CN116057259A - Exhaust purification system for internal combustion engines - Google Patents

Abstract

The exhaust purification system includes: a turbine (6T), which is arranged in the exhaust passage (4) of the internal combustion engine (1); a bypass passage (12), which bypasses the turbine; a catalyst (15), which is arranged in the bypass a channel; a regulating valve (17) for regulating the exhaust flow of the turbine and the catalyst; and a control unit (100) configured to control the regulating valve. When the load of the internal combustion engine is low, the control unit controls the regulator valve so that the exhaust gas flow rate of the catalyst increases compared with the case of high load.

Description

Exhaust purification system for internal combustion engines

technical field

The present disclosure relates to an exhaust purification system of an internal combustion engine.

Background technique

On the exhaust passage of the turbocharged internal combustion engine, the turbine of the turbocharger is arranged. In addition, in the exhaust passage, on the downstream side of the turbine, a catalyst for purifying harmful components in the exhaust gas is provided.

Prior art literature

patent documents

Patent Document 1: International Publication No. 2010/116541

Contents of the invention

The technical problem to be solved by the invention

When the turbine and the catalyst are arranged in series in this way, the heat energy of the exhaust gas is taken away by the turbine, which is disadvantageous for the temperature rise of the catalyst. In addition, since the catalyst acts as an exhaust resistance, the exhaust pressure on the upstream side of the catalyst, that is, the back pressure increases, and the efficiency of the internal combustion engine decreases.

Therefore, the present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an exhaust gas purification system for an internal combustion engine that is advantageous in suppressing the temperature rise of the catalyst and the increase in back pressure.

Technical means used to solve technical problems

According to one aspect of the present disclosure, there is provided an exhaust gas purification system for an internal combustion engine, which is characterized by comprising:

turbine, which is arranged in the exhaust passage of the internal combustion engine,

bypass passage, which bypasses the turbine,

a catalyst, which is disposed in the bypass channel,

a regulating valve for regulating the exhaust flow of the turbine and the catalyst, and

a control unit configured to control the regulating valve;

The control unit controls the regulator valve so that the flow rate of the exhaust gas of the catalyst increases when the load of the internal combustion engine is low, compared to when the load is high.

Preferably, the regulating valve is formed by a three-way solenoid valve, and the three-way solenoid valve is provided at a branch point of the bypass passage.

Preferably, the exhaust purification system further includes a branch passage that branches off from the exhaust passage that is located on the downstream side of the turbine and on the upstream side of a confluence point of the bypass passage. branch, and merge into the bypass channel located on the downstream side of the branch point of the bypass channel and on the upstream side of the catalyst;

The regulator valve is formed of a three-way solenoid valve provided at a branch point of the bypass passage, and a three-way solenoid valve provided at a branch point of the branch passage.

Preferably, the catalyst is a selective reduction NOx catalyst;

The exhaust gas purification system includes: a urea water injection valve provided in the bypass channel on the upstream side of the catalyst; and an acquisition unit that acquires the temperature of the catalyst;

The control unit makes urea water flow from the urea water injection valve when the exhaust gas flow rate of the catalyst is greater than a predetermined value and the temperature of the catalyst obtained by the obtaining unit is equal to or higher than a predetermined activation start temperature. injection.

Preferably, the exhaust purification system further includes a downstream side catalyst of the same type as the catalyst, and the downstream side catalyst is provided in the exhaust passage on the downstream side of a confluence point of the bypass passage. .

Preferably, the catalyst and the downstream side catalyst are selective reduction NOx catalysts.

Invention effect

According to the present disclosure, it is possible to provide an exhaust gas purification system of an internal combustion engine that is advantageous in suppressing the temperature rise of the catalyst and the increase in back pressure.

Description of drawings

FIG. 1 is a schematic diagram showing an exhaust purification system according to a first embodiment.

FIG. 2 shows a map for calculating a valve opening target value.

Fig. 3 is a graph showing the relationship between engine load and valve opening target value.

Fig. 4 is a flowchart of a control routine.

FIG. 5 is a diagram showing a first modified example for calculating a valve opening target value.

FIG. 6 is a diagram showing a second modified example for calculating a valve opening target value.

Fig. 7 is a schematic diagram showing an exhaust purification system according to a second embodiment.

