Exhaust purification system for internal combustion engine

Abstract

An exhaust purification system includes a turbine (6T) provided in an exhaust passage (4) of an internal combustion engine (1), a bypass passage (12) that bypasses the turbine, a catalyst (15) provided in the bypass passage, a regulating valve (17) for regulating exhaust flow rate of the turbine and the catalyst, and a control unit (100) configured to control the regulating valve. The control unit controls the regulating valve so that the exhaust flow rate of the catalyst is greater in a case where the load of the internal combustion engine is low than in a case where the load is high.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an exhaust purification system of an internal combustion engine. BACKGROUND

[0002] On an exhaust passage of a turbocharged internal combustion engine, a turbine of a turbocharger is provided. Further, in the exhaust passage, on a downstream side of the turbine, a catalyst for purifying harmful components in exhaust gas is provided.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: International Publication No. 2010 / 116541 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] When the turbine and the catalyst are provided in series as such, the heat energy of the exhaust gas is taken away by the turbine, and thus the warming-up of the catalyst is disadvantageous. Further, because the catalyst becomes a resistance to the exhaust gas, the exhaust pressure on the upstream side of the catalyst, i.e., the back pressure, rises, and the efficiency of the internal combustion engine decreases.

[0008] Therefore, the present disclosure is completed in view of the above-described circumstances, and aims to provide an exhaust purification system of an internal combustion engine in which the warming-up of the catalyst and the rise of the back pressure are advantageously suppressed.

[0009] MEANS OF SOLVING THE PROBLEMS

[0010] According to one aspect of the present disclosure, there is provided an exhaust purification system of an internal combustion engine, characterized by comprising:

[0011] a turbine provided on an exhaust passage of the internal combustion engine,

[0012] a bypass passage bypassing the turbine,

[0013] a catalyst provided on the bypass passage,

[0014] an adjustment valve for adjusting the exhaust flow rate of the turbine and the catalyst, and

[0015] a control unit configured to control the adjustment valve;

[0016] The control unit controls the adjustment valve so that the exhaust flow rate of the catalyst is larger in a case where the load of the internal combustion engine is low than in a case where the load is high.

[0017] Preferably, the adjusting valve is formed of a three-way electromagnetic valve provided at the branching point of the bypass passage.

[0018] Preferably, the exhaust purification system further includes a branching passage branching from the exhaust passage at a position on the downstream side of the turbine and on the upstream side of the merging point of the bypass passage, and merging into the bypass passage at a position on the downstream side of the branching point of the bypass passage and on the upstream side of the catalyst;

[0019] The adjusting valve is formed of a three-way electromagnetic valve provided at the branching point of the bypass passage, and a three-way electromagnetic valve provided at the branching point of the branching passage.

[0020] Preferably, the catalyst is a selective reduction type NOx catalyst.

[0021] The exhaust purification system includes a urea water injection valve provided at the bypass passage on the upstream side of the catalyst, and an acquisition unit that acquires the temperature of the catalyst.

[0022] The control unit causes urea water to be injected from the urea water injection valve when the exhaust flow rate of the catalyst is more than a predetermined value, and the temperature of the catalyst acquired by the acquisition unit is a predetermined activity start temperature or more.

[0023] Preferably, the exhaust purification system further includes a downstream side catalyst of the same kind as the catalyst, provided at the exhaust passage at a position on the downstream side of the merging point of the bypass passage.

[0024] Preferably, the catalyst and the downstream side catalyst are selective reduction type NOx catalysts.

[0025] Effects of Invention

[0026] According to the present disclosure, it is possible to provide an exhaust purification system of an internal combustion engine that is advantageous in suppressing the rise of the temperature of a catalyst and the rise of back pressure. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic view showing an exhaust purification system of Embodiment 1.

[0028] Figure 2 shows a map for calculating a valve opening target value.

[0029] Figure 3 is a graph showing the relationship between engine load and valve opening target value.

[0030] Figure 4 is a flowchart of a control routine.

[0031] Figure 5 A diagram showing a first modified example for calculating a target valve opening value.

[0032] Figure 6 A diagram showing a second modified example for calculating a target valve opening value.

[0033] Figure 7 It is a schematic diagram showing an exhaust gas purification system according to a second embodiment. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be noted that the present disclosure is not limited to the following embodiments.

[0035] [First embodiment]

[0036] exist Figure 1 , an exhaust gas purification system according to a first embodiment is shown. The internal combustion engine (engine) 1 to which this system is applied is an inline four-cylinder diesel engine for a vehicle. The vehicle (not shown) is a large vehicle such as a truck. However, the type, form, and application of the internal combustion engine are not limited.

