease, the total amount of the exhaust gas G before flowing into the selective reduction type catalyst device 13 is used. The temperature T of the selective reduction catalyst device 13 is lowered by cooling the exhaust gas G by the exhaust gas cooling device 21 and flowing the lowered exhaust gas G into the selective reduction catalyst device 13.

Further, when the exhaust gas Gb is cooled by the exhaust gas cooling device 21, the cooling capacity of the exhaust gas cooling device 21 is increased by controlling the cooling capacity of the exhaust gas cooling device 21 based on the detection value of the cooling temperature detection sensor 31. It is possible to prevent the temperature T of the selective reduction catalyst device 13 from being excessively lowered due to the temporary excessive cooling of the exhaust gas Gb.

Therefore, according to this configuration, while suppressing deterioration due to overheating of the selective reduction catalyst device 13 and a decrease in the NOx purification rate, the selective reduction catalyst device 13 due to a temporary increase in the cooling capacity of the exhaust gas cooling device 21. It is possible to suppress a decrease in the NOx purification rate.

Further, in the exhaust gas purification system 1 of the internal combustion engine, as shown in FIG. 2, the control device 40 has a NOx purification rate P of the selective reduction catalyst device 13 equal to or higher than the purification rate threshold P1 set in advance by experiments or the like. a selective reduction catalyst device 13 proper temperature range Rp temperature range as a, and sets the upper limit of the proper temperature range Rp in the cooling start temperature threshold T1, setting the target temperature range Rt to the proper temperature range Rp To do. The lower limit value T2 of the appropriate temperature range Rp is a value set in consideration of the NOx purification rate of the selective reduction catalyst device 13.

Further, the upper limit value Ta and the lower limit value Tb of the target temperature range Rt are the upper limit of the appropriate temperature range Rp in both the equations of Ta = (3 × T1 + 7 × T2) / 10 and Tb = (7 × T1 + 3 × T2) / 10. By substituting the value T1 and the lower limit value T2 for calculation, the temperature T of the selective reduction catalyst device 13 can be easily maintained in the appropriate temperature range Rp to prevent a decrease in the NOx purification rate and thermal deterioration of the catalyst. It is preferable because it can be done.

Further, from the median value T3 (= (T1 + T2) / 2) of the upper limit value T1 and the lower limit value T2 of the appropriate temperature range Rp, a temperature higher by the set temperature difference ΔT preset in an experiment or the like is set to the target temperature range Rt. When the upper limit value Ta is set and the temperature lower than the median value T3 by the set temperature difference ΔT is set to the lower limit value Tb, the temperature T of the selective reduction type catalyst device 13 can be easily maintained within the appropriate temperature range Rp. It is preferable because it can be done.

Then, after the cooling of the exhaust gas Gb by the exhaust gas cooling device 21 is started, the detection value T of the SCR temperature detection sensor 30 is continuously included in the target temperature range Rt for a set time tk preset by an experiment or the like. Occasionally, assuming that the temperature T of the selective reduction catalyst device 13 is stable within the appropriate temperature range Rp, the three-way valve 22 is controlled to control the flow of the exhaust gas G from the branch passage 20 to the exhaust passage 10. Configure to.

According to this configuration, the flow of the exhaust gas G is switched from the branch passage 20 to the exhaust passage 10 by the three-way valve 22, and immediately after the cooling of the exhaust gas G by the exhaust gas cooling device 21 is completed, the selective reduction type catalyst device 13 It is possible to prevent a situation in which the temperature T of the above becomes equal to or higher than the cooling start temperature threshold T1 and the exhaust gas G needs to be cooled again by the exhaust gas cooling device 21. In other words, the accuracy of switching the flow of the exhaust gas G by the three-way valve 22 can be improved.