Detailed ways

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In addition, it should be noted that the present disclosure is not limited to the following embodiments.

[the first embodiment]

FIG. 1 shows an exhaust purification system according to a first embodiment. An internal combustion engine (engine) 1 to which this system is applied is an inline 4-cylinder vehicle diesel engine. The vehicle (not shown) is a large vehicle such as a truck. However, the type, form, application, etc. of the internal combustion engine are not limited.

The engine 1 includes an engine body 2 , and an intake passage 3 and an exhaust passage 4 connected to the engine body 2 . The engine main body 2 includes structural components such as a cylinder head, a cylinder block, and a crankcase, and movable components such as pistons, crankshafts, and valves housed therein. The flow of intake and exhaust is indicated by blank and black arrows, respectively.

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

In exhaust passage 4 , turbine 6T of turbocharger 6 , oxidation catalyst 7 , filter 8 , urea water injection valve 9 , selective reduction NOx catalyst 10 , and ammonia oxidation catalyst 11 are arranged in this order from the upstream side.

The oxidation catalyst 7 oxidizes and purifies unburned components (hydrocarbons HC and carbon monoxide CO) in the exhaust gas, heats the exhaust gas with the heat of reaction at this time, and oxidizes NO in the exhaust gas to NO ₂ . The filter 8 is formed of a so-called continuously regenerative particulate filter with a catalyst, traps particulate matter (PM (Particulate Matter)) contained in the exhaust gas, and continuously burns and removes the trapped PM. The selective reduction NOx catalyst 10 uses ammonia as a reducing agent to reduce NOx in the exhaust gas, and the ammonia comes from urea water injected from the urea water injection valve 9 . The ammonia oxidation catalyst 11 oxidizes excess ammonia discharged from the NOx catalyst 10 to purify it.

In the engine 1, a bypass passage 12 bypassing the turbine 6T is provided. The bypass passage 12 branches off from the exhaust passage 4 at a branch point 13 located upstream of the turbine 6T, and merges at a confluence point 14 located downstream of the turbine 6T and upstream of the oxidation catalyst 7 in the exhaust channel 4.

On the bypass channel 12 a further catalyst is arranged. Specifically, this other catalyst is the selective reduction NOx catalyst 15 . Another urea water injection valve 16 is provided in the bypass passage 12 located upstream of the NOx catalyst 15 . Hereinafter, for the sake of distinction, the NOx catalyst 15 and the urea water injection valve 16 arranged on the bypass passage 12 are referred to as the front-stage catalyst 15 and the front-stage injection valve 16, and the NOx catalyst 10 arranged on the exhaust passage 4 and the urea water injection valve 9 are referred to as the post-stage catalyst 10 and the post-stage injection valve 9 .

In this manner, the rear catalyst 10 , which is the same type of downstream catalyst as the front catalyst 15 , is provided in the exhaust passage 4 downstream of the junction 14 of the bypass passage 12 .

In addition, with regard to the relationship between the front-stage catalyst 15 and the rear-stage catalyst 10 in this 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 rear catalyst 10 has a larger capacity than the front catalyst 15 . The exhaust gas always flows through the rear catalyst 10 . The front-stage catalyst 15 is used as an auxiliary mainly in a situation where NOx cannot be sufficiently removed only by the rear-stage catalyst 10 . By adding the pre-catalyst 15 in this way, the amount of NOx that can be reduced is increased, and it is possible to cope with strengthening of exhaust gas restriction.

The engine 1 is provided with a regulating valve for regulating the exhaust gas flow rate of the turbine 6T and the pre-catalyst 15 . The regulating valve in this embodiment is formed of a solenoid valve 17 provided at a branch point 13 of the bypass passage 12 . The solenoid valve 17 is formed of a three-way solenoid valve. For convenience, this solenoid valve 17 is referred to as a first solenoid valve 17 .

The first solenoid valve 17 can be switched between a first position A and a second position B, the first position A connects only the exhaust passage 4 on the upstream side to the bypass passage 12 (on the front catalyst 15 side), and the second position A Position B connects only the exhaust passage 4 on the upstream side to the exhaust passage 4 on the downstream side (turbine 6T side). In addition, the first solenoid valve 17 can be continuously and steplessly switched between the first position A and the second position. The opening S of the first electromagnetic valve 17 is 100% (fully open) when it is in the first position A, and 0% (fully closed) when it is in the second position B, and it is stepless from 0% to 100%. continuously variable.

