JP2017031872A - Exhaust emission control system for internal combustion engine, internal combustion engine and exhaust emission control method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine, the internal combustion engine and an exhaust emission control method for the internal combustion engine that enable improvement of NOx elimination performance of a selective reduction type catalyst device while maintaining supply efficiency of urea water to the selective reduction type catalyst device even in a situation where a temperature of exhaust gas is raised, such as a high-load operation of the engine and regeneration control of a particulate trapping device provided in an exhaust emission control device.SOLUTION: In an exhaust passage 11 provided upstream of a selective reduction type catalyst device 14, a bypass passage 31 having a heat exchange device 30 for cooling exhaust gas G2 is provided in parallel with the exhaust passage 11, and a three-way valve 32 for controlling a flow rate of the exhaust gas G2 passing through the bypass passage 31 is provided. An urea water supply device 20 is provided in the exhaust passage 11 between a branch point from the exhaust passage 11 to the bypass passage 31 and the selective reduction type catalyst device 14. Based on a detection value T obtained by a temperature sensor 23 provided on the inlet side of the selective reduction type catalyst device 14, the three-way valve 32 is controlled.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine configured to include a selective reduction catalyst device in an exhaust passage of the internal combustion engine, an internal combustion engine, and an exhaust gas purification method for the internal combustion engine.

In recent years, an exhaust gas purification system provided in an exhaust passage of an internal combustion engine such as a diesel engine includes a nitrogen oxide (NOx) such as nitrogen monoxide (NO) or nitrogen dioxide (NO ₂ ) contained in the exhaust gas of the internal combustion engine. In order to purify (decompose and remove)), a selective reduction catalyst device (SCR catalyst device) is provided.

In the exhaust gas purification system using this selective reduction catalyst device, ammonia (NH ₃ ) generated from urea water is often used as a reducing agent. In this case, the exhaust gas upstream of the selective reduction catalyst device is used. A urea water supply device is provided in the passage, and the urea water injected from the urea water supply device is hydrolyzed by the heat of the exhaust gas and supplied to the selective catalytic reduction catalytic converter as ammonia. NOx contained in the exhaust gas is reduced and purified by the catalytic action of the reduction catalyst device.

  The catalyst carried on the selective catalytic reduction device is activated by being heated by heat contained in the exhaust gas from the engine, and decomposes components to be purified such as NOx when the catalyst is activated. And removing. As this supported catalyst, Fe zeolite and Cu zeolite obtained by ion exchange of iron (Fe) ions and copper (Cu) ions have been put to practical use in recent years. It has a feature that the NOx purification performance decreases as the temperature becomes higher, while the NOx purification performance decreases at a lower temperature than the Fe zeolite catalyst, which has a tendency to exhibit a high purification performance with a high ability, A Cu zeolite catalyst that exhibits high NOx purification performance only in a specific temperature range has attracted attention (see FIG. 3).

  However, when the catalyst supported on the selective catalytic reduction catalyst device is a catalyst that exhibits high NOx purification performance only in a specific temperature range, such as a Cu zeolite catalyst, the NOx purification performance decreases as the temperature rises. High-temperature exhaust during high-load operation of the engine or during forced PM regeneration control of a particulate collection device that collects particulate matter (PM) contained in the exhaust gas provided in the exhaust gas purification device In a situation where the gas passes through the selective catalytic reduction device and the selective catalytic reduction device is exposed to a high temperature, the selective catalytic reduction device cannot sufficiently purify NOx, and a relatively high concentration of NOx is discharged to the atmosphere. There is a concern that will be done.

  In this connection, the exhaust pipe is branched between the SCRF (SCR-coated filter) and the SCR, and the branch pipe is provided with a cooling element for cooling the exhaust gas passing through the branch pipe by air cooling or water cooling, When cooling is not required, the exhaust control valve allows all of the exhaust from the SCRF to pass only through the exhaust pipe and flow into the SCR. When cooling is required, the branch pipe is set according to the target catalyst temperature. An exhaust gas purification system for an internal combustion engine that controls the temperature of the exhaust gas flowing into the SCR by increasing the amount of exhaust gas passing through and the flow rate of water or air flowing through the cooling element as necessary has been proposed (for example, patents) Reference 1).