Further, in the exhaust gas purification system 1 of the internal combustion engine, the control device 40 has a temperature lower than the lower limit value Tb of the target temperature range Rt, although the detection value T of the SCR temperature detection sensor 30 is included in the appropriate temperature range Rp. When (T2 ≦ T <Tb), the three-way valve 22 is controlled to switch the flow of the exhaust gas G from the branch passage 20 to the exhaust passage 10, and the selective reduction type catalyst device 13 It is possible to prevent the temperature T from becoming excessively low below the lower limit value T2 of the appropriate temperature range Rp.

Although the three-way valve 22 is provided as the flow path switching device in FIG. 1, a flow rate adjusting valve (flow rate adjusting device) 22 having a flow rate adjusting function as well as a flow rate switching function may be provided instead. In this case, the exhaust gas G is not circulated through either the exhaust passage 10 or the branch passage 20 as in the three-way valve 22, but the exhaust gas G is passed through the exhaust passage 10 or the branch passage 20 or both. Can be distributed.

Therefore, when the control device 40 switches the flow of the exhaust gas G between the exhaust passage 10 and the branch passage 20, it can be switched gradually or stepwise, instead of switching immediately as in the three-way valve 22. Therefore, it is possible to prevent a sudden change in the temperature of the selective reduction catalyst device 13 and prevent a sudden change in the NOx purification rate.

On the other hand, if the configuration is such that the flow of the exhaust gas G between the exhaust passage 10 and the branch passage 20 is immediately switched like the three-way valve 22, the temperature of the exhaust gas G flowing into the selective reduction type catalyst device 13 can be quickly changed. Since the temperature T of the selective reduction catalyst device 13 can be lowered immediately within the target temperature range Rt, deterioration due to overheating of the selective reduction catalyst device 13 can be more reliably prevented.

Further, when the control device 40 switches the flow of the exhaust gas G between the exhaust passage 10 and the branch passage 20, the control device 40 passes through the branch passage 20 as the fluctuation amount ΔTT of the detection value of the cooling temperature detection sensor 31 increases. The fluctuation amount ΔV of the flow rate of the exhaust gas Gb is set small to control the flow rate adjusting valve 22.

According to this configuration, when the fluctuation amount ΔTT becomes large, assuming that the cooling capacity of the exhaust gas cooling device 21 is temporarily excessive, the fluctuation amount ΔV is reduced by the flow rate adjusting valve 22 to reduce the fluctuation amount ΔV, and the exhaust gas cooling device 21 Since the increase in the flow rate of the exhaust gas Gb cooled by the above is suppressed, it is possible to suppress the exhaust gas G flowing into the selective reduction catalyst device 13 from becoming excessively low in temperature, and the NOx of the selective reduction catalyst device 13 can be suppressed. It is possible to suppress a decrease in the purification rate.

Next, the control flow of the exhaust gas purification method of the internal combustion engine of the present invention using the exhaust gas purification system 1 of the internal combustion engine will be described with reference to FIG. The control flow of FIG. 3 is a control flow that is called from a higher-level control flow and starts at each control time preset by an experiment or the like during operation of the engine 2.

When the control flow of FIG. 3 starts, in step S10, the exhaust gas G flowing into the selective reduction catalyst device 13 is cooled by the exhaust gas cooling device 21, and the selective reduction catalyst device 13 is deteriorated due to overheating and NOx purification. Determine if it is necessary to prevent the rate from dropping. This determination is made based on whether or not the temperature T of the selective reduction catalyst device 13 (detected value of the temperature detection sensor 30 for SCR) T is equal to or higher than the cooling start temperature threshold value T1.

In step S10, when the temperature T of the selective reduction catalyst device 13 is less than the cooling start temperature threshold value T1 (NO), it is assumed that the exhaust gas G does not need to be cooled, and the process proceeds to return to perform this control flow. finish.

On the other hand, in step S10, when the temperature T of the selective reduction catalyst device 13 is equal to or higher than the cooling start temperature T1 (YES), it is assumed that the exhaust gas G needs to be cooled, and the process proceeds to step S20 and proceeds to step S20. The flow path switching device 22 is controlled to switch the flow of the exhaust gas G from the exhaust passage 10 to the branch passage 20, and the cooling capacity of the exhaust gas cooling device 21 is changed to the exhaust gas Gb immediately after passing through the exhaust gas cooling device 21. (Detected value of the cooling temperature detection sensor 31) Adjustment and control are performed based on the TT. After performing the control in step S20, the process proceeds to step S30.