The engine 1 is additionally provided with an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 constituting a control unit, a circuit or a controller. The ECU 100 is configured to control the injectors, the post-stage injection valve 9 , the front-stage injection valve 16 , and the first solenoid valve 17 .

Electrically connected to the ECU100 are: a rotational speed sensor 40, which is used to detect the rotational speed of the engine (specifically, the rotational speed per minute (rpm)); The amount of pedal operation related or proportional to the accelerator opening is detected. In addition, the ECU 100 is electrically connected to: an exhaust gas temperature sensor 42 for detecting the exhaust gas temperature on the inlet side of the rear catalyst 10 ; Exhaust temperature is checked.

The ECU 100 calculates the amount of fuel injected from the injector based on the engine speed Ne and the accelerator opening Ac detected by the rotational speed sensor 40 and the accelerator opening degree sensor 41 according to a predetermined map (may also be a function; the same applies hereinafter). The target value is the target fuel injection quantity Q. The target fuel injection amount Q is a parameter representing the engine load. For this parameter, instead of the target fuel injection amount Q, other parameters such as the accelerator opening Ac and the required torque can be used.

Also, the ECU 100 estimates the temperature of the pre-catalyst 15 based on the exhaust gas temperature detected by the exhaust gas temperature sensor 43 . Alternatively, an exhaust gas temperature sensor may also be provided on the outlet side of the pre-catalyst 15, and the temperature of the pre-catalyst 15 may be estimated based on detection values of the exhaust gas temperature sensors on the inlet side and the outlet side. As the estimation method, any method including known methods can be adopted. Alternatively, the ECU 100 may directly detect the temperature of the pre-catalyst 15 through a temperature sensor provided on the pre-catalyst 15 itself. These presumptions and detections are collectively referred to as acquisitions. In the present embodiment, acquisition means is constituted by the exhaust gas temperature sensor 43 and the ECU 100 .

ECU 100 also estimates the temperature of rear catalyst 10 based on the exhaust gas temperature detected by exhaust gas temperature sensor 42 . The points that can also be estimated including the detection value of the exhaust gas temperature sensor on the outlet side of the rear-stage catalyst 10 and the point that the temperature of the rear-stage catalyst 10 can be directly detected are the same as described above.

In addition, in the present embodiment, the exhaust gas temperature sensors 42, 43 are respectively provided on the downstream side of the post-stage injection valves 9, 16, but may be provided on the upstream side.

Here, as a comparative example different from the present embodiment, consider an example in which the bypass passage 12 and the first solenoid valve 17 are omitted, and the urea water injection valve 16, the exhaust gas temperature sensor 43, and the pre-catalyst 15 are provided at relatively low positions. The exhaust passage 4 on the downstream side of the turbine 6T and on the upstream side of the oxidation catalyst 7 . In this case, the turbine 6T and the pre-catalyst 15 are provided in the exhaust passage 4 in series.

In this case, the heat energy of the exhaust gas is taken away by the turbine 6T, which is disadvantageous for the temperature rise and activation of the pre-catalyst 15 . In addition, since the pre-catalyst 15 acts as an exhaust resistance, the exhaust pressure on the upstream side of the pre-catalyst 15 , that is, the back pressure increases, and the efficiency of the internal combustion engine decreases. In addition, when the exhaust pressure on the upstream side of the pre-catalyst 15 increases, the differential pressure between the inlet side and the outlet side of the turbine 6T decreases, and thus the efficiency of the turbine 6T decreases.

Therefore, in this embodiment, in order to solve this problem, the above-mentioned configuration is employed, and the following controls are collectively executed. To describe its outline, the ECU 100 controls the first solenoid valve 17 so that the exhaust gas flow rate of the pre-catalyst 15 increases when the load on the engine is low compared to when the load is high.