  However, in this exhaust gas purification system for an internal combustion engine, an exhaust control valve and a cooling element are provided on the downstream side of the reducing agent injection valve. Therefore, urea aqueous solution or urea aqueous solution as a reducing agent injected from the reducing agent injection valve is decomposed. Since products (biuret, isocyanic acid, cyanuric acid, ammonia, etc.) flow into the cooling element, problems such as clogging and corrosion of the cooling element occur, and the supply efficiency of the reducing agent to the SCR decreases. There is a problem of fear.

Japanese Unexamined Patent Publication No. 2015-86848

  The present invention has been made in view of the above, and an object thereof is related to an exhaust gas purification system for an internal combustion engine configured to include a selective reduction catalyst device in an exhaust passage of the internal combustion engine. While maintaining high urea water supply efficiency to the selective catalytic reduction catalyst device even in situations where the exhaust gas is at a high temperature, such as during high-load operation or regeneration control of the particulate collection device provided in the exhaust gas purification device, Exhaust gas purification system for internal combustion engine, internal combustion engine, and internal combustion engine capable of improving NOx purification performance of selective reduction catalyst device by keeping temperature of selective reduction catalyst device within temperature range exhibiting high NOx purification performance It is in providing the exhaust-gas purification method of this.

  In order to achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention is an exhaust gas purification system for an internal combustion engine comprising a selective reduction catalyst device in an exhaust passage of the internal combustion engine. A temperature detection device for detecting the temperature of the exhaust gas flowing into the selective reduction catalyst device is provided on the inlet side of the catalyst device, and the exhaust gas is cooled in the exhaust passage upstream of the selective reduction catalyst device. A bypass passage provided with a heat exchange device is provided in parallel with the exhaust passage, and further, a flow rate adjusting mechanism for adjusting a flow rate of exhaust gas passing through the bypass passage is provided, and a branch from the exhaust passage to the bypass passage is provided. A control device configured to provide a urea water supply device in the exhaust passage between the point and the selective reduction catalyst device, and to control the exhaust gas purification system, Based on the detected value of the serial temperature sensing device adapted to control the flow rate adjusting mechanism.

  That is, the selective reduction type catalytic device is provided with a temperature detection device (temperature sensor or the like) on the inlet side of the selective reduction type catalytic device, and the temperature of the exhaust gas detected by this temperature detection device is set based on the engine operating state The flow rate adjusting mechanism (open / close valve, three-way valve, etc.) is feedback-controlled so that the exhaust gas temperature corresponding to the target temperature of the exhaust gas is adjusted to control the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst device. Note that the target temperature of the exhaust gas is set in advance based on experimental results and the like in consideration of the characteristics (activation temperature range) of the catalyst carried on the selective catalytic reduction device.

  More specifically, when the detected value of the temperature detection device is higher than the target temperature of the exhaust gas, the flow rate of the exhaust gas cooled through the bypass passage (the flow rate of the exhaust gas cooled by the heat exchange device) is The flow rate adjusting mechanism is controlled so as to increase the temperature of the exhaust gas after joining the exhaust gas that does not pass through the bypass passage and the exhaust gas that passes through it. On the other hand, when the detected value of the temperature detection device is lower than the target temperature of the exhaust gas, the flow rate adjustment mechanism is controlled so that the flow rate of the exhaust gas cooled by passing through the bypass passage is reduced, and passes through the bypass passage. The temperature of the exhaust gas after joining the exhaust gas not passing through and the exhaust gas passing through is raised. The cooling medium for the heat exchange device may be water such as engine cooling water, oil, air, or the like.

  Therefore, according to this configuration, the exhaust gas flows into the selective catalytic reduction catalyst device even when the exhaust gas is at a high temperature, such as during high-load operation of the engine or during regeneration control of the particulate collection device provided in the exhaust gas purification device. By adjusting and controlling the temperature of the exhaust gas to be adjusted, the temperature of the catalyst supported on the selective reduction catalyst device can be adjusted to a temperature range that exhibits high NOx purification performance. Therefore, the NOx purification performance of the selective reduction catalyst device Can be improved. In particular, the present invention is extremely effective when the catalyst supported on the selective catalytic reduction apparatus is a catalyst having high NOx purification performance only in a specific temperature range such as a Cu zeolite catalyst.