[0037] Engine 1 includes an engine body 2, and an intake duct 3 and an exhaust duct 4 connected to the engine body 2. The engine body 2 includes structural components such as the cylinder head, cylinder block, and crankcase, as well as movable components such as the piston, crankshaft, and valves housed therein. The flow of intake air and exhaust air is represented by blank arrows and black arrows, respectively.

[0038] Each cylinder is provided with an injector (not shown) that directly injects fuel into the cylinder 5. In the intake passage 3, a compressor 6C of a turbocharger 6 is provided.

[0039] The exhaust passage 4 is provided with a turbine 6T of a turbocharger 6 , an oxidation catalyst 7 , a filter 8 , a urea water injection valve 9 , a NOx selective reduction catalyst 10 , and an ammonia oxidation catalyst 11 in this order from the upstream side.

[0040] The oxidation catalyst 7 oxidizes and purifies unburned components (hydrocarbons HC and carbon monoxide CO) in the exhaust gas. The resulting reaction heat heats the exhaust gas and oxidizes NO in the exhaust gas into NO2. The filter 8 is a so-called continuously regenerating catalyst-carrying particulate filter that captures particulate matter (PM) contained in the exhaust gas and continuously burns and removes the captured PM. The selective NOx reduction catalyst 10 uses ammonia as a reducing agent to reduce NOx in the exhaust gas. This ammonia is derived from urea solution injected from the urea solution injection valve 9. The ammonia oxidation catalyst 11 oxidizes and purifies the excess ammonia emitted from the NOx catalyst 10.

[0041] In the engine 1, a bypass passage 12 that bypasses the turbine 6T is provided. The bypass passage 12 branches from the exhaust passage 4 at a branch point 13 located on the upstream side than the turbine 6T, and merges into the exhaust passage 4 at a merging point 14 located on the downstream side than the turbine 6T and on the upstream side than the oxidation catalyst 7.

[0042] On the bypass passage 12, another catalyst is provided. The other catalyst is specifically a selective reduction type NOx catalyst 15. On the bypass passage 12 at the upstream side than the NOx catalyst 15, another urea water injection valve 16 is provided. Hereinafter, for the sake of distinction, the NOx catalyst 15 and the urea water injection valve 16 provided on the bypass passage 12 are referred to as a front stage catalyst 15 and a front stage injection valve 16, and the NOx catalyst 10 and the urea water injection valve 9 provided on the exhaust passage 4 are referred to as a rear stage catalyst 10 and a rear stage injection valve 9.

[0043] Thus, on the exhaust passage 4 at the downstream side than the merging point 14 of the bypass passage 12, a downstream side catalyst, i.e., the rear stage catalyst 10, of the same kind as the front stage catalyst 15 is provided.

[0044] Further, with respect to the relationship between the front stage catalyst 15 and the rear stage catalyst 10 in the present embodiment, it is exemplarily described that the rear stage catalyst 10 is a main catalyst, and the front stage catalyst 15 is an auxiliary catalyst. Therefore, the capacity of the rear stage catalyst 10 is larger than that of the front stage catalyst 15. The exhaust gas always flows through the rear stage catalyst 10. The front stage catalyst 15 is used as an auxiliary mainly in a situation where the NOx cannot be sufficiently removed by only the rear stage catalyst 10. By adding the front stage catalyst 15 like this, the amount of NOx that can be reduced is increased, and the tightening of the exhaust gas regulations can be coped with.

[0045] In the engine 1, a regulating valve for regulating the exhaust gas flow rate of the turbine 6T and the front stage catalyst 15 is provided. The regulating valve of the present embodiment is formed by an electromagnetic valve 17 provided at the branch point 13 of the bypass passage 12. The electromagnetic valve 17 is formed by a three-way electromagnetic valve. For the sake of convenience, the electromagnetic valve 17 is referred to as a first electromagnetic valve 17.

[0046] The first electromagnetic valve 17 is capable of switching to a first position A that connects only the upstream side exhaust passage 4 to the bypass passage 12 (the upstream side of the front catalyst 15) and a second position B that connects only the upstream side exhaust passage 4 to the downstream side exhaust passage 4 (the turbine 6T side). Further, the first electromagnetic valve 17 is capable of switching steplessly and continuously between the first position A and the second position B. The opening degree S of the first electromagnetic valve 17 is 100% (fully open) when in the first position A and 0% (fully closed) when in the second position B, and is steplessly and continuously variable from 0% to 100%.

[0047] In the engine 1, an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 that constitutes a control unit, circuitry, or controller is provided. The ECU 100 is configured to control the injector, the post-injection valve 9, the pre-injection valve 16, and the first electromagnetic valve 17.