Specifically, the ECU 100 calculates the valve opening target value St corresponding to the engine speed Ne and the load L according to a predetermined map shown in FIG. The actual opening degree S (%) of 17 is controlled to be equal to the valve opening degree target value St. Specifically, the load L is the target fuel injection amount Q, and the more the load L increases, the more the target fuel injection amount Q increases. In this map, FIG. 3 shows the relationship between the engine load L and the valve opening degree target value St when the engine speed Ne is a certain constant speed.

In FIG. 3 , the vertical axis represents the opening degree S (%) of the first electromagnetic valve 17 , where 0 (%) is fully closed and 100 (%) is fully open. When fully closed, the bypass passage 12 is completely closed, and the exhaust gas flow rate of the pre-catalyst 15 becomes zero. Therefore, the entire amount of the exhaust gas supplied from the engine main body 2 to the branch point 13 is supplied to the turbine 6T, and the exhaust gas flow rate of the turbine 6T becomes the maximum.

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

Let the exhaust gas flow rate supplied to the branch point 13 be F0, the exhaust gas flow rate of the pre-catalyst 15 be F1, the exhaust gas flow rate of the turbine 6T be F2, and R1=F1/F0 be the front stage The first distribution ratio which is the distribution ratio of the exhaust flow in the catalyst 15 is represented by R2 = F2 / F0 as the second distribution ratio which is the distribution ratio of the exhaust flow in the turbine 6T. In this case, as the opening S of the first electromagnetic valve 17 increases, the first distribution ratio R1 increases and the second distribution ratio R2 decreases.

The horizontal axis of the map represents the engine load L. Lmin is the minimum load, which corresponds to the engine load when the accelerator pedal is fully returned and the accelerator opening Ac is 0 (%) which is the minimum value. The target fuel injection amount Q at this time is equal to the fuel injection amount during idling. Lmax is the maximum load, which corresponds to the engine load when the accelerator pedal is depressed most and the accelerator opening Ac is 100 (%) which is the maximum value.

In an intermediate load between these minimum load Lmin and maximum load Lmax, the threshold Ls is set in advance. Furthermore, the valve opening degree target value St indicated by the thick solid line is set to 100(%) when L≦Ls, and is set to 0(%) when L>Ls.

According to this map, the ECU 100 controls the opening S of the first solenoid valve 17 to 100 (%) equal to the valve opening target value St when the actual engine load L is low load below the threshold Ls. Also, when the actual engine load L is a high load greater than the threshold value Ls, the opening S of the first solenoid valve 17 is controlled to be 0 (%) equal to the valve opening target value St. In addition, the actual engine load L corresponds to the actual target fuel injection amount Q, and the threshold Ls corresponds to the target fuel injection amount Q corresponding to the threshold Ls.

When the opening degree S of the first solenoid valve 17 is set to 100(%) at low load, the exhaust flow rate of the pre-catalyst 15 becomes maximum and the exhaust flow rate of the turbine 6T becomes zero as described above. Therefore, the high-temperature exhaust gas supplied from the engine main body 2 can be supplied to the front catalyst 15 to the maximum. In addition, since the pre-catalyst 15 is provided in the bypass passage 12 in parallel with the turbine 6T, it is not necessary to supply the exhaust gas deprived of thermal energy by passing through the turbine to the pre-catalyst 15 . This is very advantageous for raising the temperature and activating the pre-catalyst 15 . In particular, during idling warm-up after a cold start, the exhaust gas from the engine body 2 can be directly supplied to the pre-catalyst 15 without intervening the turbine 6T, so that the pre-catalyst 15 can be activated early. When the load is low, the need for supercharging by the turbocharger 6 is small, so even if the exhaust gas flow rate of the turbocharger 6T becomes zero, there is no particular problem.

On the other hand, when the opening degree S of the first solenoid valve 17 is set to 0 (%) at high load, the exhaust flow rate of the turbine 6T becomes the maximum as described above, and the exhaust flow rate of the pre-catalyst 15 will become zero. Therefore, it is possible to supply the entire amount of exhaust gas to the turbine 6T, thereby performing necessary and sufficient supercharging by the turbocharger 6 . In addition, at this time, it is not necessary to flow the exhaust gas through the pre-catalyst 15 , and therefore it is possible to suppress an increase in back pressure and a decrease in engine efficiency due to the presence of the pre-catalyst 15 . It is also possible to suppress a decrease in turbine efficiency due to an increase in back pressure. Since the exhaust after passing through the turbine passes through the rear catalyst 10 , even if it bypasses the front catalyst 15 , it can pass through the rear catalyst 10 to purify NOx in the exhaust without hindrance.