  In addition, since a urea water supply device is provided in the exhaust passage between the branch point from the exhaust passage to the bypass passage and the selective catalytic reduction device, urea water and urea water decomposition products (biuret, isocyanate, cyanuric) Acid, ammonia, etc.) does not enter the heat exchange device, so that troubles such as clogging and corrosion of the heat exchange device can be prevented, and the supply efficiency of urea water to the selective catalytic reduction catalyst device can be maintained.

  In the exhaust gas purification system for an internal combustion engine, when the detection value of the temperature detection device is less than a preset value, the flow rate of the exhaust gas passing through the bypass passage is zero. As described above, the flow rate adjustment mechanism is controlled, and when the value is equal to or greater than the set value, the flow rate adjustment mechanism is controlled so that the detected value is less than the set value. This set value is set to a value within a temperature range of 250 ° C. to 500 ° C., preferably a value within a temperature range of 300 ° C. to 400 ° C.

  According to this configuration, the temperature of the catalyst supported on the selective reduction catalyst device can be reliably adjusted to a temperature range that exhibits high NOx purification performance.

  In order to achieve the above object, an internal combustion engine of the present invention is configured to include the exhaust gas purification system of the internal combustion engine, and has the same effects as the exhaust gas purification system of the internal combustion engine. it can.

  An exhaust gas purification method for an internal combustion engine of the present invention for achieving the above object includes a selective reduction catalyst device in an exhaust passage of the internal combustion engine, and the exhaust passage upstream of the selective reduction catalyst device. In addition, a bypass passage provided with a heat exchange device for cooling the exhaust gas is provided in parallel with the exhaust passage, a flow rate adjusting mechanism for adjusting the flow rate of the exhaust gas passing through the bypass passage is provided, and the exhaust passage In the exhaust gas purification method for an internal combustion engine, in which an urea water supply device is provided in the exhaust passage between the branch point from the bypass passage to the bypass passage and the selective reduction catalyst device, the inlet of the selective reduction catalyst device A temperature detection device is provided on the side, the temperature detection device detects the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst device, and based on the detection value of the temperature detection device. There are a method and controlling the flow rate adjustment mechanism.

  Further, in the exhaust gas purification method for an internal combustion engine, when the detected value of the temperature detection device is less than a preset set value, the flow rate of the exhaust gas passing through the bypass passage becomes zero. The flow rate adjusting mechanism is controlled, and when it is equal to or higher than the set value, the flow rate adjusting mechanism is controlled so that the detected value is less than the set value.

  According to these methods, the same operational effects as the exhaust gas purification system of the internal combustion engine can be obtained.

  According to the exhaust gas purification system for an internal combustion engine, the internal combustion engine, and the exhaust gas purification method for the internal combustion engine of the present invention, during high-load operation of the engine, during regeneration control of the particulate collection device provided in the exhaust gas purification device, etc. The temperature range in which the temperature of the catalyst carried on the selective catalytic reduction catalyst device exhibits a high NOx purification performance by adjusting and controlling the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst device even in a situation where the exhaust gas temperature rises Therefore, the NOx purification performance of the selective catalytic reduction catalyst device can be improved. In particular, the present invention is extremely effective when the catalyst supported on the selective catalytic reduction apparatus is a catalyst having high NOx purification performance only in a specific temperature range such as a Cu zeolite catalyst.

  In addition, since a urea water supply device is provided in the exhaust passage between the branch point from the exhaust passage to the bypass passage and the selective catalytic reduction device, urea water and urea water decomposition products (biuret, isocyanate, cyanuric) Acid, ammonia, etc.) does not enter the heat exchange device, so that troubles such as clogging and corrosion of the heat exchange device can be prevented, and the supply efficiency of urea water to the selective catalytic reduction catalyst device can be maintained.

It is a figure showing typically composition of an exhaust-gas purification system of an internal-combustion engine of an embodiment concerning the present invention. It is a figure which shows an example of the control flow of the exhaust gas purification method of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows the relationship between the temperature of the selective reduction type | mold catalyst apparatus which supported each catalyst of the Fe zeolite catalyst and the Cu zeolite catalyst, and the NOx purification rate. It is a figure which shows typically the structure of the exhaust-gas purification system of the internal combustion engine which concerns on a prior art.