[0048] To the ECU 100, a rotation speed sensor 40 for detecting the rotation speed (specifically, the rpm) of the engine and a throttle opening degree sensor 41 for detecting the throttle opening degree that is related to or proportional to the amount of operation of the throttle pedal of the driver are electrically connected. Further, to the ECU 100, an exhaust temperature sensor 42 for detecting the exhaust temperature on the inlet side of the post catalyst 10 and an exhaust temperature sensor 43 for detecting the exhaust temperature on the inlet side of the pre catalyst 15 are electrically connected.

[0049] The ECU 100 calculates the target value of the fuel injection amount, that is, the target fuel injection amount Q, of the fuel injected from the injector on the basis of the engine rotation speed Ne and the throttle opening degree Ac detected by the rotation speed sensor 40 and the throttle opening degree sensor 41, respectively, in accordance with a predetermined map (may also be a function. The same applies hereinafter). The target fuel injection amount Q is a parameter that indicates the engine load. Instead of the target fuel injection amount Q, another parameter such as the throttle opening degree Ac or the required torque can also be used.

[0050] Further, the ECU 100 estimates the temperature of the pre catalyst 15 on the basis of the exhaust temperature detected by the exhaust temperature sensor 43. Instead, an exhaust temperature sensor can also be provided on the outlet side of the pre catalyst 15, and the temperature of the pre catalyst 15 can be estimated on the basis of the detection values of the exhaust temperature sensors on the inlet side and the outlet side. As for the estimation method, a publicly known method is included, and any method can be adopted. Instead, the ECU 100 can directly detect the temperature of the pre catalyst 15 by a temperature sensor provided to the pre catalyst 15 itself. These estimation and detection are collectively referred to as acquisition. In the present embodiment, the acquisition unit is constituted by the exhaust temperature sensor 43 and the ECU 100.

[0051] ECU 100 similarly estimates the temperature of post-stage catalyst 10 based on the exhaust temperature detected by exhaust temperature sensor 42. The estimation can also include the detection value of the exhaust temperature sensor at the outlet of post-stage catalyst 10, and the temperature of post-stage catalyst 10 can be directly detected, as described above.

[0052] In the present embodiment, the exhaust temperature sensors 42 and 43 are provided on the downstream side of the subsequent injection valves 9 and 16, respectively, but may be provided on the upstream side.

[0053] Here, as a comparative example different from the present embodiment, an example is assumed in which the bypass passage 12 and the first solenoid valve 17 are omitted, and the urea water injection valve 16, the exhaust temperature sensor 43, and the pre-catalyst 15 are provided in the exhaust passage 4 downstream of the turbine 6T and upstream of the oxidation catalyst 7. In this case, the turbine 6T and the pre-catalyst 15 are provided in series in the exhaust passage 4.

[0054] In this case, the exhaust gas's thermal energy is taken away by the turbine 6T, hindering the temperature rise and activation of the pre-catalyst 15. Furthermore, because the pre-catalyst 15 acts as an exhaust resistance, the exhaust pressure upstream of the pre-catalyst 15, or back pressure, increases, reducing the efficiency of the internal combustion engine. Furthermore, when the exhaust pressure upstream of the pre-catalyst 15 increases, the differential pressure between the inlet and outlet of the turbine 6T decreases, reducing the efficiency of the turbine 6T.

[0055] Therefore, in order to solve this problem, the present embodiment adopts the above configuration and also executes the following control: Briefly, when the engine load is low, the ECU 100 controls the first solenoid valve 17 so that the exhaust flow rate of the front catalyst 15 increases compared to when the engine load is high.

[0056] Specifically, the ECU 100 performs the following Figure 2 The predetermined map (which may also be a function. The same applies below) shown in FIG. 1 is used to calculate the valve opening target value St corresponding to the engine speed Ne and the load L, and the actual opening S (%) of the first solenoid valve 17 is controlled to be equal to the valve opening target value St. The load L is specifically the target fuel injection amount Q. The target fuel injection amount Q increases as the load L increases. In this map, the relationship between the engine load L and the valve opening target value St when the engine speed Ne is a certain fixed speed is shown in FIG. Figure 3 Shown in.

[0057] exist Figure 3In this case, the ordinate is the opening degree S (%) of the first electromagnetic valve 17, 0 (%) is full closing, and 100 (%) is full opening. At full closing, the bypass passage 12 is completely closed, and the exhaust flow rate of the pre-stage catalyst 15 becomes zero. Therefore, as for the exhaust gas supplied from the engine main body 2 to the branch point 13, the entire amount thereof is supplied to the turbine 6T, and the exhaust flow rate of the turbine 6T becomes maximum.