At the time of this switching, it is more preferable to control the flow rate adjusting valve 22 to set the fluctuation amount ΔV of the flow rate of the exhaust gas Gb passing through the branch passage 20 to be smaller as the fluctuation amount ΔTT of the temperature of the exhaust gas Gb increases. ..

In step S30, it is determined whether or not cooling of the exhaust gas G flowing into the selective reduction catalyst device 13 is no longer necessary. In this determination, the temperature T of the selective reduction catalyst device 13 is continuously included in the target temperature range Rt shown in FIG. 2 for a set time ct continuously, or is included in the appropriate temperature range Rp but is included in the target temperature range Rt. This is performed by assuming that cooling of the exhaust gas G is no longer necessary when the temperature is lower than the lower limit value Tb (T2 ≦ T <Tb). If the above determination is not established in step S30 (NO), it is determined that the exhaust gas G still needs to be cooled, and after the control time preset by an experiment or the like has elapsed, the determination in step S30 is performed again. I do.

On the other hand, if the above determination is established in step S30 (YES), it is determined that the cooling of the exhaust gas G is no longer necessary, the process proceeds to step S40, and the flow path switching device 22 is switched in step S40. By controlling, the flow of the exhaust gas G is switched from the branch passage 20 to the exhaust passage 10, and the cooling capacity of the exhaust gas cooling device 21 is returned to the cooling capacity in the normal operating state. After performing the control in step S40, the process proceeds to return and the present control flow is terminated.

Based on the above, the exhaust gas purification method for the internal combustion engine of the present invention, which is based on the exhaust gas purification system 1 for the internal combustion engine of the present invention, is to selectively reduce the urea water supply device 15 to the exhaust passage 10 of the engine 2 in order from the upstream side. A branch passage 20 having an exhaust gas cooling device 21 is provided in parallel with the exhaust passage 10 in the exhaust passage 10 on the upstream side of the urea water supply device 15 in addition to the type catalyst device 13, and the branch passage 20 is provided from the exhaust passage 10. When the temperature T of the selective reduction type catalyst device 13 becomes equal to or higher than the preset cooling start temperature threshold T1 in the exhaust gas purification method of the internal combustion engine provided with the flow path switching device 22 at the branch point to , The flow path switching device 22 is controlled to switch the flow of the exhaust gas G from the exhaust passage 10 to the branch passage 20, and the cooling capacity of the exhaust gas cooling device 21 is changed to that of the exhaust gas Gb immediately after passing through the exhaust gas cooling device 21. The method is characterized by controlling based on temperature.

According to the exhaust gas purification system 1 of the internal combustion engine and the exhaust gas purification method of the internal combustion engine of the present invention, the exhaust gas cooling device 21 can suppress the deterioration of the selective reduction catalyst device 13 due to overheating and the decrease of the NOx purification rate. It is possible to suppress a decrease in the NOx purification rate of the selective reduction catalyst device 13 due to a temporary excess of the cooling capacity.

Further, since the temperature of the exhaust gas G flowing into the selective reduction catalyst device 13 is controlled based on the cooling capacity of the exhaust gas cooling device 21, the urea water supply device 15 arranged on the upstream side of the selective reduction catalyst device 13 The temperature of the exhaust gas G can be reliably maintained in a temperature range in which the hydrolysis reaction of the urea water U supplied from the source to ammonia is promoted.

Further, since the exhaust gas cooling device 21 can lower the temperature of the exhaust gas G flowing into the selective reduction catalyst device 13, the temperature of the selective reduction catalyst device 13 can be lowered to increase the ammonia storage capacity thereof. can do. As a result, the amount of ammonia flowing out (slip) from the selective reduction catalyst device 13 can be suppressed to such a small amount that the installation of the ammonia slip catalyst device 14 shown in FIG. 4 becomes unnecessary.