Thus, according to the present embodiment, when the engine load is low (L≦Ls), the first solenoid valve 17 is controlled so that the precatalyst 15 Since the flow rate of the exhaust gas increases, it is possible to provide an exhaust purification system that is advantageous in suppressing the increase in the temperature rise of the pre-catalyst 15 and the increase in the back pressure.

From the above point of view, the engine load threshold Ls is preferably set to a value that optimally balances the emission requirement to increase the activity of the front catalyst 15 and the engine output requirement due to supercharging. In addition, the threshold Ls can also be changed according to the engine rotation speed Ne.

In addition, as long as the temperature Tc2 of the latter catalyst 10 is not equal to or higher than the predetermined activation start temperature Tc2s, NOx cannot be substantially purified. Therefore, the ECU 100 operates the rear injection valve 9 only when the estimated temperature Tc2 of the rear catalyst 10 is equal to or higher than the activation start temperature Tc2s, and stops the rear injection valve 9 otherwise. Thereby, unnecessary urea water injection by the post-stage injection valve 9 can be suppressed. The same applies to the combination of the front catalyst 15 and the front injection valve 16 .

However, even if the temperature Tc1 of the pre-catalyst 15 is equal to or higher than the predetermined activation start temperature Tc1s, it is not necessary to inject urea water through the pre-injection valve 16 when the exhaust gas flow rate of the pre-catalyst 15 is zero. Therefore, in the present embodiment, the ECU 100 sets the exhaust gas flow rate F1 at the pre-catalyst 15 to be greater than a predetermined value F1s (specifically, zero), and the estimated temperature Tc1 of the pre-catalyst 15 is set to a predetermined value. When the activation start temperature Tc1 of Tc1 is above, the pre-stage injection valve 16 is operated, and when it is otherwise, the pre-stage injection valve 16 is stopped. Thereby, unnecessary injection of urea water by the pre-injection valve 16 can be suppressed.

For example, assuming that the engine load L is higher than the threshold value Ls (the exhaust gas flow rate F1 of the front catalyst 15 is zero), and the temperature Tc1 of the front catalyst 15 is lower than the activation start temperature Tc1, the engine load is changed to The second state in which L is lower than the threshold value Ls (the exhaust gas flow rate F1 of the front catalyst 15 is greater than zero). At this time, at the point of time immediately after the change, the temperature Tc1 of the pre-catalyst 15 is still lower than the activation start temperature Tc1, so the urea water injection by the pre-stage injection valve 16 will not be performed. However, when a certain time elapses after the change, the temperature Tc1 of the pre-catalyst 15 rises above the activation start temperature Tc1, so that the urea water injection by the pre-stage injection valve 16 is executed. In this way, it is possible to effectively suppress the injection of urea water before the activation start temperature Tc1 or higher.

In addition, the predetermined value F1s of the exhaust gas flow rate is not limited to zero, and may be a value slightly larger than zero. The reason for this is that when the flow rate of the exhaust gas is slightly greater than zero, the amount of NOx contained in the exhaust gas is also small, so even if the injection of urea water is stopped, there is substantially no problem.

Next, a control routine in this embodiment will be described with reference to FIG. 4 . The illustrated routine is repeatedly executed by ECU 100 every predetermined calculation cycle τ (for example, 10 ms).

First, in step S101 , the ECU 100 acquires the values of the actual engine speed Ne and the engine load L.

Next, in step S102 , ECU 100 calculates valve opening degree target value St from the map shown in FIG. 2 based on acquired engine speed Ne and engine load L.

Next, in step S103 , the ECU 100 controls the actual opening S of the first electromagnetic valve 17 to an opening equal to the valve opening target value St.

Then, in step S104, the ECU 100 judges whether the valve opening target value St is greater than 0 (%), that is, whether the exhaust gas flow rate F1 of the pre-catalyst 15 is greater than a predetermined value F1s, ie, zero.