  Hereinafter, an exhaust gas purification system for an internal combustion engine, an internal combustion engine, and an exhaust gas purification method for the internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. Note that an internal combustion engine according to an embodiment of the present invention includes an exhaust gas purification system 1 for an internal combustion engine according to an embodiment of the present invention, which will be described later, and is provided by an exhaust gas purification system 1 for the internal combustion engine described later. The same operational effects as the operational effects can be achieved.

  In the present embodiment, a selective reduction catalyst device (SCR catalyst device) is described by taking a urea (or ammonia) selective reduction catalyst device using ammonia generated from urea water as a reducing agent as an example. A reducing agent may be used, and in that case, the selective catalytic reduction apparatus may be a selective catalytic reduction apparatus corresponding to the reducing agent.

  As shown in FIG. 1, an exhaust gas purification system 1 for an internal combustion engine according to an embodiment of the present invention oxidizes an exhaust passage 11 of an engine (internal combustion engine) (not shown) in order from the upstream side (engine side). This is a system comprising an exhaust gas purification device such as a catalyst device 12, a fine particle collecting device 13, a selective reduction catalyst device 14 carrying a Cu zeolite catalyst, an ammonia slip catalyst device 15, and the like.

  Further, a urea water supply device 20 that injects urea water U toward the selective reduction catalyst device 14 is provided in the exhaust passage 11 upstream of the selective reduction catalyst device 14 based on the operating state of the engine. The urea water supply device 20 is supplied with the urea water U stored in the urea water tank 22 by the urea water supply pump 21, and the injection amount of the urea water U is a urea water supply control device (DCU: dosing control unit) to be described later. ) 40 is controlled by adjusting and controlling the output of the urea water supply pump 21. Note that the injection amount of the urea water U may be controlled by adjusting and controlling the valve opening of the urea water supply device 20.

  A temperature sensor (temperature detection device) 23 is provided at the inlet of the selective catalytic reduction catalyst device 14, and a NOx concentration sensor 24 and an ammonia concentration sensor 25 are provided in the exhaust passage 11 downstream of the ammonia slip catalyst device 15. It is done.

  Further, a urea water supply control unit (DCU) 40 for controlling the exhaust gas purification system 1 for an internal combustion engine of the present invention is provided. The urea water supply control device 40 receives necessary data such as data related to the intake air flow rate to the engine from an engine control device (ECU: engine control unit) 41 that controls the operating state of the engine, and the temperature sensor 23, The data of the detected values of the NOx concentration sensor 24 and the ammonia concentration sensor 25 are received, and based on these received data, the output of the urea water supply pump 21 is adjusted and controlled, and urea from the urea water supply device 20 is controlled. It is a device that controls the injection amount of water U.

  Regarding the exhaust gas purification system 1 for an internal combustion engine of the present invention, the configuration and control described above are the same as those of the exhaust gas purification system 1X for an internal combustion engine of the prior art shown in FIG.

  In the exhaust gas purification system 1 for an internal combustion engine according to the present invention, unlike the exhaust gas purification system 1X for an internal combustion engine according to the prior art, the exhaust gas G2 is cooled in the exhaust passage 11 upstream of the selective catalytic reduction device 14. A bypass passage 31 provided with the heat exchange device 30 is provided in parallel with the exhaust passage 11, and a three-way valve (flow rate adjusting mechanism) 32 that adjusts the flow rate of the exhaust gas G <b> 2 passing through the bypass passage 31 is provided.

  The flow rate adjusting mechanism 32 may be any mechanism that can adjust the flow rate of the exhaust gas G2 that passes through the bypass passage 31, so that an on-off valve may be provided in the bypass passage 31 instead of the three-way valve 32, Open / close valves may be provided in both the exhaust passage 11 and the bypass passage 31 between the branch point from the passage 11 to the bypass passage 31 and the junction.

  More specifically, the heat exchanger 30 cools the exhaust gas G2 that is diverted through the three-way valve 32 from the exhaust gas G that has passed through the particulate collection device 13 using engine cooling water as a cooling medium. Device. The cooling medium of the heat exchange device 30 may be a water-cooled cooling medium other than engine cooling water, or a cooling medium such as oil or air.

  In the prior art, the urea water supply device 20 is provided in the exhaust passage 11 upstream of the selective reduction catalyst device 14. However, in the present invention, the branch point from the exhaust passage 11 to the bypass passage 31 and the selective reduction type are provided. A urea water supply device 20 is provided in the exhaust passage 11 between the catalyst devices 14.