1, 1X Exhaust gas purification system for internal combustion engine 2 Engine 10 Exhaust passage 13 Selective catalytic reduction (SCR)
15 Urea water supply device 20 Branch passage 21 Exhaust gas cooling device 22 Three-way valve (flow path switching device), flow rate adjusting valve (flow rate adjusting device)
30 SCR temperature detection sensor (SCR temperature detection device)
31 Cooling temperature detection sensor (cooling temperature detection device)
40 Control device G Exhaust gas Ga Exhaust gas passing through the exhaust passage Gb Exhaust gas passing through the branch passage Rp Appropriate temperature range Rt Target temperature range T Temperature of selective reduction catalyst device (detection value of temperature detection sensor for SCR)
T1 Cooling start temperature threshold (upper limit of proper temperature range)
Tb Lower limit of target temperature range P NOx purification rate of selective reduction catalyst device P1 NOx purification rate threshold tc Setting time TT Exhaust gas temperature immediately after passing through the exhaust gas cooling device (detection value of cooling temperature detection sensor)
ΔTT Fluctuation amount of detection value of cooling temperature detection sensor ΔV Fluctuation amount of exhaust gas flow rate passing through branch passage

Claims (5)

In an exhaust gas purification system of an internal combustion engine, which is provided with a urea water supply device and a selective reduction catalyst device in order from the upstream side in the exhaust passage of the internal combustion engine.
A branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and a flow path switching device is provided at a branch point from the exhaust passage to the branch passage. Be prepared and
A temperature detection device for SCR is provided inside the selective reduction catalyst device or in the exhaust passage on the upstream side or downstream side of the selective reduction catalyst device, and cooling is performed in the branch passage on the downstream side of the exhaust gas cooling device. Equipped with a temperature detector for
The control device that controls the exhaust gas purification system
When the detection value of the SCR temperature detection device becomes equal to or higher than the preset cooling start temperature threshold value, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage. , The cooling capacity of the exhaust gas cooling device is controlled based on the detection value of the cooling temperature detecting device .
The temperature range of the selective reduction catalyst device in which the NOx purification rate of the selective reduction catalyst device is equal to or higher than the preset purification rate threshold value is set as the appropriate temperature range, and the upper limit of the appropriate temperature range is set as the cooling start temperature threshold value. As well as setting
Further, a target temperature range is set within the appropriate temperature range, and the temperature range is set.
When the detection value of the SCR temperature detection device is continuously included in the target temperature range for a preset time, the flow path switching device is controlled to flow the exhaust gas flow through the branch passage. An exhaust gas purification system for an internal combustion engine configured to control switching from the exhaust gas to the exhaust passage . In the exhaust gas purification system of an internal combustion engine, which is configured by equipping the exhaust passage of the internal combustion engine with a urea water supply device and a selective reduction catalyst device in order from the upstream side.
A branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and a flow path switching device is provided at a branch point from the exhaust passage to the branch passage. Be prepared and
A temperature detection device for SCR is provided inside the selective reduction catalyst device or in the exhaust passage on the upstream side or downstream side of the selective reduction catalyst device, and cooling is performed in the branch passage on the downstream side of the exhaust gas cooling device. Equipped with a temperature detector for
The control device that controls the exhaust gas purification system
When the detection value of the SCR temperature detection device becomes equal to or higher than the preset cooling start temperature threshold value, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage. , The cooling capacity of the exhaust gas cooling device is controlled based on the detection value of the cooling temperature detecting device.
The temperature range of the selective reduction catalyst device in which the NOx purification rate of the selective reduction catalyst device is equal to or higher than the preset purification rate threshold value is set as the appropriate temperature range, and the upper limit of the appropriate temperature range is set as the cooling start temperature threshold value. Set, and further set the target temperature range within the appropriate temperature range,
When the detection value of the SCR temperature detection device is included in the appropriate temperature range but is lower than the lower limit value of the target temperature range, the flow path switching device is controlled to control the flow of exhaust gas. An exhaust gas purification system for an internal combustion engine configured to control switching from the branch passage to the exhaust passage. In the exhaust gas purification system of an internal combustion engine, which is configured by equipping the exhaust passage of the internal combustion engine with a urea water supply device and a selective reduction catalyst device in order from the upstream side.