When the valve opening target value St is greater than 0 (%), that is, when the exhaust gas flow rate F1 of the pre-catalyst 15 is greater than zero, the ECU 100 proceeds to step S105 to determine whether the temperature Tc1 of the pre-catalyst 15 is the activation start temperature. Tc1s or more to judge.

If it is equal to or higher than the activation start temperature Tc1s, the ECU 100 proceeds to step S106 to operate (ON) the front injection valve 16 and end the routine.

On the other hand, in the case where the valve opening target value St is equal to 0 (%) in step S104, that is, in the case where the exhaust gas flow rate F1 of the pre-catalyst 15 is zero, and the temperature Tc1 of the pre-catalyst 15 is zero in step S105, If it is lower than the activation start temperature Tc1s, the ECU 100 proceeds to step S107 to stop (OFF) the pre-injection valve 16 and end the routine.

In addition, in the basic control example described here, as shown in FIG. 3 , the valve opening target value St is switched to two levels of 100% and 0% with the engine load threshold Ls as the boundary. However, it is not necessary to switch between 100% and 0%. Instead of 100%, values smaller than 100% (eg 80%) can also be used, and instead of 0% values greater than 0% (eg 20%) can also be used. However, it is necessary to make the former greater than the latter.

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

(1st modified example)

In the aforementioned basic control example, as shown in FIG. 3 , the valve opening degree target value St is simply switched to two stages.

On the other hand, in the first modified example described here, as shown in FIG. 5 , the switching method of the valve opening degree target value St is different. That is, in the map shown in FIG. 5, when the engine load L is greater than the threshold value Ls, the valve opening target value St is set to a fixed 0 (%) as in the basic control example, but when the engine load L is the threshold value When Ls is less than or equal to the engine load L, the valve opening target value St is continuously and steplessly increased from 0(%) to 100(%).

According to this map, the exhaust gas flow rate of the precatalyst 15 can be increased when the engine load L is equal to or less than the threshold value Ls than when it is greater than the threshold value Ls, so that the same operation and effect as the basic control example can be exhibited. In addition, when the engine load L is equal to or less than the threshold value Ls, the higher the engine load L is, the more the exhaust gas flow rate of the pre-catalyst 15 can be reduced. is advantageous.

The control routine in this first modification is the same as the control routine shown in FIG. 4 . However, in the first modified example, when the engine load L is equal to or less than the threshold value Ls, the higher the engine load L is, the smaller the exhaust gas flow rate of the pre-catalyst 15 becomes. The higher the load L is, the smaller the urea water injection amount is when the front injection valve 16 is operated (ON) (step S106 ).

(Second modified example)

In the second modification, as shown in FIG. 6 , the method of changing the valve opening target value St when the engine load L is equal to or less than the threshold Ls is different from the first modification. That is, in the map shown in FIG. 6 , when the engine load L is larger than the threshold value Ls, the valve opening degree target value St is set to be fixed at 0 (%) as in the basic control example and the first modified example. When the engine load L is equal to or less than the threshold value Ls, the valve opening target value St is gradually increased from 0 (%) to 100 (%) as the engine load L decreases. By doing so, the same operational effect as that of the first modified example can be exhibited. In addition, the number of stages is arbitrary, and is set to five stages in the present embodiment. The control routine is the same as that of the first modified example.

[the second embodiment]

Next, a second embodiment of the present disclosure will be described. In addition, description of the same parts as those of the first embodiment will be omitted, and differences from the first embodiment will be mainly described below.

In FIG. 7, the exhaust purification system of 2nd Embodiment is shown. The exhaust purification system further includes a branch passage 20 that branches off from the exhaust passage 4 and merges into the bypass passage 12 .

The branch passage 20 branches off from the exhaust passage 4 at a branch position 21 located on the downstream side of the turbine 6T and on the upstream side of the confluence point 14 of the bypass passage 12 . Further, the branch passage 20 merges with the bypass passage 12 at a merging position 22 located on the downstream side from the branch point 13 of the bypass passage 12 and on the upstream side from the front-stage catalyst 15 .

The regulating valve of this embodiment is formed by the above-mentioned first electromagnetic valve 17 and the second electromagnetic valve 18 which is another electromagnetic valve. The second solenoid valve 18 is formed of a three-way solenoid valve, and is provided at a branch point 21 of the branch passage 20 .