[0058] As the opening degree S increases, the opening amount of the bypass passage 12 and the exhaust flow rate of the pre-stage catalyst 15 increase, and the exhaust flow rate of the turbine 6T decreases. When the opening degree S reaches 100 (%), the opening amount of the bypass passage 12 and the exhaust flow rate of the pre-stage catalyst 15 become maximum, and the exhaust flow rate of the turbine 6T becomes zero.

[0059] The exhaust flow rate to be supplied to the branch point 13 is denoted by F0, the exhaust flow rate of the pre-stage catalyst 15 is denoted by Fl, and the exhaust flow rate of the turbine 6T is denoted by F2. Rl = Fl / F0 is denoted as the distribution ratio of the exhaust flow rate in the pre-stage catalyst 15, that is, the first distribution ratio, and R2 = F2 / F0 is denoted as the distribution ratio of the exhaust flow rate in the turbine 6T, that is, the second distribution ratio. In this case, the more the opening degree S of the first electromagnetic valve 17 increases, the more the first distribution ratio Rl increases, and the more the second distribution ratio R2 decreases.

[0060] The abscissa of the map is the engine load L. Lmin is the minimum load, which corresponds to the engine load when the accelerator pedal is completely returned and the accelerator opening degree Ac is the minimum value, that is, 0 (%). At this time, the target fuel injection amount Q is equal to the fuel injection amount at idling. Lmax is the maximum load, which corresponds to the engine load when the accelerator pedal is maximally depressed and the accelerator opening degree Ac is the maximum value, that is, 100 (%).

[0061] In the intermediate load between the minimum load Lmin and the maximum load Lmax, a threshold value Ls is set in advance. Also, the valve opening target value St indicated by the thick solid line is set to 100 (%) when L ≤ Ls and is set to 0 (%) when L > Ls.

[0062] According to this map, the ECU 100 controls the opening degree S of the first electromagnetic valve 17 to 100 (%) which is equal to the valve opening target value St when the actual engine load L is a low load which is equal to or lower than the threshold value Ls. Also, the ECU 100 controls the opening degree S of the first electromagnetic valve 17 to 0 (%) which is equal to the valve opening target value St when the actual engine load L is a high load which is higher than the threshold value Ls. In addition, the actual engine load L corresponds to the actual target fuel injection amount Q, and the threshold value Ls corresponds to the target fuel injection amount Q which is equal to the threshold value Ls.

[0063] When the opening degree S of the first electromagnetic valve 17 is set to 100 (%) at the time of low load, as described above, the exhaust gas flow rate of the pre-catalyst 15 becomes maximum and the exhaust gas flow rate of the turbine 6T becomes zero. Therefore, the high-temperature exhaust gas supplied from the engine main body 2 can be supplied to the pre-catalyst 15 to the maximum. Further, since the pre-catalyst 15 is arranged in parallel with the turbine 6T in the bypass passage 12, the exhaust gas after the heat energy is taken by the turbine does not need to be supplied to the pre-catalyst 15. Thus, it is very advantageous for the pre-catalyst 15 to be warmed up and activated. In particular, during the idling warm-up after the cold start, the exhaust gas from the engine main body 2 can be directly supplied to the pre-catalyst 15 without passing through the turbine 6T, so the pre-catalyst 15 can be activated early. At the time of low load, the necessity of supercharging by the turbocharger 6 is small, so even if the exhaust gas flow rate of the turbine 6T becomes zero, there is no particular problem.

[0064] On the other hand, when the opening degree S of the first electromagnetic valve 17 is set to 0 (%) at the time of high load, as described above, the exhaust gas flow rate of the turbine 6T becomes maximum and the exhaust gas flow rate of the pre-catalyst 15 becomes zero. Therefore, the entire amount of the exhaust gas can be supplied to the turbine 6T, so necessary and sufficient supercharging by the turbocharger 6 can be performed. Further, at this time, the exhaust gas does not need to flow through the pre-catalyst 15, so the increase in back pressure due to the presence of the pre-catalyst 15, or even the decrease in engine efficiency, can be suppressed. The decrease in turbine efficiency due to the increase in back pressure can also be suppressed. Since the exhaust gas after the turbine passes through the post-catalyst 10, even if it bypasses the pre-catalyst 15, the NOx in the exhaust gas can be purified without any problem by the post-catalyst 10.