A branch passage having an exhaust gas cooling device is provided in parallel with the exhaust passage in the exhaust passage on the upstream side of the urea water supply device, and a flow path switching device is provided at a branch point from the exhaust passage to the branch passage. In addition, the flow path switching device is configured as a flow rate adjusting device capable of flowing exhaust gas to both the exhaust passage and the branch passage.
Further, an SCR temperature detection device is provided inside the selective reduction catalyst device or in the exhaust passage on the upstream side or downstream side of the selective reduction catalyst device, and the branch passage on the downstream side of the exhaust gas cooling device. Equipped with a cooling temperature detector
The control device that controls the exhaust gas purification system
When the detection value of the SCR temperature detection device becomes equal to or higher than the preset cooling start temperature threshold value, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage. , The cooling capacity of the exhaust gas cooling device is controlled based on the detection value of the cooling temperature detecting device.
When switching the flow of exhaust gas between the exhaust passage and the branch passage,
An internal combustion engine configured to control the flow rate adjusting device by setting a small fluctuation amount of the flow rate of exhaust gas passing through the branch passage as the fluctuation amount of the detected value of the cooling temperature detecting device increases. Exhaust gas purification system. The exhaust passage of the internal combustion engine is provided with a urea water supply device and a selective reduction catalyst device in this order from the upstream side, and a branch passage having an exhaust gas cooling device is provided in the exhaust passage on the upstream side of the urea water supply device. In the exhaust gas purification method of an internal combustion engine configured by providing a flow path switching device at a branch point from the exhaust passage to the branch passage in parallel with the above.
When the temperature of the selective reduction catalyst device becomes equal to or higher than a preset cooling start temperature threshold, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage, and at the same time. The cooling capacity of the exhaust gas cooling device is controlled based on the temperature of the exhaust gas immediately after passing through the exhaust gas cooling device .
The temperature range of the selective reduction catalyst device in which the NOx purification rate of the selective reduction catalyst device is equal to or higher than the preset purification rate threshold value is set as the appropriate temperature range, and the upper limit of the appropriate temperature range is set as the cooling start temperature threshold value. Set, and further set the target temperature range within the appropriate temperature range,
When the temperature of the selective reduction catalyst device is continuously included in the target temperature range for a preset time, the flow path switching device is controlled to flow the exhaust gas flow from the branch passage. An exhaust gas purification method for an internal combustion engine, which controls switching to the exhaust passage . The exhaust passage of the internal combustion engine is provided with a urea water supply device and a selective reduction catalyst device in this order from the upstream side, and a branch passage having an exhaust gas cooling device is provided in the exhaust passage on the upstream side of the urea water supply device. In the exhaust gas purification method of an internal combustion engine configured by providing a flow path switching device at a branch point from the exhaust passage to the branch passage in parallel with the above.
When the temperature of the selective reduction catalyst device becomes equal to or higher than a preset cooling start temperature threshold, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the branch passage, and at the same time. The cooling capacity of the exhaust gas cooling device is controlled based on the temperature of the exhaust gas immediately after passing through the exhaust gas cooling device.
The temperature range of the selective reduction catalyst device in which the NOx purification rate of the selective reduction catalyst device is equal to or higher than the preset purification rate threshold value is set as the appropriate temperature range, and the upper limit of the appropriate temperature range is set as the cooling start temperature threshold value. Set, and further set the target temperature range within the appropriate temperature range,
When the temperature of the selective reduction catalyst device is included in the appropriate temperature range but is lower than the lower limit of the target temperature range, the flow path switching device is controlled to control the flow of exhaust gas. An exhaust gas purification method for an internal combustion engine, which controls switching from a branch passage to the exhaust passage.

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