  In the exhaust gas purification system 1 for an internal combustion engine according to the present invention, the urea water supply control device 40 is configured to control the three-way valve 32 based on the detection value T of the temperature sensor 23.

  That is, a temperature sensor 23 is provided on the inlet side of the selective catalytic reduction device 14, and the temperature T of the exhaust gas G (= G1 + G2) detected by the temperature sensor 23 is set based on the engine operating state. The three-way valve 32 is feedback-controlled so that the target temperature Tt of the exhaust gas G corresponding to the target temperature of the catalyst device 14 is adjusted, and the temperature of the exhaust gas G flowing into the selective catalytic reduction device 14 is adjusted and controlled. The target temperature Tt of the exhaust gas G is set in consideration of the characteristics of the catalyst carried on the selective reduction catalyst device 14.

  More specifically, when the detected value T of the temperature sensor 23 is higher than the target temperature Tt of the exhaust gas G, the flow rate of the exhaust gas G2 passing through the bypass passage 31 (the exhaust gas G2 cooled by the heat exchange device 30). The flow rate of the exhaust gas G after the exhaust gas G1 that does not pass through the bypass passage 31 and the exhaust gas G2 that passes through it is controlled by controlling the three-way valve 32 so that the flow rate) increases. The temperature of the exhaust gas G flowing into the engine 14 is lowered. On the other hand, when the detected value T of the temperature sensor 23 is lower than the target temperature Tt of the exhaust gas G, the bypass passage 31 is controlled by controlling the three-way valve 32 so that the flow rate of the exhaust gas G2 passing through the bypass passage 31 decreases. The temperature of the exhaust gas G after joining the exhaust gas G1 that does not pass through and the exhaust gas G2 that passes through is raised.

  Note that it is sufficient that the temperature of the exhaust gas G flowing into the selective catalytic reduction device 14 can be adjusted and controlled. Therefore, instead of controlling the three-way valve 32 or together with the control of the three-way valve 32, the cooling medium flowing into the heat exchange device 30 The temperature of the exhaust gas G may be adjusted and controlled by controlling the cooling capacity of the heat exchange device 30 by adjusting and controlling the flow rate. However, if the temperature of the exhaust gas G is adjusted and controlled only by controlling the three-way valve 32, the control is simplified, and the responsiveness is improved.

  Further, a configuration in which the heat exchange device 30 is provided in the exhaust passage 11 without providing the bypass passage 31 to control the flow of the cooling medium to the heat exchange device 30 is conceivable. In this case, the heat exchange device 30 is also possible. Must be provided in the exhaust passage 11 upstream of the urea water supply device 20. When the heat exchange device 30 is provided in the exhaust passage 11 downstream from the urea water supply device 20, urea water U and decomposition products of the urea water U (biuret, isocyanic acid, cyanuric acid, ammonia, etc.) are transferred to the heat exchange device 30. This is because it may flow in and cause clogging or malfunction of the heat exchange device 30.

  However, even when the heat exchange device 30 is provided in the exhaust passage 11 upstream of the urea water supply device 20, the decomposition efficiency of the urea water U into ammonia is reduced by the temperature drop of the exhaust gas G by the heat exchange device 30. There is a possibility that the temperature decreases, the temperature increase rate of the selective catalytic reduction catalyst 14 on the downstream side decreases due to the temperature decrease of the exhaust gas G by the heat exchange device 30 in the warm-up process, and the heat exchange device 30 In consideration of the possibility that the pressure loss of the exhaust gas G increases to adversely affect the fuel consumption, etc., the bypass passage 31 is provided as in the present invention, and the heat exchange device 30 is provided in the bypass passage 31. Is more preferable.

  In addition, when the detected value T of the temperature sensor 23 is less than the preset set value T1, the urea water supply control device 40 is configured so that the flow rate of the exhaust gas G2 passing through the bypass passage 31 becomes zero. 32 may be controlled so that when the set value is equal to or greater than the set value T1, the three-way valve 32 may be controlled so that the detected value T is less than the set value T1. This set value is set to a value within a temperature range of 250 ° C. to 500 ° C., preferably a value within a temperature range of 300 ° C. to 400 ° C.