[0065] Thus, according to the present embodiment, at the time of low engine load (L≤Ls), the first electromagnetic valve 17 is controlled so that the exhaust gas flow rate of the pre-catalyst 15 becomes larger than at the time of high engine load (L>Ls), so an exhaust gas purification system that is advantageous for the pre-catalyst 15 to be warmed up and the increase in back pressure to be suppressed can be provided.

[0066] In view of the above points, the threshold value Ls of the engine load is preferably set to a value at which the emission requirement for the activity of the pre-catalyst 15 to be increased and the engine output requirement based on supercharging are optimally balanced. Further, the threshold value Ls can be changed in accordance with the engine speed Ne.

[0067] Furthermore, the rear-stage catalyst 10 cannot substantially remove NOx unless its temperature Tc2 is at least the predetermined activation start temperature Tc2s. Therefore, the ECU 100 activates the rear-stage injection valve 9 only when the estimated temperature Tc2 of the rear-stage catalyst 10 is at least the activation start temperature Tc2s. Otherwise, the ECU 100 deactivates the rear-stage injection valve 9. This prevents unnecessary injection of urea solution by the rear-stage injection valve 9. The same applies to the combination of the front-stage catalyst 15 and the front-stage injection valve 16.

[0068] However, even if the temperature Tc1 of the front catalyst 15 is above the predetermined activation start temperature Tc1s, it is unnecessary to inject urea solution through the front injection valve 16 when the exhaust flow rate of the front catalyst 15 is zero. Therefore, in this embodiment, the ECU 100 is configured to activate the front injection valve 16 when the exhaust flow rate F1 of the front catalyst 15 is greater than a predetermined value F1s (specifically, zero) and the estimated temperature Tc1 of the front catalyst 15 is above the predetermined activation start temperature Tc1, and to deactivate the front injection valve 16 at other times. This prevents unnecessary injection of urea solution by the front injection valve 16.

[0069] For example, suppose the system changes from a first state in which the engine load L exceeds the threshold value Ls (the exhaust flow rate F1 of the front catalyst 15 is zero) and the temperature Tc1 of the front catalyst 15 is less than the activation start temperature Tc1 to a second state in which the engine load L falls below the threshold value Ls (the exhaust flow rate F1 of the front catalyst 15 is greater than zero). In this case, immediately after the change, the temperature Tc1 of the front catalyst 15 is still less than the activation start temperature Tc1, so urea-water injection by the front injection valve 16 is not performed. However, after a certain period of time has passed since the change, the temperature Tc1 of the front catalyst 15 rises above the activation start temperature Tc1, and urea-water injection by the front injection valve 16 is performed. This effectively suppresses urea-water injection before the temperature reaches or exceeds the activation start temperature Tc1.

[0070] The predetermined exhaust flow rate F1s is not limited to zero, but may be slightly larger than zero. This is because when the exhaust flow rate is slightly larger than zero, the amount of NOx contained in the exhaust gas is small, so stopping the urea water injection does not substantially cause any problem.

[0071] Next, refer to Figure 4 The control routine of this embodiment will be described. The illustrated routine is repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (eg, 10 ms).

[0072] First, in step S101 , the ECU 100 obtains the actual values ​​of the engine speed Ne and the engine load L.

[0073] Next, in step S102, the ECU 100 calculates the engine speed Ne and the engine load L based on the obtained engine speed Ne and the engine load L. Figure 2 The valve opening target value St is calculated using the map shown in FIG.

[0074] Next, in step S103 , the ECU 100 controls the actual opening degree S of the first solenoid valve 17 to an opening degree equal to the valve opening degree target value St.

[0075] Then, in step S104 , the ECU 100 determines whether the valve opening target value St is greater than 0 (%), that is, whether the exhaust flow rate F1 of the front catalyst 15 is greater than a predetermined value F1s, that is, zero.

[0076] When the valve opening target value St is greater than 0 (%), that is, when the exhaust flow rate F1 of the front catalyst 15 is greater than zero, the ECU 100 proceeds to step S105 to determine whether the temperature Tc1 of the front catalyst 15 is greater than the activation start temperature Tc1s.

[0077] If the temperature is equal to or higher than the activation start temperature Tc1s, the ECU 100 proceeds to step S106, activates (turns on) the front injection valve 16, and ends the routine.

[0078] On the other hand, when the valve opening target value St is equal to 0(%) in step S104, that is, when the exhaust flow rate F1 of the front-stage catalyst 15 is zero, and when the temperature Tc1 of the front-stage catalyst 15 is less than the activation start temperature Tc1s in step S105, the ECU 100 proceeds to step S107, stops (OFF) the front-stage injection valve 16, and ends the routine.