The second solenoid valve 18 can be switched between a first position A that connects the exhaust passage 4 on the upstream side only to the branch passage 20 (on the front catalyst 15 side), and a second position B that connects the exhaust passage 4 on the upstream side thereof. In position B, the exhaust passage 4 on the upstream side is connected only to the exhaust passage 4 on the downstream side (on the rear catalyst 10 side). In addition, the second solenoid valve 18 can be continuously and steplessly switched between the first position A and the second position. The opening S of the second solenoid valve 18 is 100% (fully open) when it is in the first position A, and 0% (fully closed) when it is in the second position B, and it is stepless from 0% to 100%. continuously variable.

The control in this embodiment is roughly divided into control when the load L of the engine is low (below the threshold value Ls), and control when the load L of the engine is high (greater than the threshold value Ls). Also, each control is changed according to the estimated temperature T of the rear-stage catalyst 10 .

First, control when the load L of the engine is low (less than or equal to the threshold value Ls) will be described. When the temperature Tc2 of the latter stage catalyst 10 is a low temperature, that is, when it is less than the activation start temperature Tc for 2s, the opening S of the first electromagnetic valve 17 is controlled to be 100%, and the opening S of the second electromagnetic valve 18 is controlled to be 0%. In this way, when the rear catalyst 10 is inactive, the exhaust flow rate of the front catalyst 15 is set to the maximum and the exhaust flow rate of the turbine 6T is set to zero, so that the front catalyst 15 can be utilized to the maximum to purify NOx. .

On the other hand, when the temperature Tc2 of the rear-stage catalyst 10 is a high temperature, that is, when the activation start temperature Tc2s is above, the opening S of the first electromagnetic valve 17 and the second electromagnetic valve 18 is controlled to be: between the front-stage catalyst 15 and the turbine 6T The exhaust flow rates are equalized (50% of the whole). For example, the opening S of the first electromagnetic valve 17 is controlled to be 50%, and the opening S of the second electromagnetic valve 18 is controlled to be 0%. When the rear-stage catalyst 10 is activated in this way, the rear-stage catalyst 10 can purify NOx, so the exhaust gas flow rate of the front-stage catalyst 15 is reduced, and the exhaust gas flow rate of the turbine 6T is increased accordingly. Accordingly, it is possible to suppress an increase in back pressure and improve combustion efficiency by utilizing the turbocharger 6 .

Next, control when the load L of the engine is high (greater than the threshold Ls) will be described. When the temperature Tc2 of the rear-stage catalyst 10 is lower than the activation start temperature Tc2s, the opening S of the first electromagnetic valve 17 is controlled to be 0%, and the opening S of the second electromagnetic valve 18 is controlled within a range of 0 to 50%, for example. change control.

In this way, the exhaust gas supplied from the engine main body 2 is supplied to the turbine 6T in its entirety without branching into the bypass passage 12 . And, of the exhaust gas passing through the turbine 6T, a part is supplied to the front-stage catalyst 15 through the branch passage 20 , and the remaining part is supplied to the rear-stage catalyst 10 .

In this case, since the engine load L is high and high output torque is required, the entire amount of exhaust gas is supplied to the turbine 6T, and supercharging by the turbocharger 6 is performed to the maximum. Then, a part of the exhaust gas is supplied to the pre-catalyst 15 , and the NOx is purified by the pre-catalyst 15 . At this time, when a lot of exhaust gas is supplied to the front catalyst 15, the back pressure will increase, so the opening degree of the second solenoid valve 18 is limited to a value smaller than 100%, for example, within a range of 0 to 50%. By doing so, it is possible to suppress back pressure rise and maximize engine efficiency.

The opening degree S of the second solenoid valve 18 is reduced as the engine load L becomes higher. Accordingly, the higher the engine load L is, the more the exhaust gas flow rate of the pre-catalyst 15 can be reduced, and the increase in back pressure can be suppressed.

On the other hand, when the temperature Tc2 of the rear-stage catalyst 10 is equal to or higher than the activation start temperature Tc2s, the opening S of the first electromagnetic valve 17 is controlled to be 0%, and the opening S of the second electromagnetic valve 18 is also controlled to be 0%. .