  A control flow relating to the control of the three-way valve 32 is shown in FIG. The control flow of FIG. 2 is called and executed from the advanced control flow at every preset control time, and returns to the advanced control flow after being executed. The control is repeatedly called as long as the engine is in the operating state. Shown as a flow. In the middle of the control based on the control flow of FIG. 2, when the engine is stopped, an interrupt is generated, the return is made and the control flow returns to the advanced control flow, and the process ends with the end of the advanced control flow. .

  The control flow of FIG. 2 will be described. When the control flow of FIG. 2 starts, it is determined in step S11 whether or not the detected value T of the temperature sensor 23 is less than a preset set value T1. When the detected value T of the temperature sensor 23 is less than the set value T1 (YES: T <T1), the temperature of the selective catalytic reduction device 14 rises to a temperature exceeding the high efficiency range of the NOx purification performance of the Cu zeolite catalyst. In step S12, the flow rate of the exhaust gas G2 passing through the bypass passage 31 is set to zero in step S12. In addition, the three-way valve 32 is controlled. After the control of the three-way valve 32, the process returns to the advanced control flow.

  On the other hand, when the detected value T of the temperature sensor 23 is equal to or greater than the set value T1 (NO: T ≧ T1), the temperature at which the selective catalytic reduction catalyst device 14 exceeds the high efficiency range of the NOx purification performance of the Cu zeolite catalyst. It is determined that the exhaust gas G2 needs to be cooled by the heat exchange device 30, and the process proceeds to step S13. In step S13, the detected value T is less than the set value T1. The valve 32 is controlled. After the control of the three-way valve 32, the process returns to the advanced control flow.

  As described above, the exhaust gas purification method for an internal combustion engine according to the present invention based on the exhaust gas purification system 1 for the internal combustion engine according to the present invention includes the selective reduction catalyst device 14 in the exhaust passage 11 of the internal combustion engine, and this selection. A bypass passage 31 provided with a heat exchange device 30 for cooling the exhaust gas G is provided in parallel to the exhaust passage 11 in the exhaust passage 11 upstream of the reduction catalyst device 14, and the exhaust gas passing through the bypass passage 31 is further provided. A three-way valve 32 for adjusting the flow rate of G is provided, and a urea water supply device 20 is provided in the exhaust passage 11 between the branch point from the exhaust passage 11 to the bypass passage 31 and the selective reduction catalyst device 14. In the exhaust gas purification method for an internal combustion engine, a temperature sensor 23 is provided on the inlet side of the selective catalytic reduction device 14, and the temperature sensor 23 flows into the selective catalytic reduction device 14. It detects the temperature T of the air gas G, on the basis of the detected value T of the temperature sensor 23, a method characterized by controlling the three-way valve 32.

  Further, in the above exhaust gas purification method for an internal combustion engine, when the detected value T of the temperature sensor 23 is less than the preset set value T1, the flow rate of the exhaust gas G2 passing through the bypass passage 31 becomes zero. The three-way valve 32 is controlled, and when the set value is equal to or greater than the set value T1, the three-way valve 32 is controlled so that the detected value T is less than the set value T1.

  According to the exhaust gas purification system 1 for an internal combustion engine, the internal combustion engine, and the exhaust gas purification method for an internal combustion engine of the present invention, during high-load operation of the engine, regeneration control of the particulate collection device provided in the exhaust gas purification device, etc. Even in a situation where the exhaust gas G is heated, the temperature of the catalyst carried on the selective reduction catalyst device 14 is increased by NOx purification by adjusting and controlling the temperature T of the exhaust gas G flowing into the selective reduction catalyst device 14. Since it can be adjusted to a temperature range that exhibits performance, the NOx purification performance of the selective catalytic reduction device 14 can be improved. In particular, the present invention is extremely effective when the catalyst supported on the selective catalytic reduction device 14 is a catalyst having high NOx purification performance only in a specific temperature range such as a Cu zeolite catalyst.

  Further, since the urea water supply device 20 is provided in the exhaust passage 11 between the branch point from the exhaust passage 11 to the bypass passage 31 and the selective catalytic reduction catalyst device 14, the urea water U and the decomposition products of the urea water U are provided. (Biuret, isocyanic acid, cyanuric acid, ammonia, etc.) does not enter the heat exchange device 30 and can prevent problems such as clogging and corrosion of the heat exchange device 30 and the urea water U to the selective catalytic reduction device 14. Supply efficiency can be maintained.