[0079] In addition, in the basic control example described here, Figure 3 As shown, the valve opening target value St is switched between two levels: 100% and 0%, with the engine load threshold value Ls as the boundary. However, it is not necessary to switch between 100% and 0%. Instead of 100%, a value less than 100% (e.g., 80%) can be used, and instead of 0%, a value greater than 0% (e.g., 20%) can be used. However, the former must be greater than the latter.

[0080] Next, a modified example of the control will be described.

[0081] (First Modification)

[0082] In the above basic control example, Figure 3 As shown, the valve opening target value St is simply switched to two levels.

[0083] On the other hand, in the first modification described here,Figure 5 As shown in the map illustrated in FIG. 6, the valve opening target value St is set to a fixed 0 (%) when the engine load L is greater than the threshold value Ls, but is increased stepwise from 0 (%) to 100 (%) as the engine load L decreases when the engine load L is the threshold value Ls or less. By doing so, the exhaust gas flow rate of the pre-stage catalyst 15 can be made to be greater than that when the engine load L is greater than the threshold value Ls, and thus the same effect as the basic control example can be exerted. Figure 5

[0084] According to this map, the exhaust gas flow rate of the pre-stage catalyst 15 can also be made to be greater than that when the engine load L is greater than the threshold value Ls when the engine load L is the threshold value Ls or less, and thus the same effect as the basic control example can be exerted. Further, the exhaust gas flow rate of the pre-stage catalyst 15 can be made to be less as the engine load L becomes higher when the engine load L is the threshold value Ls or less, and thus the rise in back pressure can be suppressed more than in the basic control example.

[0085] The control routine in this first modification example is the same as that illustrated in FIG. 5. However, in the first modification example, the exhaust gas flow rate of the pre-stage catalyst 15 becomes less as the engine load L becomes higher when the engine load L is the threshold value Ls or less, and thus it is preferable that, in coordination therewith, the amount of urea water to be made to be less as the pre-stage injection valve 16 is made to operate (ON) (step S106) as the engine load L becomes higher. Figure 4 (Second Modification Example)

[0086] In the second modification example, as shown in the map illustrated in FIG. 7, the method of changing the valve opening target value St when the engine load L is the threshold value Ls or less is different from that in the first modification example. That is, in the map illustrated in FIG. 7, the valve opening target value St is set to a fixed 0 (%) when the engine load L is greater than the threshold value Ls, but is increased stepwise from 0 (%) to 100 (%) as the engine load L decreases when the engine load L is the threshold value Ls or less. By doing so, the same effect as the first modification example can be exerted. Further, the number of steps is arbitrary, and is set to five in this embodiment. The control routine is the same as in the first modification example.

[0087] Figure 6 Figure 6 According to this map, the exhaust gas flow rate of the pre-stage catalyst 15 can also be made to be greater than that when the engine load L is greater than the threshold value Ls when the engine load L is the threshold value Ls or less, and thus the same effect as the basic control example can be exerted. Further, the exhaust gas flow rate of the pre-stage catalyst 15 can be made to be less as the engine load L becomes higher when the engine load L is the threshold value Ls or less, and thus the rise in back pressure can be suppressed more than in the basic control example.

[0088] [Second Embodiment]

[0089] Next, a second embodiment of the present disclosure will be described. In addition, the same parts as those of the first embodiment will be omitted from the description, and the following description will mainly focus on the differences from the first embodiment.

[0090] In the first embodiment, the method of changing the valve opening target value St when the engine load L is the threshold value Ls or less is different from that in the basic control example. That is, in the map illustrated in FIG. 6, the valve opening target value St is set to a fixed 0 (%) when the engine load L is greater than the threshold value Ls, but is increased stepwise from 0 (%) to 100 (%) as the engine load L decreases when the engine load L is the threshold value Ls or less. By doing so, the exhaust gas flow rate of the pre-stage catalyst 15 can be made to be greater than that when the engine load L is greater than the threshold value Ls, and thus the same effect as the basic control example can be exerted. Figure 7 ​​​In the second embodiment, an exhaust purification system is shown. The exhaust purification system further includes a branch passage 20 that branches from the exhaust passage 4 and merges into the bypass passage 12.

[0091] The branch passage 20 branches from the exhaust passage 4 at a branch position 21 that is located at a downstream side than the turbine 6T and at an upstream side than the merging point 14 of the bypass passage 12. Further, the branch passage 20 merges into the bypass passage 12 at a merging position 22 that is located at a downstream side than the branch point 13 of the bypass passage 12 and at an upstream side than the upstream catalyst 15.