Accordingly, the exhaust gas supplied from the engine main body 2 is supplied to the rear-stage catalyst 10 after being fully supplied to the turbine 6T. Since the exhaust gas flow rate of the pre-catalyst 15 becomes zero, it is possible to minimize the increase in back pressure and maximize the engine efficiency.

In addition, the control routine is the same as that of the first embodiment, and in the above-mentioned step S103 , the openings S of the first electromagnetic valve 17 and the second electromagnetic valve 18 are controlled as in the present embodiment.

The embodiments of the present disclosure have been described in detail above, but there are various other considerations for the embodiments and modifications of the present disclosure.

(1) For example, the front-stage catalyst 15 and the rear-stage catalyst 10 may not be selective reduction NOx catalysts. For example, it may be an absorption-reduction NOx catalyst, or may be a catalyst other than an NOx catalyst, such as an oxidation catalyst or a three-way catalyst. In addition, the catalyst includes a particulate filter carrying a catalyst like the filter 8 described above. The types of catalysts may be different between the front-stage catalyst 15 and the rear-stage catalyst 10 .

(2) The post catalyst 10 may be omitted as needed.

(3) The configuration of the regulating valve can be changed in various ways. For example, instead of one three-way solenoid valve, two two-way solenoid valves may be provided to realize the same function.

Embodiments of the present disclosure are not limited to the foregoing embodiments, and all modifications, application examples, and equivalents included in the concept of the present disclosure defined by the scope of protection are included in the present disclosure. Therefore, the present disclosure should not be limitedly interpreted, but can also be applied to other arbitrary technologies belonging to the scope of thought of the present disclosure.

This application is based on Japanese patent application (Japanese Patent Application No. 2020-146010) filed on August 31, 2020, the contents of which are incorporated herein by reference.

industrial availability

According to the present disclosure, there is provided an exhaust gas purification system of an internal combustion engine which is advantageous in suppressing the temperature rise of the catalyst and the increase in back pressure.

Explanation of reference signs

4 exhaust channels

6T Turbo

10NOx catalyst (rear stage catalyst)

12 bypass channels

13 Bifurcation point

14 confluence point

15NOx catalyst (pre-catalyst)

16 Urea water injection valve (pre-stage injection valve)

17 1st solenoid valve

18 Second solenoid valve

20 branching passages

21 Bifurcation point

43 Exhaust gas temperature sensor

100 electronic control unit (ECU)

Claims (6)

1. An exhaust gas purification system of an internal combustion engine, characterized by comprising:

a turbine provided in an exhaust passage of the internal combustion engine,

a bypass passage that bypasses the turbine,

a catalyst provided in the bypass passage,

a regulating valve for regulating the exhaust gas flow rates of the turbine and the catalyst, and

a control unit configured to control the regulator valve;

the control unit controls the regulator valve such that the flow rate of the exhaust gas of the catalyst becomes larger when the load of the internal combustion engine is low than when the load is high.

2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein,

the regulating valve is formed of a three-way electromagnetic valve provided at a branching point of the bypass passage.

3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein,

further comprising a branching passage branching from the exhaust passage at a downstream side of the turbine and at an upstream side of a junction point of the bypass passage, and joining to the bypass passage at a downstream side of a branching point of the bypass passage and at an upstream side of the catalyst;

the regulator valve is formed of a three-way solenoid valve provided at a branching point of the bypass passage, and a three-way solenoid valve provided at a branching point of the branching passage.

4. An exhaust gas purification system for an internal combustion engine as claimed in any one of claims 1 to 3, wherein,

the catalyst is a selective reduction type NOx catalyst;

the exhaust gas purification system includes: a urea water injection valve provided in the bypass passage on the upstream side of the catalyst; and an acquisition unit that acquires a temperature of the catalyst;

the control means causes the urea solution to be injected from the urea solution injection valve when the exhaust gas flow rate of the catalyst is greater than a predetermined value and the temperature of the catalyst acquired by the acquisition means is equal to or higher than a predetermined activity start temperature.

5. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4, wherein,

and a downstream side catalyst of the same kind as the catalyst, the downstream side catalyst being provided to the exhaust passage at a downstream side from a junction point of the bypass passage.

6. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein,

the catalyst and the downstream side catalyst are NOx selective reduction catalysts.

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