  Furthermore, since the exhaust gas G before the urea water U is supplied is cooled by the heat exchange device 30, compared to the case where the exhaust gas G whose temperature has decreased due to the supply of the urea water U is cooled by the heat exchange device 30. In addition, the cooling efficiency of the exhaust gas G in the heat exchange device 30 can be increased.

  Further, when the heat exchange device 30 is provided not in the bypass passage 31 but in the exhaust passage 11 upstream of the urea water supply device 20 without providing the bypass passage 31, the temperature of the exhaust gas G decreases. There is a risk that the decomposition efficiency of the urea water U may decrease due to the heat exchange device 30, the selective reduction catalyst device 14 may not be easily warmed during the engine warm-up process, and the heat exchange device 30 is always constant. The pressure loss in the exhaust passage 11 may increase and adversely affect the combustion and fuel consumption in the cylinder.

1, 1X Exhaust gas purification system 11 of internal combustion engine 11 Exhaust passage 12 Oxidation catalyst device (DOC)
13 Fine Particle Collection Device 14 Selective Reduction Catalyst Device (SCR)
15 Ammonia slip catalyst device (ASC)
20 Urea water supply device 21 Urea water supply pump 22 Urea water tank 23 Temperature sensor (temperature detection device)
24 NOx concentration sensor 25 Ammonia concentration sensor 30 Heat exchange device 31 Bypass passage 32 Three-way valve (flow rate adjusting mechanism)
40 Urea water supply control device (control device)
41 Engine control device T Temperature sensor detection value T1 Set value G Generated exhaust gas G1 Exhaust gas G2 not passing through the bypass passage Exhaust gas Gc passing through the bypass passage Purified exhaust gas

Claims (5)

In an exhaust gas purification system of an internal combustion engine configured to include a selective reduction catalyst device in an exhaust passage of the internal combustion engine,
Provided on the inlet side of the selective catalytic reduction device is a temperature detection device for detecting the temperature of the exhaust gas flowing into the selective catalytic reduction device,
In the exhaust passage upstream of the selective catalytic reduction device, a bypass passage provided with a heat exchange device for cooling exhaust gas is provided in parallel with the exhaust passage,
Furthermore, while providing a flow rate adjusting mechanism for adjusting the flow rate of the exhaust gas passing through the bypass passage,
A urea water supply device is provided in the exhaust passage between the branch point from the exhaust passage to the bypass passage and the selective catalytic reduction device,
A control device for controlling the exhaust gas purification system,
An exhaust gas purification system for an internal combustion engine configured to control the flow rate adjustment mechanism based on a detection value of the temperature detection device. The control device is
When the detected value of the temperature detection device is less than a preset value, the flow rate adjusting mechanism is controlled so that the flow rate of the exhaust gas passing through the bypass passage becomes zero,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the flow rate adjustment mechanism is controlled so that the detected value is less than the set value when the set value is equal to or greater than the set value.   An internal combustion engine comprising the exhaust gas purification system for an internal combustion engine according to claim 1 or 2. The exhaust passage of the internal combustion engine is provided with a selective reduction catalyst device, and a bypass passage provided with a heat exchange device for cooling the exhaust gas in the exhaust passage upstream of the selective reduction catalyst device is provided in parallel with the exhaust passage. And a flow rate adjusting mechanism for adjusting the flow rate of the exhaust gas passing through the bypass passage, and the exhaust passage between the branch point from the exhaust passage to the bypass passage and the selective catalytic reduction device. In the exhaust gas purification method for an internal combustion engine configured by providing a urea water supply device,
A temperature detection device is provided on the inlet side of the selective reduction catalyst device, the temperature detection device detects the temperature of the exhaust gas flowing into the selective reduction catalyst device, and
An exhaust gas purification method for an internal combustion engine, wherein the flow rate adjusting mechanism is controlled based on a detection value of the temperature detection device. When the detected value of the temperature detection device is less than a preset value, the flow rate adjusting mechanism is controlled so that the flow rate of the exhaust gas passing through the bypass passage becomes zero,
5. The exhaust gas purification method for an internal combustion engine according to claim 4, wherein the flow rate adjusting mechanism is controlled so that the detected value is less than the set value when the set value is exceeded.

Images