[0092] The regulating valve of the present embodiment is formed of the aforementioned first electromagnetic valve 17 and a second electromagnetic valve 18 as another electromagnetic valve. The second electromagnetic valve 18 is formed of a three-way electromagnetic valve and is provided at the branch point 21 of the branch passage 20.

[0093] The second electromagnetic valve 18 is switchable to a first position A that connects the exhaust passage 4 at its upstream side to only the branch passage 20 (upstream catalyst 15 side) and a second position B that connects the exhaust passage 4 at its upstream side to only the downstream exhaust passage 4 (downstream catalyst 10 side). Further, the second electromagnetic valve 18 is steplessly and continuously switchable between the first position A and the second position B. The opening degree S of the second electromagnetic valve 18 is 100% (fully open) when in the first position A and 0% (fully closed) when in the second position B, and is steplessly and continuously variable from 0% to 100%.

[0094] The control of the present embodiment is roughly divided into control when the load L of the engine is a low load (below a threshold value Ls) and control when the load L is a high load (greater than the threshold value Ls). Further, each control is changed according to the estimated temperature T of the downstream catalyst 10.

[0095] First, the control when the load L of the engine is a low load (below the threshold value Ls) is described. When the temperature Tc2 of the downstream catalyst 10 is a low temperature, i.e., less than the activity start temperature Tc2s, the opening degree S of the first electromagnetic valve 17 is controlled to 100% and the opening degree S of the second electromagnetic valve 18 is controlled to 0%. As such, when the downstream catalyst 10 is inactive, the exhaust flow rate of the upstream catalyst 15 is set to the maximum and the exhaust flow rate of the turbine 6T is set to zero, so the upstream catalyst 15 can be used to the maximum to purify NOx.

[0096] On the other hand, when the temperature Tc2 of the rear catalyst 10 is high, i.e., above the activity start temperature Tc2s, the opening degree S of the first electromagnetic valve 17 and the second electromagnetic valve 18 is controlled so that the exhaust gas flow rates of the front catalyst 15 and the turbine 6T become equal (each 50% of the total). For example, the opening degree S of the first electromagnetic valve 17 is controlled to 50%, and the opening degree S of the second electromagnetic valve 18 is controlled to 0%. When the rear catalyst 10 is activated like this, the NOx can be purified by the rear catalyst 10, so the exhaust gas flow rate of the front catalyst 15 decreases, and the exhaust gas flow rate of the turbine 6T increases accordingly. Thus, the rise in the back pressure can be suppressed, and the combustion efficiency can be improved by using the turbocharger 6.

[0097] Next, the control when the load L of the engine is high (greater than the threshold value Ls) will be described. When the temperature Tc2 of the rear catalyst 10 is less than the activity start temperature Tc2s, the opening degree S of the first electromagnetic valve 17 is controlled to 0%, and the opening degree S of the second electromagnetic valve 18 is variably controlled, for example, in the range of 0 to 50%.

[0098] Thus, the exhaust gas supplied from the engine main body 2 does not branch to the bypass passage 12, but is supplied in the total amount to the turbine 6T. Also, of the exhaust gas after passing through the turbine 6T, a part is supplied to the front catalyst 15 through the branch passage 20, and the remaining part is supplied to the rear catalyst 10.

[0099] In this case, the engine load L is high, and a high output torque is required, so the exhaust gas is supplied in the total amount to the turbine 6T, and the supercharging based on the turbocharger 6 is performed to the maximum. Then, a part of the exhaust gas is supplied to the front catalyst 15, and the NOx is purified by the front catalyst 15. At this time, when a large amount of exhaust gas is supplied to the front catalyst 15, the back pressure rises, so the opening degree of the second electromagnetic valve 18 is limited to a value less than 100%, for example, in the range of 0 to 50%. By doing so, the rise in the back pressure can be suppressed, and the engine efficiency can be improved to the maximum.

[0100] The higher the engine load L becomes, the more the opening degree S of the second electromagnetic valve 18 decreases. Thus, the higher the engine load L becomes, the more the exhaust gas flow rate of the front catalyst 15 can be decreased, and the rise in the back pressure can be suppressed.

[0101] On the other hand, when the temperature Tc2 of the rear catalyst 10 is above the activity start temperature Tc2s, the opening degree S of the first electromagnetic valve 17 is controlled to 0%, and the opening degree S of the second electromagnetic valve 18 is also controlled to 0%.

[0102] Thus, the exhaust gas supplied from the engine main body 2 is supplied to the rear catalyst 10 after being supplied in full to the turbine 6T. Since the exhaust gas flow rate of the front catalyst 15 becomes zero, the back pressure rise can be suppressed to the maximum, and the engine efficiency can be maximized.

[0103] Further, with respect to the control routine, the opening degree S of the first electromagnetic valve 17 and the second electromagnetic valve 18 is controlled as in the first embodiment in the above-described step S103.

[0104] The above-described embodiments of the present disclosure have been described in detail, but there are various other considerations for the embodiments of the present disclosure and modified examples.

[0105] (1) For example, the front catalyst 15 and the rear catalyst 10 can not be selective reduction type NOx catalysts. For example, they can be absorption reduction type NOx catalysts, or catalysts other than NOx catalysts, such as oxidation catalysts or three-way catalysts. Further, among the catalysts, there are particulate filters that carry a catalyst like the filter 8. The types of catalysts can be different between the front catalyst 15 and the rear catalyst 10.

[0106] (2) It can be that the rear catalyst 10 is omitted as needed.

[0107] (3) The constitution of the regulating valve can be variously changed. For example, instead of one three-way electromagnetic valve, two two-way electromagnetic valves can be provided to achieve the same function.

[0108] The embodiments of the present disclosure are not limited to the foregoing embodiments, and all modified examples or application examples, equivalents, included in the idea of the present disclosure defined by the scope of the claims are included in the present disclosure. Therefore, the present disclosure should not be interpreted limitatively, and can be applied to other arbitrary technologies within the scope of the idea of the present disclosure.

[0109] This application is based on Japanese Patent Application (JP-A) No. 2020-146010 filed on August 31, 2020, and the content thereof is incorporated herein by reference.

[0110] Industrial applicability

[0111] With the present disclosure, an exhaust gas purification system for an internal combustion engine that is advantageous in suppressing the rise in back pressure and the temperature rise of a catalyst is provided.

[0112] Explanation of reference signs

[0113] 4 exhaust passage

[0114] 6T turbine

[0115] 10 NOx catalyst (rear catalyst)

[0116] 12 bypass passage

[0117] 13 branch point

[0118] 14 junction point

[0119] 15 NOx catalyst (pre-catalyst)

[0120] 16 urea water injection valve (pre-injection valve)

[0121] 17 first electromagnetic valve

[0122] 18 second electromagnetic valve

[0123] 20 branch passage

[0124] 21 branch point

[0125] 43 exhaust gas temperature sensor

[0126] 100 electronic control unit (ECU)

Claims

1. An exhaust purification system of an internal combustion engine characterized by comprising: comprising: a turbine provided in an exhaust passage of an internal combustion engine, a bypass passage bypassing the turbine, a catalyst provided in the bypass passage, a regulating valve for regulating exhaust gas flow to the turbine and the catalyst, and a control unit configured to control the regulating valve; the control unit controls the regulating valve so that exhaust gas flow to the catalyst is more than in a case where the load of the internal combustion engine is high, in a case where the load of the internal combustion engine is low, further comprising a branched passage branched from the exhaust passage at a position on a downstream side of the turbine and on an upstream side of a merging point of the bypass passage, and merging into the bypass passage at a position on a downstream side of the merging point of the bypass passage and on an upstream side of the catalyst; the regulating valve is formed of a first three-way solenoid valve provided at the merging point of the bypass passage, and a second three-way solenoid valve provided at the merging point of the branched passage, in a case where the load of the internal combustion engine is high, the opening degree of the first three-way solenoid valve is controlled to 0%, exhaust gas supplied from an engine main body is not branched to the bypass passage but is supplied in full amount to the turbine, the higher the load of the internal combustion engine, the smaller the opening degree of the second three-way solenoid valve is made, the exhaust gas flow supplied to the catalyst via the branched passage is reduced, and the exhaust gas flow supplied from the second three-way solenoid valve to the merging point without passing through the branched passage is increased.

2. The exhaust purification system of an internal combustion engine according to claim 1, wherein the catalyst is a selective reduction type NOx catalyst; the exhaust purification system includes a urea water injection valve provided in the bypass passage on an upstream side of the catalyst, and an acquisition unit that acquires the temperature of the catalyst; the control unit causes urea water to be injected from the urea water injection valve when the exhaust gas flow to the catalyst is more than a predetermined value, and the temperature of the catalyst acquired by the acquisition unit is a predetermined active start temperature or more.

3. The exhaust purification system of an internal combustion engine according to claim 1 or 2, wherein further comprising a downstream side catalyst of the same kind as the catalyst provided in the exhaust passage at a position on a downstream side of the merging point of the bypass passage.

4. The exhaust purification system of an internal combustion engine according to claim 3, wherein the catalyst and the downstream side catalyst are selective reduction type NOx catalysts.

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